WO2018069199A1

WO2018069199A1 - Catalytic converter arrangement

Info

Publication number: WO2018069199A1
Application number: PCT/EP2017/075583
Authority: WO
Inventors: Thomas UTSCHIG; Frank Adam; Ruediger Hoyer
Original assignee: Umicore Ag & Co. Kg
Priority date: 2016-10-10
Filing date: 2017-10-09
Publication date: 2018-04-19
Also published as: DE112017005130A5

Abstract

The present invention relates to a catalytic converter arrangement which comprises a) a three-way catalyst A on a carrier substrate T_A b) a catalyst B on a carrier substrate T_B, which comprises two material zones B1 and B2, and/or c) a catalyst C on a carrier substrate T_C, which comprises two material zones C1 and C2.

Description

catalyst assembly

The present invention relates to a catalyst arrangement for purifying exhaust gas from lean-burn gasoline engines.

In addition to carbon monoxide (CO) and nitrogen oxides (NOx), the exhaust gas of motor vehicles fueled by lean-burn direct-injection gasoline engines also contains residual hydrocarbons (HC) resulting from incomplete combustion of the fuel in the combustion chamber of the cylinder.

The constituents mentioned must be converted as completely as possible into harmless compounds, which is possible only with the use of suitable catalysts.

To purify exhaust gas of stoichiometric air / fuel ratio operated gasoline engines so-called three-way catalysts are known. These are capable of producing carbon monoxide and

Hydrocarbons to oxidize, and at the same time to nitrogen oxides

to reduce. However, this reduction no longer succeeds in lean exhaust gas.

To remove the nitrogen oxides are so-called nitrogen oxide storage catalysts, for which the term "Lean NOx trap" or "LNT is common .. Their cleaning effect is based on the fact that in a lean operating phase of the engine, the nitrogen oxides from the storage material of the storage catalyst predominantly in the form of Nitrates are stored and these decomposed in a subsequent rich phase of the engine engine again and the thus released nitrogen oxides with the reducing

Exhaust gas shares on the storage catalyst to nitrogen, carbon dioxide and

Water to be implemented. This procedure is described for example in SAE SAE 950809. Suitable storage materials are, in particular, oxides, carbonates or hydroxides of magnesium, calcium, strontium, barium, the alkali metals, the rare earth metals or mixtures thereof. Due to their basic properties, these compounds are able to form nitrates with the acid nitrogen oxides of the exhaust gas and to store them in this way. They are suitable for generating a large interaction area with the exhaust gas in the highest possible dispersion

Carrier materials deposited. In addition, nitrogen oxide storage catalysts generally contain noble metals such as platinum, palladium and / or rhodium as catalytically active components. Their task is on the one hand to oxidise NO to NO2 under lean conditions as well as CO and HC to CO2 and H2O and on the other hand during the rich

Operating phases in which the nitrogen oxide storage catalyst is regenerated to reduce released NO2 to nitrogen.

Modern nitrogen oxide storage catalysts are described for example in EP0885650 A2, US2009 / 320457, WO2012 / 029050 AI and WO2016 / 020351 AI.

CN 105916578A (equivalent to EP 3 097 977 A1) discloses inter alia a two-layer catalyst which is present in both layers

Cerium oxide, barium oxide and precious metal. The document broadly indicates that this catalyst can be combined with other catalysts, for example, a three-way catalyst. A similar disclosure is also contained in US 2014/260214. Another known method for removing nitrogen oxides from exhaust gases in the presence of oxygen is the selective catalytic

Reduction (SCR process) using ammonia on a suitable catalyst. In this method, the nitrogen oxides to be removed from the exhaust gas are reacted with ammonia to nitrogen and water.

The ammonia used as the reducing agent can be made available in the "SCR active process" by metering an ammonia precursor compound, such as urea, ammonium carbamate or ammonium formate, into the exhaust gas line and subsequent hydrolysis. In the alternative "passive SCR process", however, the ammonia is formed from nitrogen oxide storage catalyst arranged on the upstream side of nitrogen oxides, that is to say it does not have to be added from an off-engine source WO2010 / 114873A2 discloses such a process.

It is believed that the formation of ammonia from nitric oxide according to the equation

2NO + 3H ₂ + 2CO ^ 2NH ₃ + 2C0 ₂

he follows. The necessary hydrogen becomes carbon monoxide and water according to the equation

CO + H ₂ 0 tj H ₂ + C0 ₂

formed, which is also known as a water gas shift reaction.

JP2008-121575A describes a catalyst arrangement which comprises a nitrogen oxide storage catalyst and a hydrogen-forming catalyst arranged upstream thereof. The hydrogen formed in a rich operating phase serves as a reducing agent for the reduction of nitrogen oxide, which is released from the nitrogen oxide storage catalyst.

The hydrogen-forming catalyst has a two-layer structure in which the lower layer contains a noble metal other than rhodium, for example, platinum, and the upper layer contains rhodium. Of the

The downstream part of the upper rhodium-containing layer further comprises small amounts of ceria. With the change of the exhaust gas legislation including the

Real Driving Emissions (RDE) emissions are the future exhaust systems both cold city and high temperatures, ie. at high loads, must have sufficient exhaust gas conversion.

Since the exhaust systems available to date do not meet these requirements or not sufficiently, there is a need for systems that meet the requirements of future emissions legislation. It has now been found that a specific catalyst arrangement which combines different catalyst properties and which can be preceded by an SCR catalyst fulfills the stated requirements.

