WO2007000068A1 - Manufacturing process for catalytic active material - Google Patents

Abstract

The present invention relates to a process for the production of a catalyst comprising the step of dry deposition of gasborne, catalytic active material on a porous support wherein the catalytic active material have an external surface area between 0,3 to 1000m2/g; to catalysts obtained by such a manufacturing process; to the use of such catalysts in chemical reactions.

Description

MANUFACTURING PROCESS FOR CATALYTIC ACTIVE MATERIAL

Cross References to Related Applications

This application claims the priority of US Provisional patent application No. 60/694,954, filed 29 June 2005, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a process for the production of a catalyst, to catalysts obtained by such a production method, to the use of such catalysts in chemical reactions. In particular, the invention relates to catalysts and the manufacture of catalysts useful in oxidation reactions, like partial oxidation of xylene to phthalic acid anhydride (PA).

Summary of the invention

The present invention relates to a process for the production of a catalyst comprising the step of deposition of gasborne, catalytic active material on porous supports. Further, the invention relates to a process for the production of a catalyst comprising the step of deposition of catalytic active gas phase-made particles on porous supports, preferably foam- and/or sponge like structure.

Further, the invention relates to a process for the production of a catalyst comprising the step of deposition of particles made by flame spray pyrolysis on ceramic foams.

Further, the present invention relates to catalysts obtained by such a manufacturing process. Further, the present invention relates to the use of catalysts obtained by such a manufacturing process in chemical reactions.

Further, the invention relates to the use of thus obtained catalyst for the manufacture of phthalic anhydride.

Background Art

Flame synthesis has been used for the production of vanadia/titania mixed o oxide nanoparticles, containing large anatase fractions [I]. However, this document neither discloses catalysts, comprising a support coated with such nano particles nor a process to obtain such catalysts.

Further, flame-spray pyrolysis (FSP) has been used for the direct deposition of porous catalytic materials into microsystems, exhibiting good adhesion and 5 thermal contact to the support [2]. Studies of FSP-made particles direct deposited on flat surfaces show porosities of the deposited layer above 98% [3]. However, these documents teach to treat Microsystems, i.e. material that has flat surfaces and is not porous. The gasborne catalytic material used in this process does not pass through the material. o Further, it is known that flame-made particles can be agglomerated and exhibit, beside the high external surface area, an open-pore structure that might facilitate mass transfer limited reactions compared to wet-phase made catalysts [4]. It is speculated that the deposition of airborne particles on porous supports (e.g. ceramic foams) can lead to a different agglomerate and pore size structure than obtained by 5 means of multi-step coating techniques in the wet-phase. The open-pore structure may be retained, promoting the gas penetration into the active layer, hi contrast, particle deposition by multiple dip-coating and subsequent drying can result in a catalytic layer with smaller pore sizes that might reduce the accessibility of the active surface. o Further, it is known that phthalic anhydride (PA) , is made by partial oxidation of o-xylene with O₂ from air in multiple parallel fixed bed reactors on a large commercial scale [5]. For this reaction, vanadia/titania is one of the most commonly used catalysts [5, 6]. Eggshell catalyst pellets of millimeter size with solid, inert cores are packed into a fixed bed [7]. The thickness of the shell typically amounts up to 300 micrometers. This special catalyst type is used to prevent activity and PA selectivity reduction by mass transfer limitations inside the porous catalyst. However, the pressure drop over packed beds limits the PA productivity. The pellet shape determines the catalyst bed porosity which influences the pressure drop which often limits the space-time-yields of fixed bed reactors. Therefore hollow cylinders or rings are commonly used as catalyst shapes to keep the pressure drop as low as possible [5, 8, 9]. The partial oxidation of o-xylene to PA is a highly exothermic reaction (typically 1300 to 1800 kJ mol^"1) [5]. The evolving heat has to be transferred effectively out of the catalyst bed, because hot spots above 500 °C deactivate the catalyst irreversibly [7, 8] and lead to an increased risk of thermal reactor runaway [10]. Porous supports such as ceramic foams can improve the heat transfer compared to packed beds of spheres [11]. An open-pore structure and a high void fraction lead to a lower pressure drop and an increased heat transfer by radiation over the foam height compared to packed beds [12]. The possible formation of a turbulent gas flow can increase the heat and mass transfer compared to a laminar flow in honeycombs [12, 13]. In addition, thermal conductivity and surface properties can be modified because a large variety of foam materials is available [14]. Thus, it can be expected that foams can combine properties of packed beds and honeycombs in a beneficial way [11, 12].

Further, it is known that in commonly used vanadia/titania catalysts, the anatase crystal structure shows higher catalytic activity than other crystal structures. A high dispersion of vanadia on titania, enabling a good accessibility, is regarded crucial for a high activity. The activity is also influenced by the morphology of the vanadia. Monomeric and polymeric vanadia species show enhanced reactivity in selective oxidations as compared to crystalline vanadia. The selectivity is mainly influenced by the oxidation state of the vanadium itself and the modifications taking place during the catalytic reaction [15]. Disclosure of the Invention

Hence, it is a general object of the invention to provide an alternative, in particular more simple, process of manufacturing catalysts coated with micro and /or nano particles.

It is a further aim of the present invention to provide catalysts with improved catalytic performance.

It is a further aim of the present invention to provide an alternative, in particular improved, catalysts for the manufacturing of PA. o It is a further aim of the present invention to provide a process to manufacture a ready-to-use catalyst.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the manufacture of a catalyst is manifested by a process comprising the step of dry s deposition of gasborne catalytic active material on a porous support wherein the catalytic active material have an external surface area (measured e.g. by nitrogen adsorption) between 0.3 and 1000m²/g.

One or more of the objectives as described herein are also achieved by a process comprising the step of deposition of particles on a porous support with a o foam- and/or sponge-like structure.

It is believed that, by combining the high surface area of the particles and the open-pore structure of the porous supports, benefits from the advantages of these materials mentioned before by means of catalytic performance are achieved. The deposition and the adhesion of the particles on the support surface as well as control 5 of the deposited active mass are crucial for the catalytic purpose of the coated porous support.

Inter alia, this invention discloses i) a process of coating a solid foam- and/or sponge like material with flame-made catalytic active mixed metal oxides; ii) a successful working system in terms of production and coating; iii) application of the o produced catalysts in an exemplary chemical reaction, the oxidation of xylene to PA.

Vanadia doped titania nano particles were produced in single step flame-spray process. The direct deposition of flame-made vanadia/titania could be controlled by the pressure drop over the filter and the foam, resulting in low dispersion (patchy) to high dispersion (almost homogenous) coatings. The mass of deposited V₂CVTiO₂ was controlled by the pressure drop over the filter and the foam and by the sampling time.

Further, this invention compares catalysts according to this invention with known wet-phase made catalyst. The catalyst manufactured contained 7 and 10 wt.% V₂O₅, most commonly used for the oxidation of xylene to PA [6, 16]. The influence of external surface area, deposition time and pressure drop over the filter and deposited mass of vanadia/titania on the foam are investigated systematically. Catalytic activity and selectivity of FSP-made catalysts are compared to a wet-phase made reference catalyst. The catalyst according to the invention revealed significantly higher catalytic activity and similar selectivity to phthalic anhydride at high o-xylene conversion compared to the wet-phase made catalyst. Further, it was found that in the tested reaction low dispersion coatings and V₂O₅ZTiO₂ with small external surface area showed higher yield than the high dispersion coating and vanadia/titania with high external surface area.

In summary, catalysts according to the invention combine high catalytic yield with favorable support structures (low pressure drop, good heat transfer), highly porous coatings and fast production routes. These properties make the catalysts according to the invention interesting for possible applications in catalytic reaction.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed figures, which are explained below:

Figure 1: Scheme of the FSP-setup. The precursor is dispersed by oxygen and the resulting spray is ignited by a premixed methane/oxygen flame. Supplying additional oxygen assures oxidation of all precursors in the flame.

• a indicates the Met of premixed CIVO₂ for the supporting flame

• b indicates the inlet of the metal containing liquid precursor

• c indicates the inlets of O₂ as dispersion and sheath gas Figure 2: Scheme of the apparatus for the deposition of vanadia/titania on ceramic foams. Particle loaded gas was sucked through the water-cooled deposition zone, in which the foam was mounted. The magnitude of the gas flows were controlled through adjustment of the pressure drop over filter and foam.

