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WO2015082912A1 - Catalysts - Google Patents

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Publication number
WO2015082912A1
WO2015082912A1 PCT/GB2014/053584 GB2014053584W WO2015082912A1 WO 2015082912 A1 WO2015082912 A1 WO 2015082912A1 GB 2014053584 W GB2014053584 W GB 2014053584W WO 2015082912 A1 WO2015082912 A1 WO 2015082912A1
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Prior art keywords
metal oxide
crystalline metal
optionally
nickel
barium
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PCT/GB2014/053584
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French (fr)
Inventor
Richard J. DARTON
R. Mark ORMEROD
John Z. STANIFORTH
Samuel E. EVANS
Oliver J. GOOD
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University Of Keele
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Publication of WO2015082912A1 publication Critical patent/WO2015082912A1/en

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    • C—CHEMISTRY; METALLURGY
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • C01B3/40—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts characterised by the catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/78—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali- or alkaline earth metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/036—Precipitation; Co-precipitation to form a gel or a cogel
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/323—Catalytic reaction of gaseous or liquid organic compounds other than hydrocarbons with gasifying agents
    • C01B3/326—Catalytic reaction of gaseous or liquid organic compounds other than hydrocarbons with gasifying agents characterised by the catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/613—10-100 m2/g
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B01J37/10—Heat treatment in the presence of water, e.g. steam
    • C—CHEMISTRY; METALLURGY
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    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
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    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0238—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a carbon dioxide reforming step
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    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
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    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/025—Processes for making hydrogen or synthesis gas containing a partial oxidation step
    • C01B2203/0261—Processes for making hydrogen or synthesis gas containing a partial oxidation step containing a catalytic partial oxidation step [CPO]
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    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0266—Processes for making hydrogen or synthesis gas containing a decomposition step
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    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
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    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
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    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
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    • C01B2203/1229—Ethanol
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    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
    • C01B2203/1235—Hydrocarbons
    • C01B2203/1241—Natural gas or methane
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    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
    • C01B2203/1235—Hydrocarbons
    • C01B2203/1247—Higher hydrocarbons
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/141—Feedstock
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • the present invention relates to new crystalline metal oxide catalysts, methods of making crystalline metal oxide catalysts and their use in fuel reforming reactions, particularly for use in the manufacture of syngas.
  • Syngas is a gaseous mixture composed principally of hydrogen and carbon monoxide and is an important commercial product.
  • a large proportion of commercial hydrogen gas is manufactured from syngas and syngas is the principal commercial source of carbon monoxide (used in the preparation of chemical reagents and in synthetic processes, such as carbonylation reactions).
  • Research into the production of syngas has attracted attention in recent years due to its growing potential as a "greener" alternative to conventional fuel sources in a number of processes.
  • syngas is presently used as an alternative to natural gas in power-generating processes (e.g. for use in fuel cells).
  • syngas offers an alternative to fossil fuels as a feedstock for the manufacture of chemicals such as methanol and long chain hydrocarbons via the Fisher-Tropsch process (useful in preparing transportation fuels and polymers).
  • syngas can be prepared on a commercial scale by reforming the potent greenhouse gases methane and carbon dioxide.
  • Typical reforming methods for producing syngas include dry reforming, steam reforming, and partial oxidation of various fuel gases.
  • a catalyst usually a metal supported on a ceramic material.
  • Nickel-based catalysts such as nickel-doped yttria-stabilised zirconia (Ni/YSZ) cermet are conventionally used.
  • Ni/YSZ nickel-doped yttria-stabilised zirconia
  • Other side reactions can occur, such as the reduction of carbon dioxide with hydrogen to form carbon monoxide and water. It is therefore essential to provide reaction conditions that are selective for the syngas forming reaction. From an environmental perspective, "biogas" (i.e.
  • syngas is produced by reforming the fuel, e.g. methane in the presence of a catalyst (e.g. Ni YSZ cermet) using steam as an oxidant.
  • a catalyst e.g. Ni YSZ cermet
  • the desired methane reforming reaction is CH + H2O ⁇ CO + 3H 2 (1 ).
  • the syngas produced is hydrogen rich (1 :3 CO.H2), providing a useful alternative to syngas produced by dry reforming.
  • Steam reforming of methane can involve two further competing reactions which operate in thermodynamic equilibrium to the main gas reforming reaction (1 ), namely:
  • Preparation of syngas by partial oxidation involves the reaction of fuel, e.g. methane with limited amounts of oxygen over a catalyst, using either pure oxygen or air as an oxygen source.
  • fuel e.g. methane
  • partial oxidation of methane is overall slightly exothermic and could therefore provide more efficient access to syngas.
  • reported partial oxidation methods have so far been unable to match the efficiency of dry and steam reforming reactions described above. It is therefore desirable to provide new catalysts for use in methods of preparing syngas by partial oxidation.
  • the reforming of methane in oxygen is characterised by a competition between the complete oxidation pathway (CH 4 + 20 2 ⁇ C0 2 + 2H 2 0) and the partial oxidation pathway (CH 4 + 1/2 0 2 ⁇ CO + 2H 2 ). In order to exploit this reaction to produce syngas, it is therefore necessary to provide reaction conditions that favour the partial oxidation pathway. Thus, there is a desire for catalysts that are able to promote the partial oxidation pathway selectively.
  • catalyst surfaces Carbon deposition on catalyst surfaces (“coking") is commonly encountered in the reforming processes described above. This is understood to be caused primarily by cracking of hydrocarbons on the catalyst surface (e.g. for methane, CH 4 ⁇ C + 2H 2 ), and where carbon monoxide is present, also as a result of the Boudouard reaction (2CO « ⁇ C + C0 2 ). Catalyst coking leads to reduction in catalyst activity and, in severe cases, complete deactivation of the catalyst. Where coking occurs in practice, fresh catalyst must be added to the reaction to supplement the deactivated catalyst, or the reaction must be stopped and the deactivated catalyst treated or replaced before the reaction can be continued. Thus, catalyst coking leads to reduced efficiency, increased levels of process complexity and ultimately, increased cost. It is therefore desirable to provide catalysts that are less susceptible to coking and / or which better tolerate coking.
  • Sulfur impurities present in a fuel feed can cause rapid poisoning and deactivation of a gas reforming catalyst in as low as a few parts per million.
  • sulfur poisoning leads to reduced efficiency, increased levels of process complexity and ultimately, increased cost.
  • This problem is commonly encountered where natural fuel sources are used (e.g. when biogas is used as a methane source). Sulfur poisoning therefore represents a significant hurdle that must be overcome before natural fuels such as biogas could represent commercially viable starting materials for gas reforming processes.
  • Crystalline metal oxides have found use in solid oxide fuel cells (SOFCs) due to their high refractive and electrically conductive properties.
  • SOFCs solid oxide fuel cells
  • Such oxides are provided in the form of a cermet (a ceramic-metal composite).
  • the metal component of the composite is required to perform the catalytic reaction and the ceramic component provides an ionically conducting porous and, preferably, refractory substrate.
  • Ni/YSZ cermets are commonly used on a commercial scale as they are relatively inexpensive.
  • PC-SOFCs proton-conducting SOFCs
  • Protonic conductors allow the SOFC to be run at lower temperatures than traditional SOFCs.
  • cermets containing ytterbium-doped barium zirconate as the ceramic component and nickel metal as the catalytic metal component of the composite have been reported as anode substrates for use in PC-SOFCs (Park er al. Ceramics International, 39 (2013) 2581-2587).
  • Rh- and Ru-based catalysts Some success in avoiding coking has been reported with Rh- and Ru-based catalysts (Hayakawa, T. et al. Applied Catalysts A: General 1999, 183, 273-285 - see page 274 left hand column). Limited success has also been achieved with nickel-based catalysts in dry reforming reactions. For instance, Hayakawa, T. et al. ⁇ Applied Catalysts A: General 1999, 183, 273-285) describes nickel-containing alkaline earth titanates (experimental, page 274), i.e. Ni/MgTiOs, Ni/CaTi0 3 , Ni/SrTi0 3 , Ni/BaTi0 3l Ni/Ca 0 8 Mg 02 Ti0 3 ,
  • Ni/TiCh i Cao.sSro.2Ti03 and Ni/Cao.sBao ⁇ TiC , each containing an Ni Ti ratio of 0.2/1.0 (which would correspond to material containing 3.3 atom% nickel within the crystal lattice) and metal oxides containing 10.3 wt% nickel (Ni/TiCh, Ni/Zr02, N1/AI2O3, Ni/Si02 and Ni/MgO).
  • the alkaline earth nickel titanates were of poor phase purity and contained NiO, indicating poor homogeneity of nickel within the catalytic material (and thus indicating that less than 3.3 atom% nickel must have been incorporated homogeneously into the crystal lattice).
  • This problem was also reported by Takehira, K. et al. Journal of Catalysis 2002, 207, 307-316 (see, e.g. Figure 2 of that document, showing presence of NiO and Ni phase impurities).
  • US 2012/0198536 A1 discloses perovskite-type strontium titanate catalysts doped with nickel and yttrium and the use of these catalysts in the formation of hydrogen-rich gas products from diesel fuel by autothermal reforming. These catalysts are alleged to show tolerance to coking and sulfur poisoning in such reactions. Catalysts containing up to 1.6 atom% nickel are reported
  • Ni YSZ cermet Traditional methods of producing crystalline metal oxide catalysts, such as nickel- based metal oxides (e.g. Ni YSZ cermet) typically involve very high temperatures ( ⁇ 1200 °C) and often require multiple steps of mixing and heating before high quality phase-pure material is produced.
  • US 2012/0198536 A1 discloses the preparation of perovskite-type strontium titanate catalysts involving the use of citric acid and ethylene glycol as complexing agents and a calcination step performed at about 700 °C to 1000 °C. Similar citrate-based methods requiring high temperature calcination for the synthesis of doped barium zirconates are disclosed in Cifa, F. et al Applied Catalysis B: Environmental 46 (2003) 463-471 , Viparelli, P. et al (Applied Catalysis A: General 280 (2005) 225-232) and Gallucci, K. et al. ⁇ Catalysis Today 197 (2012) 236-242). Park, et al.
  • Athawale, A. A. et al. discloses the formation of strontium zirconate by mixing metal nitrates with concentrated nitric acid followed by basification with potassium hydroxide.
  • the steps of adding concentrated nitric acid followed by potassium hydroxide are not desirable from a practical perspective as this would require intensive process control to avoid excess gas evolution and runaway increases in reaction temperature.
  • the present disclosure provides new solid crystalline metal oxides that exhibit catalytic activity in the reforming of fuels, such as hydrocarbons (e.g. methane) and oxygenated hydrocarbons (e.g. alcohols, such as ethanol), particularly to produce syngas.
  • fuels such as hydrocarbons (e.g. methane) and oxygenated hydrocarbons (e.g. alcohols, such as ethanol), particularly to produce syngas.
  • the invention provides nickel barium zirconates, nickel barium hafnates and solid solutions of nickel barium zirconate and nickel barium hafnate (i.e. barium zirconates, barium hafnates and solid solutions of barium zirconate and barium hafnate that are doped with nickel) that have utility in reforming hydrocarbon-containing fuels to produce hydrogen-rich gas products, particularly syngas.
  • the present catalysts are thus attractive for use in "green " ' technologies which convert greenhouse gases such as methane and C0 2 into useful feedstock for industry.
  • the present invention also provides hydrothermal processes for preparing these crystalline metal oxides.
  • a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide has a unit cell structure of the general formula AB0 3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide has a unit cell structure of the general formula AB0 3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • the invention is a method of preparing syngas.
  • the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide has a unit cell structure of the general formula AB0 3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • the invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide has a unit cell structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas.
  • ABO3 refers to a crystal lattice structure containing A, B and O lattice points, which occupy different lattice environments in the crystal.
  • the component metals in the crystalline metal oxide occupy A and B sites and oxygen the O sites.
  • the crystal lattice structures may include one or more A-site, B-site and / or O-site defects, e.g. wherein there is an absence of one or more atoms / ions at one or more A-site, B-site and / or O-site lattice points.
  • the crystalline metal oxide of the present invention includes material having one or more A-site and / or B-site defects.
  • the crystalline metal oxide includes one or more A- site or B-site defects, such as one or more A-site defects.
  • the crystalline metal oxide of the present invention includes one or more B-site defects.
  • the crystalline metal oxide includes A-site and B-site defects.
  • the crystalline metal oxide contains less than 10 % of A-site, B-site and / or O-site defects (e.g. wherein less than 10 % of the respective number of A, B and/or O sites in the lattice are absent of atoms/ions). In embodiments, the crystalline metal oxide contains less than 8 % A-site, B-site and / or O-site defects, preferably less than 6%, 4%, 2%, or more preferably less than 1%. Indeed, in some embodiments, the crystalline metal oxide of the invention is free of A-site, B-site and / or O-site defects.
  • the crystalline metal oxide comprises barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • substantially all of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • At least 90 mol% and preferably at least 95 mol%, 98 mol% or 99 mol% of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • at least 90 wt% and preferably at least 95 wt%, 98 wt% or 99 wt% of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • 100% of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
  • the crystalline metal oxide of the above aspect and embodiments comprises zirconium and / or hafnium at B sites.
  • the crystalline metal oxide comprises zirconium at B sites, typically wherein the crystalline metal oxide comprises zirconium but not hafnium at B sites.
  • the crystalline metal oxide comprises hafnium at B sites, typically wherein the crystalline metal oxide comprises hafnium but not zirconium at B sites.
  • the crystalline metal oxide may comprise zirconium and hafnium at B sites (i.e. wherein each zirconium and each hafnium occupy different B-sites).
  • y 1.0.
  • y 0 0.
  • the crystalline metal oxide of the above aspect and embodiments comprises nickel at A and / or B sites.
  • the nickel is at A and B sites.
  • the nickel is at A or B sites, for example B sites.
  • the nickel is at A-sites.
  • nickel is present in at least 1 % of A and / or B sites, such as at least 2%, 5%, 10 %, 20 %, or 30 %. In embodiments, nickel is present in at least 1 % of A and B sites, such as at least 2 %, 5 %, 10 %, 20 %, or 30 % of A and B sites. In embodiments, nickel is present in at least 1 % of A or B sites, suitably in at least 2%, 5%, 10 %, 20 %, or 30 % of A or B sites, for example, B sites. Preferably, the nickel is present in at least 1 % of A-sites, suitably in at least 2%, 5%, 10 %, 20 %, or 30 % of A-sites.
  • At least half and preferably more than half of the nickel is at A sites.
  • at least half and preferably more than half of the nickel is at A sites.
  • at least 90% of the nickel may be at A sites.
  • at leas 95%, 98% or 99% of the nickel may be at A sites.
  • the nickel is at A sites but not B sites
  • At least half and preferably more than half of the nickel is at B sites.
  • at least 90% of the nickel may be at B sites.
  • at least 95%, 98% or 99% of the nickel may be at B sites.
  • the nickel is at B sites but not A sites (i.e. wherein 100% of the nickel is at B sites). Amount of nickel
  • the amount of nickel in the crystalline metal oxides of the invention may be selected according to the desired properties of the material.
  • the nickel may be present in the crystalline metal oxide in an amount of at least 0.2 atom%, suitably at least 0.4 atom%, such as at least 0.6 atom% or 0.8 atom%, preferably at least 1 atom%, 2 atom%, 4 atom% or 6 atom%.
  • the nickel is present in an amount of at least 1 atom%.
  • the nickel is present in an amount of 12 atom% or less, suitably 10 atom % or less, 8 atom % or less, preferably 6 atom% or less, such as 4 atom% or less, 2 atom% or less, 1 atom% or less, 0.8 atom% or less, 0.6 atom% or less, or 0.4 atom% or less.
  • the nickel is present in an amount of from 0.2 atom% to 12 atom%, suitably from 0.4 atom% to 12 atom%, 0.6 atom% to 10 atom%, 0.8 atom% to 8 atom% or 1 atom% to 6 atom%.
  • the nickel is present in an amount of from 0.2 atom% to 7 atom%.
  • the crystalline metal oxide further comprises one or more additives (i.e. dopants) at A and / or B sites.
  • one or more additives may be at A and B sites.
  • the one or more additives are at A or B sites, for instance B sites.
  • one or more additives are at A sites.
  • the one or more additives may be present in the crystalline metal oxide in an amount of up to 6 atom%, such as up to 4 atom%, 2 atom%, 1 atom%, 0.8 atom%, 0.6 atom%, 0.4 atom%, 0.2 atom% or 0.1 atom%.
  • the atomic ratio of crystalline metal oxides of the invention can be determined by EDX analysis and / or can be inferred based on the XRPD pattern. Elemental analysis data may be collected using a Hitachi TM3000 scanning electron microscope equipped with a Bruker Quantax 70 EDS system. Powder X-ray diffraction data may be collected using a Bruker D8 Advance diffractometer using a Cu Ka source and a flat disc sample holder.
  • the crystalline oxide may for example be a crystalline metal oxide as described in any aspect and embodiment herein having a unit cell structure of the general formula AB0 3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. Second aspect
  • a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate.
  • the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate.
  • the invention is a method of preparing syngas.
  • the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate.
  • the invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate.
  • Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas.
  • Nickel such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas.
  • the nickel is present in the crystal lattice in an amount of at least 0.2 atom%, optionally at least 0.4 atom%, optionally at least 1 atom%, optionally at least 2 atom%, optionally at least 4 atom%, optionally at least 6 atom%. In embodiments, the nickel is present in an amount of 12 atom% or less, suitably 10 atom% or less, 8 atom% or less, preferably 6 atom% or less, such as 4 atom% or less, 2 atom% or less, 1 atom% or less, 0.8 atom% or less, 0.6 atom% or less, or 0.4 atom% or less.
  • the nickel is present in an amount of from 0.2 atom% to 12 atom%, suitably from 0.4 atom% to 12 atom%, 0.6 atom% to 10 atom%, 0.8 atom% to 8 atom% or 1 atom% to 6 atom%.
  • the nickel is present in an amount of from 0.2 atom% to 7 atom%.
  • the crystalline metal oxide is selected from nickel barium zirconate nickel barium hafnate and solid solution of nickel barium zirconate and nickel barium hafnate represented by the formula >1 % Ni/BaZr0 3 , >2% Ni/BaZr0 3 , >2% Ni/BaZr0 3 , >5% Ni/BaZr0 3 , >10% Ni/BaZr0 3 , >20% Ni/BaZr0 3 , >30% Ni/BaZr0 3 , >40% Ni/BaZr0 3 , >45% Ni/BaZr0 3 , >1 % Ni/BaHf0 3 ,
  • Ni/BaHfOs >2% Ni/BaHf0 3> >5% Ni/BaHf0 3 .
  • Ni/BaHf0 3 >10% Ni/BaHf0 3 , >20% Ni/BaHf0 3 , ⁇ 30% Ni/BaHf0 3 , >40% Ni/BaHf0 3 . or >45% Ni/BaHf0 3 .
  • the nickel amount in said crystalline metal oxides is less than 50atom% Ni/BaHf0 3 , such as less than 45atom% Ni/BaHf0 3 less than 40atom% Ni/BaHf0 3 or less than
  • Ni/BaHf0 3 refers to the atom% nickel incorporated relative to the theoretical amount of barium or zirconium in barium zirconate / hafnate.
  • >20% Ni/BaZrCb refers to materials including at least 20atom% nickel relative to the theoretical amount of barium or zirconium/hafnium in nickel-free barium zirconate/hafnate material.
  • the theoretical atom% of barium or zirconium/hafnium in barium zirconate (BaZrOa) is 20atom% (i.e. one in 5 atoms is a barium).
  • 20% Ni/BaZrOs refers to nickel barium zirconate wherein 4atom% nickel is incorporated homogeneously in solid solution in the BaZr0 3 crystal lattice (typically in place of a corresponding amount of said barium and/ or zirconium/hafnium).
  • 20% Ni/BaZr03 includes crystalline metal oxides of the general formula Ni 02 Ba 0 8Zr0 3 .
  • the nickel, barium, zirconium and / or hafnium in the crystal lattice is replaced by one or more additives, i.e. wherein the crystal lattice includes one or more additives (i.e. dopants) in addition to the nickel, barium, zirconium and / or hafnium in the crystal oxide lattice (homogeneously incorporated in solid solution).
  • additives i.e. dopants
  • At least 1 atom% of the nickel, barium, zirconium and / or hafnium is replaced by one or more additives, suitably at least 2 atom%, preferably at least 5 atom%, at least 10 atom%, at least 20 atom%, or at least 30 atom% of the nickel, barium, zirconium and / or hafnium is replaced by one or more additives.
  • the one or more additives may be present in the crystalline metal oxide in an amount of up to 6 atom%, such as up to 4 atom%, 2 atom%. 1 atom%, 0.8 atom%, 0.6 atom%, 0.4 atom%. 0.2 atom% or 0.1 atom%.
  • nickel barium zirconate, nickel barium hafnate, and / or solid solution of nickel barium zirconate and nickel barium hafnate may be as further described according to any other aspect and embodiment herein.
  • embodiments of the second aspect and embodiments may have a unit cell structure of the general formula ABC comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites as described above for the first aspect and embodiments.
  • nickel barium zirconate, nickel barium hafnate, and solid solution of nickel barium zirconate and nickel barium hafnate may be of general formula (I) or (II) or embodiments thereof as described for the aspects and embodiments below.
  • a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide has the general formula (I):
  • the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (I):
  • the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide has the general formula (I):
  • the invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (I):
  • Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas.
  • "a” is 0.8 to 1 .2, thus allowing for a deficiency (where a ⁇ 1 ) or abundance (where a>1 ) of barium relative to the amount of zirconium / hafnium in the crystalline metal oxide of the invention.
  • "a” may be 0.8, 0.9, 1 .0, 1 .1 or 1 .2.
  • "a” is 1 (i.e. wherein the amount of barium relative to the amount of zirconium / hafnium is the same).
  • "y” is 0.0 to 1.0.
  • “y” may be 0.0 (i.e. wherein hafnium is absent), 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0 (i.e. wherein zirconium is absent).
  • "y" is 0.0 or 1.0.
  • "y" is 0.0.
  • "y" may be 1.0.
  • At least some of the barium, zirconium and / or hafnium is replaced by nickel.
  • at least some of the barium, zirconium and / or hafnium in general formula (I), above, is substituted in the formula by nickel.
  • at least 1 % of the barium, zirconium and / or hafnium in general formula (I) is replaced by nickel, suitably at least 2%, preferably at least 5%, at least 10 %, at least 20 %, or at least 30 %.
  • the nickel is present in the crystalline metal oxide in an amount of at least 0.2 atom%, optionally at least 0.4 atom%.
  • the nickel is present in an amount of 12 atom% or less, suitably 10 atom% or less, 8 atom% or less, preferably 6 atom% or less, such as 4 atom% or less, 2 atom% or less, 1 atom% or less, 0.8 atom% or less, 0.6 atom% or less, or 0.4 atom% or less.
  • the nickel is present in an amount of from 0.2 atom% to 12 atom%, suitably from 0.4 atom% to 12 atom%, 0.6 atom% to 10 atom%, 0.8 atom% to 8 atom% or 1 atom% to 6 atom%.
  • the nickel is present in an amount of from 0.2 atom% to 7 atom%.
  • At least 90% of the nickel replaces barium in general formula (I), suitably at least 95%, at least 98%, or at least 99%, for example wherein 100% of the nickel replaces barium.
  • at least 90% of the nickel replaces zirconium and / or hafnium in general formula (I), suitably at least 95%, at least 98%, or at least 99%, for example wherein 100% of the nickel replaces zirconium and / or hafnium.
  • the crystalline metal oxide of general formula (I) has an ABO-, crystalline unit cell structure as defined above for the first aspect an embodiments above.
  • the barium, (i.e. Ba) is at A-sites in the crystal lattice and the zirconium and / or hafnium (i.e. Zn y Hf v ) is at B-sites.
  • the nickel may be at A and / or B sites depending on whether the nickel replaces barium, zirconium and / or hafnium in the crystal lattice.
  • the barium, zirconium and / or hafnium is replaced in general formula (I) by one or more additives (i.e. dopants) in addition to nickel.
  • at least 1 atom% of the barium, zirconium and / or hafnium is replaced by one or more additives, for instance at least 2 atom%. at least 5 atom%, at least 10 atom%, at least 20 atom%, or at least 30 atom% of the barium, zirconium and / or hafnium is replaced by one or more additives.
  • the one or more additives may be present in the crystalline metal oxide of general formula (I) in an amount of up to 6 atom%, such as up to 4 atom%, 2 atom%, 1 atom%,
  • Embodiments of the aspects and embodiments above may have a unit celt structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites as described above for the first aspect an embodiments.
  • Fourth aspect of the aspects and embodiments above may have a unit celt structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites as described above for the first aspect an embodiments.
  • a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide has the general formula (II):
  • the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (II):
  • the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide has the general formula (II):
  • the invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (II):
  • Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas.
  • a fuel such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas.
  • m is 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5.
  • n is 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5.
  • n is 0.
  • m is 0.0 to 0.5 (such as 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5) and n is 0.
  • n is 0.0 to 0.5 (such as 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5) and m is 0.
  • m and n are each 0.
  • the crystalline metal oxide has the general formula (III):
  • a is 0.8 to 1.2, thus allowing for a deficiency (where a ⁇ 1 ) or abundance (where a>1 ) of the (Bai. x Q x ) component relative to the ((Zri.yHf v .)i- z Q z) component in the crystalline metal oxide.
  • “a” may be 0.8, 0.9, 1.0, 1.1 or 1.2.
  • “a” is 1 (i.e. wherein formula (II) and (III), above are formulae (Ha) and (Ilia) respectively:
  • x and z are each independently 0.0 to 0.9 provided that x+z > 0.01.
  • x is 0.0 to 0.9.
  • x may be 0.0, 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9.
  • x is 0.01 to 0.9 (such as 0.01 , 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9) and z is 0.