The present invention relates to a catalyst arrangement which

a) a three-way catalyst A on a carrier substrate TA and b) a catalyst B on a carrier substrate TB, the two

Material zones includes Bl and B2, wherein material zone B2 is seconded over material zone Bl and

Material zone Bl ceria, an alkaline earth compound and / or an alkali compound, as well as platinum and / or palladium and contains

Material zone B2 cerium oxide or cerium / zirconium mixed oxide having a cerium oxide content of> 60 wt .-%, based on the weight of the mixed oxide, and palladium or platinum and palladium in

Weight ratio Pt: contains Pd <1 and is free of alkaline earth and alkali compounds, and / or

c) a catalyst C on a carrier substrate Tc, the two

Material zones C1 and C2 comprises, wherein material zone C2 is seconded over material zone Cl and

Material zone Cl ceria, an alkaline earth compound and / or an alkali compound, as well as platinum and / or palladium and contains

Material zone C2 Cerium oxide or cerium / zirconium mixed oxide having a cerium oxide content of> 60% by weight, based on the weight of the mixed oxide, platinum and palladium in the weight ratio Pt: Pd> 2 u rhodium in an amount> 0.1 g / l, based on the volume of carrier substrate contains Tc and is free of alkaline earth and alkali compounds,

includes.

As a three-way catalyst A, all known in the art

Three-way catalysts can be used. These contain in particular one or more precious metals, in particular platinum, palladium and / or Rhodium, as well as an oxygen storage component. As the latter, in particular mixed oxides of cerium oxide, zirconium oxide and optionally other oxides such as lanthanum oxide, niobium oxide, praseodymium oxide, yttrium oxide or neodymium oxide come into question.

In one embodiment of the present invention, the

Dreiwegekatalysator A a single material zone, all components, ie in particular platinum, palladium and / or rhodium, and a

Contains oxygen storage component.

In another embodiment of the present invention, the three-way catalyst A comprises two material zones AI and A2, wherein material zone A2 is arranged over material zone AI and wherein

Material zone AI at least one platinum group metal, and a

Contains cerium / zirconium / SE mixed oxide and

Material zone A2 at least one platinum group metal, and a

Contains cerium / zirconium / SE mixed oxide,

wherein SE is a rare earth metal other than cerium and the proportion of SE oxide in the cerium / zirconium / SE mixed oxide of layer AI is smaller than the proportion of the SE oxide in cerium / zirconium / SE mixed oxide of layer A2, respectively Wt .-% and based on the cerium / zirconium / SE mixed oxide.

The material zones AI and A2 contain as platinum group metal independently of one another in particular platinum, palladium, rhodium or mixtures of at least two of these platinum group metals.

For example, both material zones AI and A2 contain palladium as the only platinum group metal. However, it may also be, for example, material zone AI platinum, palladium or platinum and palladium and material zone A2

Palladium, rhodium or palladium and rhodium.

In particular, material zone AI contains palladium and material zone A2 rhodium or palladium and rhodium.

The three-way catalyst A is free of platinum, for example. The term "cerium / zirconium / SE mixed oxide" in the context of the present invention excludes physical mixtures of cerium oxide, zirconium oxide and SE oxide. "Cerium / zirconium / SE mixed oxides" are characterized by a substantially homogeneous, three-dimensional crystal structure which

ideally free of phases of pure ceria, zirconia or SE oxide. Depending on the manufacturing process, however, it is also possible for products which are not completely homogeneous to form, which as a rule can be used without disadvantage. Suitable rare earth metal oxides in the cerium / zirconium / SE mixed oxides are, for example, lanthanum oxide, yttrium oxide, praseodymium oxide, neodymium oxide, samarium oxide and mixtures of one or more of these metal oxides.

Lanthanum oxide, yttrium oxide, praseodymium oxide and mixtures of one or more of these metal oxides are preferred. Particularly preferred are lanthanum oxide, yttrium oxide and very particularly preferred is a mixture of lanthanum oxide and yttrium oxide.

The proportion of the SE oxide in the cerium / zirconium / SE mixed oxide of material zone AI is smaller than the proportion of the SE oxide in the cerium / zirconium / SE mixed oxide of material zone A2, in each case calculated in% by weight and based on the cerium / Zirconium / SE mixed oxide.

The proportion of the SE oxide in material zone Al is in particular 1 to 12 wt .-%, preferably 3 to 10 wt .-% and particularly preferably 6 to 9 wt .-%, each based on the cerium / zirconium / SE mixed oxide.

The proportion of the SE oxide in material zone A2 is in particular 2 to 25% by weight, preferably 10 to 20% by weight and particularly preferably 14 to 18% by weight, in each case based on the cerium / zirconium / SE mixed oxide.

The ratio of ceria to zirconia in the cerium / zirconium / Se mixed oxides can vary widely. In material zone AI, it is, for example, 0.1 to 1.0, preferably from 0.2 to 0.7, particularly preferably from 0.3 to 0.5. In material zone A2, it is for example 0.1 to 1.0, preferably from 0.2 to 0.7, particularly preferably from 0.3 to 0.5.

In particular, the cerium / zirconium / SE mixed oxides of the three-way catalyst A contain no aluminum oxide. In embodiments of the present invention contain material zone AI and / or A2, an alkaline earth compound such. B. barium oxide or

Barium sulfate. Preferred embodiments contain barium sulfate in material zone AI. The amount of barium sulfate is in particular 5 to 20 g / l based on the volume of the carrier substrate TA.

In further embodiments of the present invention, material zone AI and / or A2 additionally contain additives such as rare earth compounds such. B. lanthanum oxide and / or binders, such as. B. aluminum compounds. These additives are used in amounts which can vary within wide limits and which the skilled person can determine in a concrete case by simple means.