• 1 indicates the particle laden gasflow

• 2 indicates the filter for collecting the excess particles

• 3 indicates the pressure indicator control unit

• a indicates the inlet of cooling water • b indicates the outlet of cooling water

• c indicates the deposition zone

Figure 3: Production conditions of the powder produced by spray flame pyrolysis. Specific surface area (squares), BET-diameter (circles) and anatase crystal size (diamonds) of the vanadia/titania with constant flame conditions: 5 ml min-1 precursor; 5 nL min-1 dispersion gas. Precursor concentration was in the range of 0.1 to 3.4M (pure) titamurn-tetra-iso-propoxide.

• x axis represents the production rate in g(V₂Os/Tiθ2) h^"1

• left y axis represents the specific surface area (SSA) in mV σ * • right y axis represents the BET-diameter and the anatase crystal size in nm

Figure 4: TEM images with electron diffraction patterns (inset) of the flame made vanadia/titania powders with (a) high (93 m² g^"1), 17 g(V₂θ₅/Tiθ₂) h^"1, and (b) small (53 m² g^'1), 87

h^"1, specific surface area.

Figure 5- TEM image (a) with a electron diffraction pattern (inset) of the uncalcinated powder fraction and SEM image (b) of the calcinated (45O⁰C, Ih) split fraction of the wet-phase reference catalyst- Figure 6: Pore size distributions of (a) the flame-made catalytic active material and (b) the split catalysts. Vanadia/titania with small (53 m² g^"1) and high (93 m² g^"1) specific surface area, FSP-made split and wet-phase made reference. • x axis in a and b represents the pore diameter in nm • left y axis in a and right y axis in b represent the pore volume in arbitary units

• 1 indicates the data of the small SSA particles

• 2 indicates the data of the high SSA particles » 3 indicates the data of the FSP made split

• 4 indicates the data of the wet-made split

Figure 7:. Influence of the coating conditions on the foam coating, (a)

Represents a uncoated foam. High dispersion coating (b) was achieved by a constant pressure drop above filter of 80 mbar Deposition time was 300s, deposited mass was

25 mg. Low dispersion coating (c) was achieved by a constant volume flow of 12.5 m³ h^"1 of the vacuum pump. Deposition time was 150s, deposited mass was 38 mg.

• the arrows indicate the flow direction of the particle laden gas flow during deposition Figure 8:. SEM image of a cross-section of low dispersed coated foam.

Deposited mass was 50 mg resulting in a coating thickness ranging from 150 to 200 μm.

Figure 9: Dependence of deposited vanadia/titania mass (squares) on the foam with respect to pressure drop (a) behind filter and sampling time (b). Average BET-diameter (circles) of the active component does not change by changing deposition conditions.

• x axis in a represents the pressure drop over filter and foam in mbar

• x axis in b represents the deposition time in s

• left y axis in a represents the deposited mass of vanadia/titania in mg • right y axis in b represents the BET diameter in nm

Figure 10: Scheme of the experimental set-up for direct deposition of FSP- made particles on porous supports.

• 1 indicates the inlet of premixed CH₄ZO₂ for the supporting flame • 2 indicates the inlet of the metal containing liquid precursor

• 3 indicates the inlets of O₂ as dispersion and sheath gas

• 4 indicates the pressure indicator control unit • a indicates the inlet of cooling water

• b indicates the outlet of cooling water

• c indicates the deposition zone with the porous support (ceramic foam) • d indicates the glas fibre filter for collecting excess particles

• e TEM image of the FSP-made particles (high SSA)

• f image of particley deposited on a ceramic foam (low dispersion)

• S SEM image of a cross-section of low dispersed coated foam

Detailed Description of the invention

Unless otherwise stated, the following definitions shall apply in this specification:

"Particles" refers to solid material having a size / size distribution of any particles in the range of 10^"9 to 10^"6 m. Characterization of the particles is possible by directly indication of the size, which is in general lnm - lOμm, preferably 5 - 200 nm, for example 20 nm. Alternatively, an indirect characterization is possible by indicating the external surface area per mass; e.g. 0.3 - 1000m²/g (e.g. measured by nitrogen adsorption, also referred to as specific surface area SSA), preferably above 53m²/g; regardless of the agglomerate size. Particles according to the invention may consist of organic, inorganic matter such as metals, -oxides, -nitrides, -sulfides, -halogenides, -borides, -phosphates and any mixtures of those. Particles can be produced by any method known to the skilled person, such as gas, plasma or wet- phase synthesis. "Particles" also include "catalytic active material" as described in this invention.

"Catalytic active material" generally refers to any material that is solid and has a catalytic effect in a chemical reaction. Preference is given to such catalytic material that is already used in commercial processes, such as metals and metal oxides and any mixture of those; e.g. Pd, Pt, V₂O₅, TiO₂, V₂O₅ATiO₂. "Airborne particles" refers to particles that are dispersed in an air stream.

Similarily, "gasbome particles" refers to particles that are dispersed in a gas stream. "Porous support" refers to any material that is suitable to support the catalytic active material and can be penetrated by a particle laden gas stream. Supports maybe of metal or alloys; Carbides such as SiC; ceramic materials such as oxides of Aluminium, Silicium or Zirconium and any mixture of those. The porous 5 support exhibits open or partially open cells, e.g. foam- and/or sponge like structures. The porous support and the catalytic active material may be the same material. The porous support may consist of solid or porous material itself. It may have void fractions ranging from 20 up to 95 %; Void sizes of the support can range from nanometers up to a few centimeters. The porous support may be, depending on the o intended use, made of stiff material or of flexible material. Such supports are known in the field and commercially available or obtainable according to known methods. "Coating" refers to the particles deposited on the support. It is understood that the definitions, specifications, and embodiments their preferences and particular preferences as provided herein may be combined at will. s Further, selected definitions or specifications may not apply.

In a first aspect, the invention relates to a process for the production of a catalyst comprising the step of dry deposition of gasborne. catalytic active material on a porous support wherein the catalytic active material have an external surface area o between 0,3 to 1000m²/g.

The expression "dry deposition" refers to the fact that no solvent is used in this process. This is an advantage, as it overcomes various problems of known processes for catalyst manufacture. In particular, the process is simpler (no solvent handling), safer (risk of explosion, hazardous solvents) and more cost efficient (less 5 equipment necessary; no need to remove solvent from the catalyst, no waste disposal).

In the process according to this invention, the particle-laden gas stream flows through a porous support of any shape in any direction. In general, the flow of the gas stream may be varied in a broad range. Thus, nano particles can be deposited in a o laminar, turbulent or intermediate flow; preference is given to a laminar flow.

Deposition of particles can be controlled e.g. by the gas flow rate, particles size, deposition time, flow regime or pressure drop over the foam. The Carrier fluid as used in this process can be any gas such as air, combustion gases, nitrogen, argon, oxygen, off-gases or any combination thereof.

Deposition temperatures may vary in a broad range. Generally, temperatures below ambient up to 2000°C are feasible. In one embodiment of the invention, the deposition temperature is chosen to affect the particles to sinter onto the porous support. Such sintering may improve properties of the thus manufactured catalyst; e.g. by increasing the catalytic yield or improving mechanical properties of the catalyst such as the adhesion of the particles to the support.

Deposition times can vary in a broad range. Typically, deposition times are in the range from seconds up to hours, preferably from seconds to a few minutes. Such deposition times give adequate coatings, being much faster than common coating techniques such as dip-coating or precipitation.

The deposited catalytic active material according to the present invention, is "gasborne". This term describes the fact that the particles are dispersed in a gas stream that passes the porous support and, upon passing the support, at least part of the material is deposited on said support. In one embodiment of the invention the gas stream consist of air. Ih one embodiment of the invention the particles employed in the process are prepared beforehand by known methods and are dispersed in a. gas flow. In an alternative embodiment of the invention, the particles employed are directly produced, e.g. by condensation or by a chemical reaction, in the gas flow (c.f. examples).

In a preferred embodiment, the particles used in the manufacturing of the catalyst are manufactured by flame synthesis.

In a particularly preferred embodiment, the particles are manufactured by flame spray pyrolysis (FSP). A device for FSP is shown in Figure 1. The liquid precursor is fed to a flame, where it converts to the catalytic active material having the desired particle size. The resulting gas-flow, which contains the catalytic active material, passes a deposition zone where the porous support is located (Figure 2). The thus formed catalyst may be removed once the desired amount of material is deposited.