  • x > 0.01 suitably > 0.02, > 0.05, > 0.1 , > 0.2, or > 0.3.
  • x ⁇ 0.9, suitably ⁇ 0.8, ⁇ 0.7, ⁇ 0.6, ⁇ 0.5, preferably ⁇ 0.4, ⁇ 0.3, ⁇ 0.2 or ⁇ 0.1.
  • x is 0.05, 0.1 , 0.2, 0.3, 0.4, 0.45, or 0.5.
  • x 0, i.e. wherein general formula (II) is of general formula (lib):
  • z is 0.0 to 0.9.
  • z may be 0.0, 0.1 , 0.2. 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9.
  • z is 0.01 to 0.9 (such as 0.01 , 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9) and x is 0.
  • z > 0.01 suitably > 0.02, > 0.05, > 0.1 , > 0.2, or > 0.3.
  • z 0, i.e.
  • “y” is 0.0 to 1.0.
  • “y” may be 0.0 (i.e. wherein hafnium is absent), 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 0 (i.e. wherein zirconium is absent).
  • "y" is 0.0 or 1.0.
  • "y" is 0.0.
  • "y” may be 1.0.
  • the general formula (II) is of formula (IVa) or (IVb):
  • the crystalline metal oxide of general formulae (II), (lla), (lib), (lie), (III), (IVa) and / or (IVb) may have an ABO3 crystalline unit cell structure as described according to the first embodiment thereof above.
  • the (Bai. x Q x ) is at A-sites in the crystal lattice and the ((Zri. y Hf y )i. Q 1 z ) is at B-sites.
  • the nickel may therefore be at A and / or B sites.
  • the method of reforming is selected from the group consisting of dry reforming, autothermal reforming, steam reforming, partial oxidation and thermal decomposition.
  • the method of reforming may be selected from the group consisting of dry reforming, autothermal reforming, steam reforming and partial oxidation, preferably dry reforming, steam reforming and partial oxidation, such as steam reforming.
  • the method of reforming is partial oxidation.
  • the method of reforming may be dry reforming, optionally wherein a biofuel, such as biogas, is used as the hydrocarbon (e.g. methane) fuel source.
  • a biofuel such as biogas
  • the methods in the above aspects and embodiments comprise contacting the crystalline metal oxide with the fuel.
  • the step of contacting the crystalline metal oxide with the fuel is performed in the presence of an oxidant, such as water (e.g. steam), oxygen and / or carbon dioxide.
  • an oxidant such as water (e.g. steam), oxygen and / or carbon dioxide.
  • a fuel described in any of the above aspects and embodiments said crystalline metal oxide provides more sustained activity over longer periods compared to alternative catalysts.
  • the uses and methods described above or the crystalline metal oxides described above for use in said methods provide a fuel conversion rate (typically methane conversion) during partial oxidation (reaction with limited amounts of oxygen, typically 50% stoichiometric ratio of oxygen) at 700 °C that is at least 5%, suitably at least 10%, preferably at least 15% and more preferably at least
  • the uses and methods described above or the crystalline metal oxides described above for use in said methods provide an average fuel conversion rate (typically methane conversion) during partial oxidation (reaction with limited amounts of oxygen, typically 50% stoichiometric ratio of oxygen) at 900 °C that is at least 60%, such as at least 70%, at least 75%, suitably at least 80%, preferably at least 85%, more preferably at least 90% and most preferably at least 95% over a period of 5 hours.
  • an average fuel conversion rate typically methane conversion
  • partial oxidation reaction with limited amounts of oxygen, typically 50% stoichiometric ratio of oxygen
  • said method is a method of preparing syngas.
  • the reforming is conducted at a temperature of less than 1000 °C, suitably less than 950 °C, such as less than 900 °C, or less than 850 °C, typically around 800 °C.
  • the reforming is performed at an average temperature at least 700 °C, such as at least 750 °C, preferably at least 800 °C, or at least 850 °C.
  • the fuel may be selected from a hydrocarbon and an oxygenated hydrocarbon.
  • Said fuel i.e. said hydrocarbon and / or oxygenated hydrocarbon may be provided to the reaction mixture as the sole fuel component or may be a component part of a fuel composition comprising other chemical compounds, such as other fuel compounds and / or inert carriers.
  • the hydrocarbon may be provided as part of a mixture of hydrocarbon compounds and / or oxygenated hydrocarbons as defined herein.
  • the oxygenated hydrocarbon may be provided as part of a mixture of hydrocarbon compounds and / or oxygenated hydrocarbons as defined herein.
  • Said fuel / fuel composition may be provided to the reaction vessel separately, or as part of a mixture of other chemical compounds not including hydrocarbons and / or oxygenated hydrocarbons.
  • each fuel may independently be provided to the reaction vessel as a mixture with inert gases and / or oxidants, etc. needed for the reaction.
  • the respective hydrocarbon and / or oxygenated hydrocarbon may be supplied to the reaction vessel substantially free of other compounds that are not hydrocarbons / oxygenated hydrocarbons.
  • oxygenated hydrocarbon refers to a hydrocarbon wherein one or more hydrogen atoms is notionally substituted by one or more oxygen substituents (e.g. 1 , 2, 3, 4, or 5 oxygen substituents) and / or wherein one or more methylene groups (i.e. -CH 2 -) in the hydrocarbon (e.g. 1 , 2, 3, 4, or 5 methylene groups) is notionally replaced by an oxygen (i.e.-O-).
  • oxygenated hydrocarbon includes hydrocarbons substituted by one or more oxygen substituents selected
  • no more than two oxygen atoms may be adjacent (such as present in peroxides and peracids), i.e. suitably, chains of three or more oxygen atoms are not included.
  • oxygenated hydrocarbons are therefore alcohols, epoxides, aldehydes, ketones, carboxylic acids, carboxylic acid esters, ethers, peroxides and peracids.
  • the fuel is a hydrocarbon.
  • the fuel is an oxygenated hydrocarbon.
  • said oxygenated hydrocarbon is a hydrocarbon substituted by one or more substituents (e.g.
  • said oxygenated hydrocarbon preferably comprises only one of said substituents. In further embodiments, said oxygenated hydrocarbon comprises more than one of the substituents, e.g. 2, 3. 4, or 5 substituents. Suitably, said oxygenated hydrocarbon is substituted by 2, 3, or 4 of substituents, for instance 2 or 3. particularly 2.
  • one or more methylene groups i.e. -CH2-
  • oxygen i.e.-O-
  • more than one methylene group (i.e. -CH 2 -) is substituted by oxygen (i.e.-O-), e.g. 2, 3, 4, or 5 methylene groups are substituted.
  • 2, 3, or 4 methylene groups are substituted, for instance 2 or 3, particularly 2.
  • the fuel is selected from the group consisting of a hydrocarbon (e.g. methane), an alcohol (e.g. ethanol), an ether, a ketone
  • the fuel is selected from the group consisting of a hydrocarbon (e.g. methane), an alcohol (e.g. ethanol), and a carboxylic acid
  • the fuel is selected from the group consisting of a hydrocarbon and an alcohol, e.g. an alcohol (such as ethanol).
  • the fuel is a hydrocarbon (such as methane).
  • the fuel may be selected from methane and ethanol, e.g. methane.
  • the fuel is a carboxylic acid (e.g. acetic acid).
  • said hydrocarbon or oxygenated hydrocarbon may be a component of a mixture.
  • the mixture may comprise inert materials such as inert carriers (e.g. Nobel gases) and / or additional reactive materials, such as other fuels, oxidants and fuel additives.
  • the mixture may include one or more fuels selected from the group consisting of a hydrocarbon (e.g. methane) and an oxygenated hydrocarbon such as one or more fuels selected from the group consisting of a hydrocarbon, an alcohol (e.g. ethanol), an ether (e.g. dimethyl ether and diethyl ether), a ketone (e.g. acetone), an aldehyde, a carboxylic acid (e.g. acetic acid) and a carboxylic acid ester.
  • a hydrocarbon e.g. methane
  • an oxygenated hydrocarbon such as one or more fuels selected from the group consisting of a hydrocarbon, an alcohol (e.g. ethanol), an ether (e.g
  • the hydrocarbon may be selected from one or more of the group consisting of a Ci-25alkane, a Ca-asalkene and a C 2 - 2 5alkyne.
  • the hydrocarbon may be selected from the group consisting of a Ci- 25 alkane and a C 2 -2salkene.
  • the hydrocarbon is selected from the group consisting of a and a C 2 - 2 5alkyne.
  • the hydrocarbon is a
  • the d ⁇ alkane, C2- 2 salkene and C 2 - 2 5alkyne may respectively be a Ci-ioalkane, a C 2 -ioalkene and a C 2 -ioalkyne, more preferably a C-- S alkane, C2-ealkene and C 2 -6alkyne, e.g. a Ci-4alkane, C2-4alkene and C2-4alkyne.
  • the hydrocarbon when it is a it is suitably a Ci i 0 alkane, preferably a d-ealkane, more preferably a Ci-4alkane (i.e. methane, ethane, propane or butane), most preferably methane.
  • a Ci-4alkane i.e. methane, ethane, propane or butane
  • methane examples include methane, ethane propane, butane, petroleum, diesel and kerosene.
  • the hydrocarbon is selected from methane, ethane, propane, butane, petroleum, diesel and kerosene.
  • the hydrocarbon may be selected from methane, butane, petroleum, diesel and kerosene, such as petroleum, diesel and kerosene, but preferably methane and butane, more preferably methane.
  • the fuel composition may comprise less than 50 ppm sulfur-containing compounds, e.g. less than 40 ppm, 30 ppm, 20 ppm, 10 ppm or 5 ppm.
  • Said hydrocarbon and / or oxygenated hydrocarbon may be provided as a component part of biofuel mixtures, such as biogas.
  • biofuel mixtures such as biogas.
  • methane when used as a hydrocarbon fuel, it may be provided in a mixture, such as biogas or simulated biogas (e.g. a mixture of about 2:1 CH ⁇ CC ⁇ ).
  • the fuel used in the methods of reforming defined in the above aspects and embodiments is a biofuel, such as biogas.
  • the carboxylic acid may be selected from one or more of the group consisting of a Ci-25alkanoic acid, a C ⁇ salkenoic acid and a C ⁇ salkynoic acid. Typically, the carboxylic acid is a C 25alkanoic acid.
  • the Ci- 2 salkanoic acid, C3 2&alkenoic acid and C ⁇ alkynoic acid may respectively be a Ci ioaikanoic acid, a C 3 -ioalkenoic acid and a C 3 -ioalkynoic acid, more preferably a Ci. s alkanoic acid, C3-ealkenoic acid and Cs-ealkynoic acid, e.g.
  • alkane as described herein includes branched or unbranched. cyclic or acyclic alkanes. Typically the alkane is acyclic. Typically the alkane is unbranched, preferably unbranched and acyclic.
  • alkene refers to a group derived from an alkane and comprising one or more carbon-carbon double bonds. Typically the alkene is unbranched, preferably unbranched and acyclic.
  • alkyne refers to a group derived from an alkane and comprising one or more carbon-carbon triple bonds. Typically the alkyne is unbranched, preferably unbranched and acyclic.
  • an ether includes a hydrocarbon or oxygenated hydrocarbon substituted according to any definition as described above, wherein one or more methylene groups (i.e. -CH 2 -) in the hydrocarbon or oxygenated hydrocarbon are substituted by oxygen (i.e.-O-) to form an ether moiety.
  • an ether includes alkane ethers, alkene ethers and alkyne ethers containing one or more ether oxygen atoms, such as one to three ether oxygen atoms, preferably one ether oxygen atom.
  • the ether typically contains from 2-24 carbon atoms, such as 2-9, preferably 2-5, more preferably 2-3 carbon atoms, e.g. two).
  • alcohol includes hydrocarbons or oxygenated hydrocarbons substituted according to any definition as described above, wherein one or more substituents (e.g. 1 , 2, 3, 4, or 5 substituents, preferably 1 , 2, or 3, more preferably 1 ) is -OH.
  • substituents e.g. 1 , 2, 3, 4, or 5 substituents, preferably 1 , 2, or 3, more preferably 1
  • alcohol includes alkanols, alkenols and alkynois including one or more hydroxy! groups, such as one to three hydroxy! groups, preferably one hydroxy I group.
  • the alcohol contains from 1-25 carbon atoms, such as 1-10, preferably 1-6, more preferably 1-4 carbon atoms, e.g. one or two).
  • the alcohol e.g.
  • alkanol, alkenol and / or alkynol may be branched or unbranched, cyclic or acyclic.
  • the alcohol e.g. the respective alkanol, alkenol and / or alkynol
  • the alcohol is unbranched, and more preferably unbranched and acyclic.
  • the alcohol may be selected from the group consisting of an alkanol, alkenols and an alkynol, such as an alkanol and an alkenol.
  • the alcohol is selected from the group consisting of an alkanol and an alkynol, preferably an alkanol.
  • the alkanol, alkenol and alkynol may respectively be a d.-ioalkanol, a C2-toalkenol, and a C 2 -ioalkynol, more preferably a Ci. 6 alkanol, C 2 . 6 alkenol and C2- 6 alkynol, e.g. a
  • Ci- 4 alkanol C 2 - 4 alkenol and C 2 . alkynol.
  • the alcohol is a Ci-ioalkanol.
  • Ci-ealkanol more preferably a (i.e. methanol, ethanol. propanol or butanol), most preferably ethanol.
  • ethanol When ethanol is used as a fuel, it may be provided as bioethanol.
  • aldehyde includes alkanals, alkenals and alkynals including one or more aldehyde moieties, such as one to three, preferably one.
  • the aldehyde contains from 1-25 carbon atoms, such as from 1-10, preferably 1-6, more preferably 1-4 carbon atoms, e.g. two).
  • the aldehyde e.g.
  • the respective alkanals, alkenals and alkynals may be branched or unbranched, cyclic or acyclic.
  • the aldehyde is unbranched, and more preferably unbranched and acyclic.
  • the aldehyde may be selected from the group consisting of an alkanal, an alkenal and an alkynal, such as an alkanal and an alkenal.
  • the aldehyde is selected from the group consisting of an alkanol and an alkynal, preferably an alkanal.
  • the alkanal, alkenal and alkynal may respectively be a Ci-i 0 alkanal, a C ⁇ oalkenal, and a C3.ioalkynal, more preferably a Ci. 6 alkanal, C 3 -6alkenal and Cs-ealkynal, e.g. a
  • the aldehyde is a Ci i 0 alkanal.
  • the aldehyde is suitably a d ealkanal, more preferably a (i.e. methanal (formaldehyde), ethanal (acetaldehyde), propanal or butanal). More preferably, the aldehyde is ethanal.
  • the respective alkanones, alkenones and alkynones may be branched or unbranched, cyclic or acyclic.
  • the ketone is unbranched, and more preferably unbranched and acyclic.
  • the ketone may be selected from the group consisting of an alkanone. alkenone and alkynone, such as an alkanone and an alkenone.
  • the ketone is selected from the group consisting of an alkanone and alkynone, preferably an alkanone.
  • the alkanone, alkenone and alkynone may respectively be a C ⁇ , loalkanone, a C 4 .ioalkenone, and a -ioalkynone, more preferably a d-ealkanone, C 4 ⁇ salkenone and C.. 6 alkynone, e.g. a C ⁇ alkanone, C 4 alkenone and C 4 alkynone.
  • the ketone is a Cviaalkanone.
  • the ketone is a C 3 .ioalkanone, it is suitably a Cs-ealkanone, more preferably a C ⁇ alkanone (i.e. propanone (acetone), or butanone).
  • the ketone is propanone (i.e. acetone).
  • carboxylic acid includes aikanoic acids, alkenoic acids and alkynoic acids including one or more carboxyl groups, such as one to three carboxyl groups, preferably one carboxyl group.
  • the carboxylic acid contains from 1-25 carbon atoms, such as from 1-10, preferably 1-6, more preferably 1-4 carbon atoms, e.g. one or two).
  • the carboxylic acid e.g. the respective aikanoic acids, alkenoic acids and alkynoic acids
  • the carboxylic acid e.g. the respective aikanoic acids, alkenoic acids and alkynoic acids
  • the carboxylic acid may be selected from the group consisting of an aikanoic acid, an alkenoic acid and an alkynoic acid, such as an aikanoic acid and an alkenoic acid.
  • the carboxylic acid is selected from the group consisting of an aikanoic acid and an alkynoic acid, preferably an aikanoic acid.
  • the aikanoic acid, alkenoic acid and alkynoic acid may respectively be a Ci ioalkanoic acid, a
  • Ca-ioalkenoic acid, and a Ca ioalkynoic acid more preferably a Ci. 6 alkanoic acid, Ca-ealkenoic acid and C ⁇ alkynoic acid, e.g. a C M alkanoic acid, C 3 ⁇ alkenoic acid and C3- 4 alkynoic acid.
  • the carboxylic acid is a Ci- ⁇ oaikanoic acid.
  • the carboxylic acid is a Ci-i Q alkanoic acid
  • it is suitably a Ci- 6 alkanoic acid, more preferably a d ⁇ alkanoic acid (i.e. methanoic acid, ethanoic acid (i.e. acetic acid), propanoic acid or butanoic acid).
  • the carboxylic acid is ethanoic acid (i.e. acetic acid).
  • a 0 substituent is bonded to a carbon adjacent to an ether oxygen atom to form a carboxylic acid ester group.
  • carboxylic acid ester includes aikanoic acid esters, alkenoic acid esters and alkynoic acid esters including one or more carboxylic acid ester groups, such as one to three carboxylic acid ester groups, preferably one carboxylic acid ester groups.
  • carboxylic acid ester contains from 2-25 carbon atoms, such as from 2-10, preferably 2-6, more preferably 2-4 carbon atoms, e.g. one or two).
  • the carboxylic acid ester e.g.
  • the respective aikanoic acid esters, alkenoic acid esters and alkynoic acid esters may be branched or unbranched, cyclic or acyclic.
  • the carboxylic acid ester is unbranched, and more preferably unbranched and acyclic.
  • the carboxylic acid ester may be selected from the group consisting of an alkanoic acid ester, an alkenoic acid ester and an alkynoic acid ester, such as an alkanoic acid ester and an alkenoic acid ester.
  • the carboxylic acid ester is selected from the group consisting of an alkanoic acid ester and an alkynoic acid ester, preferably an alkanoic acid ester.
  • the alkanoic acid ester, alkenoic acid ester and alkynoic acid ester may respectively be a C 2 -ioalkanoic acid ester, a Ci ioalkenoic acid ester, and a C 4 .i 0 alkynoic acid ester, more preferably a C 2 -6alkanoic acid ester, C+ ⁇ alkenoic acid ester and Ct-ealkynoic acid ester, e.g. a C 2 4 alkanoic acid ester, C 4 alkenoic acid ester and C 4 alkynoic acid ester.
  • the carboxylic acid ester is a C 2 .ioalkanoic acid ester.
  • the carboxylic acid ester is a C 2 -ioalkanoic acid ester
  • it is suitably a C 2 -6alkanoic acid ester, more preferably a C 2 4 alkanoic acid ester, e.g. a C 2 alkanoic acid ester (i.e. methyl methanoate).
  • the fuel is selected from a Ci . 2i ,alkane, a Ci ioalkanol and a Ci-ioalkanoic acid.
  • the fuel is selected from the group consisting of methane, ethane, propane, butane, ethanol, acetone, ethanoic acid, petroleum, diesel, kerosene and mixtures thereof.
  • the fuel may be selected from the group consisting of methane, butane, ethanol, ethanoic acid, petroleum, diesel, kerosene and mixtures thereof, such as petroleum, diesel, kerosene and mixtures thereof, preferably methane, butane, ethanol and ethanoic acid, more preferably methane, butane and ethanol.
  • the fuel may therefore be selected from the groups consisting of methane and ethanol, preferably methane.
  • the fuel is biogas, simulated biogas or bioethanol, suitably biogas or simulated biogas, e.g. biogas.
  • the fuel is bioethanol.
  • the fuel may be supplied to the reactor separately to the other gaseous reactants (such as steam, CO, etc.) or may be provided as a mixture with the other gaseous reactants.
  • gaseous reactants such as steam, CO, etc.
  • biogas is a mixture including methane biogas and carbon dioxide (e.g. a mixture of CH 4 :C02. 2:1 ).
  • syngas preferably from methane, such as from biogas.
  • syngas is a gaseous mixture that is principally composed of hydrogen and carbon monoxide.
  • the product of the reaction may consist of at least 10mol% syngas, such as at least 20mol%, at least 30mol%, at least 40mol%, at least 50mol%, at least 60mol%, at least 70mol%, at least 80mol% or at least at least 90mol%.
  • the reaction product consists substantially of syngas (such as by mol%, i.e. wherein at least 95mol%, such as at least 98mol%, more preferably at least 99mol% of the reaction product is syngas), more preferably consists of syngas.
  • the product of the reaction may consist of at least 10vol% syngas, such as at least 20vol%, at least 30vo!%, at least 40vol%, at least 50vol%. at least 60vol%, at least 70vol%, at least 80vol% or at least at least 90vol%.
  • the reaction product consists substantially of syngas by volume (i.e. wherein at least 95vol%, such as at least 98vol%, more preferably at least 99vol% of the reaction product is syngas), more preferably consists of syngas.
  • the product of the reaction may consist of at least 10 wt.% syngas, such as at least 20 wt.%, at least 30 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.% or at least at least 90 wt.%.
  • the reaction product consists substantially of syngas by weight (i.e. wherein at least 95 wt.%, such as at least 98 wt.%. more preferably at least 99 wt.% of the reaction product is syngas), more preferably consists of syngas.
  • the method includes the step of isolating and / or purifying the reaction product.
  • the method includes the step of isolating and / or purifying the reaction product so as to provide syngas.
  • the crystalline metal oxide is not
  • said crystalline metal oxide is not crystalline metal oxide having a general formula
  • a crystalline metal oxide having an ABO3 unit cell structure comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites, provided the crystalline metal oxide is not BaZromigNio 1351O3 or BaZro 729eNio 270203.
  • said crystalline metal oxide may be as defined according to the first aspect and any embodiment thereof above, provided the crystalline metal oxide is not or BaZ 0 .7298 io . 27020 3 .
  • the crystalline metal oxide of the fifth aspect and embodiments is not crystalline metal oxide having a general formula BaZr (0 84 to o.88)Ni ( o. i2 to o.ie * or
  • the crystalline metal oxides of the present invention exhibit excellent activity in reforming reactions to form syngas selectively over alternative reaction pathways.
  • This excellent catalytic activity and selectivity is exhibited in a variety of reforming reactions, including dry reforming, steam reforming and partial oxidation, showing the versatility of the crystalline metal oxides of the present invention in the production of syngas.
  • crystalline metal oxides of the present invention allow surprisingly high levels of active nickel to be incorporated homogenously within the crystal lattice (i.e. in solid solution).
  • example 1 and figure 3 show that crystalline metal oxides of the invention can be obtained in high phase purity even at high nickel loadings, such as 6 atom% nickel (i.e. 30% Ni/BaZr0 3 ).
  • Crystalline metal oxides of the invention containing up to 10atom% nickel were prepared and tested by the present inventors (see Examples) and even at this high level of nickel loading only small amounts of impurities (e.g. Zr02 and Ni(OH)2) were detected in the material. Nonetheless, each of these materials showed good catalytic activity in a variety of reforming reactions to produce syngas.
  • Crystalline metal oxides of the present invention show good resistance to coking (see e.g. Examples 5 and 6). This is particularly surprising given the high nickel content of these catalysts.
  • the materials of the present invention provide a valuable alternative to conventional nickel based catalysts (such as Ni/YSZ cermet) in reforming reactions, and would be particularly useful in the reforming of fuel derived from natural sources, such as biofuels, e.g. biogas.
  • a crystalline metal oxide selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate, provided the crystalline metal oxide is not BaZro s649Nio 1351O3 or BaZro 729sNio 27 ⁇ 03.
  • the crystalline metai oxide may be as defined in the second aspect and any embodiment thereof above, provided the crystalline metal oxide is not
  • the crystalline metal oxide of the sixth aspect and embodiments thereof is not crystalline metal oxide having a general formula BaZr ⁇ o w to o 88>Ni(o 12 to aiejQa or BaZr ⁇ o , > o to o.74) i
  • the nickel barium zirconate, nickel barium hafnate, and / or solid solution of nickel barium zirconate and nickel barium hafnate of the sixth aspect and embodiments may be as further described according to any other aspect and embodiment herein, suitably wherein the crystalline metal oxide is not
  • embodiments of the sixth aspect and embodiments may have a unit cell structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites as described above for the first aspect and embodiments.
  • the nickel barium zirconate, nickel barium hafnate, and solid solution of nickel barium zirconate and nickel barium hafnate may be of general formula (I) or (II) as described below for the seventh and eighth aspects and embodiments. Seventh aspect
  • a crystalline metal oxide has the general formula (I):
  • crystalline metal oxide may thus be as defined according to the third aspect and any embodiment thereof above, provided the crystalline metal oxide is not
  • the crystalline metal oxide of the seventh aspect and embodiments is not crystalline metal oxide having a general formula BaZr.o 34 to 088> i(o 12 to ⁇ . ⁇ ) ⁇ 3 or BaZr ⁇ o 70 to o.74iNi(o.26 to 030O3.
  • the crystalline metal oxide of general formula (I) may have an ABO3 crystalline unit cell structure as defined above for the first aspect an embodiments above.
  • the barium i.e. Ba
  • the zirconium and / or hafnium i.e. Zri- y Hf y
  • the nickel may be at A and / or B sites depending on whether the nickel replaces barium, zirconium and / or hafnium in the crystal lattice.
  • each L is independently one or more additives:
  • m and n are each independently 0.0 to 0.5, provided the crystalline metal oxide is not BaZr 0 .864g io.i35i03 or
  • said crystalline metal oxide of general formula (II) may be as defined according to the fourth aspect and any embodiment thereof above, provided the crystalline metal oxide is not BaZr 0 8649N10 1351 ⁇ 3 or BaZro 729s io 2702O3.