In one embodiment of the present invention

Material zone AI palladium, and a cerium / zirconium / lanthanum / yttrium mixed oxide and

Material zone A2 rhodium or palladium and rhodium, and a

Cerium / zirconium / lanthanum / yttrium mixed oxide, wherein

the proportion of the sum of lanthanum oxide and yttrium oxide in

Cerium / zirconium / lanthanum / yttrium mixed oxide of material zone AI is smaller than the proportion of the sum of lanthanum oxide and yttrium oxide in

Cerium / zirconium / lanthanum / yttrium mixed oxide of material zone A2, in each case calculated in% by weight and based on the cerium / zirconium / lanthanum / yttrium mixed oxide. In this case, it is preferable if the proportion of the total

Lanthan oxide and yttrium oxide in cerium / zirconium / lanthanum / yttrium mixed oxide of the material zone AI 6 to 9 wt .-% based on the

Cerium / zirconium / lanthanum / yttrium mixed oxide of material zone AI and in Cerium / zirconium / lanthanum / yttrium mixed oxide of material zone A2 is from 14 to 18% by weight, based on the cerium / zirconium / lanthanum / yttrium mixed oxide of material zone A2, in each case calculated in% by weight and based on the cerium / zirconium / Lanthanum / yttrium mixed oxide.

In a further embodiment of the present invention

Material zone AI directly on the carrier substrate TA, i. There is no further layer or "undercoat" between the carrier substrate TA and material zone AI.

In a further embodiment of the present invention, material zone A2 is in direct contact with the exhaust stream, i. E. on

Material zone A2 is no further layer or "overcoat".

The cerium oxide used in the material zones B1, B2, C1 and C2 is usually of commercial quality, ie. may have a cerium oxide content of 90 to 100 wt .-%.

The cerium / zirconium mixed oxide used in the material zones B2 and C2 is likewise usually of commercial quality. Its ceria content is> 60 wt .-%, based on the total weight of the mixed oxide, is therefore for example 60 to 90 wt .-%, in particular 65 to 75 wt .-%. The cerium / zirconium mixed oxide used in the material zones B2 and C2 may also contain other rare earth oxides other than cerium oxide. In particular, lanthanum oxide, neodymium oxide, praseodymium oxide, niobium oxide and yttrium oxide come into question. They are used, for example, in amounts of up to 10% by weight, for example from 2 to 8% by weight, based on the total weight of the mixed oxide.

As an alkaline earth compound in the material zones Bl and Cl come

especially oxides, carbonates or hydroxides of magnesium, strontium and barium in question, especially magnesium oxide, barium oxide and

Strontium oxide. As the alkali compound in the material zones Bl and Cl are in particular oxides, carbonates or hydroxides of lithium, potassium and sodium in question.

If the catalyst arrangement according to the invention comprises the catalyst B and the catalyst C, the material zones Bl and Cl are independent of one another with regard to the alkaline earth or alkali compounds. Thus, both material zones Bl and Cl can contain the same or different alkaline earth metal or alkali compounds.

Preferably, the alkaline earth or alkali compound in amounts of 10 to 50 g / l, especially 15 to 20 g / l, calculated as alkaline earth or alkali oxide, based on the volume of the carrier substrate TB and the carrier substrate Tc, before.

If the catalyst arrangement according to the invention comprises the catalyst B and the catalyst C, the material zones B1 and C1 are also independent of one another with regard to the amounts of alkaline earth or alkali compounds. Thus, both material zones Bl and Cl may contain the same or different amounts of alkaline earth or alkali compounds.

The material zones Bl and Cl independently contain platinum or palladium or platinum and palladium. In the latter case, the

Platinum to palladium ratio, for example, 4: 1 to 18: 1 or 6: 1 to 16: 1, for example, 8: 1, 10: 1, 12: 1 or 14: 1.

Material zone B2 contains Pd and optionally Rh or Pt and Pd with a weight ratio of Pt: Pd <2 and optionally Rh. Das

Weight ratio of Pt: Pd in material zone B2 is in particular 2: 1 to 1: 6.

In material zone C2, the weight ratio of Pt: Pd> 2, the expert speaks of a platinum-rich material zone. The weight ratio of Pt: Pd in material zone C2 is for example 2: 1 to 20: 1 or 2.1 to 14: 1, but in particular 2: 1 to 12: 1.

While material zone C2 contains rhodium as another precious metal, material zones B2 optionally contain rhodium. Rhodium is in these cases in particular in amounts of 0.1 to 12 g / ft ³ (corresponding to 0.003 to 0.42 g / l), based on the volume of the carrier substrate TB or of the carrier substrate Tc, before. Usually, the noble metals platinum and palladium and optionally rhodium are present on suitable carrier materials in all material zones AI, A2, B1, B2, C1 and C2. Suitable carrier materials are all materials which are familiar to a person skilled in the art for this purpose. Such materials have a BET surface area of 30 to 250 m ² / g, preferably from 100 to 200 m ² / g (determined according to DIN 66132) and are in particular alumina, silica, magnesium oxide, titanium oxide, cerium oxide, and mixtures or mixed oxides of at least two of these materials.

Preference is given to aluminum oxide, magnesium / aluminum mixed oxides and aluminum / silicon mixed oxides. If alumina is used, it is particularly preferably stabilized, for example with 1 to 6 wt .-%, in particular 4 wt .-%, lanthanum oxide.

In the material zones AI and A2 can serve as support materials for the platinum group metals beyond the cerium / zirconium / SE mixed oxides.