In a particular preferred embodiment, the catalytic active material is selected from the group OfV₂O₅; V₂O₅/TiO₂; V₂0₅/Cs₂0/Ti0_2; e.g. V₂O₅ATiO₂. Coatings can range from nanometers up to a few millimeters thickness. Most commonly used are coatings of micrometer size. In a preferred embodiment, the coating has a thickness of about 50 - 500 micrometers, preferably 100 — 200 micrometers. Coatings can range from low (patchy) to high dispersion (evenly distributed) on the support surface.

In a further embodiment, surface properties of the catalytic active coating are modified during deposition and/or after the deposition and/or in the application of the catalyst. Such further modification may be beneficial to increase catalyst performance. Thus, particle surfaces can be modified after deposition on the porous support by various treatments, such as atomic layer deposition, chemical vapor deposition or thermal treatment (e.g. sintering, activation).

In one embodiment, the catalysts obtained according to the described process are ready-to-use without any further processing steps, meaning the manufactured catalyst can be installed right after the deposition step in the reactor without any post processing steps to activate (sintering) the catalytic active material.

It was now surprisingly found that particles, in particular nano particles retain an open-pore structure with void fractions ranging from 40 up to 99.9 % when subjected to the manufacturing process as described herein. Without being bound to theory, it is believed that this results in a high accessibility and thus facilitating gas penetration into the catalytic active layer.

Without being bound to theory, it is believed that deposition mechanisms of the particles on the support can take place by impaction, therrnophoresis, diffusion or any combination of the aforementioned mechanisms.

The porous support is defined above. Preference is given to foam- and/or sponge-like structures, preferably metal, ceramic or carbide foams.. In a preferred embodiment, the porous support increases the heat transfer an reduces the pressure drop in the reactor in comparison to commonly used eggshell or full contact catalysts.

In summary, the manufacturing of a catalyst according to the process as described above meets one or more of the following criteria: i) a fast and easy process ; ii) a ready-to-use catalysts or catalyst preforms; iii) deposition times of catalytic active material are short (and faster when compared with common coating techniques such as dip-coating or precipitation). In a second aspect, the invention relates to a catalyst obtained by a process as described herein.

A preferred catalyst is obtained by a process as described herein has void fractions of the coating in the range of 40 - 99.9%. In summary, a catalyst according to this invention meets one or more of the following criteria: i) decreased the pressure drop over a fixed bed (which, in turn increases the productivity of the process) when compared to commonly used catalysts such as spheres, solid or hollow cylinders; ii) increased radial and axial heat transfer within the reactor when compared to commonly used catalysts such as spheres, solid or hollow cylinders; iii) improved catalytic parameters, such as activity, selectivity, conversion, yield and lower residence tune of reactants; iv) facilitates any reaction with inner mass transport limitation.

hi a third aspect, the invention relates to the use of a catalyst as described herein in a chemical reaction.

Depending on the catalyst manufactured, any endo- or exothermic reaction, such as oxidation, partial oxidation, waste gas cleaning, hydrogenation, steam reforming, or dehydrogenation, maybe subject to the use of a catalyst as described herein. Preferred reactions are oxidation reactions, such as the oxidation of xylene to obtain PA.

hi summary, to use a catalyst as described herein in a chemical reaction provides one or more of the following advantages: i) a reduced risk of hot spots or thermal runaways (which may deactivate the catalysts irreversibly) when compared to commonly used shaped catalyst bodies, such as spheres, solid or hollow cylinders; ii) facilitated heat transfer (by radiation) in high temperature reactions.

hi a fourth aspect, the invention relates to a catalyst comprising i) a ceramic foam and ii) catalytic active particles, wherein the particles are seleced from the group of TiO₂/V₂O₅ or TiO₂/V₂O₅/Cs₂O wherein the particles materials have an external surface area between 0.3 to 100OmVg. EXAMPLES

The following examples relate to the manufacture and characterization of catalysts suitable for the oxidation of xylene to PA and to the use of the obtained catalysts in this reaction. The examples are intended to illustrate the invention. These examples are not meant to limit the invention.

1. Preparation of Catalyst

Precursor preparation: For the precursor preparation, the solvents xylene o (Fluka, >98.5%) and acetonitrile (Fluka, >99.5%) were mixed (11 :5 by volume).

Appropriate amounts titaniumtetraisopropoxide (TTIP₅ Aldrich >97%) and vanadium oxo-triisopropoxide (Strem Chemicals, >98%) were added, resulting in total metal concentrations ranging from 0.1 to 3.4 (without solvent) mol L^"1 with 10 wt.% V₂O₅ content in the resulting powder product. In order to prepare for example a liquid 5 precursor with a concentration of 0.67 M TTIP, 18.3 niL TTIP, 1.5 mL vanadium oxo-triisopropoxide, 56.1 mL xylene and 25.5 mL acetonitrile were mixed.

Flame spray synthesis (FSP): The vanadia/titania mixed oxides were synthesized by flame spray pyrolysis (FSP) in a laboratory-scale reactor. A concentric o two-phase nozzle with a capillary (inner diameter of 0.42 mm) through which the liquid precursor was fed the reactor. Through a second annulus (inner/outer diameter 0.71/0.95 mm) the dispersion gas (O₂, Pan Gas, 99.95%) was added (Fig. 1). The area of the annular gap (maximum 0.25 mm²) was adjusted to achieve a pressure drop of 1.5 bar of the dispersion gas. In all experiments the precursor solution was fed by a 5 syringe pump (Inotec, IER-560) into the flame through the innermost capillary, where it was dispersed by a defined O₂ flow (5 L min^"1) through the 1^st annulus. The spray was ignited by a circular premixed flame (inner diameter 6 mm, slit width 10 μm) of CH₄ (1.5 L min^"1, Pan Gas 99.5%) and O₂ (3.2 L min^"1). An additional O₂ sheath (5 L min^"1) to guarantee total combustion of the precursor was supplied through a ring 0 of sintermetal (inner/outer diameter 11/18 mm). AU gas-flow rates were adjusted by calibrated mass-flow controllers (Bronkhorst). The powders were collected on a glass microfibre filter (Whatman GFfD 257 mm in diameter), by sucking the gas-flow through the filter by a downstream installed vacuum pump (Busch SV 1025 B). The production rate (g(V₂0₅/Ti0₂) h^"1) was adjusted via the metal concentration in the liquid precursor.

Deposition of FSP-powder on ceramic foams: In order to deposit the airborne active component (vanadia/titania) on the porous support, ceramic foams were installed in the deposition zone. In the following the foam coated with vanadia/titania will be referred to as the catalyst. The foams were fixed in a cooled (H₂O, 69 EnLmUi^"1) double wall tube (1^st inner/outer diameter 16/18 mm, 2^nd inner/outer diameter 26/27 mm, length 160 mm) about 300 mm above the nozzle. The o ceramic foams (Vesuvius, mullite, Al₆O_1SSi₂, 20 pores per inch (ppi); porosity 0.85) used, exhibited a diameter of 15 mm and a length of 50 mm. To avoid wall slip of gases and particles, the foam support was wrapped into a glass fiber tape (Horst, GB25) before installation. In order to the later estimation of the deposited active component on the support the unloaded weight of the foams were determined (Mettler s Toledo, AB204S) before coating. In order to evaluate a possible mass loss one uncoated foam was installed in the deposition zone, build out and weighed. This sequence was repeated three times with no indication of loosing foam mass. All FSP- made catalysts were coated with a comparable mass OfV₂O₅ZTiO₂ (21 to 27 mg).

o Preparation of wet phase catalyst: For the purpose of a comparison with a wet-phase made reference, a wet-phase made 7 and 10 wt.% vanadia/titania catalyst was prepared by precipitation method, dried and then crushed to obtain the desired particle fraction size. For validation of isothermal conditions inside the catalyst bed for the FSP-made catalysts, flame made vanadia/titania was pelletized (70 MPa) and 5 crushed in order to get a split fraction in the same particle size fraction as the wet- phase reference catalyst size. The pressed flame-made catalyst is later described as FSP-made split. Contrary to the FSP-made catalysts, the wet-phase made reference was calcined for 1 hour at 450°C, a common production step for wet-phase made catalyst preparation [16] to ensure the evaporation of precursor residuals. 0

2. Characterization of Catalyst

Specific surface areas: Specific surface areas (SSA, m² g^"1) of the powders were determined from the adsorption of nitrogen (Pan Gas, >99.999%) at 77 K using the Brunauer-Emmett-Teller (BET) method with a Microraeritics Tristar 3000 (five point-isotherm, O.O5<p/po<O.25). Assuming spherical, monodisperse primary particles with homogenous density, the average BET-equivalent particle diameter (d_BET) was calculated with equation(l).