  • the crystalline metal oxide of the eighth aspect and embodiments is not crystalline metal oxide having a general formula
  • the crystalline metal oxide of general formulae (II), (lla), (lib), (lie), (III), (IVa) and / or (IVb) may have an AB0 3 crystalline unit cell structure as described according to the first embodiment thereof above.
  • the (Bai- X Q X ) is at A-sites in the crystal lattice and the ((Zri. y Hf y )i- z Q 1 z) is at B-sites.
  • the nickel may therefore be at A and / or B sites.
  • the crystalline metal oxide is selected from the group consisting of 3%-7% Ni/BaZrOs; 8-12% Ni/BaZrC ; 18-22% Ni/BaZr0 3 ; 23-27% Ni/BaZrCfe; 28-32% Ni/BaZrOs; 38-42% Ni/BaZr0 3 ; 43-47% Ni/BaZr0 3 ; 48-52% Ni/BaZr0 3 ; 3-7% Ni/BaHfC ; and 18-22% Ni/BaHf0 3 .
  • the reference to X% Ni/BaZrOs refers to the atom% nickel incorporated relative to the theoretical amount of barium or zirconium in barium zirconate / hafnate.
  • the %nickel content relative to the theoretical amount of barium in the barium zirconate/hafnate crystal lattice may be anywhere with the range.
  • 20% Ni/BaZrOa for example includes crystalline metal oxide of the formula Nfo 2Ba 0 eZr0 3 .
  • the crystalline metal oxide has a general formula selected from the group consisting of: 5% Ni/BaZr0 3 , 10% Ni/BaZrCb, 20% Ni/BaZr0 3 , 25% Ni/BaZr0 3 , 30% Ni/BaZr0 3 , 40% Ni/BaZrOs, 45% Ni/BaZr0 3 , 50% Ni/BaZrO.,, 5% Ni/BaHf0 3 and 20% Ni/BaHfOs.
  • the crystalline metal oxide has a general formula selected from the group consisting of:
  • Ni + Ba 1.
  • the crystalline metal oxide has a general formula selected from the group consisting of:
  • the crystalline metal oxide has a general formula selected from the group consisting of Nio.osBao ss rCh, Ni 0 iBao gZrCb,
  • the crystalline metal oxide has a general formula selected from the group consisting of N osBao 95Zr0 3j Ni 0 iBa 0 gZrC , Ni 0 2 Ba 0 sZr0 3 , Ni 03 Bao jZrOs, io Bao eZrOr,, Nio45Ba 0 55Zr0 3 and Nio.sBaasZrOs.
  • the crystalline metal oxide has a general formula selected from the group consisting of Nio osBao.asHfC and Ni 0 2 Ba 0 sHfOa.
  • the crystalline metal oxide has the general formula 20% Ni/BaZrOa, i.e. barium zirconate comprising 4% nickel incorporated homogeneously in the barium zirconate crystal lattice (in sold solution),
  • a crystalline nickel barium zirconate characterized by X-ray powder diffraction peaks at about 30.3°, 37.4°, 43.3°, 53.8°, and 64.0° ⁇ 0.2° 2 ⁇ .
  • This material is typically 20% Ni/BaZr0 3 , i.e. barium zirconate comprising 4% nickel incorporated homogeneously in the barium zirconate crystal lattice (in sold solution).
  • a crystalline nickel hafnium zirconate characterized by X-ray powder diffraction peaks at about 30.4°, 43.5°, 54.0°, and 63.2° ⁇ 0.2" 2 ⁇ .
  • This material is typically 20% Ni/BaHf0 3 , i.e. barium zirconate comprising 4% nickel incorporated homogeneously in the barium zirconate crystal lattice (in sold solution). These XRPD peaks were obtained using the conditions set out in the Examples section. Purity
  • the crystalline metal oxides as described in any of the above aspects and embodiments may be substantially phase pure.
  • the crystalline metal oxide of the present invention has a phase purity of at least 80 mol%, suitably at least 90 mol%, preferably at least 95 mol%, at least 98 mol% or more preferably at least 99 moi%.
  • the crystalline metal oxide of the present invention has a phase purity of at least 80 wt%, suitably at least 90 wt%, preferably at least 95 wt%, at least 98 wt% or more preferably at least
  • the hydrothermai methods of the present disclosure provide material of high phase purity. Phase impurities may be reduced / removed by washing in acid, such as HN0.3. In preferred embodiments, the crystalline metal oxides of the present invention are completely (i.e. 100%) phase pure.
  • the crystalline metal oxides of the present invention are able to incorporate surprisingly high levels of nickel homogeneously into the crystal lattice structure without detriment to the phase purity (see, e.g. Figure 1 showing phase pure material having levels of 4 atom 0 / ⁇ nickel).
  • High phase purity is desirable as it typically provides greater catalyst stability and more predictable catalytic reaction profiles.
  • the crystalline metal oxide has a perovskite-type unit cell structure.
  • perovskite-type refers to a crystal unit cell structure analogous to that adopted by perovskite, as well as distorted perovskite unit cell structures.
  • the crystalline metal oxides of the invention have a perovskite unit cell structure, i.e. a unit cell structure analogous to that adopted by perovskite.
  • the crystalline metal oxides according to any aspect or embodiment thereof described herein has a surface area greater than 5 m 2 /g, such as greater than 10 m 2 /g or 15 m 2 /g, preferably greater than 20 m 2 /g, 22 m 2 /g, 25 m 2 /g, 30 m 2 /g, more preferably greater than 35 m 2 /g.
  • the crystalline metal oxide has a surface area of up to 80 m 2 /g, for example up to 70 n Vg, 60 m /g, 50 m 2 /g, 40 m 2 /g, 30 m 2 /g, or 20 m /g.
  • the crystalline metal oxide has a surface area of 5-80 m 2 /g, suitably 15-70 m 2 /g, 20-60 m 2 /g, 30-50 m /g. or 35- 45 m 2 /g, typically around 40-50 m 2 /g.
  • the crystalline metal oxide has a surface area of between 5 - 30 m 2 /g or 8 - 25 m 2 /g, such as 10-20 m 2 /g.
  • the crystalline metal oxides of the present invention suitably exhibit high surface area (particularly when prepared according to hydrothermal methods disclosed herein) without requiring further mechanical manipulation such as milling or grinding, etc. High surface area is desirable for heterogeneous catalytic reactions where access to the catalyst surface is a determining factor in reaction rate.
  • the crystalline metal oxides of the present invention may comprise particle sizes having a length of from 0.1-20 pm.
  • the present invention provides solid crystalline oxides having a particle size in the range of 0.1-10 pm, such as 0.1 pm to 5 pm, for example 0.1 pm to 2 pm, and in typical embodiments from 0.1 pm-1 pm.
  • the present invention provides solid crystalline nickel barium zirconate material having a maximum particle size in the range of 1 - 2 pm, typically 1 pm.
  • the present invention provides solid crystalline nickel barium hafnate having a maximum particle size in the range of 0.5-2 pm, such as 1 pm.
  • the methods of preparation of the crystalline metal oxides of the present invention disclosed herein provide particle sizes in the ranges above without need for additional mechanical manipulation of the resulting crystals, e.g. such as milling or grinding.
  • the metal chloride may be a metal oxychloride.
  • the present process is procedurally simple (mixing the starting materials in an autoclave) and heating and does not require addition of
  • the reaction proceeds at relatively low temperature (e.g. 180 °C) to provide high-quality crystalline metal oxide material (i.e. highly phase pure material - see example 1 ).
  • relatively low temperature e.g. 180 °C
  • high-quality crystalline metal oxide material i.e. highly phase pure material - see example 1 .
  • the present process is useful for preparing crystalline metal oxides including barium.
  • the crystalline metal oxide may thus be as defined according to any of the first to eighth aspects and embodiments thereof as disclosed above.
  • the process may be a process of preparing a crystalline metal oxide having a unit cell structure of the general formula ABO3 comprising metals at A sites and B sites, typically where barium is at A-sites.
  • barium salt provides for A-sites
  • metal chloride provides said metal for incorporation at B-sites.
  • the present process is procedurally simple (reacting the starting materials in an autoclave) and advantageously proceeds at relatively low temperature (e.g. 180 °C) to provide high quality crystalline metal oxide material (i.e. highly phase pure material - see example 1 ).
  • relatively low temperature e.g. 180 °C
  • B-metal chlorides in the present process provides suitable reactivity, avoiding the introduction of carbonaceous materials (such as carbonaceous counter ions or complexing agents), which can lead to phase impurities.
  • Barium salts such as carbonaceous counter ions or complexing agents
  • the barium salt is a barium nitrate or a barium chloride, preferably a barium nitrate, e.g. Ba(NO?) 2 .
  • the barium salt is a barium chloride, e.g. BaC .
  • the metal chloride is selected from transition metal chlorides.
  • the metal chloride is a metal oxychloride. such as a transition metal oxychloride.
  • the transition metal chloride is selected from one or more of titanium chloride, zirconium oxychloride and hafnium oxychloride.
  • the metal oxychloride is zirconium oxychloride or hafnium oxychloride, or a combination thereof.
  • the metal oxychloride is zirconium oxychloride.
  • the metal oxychloride is hafnium oxychloride.
  • more than one metal oxychloride is provided, such as a combination of zirconium oxychloride and hafnium oxychloride.
  • Basic hydroxide such as a combination of zirconium oxychloride and hafnium oxychloride.
  • any suitable hydroxide may be used in the present process, provided it is basic (i.e. of basic pH).
  • the basic hydroxide is selected from metal hydroxides and ammonium hydroxides.
  • the basic hydroxide is an ammonium hydroxide.
  • the basic hydroxide is a metal hydroxide.
  • metal hydroxides are alkali metal or alkaline earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, e.g. potassium hydroxide.
  • Sodium hydroxide is particularly preferred.
  • the solution comprising the barium salt further comprises at least one further metal salt, suitably only one further metal salt or in alternative
  • the one or more further metal salts may be selected independently from salts of alkali metals, alkaline earth metals, transition metals, lanthanides and actinides.
  • the one or more further metal salts may be selected independently from salts of alkaline earth metals, transition metals and lanthanides, preferably from alkaline earth metal salts and transition metal salts, e.g. transition metal salts, such as nickel salts.
  • the at least one further metal salt may be independently selected from metal nitrates or metal chlorides, e.g. nitrates such as nickel nitrate.
  • a basic hydroxide is also added to the aqueous solution in step a).
  • the basic hydroxide may be as defined above for the ninth aspect and embodiments thereof.
  • the present process is useful for preparing crystalline metal oxides.
  • the reaction involves the use of barium, nickel and zirconium and / or hafnium salts (for instance zirconium and hafnium, or zirconium or hafnium).
  • the resulting crystalline metal oxide may thus be defined according to any of the first to eighth aspects or embodiments thereof as described above.
  • the barium, nickel and zirconium and / or hafnium salts may be selected
  • the barium salt may be a chloride or nitrate, preferably a nitrate.
  • the nickel is a chloride or nitrate, preferably a nitrate.
  • both barium and nickel salts are nitrates.
  • the zirconium and / or hafnium salts may be selected independently from chlorides or nitrates, typically chlorides.
  • the zirconium and / or hafnium chlorides are oxy chlorides, such as wherein the oxychloride is an oxychloride hydrate, e.g. an oxychloride octahydrate.
  • the process includes mixing at least one further metal salt in step a), suitably only one further metal salt or in alternative embodiments more than one (e.g. two) further metal salts.
  • the one or more further metal salts may be selected independently from alkali metals, alkaline earth metals, transition metals, lanthanides and actinides.
  • the one or more further metal salts may be selected independently from alkaline earth metals, transition metals and lanthanides, preferably from alkaline earth metal salts and transition metal salts, e.g. transition metal salts.
  • the at least one further metal salt may be independently selected from metal nitrates or metal chlorides.
  • the present invention also provides a process for preparing a crystalline metal oxide as defined in any of the first to eighth aspects and embodiments thereof.
  • the process for preparing a crystalline metal oxide as described in any of the first to eighth aspects and embodiments is as defined in the ninth and tenth aspects and embodiments.
  • the present invention thus provides a process as defined in the ninth or tenth aspect and embodiments thereof for preparing a crystalline metal oxide as defined in any of the first to eighth aspects and embodiments thereof.
  • the average temperature does not exceed 500 "C.
  • the average temperature refers to the temperature of the reaction averaged over the duration of the reaction.
  • the average temperature during the process does not exceed 450 °C, preferably 400 °C, 350 °C, 300 °C, 250 °C or more preferably 200 °C.
  • the reaction temperature does not exceed 500 X, suitably 450 °C, preferably 400 °C, 350 °C, 300 °C, 250 °C or more preferably 200 °C.
  • the reaction is performed at around 180 °C.
  • the process does not include a calcination (calcining) step.
  • the present processes advantageously do not require the addition of chelating agents, such as ethylene glycol or citric acid.
  • the processes of the invention do not include the addition of complexing or chelating agents, such as ethylene glycol or citric acid.
  • the present processes advantageously do not require the addition of concentrated acids, such as HN0 3 .
  • the processes of the invention do not include the addition of concentrated acids, such as HNO s
  • the heating step in the above processes is performed in an autoclave.
  • the processes defined in the above aspects and embodiments of the invention further comprising the step of isolating the solid product (i.e. the crystalline metal oxide).
  • the processes comprise the step of purifying the product (i.e. crystalline metal oxide).
  • the purification comprises centrifugation and / or washing of the solid product (i.e. crystalline metal oxide).
  • the processes of the present invention comprise the steps of incorporating the solid product (i.e. crystalline metal oxide) into a catalytic composition and / or packaging the solid product (i.e. crystalline metal oxide).
  • a crystalline metal oxide obtainable by any process as defined in the ninth or tenth aspects and their embodiments.
  • compositions comprising a crystalline metal oxide as defined according to any of the aspects and embodiments described herein, e.g. in the first to eighth aspects and embodiments.
  • the composition may comprise one or more carriers.
  • the composition may comprise a crystalline metal oxide of the invention supported on, or as part of (e.g. interspersed within), a carrier substrate.
  • Suitable carriers and / or supports will be apparent to a skilled person and include conventional catalyst support materials, such as ceramics and oxides, e.g. alumina and / or silica.
  • the composition may further comprise one or more catalysts (i.e. which may thus be in addition to the crystalline metal oxide of the invention).
  • the one or more catalysts may be selected from methane reforming catalysts.
  • the catalyst(s) is solid oxide fuel cell anode cermet, preferably Ni/YSZ anode cermet.
  • the composition includes at least a second crystalline metal oxide of the invention as described in any of the above aspects and embodiments.
  • a catalyst comprising a crystalline metal oxide as defined in any of the above aspects and embodiments thereof (e.g. as in the first to eleventh aspects and embodiments thereof, preferably the first to eighth aspects and embodiments thereof) or a composition as defined above in the twelfth aspect and any of its embodiments, and one or more carriers.
  • the catalyst may comprise a crystalline metal oxide or composition supported on, or as part of (e.g. interspersed within), a carrier substrate.
  • a product comprising a crystalline metal oxide according any of the above aspects and embodiments, a composition according to any of the twelfth aspect and embodiments, or a catalyst as defined in the thirteenth aspect or any embodiments thereof.
  • the product comprises the crystalline metal oxide, composition or catalyst of the invention as defined above within the product and / or on the surface of the product.
  • the crystalline metal oxide, composition or catalysts of the invention may be provided as a coating on a product, such as on an electrode.
  • the product is a reactor, such as a fuel cell.
  • the product may be a vehicle, such as a motor vehicle.
  • the product consists of the crystalline metal oxide, composition or catalyst of the invention as described herein above.
  • Such compositions, catalysts and / or products as defined above may suitably be used as the source of the crystalline metal oxide in the methods of reforming fuels as defined in any of the above aspects and embodiments.
  • the uses and methods of reforming a fuel as defined according to any aspect or embodiment described above may use a composition, catalyst and / or product as defined above.
  • additives or “dopants” in the context of crystalline metal oxides of the invention refer to substances that are incorporated into the crystalline metal oxides of the invention alongside nickel, barium, zirconium and / or hafnium, and oxygen.
  • the additives or dopants in the crystalline metal oxides of the invention described above may be independently selected from metals and / or non-metals, typically metals.
  • Suitable metals may be selected from alkali metals, alkaline earth metals, transition metals, lanthanides, actinides and other conventional additives (i.e. dopants).
  • references to metals such as barium, zirconium, hafnium and nickel in the context of crystalline metal oxides of the invention typically refers to the respective metal ions (i.e. cations) due to the large difference in electronegativity between metals and oxygen (i.e. forming oxide anions).
  • some degree of covalent character in the bonds between these species in the crystal lattice may be observed, for instance depending on the interaction of the A and B metal species with oxygen.
  • Atom% refers to a percentage of a given amount of atoms.
  • the material Nio 2 Bao eZrC>3 contains 4 atom% nickel, 16 atom% barium, 20 atom% zirconium and 60 atom% oxygen atoms.
  • Ni/BaZr0 3 refers to the atom% nickel incorporated relative to the theoretical amount of barium or zirconium in nickel-free barium zirconate / hafnate.
  • >20% Ni/BaZr0 3 refers to materials including at least 20atom% nickel relative to the theoretical amount of barium or zirconium/hafnium in nickel-free barium zirconate/hafnate material.
  • 20% Ni/BaZrf3 ⁇ 4 includes crystalline metal oxide of the formula io ⁇ Bao eZrOs.
  • Figure 1 shows the powder X-ray diffraction data for Ni/BaZr0 3 comprising 4 atom% nickel incorporated homogeneously into the crystal lattice as prepared according to the method of Example 1a.
  • the lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e. NioaBaosZrCh).
  • Figure 2 shows a scanning electron microscopy (SEM) image of the material described in Figure 1.
  • Figure 3 shows the powder X-ray diffraction data for Ni/BaZr0 comprising 5 atom% nickel incorporated homogeneously into the crystal lattice prepared according to a method analogous to Example 1a.
  • the lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e.
  • Figure 4 shows the powder X-ray diffraction data for Ni/BaHf0 3 comprising 4 atom% nickel incorporated homogeneously into the crystal lattice as prepared according to a method of Example 1 b.
  • the lack of impurity peaks in the XRPD pattern indicates that the material is phase-pure (i.e. Ni 0 2Ba 0 8HfO 3 ).
  • Figure 5 shows a reverse temperature-programmed profile for the reaction of methane with stoichiometric steam over Ni/BaZrCb comprising 4 atom% nickel (Nio.2Bao.8Zr03)as described in Example 2.
  • the graph plots molar equivalents of product gases against temperature.
  • Figure 6 shows a reverse temperature-programmed profile for the reaction of methane with stoichiometric steam over conventional Ni/YSZ anode cermet
  • Figure 7 shows a reverse temperatu re-prog ra m med profile for the reaction of methane with limited amounts of oxygen over Ni/BaZrOi comprising 4 atom% nickel ( io ⁇ BaosZrOs) as described in Example 3.
  • the graph plots molar equivalents of product gases against temperature.
  • Figure 8 shows a temperature-programmed profile for the reaction of methane with limited amounts of oxygen over perovskite-type La 07 Sr 0 3 n0 3 as described in Comparative Example 2.
  • the graph plots molar equivalents of product gases against temperature.
  • Figure 9 shows a temperature-programmed profile for the reaction of methane with limited amounts of oxygen over conventional Ni YSZ anode cermet. (Comparative Example 3) The graph plots molar equivalents of product gases against temperature.
  • Figure 10 shows a comparison between the methane conversion data for the reaction of methane with limited amounts of oxygen over Ni/BaZr0 3 comprising 4 atom% nickel and conventional Ni/YSZ anode cermet and corresponding to the reaction profiles in Figures 7 and 9.
  • the graph plots percentage methane conversion against temperature.
  • the upper line at 800 °C is for Ni/BaZr03 comprising 4 atom% nickel and the lower is for conventional Ni/YSZ anode cermet.
  • Figure 11 shows a comparison between the methane conversion data for the reaction of methane with limited amounts of oxygen over Ni/BaZr0 3 comprising 4 atom% nickel and Ni/BaHfCb comprising 4 atom% nickel.
  • the data were obtained by a reverse temperature-programme analogous to that shown in Figure 7 and the graph plots percentage methane conversion against temperature for each catalyst.
  • Figure 12 shows the isothermal reaction profile showing methane conversion in limited oxygen over Ni/BaZr0 3 comprising 4 atom% nickel (as produced according to example 1 ) at 800°C.
  • Figure 13 shows the reaction profile for the isothermal reaction of methane with limited oxygen over Ni/BaZr0 3 comprising 4 atom% nickel (as produced according to example 1 ) at 800 °C to investigate susceptibility to coking.
  • the graph plots molar equivalents of product gases against reaction time.
  • Figure 14 shows the temperature-programmed profile for the reforming of simulated biogas (methane / carbon dioxide in a 2:1 ratio) over Ni/BaZr0 3 comprising 4 atom% (corresponding to Figure 1 - i.e. as produced according to Example 1 ).
  • Figure 18 shows the powder X-ray diffraction data for Ni/BaZrOs comprising 2 atom% nickel incorporated homogeneously into the crystal lattice prepared according to a method analogous to Example 1 a (i.e. corresponding to Ni 0 iBa 0 gZrO 3 ).
  • the lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e. Nio iBao gZrOs).
  • Figure 19 shows the powder X-ray diffraction data for Ni/BaZr0 3 comprising 1 atom% nickel incorporated homogeneously into the crystal lattice prepared according to a method analogous to Example 1a.
  • the lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e. Nio osBao gsZrCh).
  • Figure 20 shows a temperature programmed thermal decomposition of acetic acid over Nio 2Bao e r0 3 .
  • the graph plots molar equivalents of product gases against temperature.
  • Figure 21 shows a reverse temperature programmed thermal decomposition of acetic acid over io ⁇ Bao.s rOs.
  • the graph plots molar equivalents of product gases against temperature.
  • Figure 22 shows a temperature programmed steam reforming of acetic acid over Mb 2 Ba 0 s rC .
  • the graph plots molar equivalents of product gases against temperature.
  • Figure 23 shows a reverse temperature programmed steam reforming of acetic acid over io . 2Bao e r03. The graph plots molar equivalents of product gases against temperature.
  • EDX elemental analysis data were collected using a Hitachi TM3000 scanning electron microscope equipped with a Bruker Quantax 70 EDS system.
  • Example 1 Preparation of exemplary crystalline metal oxides of the invention by hydrothermal methods of the invention a. Preparation of nickel barium zirconate
  • barium nitrate (1.30 g, 4.96 mmol) and nickel nitrate hexahydrate (0.36g, 1.24 mmol) were dissolved in deionised water (8 ml, 400 mmol).
  • Zirconium oxychloride octa hydrate (2.0 g, 6.20 mmol) was then added, followed by sodium hydroxide (2 g, 50 mmol).
  • the mixture was stirred by hand to produce a thick gel, before being transferred to a 23 ml Teflon-lined stainless steel autoclave and heated in a forced air oven at 180 °C. After 72 hours the autoclave was removed and allowed to cool to room temperature.
  • Typical uncertainties for the atomic compositions were ⁇ 1.2% (Zr), ⁇ 1.1% (Ba), ⁇ 2% (O), ⁇ 0.2% (Ni).
  • Ni/BaZr0 3 5% Ni/BaZr0 3 , 10% Ni/BaZrQ 3 , 25% Ni/BaZrCb, 30% Ni/BaZrOs, 40% Ni/BaZr0 3 , 45% Ni/BaZr0 3 and 50% Ni/BaZr0 3 , respectively).
  • this material corresponds to a final product having the following atomic ratios: io.o5Ba 0 .95Zr0 3 , Nio.iBa 0 .9Zr0 3 , io ⁇ Bao.zsZrOa, Ni 0 3 Ba 0 .7ZrO 3 , Nio.4Ba 0 .6Zr0 3 , i 0 .45Ba 0 . 6 5ZrO 3 and Ni 0 5 Ba 0 5ZrO 3 respectively.
  • Reaction conditions analogous to those in Example 1a were used to prepare corresponding nickel barium hafnate material, substituting hafnium oxychloride for zirconium oxychloride.
  • catalysts containing 4 atom% nickel and 1 atom% nickel were prepared (i.e. wherein 20 mol% nickel and 5 mol% nickel is provided in the reaction relative to the combined molar amount of barium and nickel salts respectively).
  • Powder X-ray diffraction for the 4 atom% nickel material showed the respective material to be highly crystalline and highly phase-pure with AB0 3 -type perovskite structures, thus confirming that the nickel was incorporated completely into the crystal lattices, forming a solid solution corresponding to Ni/BaHf0 3 comprising 4 atom% nickel, i.e. 20% Ni/BaHfCb, corresponding to Nio ⁇ BaoeHfCb.
  • Nickel barium zirconates can provide nickel barium zirconates.
  • Exemplary materials of the invention prepared as described above showed excellent catalytic properties in a variety of gas reforming reactions as described in the Experimental Data section below.
  • the hydrothermal methods of the present invention such as described in Example 1 therefore provide crystalline metal oxides using a simple procedure (the starting metal salts are simply mixed in aqueous solution in a single step without prior manipulation), at relatively low temperature (such as compared to methods which require a calcination step) and whilst avoiding both the introduction of carbonaceous materials that can contaminate the product (such as ethylene glycol or citric acid complexing agents - as required in prior art citrate methods) and the use of harshly acidic conditions.
  • the reaction provides high-quality crystalline metal oxide material (i.e. highly phase pure material - see example 1 and figure 1 ) in high yield (typically in essentially stoichiometric yield).
  • hydrothermal methods of the present disclosure therefore provide an excellent way to access the materials of the present invention.
  • metal chlorides e.g. oxychlorides in the crystal lattice forming reaction
  • materials produced according to Example 1 were tested for catalytic performance in gas reforming reactions to produce syngas.