In one embodiment of the present invention, catalyst B comprises the material zones B1 and B2, wherein both material zones contain cerium oxide and material zone B2 is present in an amount of 50 to 200 g / l, based on the volume of the carrier substrate TB, and the minimum mass fraction in%. of cerium oxide in the material zone B2 is of the formula

0.1 x amount of material zone B2 in g / l + 30 calculated.

The expression "amount of washcoat B in g / l" in this formula means the dimensionless number which corresponds to the amount of material zone B2 indicated in g / l. For a washcoat loading of 50 g / l, this results in a minimum mass fraction of cerium oxide of 35%, corresponding to 17.5 g / l based on the volume of the carrier substrate TB.

For a washcoat loading of 200 g / l, this results in a minimum mass fraction of cerium oxide of 50%, corresponding to 100 g / l based on the volume of the carrier substrate TB.

In a variant of this embodiment, the mass fraction of cerium oxide in the material zone B2 is at least 50%, whichever is the case

Total loading of material zone B2 amounts of at least 25 to 100 g / l, based on the volume of the carrier substrate TB, corresponds.

In a further variant of this embodiment, the material zone B2 is in an amount of 75 to 150 g / l, based on the volume of

Carrier substrate TB, before. Accordingly, in this case, the amounts of ceria are at least 28.1 to 67.5 g / l, each based on the volume of the carrier substrate TB.

In another variant of this embodiment, the material zone B2 is in an amount of 80 to 130 g / l, based on the volume of

Carrier substrate TB, before. Accordingly, in this case, the amounts of ceria are at least 30.4 to 55.9 g / l, each based on the volume of the carrier substrate TB. The upper limit of the amount of cerium oxide contained in material zone B2 results from the maximum washcoat loading of 200 g / l less the amounts of noble metal and the support materials for the noble metals, and optionally contained further constituents of material zone B2. However, in preferred embodiments of the present invention, material zone B2 contains no further constituents besides cerium oxide, noble metal and support materials for the noble metal.

The maximum amount of cerium oxide, which may be contained in material zone B2, can therefore be calculated in a simple manner. In this embodiment, cerium oxide in the material zone Bl

in particular in an amount of 30 to 120 g / l, in particular 30 to 80 g / l, based on the volume of the carrier substrate TB used.

In another embodiment of the present invention, catalyst B comprises the material zones Bl and B2, wherein both material zones contain cerium oxide and the ratio of cerium oxide in material zone B2 to cerium oxide in material zone Bl, calculated in g / l and based on the volume of carrier substrate TB, respectively. 1: 2 to 3: 1. In this case, the sum of cerium oxide in material zone B1 and material zone B2, calculated in g / l and based on the volume of the carrier substrate TB, is in particular 100 to 240 g / l. In this embodiment of the present invention, this is

Ratio of cerium oxide in material zone B2 to cerium oxide in material zone B1, calculated in each case in g / l and based on the volume of the carrier substrate TB, for example 1: 2 to 2.5: 1, in particular 1: 1 to 2: 1.

In particular, cerium oxide is used in the material zone B2 in an amount of 46 to 180 g / l, preferably of 46 to 90 g / l and particularly preferably of 46 to 70 g / l, in each case based on the volume of the carrier substrate TB. In the material zone B1, cerium oxide is used in amounts of from 14 to 95 g / l, preferably from 25 to 95 g / l and particularly preferably from 46 to 95 g / l, in each case based on the volume of the carrier substrate TB.

In further embodiments, cerium oxide is used in material zone B1 in an amount of 25 to 120 g / l and in material zone B2 in an amount of 50 to 180 g / l, in each case based on the volume of carrier substrate TB

used.

The total washcoat loading of the carrier substrate TB is in

Embodiments of the present invention 300 to 600 g / l, based on the volume of the carrier substrate TB. In particular, the loading is with material zone B1 150 to 500 g / l and the loading with material zone B2 50 to 300 g / l, in each case based on the volume of the carrier substrate TB. In further embodiments, the loading with material zone B1 is 250 to 300 g / l, and with material zone B2 100 to 200 g / l, in each case based on the volume of carrier substrate TB.

In one embodiment of the present invention, catalyst C comprises the material zones Cl and C2, both of which material zones contain ceria. The distribution of the cerium oxide onto the material zones C1 and C2 takes place in particular as described above for the material zones B1 and B2, but independently of this.

In one embodiment of the present invention, the

Catalyst arrangement according to the invention the three-way catalyst A and the catalyst B. In particular, there is no further catalyst between the catalysts A and B.

In another embodiment of the present invention, the catalyst arrangement according to the invention comprises the three-way catalyst A and the catalyst C. In particular, there is no further catalyst between the catalysts A and C.

In a further embodiment of the present invention, the catalyst arrangement according to the invention comprises in this order

Three-way catalyst A, catalyst B and catalyst C.

In particular, there is no further catalyst between the catalysts A and B and between the catalysts B and C.

The material zones AI, A2, B1, B2, C1 and C2 generally extend over the entire length of the carrier substrate TA, TB or Tc.

But it is also possible that, for example, the material zones AI, Bl and Cl independently starting from one end of the Carrier substrate TA, TB or Tc to 10 to 80% of their length and the material zones A2, B2 and C2 over the entire length of

Support substrates TA, TB and Te extend.

Likewise, conversely, it is also possible for the material zones A2, B2 and C2 to start independently of one another starting from one end of the

Carrier substrate TA, TB or Tc to 10 to 80% of their length and the material zones AI, Bl and Cl over the entire length of

Support substrates TA, TB and Te extend. Suitable carrier substrates TA, TB or Tc are in principle all known catalytically inert carrier bodies for heterogeneous catalysts.