^d-⁼db ^{■ (i)}

With the mean vanadia/titania density 3.83 g cm^"3 of the 90 wt.% titania (p = 3.85 g cm^'3, 90wt.% anatase, p = 3.84 g cm^'3 and 10 wt.% rutile, p = 4.3 g cm^'3) and 10 wt.% vanadia (p = 3.36 g cm^'3). Pore size distributions were determined from the measured desorption isotherms (Micromeritic ASAP 2010 Multigas system) using the i o method of Barret, Joyner and Halenda (BJH) [17].

X-ray diffraction: XRD measurements were performed on a Bruker D8 Advance diffractometer, applying a step size of 0.03°, a scan speed of 0.60 rnin^"1 and Cu Ka radiation. The weight contents and crystal sizes of the titania structures were 15 obtained using the Topas 2.0 software (Model AXS 2000, Bruker). Patterns were fitted between 2Θ = 19 and 33° using crystal structures of anatase (ICSD collection code 9853; [18]), rutile (ICSD collection code 82656; [19]) and vanadia (ICSD collection code 24042 [20]).

20 Temperature programmed reduction (TPR): TPR was applied in order to estimate the average oxidation state and reducibility of the vanadia for the stability tests. The experiments were carried out on a Micromeritics Autochem II 2920 unit, equipped with a TCD-detector, by flowing a mixture of 5 vol-% H₂ in Ar (Pan Gas, 20 mL rnin^"1) over the sample. The temperature was increased from 50 to

25 95O⁰C at a heating rate of 10°C rnin^"1. Prior to this analysis the sample was freshly oxidized in flowing oxygen at 300°C for 30 minutes to assure a complete oxidation of the vanadia without changing the elemental distribution and the particle morphology.

Raman spectroscopy: Raman spectroscopy for the sinter study and 3 o identifying different vanadia species on the titania was done with a Renishaw InVia Reflex Raman system equipped with a 785 nm diode (solid state, 300 mW) laser as excitation source. Samples were focused by a microscope (Leica, magnification x50). The spectra were recorded on a CCD camera after diffraction (1200 lines per millimeter) at reduced laser energy of 0.3 mW to ensure no thermal change of the sample by excitation with the laser beam [21]. Exposure time was 30s by 3 accumulations for all scans.

Transmission and scanning electron microscopy: In order to carry out transmission electron microscopy (TEM) investigation, the material was deposited onto a carbon foil supported by a copper grid. TEM analysis was performed with a o CM30ST microscope (Philips; LaB6 cathode, operated at 300 IcV, point resolution ~2A). SEM analysis was carried out on a Leo 1530 Gemini microscope (Zeiss, operated at 2 kV field emission gun).

3. Reactor for catalytic experiments; 5 The catalysts were tested in the partial oxidation of o-xylene using a fixed bed plug flow reactor. It consists of a gas feed section with supply of o-xylene, the reactor and the product analysis by means of gas chromatography.

Gas feeding (FIC): All gases (N₂, Air liquide >99.996%, and O₂, Air o liquide >99.95%) were fed by mass-flow controllers (Bronkhorst). As an internal standard for the analysis by gas chromatography, ethane (Air liquide, 19.6 vol.%, >99.5% in N₂, >99.999%) was added via a mass-flow controller (Brooks).

Pressure control: The pressure in the reactor was indicated by a manometer 5 and adjusted by a manual needle valve downstream to the reactor. In order to assure a stationary evaporation of the o-xylene, the pressure in the evaporation zone was adjustable by a manual needle valve. Both, the pressures in the reactor and in the evaporation zone were kept constant during the experiments.

o O-xylene supply: O-xylene was fed via a μ-flow controller (Bronkhorst).

The nitrogen was then added to the liquid flow. The pipes were electrically heated in two temperature zones (T₁= 100°C, T₂= 14O⁰C) for full o-xylene vaporization. Before entering either the bypass or the reactor, oxygen was added. Gas and liquid flows were adjusted such that the flow entering the reactor had an o-xylene molar traction of x = 0.005 and an oxygen molar fraction of x = 0.2.

Reactor: The reactor consisted of a vertically installed stainless steel tube of 16 mm inner diameter and a length of 380 mm, electrically heated. The reactor, parts of the feed pipes, and the 6 port valve were in housed a glass wool isolated box heated electrically to 26O⁰C to support isothermal conditions throughout the reaction zone and prevent condensation.

The gas-flow enters the reactor from the top. The fixed bed consists of three o zones.

1. Initial break-in zone (length ~ 120 mm). It consists of either SiC particles (particle size 1 mm) or SiC particles and an additional uncoated foam for the test of the foam catalysts. In this zone, the desired plug flow regime develops and the reactant gas-flow is heated. 5 2. Catalyst zone (length ~ 120 mm); either particles (wet-phase or FSP-made split catalyst, diluted in SiC, 1 mm) or of coated ceramic foams. The coated foams were installed in the isothermal zone of the reactor in the same orientation with respect to gas flow direction as they were coated before with FSP.

3. SiC particles (1 mm) to fill of the remaining reactor volume o (length ~ 80 mm).

Glass wool was packed to prevent entrainment of SiC among each other. In case of the wet-phase reference and the FSP-made split catalyst measurements the reactor was equipped with a thermowell (inner diameter 1 mm) located at the radial center of the reactor tube. A thermocouple inserted in the thermowell measured the 5 temperature along the catalyst bed. Using a 4 port valve, the reactant gas flow can be piped through either the bypass or the reactor.

Gas analysis (GC): Online gas chromatography is used for the quantitative determination of the amount of products. A sample for analysis is fed into the gas o chromatograph (GC) (Hewlett Packard, Gl 540A) via a pneumatic controlled loop valve into a column (WCOT, Fused silica VF-5ms) in a He carrier gas stream (Air liquide, >99.996%) mixed with H₂ (Air liquide, >99.999%) and synthetic air (Air liquide, >99.999%) and fed into the flame ionization detector (FDD). Molar concentrations in the product gas stream were calculated from the peak areas (equation(2)), knowing the signal of the internal standard. Resulting in different signal intensities, correction factors have to be used for each compound and were calibrated prior the experiments (appendix). For ethane the correction factor was set to one. a-M ₍2)

Afterburner and off-gas analysis: The complete gas flow from the reactor outlet together with compressed air (800 niL min^"1) is directed to a catalytic afterburner (CAB) coated with a spherical Al₂O₃ supported Pd catalyst. The CAB is o an electrically heated (450°C) tubular reactor with a length of 250 mm and an inner diameter of 20 mm.

The off-gas after the CAB was analyzed continuously by an infrared- detectors (Leybold-Haereus, Binosl) for of CO and CO₂. During a catalytic experiment, the CAB was bypassed to determine the amount of CO and CO₂ 5 produced during reaction.

4. Catalytic Experiments

During the catalytic experiments, the following parameters were kept constant: total pressure in the reactor: p_total = 1.3 bar; reactor temperature: T_r = 360⁰C; o volume flow internal standard (50.89 mL min^"1).

The total volume gas-flows of the outlet were varied between 120 and 600 mL min^"1 in order to adjust different residence times. The mass of the active component in the reactor ranged from 15 to 45 mg in case of the FSP made catalysts and from 0.5 to 1.5 g in case of the wet-phase made catalysts. Temperature 5 measurements inside the catalytic bed showed constant temperatures throughout the fixed bed around 366⁰C ± 1°C. Therefore, isothermal conditions for both, FSP-made and wet-phase made reference catalysts, were assumed.