  • Corresponding data for other catalysts including lanthanum barium manganite and standard nickel anode cermet, i.e. nickel-doped yttria-stabilised zirconia (Ni/YSZ) are also provided for comparative purposes.
  • methane reforming was performed over Ni/BaZrC comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZrOs, corresponding to Nio 2 Ba 0 eZr0 3 as a solid solution) as prepared according to Example 1a.
  • a reverse temperature-programmed reaction profile was obtained by incrementally decreasing the reaction temperature as illustrated in Figure 5.
  • Example 2 For comparative purposes, the analogous reaction conditions to Example 2 were provided but using conventional Ni/YSZ cermet in place of the nickel barium zirconate of the present invention.
  • the corresponding reaction profile is illustrated in Figure 6.
  • the material of the present invention exhibits excellent steam reforming activity with an initial activation temperature significantly lower (around 200 °C lower) than conventional Ni/YSZ cermet.
  • Optimum reforming begins at around 750 °C for the present catalysts, proving the catalysts of the invention to be comparable to conventional Ni/YSZ cermet in steam reforming based on catalytic activity.
  • Ni/BaZr0 3 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZrOs, corresponding to Nio ⁇ Bao.eZrOa as a solid solution) as prepared according to Example 1a.
  • a reverse temperature-programmed reaction profile was obtained by incrementally decreasing the temperature as illustrated in Figure 7.
  • hydrogen and carbon monoxide are the major reaction products above 700 °C ( Figure 7). with low amounts of total oxidation products in evidence.
  • Comparative Example 2 Comparative Example 2:
  • the comparison shows the crystalline metal oxide of the present invention to have greater selectivity for partial oxidation of methane compared to Lao jSr 0 3Mn0 3 , with very low amounts of complete oxidation products in evidence above 700 °C.
  • Ni YSZ anode cermet which is known to provide desirable selectivity in partial oxidation reforming reactions.
  • the temperature-programmed reaction profile is provided in Figure 9 showing Ni/YSZ anode cermet to have good selectivity for partial oxidation from around 650 °C upwards.
  • Ni/BaZr(3 ⁇ 4 comprising 4 atom% nickel in solid solution i.e. 20% Ni/BaZrOs, corresponding to Nio-Bao sZr0 3 as a solid solution
  • methane conversion and gas production shows that crystalline metal oxides of the present invention advantageously display a similar reaction profile to Ni/YSZ at similar operating temperatures while showing greatly increased methane conversion during methane reforming (approx.
  • Example 4 - comparison of activity of zirconate and hafnate Figure 11 shows a comparison of methane conversion data for Ni/BaZrOa comprising 4 atom% nickel in solid solution (i.e.
  • Ni/BaZr0 3 corresponding to Nio JBao sZ Oa as a solid solution
  • Ni/BaHf0 3 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaHf0 3 , corresponding to Nio 2Bao 8 Hf0 3 as a solid solution) as prepared according to Example 1b.
  • These two materials gave similar reaction profiles but with a slightly increased conversion rate for the zirconate, which may be attributable to the higher nickel content per 20 mg of catalyst in the zirconate catalysts.
  • the partial oxidation of methane over Ni/BaZr0 3 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZrG 3 , corresponding to Nio 2 Ba 0 8Zr0 3 as a solid solution) as prepared according to Example 1a was conducted under isothermal conditions at 700 °C, 800 °C and 900 °C.
  • the isothermal reaction profile at 800 °C over 20 h is provided at Figure 13. No degradation in catalytic activity is observed over 20 hours, as exemplified by the methane conversion data in Figure 12 (conducted at 800 °C) showing excellent resistance to coking over long periods.
  • Ni/BaZr0 3 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr0 3 , corresponding to Ni 02 Ba 0 eZr0 3 as a solid solution) as prepared according to Example 1a occurs at just under 500 °C with stoichiometric conversion (50% methane conversion) occurring rapidly at roughly 800 °C.
  • This nickel barium zirconate produces hydrogen selectively over carbon monoxide at lower temperatures without increased carbon deposition, suggesting true reforming is occurring.
  • the temperature-programmed reaction profile is shown in Figure 14.
  • Figure 15 shows the reaction profile for an extended catalytic reforming reaction (run over 10 days) of simulated biogas over Ni/BaZrCh comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr0 3 , corresponding to Ni 0 2Bao8Zr0 3 as a solid solution) as prepared according to Example 1a at 850 °C.
  • the reaction equilibrates quickly to provide 50% methane conversion corresponding to the desired dry reforming reaction between 1 mol. eq. CH 4 with 1 mol. eq. CQ 2 (i.e. leaving 1 mol. eq. CH unreacted in the reaction mixture, i.e. 50% of initial amount) - see also for example Figure 17 which shows the methane conversion data over 3h.
  • the results show that the catalyst of the invention can reform biogas for long periods of time with negligible carbon deposition. In this reaction only 1.85 mg of carbon was deposited
  • the reaction over Ni/YSZ cermet equilibrates to a level closer to 60% methane conversion (i.e. which exceeds the stoichiometric amount of 50% methane conversion expected in a perfect dry reforming reaction), indicating that excess methane is being cracked, leading to coking of the catalyst surface.
  • the reaction profile for Ni/YSZ cermet at 850 °C over 20 h showing gaseous products relative to methane is provided in Figure 16.
  • the respective methane conversion profile of Ni/YSZ compared to Ni/BaZr0 3 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr0 3 , corresponding to io 2Bao.8Zr0 3 as a solid solution) as prepared according to Example 1a over 3 h is provided in Figure 17.
  • the crystalline metal oxides of the present invention reform simulated biogas at lower temperatures compared to Ni/YSZ cermet (i.e. with reforming starting just under 500 °C) with stoichiometric conversion (i.e.
  • the crystalline metal oxides of the present invention produce syngas selectively and show substantially less coking than Ni/YSZ cermet, even over long reaction times (e.g. 10 days - Figure 15). In particular, in the reaction over 10 days ( Figure 15), only 1.85 mg carbon was deposited, a surprisingly low amount.
  • the crystalline metal oxides of the present invention steam reform acetic acid at reasonable temperatures.
  • the crystalline metal oxides of the present invention exhibit excellent activity in a variety of reforming reactions to form syngas selectively over alternative reaction pathways. These reforming reactions include dry reforming, steam reforming and partial oxidation, showing the versatility of the crystalline metal oxides of the present invention in reforming reactions for the production of syngas.
  • crystalline metal oxides of the present invention are able to tolerate surprisingly high levels of active nickel incorporated homogenously within the crystal lattice (i.e. in solid solution) whilst retaining high levels of phase purity. Crystalline metal oxides of the present invention show excellent resistance to coking. This is particularly surprising given the high nickel content of the tested catalysts.
  • the materials of the present invention provide a valuable alternative to conventional nickel based catalysts (such as Ni/YSZ cermet) in reforming reactions for the production of syngas, particularly in the reforming of fuel derived from natural sources, including biofuels, such as biogas.
  • nickel based catalysts such as Ni/YSZ cermet

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Abstract

The present invention provides new crystalline metal oxides, particularly nickel barium zirconate / hafnate, having utility in catalysing a variety of fuel reforming reactions for the production of syngas. New methods for producing crystalline metal oxides are also described.

Description

Catalysts
STATEMENT OF INVENTION
The present invention relates to new crystalline metal oxide catalysts, methods of making crystalline metal oxide catalysts and their use in fuel reforming reactions, particularly for use in the manufacture of syngas.
BACKGROUND
Syngas is a gaseous mixture composed principally of hydrogen and carbon monoxide and is an important commercial product. A large proportion of commercial hydrogen gas is manufactured from syngas and syngas is the principal commercial source of carbon monoxide (used in the preparation of chemical reagents and in synthetic processes, such as carbonylation reactions). Research into the production of syngas has attracted attention in recent years due to its growing potential as a "greener" alternative to conventional fuel sources in a number of processes. For example, syngas is presently used as an alternative to natural gas in power-generating processes (e.g. for use in fuel cells). For instance, syngas offers an alternative to fossil fuels as a feedstock for the manufacture of chemicals such as methanol and long chain hydrocarbons via the Fisher-Tropsch process (useful in preparing transportation fuels and polymers).
Gas reforming reactions offer a useful way to prepare syngas. For instance, syngas can be prepared on a commercial scale by reforming the potent greenhouse gases methane and carbon dioxide. Typical reforming methods for producing syngas include dry reforming, steam reforming, and partial oxidation of various fuel gases.
Dry reforming
This typically involves reforming a mixture of carbon-based fuel (such as methane) and carbon dioxide in the presence of a catalyst, usually a metal supported on a ceramic material. Nickel-based catalysts such as nickel-doped yttria-stabilised zirconia (Ni/YSZ) cermet are conventionally used. This endothermic reaction requires a large input of energy. The reaction with methane can be described by the equation CH4 + CO2 «-> 2CO + 2H2. Other side reactions can occur, such as the reduction of carbon dioxide with hydrogen to form carbon monoxide and water. It is therefore essential to provide reaction conditions that are selective for the syngas forming reaction. From an environmental perspective, "biogas" (i.e. the product of the breakdown of organic matter in the absence of oxygen) is an attractive fuel source as it contains predominantly methane and carbon dioxide (usually in a 2:1 ratio). However, the presence of sulfur residues in biogas can lead to catalyst poisoning and failure, particularly when conventional nickel-based catalysts are used. Before biogas reforming can be considered efficient enough for commercial use, catalysts which are more resistant to sulfur poisoning are required. Steam reforming
Presently the most common method of producing syngas is by reforming the fuel, e.g. methane in the presence of a catalyst (e.g. Ni YSZ cermet) using steam as an oxidant. Using methane as an example, the desired methane reforming reaction is CH + H2O <→ CO + 3H2 (1 ). As with dry reforming, the overall reaction is endothermic and so requires a large energy input. The syngas produced is hydrogen rich (1 :3 CO.H2), providing a useful alternative to syngas produced by dry reforming. Steam reforming of methane can involve two further competing reactions which operate in thermodynamic equilibrium to the main gas reforming reaction (1 ), namely:
a) CO + H2O <→ C02 + H2 (slightly exothermic); and
b) CH4 + 2H20 <→ C02 + 4H2 (highly endothermic).
It is therefore desirable to provide reaction conditions that are selective for the initial syngas reforming reaction (1 ) above over the competing reactions in steps a) and b). Unless hydrogen is the desired product, in which case it is desirable to promote steps a) and b).
Partial oxidation
Preparation of syngas by partial oxidation involves the reaction of fuel, e.g. methane with limited amounts of oxygen over a catalyst, using either pure oxygen or air as an oxygen source. There is growing interest in producing syngas by partial oxidation because unlike the reforming methods above, partial oxidation of methane is overall slightly exothermic and could therefore provide more efficient access to syngas. However, reported partial oxidation methods have so far been unable to match the efficiency of dry and steam reforming reactions described above. It is therefore desirable to provide new catalysts for use in methods of preparing syngas by partial oxidation. The reforming of methane in oxygen is characterised by a competition between the complete oxidation pathway (CH4 + 202 <→ C02 + 2H20) and the partial oxidation pathway (CH4 + 1/2 02 <→ CO + 2H2). In order to exploit this reaction to produce syngas, it is therefore necessary to provide reaction conditions that favour the partial oxidation pathway. Thus, there is a desire for catalysts that are able to promote the partial oxidation pathway selectively.
Coking
Carbon deposition on catalyst surfaces ("coking") is commonly encountered in the reforming processes described above. This is understood to be caused primarily by cracking of hydrocarbons on the catalyst surface (e.g. for methane, CH4 <→ C + 2H2), and where carbon monoxide is present, also as a result of the Boudouard reaction (2CO «→ C + C02). Catalyst coking leads to reduction in catalyst activity and, in severe cases, complete deactivation of the catalyst. Where coking occurs in practice, fresh catalyst must be added to the reaction to supplement the deactivated catalyst, or the reaction must be stopped and the deactivated catalyst treated or replaced before the reaction can be continued. Thus, catalyst coking leads to reduced efficiency, increased levels of process complexity and ultimately, increased cost. It is therefore desirable to provide catalysts that are less susceptible to coking and / or which better tolerate coking.
Sulfur poisoning
Sulfur impurities present in a fuel feed can cause rapid poisoning and deactivation of a gas reforming catalyst in as low as a few parts per million. Thus, as with coking, sulfur poisoning leads to reduced efficiency, increased levels of process complexity and ultimately, increased cost. This problem is commonly encountered where natural fuel sources are used (e.g. when biogas is used as a methane source). Sulfur poisoning therefore represents a significant hurdle that must be overcome before natural fuels such as biogas could represent commercially viable starting materials for gas reforming processes.
Crystalline metal oxides
Crystalline metal oxides have found use in solid oxide fuel cells (SOFCs) due to their high refractive and electrically conductive properties. Typically, such oxides are provided in the form of a cermet (a ceramic-metal composite). The metal component of the composite is required to perform the catalytic reaction and the ceramic component provides an ionically conducting porous and, preferably, refractory substrate. Ni/YSZ cermets are commonly used on a commercial scale as they are relatively inexpensive. More recently, proton-conducting SOFCs (PC-SOFCs) have been developed which facilitate transportation of protons through the electrolyte. Protonic conductors allow the SOFC to be run at lower temperatures than traditional SOFCs. For instance, cermets containing ytterbium-doped barium zirconate as the ceramic component and nickel metal as the catalytic metal component of the composite have been reported as anode substrates for use in PC-SOFCs (Park er al. Ceramics International, 39 (2013) 2581-2587).
The use of certain crystalline metal oxides in the total combustion of methane has also been reported. For instance, barium zirconate catalysts have been reported to show activity in the total combustion of methane (i.e. the complete oxidation of methane under a stoichiometric excess of oxygen to form carbon dioxide and water) when zirconium is partially replaced in the crystal lattice by amounts of Rh, Pd, Mn, Ni, Ru, Pt or Co (Gallucci, K. et al. Catalysis Today 197 (2012) 236-242; and Cifa, F. et al Applied Catalysis B: Environmental 46 (2003) 463-471 ).
Production of syngas
On a commercial scale, fuel reforming reactions for producing syngas are typically conducted over Ni/YSZ cermet catalyst because it offers high reaction rates and is relatively inexpensive. However, it is highly prone to deactivation by coking and sulfur poisoning. There is therefore considerable interest in providing alternative materials which show selective fuel reforming activity for producing syngas whilst exhibiting resistance to coking and / or sulfur poisoning.
Alternative crystalline metal oxides for use in syngas production have been reported. Viparelii, P. et al. has reported that barium zirconate catalysts incorporating Rh in the crystal lattice in partial replacement of zirconium show activity in forming syngas by partial oxidation of methane (Applied Catalysis A: General 280 (2005) 225-232). These Rh-doped catalysts however contain significant levels of BaC03 phase impurity, particularly at higher levels of Rh concentration.
Some success in avoiding coking has been reported with Rh- and Ru-based catalysts (Hayakawa, T. et al. Applied Catalysts A: General 1999, 183, 273-285 - see page 274 left hand column). Limited success has also been achieved with nickel-based catalysts in dry reforming reactions. For instance, Hayakawa, T. et al. {Applied Catalysts A: General 1999, 183, 273-285) describes nickel-containing alkaline earth titanates (experimental, page 274), i.e. Ni/MgTiOs, Ni/CaTi03, Ni/SrTi03, Ni/BaTi03l Ni/Ca0 8Mg02Ti03,
i Cao.sSro.2Ti03 and Ni/Cao.sBao^TiC , each containing an Ni Ti ratio of 0.2/1.0 (which would correspond to material containing 3.3 atom% nickel within the crystal lattice) and metal oxides containing 10.3 wt% nickel (Ni/TiCh, Ni/Zr02, N1/AI2O3, Ni/Si02 and Ni/MgO). These catalysts showed activity in dry reforming of methane with carbon dioxide, and both the alkaline earth titanates as well as certain titanium oxides were reported to have shown resistance to coking. Undesirably, however, the alkaline earth nickel titanates were of poor phase purity and contained NiO, indicating poor homogeneity of nickel within the catalytic material (and thus indicating that less than 3.3 atom% nickel must have been incorporated homogeneously into the crystal lattice). This problem was also reported by Takehira, K. et al. Journal of Catalysis 2002, 207, 307-316 (see, e.g. Figure 2 of that document, showing presence of NiO and Ni phase impurities).
Similarly, US 2012/0198536 A1 discloses perovskite-type strontium titanate catalysts doped with nickel and yttrium and the use of these catalysts in the formation of hydrogen-rich gas products from diesel fuel by autothermal reforming. These catalysts are alleged to show tolerance to coking and sulfur poisoning in such reactions. Catalysts containing up to 1.6 atom% nickel are reported
(i.e. (Sro 97Y01 )(Tio 92 10 oe)03. see table 1 ) but these materials contained phase impurities (paragraph 72 and figure 1 ) and attempts to increase the nickel content to 2 atom% led to an increase in secondary phases (paragraph 73). The resulting lack of phase impurity of the material is undesirable as the respective phases are prone to forming pockets of catalytic material, thus leading to unpredictable reaction profiles (for instance due to sintering and loss of selectivity) and catalyst instability. It is therefore desirable to provide new catalytic materials that obviate or mitigate the problems above. In particular, it is desirable to provide new catalysts that are of high quality (i.e. of high phase purity), exhibit high catalytic activity and / or high catalytic selectivity in syngas producing reactions (preferably in a wide range of syngas producing reactions), exhibit tolerance to high active species loading and / or good resistance to coking and / or sulfur poisoning. Catalyst preparation
Traditional methods of producing crystalline metal oxide catalysts, such as nickel- based metal oxides (e.g. Ni YSZ cermet) typically involve very high temperatures (≥1200 °C) and often require multiple steps of mixing and heating before high quality phase-pure material is produced.
Other methods, such as sol-gel and co-precipitation techniques, also involve a final firing step at temperatures well above 600 °C and do not always produce phase-pure materials. Thus, these synthetic methods tend to be wasteful, use large amounts of energy, and allow very little control of the morphology and properties of the final materials.
US 2012/0198536 A1 (paragraphs 55-65) for instance discloses the preparation of perovskite-type strontium titanate catalysts involving the use of citric acid and ethylene glycol as complexing agents and a calcination step performed at about 700 °C to 1000 °C. Similar citrate-based methods requiring high temperature calcination for the synthesis of doped barium zirconates are disclosed in Cifa, F. et al Applied Catalysis B: Environmental 46 (2003) 463-471 , Viparelli, P. et al (Applied Catalysis A: General 280 (2005) 225-232) and Gallucci, K. et al. {Catalysis Today 197 (2012) 236-242). Park, et al. (Ceramics International, 39 (2013) 2581-2587) and Hayakawa, T. et al. Applied Catalysts A: General 1999, 183, 273-285 also disclose processes involving calcination at high temperatures, and in the case of Hayakawa et al. a multi-stage heating protocol. Methods of preparing crystalline metal oxide catalysts (such as nickel-based metal oxides) at lower temperatures are disclosed in the prior art. Beale, A.M. et al.
(J. Mater. Chem. 2009, 19, 4391-4400) discloses a method involving mixing nickel nitrate tetrahydrate, strontium chloride hexahydrate, ethylene glycol, titanium tert- butoxide and potassium hydroxide in an autoclave at 120 °C for 20 h. However, this method is susceptible to producing metal carbonate phase impurities (see figure 2 at page 4394). Phule, P. et al. (Materials Science and Engineering, B23 (1994) 29-35) discloses a low temperature sol-precipitation route to barium zirconate, but this requires a significant amount of carbonaceous material and concentrated acid (barium is provided as barium acetate, and the zirconium is provided as zirconium acetylacetonate dissolved in glacial acetic acid). Maksimov, V.D. et al. (Inorganic Materials 2007, Vol 43, No. 9, pp 988-993) discloses a hydrothermal method of preparing barium zirconates and barium hafnates (experimental section at page 989), involving the heating of a suspension of amorphous zirconium hydroxide or hafnium hydroxide in barium hydroxide solution in a sealed Teflon cell mounted in an autoclave for 3 h. However this method is procedurally complex as it requires the multi-step synthesis of amorphous zirconium/hafnium hydroxides starting from zirconium oxynitrate and hafnium chloride respectively.
Athawale, A. A. et al. (Materials Science and Engineering B 119 (2005) 87-93) discloses the formation of strontium zirconate by mixing metal nitrates with concentrated nitric acid followed by basification with potassium hydroxide. However, the steps of adding concentrated nitric acid followed by potassium hydroxide are not desirable from a practical perspective as this would require intensive process control to avoid excess gas evolution and runaway increases in reaction temperature.
There is therefore a need to provide alternative methods for preparing crystalline metal oxides (particularly barium metal oxides) that obviate or mitigate the problems identified above. In particular it is desirable that such methods are procedurally non-complex, require use of less corrosive materials, produce less toxic / corrosive bi-products (i.e. are environmentally friendly), efficient, provide good control of chemical stoichiometry in the crystalline oxide product, provide material of desirable surface area, and / or produce high quality materials (i.e. having high phase purity).
SUMMARY OF INVENTION
In its most general, the present disclosure provides new solid crystalline metal oxides that exhibit catalytic activity in the reforming of fuels, such as hydrocarbons (e.g. methane) and oxygenated hydrocarbons (e.g. alcohols, such as ethanol), particularly to produce syngas. In particular, the invention provides nickel barium zirconates, nickel barium hafnates and solid solutions of nickel barium zirconate and nickel barium hafnate (i.e. barium zirconates, barium hafnates and solid solutions of barium zirconate and barium hafnate that are doped with nickel) that have utility in reforming hydrocarbon-containing fuels to produce hydrogen-rich gas products, particularly syngas.
The present catalysts are thus attractive for use in "green"' technologies which convert greenhouse gases such as methane and C02 into useful feedstock for industry. The present invention also provides hydrothermal processes for preparing these crystalline metal oxides.
DESCRIPTION OF INVENTION
In a first aspect of the invention is provided the use of a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide has a unit cell structure of the general formula AB03 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. Thus, the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide has a unit cell structure of the general formula AB03 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. Preferably said method is a method of preparing syngas. Thus, the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide has a unit cell structure of the general formula AB03 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. The invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide has a unit cell structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas.
ABO3 unit ceil structure
As will be understood by the skilled person, the formula ABO3 refers to a crystal lattice structure containing A, B and O lattice points, which occupy different lattice environments in the crystal. The component metals in the crystalline metal oxide occupy A and B sites and oxygen the O sites.
The crystal lattice structures may include one or more A-site, B-site and / or O-site defects, e.g. wherein there is an absence of one or more atoms / ions at one or more A-site, B-site and / or O-site lattice points. In embodiments, the crystalline metal oxide of the present invention includes material having one or more A-site and / or B-site defects. In embodiments, the crystalline metal oxide includes one or more A- site or B-site defects, such as one or more A-site defects. In embodiments, the crystalline metal oxide of the present invention includes one or more B-site defects. In embodiments, the crystalline metal oxide includes A-site and B-site defects.
In some embodiments, the crystalline metal oxide contains less than 10 % of A-site, B-site and / or O-site defects (e.g. wherein less than 10 % of the respective number of A, B and/or O sites in the lattice are absent of atoms/ions). In embodiments, the crystalline metal oxide contains less than 8 % A-site, B-site and / or O-site defects, preferably less than 6%, 4%, 2%, or more preferably less than 1%. Indeed, in some embodiments, the crystalline metal oxide of the invention is free of A-site, B-site and / or O-site defects.
Nickel, barium, zirconium and / or hafnium
The crystalline metal oxide comprises barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
In embodiments, substantially all of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
Suitably at least 90 mol% and preferably at least 95 mol%, 98 mol% or 99 mol% of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. In alternative embodiments, at least 90 wt% and preferably at least 95 wt%, 98 wt% or 99 wt% of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. In embodiments, 100% of the crystalline metal oxide consists of barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
Zirconium and / or hafnium at B sites
The crystalline metal oxide of the above aspect and embodiments comprises zirconium and / or hafnium at B sites. In embodiments, the crystalline metal oxide comprises zirconium at B sites, typically wherein the crystalline metal oxide comprises zirconium but not hafnium at B sites. In embodiments, the crystalline metal oxide comprises hafnium at B sites, typically wherein the crystalline metal oxide comprises hafnium but not zirconium at B sites. Suitably, the crystalline metal oxide may comprise zirconium and hafnium at B sites (i.e. wherein each zirconium and each hafnium occupy different B-sites). In embodiments, the relative proportions of zirconium and hafnium at B sites may be represented by the formula Zri-yHfy> wherein y = 0.0-1.0, for instance wherein y is 0.0, 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0. Thus, in embodiments, y = 1.0. In other embodiments, y= 0 0.
Incorporation of nickel at A and / or B sites
The crystalline metal oxide of the above aspect and embodiments comprises nickel at A and / or B sites. In embodiments, the nickel is at A and B sites. In embodiments, the nickel is at A or B sites, for example B sites. Preferably, the nickel is at A-sites.
In embodiments, nickel is present in at least 1 % of A and / or B sites, such as at least 2%, 5%, 10 %, 20 %, or 30 %. In embodiments, nickel is present in at least 1 % of A and B sites, such as at least 2 %, 5 %, 10 %, 20 %, or 30 % of A and B sites. In embodiments, nickel is present in at least 1 % of A or B sites, suitably in at least 2%, 5%, 10 %, 20 %, or 30 % of A or B sites, for example, B sites. Preferably, the nickel is present in at least 1 % of A-sites, suitably in at least 2%, 5%, 10 %, 20 %, or 30 % of A-sites.