Preference is given to monolithic flow honeycomb bodies made of ceramic or metal, as they are usually used for cleaning exhaust gases from internal combustion engines. Very particular preference is given to ceramic flow honeycomb bodies made of cordierite.

In a further embodiment of the present invention, catalyst B or, if catalyst C is present, catalyst C is followed by a catalyst D on a carrier substrate TD, the catalyst D comprising an SCR catalytically active material zone D1.

SCR catalysts are, for example, mixed oxides, in particular titanium dioxide and / or oxides of vanadium, for example

Vanadium pentoxide, and may contain other oxides, such as those of silicon, molybdenum, manganese, tungsten and others. These catalysts are described in detail in the literature, see for example WO89 / 03366 Al, EP 0 345 695 A2, EP 0 385 164 A2 and WO2011 / 013006 A2.

Other SCR catalysts are based on metal-exchanged zeolites, for example, zeolites of the zeolites beta zeolite, ZSM-5, ZSM-20, USY and MOR exchanged with copper and / or iron. Preferably, however, SCR catalysts are used according to the invention, which contain a small-pore zeolite having a maximum ring size of eight tetrahedral atoms and a transition metal. Such SCR catalysts are described, for example, in EP 2 117 707 A1 and WO2008 / 132452.

Particularly preferred zeolites include the framework types AEI, AFX, CHA, KFI, ERI, LEV, MER or DDR, very particularly preferably the framework types AEI, CHA or LEV, which are particularly preferably cobalt, iron, copper or mixtures of two or three these metals are exchanged.

In particular, they are copper, iron or copper and iron

replaced.

The term "zeolites" also includes molecular sieves, which are sometimes referred to as "zeolite-like" compounds Molecular sieves are preferred if they belong to one of the abovementioned types of skeletons Examples are silica-aluminum-phosphate zeolites which are known by the term SAPO and Aluminum phosphate zeolites known by the term AIPO.

These are also particularly preferred when they are exchanged with cobalt, iron, copper or mixtures of two or three of these metals.

Preferred zeolites or molecular sieves are furthermore those which have a SAR (silica-to-alumina) value of 2 to 100, in particular of 5 to 50.

The zeolites or molecular sieves contain transition metal, in particular in amounts of 1 to 10 wt .-%, in particular 2 to 5 wt .-%, calculated as metal oxide, that is, for example, as Fe ₂ C> 3 or CuO.

Preferred embodiments of the present invention include SCR catalysts with copper, iron or copper and iron exchanged zeolites or molecular sieves of the chabazite or levyne type. Appropriate Zeolites or molecular sieves are known, for example, under the designations SSZ-13, SSZ-62, SAPO-34, AIPO-34, Nu-3, ZK-20, LZ-132, SAPO-35 and AIPO-35. In one embodiment of the present invention, catalyst D comprises, in addition to the SCR catalytically active material zone D1, an oxidation-catalytically active material zone D2.

In one embodiment of the present invention, the

Oxidation catalytically active material zone D2 up to a catalyst inlet temperature of 300 ° C. Nitrogen oxides.

Material zone D2 comprises in particular one or more platinum group metals, in particular platinum or platinum and palladium. Material zone D2 additionally comprises, in particular, cerium oxide. As support materials for the platinum group metals are all the

Professional considering materials for this purpose. Such materials have a BET surface area of 30 to 250 m ² / g, preferably from 100 to 200 m ² / g (determined according to DIN 66132) and are in particular alumina, silica, magnesium oxide, titanium oxide, cerium oxide, and mixtures or mixed oxides of at least two of these materials.

In one embodiment, the material zones D1 and D2 are in zoned form, i. Material zones Dl and material zone D2 are arranged one behind the other on the carrier substrate TD in such a way that

Material zone Dl points in the direction of the catalyst B and in the direction of the catalyst C. The material zone Dl extends

for example, over 65 to 98% and material zone D2 over 2 to 35% of the total length of the carrier substrate TD. In another embodiment, material zone D2 is arranged wholly or partly on material zone Dl. The material zone Dl extends for example over 90 to 100% and material zone D2 over 2 to 35% of the total length of the carrier substrate TD. Material zone D2 is arranged on the catalyst B or catalyst C side facing away from the catalyst D.

In a further embodiment of the present invention, catalyst D is followed by catalyst E on a carrier substrate TE, wherein catalyst E comprises a nitrogen oxide storage catalyst.

Catalyst E comprises in particular material zones E1 and E2, wherein E1 and E2 are defined as the material zones B1 and B2, but independently of B1 and B2. The carrier substrates TD and TE, like the carrier substrates TA, TB and Tc, can be flow substrates, in particular cordierite. In addition, the carrier substrates TD and / or TE can also be wall-flow filters. In contrast to the flow-through substrate, in which open channels extend at both ends in parallel between its two ends, the channels are in the

Wandflussfilter alternately sealed either at the first or at the second end gas-tight. Gas entering a channel at one end can thus leave the wall-flow filter only if it enters through the channel wall into a channel which is open at the other end. The channel walls are usually porous and have uncoated

Condition, for example, porosities of 30 to 80, especially 50 to 75%. Their average pore size when uncoated, for example, 5 to 30 microns.