The data reported refer to average values calculated from 4 to 6 analyses at steady state conditions. 0

5. Results of the characterization of the catalytically active component Specific surface area and X-ray diffraction: Figure 3 shows the dependence of specific surface area (SSA) of flame-made vanadia/titania on the production rate. The liquid feed rate and the dispersion gas feed rate was kept constant during experiments. The SSA (squares) of the powders decreases with increasing the total metal concentration in the precursor solution, which is consistent with the results of other studies on mixed metal oxides produced by flame spray pyrolysis [22, 23]. Higher combustion enthalpy densities and high titania concentrations favor the agglomeration and coalescence of the particles in the gas- phase, reducing the overall specific surface area [24]. At the lowest production rate (2.6 g(V₂0₅/Ti0₂) h^'1) the active component exhibits 195 m² g^"1 SSA. This decreases with increasing precursor concentration until it approaches a constant value at

The anatase crystal size increased with increasing production rate from s 10 nm up to 32 nm. Crystal sizes (diamonds) correspond very well to calculated dβ_ET (circles), which are slightly below. Small deviation between dβ_ET and anatase crystal size are due to the simpUfying assumptions made in the calculation of the dβ_ET- For 2.6 g(V2θ5/TiO₂) h^"1 production rate the lowest anatase content of 82 wt.% was found. For production rates above 17 g(V₂0s/Ti0₂) h^'1 > 94 wt.% anatase content 0 were obtained.

Two different vanadia/titania powders were produced by FSP for the direct deposition experiments and the catalytic measurements. Samples with SSA of 93 m² g^"1 (dsET ⁼ 17 nm) correspond to a precursor concentration of 0.67 M TTEP (production rate 17 g(V₂θs/TiO₂) h^"1). Vanadia/titania produced by spraying a 5 mixture of pure (3.4 M) TTIP and vanadium oxo-triisopropoxide as liquid precursor solution, had a much smaller SSA of about 53 m² g^"1

29 nm). The powder for the FSP-split catalyst for the isothermal testing had an initial SSA of 70 m² g^"1. By pressing into tablets and subsequent crushing no SSA loss was measured. The wet- phase made reference sample had a SSA of 8 m² g^"1 (dβ_ET ⁼ 200 nm). o The FSP-made as prepared vanadia/titania shows an almost pure anatase crystal phase (> 94 wt.%) and no evidence of any vanadia crystal structure.

Sintering the flame-made V₂CVTiO₂ for 5h (5°C min^"1) did not change the composition or crystallinity up to 450°C. Starting at 500°C the anatase crystal structure changed into the rutile crystal structure, corresponding to earlier titania studies [25]. At 600⁰C all anatase is converted into rutile. First vanadia crystal structures were detected at sinter temperatures above 500⁰C in the XRD patterns. The content of the crystal vanadia ranged from 4 to 5 wt.% and crystal sizes increased from 30 to 65 nm with increasing sinter temperature.

The calcined wet-phase reference in contrary showed peaks of crystalline vanadia with a crystal size of 56 nm, crystal vanadia content was around 4 wt.%.

The synthesis of vanadia/titania with high anatase weight content even at high production rates corroborates that flame spray pyrolysis is suitable to produce vanadia/titania nano particles with high surface area and anatase content favored in many catalytic applications. The anatase content is significantly higher than contents achieved by the flame aerosol synthesis of vanadia/titania nano particles at comparable production rates [24]. In contrast to the flame aerosol process the anatase contents increase (82 to >94 wt.%) with increasing production rate.

Transmission and scanning electron microscopy: TEM images of V₂O₅ATiO₂ with high (a, 17 g(V₂0₅/Ti0₂) h^"1) and small (b, 89 g(V₂0₅/Ti0₂) h^"1) SSA are shown in Figure 4, Producing vanadia/titania at production rates ranging from 2.6 g(V₂0₅/Ti0₂) h^'1 up to 89 g(V₂0₅/Ti0₂) h^"1 resulted in mostly spherical particles. The absence of particle in micrometer size indicates a monomodal particle size distribution for both materials. The particle size corroborates the results of nitrogen adsorption, for both materials (a, 17 nm and b, 29 nm) quantitatively. Rings in the electron diffraction pattern show the crystalline structure of the particles.

Figure 5 shows TEM (a) and SEM (b) images of primary particles of the wet-phase catalyst. Primary particles are non-spherical and sizes are mainly above 100 nm. Electron diffraction analysis shows the crystalline structure of the particles. The SEM image shows the calcined split fraction of the wet-phase made V₂O₅ZTiO₂ (0.244 to 0.5 mm) as it was used for the catalytic test. Sieved split agglomerates consist of many primary particles with no or slight indication of sintering. Pore size distribution: The pore size distributions of different powders are shown in Figure 6. The production rate has almost no significant influence on the pore size distribution of the flame-made V₂0s/Ti0₂ for SSAs ranging from small (89 g(V₂0₅/Ti0₂) h^'1) to high (17 g(V₂0₅/Ti0₂) h^'1) (a). Pressing FSP-made particles into a split resulted in smaller pores (10 to 30 nm) than for the untreated powder (20 to 110 nm). During the split preparation, particles were packed closely to each other thereby reducing the average pore size. The wet-phase made V₂CVTiO₂ exhibited pore sizes ranging from 20 to 160 nm lying in the range of the wet-phase made particle size, therefore representing the interparticle voids. An open pore o structure is favored for this reaction that is inner mass transfer limited.

Temperature programmed reduction: The as prepared FSP-made V₂CVTiO₂ showed one distinct reduction peak at a T_max of 483 °C as observed for flame aerosol made V₂OsZTiOi [I]. Peak temperatures of less than 500°C show the 5 presence of dominantly monomeric vanadia species on the titania, being reduced more easily than polymeric (T_max « 483°C) or bulk (T_max > 580⁰C) vanadia [15, 26].

For the sintered FSP-made V₂0s/Ti0₂ no significant change in the TPR signal was found for sintering temperatures up to 450°C, corroborating the XRD results. For higher sinter temperatures a shift of the reduction peak towards higher o T_max values is observed, indicating a change of the vanadia species on the titania surface from dominantly monomeric over polymeric (500-600°C) to bulk vanadia (65O⁰C).

FSP-made vanadia/titania (< 600°C) had a monolayer (ML) coverage below 3 (Table 1), and showed therefore only one distinct reduction peak [27]. Particles 5 sintered at 65O⁰C had a ML coverage of 23, resulting in a distinct peak around 650⁰C and the onset of a second peak ranging from 700 to 800⁰C. m contrast the wet-phase reference with ML coverage of over 4 has two distinct peaks at 525°C and 843⁰C as was expected [27]. Assuming to correspond to rather polymeric (T_max ~ 540⁰C) and bulk (T_max > 580⁰C) than monomeric vanadia o species [26], coaborrating the XRD results presented before.

The FSP-made V₂O₅/TiO₂ with 53 m² g^"1 SSA had a ML coverage close to 1 and one distinct peak at 512°C, indicating also polymeric V₂O₅ structure on the titania surface [27]. Table 1. Analyzed 10 wt.% FSP-made vanadia/titania powders and 7 + 10 wt.% wet- made catalyst for catalytic measurements anatase

SSA in dsET Ul anatase in monolayer T_1110x ^c rn active component crystal mV run wt.% coverage ⁰C srze^ain nm

FSP-made split 70 22 >92 27 0.67 483

FSP-made high SSA 93 17 >94 17 0.7 483

FSP-made small SSA 53 29 >98 32 1.2 512

¹ determined by XRD fitting with the TOPAS 2.0 Software 5 ^b calculated by assuming ML = 10 V-atoms nm^"2 monolayei coverage [28, 29] ^c temperature of maximum peak of TPR hydrogen consumption ^d average oxidation state, determined from the total hydrogen consumption of TPR experiments

The vanadia species was stable on the titania up to 450⁰C sinter temperature. o The SSA retained constant up to 45O⁰C. Increasing the sinter temperature from 450 up to 900°C resulted in a steep decrease of the SSA from 83 m² g^"1 to 0.5 m² g^"1. The dramatic decrease in the SSA corresponds to transformation of titania crystal structures and restructuring of vanadia species. Vanadia, being liquid above 670⁰C₃ may have acted as flow agent during titania sintering. 5

Raman spectroscopy: The as-prepared flame-made and flame-made powders sintered up to 450⁰C showed a shoulder starting at a wavelength of 1033 cm^{" l}. Corresponding to isolated monomelic vanadia species [21, 26, 30-32]. The peak maxima are located at about 1005 cm^'1. Deviations from Raman shifts of monomelic o vanadia from literature ( 1033 cm^"1) may result from partially hydrated V=O bonds shifting the Raman bands to lower wavelengths [21, 33]. Even though this Raman band lays close to that of crystalline vanadia (994 cm^"1) this vanadia morphology cannot be verified because of the missing second Raman band for crystalline species at 708 cm^"1. Results from XRD and TPR did not show any crystalline vanadia for 5 these conditions corroborating this vanadia morphology. The intensity of the shoulder decreases with increasing sinter temperature as vanadia forms larger clusters at increased temperatures resulting in Raman shifts of polymeric or crystalline vanadia. The Raman spectra OfV₂O₅ZTiO₂ did not change up to 450°C sinter temperature. At 500⁰C sinter temperature and above distinct crystalline vanadia bands appear at 708 and 994 cm^"1 corresponding to a recent study [32]. The phase transformation of the anatase crystal phase into the rutile crystal phase at sinter temperatures higher than 500°C was observed by Raman spectroscopy. In the spectra of the 500°C sintered V₂O₅/TiO₂ only the anatase band (638 cm^"1) was detected. By increasing the sinter temperature the rutile band intensity (608 cm^"1) increased while the anatase band intensity decreased until at 600⁰C only rutile was detected. Raman o shifts of the polymeric vanadia (940 cm^"1) have not been observed for any material in contrast to TPR.