In embodiments, at least half and preferably more than half of the nickel is at A sites. In other words, where nickel is present at A and B sites in the ABO3 crystal lattice, at least half and preferably more than half of the nickel is at A sites. Typically, at least 90% of the nickel may be at A sites. Suitably, at leas 95%, 98% or 99% of the nickel may be at A sites. In embodiments, the nickel is at A sites but not B sites
(i.e. wherein 100% of the nickel is at A sites). In other embodiments, at least half and preferably more than half of the nickel is at B sites. In embodiments, at least 90% of the nickel may be at B sites. Suitably, at least 95%, 98% or 99% of the nickel may be at B sites. In embodiments, the nickel is at B sites but not A sites (i.e. wherein 100% of the nickel is at B sites). Amount of nickel
The amount of nickel in the crystalline metal oxides of the invention may be selected according to the desired properties of the material.
In the above aspects and embodiments, the nickel may be present in the crystalline metal oxide in an amount of at least 0.2 atom%, suitably at least 0.4 atom%, such as at least 0.6 atom% or 0.8 atom%, preferably at least 1 atom%, 2 atom%, 4 atom% or 6 atom%. Preferably, the nickel is present in an amount of at least 1 atom%. In embodiments, the nickel is present in an amount of 12 atom% or less, suitably 10 atom % or less, 8 atom % or less, preferably 6 atom% or less, such as 4 atom% or less, 2 atom% or less, 1 atom% or less, 0.8 atom% or less, 0.6 atom% or less, or 0.4 atom% or less. For instance, in embodiments the nickel is present in an amount of from 0.2 atom% to 12 atom%, suitably from 0.4 atom% to 12 atom%, 0.6 atom% to 10 atom%, 0.8 atom% to 8 atom% or 1 atom% to 6 atom%. Preferably, the nickel is present in an amount of from 0.2 atom% to 7 atom%.
Additives
In embodiments, the crystalline metal oxide further comprises one or more additives (i.e. dopants) at A and / or B sites. Suitably one or more additives may be at A and B sites. In embodiments, the one or more additives are at A or B sites, for instance B sites. Preferably, one or more additives are at A sites. In embodiments, the one or more additives may be present in the crystalline metal oxide in an amount of up to 6 atom%, such as up to 4 atom%, 2 atom%, 1 atom%, 0.8 atom%, 0.6 atom%, 0.4 atom%, 0.2 atom% or 0.1 atom%.
The atomic ratio of crystalline metal oxides of the invention can be determined by EDX analysis and / or can be inferred based on the XRPD pattern. Elemental analysis data may be collected using a Hitachi TM3000 scanning electron microscope equipped with a Bruker Quantax 70 EDS system. Powder X-ray diffraction data may be collected using a Bruker D8 Advance diffractometer using a Cu Ka source and a flat disc sample holder. The crystalline oxide may for example be a crystalline metal oxide as described in any aspect and embodiment herein having a unit cell structure of the general formula AB03 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites. Second aspect
In a second aspect of the invention is provided the use of a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate. Thus, the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate.
Preferably said method is a method of preparing syngas. Thus, the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate. The invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate. Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas. Nickel
In embodiments, the nickel is present in the crystal lattice in an amount of at least 0.2 atom%, optionally at least 0.4 atom%, optionally at least 1 atom%, optionally at least 2 atom%, optionally at least 4 atom%, optionally at least 6 atom%. In embodiments, the nickel is present in an amount of 12 atom% or less, suitably 10 atom% or less, 8 atom% or less, preferably 6 atom% or less, such as 4 atom% or less, 2 atom% or less, 1 atom% or less, 0.8 atom% or less, 0.6 atom% or less, or 0.4 atom% or less. For instance, in embodiments the nickel is present in an amount of from 0.2 atom% to 12 atom%, suitably from 0.4 atom% to 12 atom%, 0.6 atom% to 10 atom%, 0.8 atom% to 8 atom% or 1 atom% to 6 atom%. Preferably, the nickel is present in an amount of from 0.2 atom% to 7 atom%.
Thus, in embodiments of this aspect, the crystalline metal oxide is selected from nickel barium zirconate nickel barium hafnate and solid solution of nickel barium zirconate and nickel barium hafnate represented by the formula >1 % Ni/BaZr03, >2% Ni/BaZr03, >2% Ni/BaZr03, >5% Ni/BaZr03, >10% Ni/BaZr03, >20% Ni/BaZr03, >30% Ni/BaZr03, >40% Ni/BaZr03, >45% Ni/BaZr03, >1 % Ni/BaHf03,
≥2% Ni/BaHfOs, >2% Ni/BaHf03> >5% Ni/BaHf03. >10% Ni/BaHf03, >20% Ni/BaHf03, ≥30% Ni/BaHf03, >40% Ni/BaHf03. or >45% Ni/BaHf03. Preferably the nickel amount in said crystalline metal oxides is less than 50atom% Ni/BaHf03, such as less than 45atom% Ni/BaHf03 less than 40atom% Ni/BaHf03 or less than
30atom% Ni/BaHf03. In such embodiments, the reference to X% Ni/BaZr03 refers to the atom% nickel incorporated relative to the theoretical amount of barium or zirconium in barium zirconate / hafnate. Thus, >20% Ni/BaZrCb refers to materials including at least 20atom% nickel relative to the theoretical amount of barium or zirconium/hafnium in nickel-free barium zirconate/hafnate material. The theoretical atom% of barium or zirconium/hafnium in barium zirconate (BaZrOa) is 20atom% (i.e. one in 5 atoms is a barium). Thus, 20% Ni/BaZrOs refers to nickel barium zirconate wherein 4atom% nickel is incorporated homogeneously in solid solution in the BaZr03 crystal lattice (typically in place of a corresponding amount of said barium and/ or zirconium/hafnium). For example, 20% Ni/BaZr03, includes crystalline metal oxides of the general formula Ni02Ba08Zr03.
Additives
In embodiments, at least some of the nickel, barium, zirconium and / or hafnium in the crystal lattice is replaced by one or more additives, i.e. wherein the crystal lattice includes one or more additives (i.e. dopants) in addition to the nickel, barium, zirconium and / or hafnium in the crystal oxide lattice (homogeneously incorporated in solid solution). In suitable embodiments, at least 1 atom% of the nickel, barium, zirconium and / or hafnium is replaced by one or more additives, suitably at least 2 atom%, preferably at least 5 atom%, at least 10 atom%, at least 20 atom%, or at least 30 atom% of the nickel, barium, zirconium and / or hafnium is replaced by one or more additives. In embodiments, the one or more additives may be present in the crystalline metal oxide in an amount of up to 6 atom%, such as up to 4 atom%, 2 atom%. 1 atom%, 0.8 atom%, 0.6 atom%, 0.4 atom%. 0.2 atom% or 0.1 atom%.
The nickel barium zirconate, nickel barium hafnate, and / or solid solution of nickel barium zirconate and nickel barium hafnate may be as further described according to any other aspect and embodiment herein. For instance, embodiments of the second aspect and embodiments may have a unit cell structure of the general formula ABC comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites as described above for the first aspect and embodiments.
Alternatively or additionally, the nickel barium zirconate, nickel barium hafnate, and solid solution of nickel barium zirconate and nickel barium hafnate may be of general formula (I) or (II) or embodiments thereof as described for the aspects and embodiments below. Third aspect
In a third aspect of the invention is provided the use of a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide has the general formula (I):
Figure imgf000015_0001
wherein a = 0.8 to 1.2 and y = 0.0 to 1 .0, wherein at least some of the barium, zirconium and / or hafnium is replaced by nickel. Thus, the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (I):
Figure imgf000015_0002
wherein a = 0.8 to 1 .2 and y = 0.0 to 1 .0, wherein at least some of the barium, zirconium and / or hafnium is replaced by nickel. Preferably said method is a method of preparing syngas. Thus, the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide has the general formula (I):
Figure imgf000015_0003
wherein a = 0.8 to 1 .2 and y = 0.0 to 1.0, wherein at least some of the barium, zirconium and / or hafnium is replaced by nickel. The invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (I):
Figure imgf000015_0004
wherein a = 0.8 to 1 .2 and y = 0.0 to 1 .0, wherein at least some of the barium, zirconium and / or hafnium is replaced by nickel. Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas. a
In general formula (I), "a" is 0.8 to 1 .2, thus allowing for a deficiency (where a<1 ) or abundance (where a>1 ) of barium relative to the amount of zirconium / hafnium in the crystalline metal oxide of the invention. Suitably, "a" may be 0.8, 0.9, 1 .0, 1 .1 or 1 .2. Preferably, "a" is 1 (i.e. wherein the amount of barium relative to the amount of zirconium / hafnium is the same). y
In general formula (I), "y" is 0.0 to 1.0. Suitably, "y" may be 0.0 (i.e. wherein hafnium is absent), 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0 (i.e. wherein zirconium is absent). Preferably, "y" is 0.0 or 1.0. In embodiments, "y" is 0.0. Alternatively, "y" may be 1.0.
Nickel
At least some of the barium, zirconium and / or hafnium is replaced by nickel. In other words, at least some of the barium, zirconium and / or hafnium in general formula (I), above, is substituted in the formula by nickel. In embodiments, at least 1 % of the barium, zirconium and / or hafnium in general formula (I) is replaced by nickel, suitably at least 2%, preferably at least 5%, at least 10 %, at least 20 %, or at least 30 %. In embodiments, the nickel is present in the crystalline metal oxide in an amount of at least 0.2 atom%, optionally at least 0.4 atom%. optionally at least 1 atom%, optionally at least 2 atom%, optionally at least 4 atom%, optionally at least 6 atom%. In embodiments, the nickel is present in an amount of 12 atom% or less, suitably 10 atom% or less, 8 atom% or less, preferably 6 atom% or less, such as 4 atom% or less, 2 atom% or less, 1 atom% or less, 0.8 atom% or less, 0.6 atom% or less, or 0.4 atom% or less. For instance, in embodiments the nickel is present in an amount of from 0.2 atom% to 12 atom%, suitably from 0.4 atom% to 12 atom%, 0.6 atom% to 10 atom%, 0.8 atom% to 8 atom% or 1 atom% to 6 atom%. Preferably, the nickel is present in an amount of from 0.2 atom% to 7 atom%.
In embodiments, at least 90% of the nickel replaces barium in general formula (I), suitably at least 95%, at least 98%, or at least 99%, for example wherein 100% of the nickel replaces barium. In alternative embodiments, at least 90% of the nickel replaces zirconium and / or hafnium in general formula (I), suitably at least 95%, at least 98%, or at least 99%, for example wherein 100% of the nickel replaces zirconium and / or hafnium.
Suitably, the crystalline metal oxide of general formula (I) has an ABO-, crystalline unit cell structure as defined above for the first aspect an embodiments above. In other words, in embodiments, in general formula (I) the barium, (i.e. Ba) is at A-sites in the crystal lattice and the zirconium and / or hafnium (i.e. Zn yHfv) is at B-sites. Thus, in such embodiments the nickel may be at A and / or B sites depending on whether the nickel replaces barium, zirconium and / or hafnium in the crystal lattice.
Additives
In embodiments, at least some of the barium, zirconium and / or hafnium is replaced in general formula (I) by one or more additives (i.e. dopants) in addition to nickel. In suitable embodiments, at least 1 atom% of the barium, zirconium and / or hafnium is replaced by one or more additives, for instance at least 2 atom%. at least 5 atom%, at least 10 atom%, at least 20 atom%, or at least 30 atom% of the barium, zirconium and / or hafnium is replaced by one or more additives. In embodiments, the one or more additives may be present in the crystalline metal oxide of general formula (I) in an amount of up to 6 atom%, such as up to 4 atom%, 2 atom%, 1 atom%,
0.8 atom%, 0 6 atom%, 0.4 atom%, 0.2 atom% or 0.1 atom%. Embodiments of the aspects and embodiments above may have a unit celt structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites as described above for the first aspect an embodiments. Fourth aspect
In a fourth aspect is provided the use of a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide has the general formula (II):
(Ba,.xQx)a((Zr,.vHfy),-,Q',)03 (II)
wherein a = 0.8 to 1.2, x = 0 to 0.9, y = 0.0 to 1.0, z = 0 to 0.9 wherein x+z≥ 0.0 , Q is h r„Lm and Q1 is Nil„Ln wherein each L is independently one or more additives and m and n are each independently 0 to 0.5.
Thus, the invention provides a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (II):
(Bai-xQx)a((Zri-yHfy)i.zQ1 z)03 (II)
wherein a = 0.8 to 1.2, x = 0 to 0.9, y = 0.0 to 1.0, z = 0 to 0.9 wherein x+z > 0.01 , Q is h.mLm and Q1 is Nii-nLn wherein each L is independently one or more additives and m and n are each independently 0 to 0.5. Preferably said method is a method of preparing syngas. Thus, the invention also provides the use of a crystalline metal oxide in a method of preparing syngas, wherein the crystalline metal oxide has the general formula (II):
Figure imgf000018_0001
wherein a = 0.8 to 1.2, x = 0 to 0.9, y = 0.0 to 1.0, z = 0 to 0.9 wherein x+z > 0.01 , Q is Ni-i-mLm and Q1 is Nii nLn wherein each L is independently one or more additives and m and n are each independently 0 to 0.5. The invention also provides a method of preparing syngas using a crystalline metal oxide, wherein the crystalline metal oxide has the general formula (II):
(Bai-xQx)a((Zri-yHfy)i-zQ1z)03 (II)
wherein a = 0.8 to .2, x = 0 to 0.9, y = 0.0 to 1.0, z = 0 to 0.9 wherein x+z≥ 0.01 , Q is h-mLm and Q is Nii-nLn wherein each L is independently one or more additives and m and n are each independently 0 to 0.5. Said method may suitably include reforming a fuel, such as a fuel selected from a hydrocarbon and an oxygenated hydrocarbon as described above, i.e. so as to produce said syngas. m and n
In embodiments, m is 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5. Typically, m is 0. In embodiments, n is 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5. Typically, n is 0. In embodiments, m is 0.0 to 0.5 (such as 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5) and n is 0. In other embodiments, n is 0.0 to 0.5 (such as 0.0, 0.1 , 0.2, 0.3, 0.4 or 0.5) and m is 0. Typically, m and n are each 0. For instance, in embodiments, the crystalline metal oxide has the general formula (III):
(Bai-xNix)a((Zri-yHfy)i-zNiz)03 (III),
wherein a, x, y, z, are as defined above. a
As described above, "a" is 0.8 to 1.2, thus allowing for a deficiency (where a<1 ) or abundance (where a>1 ) of the (Bai.xQx) component relative to the ((Zri.yHfv.)i-zQ z) component in the crystalline metal oxide. Suitably, "a" may be 0.8, 0.9, 1.0, 1.1 or 1.2. Preferably, "a" is 1 (i.e. wherein formula (II) and (III), above are formulae (Ha) and (Ilia) respectively:
Figure imgf000018_0002
(Β3ι-χ ίχ)((ΖΓ Ηίγ)ι-ζΝίζ)03 (Ilia). x and z
In the compounds of general formula (II), x and z are each independently 0.0 to 0.9 provided that x+z > 0.01. Suitably, x+z > 0.02, preferably≥ 0.05, > 0.1 , > 0.2, such as > 0.3. In embodiments, x+z < 0.9, suitably x+z≤ 0.8, preferably < 0.7, < 0.6, < 0.5, more preferably < 0.4, or < 0.3.
In the compounds of general formula (II), x is 0.0 to 0.9. Suitably x may be 0.0, 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9. In embodiments, x is 0.01 to 0.9 (such as 0.01 , 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9) and z is 0. In embodiments, x > 0.01 , suitably > 0.02, > 0.05, > 0.1 , > 0.2, or > 0.3. In embodiments, x < 0.9, suitably < 0.8, < 0.7, < 0.6,≤ 0.5, preferably < 0.4, < 0.3,≤ 0.2 or < 0.1. In typical embodiments, x is 0.05, 0.1 , 0.2, 0.3, 0.4, 0.45, or 0.5. In some embodiments, x = 0, i.e. wherein general formula (II) is of general formula (lib):
( Ba )a( (Zri yHfy)i zNiz)03 (lib) wherein a, y and z are as defined herein.
In the compounds of general formula (II), z is 0.0 to 0.9. Suitably z may be 0.0, 0.1 , 0.2. 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9. In embodiments, z is 0.01 to 0.9 (such as 0.01 , 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9) and x is 0. In embodiments, z > 0.01 , suitably > 0.02, > 0.05, > 0.1 , > 0.2, or > 0.3. In embodiments, z < 0.9, suitably≤ 0.8, < 0.7,≤ 0.6, < 0.5, preferably < 0.4, or < 0.3. In typical embodiments, z = 0, i.e.
wherein general formula (II) is of general formula (lie):
(Bai xNix)a(Zri yHfy)03 (He), wherein a, y and z are as defined herein. y
As described above, "y" is 0.0 to 1.0. Suitably, "y" may be 0.0 (i.e. wherein hafnium is absent), 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 0 (i.e. wherein zirconium is absent). Preferably, "y" is 0.0 or 1.0. In embodiments, "y" is 0.0. Alternatively, "y" may be 1.0. For instance, in embodiments when y is 0 or 1 , the general formula (II) is of formula (IVa) or (IVb):
(Bai-xNix)aZr03 (IVa),
(Ba,-xNix)aHf03 (IVb),
wherein a and x are as defined above.
Suitably, the crystalline metal oxide of general formulae (II), (lla), (lib), (lie), (III), (IVa) and / or (IVb) may have an ABO3 crystalline unit cell structure as described according to the first embodiment thereof above. In other words, in embodiments, the (Bai.xQx) is at A-sites in the crystal lattice and the ((Zri.yHfy)i. Q1 z) is at B-sites. Thus, in such embodiments the nickel may therefore be at A and / or B sites.
Methods of reforming
In embodiments of methods of reforming described herein, the method of reforming is selected from the group consisting of dry reforming, autothermal reforming, steam reforming, partial oxidation and thermal decomposition. Suitably, the method of reforming may be selected from the group consisting of dry reforming, autothermal reforming, steam reforming and partial oxidation, preferably dry reforming, steam reforming and partial oxidation, such as steam reforming. In still further
embodiments, the method of reforming is partial oxidation. Alternatively, the method of reforming may be dry reforming, optionally wherein a biofuel, such as biogas, is used as the hydrocarbon (e.g. methane) fuel source. Suitably, the methods in the above aspects and embodiments comprise contacting the crystalline metal oxide with the fuel. Typically, the step of contacting the crystalline metal oxide with the fuel is performed in the presence of an oxidant, such as water (e.g. steam), oxygen and / or carbon dioxide. Preferably, in the methods of reforming a fuel described in any of the above aspects and embodiments said crystalline metal oxide provides more sustained activity over longer periods compared to alternative catalysts. Preferably, in the methods of reforming a fuel described in any of the above aspects and embodiments, the fuel reforming activity of the crystalline method oxide in the isothermal reaction of simulated biogas (CH4:C02 = 2:1 ) at 850 °C over 10 days as measured by methane conversion rate does not decrease more than 10% over at least 10 days at 850 °C, suitably, over at least 15 days, preferably over at least 20 days.
Suitably, the uses and methods described above or the crystalline metal oxides described above for use in said methods provide a fuel conversion rate (typically methane conversion) during partial oxidation (reaction with limited amounts of oxygen, typically 50% stoichiometric ratio of oxygen) at 700 °C that is at least 5%, suitably at least 10%, preferably at least 15% and more preferably at least
20% greater than the fuel conversion rate (by %) obtained for an analogous molar amount of Ni/YSZ cermet catalyst. Suitably, the uses and methods described above or the crystalline metal oxides described above for use in said methods provide an average fuel conversion rate (typically methane conversion) during partial oxidation (reaction with limited amounts of oxygen, typically 50% stoichiometric ratio of oxygen) at 900 °C that is at least 60%, such as at least 70%, at least 75%, suitably at least 80%, preferably at least 85%, more preferably at least 90% and most preferably at least 95% over a period of 5 hours.
In preferred embodiments of the uses and methods of the above aspects and embodiments, said method is a method of preparing syngas.
Preferably, the reforming is conducted at a temperature of less than 1000 °C, suitably less than 950 °C, such as less than 900 °C, or less than 850 °C, typically around 800 °C. Typically, the reforming is performed at an average temperature at least 700 °C, such as at least 750 °C, preferably at least 800 °C, or at least 850 °C.
Fuel
In aspects and embodiments of the methods of reforming a fuel disclosed herein, the fuel may be selected from a hydrocarbon and an oxygenated hydrocarbon.
Said fuel, i.e. said hydrocarbon and / or oxygenated hydrocarbon may be provided to the reaction mixture as the sole fuel component or may be a component part of a fuel composition comprising other chemical compounds, such as other fuel compounds and / or inert carriers. For instance, the hydrocarbon may be provided as part of a mixture of hydrocarbon compounds and / or oxygenated hydrocarbons as defined herein. Likewise, the oxygenated hydrocarbon may be provided as part of a mixture of hydrocarbon compounds and / or oxygenated hydrocarbons as defined herein. Said fuel / fuel composition may be provided to the reaction vessel separately, or as part of a mixture of other chemical compounds not including hydrocarbons and / or oxygenated hydrocarbons. For instance, each fuel may independently be provided to the reaction vessel as a mixture with inert gases and / or oxidants, etc. needed for the reaction. Alternatively, the respective hydrocarbon and / or oxygenated hydrocarbon may be supplied to the reaction vessel substantially free of other compounds that are not hydrocarbons / oxygenated hydrocarbons.
The term "oxygenated hydrocarbon" refers to a hydrocarbon wherein one or more hydrogen atoms is notionally substituted by one or more oxygen substituents (e.g. 1 , 2, 3, 4, or 5 oxygen substituents) and / or wherein one or more methylene groups (i.e. -CH2-) in the hydrocarbon (e.g. 1 , 2, 3, 4, or 5 methylene groups) is notionally replaced by an oxygen (i.e.-O-). Thus, the term oxygenated hydrocarbon includes hydrocarbons substituted by one or more oxygen substituents selected
independently from the group consisting of -OH and =0; and / or wherein one or more methylene groups (i.e. -CH2-) (e.g. 1 , 2, 3, 4, or 5 methylene groups) is replaced by an oxygen (i.e.-O-) (e.g. forming an ether moiety). More than one of said -OH and =0 groups may be bonded to the same carbon atom. For instance, a carboxylic acid is formed when -OH and =0 substituents are bonded to the same terminal carbon atom and a carboxylic acid ester results when a =0 substituent is bonded to a carbon atom adjacent to an ether oxygen atom. The skilled person will understand that substitution with =0 involves the notional substitution of two hydrogen atoms attached to the same carbon. Suitably, wherein more than one methylene group is substituted by an oxygen, no more than two oxygen atoms may be adjacent (such as present in peroxides and peracids), i.e. suitably, chains of three or more oxygen atoms are not included. In embodiments, the oxygenated
hydrocarbon also does not include the notional substitution of two =0 groups on one carbon atom, i.e. carbon dioxide. Examples of oxygenated hydrocarbons are therefore alcohols, epoxides, aldehydes, ketones, carboxylic acids, carboxylic acid esters, ethers, peroxides and peracids.
Accordingly, in embodiments, the fuel is a hydrocarbon. In alternative embodiments, the fuel is an oxygenated hydrocarbon. For instance, in embodiments, the oxygenated hydrocarbon is a hydrocarbon substituted by one or more substituents (e.g. 1 , 2, 3, 4, or 5 substituents) selected independently from the group consisting of -OH and =0; and / or wherein one or more methylene groups (i.e. -CH2-) (e.g. 1 , 2, 3, 4, or 5 methylene groups) is replaced by an oxygen (i.e.-O-). In embodiments, said oxygenated hydrocarbon is a hydrocarbon substituted by one or more substituents (e.g. 1 , 2, 3, 4, or 5 substituents) selected independently from the group consisting of -OH and =0, preferably OH. In suitable embodiments, said oxygenated hydrocarbon is a hydrocarbon substituted by one or more -OH and =0 groups, for instance wherein said oxygenated hydrocarbon is a carboxylic acid.
In the embodiments above, said oxygenated hydrocarbon preferably comprises only one of said substituents. In further embodiments, said oxygenated hydrocarbon comprises more than one of the substituents, e.g. 2, 3. 4, or 5 substituents. Suitably, said oxygenated hydrocarbon is substituted by 2, 3, or 4 of substituents, for instance 2 or 3. particularly 2. In the embodiments above, when one or more methylene groups (i.e. -CH2-) (e.g. 1 , 2, 3, 4, or 5 methylene groups) are substituted by oxygen (i.e.-O-), preferably only one methylene group (i.e. -CH2-) is substituted by an oxygen (i.e.-O-). In alternative embodiments, more than one methylene group (i.e. -CH2-) is substituted by oxygen (i.e.-O-), e.g. 2, 3, 4, or 5 methylene groups are substituted. Suitably, 2, 3, or 4 methylene groups are substituted, for instance 2 or 3, particularly 2.
Thus, in embodiments, the fuel is selected from the group consisting of a hydrocarbon (e.g. methane), an alcohol (e.g. ethanol), an ether, a ketone
(e.g. acetone), an aldehyde, a carboxylic acid (e.g. ethanoic acid) and a carboxylic acid ester. In embodiments, the fuel is selected from the group consisting of a hydrocarbon (e.g. methane), an alcohol (e.g. ethanol), and a carboxylic acid
(e.g. acetic acid). In preferred embodiments, the fuel is selected from the group consisting of a hydrocarbon and an alcohol, e.g. an alcohol (such as ethanol).
Preferably the fuel is a hydrocarbon (such as methane). For example, the fuel may be selected from methane and ethanol, e.g. methane. In other embodiments, the fuel is a carboxylic acid (e.g. acetic acid).
Suitably, said hydrocarbon or oxygenated hydrocarbon (e.g. alcohol, ether, ketone, aldehyde, carboxylic acid and / or carboxylic acid ester) may be a component of a mixture. The mixture may comprise inert materials such as inert carriers (e.g. Nobel gases) and / or additional reactive materials, such as other fuels, oxidants and fuel additives. For instance, the mixture may include one or more fuels selected from the group consisting of a hydrocarbon (e.g. methane) and an oxygenated hydrocarbon such as one or more fuels selected from the group consisting of a hydrocarbon, an alcohol (e.g. ethanol), an ether (e.g. dimethyl ether and diethyl ether), a ketone (e.g. acetone), an aldehyde, a carboxylic acid (e.g. acetic acid) and a carboxylic acid ester.