As a rule, the pores of the wall-flow filter are so-called open pores, that is to say they have a connection to the channels. Furthermore, the pores are usually interconnected. This allows, on the one hand, the slight coating of the inner pore surfaces and, on the other hand, an easy passage of the exhaust gas through the porous walls of the wall-flow filter. In embodiments of the present invention, material zone D and / or material zone E exist on the porous channel walls of the wallflow filter. Preferably, however, they lie in the porous walls of the carrier substrate Tü or of the carrier substrate TE VOT.

Wall-flow filters which can be used in accordance with the present invention are known and available on the market. They consist for example of silicon carbide, aluminum titanate or cordierite. The application of the material zones A1, A2, B1, B2, C1, C2, D1, D2 and E or El and E2 to the corresponding carrier substrate is usually carried out with the aid of appropriate coating suspensions (washcoat) according to the customary dip coating methods or pumping and suction Coating process with subsequent thermal aftertreatment (calcination and optionally reduction with forming gas or hydrogen). These methods are well known in the art.

Incidentally, it is known to those skilled in the art that in the case of Wandflussfiltern their average pore size and the average particle size of the particles contained in the coating suspensions for the preparation of the material zone D or E particles can be coordinated so that the material zone D or E on the porous walls that the channels of the

Form wall flow filters lie (on-wall coating). Alternatively, they are chosen so that the material zone D or E in the porous walls, which form the channels of the wall flow filter are, that is a

Coating of the inner pore surfaces takes place (in-wall coating). In this case, the average particle size must be small enough to be able to penetrate into the pores of the wall-flow filter.

In embodiments of the present invention comprising catalysts B and C, catalysts B and C may be used on a

be applied common carrier substrate (TB = Tc). The volume ratios of the catalysts B and C may be 10: 1 to 1:10. The catalyst arrangement according to the invention is outstandingly suitable for the purification of exhaust gas of a lean-burn gasoline engine. Here comes the three-way catalyst A in all modes of the

Ottomotors the task to oxidize carbon monoxide and hydrocarbons, while the catalysts B and C store stoichiometric and especially in lean operation nitrogen oxides and reduce some of it during the fat phase to ammonia. The inventive

Catalyst arrangement is in particular capable of reducing hydrogen by means of the hydrogen formed via the water gas shift reaction

Nitrogen oxides to optimize ammonia. The formation of ammonia is thus fuel-efficient and with high selectivity.

This ammonia thus formed can be used to operate a downstream SCR catalyst, which reacts with this ammonia still remaining nitrogen oxides to nitrogen and water. The SCR catalyst can thus be operated "passively", ie the addition of

Ammonia or an ammonia precursor compound from a separately entrained reservoir can be omitted.

For this purpose, the exhaust gas is to be passed through the catalyst arrangement according to the invention such that it is first by the three-way catalyst A, then by catalyst B or catalyst C or if the catalysts B and C are both present, by catalyst B and then catalyst C and finally optionally through catalyst D and optionally through catalyst E.

It is particularly expedient, the catalyst arrangement according to the invention from the three-way catalyst A and the catalysts B and / or C close to the engine, i. directly behind the exhaust manifold or

Turbocharger, to place. If the inventive

Catalyst arrangement, a catalyst D and optionally a

Catalyst E includes, they may be arranged in the underbody of the vehicle.

The present invention thus also relates to a method for purifying exhaust gas from lean-burn gasoline engines, characterized is characterized in that the exhaust gas via an inventive

Catalyst arrangement is passed.

example 1

a) For the preparation of a catalyst arrangement according to the invention in the first step, a commercially available honeycomb flow-through ceramic carrier is coated over its entire length with a first material zone, the 4.803 g / l palladium supported on a lanthanum-stabilized

Alumina, a cerium, zirconium, yttrium and lanthanum containing mixed oxide, barium sulfate and lanthanum oxide.

After drying, the coated carrier is coated with a second material zone which also extends the full length of the flow-through ceramic carrier. The material zone contains 0.353 g / l rhodium and 0.141 g / l palladium supported on a lanthanum stabilized

Alumina, as well as a cerium, zirconium, yttrium and lanthanum

containing mixed oxide and 1 g / l lanthanum oxide.

After drying and calcination, the three-way catalyst A is present. b) In the second step, a commercial honeycomb flow-through ceramic carrier is coated over its entire length with a first zone of material carrying 0.883 g / L of platinum supported on a cerium-doped aluminum / magnesium mixed oxide, 0.0883 g / L of palladium, ceria a cerium doped aluminum / magnesium mixed oxide supported barium oxide, and magnesium oxide.

After drying, the coated support is coated with a second material zone which also extends the full length of the flow-through ceramic support. The material zone contains 0.424 g / l rhodium and 2.119 g / l palladium supported on a lanthanum stabilized

Alumina, and ceria.

After drying and calcination, the catalyst B is present. c) In the third step, a commercially available honeycomb flow-through ceramic carrier along its entire length with a first material zone coated containing 0.883 g / l of platinum and 0.0883 g / l of palladium supported on a lanthanum-stabilized alumina, ceria, on a cerium doped aluminum / magnesium mixed oxide supported barium oxide, and magnesium oxide.

After drying, the coated carrier is coated with a second material zone which also extends the full length of the flow-through ceramic carrier. The material zone contains 0.1766 g / l rhodium, 0.883 g / l platinum and 0.0883 g / l palladium supported on a lanthanum-stabilized alumina, as well as ceria.

After drying and calcination, the catalyst C is present. d) The catalysts A, B and C are placed one behind the other in this order and thus form the catalyst arrangement KAI according to the invention. Example 2

The catalyst arrangement KAI from Example 1 was extended by an SCR catalyst D. This comprised a 3 wt% copper exchanged chabazite supported on a commercial honeycomb flow-through ceramic carrier. The catalyst arrangement according to the invention thus formed is designated KA2.