The wet-phase made shows only crystalline vanadia bands (708 cm^"1 and 994 cm^"1) [34, 35].

5 6. Direct Deposition of catalytic active material; high and low dispersion

The vanadia titania was deposited on ceramic foams by adjusting the pressure drop over the filter and foam. Figure 7 shows images of an uncoated (a) and two coated foams (b,c). Arrows indicate the gas-flow direction during deposition. o Figure 7 b shows a foam that was coated with a constant pressure drop over the foam and the filter of 80 mbar. The V₂O₅ZTiO₂ particles are almost evenly distributed on the foam surface. At these production conditions, the gas-flow through the foam is very slow so that particles deposited mainly by diffusion and thermophoretic sampling. This type of coating will be referred to as "high" dispersion 5 later on.

Figure 7 c shows a foam where particles were deposited at a constant throttle position (50%) resulting in a pressure drop of 200 to 300 mbar over the filter and foam. Deposition in this case is caused mainly by impaction resulting from the high gas-flow velocities. The vanadiaZtitania is dominantly deposited on support surfaces o facing against the particle laden gas flow, resulting in a patchy coating, to which will be referred later on as "low" dispersion.

Coating thickness for this deposition condition is in the micrometer range, as demonstrated in the SEM images (Figure 8) of the cross-section of the coated foam. In this case the deposited V₂CVTiO₂ was 50 mg resulting in a layer thickness of 150 to 200 μm. Particle layer is not uniform and rough, a highly porous layer is observed. Recently direct deposited, FSP-made nano particles on flat surfaces resulted porosities of the deposited layer around 98% [3]. Comparable particle sizes and production conditions during the vanadia/titania production may lead to similar porosities.

In case of the high dispersion coating with the high SSA (93 m² g^"1) V₂O₅ZTiO₂ the deposited mass can easily controlled as shown in Figure 9. Keeping the sampling time constant (300 s) and varying the pressure drop (Figure 9 a) in the o range of 20 to 120 mbar, the deposited vanadia/titania mass could be precisely controlled. Increasing the pressure drop over filter and foam resulted in a linear increase of deposited V₂OsATiO₂. No significant influence of pressure drop on dβ_ET was observed.

Varying the sampling time at a constant pressure drop of 80 mbar resulted in 5 an increase of deposited mass with increasing sampling time (Figure 9 b). Therefore the mass of deposited V₂OsZTiO₂ is a function of time. At even longer sampling times a steady state condition may be reached due to equilibrium between deposited and carried away V₂O₅ZTiO₂ mass by shear forces of the gas-flow. No significant influence of sampling time on O_BET was observed. o Adhesion of the vanadiaZtitania layer on the foam surface was satisfactory.

7. Catalytic experiments

Results of catalytic measurements: As the selective oxidation of o-xylene has a rather complex reaction-path, several byproducts beside the valuable product 5 phthalic anhydride are produced. During catalytic measurements phthalide (PT), maleic anhydride (MA), o-tolualdehyde (TA), CO and CO₂ were measured. Missing values, especially of CO and CO₂ are due to problems with the detectors during the experiments.

Table 2: Results of the catalytic test of the low dispersion coated foam with 0 high specific surface area

Xo-xylcne ^>PA,o-xylene SχA,o-xylene kpT.o-xylene OMA,o-xylene Scθ2,o-xylene Sco.o-xylene * P A, o-xylene ^τmod

0~4Ϊ 038 0Λ6 0~12 θ!θϊ 018 07)5 0~16 1.52E-03

0.44 0.39 0.15 0.11 0.03 - - 0.17 1.53E-03 ^■* *-o-xyleπe "PA,o-xylene SτA,o-xylene Spτ,o-xylene Sf /IA,o-xyleπe Sc02,o-xylcne ScO.o-xyleπe * PA, o-xylene ''^■mod

0.59 0.47 0.11 0.10 0.02 0.17 0.05 0.28 1.84E-03

0.66 0.50 0.10 0.09 0.02 - - 0.33 2.03E-03

0.81 0.56 0.06 0.06 0.02 0.17 0.05 0.46 2.29E-03

0.90 0.62 0.04 0.04 0.02 0.18 0.06 0.55 2.61E-03

0.97 0.65 0.02 0.02 0.02 0.20 0.06 0.63 3.05E-03

1.00 0.61 0.00 0.00 0.03 0.15 0.04 0.61 4.60E-03

1.00 0.61 0.00 0.00 0.03 0.25 0.07 0.61 4.58E-03

Table 3: Results of the catalytic test of the high dispersion coated foam with high specific surface area

-^o-xylene kpA,o-xylene £>TA,o-xylene Spτ,o-xyleπe Sj vIA,o-xyIene ScO2,o-xylene Scθ,o-xyleπe * PA, o-xylene ^mod

0.24 0.23 0.24 0.12 0.01 0.21 - 0.06 1.29E-03

0.28 0.25 0.21 0.12 0.01 - - 0.07 1.55E-03

0.36 0.30 0.18 0.13 0.01 0.24 0.02 0.11 1.94E-03

0.40 0.34 0.17 0.13 0.01 0.28 0.05 0.13 2.22E-03

0.50 0.38 0.13 0.12 0.01 0.22 0.04 0.19 2.58E-03

0.58 0.41 0.11 0.12 0.01 - - 0.23 3.09E-03

0.78 0.51 0.06 0.09 0.01 0.21 0.04 0.40 3.88E-03

1.00 0.64 0.00 0.00 0.03 0.26 0.07 0.64 6.48E-03

1.00 0.63 0.00 0.00 0.03 - - 0.63 6.44E-03

Table 4: Results of the catalytic test of the low dispersion coated foam with small specific surface area

^■**-o-xyIene °PA,o-xylene ^TA,o-xylene Spτ,o-xylene SMA,o-xyleπe Sco2,o-xylene "CO.o-xylene Ϊ PA, o-xylene ''•mod

0.14 0.24 0.32 0.12 - - - 0.03 1.79E-03

0.18 0.27 0.28 0.13 - - - 0.05 2.15E-03

0.25 0.26 0.22 0.12 - - - 0.06 2.70E-03

0.36 0.31 0.16 0.11 - - - 0.11 3.60E-03

0.51 0.44 0.12 0.11 - - - 0.22 5.37E-03

0.65 0.51 0.08 0.09 - - - 0.33 6.72E-03

0.95 0.64 0.02 0.03 - - - 0.61 9.00E-03

0.96 0.67 0.02 0.02 - - - 0.64 8.98E-03 Table 5. Results of the catalytic test of the high dispersion coated foam with small specific surface area

-"^■o-xylene SpA.o-xylene SτA,o-xyleπc Spτ,o-xylcnc ^MA,o-xylene ScO2,o-xylene "CO,o-xyIene * P A, o-xyieno ''•mod

0.25 0.25 0.23 0.12 0.01 - - 0.06 2.92E-03

0.28 0.30 0.20 0.13 0.01 0.32 ^' 0.02 0.08 3.20E-03

0.29 0.29 0.21 0.13 0.01 0.27 0.05 0.08 3.48E-03

0.37 0.35 0.17 0.13 0.01 0.29 0.03 0.13 4.36E-03

0.39 0.33 0.16 0.12 0.01 0.25 0.03 0.13 4.36E-03

0.42 0.42 0.14 0.13 0.01 0.30 0.03 0.18 4.82E-03

0.50 0.40 0.12 0.12 0.01 0.25 0.04 0.20 5.79E-03

0.53 0.41 0.10 0.11 0.01 0.37 0.06 0.22 6.03E-03

0.63 0.48 0.09 0.10 0.01 0.24 0.05 0.30 6.97E-03

0.75 0.56 0.06 0.08 0.01 0.31 0.03 0.42 8.04E-03

0.85 0.59 0.04 0.06 0.02 0.25 0.05 0.50 8.69E-03

1.00 0.67 0.00 0.00 0.02 0.26 0.06 0.67 1.09E-02

1.00 0.56 0.00 0.00 0.02 0.33 0.06 0.56 1.45E-02

Table 6: Results of the catalytic test of the FSP -made split catalyst

^■Λ-o-xylene ^>PA,o-xylene SτA,o-xyiene "PT,o-xyIeπe £>MA,o-xyleπe ScO2,o-xyiene ScO.o-xylene * PA, o-xylene Tmod