The hydrocarbon may be selected from one or more of the group consisting of a Ci-25alkane, a Ca-asalkene and a C2-25alkyne. Suitably, the hydrocarbon may be selected from the group consisting of a Ci-25alkane and a C2-2salkene. In
embodiments, the hydrocarbon is selected from the group consisting of a
Figure imgf000023_0001
and a C2-25alkyne. Typically, the hydrocarbon is a
Figure imgf000023_0002
In preferred embodiments, the d^alkane, C2-2salkene and C2-25alkyne may respectively be a Ci-ioalkane, a C2-ioalkene and a C2-ioalkyne, more preferably a C--Salkane, C2-ealkene and C2-6alkyne, e.g. a Ci-4alkane, C2-4alkene and C2-4alkyne. For instance, when the hydrocarbon is a
Figure imgf000023_0003
it is suitably a Ci i0alkane, preferably a d-ealkane, more preferably a Ci-4alkane (i.e. methane, ethane, propane or butane), most preferably methane. Examples of of the present invention include methane, ethane propane, butane, petroleum, diesel and kerosene.
In embodiments, the hydrocarbon is selected from methane, ethane, propane, butane, petroleum, diesel and kerosene. Suitably, the hydrocarbon may be selected from methane, butane, petroleum, diesel and kerosene, such as petroleum, diesel and kerosene, but preferably methane and butane, more preferably methane. Where petroleum, diesel and kerosene are used, the fuel composition may comprise less than 50 ppm sulfur-containing compounds, e.g. less than 40 ppm, 30 ppm, 20 ppm, 10 ppm or 5 ppm.
Said hydrocarbon and / or oxygenated hydrocarbon may be provided as a component part of biofuel mixtures, such as biogas. For instance, when methane is used as a hydrocarbon fuel, it may be provided in a mixture, such as biogas or simulated biogas (e.g. a mixture of about 2:1 CH^CC^). Thus, in embodiments, the fuel used in the methods of reforming defined in the above aspects and embodiments is a biofuel, such as biogas.
The carboxylic acid may be selected from one or more of the group consisting of a Ci-25alkanoic acid, a C^salkenoic acid and a C^salkynoic acid. Typically, the carboxylic acid is a C 25alkanoic acid. In preferred embodiments, the Ci-2salkanoic acid, C3 2&alkenoic acid and C^alkynoic acid may respectively be a Ci ioaikanoic acid, a C3-ioalkenoic acid and a C3-ioalkynoic acid, more preferably a Ci.salkanoic acid, C3-ealkenoic acid and Cs-ealkynoic acid, e.g. a d-4alkanoic acid, C3 alkenoic acid and Cwalkynoic acid. For instance, when the hydrocarbon is a C^alkanoic acid, it is suitably a Ci.10alkanoic acid, preferably a Ci.6alkanoic acid, more preferably a Ci-4alkanoic acid (i.e. methanoic acid, ethanoic acid, propanoic acid and butanoic acid), most preferably ethanoic acid (i.e. acetic acid). The term "alkane" as described herein includes branched or unbranched. cyclic or acyclic alkanes. Typically the alkane is acyclic. Typically the alkane is unbranched, preferably unbranched and acyclic.
The term "alkene" refers to a group derived from an alkane and comprising one or more carbon-carbon double bonds. Typically the alkene is unbranched, preferably unbranched and acyclic. The term "alkyne" refers to a group derived from an alkane and comprising one or more carbon-carbon triple bonds. Typically the alkyne is unbranched, preferably unbranched and acyclic. The term "an ether" includes a hydrocarbon or oxygenated hydrocarbon substituted according to any definition as described above, wherein one or more methylene groups (i.e. -CH2-) in the hydrocarbon or oxygenated hydrocarbon are substituted by oxygen (i.e.-O-) to form an ether moiety. Thus the term "an ether" includes alkane ethers, alkene ethers and alkyne ethers containing one or more ether oxygen atoms, such as one to three ether oxygen atoms, preferably one ether oxygen atom.
Typically the ether contains from 2-24 carbon atoms, such as 2-9, preferably 2-5, more preferably 2-3 carbon atoms, e.g. two).
The term "alcohol" includes hydrocarbons or oxygenated hydrocarbons substituted according to any definition as described above, wherein one or more substituents (e.g. 1 , 2, 3, 4, or 5 substituents, preferably 1 , 2, or 3, more preferably 1 ) is -OH. Thus, the term alcohol includes alkanols, alkenols and alkynois including one or more hydroxy! groups, such as one to three hydroxy! groups, preferably one hydroxy I group. Typically the alcohol contains from 1-25 carbon atoms, such as 1-10, preferably 1-6, more preferably 1-4 carbon atoms, e.g. one or two). The alcohol (e.g. alkanol, alkenol and / or alkynol) may be branched or unbranched, cyclic or acyclic. Preferably, the alcohol (e.g. the respective alkanol, alkenol and / or alkynol) is unbranched, and more preferably unbranched and acyclic. Suitably, the alcohol may be selected from the group consisting of an alkanol, alkenols and an alkynol, such as an alkanol and an alkenol. In embodiments, the alcohol is selected from the group consisting of an alkanol and an alkynol, preferably an alkanol. In embodiments, the alkanol, alkenol and alkynol may respectively be a d.-ioalkanol, a C2-toalkenol, and a C2-ioalkynol, more preferably a Ci.6alkanol, C2.6alkenol and C2-6alkynol, e.g. a
Ci-4alkanol, C2-4alkenol and C2. alkynol. Typically, the alcohol is a Ci-ioalkanol. For instance, when the alcohol is a Cvioalkanol. it is suitably a Ci-ealkanol. more preferably a
Figure imgf000025_0001
(i.e. methanol, ethanol. propanol or butanol), most preferably ethanol. When ethanol is used as a fuel, it may be provided as bioethanol.
The term "aldehyde" includes hydrocarbons or oxygenated hydrocarbons substituted according to any definition as described above, wherein an =0 is bonded to a terminal carbon atom to form an aldehyde moiety. Typically, from 1 -5 aldehyde moieties are provided, preferably 1 -3, e.g. 1. Thus, the term aldehyde includes alkanals, alkenals and alkynals including one or more aldehyde moieties, such as one to three, preferably one. Typically the aldehyde contains from 1-25 carbon atoms, such as from 1-10, preferably 1-6, more preferably 1-4 carbon atoms, e.g. two). The aldehyde (e.g. the respective alkanals, alkenals and alkynals) may be branched or unbranched, cyclic or acyclic. Preferably, the aldehyde is unbranched, and more preferably unbranched and acyclic. Suitably, the aldehyde may be selected from the group consisting of an alkanal, an alkenal and an alkynal, such as an alkanal and an alkenal. In embodiments, the aldehyde is selected from the group consisting of an alkanol and an alkynal, preferably an alkanal. In embodiments, the alkanal, alkenal and alkynal may respectively be a Ci-i0alkanal, a C^oalkenal, and a C3.ioalkynal, more preferably a Ci.6alkanal, C3-6alkenal and Cs-ealkynal, e.g. a
Ci-4alkanal, C3-4alkenaI and C^alkynal. Typically, the aldehyde is a Ci i0alkanal. For instance, when the aldehyde is a Ci-ioalkanal, it is suitably a d ealkanal, more preferably a
Figure imgf000026_0001
(i.e. methanal (formaldehyde), ethanal (acetaldehyde), propanal or butanal). More preferably, the aldehyde is ethanal.
The term "ketone" includes hydrocarbons or oxygenated hydrocarbons substituted according to any definition as described above, wherein an =0 is bonded to a nonterminal carbon atom to form a ketone moiety. Typically, from 1-5 ketone moieties are provided, preferably 1-3, e.g. 1. Thus, the term ketone includes alkanones, alkenones and alkynones including one or more ketone moieties, such as one to three, preferably one. Typically the ketone contains from 3-25 carbon atoms, such as from 3-10, preferably 3-6, more preferably 3-4 carbon atoms, e.g. three). The ketone (e.g. the respective alkanones, alkenones and alkynones) may be branched or unbranched, cyclic or acyclic. Preferably, the ketone is unbranched, and more preferably unbranched and acyclic. Suitably, the ketone may be selected from the group consisting of an alkanone. alkenone and alkynone, such as an alkanone and an alkenone. In embodiments, the ketone is selected from the group consisting of an alkanone and alkynone, preferably an alkanone. In embodiments, the alkanone, alkenone and alkynone may respectively be a C~, loalkanone, a C4.ioalkenone, and a -ioalkynone, more preferably a d-ealkanone, C4~salkenone and C..6alkynone, e.g. a C^alkanone, C4alkenone and C4alkynone. Typically, the ketone is a Cviaalkanone. For instance, when the ketone is a C3.ioalkanone, it is suitably a Cs-ealkanone, more preferably a C^alkanone (i.e. propanone (acetone), or butanone). More preferably, the ketone is propanone (i.e. acetone). The term "carboxylic acid" includes hydrocarbons or hydrocarbons substituted according to any definition as described above, wherein an -OH and =0 are bonded to the same carbon atom to form a carboxyl group. Typically, from 1-5 carboxyl groups are provided, preferably 1-3, e.g. 1. Thus, the term carboxylic acid includes aikanoic acids, alkenoic acids and alkynoic acids including one or more carboxyl groups, such as one to three carboxyl groups, preferably one carboxyl group.
Typically the carboxylic acid contains from 1-25 carbon atoms, such as from 1-10, preferably 1-6, more preferably 1-4 carbon atoms, e.g. one or two). The carboxylic acid (e.g. the respective aikanoic acids, alkenoic acids and alkynoic acids) may be branched or unbranched, cyclic or acyclic. Preferably, the carboxylic acid (e.g. the respective aikanoic acids, alkenoic acids and alkynoic acids) are unbranched, and more preferably unbranched and acyclic. Suitably, the carboxylic acid may be selected from the group consisting of an aikanoic acid, an alkenoic acid and an alkynoic acid, such as an aikanoic acid and an alkenoic acid. In embodiments, the carboxylic acid is selected from the group consisting of an aikanoic acid and an alkynoic acid, preferably an aikanoic acid. In embodiments, the aikanoic acid, alkenoic acid and alkynoic acid may respectively be a Ci ioalkanoic acid, a
Ca-ioalkenoic acid, and a Ca ioalkynoic acid, more preferably a Ci.6alkanoic acid, Ca-ealkenoic acid and C ^alkynoic acid, e.g. a CMalkanoic acid, C3^alkenoic acid and C3-4alkynoic acid. Typically, the carboxylic acid is a Ci-<oaikanoic acid. For instance, when the carboxylic acid is a Ci-iQalkanoic acid, it is suitably a Ci-6alkanoic acid, more preferably a d^alkanoic acid (i.e. methanoic acid, ethanoic acid (i.e. acetic acid), propanoic acid or butanoic acid). More preferably, the carboxylic acid is ethanoic acid (i.e. acetic acid).
The term ' carboxylic acid ester" includes hydrocarbons or oxygenated hydrocarbons substituted according to any definition as described above comprising a carboxylic acid ester moiety, i.e. wherein a =0 substituent is bonded to a carbon adjacent to an ether oxygen atom to form a carboxylic acid ester group. Typically, from
1-5 carboxylic acid ester groups are provided, preferably 1-3, e.g. 1. Thus, the term carboxylic acid ester includes aikanoic acid esters, alkenoic acid esters and alkynoic acid esters including one or more carboxylic acid ester groups, such as one to three carboxylic acid ester groups, preferably one carboxylic acid ester groups. Typically the carboxylic acid ester contains from 2-25 carbon atoms, such as from 2-10, preferably 2-6, more preferably 2-4 carbon atoms, e.g. one or two). The carboxylic acid ester (e.g. the respective aikanoic acid esters, alkenoic acid esters and alkynoic acid esters) may be branched or unbranched, cyclic or acyclic. Preferably, the carboxylic acid ester is unbranched, and more preferably unbranched and acyclic. Suitably, the carboxylic acid ester may be selected from the group consisting of an alkanoic acid ester, an alkenoic acid ester and an alkynoic acid ester, such as an alkanoic acid ester and an alkenoic acid ester. In embodiments, the carboxylic acid ester is selected from the group consisting of an alkanoic acid ester and an alkynoic acid ester, preferably an alkanoic acid ester. In embodiments, the alkanoic acid ester, alkenoic acid ester and alkynoic acid ester may respectively be a C2-ioalkanoic acid ester, a Ci ioalkenoic acid ester, and a C4.i0alkynoic acid ester, more preferably a C2-6alkanoic acid ester, C+^alkenoic acid ester and Ct-ealkynoic acid ester, e.g. a C2 4alkanoic acid ester, C4alkenoic acid ester and C4alkynoic acid ester. Typically, the carboxylic acid ester is a C2.ioalkanoic acid ester. For instance, when the carboxylic acid ester is a C2-ioalkanoic acid ester, it is suitably a C2-6alkanoic acid ester, more preferably a C2 4alkanoic acid ester, e.g. a C2alkanoic acid ester (i.e. methyl methanoate).
Thus, in embodiments, the fuel is selected from a Ci .2i,alkane, a Ci ioalkanol and a Ci-ioalkanoic acid. In preferred embodiments, the fuel is selected from the group consisting of methane, ethane, propane, butane, ethanol, acetone, ethanoic acid, petroleum, diesel, kerosene and mixtures thereof. Suitably, the fuel may be selected from the group consisting of methane, butane, ethanol, ethanoic acid, petroleum, diesel, kerosene and mixtures thereof, such as petroleum, diesel, kerosene and mixtures thereof, preferably methane, butane, ethanol and ethanoic acid, more preferably methane, butane and ethanol. Suitably, the fuel may therefore be selected from the groups consisting of methane and ethanol, preferably methane. In embodiments, the fuel is biogas, simulated biogas or bioethanol, suitably biogas or simulated biogas, e.g. biogas. In embodiments, the fuel is bioethanol.
The fuel may be supplied to the reactor separately to the other gaseous reactants (such as steam, CO, etc.) or may be provided as a mixture with the other gaseous reactants. For instance, biogas is a mixture including methane biogas and carbon dioxide (e.g. a mixture of CH4:C02. 2:1 ).
Accordingly, in another embodiment of the invention is provided the use of a crystalline metal oxide, composition, catalyst, or product as described herein in a method of preparing syngas, preferably from methane, such as from biogas. Syngas
As will be understood by a skilled person, syngas is a gaseous mixture that is principally composed of hydrogen and carbon monoxide. In methods of preparing syngas as described above, the product of the reaction may consist of at least 10mol% syngas, such as at least 20mol%, at least 30mol%, at least 40mol%, at least 50mol%, at least 60mol%, at least 70mol%, at least 80mol% or at least at least 90mol%. Preferably, the reaction product consists substantially of syngas (such as by mol%, i.e. wherein at least 95mol%, such as at least 98mol%, more preferably at least 99mol% of the reaction product is syngas), more preferably consists of syngas.
In methods of preparing syngas as described above, the product of the reaction may consist of at least 10vol% syngas, such as at least 20vol%, at least 30vo!%, at least 40vol%, at least 50vol%. at least 60vol%, at least 70vol%, at least 80vol% or at least at least 90vol%. Preferably, the reaction product consists substantially of syngas by volume (i.e. wherein at least 95vol%, such as at least 98vol%, more preferably at least 99vol% of the reaction product is syngas), more preferably consists of syngas. In methods of preparing syngas as described above, the product of the reaction may consist of at least 10 wt.% syngas, such as at least 20 wt.%, at least 30 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.% or at least at least 90 wt.%. Preferably, the reaction product consists substantially of syngas by weight (i.e. wherein at least 95 wt.%, such as at least 98 wt.%. more preferably at least 99 wt.% of the reaction product is syngas), more preferably consists of syngas.
In embodiments of any of the methods described herein (e.g. the method of producing syngas and methods of reforming described above), the method includes the step of isolating and / or purifying the reaction product. For instance, the method includes the step of isolating and / or purifying the reaction product so as to provide syngas.
Suitably, in embodiments of any of the above methods and uses disclosed according to any of the aspects and embodiments herein, the crystalline metal oxide is not
BaZr0 864gNi0 1351 O3 or BaZro.7298Nio 270203. In alternative embodiments, said crystalline metal oxide is not crystalline metal oxide having a general formula
BaZr(0.84 to 0 88)Ni(0 12 to 0 16)03 Or BaZr(0.70 to 0.74)Ni(0.26 to 0.30)03.
Fifth aspect
In a further aspect of the invention is provided a crystalline metal oxide having an ABO3 unit cell structure comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites, provided the crystalline metal oxide is not BaZromigNio 1351O3 or BaZro 729eNio 270203. Thus, said crystalline metal oxide may be as defined according to the first aspect and any embodiment thereof above, provided the crystalline metal oxide is not
Figure imgf000030_0001
or BaZ 0.7298 io.270203. In embodiments, the crystalline metal oxide of the fifth aspect and embodiments is not crystalline metal oxide having a general formula BaZr(084 to o.88)Ni(o. i2 to o.ie * or
BaZ o 70 to 0 74)Ni(0 26 to 0.30)03. As seen in the examples, the crystalline metal oxides of the present invention exhibit excellent activity in reforming reactions to form syngas selectively over alternative reaction pathways. This excellent catalytic activity and selectivity is exhibited in a variety of reforming reactions, including dry reforming, steam reforming and partial oxidation, showing the versatility of the crystalline metal oxides of the present invention in the production of syngas.
Advantageously, crystalline metal oxides of the present invention allow surprisingly high levels of active nickel to be incorporated homogenously within the crystal lattice (i.e. in solid solution). For instance, example 1 and figure 3 show that crystalline metal oxides of the invention can be obtained in high phase purity even at high nickel loadings, such as 6 atom% nickel (i.e. 30% Ni/BaZr03). Crystalline metal oxides of the invention containing up to 10atom% nickel were prepared and tested by the present inventors (see Examples) and even at this high level of nickel loading only small amounts of impurities (e.g. Zr02 and Ni(OH)2) were detected in the material. Nonetheless, each of these materials showed good catalytic activity in a variety of reforming reactions to produce syngas.
Crystalline metal oxides of the present invention show good resistance to coking (see e.g. Examples 5 and 6). This is particularly surprising given the high nickel content of these catalysts. Thus, the materials of the present invention provide a valuable alternative to conventional nickel based catalysts (such as Ni/YSZ cermet) in reforming reactions, and would be particularly useful in the reforming of fuel derived from natural sources, such as biofuels, e.g. biogas.
Sixth aspect
In another aspect, or in embodiments of the above fifth aspect, is provided a crystalline metal oxide selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate, provided the crystalline metal oxide is not BaZro s649Nio 1351O3 or BaZro 729sNio 27∞03. Thus, the crystalline metai oxide may be as defined in the second aspect and any embodiment thereof above, provided the crystalline metal oxide is not
BaZro.8649Nio.i35i03 or BaZr0 729sNio 270203. In embodiments, the crystalline metal oxide of the sixth aspect and embodiments thereof is not crystalline metal oxide having a general formula BaZr<o w to o 88>Ni(o 12 to aiejQa or BaZr<o ,>o to o.74) i|o.26 to 0 ¾»θ3.
As described above, the nickel barium zirconate, nickel barium hafnate, and / or solid solution of nickel barium zirconate and nickel barium hafnate of the sixth aspect and embodiments may be as further described according to any other aspect and embodiment herein, suitably wherein the crystalline metal oxide is not
BaZr0.8649Ni0.i35iO3 or BaZrQ 7298 io.270203. For instance, embodiments of the sixth aspect and embodiments may have a unit cell structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites as described above for the first aspect and embodiments.
Alternatively or additionally, the nickel barium zirconate, nickel barium hafnate, and solid solution of nickel barium zirconate and nickel barium hafnate may be of general formula (I) or (II) as described below for the seventh and eighth aspects and embodiments. Seventh aspect
In a further aspect, or in embodiments of any of the above aspects, is provided a crystalline metal oxide has the general formula (I):
(Ba)a(Zri-yHfy)03 (I),
wherein a = 0.8-1.2 and y = 0.0-1.0, and wherein at least some of the barium, zirconium and / or hafnium is replaced by nickel, provided the crystalline metal oxide is not BaZro.8649 io.i35i03 or BaZr0.7298 io.270203. The crystalline metal oxide according to formula (I) may thus be as defined according to the third aspect and any embodiment thereof above, provided the crystalline metal oxide is not
BaZr08649 io 1351Ο3 or BaZ 07298Ni02702O3. In embodiments, the crystalline metal oxide of the seventh aspect and embodiments is not crystalline metal oxide having a general formula BaZr.o 34 to 088> i(o 12 to ο.ιβ)θ3 or BaZr<o 70 to o.74iNi(o.26 to 030O3.
Suitably, the crystalline metal oxide of general formula (I) may have an ABO3 crystalline unit cell structure as defined above for the first aspect an embodiments above. In other words, in embodiments, in general formula (I), the barium (i.e. Ba) is at A-sites in the crystal lattice and the zirconium and / or hafnium (i.e. Zri-yHfy) is at B-sites. Thus, in such embodiments the nickel may be at A and / or B sites depending on whether the nickel replaces barium, zirconium and / or hafnium in the crystal lattice.
Eighth aspect
In a further aspect, or in embodiments of any of the above aspects, is provided a crystalline metal oxide having the general formula (II):
(Bai.xQx)a((Zrr.yHfy)i-zQ1z)03 (II),
wherein
a = 0.8 to 1.2;
x = 0.0 to 0.9;
y = 0.0 to 1.0;
z = 0.0 to 0.9 wherein x+z > 0.01 ;
Q is Nir rnLrr,;
Figure imgf000032_0001
each L is independently one or more additives: and
m and n are each independently 0.0 to 0.5, provided the crystalline metal oxide is not BaZr0.864g io.i35i03 or
Figure imgf000032_0002
Thus, said crystalline metal oxide of general formula (II) may be as defined according to the fourth aspect and any embodiment thereof above, provided the crystalline metal oxide is not BaZr0 8649N10 1351Ο3 or BaZro 729s io 2702O3. In embodiments, the crystalline metal oxide of the eighth aspect and embodiments is not crystalline metal oxide having a general formula
BaZr(0.84 to 0.88)Ni(0.12 to 0.16)03 ΟΓ BaZr(Q.70 to 0,74)ΝΪ(0.2Θ to 0.30)03.
Suitably, the crystalline metal oxide of general formulae (II), (lla), (lib), (lie), (III), (IVa) and / or (IVb) may have an AB03 crystalline unit cell structure as described according to the first embodiment thereof above. In other words, in embodiments, the (Bai-XQX) is at A-sites in the crystal lattice and the ((Zri.yHfy)i-zQ1z) is at B-sites. Thus, in such embodiments the nickel may therefore be at A and / or B sites.
Further embodiments
Specific embodiments
In embodiments of the uses, methods and crystalline metal oxides of the aspects and embodiments above, the crystalline metal oxide is selected from the group consisting of 3%-7% Ni/BaZrOs; 8-12% Ni/BaZrC ; 18-22% Ni/BaZr03; 23-27% Ni/BaZrCfe; 28-32% Ni/BaZrOs; 38-42% Ni/BaZr03; 43-47% Ni/BaZr03; 48-52% Ni/BaZr03; 3-7% Ni/BaHfC ; and 18-22% Ni/BaHf03. In such embodiments, the reference to X% Ni/BaZrOs refers to the atom% nickel incorporated relative to the theoretical amount of barium or zirconium in barium zirconate / hafnate. Thus, where ranges are provided above, the %nickel content relative to the theoretical amount of barium in the barium zirconate/hafnate crystal lattice may be anywhere with the range. 20% Ni/BaZrOa for example includes crystalline metal oxide of the formula Nfo 2Ba0 eZr03.
In embodiments, the crystalline metal oxide has a general formula selected from the group consisting of: 5% Ni/BaZr03, 10% Ni/BaZrCb, 20% Ni/BaZr03, 25% Ni/BaZr03, 30% Ni/BaZr03, 40% Ni/BaZrOs, 45% Ni/BaZr03, 50% Ni/BaZrO.,, 5% Ni/BaHf03 and 20% Ni/BaHfOs.
Thus, in embodiments, the crystalline metal oxide has a general formula selected from the group consisting of:
NijO 03 to 007)Ba(095 to 097jZrO3; Ni(008 to 0 12)Ba(088 to 0.92)ZrO3;Ni{0_18 to 0.22)Β3(0.78 to o.32)Zr03; Ni(0 23 to 0 27>Ba(0 73 to 0.77}ZrO3; Ni(0 28 to 0 32)Ba(0 72 to 0.68)ZrO3; Ni(Q 38 to 0.42}Β3(0.62 to 0.58 Zr03;
Ni(0.43 to 047lBa(0 53 to 057)Zr03; Ni.;0 48 to 0 52]Ba(0 48 to 052>Zr03: Ni 0.03 to 0 0/)Ba,:o 93 to 097}HfO3; and i(o.i8 to o.22)Ba(o.78 to o.82)Hf03. In embodiments, Ni + Ba = 1.