Example 3

The catalyst arrangement KAI from Example 1 was extended by an SCR catalyst D. This included a Levyne exchanged with 3% by weight copper, which was on a commercial honeycomb

Flow ceramic carrier was supported. The catalyst arrangement according to the invention thus formed is designated KA3.

Example 4

The catalyst arrangement KA2 from Example 2 was supplemented by a catalyst E. This was identical to that described in Example lc)

Catalyst C. The catalyst arrangement of the invention thus formed is designated KA4. Example 5

The catalyst arrangement KA3 from Example 3 was supplemented by a catalyst E. This was identical to that described in Example lc)

Catalyst C. The catalyst arrangement of the invention thus formed is designated KA5.

Example 6

Example 2 was repeated with the difference that catalyst D on the side facing away from Catalyst C to 10% of the length of

Carrier substrate TD applied to the SCR catalyst

Material zone based on 4% lanthanum oxide stabilized

Alumina supported platinum and palladium, and ceria contained. The precious metal amount was 0.883 g / l of platinum and 0.0883 g / l of palladium. The catalyst arrangement according to the invention thus formed is designated KA6.

Example 7

Example 3 was repeated with the difference that catalyst D on the side facing away from Catalyst C to 10% of the length of

Carrier substrate TD applied to the SCR catalyst

Material zone, which was stabilized with 4% lanthanum oxide

Alumina supported platinum and palladium, and ceria contained. The precious metal amount was 0.883 g / l of platinum and 0.0883 g / l of palladium. The catalyst arrangement according to the invention thus formed is designated KA7. Example 8

Carrier substrate TD one under the SCR catalyst applied

Material zone contained (undercoat) containing on 4% lanthanum oxide stabilized alumina supported platinum and palladium, and ceria. The precious metal amount was 0.883 g / l of platinum and 0.0883 g / l of palladium. The catalyst arrangement according to the invention thus formed is designated KA8. Example 9

Carrier substrate TD one under the SCR catalyst applied

Material zone contained (undercoat) containing on 4% lanthanum oxide stabilized alumina supported platinum and palladium, and ceria. The precious metal amount was 0.883 g / l of platinum and 0.0883 g / l of palladium. The catalyst arrangement according to the invention thus formed is designated KA9. Example 10

Example 1 was repeated with the difference that catalyst B was omitted. The catalyst arrangement thus formed comprises only the catalysts A and C and is designated KA10. Comparative Example 1

a) For the preparation of a catalyst arrangement not according to the invention the three-way catalyst A of Example 1 according to the invention is prepared in the first step. b) In the second step, a commercial honeycomb flow ceramic carrier is coated over its entire length with a first zone of material containing 1.06 g / l of platinum, one doped with cerium

Aluminum / magnesium mixed oxide, 0.106 g / l palladium, an yttrium- and lanthanum-doped cerium / zirconium mixed oxide, supported on a cerium-doped aluminum / magnesium mixed oxide supported barium oxide, 0.0353 g / l rhodium and magnesium oxide.

After drying, the coated support is coated with a second material zone which also extends the full length of the flow-through ceramic support. The material zone contains 3.072 g / l of palladium supported on a lanthanum stabilized alumina, a neodymium, yttrium and lanthanum doped cerium / zirconium mixed oxide, yttrium and lanthanum doped cerium / zirconium mixed oxide, lanthana and strontium oxide. After drying and calcination, the catalyst BV is present. c) In the third step, a commercially available honeycomb flow-through ceramic carrier is coated over its entire length with a first material zone which carries 0.883 g / l of platinum supported on a cerium-doped aluminum / magnesium mixed oxide, a lanthanum-doped aluminum-cerium mixed oxide. 0.0883 g / l palladium, cerium oxide, a ceria-supported barium oxide, and magnesium oxide.

After drying, the coated carrier is coated with a second material zone which also extends the full length of the flow-through ceramic carrier. The material zone contains 0.106 g / l rhodium, 0.699 g / l platinum and 0.349 g / l palladium supported on a lanthanum-stabilized alumina and ceria.

After drying and calcining, the (TW) NSC catalyst CV according to the invention is present. d) The catalysts A, BV and CV are placed in this order one behind the other and thus form the non-inventive

Catalyst arrangement VK1.

Comparative Example 2

Example 4 (catalyst arrangement KA4) was repeated with the

Differences that the SCR catalyst D was omitted and catalyst E occupies a volume which corresponds to the volume D + E in KA4. It is therefore a catalyst arrangement of the catalysts A, B, C and E. It is called VK2.

Verqleichsversuche

a) Comparison of the water gas shift activity of component B according to Example lb and the component BV according to Comparative Example lb

For this comparison, a synthetic exhaust gas of the following

composition

C0 ₂ 14%

H ₂ 2.67%

CO 8% Water 10%

Balance is N ₂

passed through the component B or BV. The starting point of the test is 80 ° C. The temperature is raised at 7.5 ° C / min. The synthetic exhaust gas is passed through the catalysts at a space velocity of 25,000 1 / h. As can be seen from FIG. 1, catalyst B forms more hydrogen. b) Comparison of the catalyst arrangements KAI and VK1

A lean exhaust gas mixture from a lean-burned combustion engine with spray-guided combustion process (Lean GDI) is transmitted via the

Catalyst arrangements KAI or VK1 passed.

In the test, the catalyst assemblies lean NOx as long as the NOx sensor detects NOx slippage across the exhaust system of 100 ppm.