0.20 0.45 0.12 0.07 0.01 0.39 0.03 0.09 2.23E-03

0.29 0.48 0.10 0.07 0.02 0.34 0.06 0.14 3.32E-03

0.32 0.45 0.09 0.07 0.01 0.31 0.05 0.14 3.32E-03

0.41 0.50 0.08 0.06 0.02 0.29 0.05 0.20 4.45E-03

0.59 0.55 0.06 0.05 0.02 0.28 0.05 0.32 6.64E-03

0.71 0.58 0.05 0.04 0.02 0.29 0.05 0.41 8.30E-03

0.77 0.57 0.04 0.04 0.02 0.24 0.08 0.44 8.63E-03

0.87 0.55 0.03 0.02 0.02 0.27 0.07 0.47 1.11E-02

0.95 0.56 0.01 0.01 0.02 0.27 0.09 0.54 1.30E-02

0.98 0.56 0.01 0.01 0.03 0.29 0.10 0.55 1.48E-02

1.00 0.40 0.00 0.00 0.03 0.41 0.13 0.40 2.16E-02 Table 7. Results of the catalytic test of the 7 wt.% wet-phase reference catalyst

■Λ-o-xylene "PA,o-xylcne ^TA.o-xylene "PT,o-xyIene ^MA.o-xyleπc £>cO2,o-xylene ^CO,o-xyleπs I PA, o-xylene ^mod

0.37 0.52 0.18 0.08 0.02 0.19 0.02 0.19 0.04

0.43 0.57 0.15 0.07 0.02 - - 0.25 0.05

0.53 0.61 0.10 0.05 0.02 0.18 0.02 0.32 0.06

0.65 0.65 0.07 0.04 0.02 - - 0.42 0.08

0.68 0.67 0.06 0.03 0.02 0.20 0.03 0.45 0.08

0.76 0.70 0.04 0.02 0.02 0.21 0.03 0.53 0.10

0.85 0.69 0.03 0.01 0.02 0.20 0.03 0.59 0.12

0.98 0.67 0.00 0.00 0.03 0.26 0.03 0.66 0.21

Table 8. Results of the catalytic test of the 10 Wt.% wet-phase reference catalyst

Xo-xylene SpA,o-xylene SχA,o-xylene Sρχ_i0-Xyi_ene SjviA,o-xylene Scθ2,o-xyleαe Sco,o-xylene Ϊ PA, o-xylone ^τmod

0.38 0.43 0.16 0.07 0.02 0.00 0.00 0.16 0.04

0.45 0.46 0.14 0.06 0.02 0.26 0.05 0.20 0.05

0.56 0.52 0.10 . 0.05 0.02 0.27 0.05 0.29 0.06

0.69 0.59 0.07 0.03 0.02 0.27 0.06 0.41 0.08

0.71 0.59 0.06 0.03 0.02 0.00 0.00 0.42 0.08

0.80 0.63 0.04 0.02 0.02 0.27 0.06 0.50 0.10

0.91 0.65 0.02 0.01 0.02 0.27 0.06 0.60 0.13

0.98 0.61 0.01 0.00 0.02 0.30 0.06 0.60 0.16

1.00 0.59 0.00 0.00 0.03 0.35 0.07 0.58 0.21

Activity: Using flame-made vanadia/titania, little conversions such as 0.4 are reached at significant lower modified residence times (0.0015 to 0.003 g s cm^"3) than for the wet-phase made reference catalyst. The FSP-made catalysts reach full conversions after 0.004 to 0.02 g s cm^"3 being at least one order of magnitude faster than the wet-phase made reference catalysts (0.18 g s cm^"3 for 7 wt.%, 0.21 g s cm^"3 for 10 wt.%). The low dispersion coating resulted in a higher activity compared to the high dispersion coating. Comparison of the two split catalysts showed much higher activity for the FSP-made split compared to the wet-phase reference. Coated foams showed higher activity than splits made out of flame-made V₂CVTiO₂ or wet-phase made V₂O₅/TiO₂. Having a significantly higher SSA, flame-made V₂(VTiO₂ provides more external surface area than the wet-phase made V₂O₅ZTiO₂. This results in a formation of dominantly isolated monomelic vanadia species (vanadyl) on top of the titania particles, as shown in Raman spectroscopy. The high SSA and the monomelic vanadia species on titania result in higher catalytic activity compared to the wet-phase made catalyst. The FSP-made split showed slightly lower activity than the direct deposited foams. A slightly lower SSA (Table 1) and smaller pore sizes and longer diffusion ways inside the catalysts grain may have led to or even increased inner mass transfer limitations decreasing the activity of the catalyst compared to the coated foams.

The low dispersion coating showed higher activity compared to the high dispersion coated foam. Differences between the "low" and "high" dispersion catalysts with high SSA may result from non iso-thermal conditions in the low dispersion coating.

Reducing the SSA of the V₂O₅/TiO₂ from 93 down to 53 m² g^"1 resulted in a less active catalyst. Since activity was significantly lower than for the high surface area coating, an additional coated foam was installed in the reactor in order to measure full o-xylene conversions. Looking at the results of the catalysts with small SSA no significant difference for both coatings, low and high dispersion is observed corroborating the explanation of temperature effects taking place for the catalyst with the high SSA.

Selectivity: At low conversions (X_0-xyie_ne ⁼ 0.2-0.8) higher selectivity to phthalic anhydride is obtained by the wet-phase made reference compared to the foam catalysts with low, and high dispersion coating. At high conversion (> 90%) comparable results in selectivity were measured. The FSP-made split showed similar selectivity at low conversions (X_0-χ_yle_ne ⁼ 0.2-0.4) as the wet-phase made catalyst. For the wet-phase made catalyst, a maximum in selectivity of 69% (7 wt.%) was reached at conversions between 75 to 85%. After passing the maximum, selectivity decreased with increasing o-xylene conversion.

The low selectivity of the FSP-made split may be explained by the mass transfer limitations. O-xylene reacts to phthalic anhydride inside the small pores of the catalyst grain (Figure 6) being trapped inside the grain resulting oxidation of PA. Therefore large amounts of CO and CO₂ were produced.. In case of the coated foams, no indications of inner mass transfer limitations were observed, resulting in a increasing selectivity with increasing o-xylene conversion until the selectivity collapses at conversions > 99 %.

The results of selectivity of the high dispersion and low dispersion coating with small SSA showed comparable results to the low dispersion coating with the high SSA (Table 9). With lower activity and less accessable active sites higher selectivity was obtained. This indicates that the catalyst with the high SSA exhibits not the favorable vanadia species for high selectivities.

Table 9. Comparison of conversion, modified residence time, selectivity and yield for the investigated catalysts at highest conversion data point before final collapse catalyst X₀._xyi_ene in % τ_raod in g s cm^"J S_PA,_o-_xyie_ne m % Y_PA 1H %

FSP-made split high SSA 98 I ASxVT 56 55 low disp high SSA 97 4.6xlO^"3 65 61 high disp. high SSA 100 6 48xlO^"3 64 64 low disp. small SSA 96 5.7OxIO^"3 67 64 high disp. small SSA 100 1.09xl0^"2 67 67

Yield: Coated foam catalysts resulted in comparable yields (0.65) as the wet- phase reference but residence times were one order of magnitude shorter resulting from the higher activity of the foam catalysts. Therefore space time yield of the FSP- made catalysts are significantly higher (>10x) with respect to the wet-phase reference. The performance of the FSP-made split instead is significantly lower having a maximum yield of 0.58 resulting from lower catalytic activity and selectivity of the FSP-made split.