In embodiments, the crystalline metal oxide has a general formula selected from the group consisting of:
Ni(0.03 to 0.07)Ba;o.93 to 0.97)ZrO3; Νί(0.08 to 0.12)Ba(0.88 to 0.92)ZrO3; Ni(0.18 to 0.22}Ba(0.78 to 0.82)ΖΓΟ3; Νί(0,23 to 0.27)Ba{0.73 to 0.77) rO3; Ni(0.28 to 0.32)Ba(0.72 to 0.68)ZrO3; Ni(0.38 to 0.42)Ba(0.62 to o.58)Zr03;
Ni(0.43 to o.47)Ba(o.53 to o.57)Zr03; and i{o.48 to o.52)Ba(o.48 to o.52)Zr03, optionally wherein Ni + Ba = 1. In embodiments, the crystalline metal oxide has a general formula selected from the group consisting of: Ni(o 03 to 0 onBaio 93 to 0 97>HfC>3; and Ni(o.ie to 0 22>Ba(o 78 to 0 82)Hf03, optionally wherein Ni + Ba = 1. In embodiments, the crystalline metal oxide has a general formula selected from the group consisting of Nio.osBao ss rCh, Ni0 iBao gZrCb,
Ni04Ba0 eZrOa, Ni0 ^BaossZrOs, Ni0 5Ba0 sZrOs, Ni0 osBa0 gsHfOa and Ni02Ba0 8Hf03.
In embodiments, the crystalline metal oxide has a general formula selected from the group consisting of N osBao 95Zr03j Ni0 iBa0 gZrC , Ni0 2Ba0 sZr03, Ni03Bao jZrOs, io Bao eZrOr,, Nio45Ba055Zr03 and Nio.sBaasZrOs.
In embodiments, the crystalline metal oxide has a general formula selected from the group consisting of Nio osBao.asHfC and Ni0 2Ba0 sHfOa.
In preferred embodiments, the crystalline metal oxide has the general formula 20% Ni/BaZrOa, i.e. barium zirconate comprising 4% nickel incorporated homogeneously in the barium zirconate crystal lattice (in sold solution),
Figure imgf000034_0002
In an embodiment of the invention is provided a crystalline nickel barium zirconate characterized by X-ray powder diffraction peaks at about 30.3°, 37.4°, 43.3°, 53.8°, and 64.0° ±0.2° 2Θ. This material is typically 20% Ni/BaZr03, i.e. barium zirconate comprising 4% nickel incorporated homogeneously in the barium zirconate crystal lattice (in sold solution). These XRPD peaks were obtained using the conditions set out in the Examples section.
In an embodiment of the invention is provided a crystalline nickel hafnium zirconate characterized by X-ray powder diffraction peaks at about 30.4°, 43.5°, 54.0°, and 63.2° ±0.2" 2Θ. This material is typically 20% Ni/BaHf03, i.e. barium zirconate comprising 4% nickel incorporated homogeneously in the barium zirconate crystal lattice (in sold solution). These XRPD peaks were obtained using the conditions set out in the Examples section. Purity
The crystalline metal oxides as described in any of the above aspects and embodiments may be substantially phase pure. For instance, in embodiments, the crystalline metal oxide of the present invention has a phase purity of at least 80 mol%, suitably at least 90 mol%, preferably at least 95 mol%, at least 98 mol% or more preferably at least 99 moi%. In alternative embodiments, the crystalline metal oxide of the present invention has a phase purity of at least 80 wt%, suitably at least 90 wt%, preferably at least 95 wt%, at least 98 wt% or more preferably at least
99 wt%. The hydrothermai methods of the present disclosure provide material of high phase purity. Phase impurities may be reduced / removed by washing in acid, such as HN0.3. In preferred embodiments, the crystalline metal oxides of the present invention are completely (i.e. 100%) phase pure.
Advantageously, the crystalline metal oxides of the present invention are able to incorporate surprisingly high levels of nickel homogeneously into the crystal lattice structure without detriment to the phase purity (see, e.g. Figure 1 showing phase pure material having levels of 4 atom0/© nickel). High phase purity is desirable as it typically provides greater catalyst stability and more predictable catalytic reaction profiles.
Perovskite-type crystal structure
In preferred embodiments of the aspects and embodiments described herein, the crystalline metal oxide has a perovskite-type unit cell structure. The term
"perovskite-type" refers to a crystal unit cell structure analogous to that adopted by perovskite, as well as distorted perovskite unit cell structures. Preferably, the crystalline metal oxides of the invention have a perovskite unit cell structure, i.e. a unit cell structure analogous to that adopted by perovskite.
Surface area
In embodiments, the crystalline metal oxides according to any aspect or embodiment thereof described herein has a surface area greater than 5 m2/g, such as greater than 10 m2/g or 15 m2/g, preferably greater than 20 m2/g, 22 m2/g, 25 m2/g, 30 m2/g, more preferably greater than 35 m2/g. In embodiments, the crystalline metal oxide has a surface area of up to 80 m2/g, for example up to 70 n Vg, 60 m /g, 50 m2/g, 40 m2/g, 30 m2/g, or 20 m /g. For instance, in embodiments, the crystalline metal oxide has a surface area of 5-80 m2/g, suitably 15-70 m2/g, 20-60 m2/g, 30-50 m /g. or 35- 45 m2/g, typically around 40-50 m2/g. In particular embodiments, the crystalline metal oxide has a surface area of between 5 - 30 m2/g or 8 - 25 m2/g, such as 10-20 m2/g. The crystalline metal oxides of the present invention suitably exhibit high surface area (particularly when prepared according to hydrothermal methods disclosed herein) without requiring further mechanical manipulation such as milling or grinding, etc. High surface area is desirable for heterogeneous catalytic reactions where access to the catalyst surface is a determining factor in reaction rate.
Particle Size
The crystalline metal oxides of the present invention may comprise particle sizes having a length of from 0.1-20 pm. In embodiments, the present invention provides solid crystalline oxides having a particle size in the range of 0.1-10 pm, such as 0.1 pm to 5 pm, for example 0.1 pm to 2 pm, and in typical embodiments from 0.1 pm-1 pm. In embodiments, the present invention provides solid crystalline nickel barium zirconate material having a maximum particle size in the range of 1 - 2 pm, typically 1 pm. In alternative embodiments, the present invention provides solid crystalline nickel barium hafnate having a maximum particle size in the range of 0.5-2 pm, such as 1 pm.
Smaller particle sizes may improve catalytic efficiency as more active nicket species will be available at the catalytic surface due to the larger surface area to volume ratio. Suitably, the methods of preparation of the crystalline metal oxides of the present invention disclosed herein provide particle sizes in the ranges above without need for additional mechanical manipulation of the resulting crystals, e.g. such as milling or grinding. Ninth aspect
In a further aspect is provided a process for preparing a crystalline metal oxide comprising:
a) mixing an aqueous solution comprising a barium salt with a metal chloride and a basic hydroxide to form a gel; and
b) heating the gel until a solid crystalline product is obtained. Optionally, the metal chloride may be a metal oxychloride.
As seen in example 1 , the present process is procedurally simple (mixing the starting materials in an autoclave) and heating and does not require addition of
carbonaceous material which may contaminate the final product (such as ethylene glycol or citric acid complexing agents), or harshly acidic conditions. Advantageously. the reaction proceeds at relatively low temperature (e.g. 180 °C) to provide high-quality crystalline metal oxide material (i.e. highly phase pure material - see example 1 ). Without wishing to be bound by theory, it is envisaged that the high reactivity of metal chlorides in the crystal lattice-forming reaction at least in part contributes to the simplicity and ease at which the reaction can be carried out.
Crystalline metal oxide
The present process is useful for preparing crystalline metal oxides including barium. The crystalline metal oxide may thus be as defined according to any of the first to eighth aspects and embodiments thereof as disclosed above.
Thus, the process may be a process of preparing a crystalline metal oxide having a unit cell structure of the general formula ABO3 comprising metals at A sites and B sites, typically where barium is at A-sites. Typically the barium salt provides for A-sites and the metal chloride provides said metal for incorporation at B-sites.
The present process is procedurally simple (reacting the starting materials in an autoclave) and advantageously proceeds at relatively low temperature (e.g. 180 °C) to provide high quality crystalline metal oxide material (i.e. highly phase pure material - see example 1 ). The use of B-metal chlorides in the present process provides suitable reactivity, avoiding the introduction of carbonaceous materials (such as carbonaceous counter ions or complexing agents), which can lead to phase impurities. Barium salt
In embodiments, the barium salt is a barium nitrate or a barium chloride, preferably a barium nitrate, e.g. Ba(NO?)2. In embodiments the barium salt is a barium chloride, e.g. BaC . Metal chloride
In embodiments, the metal chloride is selected from transition metal chlorides.
Preferably the metal chloride is a metal oxychloride. such as a transition metal oxychloride. Suitably, the transition metal chloride is selected from one or more of titanium chloride, zirconium oxychloride and hafnium oxychloride. Preferably the metal oxychloride is zirconium oxychloride or hafnium oxychloride, or a combination thereof. In preferred embodiments, the metal oxychloride is zirconium oxychloride. In embodiments the metal oxychloride is hafnium oxychloride. In embodiments, more than one metal oxychloride is provided, such as a combination of zirconium oxychloride and hafnium oxychloride. Basic hydroxide
Any suitable hydroxide may be used in the present process, provided it is basic (i.e. of basic pH). In embodiments, the basic hydroxide is selected from metal hydroxides and ammonium hydroxides. Suitably, the basic hydroxide is an ammonium hydroxide. Preferably, the basic hydroxide is a metal hydroxide. Preferred, metal hydroxides are alkali metal or alkaline earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, e.g. potassium hydroxide. Sodium hydroxide is particularly preferred.
In embodiments, the solution comprising the barium salt further comprises at least one further metal salt, suitably only one further metal salt or in alternative
embodiments more than one (e.g. two) further metal salts. The one or more further metal salts may be selected independently from salts of alkali metals, alkaline earth metals, transition metals, lanthanides and actinides. In embodiments, the one or more further metal salts may be selected independently from salts of alkaline earth metals, transition metals and lanthanides, preferably from alkaline earth metal salts and transition metal salts, e.g. transition metal salts, such as nickel salts. The at least one further metal salt may be independently selected from metal nitrates or metal chlorides, e.g. nitrates such as nickel nitrate. Tenth aspect
In a further aspect is provided a process for preparing a crystalline metal oxide comprising:
a) mixing an aqueous solution comprising a barium salt and a nickel salt with a zirconium and / or hafnium salt to form a gel; and
b) heating the gel until a solid product is obtained.
In preferred embodiments, a basic hydroxide is also added to the aqueous solution in step a). The basic hydroxide may be as defined above for the ninth aspect and embodiments thereof. Crystalline metal oxide
The present process is useful for preparing crystalline metal oxides. The reaction involves the use of barium, nickel and zirconium and / or hafnium salts (for instance zirconium and hafnium, or zirconium or hafnium). The resulting crystalline metal oxide may thus be defined according to any of the first to eighth aspects or embodiments thereof as described above.
Barium, nickel, zirconium and / or hafnium salts
The barium, nickel and zirconium and / or hafnium salts may be selected
independently from nitrates and chlorides.
Suitably, the barium salt may be a chloride or nitrate, preferably a nitrate.
In embodiments, the nickel is a chloride or nitrate, preferably a nitrate. For instance, in preferred embodiments, both barium and nickel salts are nitrates.
Suitably, the zirconium and / or hafnium salts may be selected independently from chlorides or nitrates, typically chlorides. In preferred embodiments, the zirconium and / or hafnium chlorides are oxy chlorides, such as wherein the oxychloride is an oxychloride hydrate, e.g. an oxychloride octahydrate.
In embodiments, the process includes mixing at least one further metal salt in step a), suitably only one further metal salt or in alternative embodiments more than one (e.g. two) further metal salts. The one or more further metal salts may be selected independently from alkali metals, alkaline earth metals, transition metals, lanthanides and actinides. In embodiments, the one or more further metal salts may be selected independently from alkaline earth metals, transition metals and lanthanides, preferably from alkaline earth metal salts and transition metal salts, e.g. transition metal salts. The at least one further metal salt may be independently selected from metal nitrates or metal chlorides.
The present invention also provides a process for preparing a crystalline metal oxide as defined in any of the first to eighth aspects and embodiments thereof. In embodiments, the process for preparing a crystalline metal oxide as described in any of the first to eighth aspects and embodiments is as defined in the ninth and tenth aspects and embodiments. The present invention thus provides a process as defined in the ninth or tenth aspect and embodiments thereof for preparing a crystalline metal oxide as defined in any of the first to eighth aspects and embodiments thereof.
Temperature
In typical embodiments of the processes of the present invention described above in the ninth and tenth aspects and embodiments thereof, the average temperature does not exceed 500 "C. The average temperature refers to the temperature of the reaction averaged over the duration of the reaction. Suitably the average temperature during the process does not exceed 450 °C, preferably 400 °C, 350 °C, 300 °C, 250 °C or more preferably 200 °C. In embodiments, the reaction temperature does not exceed 500 X, suitably 450 °C, preferably 400 °C, 350 °C, 300 °C, 250 °C or more preferably 200 °C. Typically the reaction is performed at around 180 °C. In preferred embodiments of the processes of the invention the process does not include a calcination (calcining) step.
As explained above, the present processes advantageously do not require the addition of chelating agents, such as ethylene glycol or citric acid. Thus in embodiments, the processes of the invention do not include the addition of complexing or chelating agents, such as ethylene glycol or citric acid.
Likewise, the present processes advantageously do not require the addition of concentrated acids, such as HN03. Thus, in some embodiments, the processes of the invention do not include the addition of concentrated acids, such as HNOs Typically, the heating step in the above processes is performed in an autoclave.
Further process steps
In embodiments, the processes defined in the above aspects and embodiments of the invention further comprising the step of isolating the solid product (i.e. the crystalline metal oxide). In preferred embodiments, the processes comprise the step of purifying the product (i.e. crystalline metal oxide). Typically, the purification comprises centrifugation and / or washing of the solid product (i.e. crystalline metal oxide). In further embodiments, the processes of the present invention comprise the steps of incorporating the solid product (i.e. crystalline metal oxide) into a catalytic composition and / or packaging the solid product (i.e. crystalline metal oxide). Eleventh aspect
In a further aspect of the invention is provided a crystalline metal oxide obtainable by any process as defined in the ninth or tenth aspects and their embodiments. In a further embodiment is provided a crystalline metal oxide obtained by any process as defined in the ninth or tenth aspects and their embodiments.
Twelfth aspect
In a further aspect is provided a composition comprising a crystalline metal oxide as defined according to any of the aspects and embodiments described herein, e.g. in the first to eighth aspects and embodiments. The composition may comprise one or more carriers. For instance the composition may comprise a crystalline metal oxide of the invention supported on, or as part of (e.g. interspersed within), a carrier substrate. Suitable carriers and / or supports will be apparent to a skilled person and include conventional catalyst support materials, such as ceramics and oxides, e.g. alumina and / or silica.
In embodiments, the composition may further comprise one or more catalysts (i.e. which may thus be in addition to the crystalline metal oxide of the invention).
Suitably, the one or more catalysts may be selected from methane reforming catalysts. In embodiments, the catalyst(s) is solid oxide fuel cell anode cermet, preferably Ni/YSZ anode cermet.
In embodiments, the composition includes at least a second crystalline metal oxide of the invention as described in any of the above aspects and embodiments.
Thirteenth aspect
In an aspect of the invention is provided a catalyst comprising a crystalline metal oxide as defined in any of the above aspects and embodiments thereof (e.g. as in the first to eleventh aspects and embodiments thereof, preferably the first to eighth aspects and embodiments thereof) or a composition as defined above in the twelfth aspect and any of its embodiments, and one or more carriers. For instance the catalyst may comprise a crystalline metal oxide or composition supported on, or as part of (e.g. interspersed within), a carrier substrate. Fourteenth aspect
In an aspect of the invention is provided a product comprising a crystalline metal oxide according any of the above aspects and embodiments, a composition according to any of the twelfth aspect and embodiments, or a catalyst as defined in the thirteenth aspect or any embodiments thereof. In some embodiments, the product comprises the crystalline metal oxide, composition or catalyst of the invention as defined above within the product and / or on the surface of the product. For instance, the crystalline metal oxide, composition or catalysts of the invention may be provided as a coating on a product, such as on an electrode. In some embodiments, the product is a reactor, such as a fuel cell. In embodiments, the product may be a vehicle, such as a motor vehicle. In embodiments, the product consists of the crystalline metal oxide, composition or catalyst of the invention as described herein above. Such compositions, catalysts and / or products as defined above may suitably be used as the source of the crystalline metal oxide in the methods of reforming fuels as defined in any of the above aspects and embodiments. In other words, the uses and methods of reforming a fuel as defined according to any aspect or embodiment described above may use a composition, catalyst and / or product as defined above.
With respect to the above aspects, the respective embodiments are described by way of example. Other embodiments falling within the scope of the claims will however be apparent to the skilled reader. GENERAL
The terms "additives" or "dopants" in the context of crystalline metal oxides of the invention refer to substances that are incorporated into the crystalline metal oxides of the invention alongside nickel, barium, zirconium and / or hafnium, and oxygen.
Suitably, the additives or dopants in the crystalline metal oxides of the invention described above may be independently selected from metals and / or non-metals, typically metals. Suitable metals may be selected from alkali metals, alkaline earth metals, transition metals, lanthanides, actinides and other conventional additives (i.e. dopants).
The skilled person will understand that references to metals such as barium, zirconium, hafnium and nickel in the context of crystalline metal oxides of the invention typically refers to the respective metal ions (i.e. cations) due to the large difference in electronegativity between metals and oxygen (i.e. forming oxide anions). However, some degree of covalent character in the bonds between these species in the crystal lattice may be observed, for instance depending on the interaction of the A and B metal species with oxygen.
Atom% refers to a percentage of a given amount of atoms. For instance, the material Nio2Bao eZrC>3 contains 4 atom% nickel, 16 atom% barium, 20 atom% zirconium and 60 atom% oxygen atoms.
The reference to X% Ni/BaZr03 refers to the atom% nickel incorporated relative to the theoretical amount of barium or zirconium in nickel-free barium zirconate / hafnate. Thus, >20% Ni/BaZr03 refers to materials including at least 20atom% nickel relative to the theoretical amount of barium or zirconium/hafnium in nickel-free barium zirconate/hafnate material. For example, 20% Ni/BaZrf¾ includes crystalline metal oxide of the formula io^Bao eZrOs.
LIST OF FIGURES
Figure 1 shows the powder X-ray diffraction data for Ni/BaZr03 comprising 4 atom% nickel incorporated homogeneously into the crystal lattice as prepared according to the method of Example 1a. The lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e. NioaBaosZrCh).
Figure 2 shows a scanning electron microscopy (SEM) image of the material described in Figure 1.
Figure 3 shows the powder X-ray diffraction data for Ni/BaZr0 comprising 5 atom% nickel incorporated homogeneously into the crystal lattice prepared according to a method analogous to Example 1a. The lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e.
Figure imgf000043_0001
Figure 4 shows the powder X-ray diffraction data for Ni/BaHf03 comprising 4 atom% nickel incorporated homogeneously into the crystal lattice as prepared according to a method of Example 1 b. The lack of impurity peaks in the XRPD pattern indicates that the material is phase-pure (i.e. Ni02Ba08HfO3). Figure 5 shows a reverse temperature-programmed profile for the reaction of methane with stoichiometric steam over Ni/BaZrCb comprising 4 atom% nickel (Nio.2Bao.8Zr03)as described in Example 2. The graph plots molar equivalents of product gases against temperature.
Figure 6 shows a reverse temperature-programmed profile for the reaction of methane with stoichiometric steam over conventional Ni/YSZ anode cermet
(Comparative Example 1 ). The graph plots molar equivalents of product gases against temperature.
Figure 7 shows a reverse temperatu re-prog ra m med profile for the reaction of methane with limited amounts of oxygen over Ni/BaZrOi comprising 4 atom% nickel ( io^BaosZrOs) as described in Example 3. The graph plots molar equivalents of product gases against temperature.
Figure 8 shows a temperature-programmed profile for the reaction of methane with limited amounts of oxygen over perovskite-type La07Sr03 n03 as described in Comparative Example 2. The graph plots molar equivalents of product gases against temperature.
Figure 9 shows a temperature-programmed profile for the reaction of methane with limited amounts of oxygen over conventional Ni YSZ anode cermet. (Comparative Example 3) The graph plots molar equivalents of product gases against temperature.
Figure 10 shows a comparison between the methane conversion data for the reaction of methane with limited amounts of oxygen over Ni/BaZr03 comprising 4 atom% nickel and conventional Ni/YSZ anode cermet and corresponding to the reaction profiles in Figures 7 and 9. The graph plots percentage methane conversion against temperature. The upper line at 800 °C is for Ni/BaZr03 comprising 4 atom% nickel and the lower is for conventional Ni/YSZ anode cermet.
Figure 11 shows a comparison between the methane conversion data for the reaction of methane with limited amounts of oxygen over Ni/BaZr03 comprising 4 atom% nickel and Ni/BaHfCb comprising 4 atom% nickel. The data were obtained by a reverse temperature-programme analogous to that shown in Figure 7 and the graph plots percentage methane conversion against temperature for each catalyst. Figure 12 shows the isothermal reaction profile showing methane conversion in limited oxygen over Ni/BaZr03 comprising 4 atom% nickel (as produced according to example 1 ) at 800°C. Figure 13 shows the reaction profile for the isothermal reaction of methane with limited oxygen over Ni/BaZr03 comprising 4 atom% nickel (as produced according to example 1 ) at 800 °C to investigate susceptibility to coking. The graph plots molar equivalents of product gases against reaction time. Figure 14 shows the temperature-programmed profile for the reforming of simulated biogas (methane / carbon dioxide in a 2:1 ratio) over Ni/BaZr03 comprising 4 atom% (corresponding to Figure 1 - i.e. as produced according to Example 1 ).
Figure 15 shows the amount of gaseous components produced relative to the amount of methane in the isothermal reaction of simulated biogas (CH4:C02 = 2:1) over Ni/BaZrOa comprising 4 atom% nickel (i.e. Nio^Bao eZrCb - as produced according to Example 1) at 850 °C over 10 days (see Example 6).
Figure 16 shows the amount of gaseous components produced relative to the amount of methane in the reaction of simulated biogas (CH^COa = 2.1) over conventional Ni YSZ anode cermet catalysts during dry reforming of simulated biogas (CH4:C02 = 2:1 ) at 850 °C over 20 hours (Comparative Example 4).
Figure 17 shows the methane conversion profile for dry reforming of simulated biogas (CH4:C02 = 2:1) at 850 °C over both conventional Ni/YSZ anode cermet (Comparative Example 4) and also for Ni/BaZrOa comprising 4 atom% nickel (i.e. according to Nio.2Bao.sZr03 - as produced according to Example 1 ) over 3 h.
Figure 18 shows the powder X-ray diffraction data for Ni/BaZrOs comprising 2 atom% nickel incorporated homogeneously into the crystal lattice prepared according to a method analogous to Example 1 a (i.e. corresponding to Ni0 iBa0 gZrO3). The lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e. Nio iBao gZrOs).
Figure 19 shows the powder X-ray diffraction data for Ni/BaZr03 comprising 1 atom% nickel incorporated homogeneously into the crystal lattice prepared according to a method analogous to Example 1a. The lack of impurity peaks in the XRPD pattern indicates that the material is phase pure (i.e. Nio osBao gsZrCh).
Figure 20 shows a temperature programmed thermal decomposition of acetic acid over Nio 2Bao e r03. The graph plots molar equivalents of product gases against temperature.
Figure 21 shows a reverse temperature programmed thermal decomposition of acetic acid over io^Bao.s rOs. The graph plots molar equivalents of product gases against temperature.
Figure 22 shows a temperature programmed steam reforming of acetic acid over Mb 2Ba0 s rC . The graph plots molar equivalents of product gases against temperature. Figure 23 shows a reverse temperature programmed steam reforming of acetic acid over io.2Bao e r03. The graph plots molar equivalents of product gases against temperature.
EXAMPLES The present invention is described in more detail by way of example only with reference to the following Examples.
Powder X-ray diffraction data were collected using a Bruker D8 Advance
diffractometer using a Cu Ka source and a flat disc sample holder.
EDX elemental analysis data were collected using a Hitachi TM3000 scanning electron microscope equipped with a Bruker Quantax 70 EDS system.
Example 1 : Preparation of exemplary crystalline metal oxides of the invention by hydrothermal methods of the invention a. Preparation of nickel barium zirconate
In a typical synthesis, barium nitrate (1.30 g, 4.96 mmol) and nickel nitrate hexahydrate (0.36g, 1.24 mmol) were dissolved in deionised water (8 ml, 400 mmol). Zirconium oxychloride octa hydrate (2.0 g, 6.20 mmol) was then added, followed by sodium hydroxide (2 g, 50 mmol). The mixture was stirred by hand to produce a thick gel, before being transferred to a 23 ml Teflon-lined stainless steel autoclave and heated in a forced air oven at 180 °C. After 72 hours the autoclave was removed and allowed to cool to room temperature. The resulting product was subjected to repeated centrifuging (5000 rpm) and washing cycles (all products were subjected to repeated (three cycles) of washing with deionised water (~ 50 ml) followed by centnfugation at 5000 rpm) before being dried at 90 °C overnight. Analysis by powder X-ray diffraction (Figure 1 ) showed the material obtained to be highly crystalline with an ABOs-type perovskite structure. The material was phase pure, thus confirming that the nickel was incorporated entirely within the barium zirconate crystal lattice to provide Ni/BaZrC comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr03, corresponding to Ni0.2Bao sZr03 as a solid solution).
EDX analysis of the material produced confirmed this result as shown by the data below.
EDX analysis:
Figure imgf000047_0001
Typical uncertainties for the atomic compositions were ±1.2% (Zr), ±1.1% (Ba), ±2% (O), ±0.2% (Ni).
Scanning electron microscopy (Figure 2) showed the material to have an
approximately dodecahedral/spherical morphology with particles sizes ranging up to 1 pm in diameter.
Nitrogen absorption experiments indicated that the material had a moderately large surface area of approximately 10 - 20 m2/g.
Analogous conditions were also used to provide corresponding nickel barium zirconate material wherein 5 mol%. 10 mol%, 25 mol%, 30 mol%, 40 mol%, 45 mol% or 50 mol% of nickel is provided in the reaction relative to the combined molar amount of barium and nickel respectively, corresponding to nickel barium zirconate product containing 1 atom%, 2 atom%. 5 atom%, 6 atom%, 8 atom%, 9 atom% or 10 atom% nickel respectively (i.e. 5% Ni/BaZr03, 10% Ni/BaZrQ3, 25% Ni/BaZrCb, 30% Ni/BaZrOs, 40% Ni/BaZr03, 45% Ni/BaZr03 and 50% Ni/BaZr03, respectively). Thus, this material corresponds to a final product having the following atomic ratios: io.o5Ba0.95Zr03, Nio.iBa0.9Zr03, io^Bao.zsZrOa, Ni0 3Ba0.7ZrO3, Nio.4Ba0.6Zr03, i0.45Ba0.65ZrO3 and Ni0 5Ba05ZrO3 respectively.
Analysis by powder X-ray diffraction of the material obtained when 25 mol% nickel is provided in the reaction relative to the combined molar amount of barium and nickel (Figure 3) also showed that the material obtained was highly crystalline with an AB(½-type perovskite structure. The material was of high phase purity, thus confirming that the nickel was incorporated within the crystal lattice.
These results were also confirmed by EDX analysis. b. Preparation of nickel barium hafnate
Reaction conditions analogous to those in Example 1a were used to prepare corresponding nickel barium hafnate material, substituting hafnium oxychloride for zirconium oxychloride. For example, catalysts containing 4 atom% nickel and 1 atom% nickel were prepared (i.e. wherein 20 mol% nickel and 5 mol% nickel is provided in the reaction relative to the combined molar amount of barium and nickel salts respectively).
Powder X-ray diffraction for the 4 atom% nickel material (Figure 4) showed the respective material to be highly crystalline and highly phase-pure with AB03-type perovskite structures, thus confirming that the nickel was incorporated completely into the crystal lattices, forming a solid solution corresponding to Ni/BaHf03 comprising 4 atom% nickel, i.e. 20% Ni/BaHfCb, corresponding to Nio^BaoeHfCb.
Nitrogen absorption experiments indicated that the material had a moderately large surface area of approximately 10 - 20 m2/g similar to the nickel barium zirconate materia! produced in Example 1a. c. Preparation of further materials of the invention
Methods analogous to those described above can provide nickel barium zirconates. nickel barium hafnates or solid solutions of nickel barium zirconate and nickel barium hafnate in a variety of metal ratios by varying the stoichiometric ratios of the respective metal salts in the reaction. Exemplary materials of the invention prepared as described above showed excellent catalytic properties in a variety of gas reforming reactions as described in the Experimental Data section below.
The hydrothermal methods of the present invention such as described in Example 1 therefore provide crystalline metal oxides using a simple procedure (the starting metal salts are simply mixed in aqueous solution in a single step without prior manipulation), at relatively low temperature (such as compared to methods which require a calcination step) and whilst avoiding both the introduction of carbonaceous materials that can contaminate the product (such as ethylene glycol or citric acid complexing agents - as required in prior art citrate methods) and the use of harshly acidic conditions. Advantageously, the reaction provides high-quality crystalline metal oxide material (i.e. highly phase pure material - see example 1 and figure 1 ) in high yield (typically in essentially stoichiometric yield). The hydrothermal methods of the present disclosure therefore provide an excellent way to access the materials of the present invention. Without wishing to be bound by theory, it is envisaged that the high reactivity of metal chlorides, e.g. oxychlorides in the crystal lattice forming reaction contributes to the simplicity and ease at which the reaction can be carried out.
EXPERIMENTAL DATA
General methods
To exemplify the beneficial catalytic properties of materials of the present invention, materials produced according to Example 1 were tested for catalytic performance in gas reforming reactions to produce syngas. Corresponding data for other catalysts including lanthanum barium manganite and standard nickel anode cermet, i.e. nickel-doped yttria-stabilised zirconia (Ni/YSZ) are also provided for comparative purposes.
In each experiment described below, -20 mg (± 0.5 mg - 4 point balance) of respective catalyst was used. In the case of catalysts according to the present invention having the general formula Ni02Ba0 eZr03, 20 mg of catalyst corresponds to 9.0 x 104 g or 1.53 x 10'5 moles of nickel. In the case of catalysts according to the present invention having the general formula io^Bao sHfOa, 20 mg of catalyst corresponds to 3.74 x 10"4 g or 1.15 x 105 moles nickel. For standard nickel anode cermet 20 mg corresponds to 1.44 x 102 g or 2.44 x 10 moles of nickel.
All gas composition analyses were carried out by quadru polar mass spectrometry.
Steam reforming
Experiments were carried out with gas flow rates of 18 ml min ! helium, 1 ml min~1 methane and 1 ml min-1 steam. Example 2:
To illustrate the effectiveness of materials of the invention in steam reforming reactions, methane reforming was performed over Ni/BaZrC comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZrOs, corresponding to Nio 2Ba0 eZr03 as a solid solution) as prepared according to Example 1a. A reverse temperature-programmed reaction profile was obtained by incrementally decreasing the reaction temperature as illustrated in Figure 5.
Comparative Example 1 :
For comparative purposes, the analogous reaction conditions to Example 2 were provided but using conventional Ni/YSZ cermet in place of the nickel barium zirconate of the present invention. The corresponding reaction profile is illustrated in Figure 6. A comparison of Figures 5 (Example 2) and 6 (Comparative Example 1 ) shows that low levels of CO2 are observed in each case, indicating that the respective catalysts show a high selectivity for the desired steam reforming pathway over competing side reactions. The material of the present invention exhibits excellent steam reforming activity with an initial activation temperature significantly lower (around 200 °C lower) than conventional Ni/YSZ cermet. Optimum reforming begins at around 750 °C for the present catalysts, proving the catalysts of the invention to be comparable to conventional Ni/YSZ cermet in steam reforming based on catalytic activity.
Partial oxidation
Experiments were carried out with gas flow rates of 18 ml min"' helium, 2 ml mirr1 methane and 1 ml min f oxygen.
Example 3:
To illustrate the effectiveness of materials of the invention in partial oxidation reactions, a reaction was performed over Ni/BaZr03 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZrOs, corresponding to Nio^Bao.eZrOa as a solid solution) as prepared according to Example 1a. A reverse temperature-programmed reaction profile was obtained by incrementally decreasing the temperature as illustrated in Figure 7. For the nickel barium zirconate of the present invention, hydrogen and carbon monoxide are the major reaction products above 700 °C (Figure 7). with low amounts of total oxidation products in evidence. Comparative Example 2:
For comparison, the temperature-programmed profile for the reaction of methane with limited amounts of oxygen over perovskite-type LaojSro sMnCh is provided in Figure 8. The results show that for La0 ?Sr0.3MnC the main reaction products between 600 X and 900 °C are water and carbon dioxide (i.e. complete oxidation products - see Figure 8) and it is not until temperatures increase above 900 °C that any substantial partial oxidation occurs to produce the desired hydrogen and carbon monoxide syngas products, thus indicating low selectivity for partial oxidation. This is typical of many perovskite-type catalysts.
Thus the comparison shows the crystalline metal oxide of the present invention to have greater selectivity for partial oxidation of methane compared to Lao jSr03Mn03, with very low amounts of complete oxidation products in evidence above 700 °C.
Comparative Example 3:
An analogous experiment was also performed using conventional Ni YSZ anode cermet, which is known to provide desirable selectivity in partial oxidation reforming reactions. The temperature-programmed reaction profile is provided in Figure 9 showing Ni/YSZ anode cermet to have good selectivity for partial oxidation from around 650 °C upwards.
A comparison of Ni/BaZr(¾ comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZrOs, corresponding to Nio-Bao sZr03 as a solid solution) as prepared according to Example 1a and conventional Ni/YSZ anode cermet based on reaction profile, methane conversion and gas production shows that crystalline metal oxides of the present invention advantageously display a similar reaction profile to Ni/YSZ at similar operating temperatures while showing greatly increased methane conversion during methane reforming (approx. 10-20% increase in methane conversion dependent on reaction temperature - see Figure 10) from around 550 °C upwards compared to conventional Ni/YSZ anode cermet, proving the catalysts of the invention to have excellent commercial potential as alternatives to conventional Ni/YSZ anode cermet in partial oxidation reactions (based on catalytic activity and selectivity). Example 4 - comparison of activity of zirconate and hafnate Figure 11 shows a comparison of methane conversion data for Ni/BaZrOa comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr03, corresponding to Nio JBao sZ Oa as a solid solution) as prepared according to Example 1a and Ni/BaHf03 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaHf03, corresponding to Nio 2Bao 8Hf03 as a solid solution) as prepared according to Example 1b. These two materials gave similar reaction profiles but with a slightly increased conversion rate for the zirconate, which may be attributable to the higher nickel content per 20 mg of catalyst in the zirconate catalysts.
Carbon deposition (coking) during partial oxidation
Example 5
The partial oxidation of methane over Ni/BaZr03 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZrG3, corresponding to Nio 2Ba08Zr03 as a solid solution) as prepared according to Example 1a was conducted under isothermal conditions at 700 °C, 800 °C and 900 °C. The isothermal reaction profile at 800 °C over 20 h is provided at Figure 13. No degradation in catalytic activity is observed over 20 hours, as exemplified by the methane conversion data in Figure 12 (conducted at 800 °C) showing excellent resistance to coking over long periods.
These isothermal experiments allowed for an analysis of the amount of carbon deposited over time by oxidising deposited carbon and integrating the carbon dioxide released. The results, given in table 1 below, indicate the surprisingly low levels of coking observed with these catalysts:
Figure imgf000052_0002
Table 1 Total carbon deposition during partial oxidation of methane over
Figure imgf000052_0001
Dry reforming of biogas
Experiments were carried out using gas flow rates of methane 1 ml min \ carbon dioxide 0.5 ml min-1 and helium 18.5 ml min 1. Example 6
Reforming of simulated biogas (CH4:C02 = 2:1 ) over Ni/BaZr03 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr03, corresponding to Ni02Ba0 eZr03 as a solid solution) as prepared according to Example 1a occurs at just under 500 °C with stoichiometric conversion (50% methane conversion) occurring rapidly at roughly 800 °C. This nickel barium zirconate produces hydrogen selectively over carbon monoxide at lower temperatures without increased carbon deposition, suggesting true reforming is occurring. The temperature-programmed reaction profile is shown in Figure 14.
Figure 15 shows the reaction profile for an extended catalytic reforming reaction (run over 10 days) of simulated biogas over Ni/BaZrCh comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr03, corresponding to Ni02Bao8Zr03 as a solid solution) as prepared according to Example 1a at 850 °C. The reaction equilibrates quickly to provide 50% methane conversion corresponding to the desired dry reforming reaction between 1 mol. eq. CH4 with 1 mol. eq. CQ2 (i.e. leaving 1 mol. eq. CH unreacted in the reaction mixture, i.e. 50% of initial amount) - see also for example Figure 17 which shows the methane conversion data over 3h. The results show that the catalyst of the invention can reform biogas for long periods of time with negligible carbon deposition. In this reaction only 1.85 mg of carbon was deposited
Comparative Example 4 - dry reforming using Ni YSZ cermet
Reforming of simulated biogas (CH4:C02 = 2:1 ) over nickel based catalysts to produce syngas can be achieved using Ni/YSZ cermet at a variety of temperatures (700 - 900 °C) although some of the excess methane is also broken down in competing reactions (e.g. methane cracking) due to the high reactivity. The reaction over Ni/YSZ cermet equilibrates to a level closer to 60% methane conversion (i.e. which exceeds the stoichiometric amount of 50% methane conversion expected in a perfect dry reforming reaction), indicating that excess methane is being cracked, leading to coking of the catalyst surface. The reaction profile for Ni/YSZ cermet at 850 °C over 20 h showing gaseous products relative to methane is provided in Figure 16. The respective methane conversion profile of Ni/YSZ compared to Ni/BaZr03 comprising 4 atom% nickel in solid solution (i.e. 20% Ni/BaZr03, corresponding to io 2Bao.8Zr03 as a solid solution) as prepared according to Example 1a over 3 h is provided in Figure 17. Accordingly, the crystalline metal oxides of the present invention reform simulated biogas at lower temperatures compared to Ni/YSZ cermet (i.e. with reforming starting just under 500 °C) with stoichiometric conversion (i.e. 50% methane conversion) occurring rapidly at about 800 "C. In addition, the crystalline metal oxides of the present invention produce syngas selectively and show substantially less coking than Ni/YSZ cermet, even over long reaction times (e.g. 10 days - Figure 15). In particular, in the reaction over 10 days (Figure 15), only 1.85 mg carbon was deposited, a surprisingly low amount.
Thermal Decomposition of Acetic Acid
Experiments were carried out using a helium flow rate of 18 ml min 1 passing through a saturator filled with glacial acetic acid held at 25 °C. Example 7
A temperature-programmed experiment revealed that thermal decomposition of acetic acid can be achieved over Nio ^Baoe rOa at 500 °C, with optimum hydrogen production occurring at approximately 700 °C (see Figures 20 and 21 ). The syngas product is rich in hydrogen and carbon monoxide. Temperatures over 600 °C led to the production of a small amount of acetone, but with no observable drop in hydrogen output. Accordingly, the crystalline metal oxides of the present invention reform acetic acid at reasonable temperatures.
Steam Reforming of Acetic Acid
Experiments were carried out using a helium flow rate of 18 ml min 1 passing through a saturator filled with a 1 :1 mixture of water and glacial acetic acid held at 30 °C.
Example 8
A temperature-programmed experiment revealed that steam reforming of acetic acid can be achieved over Nio ?Ba0 sZrO;¾ starting at approximately 450 °C, with optimum hydrogen production occurring from 600 "C onwards (see Figures 3 and 4).
Accordingly, the crystalline metal oxides of the present invention steam reform acetic acid at reasonable temperatures. Conclusion
The crystalline metal oxides of the present invention exhibit excellent activity in a variety of reforming reactions to form syngas selectively over alternative reaction pathways. These reforming reactions include dry reforming, steam reforming and partial oxidation, showing the versatility of the crystalline metal oxides of the present invention in reforming reactions for the production of syngas. Advantageously, crystalline metal oxides of the present invention are able to tolerate surprisingly high levels of active nickel incorporated homogenously within the crystal lattice (i.e. in solid solution) whilst retaining high levels of phase purity. Crystalline metal oxides of the present invention show excellent resistance to coking. This is particularly surprising given the high nickel content of the tested catalysts. Thus the materials of the present invention provide a valuable alternative to conventional nickel based catalysts (such as Ni/YSZ cermet) in reforming reactions for the production of syngas, particularly in the reforming of fuel derived from natural sources, including biofuels, such as biogas.
A number of patents and publications are cited herein to more fully describe the invention and the state of the art to which the invention pertains. Each of these references is incorporated herein by reference in its entirety, to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference. It will be understood that the invention has been described by way of example only and modifications may be made whilst remaining within the scope and the spirit of the invention.

Claims

1. The use of a crystalline metal oxide in a method of reforming a fuel selected from a hydrocarbon and an oxygenated hydrocarbon, wherein the crystalline metal oxide is selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate, optionally wherein at least some of the nickel, barium, zirconium, and / or hafnium in the crystal lattice is replaced by one or more additives.
2. The use of a crystalline metal oxide according to claim 1 , wherein the crystalline metal oxide has a unit cell structure of the general formula ABO3 comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites.
3. The use of a crystalline metal oxide according to claim 1 or claim 2, wherein the crystalline metal oxide has the general formula (I):
Figure imgf000056_0001
wherein a = 0 8 to 1.2 and y = 0.0 to 1.0, wherein at least some of the barium, zirconium and / or hafnium is replaced by nickel and optionally one or more additives.
4. The use of a crystalline metal oxide according to any one of claims 1-3, wherein the crystalline metal oxide has the general formula (II):
{Ba1.xQx)a({Zr1-yHfy)i-zQ1 2)03 (II)
wherein a = 0.8 to 1.2, x = 0 to 0.9, y = 0.0 to 1.0, z = 0 to 0.9 wherein x+z > 0.01 , Q is il mLm and Q1 is N nLn wherein each L is independently one or more additives and m and n are each independently 0 to 0.5.
5. A crystalline metal oxide selected from a nickel barium zirconate, a nickel barium hafnate, and a solid solution of nickel barium zirconate and nickel barium hafnate, optionally wherein at least some of the nickel, barium, zirconium, and / or hafnium in the crystal lattice is replaced by one or more additives, provided the crystalline metal oxide is not BaZro.stwgN .1351Ο3 or BaZr0.7298 io.270203.
6. The crystalline metal oxide according to claim 5, wherein the crystalline metal oxide has a unit cell structure of the general formula ABO3, comprising barium at A sites, zirconium and / or hafnium at B sites, and nickel at A and / or B sites, provided the crystalline metal oxide is not BaZr08649Ni0 1351Ο3 or BaZro.729eNio 2702O3.
7. The use according to claim 2 or crystalline metal oxide according to claim 6, wherein the nickel is present in at least 1 % of A and / or B sites, optionally at least
2 %, optionally at least 5 %, optionally at least 10 %, optionally at least 20 %, optionally at least 30 %.
8. The use according to claim 2 or 7, or the crystalline metal oxide according to claim 6 or 7, wherein at least 90% of the nickel is at A sites, optionally wherein at least 95% of the nickel is at A sites, optionally wherein at least 98% of the nickel is at A sites, optionally wherein the nickel is at A sites but not B sites.
9. The crystalline metal oxide according to claim 5 or claim 6, wherein the crystalline metal oxide has the general formula (I):
(Ba)a(Zr,.yHfy)03 (I)
wherein a = 0.8 to 1.2 and y = 0.0 to 1.0, wherein at least some of the barium, zirconium and / or hafnium is replaced by nickel and optionally one or more additives, provided the crystalline metal oxide is not BaZro.8649Nio.i35i03 or BaZro zxwNio 2702O3.
10. The use according to claim 3 or the crystalline metal oxide according to claim 9, wherein at least 1 % of the barium, zirconium and / or hafnium is replaced by nickel, optionally at least 2 %, optionally at least 5 %, optionally at least 10 %, optionally at least 20 %, optionally at least 30 %.
11. The use according to any one of claims 1 , 3 and 10. or the crystalline metal oxide according to claim 9 or 10 wherein at least 90% of the nickel replaces barium, optionally at least 95%, optionally at least 98%, optionally wherein 100% of the nickel replaces barium.
12. The use or crystalline metal oxide according to any previous claim wherein the nickel is present in an amount of at least 0.2 atom% , optionally at least
0.4 atom% , optionally at least 1 atom%, optionally at least 2 atom%, optionally at least 4 atom%, optionally at least 6 atom%.
13. The crystalline metal oxide according to claim 5, claim 6 or claim 9, wherein the crystalline metal oxide having the general formula (II):
Figure imgf000058_0001
wherein a = 0.8 to 1.2, x = 0 to 0.9, y = 0.0 to 1.0, z = 0 to 0.9 wherein x+z > 0.01 , Q is Nii mLm and Q' is Nil nLn wherein each L is independently one or more additives and m and n are each independently 0 to 0.5, provided the crystalline metal oxide is not BaZr08649Nio 1351G3 or BaZr0729sNi02702O3.
14. The use according to claim 4 or the crystalline metal oxide according to claim 13 wherein m and / or n is 0.
15. The use according to claim 4 or 14, or the crystalline metal oxide according to claim 13 or 14, wherein x > 0.01 , optionally > 0.02, optionally≥ 0.05, optionally≥ 0.1 , optionally > 0.2, such as≥ 0.3.
16. The use according to any one of claims 4, 14 and 15, or the crystalline metal oxide according to any one of claims 13-15, wherein x≤ 0.9, optionally 0 8, optionally < 0.7, optionally < 0.6, optionally < 0.5, optionally < 0.4, such as < 0.3.
17. The use according to claim 4 or 14. or the crystalline metal oxide according to claim 13 or 14 wherein x = 0.
18. The use according to any one of claims 4 and 14-16, or the crystalline metal oxide according to any one of claims 13-16, wherein z = 0.
19. The use according to one of claims 4 and 14-17, or the crystalline metal oxide according to any one of claims 13-17. wherein z≥ 0.01 , optionally > 0.02, optionally
> 0.05, optionally > 0.1 , optionally > 0.2. such as > 0.3.
20. The use according to any one of claims 4, 14-17 and 19, or the crystalline metal oxide according to any one of claims 13-17 and 19, wherein z≤ 0.9, optionally 0.8, optionally < 0.7, optionally < 0.6, optionally < 0.5, optionally < 0.4,
optionally < 0.3.
21. The use according to any one of claims 3, 4 and 10-20, or the crystalline metal oxide according to any one of claims 9-20 wherein y = 0 or 1.
22. The use according to any one of claims 3, 4 and 10-21 , or the crystalline metal oxide according to any one of claims 9-21 , wherein a = 1.
23. The use or crystalline metal oxide according to any previous claim, wherein the crystalline metal oxide has a general formula 3%-7% Ni/BaZr03;
8-12% Ni/BaZr03; 18-22% Ni/BaZr03; 23-27% Ni/BaZr03; 28-32% Ni/BaZr03;
38-42% Ni/BaZr03; 43-47% Ni/BaZr03; 48-52% Ni/BaZr03; 3-7% Ni/BaHf03; or 18-22% Ni/BaHf03.
24. The use or crystalline metal oxide according to any previous claim, wherein the crystalline metal oxide has a general formula
Figure imgf000059_0001
Ni(Q 08 to 0 12)Ba(0 88 to 092) r03; Ni(0 18 to 022)Ba(0 78 to 0 82> Γ03; Ni(0 23 to 027)Ba(0.73 to 0.77)ZrO3; Nl(0 28 to 032)Ba(0 72 to 068) Γ03; Νί{0.38 to 042)Β8(062 to 058}ΖΓ03; Νϊ(043 to 0.47)Ββ(0.53 to 0.57)ΖΓΟ3; Νί(0.48 to 0.52)Ba, 48 to 052)Ζτ03; Nl(0.03 to 0.07}Ba(0.93 to Q.97)Hf03; ΟΓ
ito i8 to o.22)BaCoT8 to 082>HfO3, optionally wherein Ni + Ba = 1.
25. The use or crystalline metal oxide of claim 24 wherein the crystalline metal oxide has a general formula NioosBao 95Zr03„ Ni0 iBa09Ζ1Ό3, Ni02Ba0 eZr03,
Nio 3Ba0 7ΖΓ03, Ni04Bao6Zr03. Ni04sBa0 ssZr03. Nb.sBao.sZrOs, NioosBao 9sHf03 and Nio 2Ba0 sHfOs, optionally Nio2Ba08Zr03 or Nio2Bao 8Hf03.
26. A process for preparing a crystalline metal oxide comprising:
a) mixing an aqueous solution comprising a barium salt with a nickel salt with a zirconium and / or hafnium salt to form a gel, optionally wherein the zirconium and / or hafnium salt is zirconium and / or hafnium chloride; and
b) heating the gel until a soiid crystalline product is obtained.
27. A process according to claim 26 wherein the zirconium and / or hafnium salt is a chloride.
28 A process according to claim 27 wherein the zirconium and / or hafnium chloride is zirconium and / or hafnium oxychloride.
29. A process according to claim 27 or claim 28 wherein the solution comprising the barium salt further comprises a basic hydroxide.
30. A process according to any one of claims 27-29 wherein the barium salt is barium nitrate.
31. A process according to any one of claims 27-30 wherein the nickel salt is nickel nitrate.
32. A process according to any one of claims 26-31 wherein the crystalline metal oxide is a crystalline metal oxide as defined in any one of claims 1-25.
33. A crystalline metal oxide prepared by a process of any of claims 30-32, optionally wherein the crystalline metal oxide is as defined in any one of claims 1-25.
34. The use according to any previous claim or a crystalline metal oxide as described in any one of claims 5-25 and 33 having a perovskite-type unit cell structure.
35. The use according to any previous claim or the crystalline metal oxide as described in any one of claims 5-25 and 33-34, wherein the crystalline metal oxide has a phase purity of at least 80 mol%. optionally at least 90 mol%, optionally at least 95 mol%, optionally at least 98 mol%.
36. A composition comprising a crystalline metal oxide as defined in any previous claim and a catalyst support material.
37. A composition according to claim 36, further comprising one or more catalysts, optionally wherein the one or more catalysts comprise a solid oxide fuel cell anode cermet, optionally Ni/YSZ anode cermet.
38. A catalyst comprising a crystalline metal oxide according to any one of claims 1-25 and 32-35 or a composition according to any one of claims 36-37, and one or more carriers.
39. A product comprising a crystalline metal oxide according to any one of claims 1 -25 and 32-34, a composition according to any one of claims 36-37 or a catalyst according to claim 38.
40. The use of a crystalline metal oxide according to any one of claims 5-25 and 33-35, a composition according to any one of claims 36-37, a catalyst according to claim 38, or a product according to claim 39 in a method as defined in any one of claims 1-4.
41. The use according to any previous claim wherein the method of reforming is selected from the group consisting of dry reforming, autothermal reforming, steam reforming, partial oxidation and thermal decomposition.
42. The use according to claim 41 wherein the fuel is selected from the group consisting of a hydrocarbon, and a hydrocarbon substituted by one or more oxygen substituents selected independently from the group consisting of -OH and =0;
and / or wherein one or more methylene groups is replaced by an oxygen, optionally wherein the fuel is selected from the group consisting of an hydrocarbon, alcohol, ether, aldehyde, ketone and a carboxylic acid, optionally wherein the fuel is selected from the group consisting of a Ci.25alkane, a C,.i0alkanol and a d-ioalkanoic acid, optionally wherein the fuel is selected from the group consisting of methane, ethane, propane, butane, ethanol, acetone, ethanoic acid, petroleum, diesel, kerosene and mixtures thereof.
43. The use according to any one of claims 41-42 wherein the fuel is methane, ethanol or ethanoic acid.
44. The use according to any previous claim wherein the method of reforming a fuel is a method of preparing syngas.
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