Consequently from activity and selectivity the low dispersion coatings showed similar yield at longer residence times as the high dispersion coating. This is observed for both, active components with high SSA as well as for the active components with small SSA. All maximum yields of the different coatings are in a comparable range. The vanadia/titania with the small SSA resulted in slightly higher yields because of the higher selectivity. Results of the Cs-doped vanadia/titania active component: In literature [36, 37] Cs-doping of vanadia/titania is describe to enhance catalytic activity and selectivity to phthalic anhydride one active component with 0.3 wt.% Cs₂O content was prepared. In order to dope the vanadia/titania with Cs, cesium acetate (Strem Chemicals, 99.9%) was dissolved in acetic acid (Flulca, >99.8%) and 2-ethylhexanoic acid (Riedel-de-Haen₃ >99%, 2:1 by vol.) by refluxing (100⁰C, 2h) and subsequent distilled under N₂ (12O⁰C, ~ 4h) leading to a bright yellowish transparent solution with a cesium concentration of 0.285 M. Cs-doped active component was produced under the same conditions as were the high SSA (93 m² g^"1) sample. Production rate was 17 g(V₂0₅/Cs₂0 /TiO₂) h^"1, nominal vanadia content 10 wt.%, pressure drop behind filter was adjusted to 80 mbar. The doping with Cs results in a significantly larger SSA of 137 m² g^"1 (dBEτ⁼ 11 nm) at same precursor concentration (0.67 M TTIP) and flame conditions as of the 5 high SSA active component. Anatase content was > 94 wt.%. No evidence of Cs₂O crystals were found. TPR showed higher T_max (503⁰C) compared to the not doped V₂O₅/TiO₂ (Table 4).

TEM analysis showed mainly spherical particles. Absence of any particle in o micrometer range corroborates a monomodal particle distribution. Rings in the electron diffraction indicate clearly a crystalline structure.

For measuring the influence of Cs-doping on catalytic activity and selectivity, one single foam was coated with the Cs doped active component in a low dispersion mode, since the results of the low dispersion coating looked best in the 5 catalytic performance. Doping the vanadia/titania resulted in a lower activity performance compared to the not doped low dispersion coated foam.

Doping the vanadia/titania with 0.3 wt.% Cs₂O results in no significant improvement of the selectivity.

o Table 10. Results of the catalytic test of the low dispersion coated foam with

0.3 wt.% Cs₂O doped active component

-^^■o-xyleπe ^PA,o-xylene ^TA,o-xylene £>PT,o-xylenc ^MA,o-xylene ^CO2,α-xyIene ^CO,o-xylene I PA, o-xylene ^mod

033 033 OΪ9 OΪ2 OX)! <ΪΪ9 O04 QΛΛ 1.91E-03 ^■"-o-xylenc "PA.o-xylene "PT,o-xylcnc £>MA,o-xylene ScO2,o-xylenc Sco.o-xylcnc ^ PA, o-xyleπe ^niod

0.40 0.36 0.16 0.12 0.01 0.23 0.04 0.15 2.28E-03

0.57 0.45 0.11 0.10 0.01 0.23 0.08 0.26 2.84E-03

0.65 0.49 0.09 0.09 0.01 0.23 0.05 0.32 3.28E-03

0.82 0.59 0.06 0.06 0.02 0.19 0.05 0.48 3.79E-03

0.96 0.65 0.04 0.03 0.02 0.21 0.05 0.63 4.59E-03

1.00 0.66 0.00 0.00 0.03 0.24 0.06 0.66 5.70E-03

1.00 0.51 0.00 0.00 0.03 0.33 0.09 0.51 9.46E-03

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5

6. Appendix

The appendix provides additional information on calculations and results obtained in the experiments.

0 Calculations for gas analysis

Determination of correction factors: For determination of the correction factors the method of Ackmann [38] was used. Therefore a solution of products and educts in aceton of known concentration were mixed and injected the gas chromatograph. Table 11. Values of the correction factors for gas analysis. Calculated by prior calibaration.

correction factor value

•*o-xyleπe' ^ethane 4.0152

ΪPA'Iethane 3.153 iTA'fethaπe 3.5346 fpτ/fethane 3.6294

Amount of substances after reactor nji For the calculation of the amount of substances in the product gas a known amount of ethane, n_eti_mne is added the gas flow after the reactor. Equation (2) can than be solved for the wanted substance leading to equation (3) the correction factor of the internal standard is by definition set to 1.

n_i = Kth_ane -ψ^^± (3) ethane

GC parameters

• Split- and carrier gas: He

• Split flow: 39.9 mL rnin^"1 • Column flow: 2 mL mkf¹

• Column pressure: 0.68 bar

• Detector temperature: 350°C

• Detectorgases:

• H₂ flow: 30 mL min^"1 • Air flow: 400 mL min^"1

• Makeup flow (He): 25 mL min^"1

• Sample Loop: 280 ⁰C read (260°C real)

• Volume: 0.250 mL

• Injection time: 1.5 min • Temperature program: 60°C;lmin - 20°C/min - 100⁰C; 0,5 min - 10°C/min- 160°C; 1 min - 20°C/min - 200⁰C; 2 min.

Calculations for evaluation The modified residence time τ_mod is calculated with, equation (4). Plotting the conversion of o-xylene vs. τ_mod gives the opportunity to compare the different FSP- made and wet-phase made catalysts by means of catalytic activity.

D

With m_cat, the mass of vanadia/titania installed in the reactor and V_gas is the total volume gas flow.

Conversion of o-xylene, X₀-_Xyiene is calculated with equation(5):

Υ — I °'^χyleπe _'° o-xylene / . ...

^Λo-xylene~ • vv

0-xylene,0

Selectivity with respect to phthalic anhydride (PA) S_PA is calculated with equation (6).

Table of symbols and abbreviations

The list below summarizes the abbreviations used in this specification: symbol unit description

AOS - average oxidation state d^βET nm average BET-diameter d_p m particle diameter

Si - number of carbon atoms

Fi cm² peak area fi - correction factor

FSP - flame spray pyrolysis

MA - maelic acid g mass of vanadia/titania

ML - monolayer

TIi mol amount of substance

P bar reactor pressure

PA - phthalic anhydride

PT - phthalid

SEM - scanning electron microscopy

^i, o-xylene - selectivity of substance i

SSA specific surface area

T K reactor temperature

TA - o-tolualdehyde

TEM - transmission electron microscopy

T ⁰C temperature of maximum TPR peak

TPR - temperature programmed reduction

TTIP - titanium-tetra-isopropoxide

''-mod goat s cm modified residence time

Vi mL/min volume flow

•Λ-o-xylene - conversion of o-xylene

XRD - X-ray diffraction

Ypa yield of phthalic anhydride

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but maybe otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. A process for the production of a catalyst comprising the step of dry deposition of gasborne, catalytic active material on a porous support wherein the catalytic active material has an external surface area between 0,3 to 1000m²/g.

2. A process according to claim 1 wherein the catalytic active material has an external surface above 53 m²/g.

3. A process according to claim 1 or 2 wherein gasborne, catalytic active material is made by flame spray pyrolysis.

4. A process according to any of claims 1 to 3 wherein gasborne, catalytic active material is selected from the group consisting of V2O5/T1O2 or V2θ5/Tiθ2/Cs2θ.

5. A process according to any of claims 1 to 4 wherein the porous support is selected from the group consisting of ceramic foams.

6. A process according to any of claims 1 to 5 wherein the porous support is mullite.

7. A process according to any of claims 1 to 6 wherein the deposition temperature is adjusted to allow sintering of the deposited catalytic active material.

8. A catalyst obtained by a process according to any of claims 1 - 7.

9. A catalyst according to claim 8 wherein the catalytic active material has void fractions from 40 - 99,9%.

10. A catalyst according to claim 8 or 9 wherein the porous support has void fractions from 20 - 95%.

11. A catalyst according to any of claims 8 to 10 wherein the coating has a thickness of20 nm - 200 μm.

12. Use of a catalyst according to any of claims 8 - 11 in a chemical reaction.

13. Use of a catalyst according to any of claims 8 - 11 in the manufacture of phthalic acid anhydride.

14. Catalyst comprising a ceramic foam and catalytic active material, wherein the ceramic foam has void fractions in the range of 20 - 95 % and the catalytic active material has void fractions in the range of 40 - 99,9%.

15. Catalyst according to claim 14, wherein the catalytic active material is V₂CVTiO₂ or V₂ ⁽VTiCyCsO₂.

16. Catalyst according to claim 14 or 15 wherein the ceramic foam is mullite.