The engine then switches from lean combustion to rich combustion. In this case, the rich exhaust gas mixture over the

Catalyst system passes and reduces the stored there in the form of nitrates NOx.

If the lambda probe installed at the end of the exhaust system detects a grease breakthrough, it can be assumed that the exhaust system is exempt from the previously stored NOX.

The engine then returns to lean combustion mode. This process is repeated 7 times at a specified temperature, with the converted NOx mass calculated from the last 5 lean / rich changes.

The following specified temperatures are reached: 235 ° C, 290 ° C, 350 ° C, 400 ° C, 450 ° C, 500 ° C.

The result of this test is shown in FIG. 2. Accordingly, the catalyst arrangement KAI according to the invention converts more NOx than the catalyst arrangement VK1. c) NEDC exhaust test on the highly dynamic engine test bench In this test, the systems AB according to Example 1 and A-BV according to Comparative Example 1 were compared. The result of this test is shown in FIG. 3. Accordingly, the cumulative NO _x emission is lower in system AB.

d) NEDC exhaust test on the highly dynamic engine test bench

In this test example 4 (catalyst arrangement KA4) and

Comparative Example 2 (catalyst arrangement VK2) compared. In the case of KA4, the components A, B and C were located close to the engine and the components D and E were arranged in a position comparable to the subfloor. Analogously, in the case of VK2, the components A, B and C were arranged close to the engine and the component E in a position comparable to the subfloor. It should be noted that the catalyst volumes of the two subfloor systems (i.e., catalysts D + E and catalyst E, respectively) are comparable. In the catalyst arrangement KA4, the underfloor volume is equally divided between the SCR catalyst D and the NSC catalyst E, whereby the amount of precious metal used here in the underbody is halved in comparison to the catalyst arrangement VK2. As can be seen from FIG. 4, the catalyst arrangement KA4 according to the invention shows significant advantages in NOx conversion, despite the significantly lower amount of precious metal, especially in the more dynamic sections of the test cycle.

Claims

claims

1. Catalyst arrangement, the

a) a three-way catalyst A on a carrier substrate TA

b) a catalyst B on a carrier substrate TB, the two

Material zone B2 ceria or cerium / zirconium mixed oxide with a

Cerium oxide content of> 60 wt .-%, based on the weight of the mixed oxide, and palladium or platinum and palladium in

Weight ratio Pt: contains Pd <2 and is free of alkaline earth and alkali compounds, and / or

c) a catalyst C on a carrier substrate Tc, the two

Material zone C2 cerium oxide or cerium / zirconium mixed oxide with a

Cerium oxide content of> 60 wt .-%, based on the weight of the mixed oxide, platinum and palladium in the weight ratio Pt: Pd> 2 and rhodium in an amount> 0.1 g / l, based on the volume of the carrier substrate Tc contains and free of alkaline earth and alkali compounds,

includes.

2. Catalyst arrangement according to claim 1, characterized in that the three-way catalyst A comprises two material zones AI and A2, wherein material zone A2 is arranged over material zone AI and wherein

Material zone AI at least one platinum group metal, and a

Contains cerium / zirconium / SE mixed oxide and Material zone A2 at least one platinum group metal, and a

Contains cerium / zirconium / SE mixed oxide,

3. Catalyst arrangement according to claim 2, characterized in that the material zone AI palladium, and a cerium / zirconium / lanthanum / yttrium mixed oxide and

Material zone A2 rhodium or palladium and rhodium, and a

Cerium / zirconium / lanthanum / yttrium mixed oxide contains, wherein

the proportion of the sum of lanthanum oxide and yttrium oxide in

Cerium / zirconium / lanthanum / yttrium mixed oxide of material zone A2, in each case calculated in% by weight and based on the cerium / zirconium / lanthanum / yttrium mixed oxide.

4. Catalyst arrangement according to one or more of claims 1 to 3, characterized in that as the alkaline earth compound in the

Material zones Bl and Cl oxides, carbonates or hydroxides of magnesium, strontium or barium are used.

5. Catalyst arrangement according to one or more of claims 1 to 3, characterized in that are used as the alkali compound in the material zones Bl and Cl independently of one another oxides, carbonates or hydroxides of lithium, potassium or sodium.

6. Catalyst arrangement according to one or more of claims 1 to 5, characterized in that the alkaline earth or alkali compound in the material zones Bl and Cl independently of one another in amounts of 10 to 50 g / l, calculated as alkaline earth or alkali oxide and based on the volume of the carrier substrate TB or the carrier substrate Tc, are present.

7. Catalyst arrangement according to one or more of claims 1 to 6, characterized in that the material zones B2 as another

Contains precious metal rhodium.

8. Catalyst arrangement according to one or more of claims 1 to 7, characterized in that catalyst B comprises the material zones Bl and B2, wherein both material zones contain cerium oxide and material zone B2 in an amount of 50 to 200 g / l, based on the volume of

Support substrate TB, is present and the minimum mass fraction in% of cerium oxide in the material zone B2 from the formula

0.1 x amount of material zone B2 in g / l + 30 calculated.

9. Catalyst arrangement according to one or more of claims 1 to 7, characterized in that catalyst B comprises the material zones Bl and B2, wherein both material zones contain cerium oxide and the ratio of cerium oxide in material zone B2 to ceria in material zone Bl, calculated in g / l and based on the volume of the carrier substrate TB, 1: 2 to 3: 1.

10. Catalyst arrangement according to one or more of claims 1 to 9, characterized in that it comprises the three-way catalyst A and the

Catalyst B comprises.

Catalyst arrangement according to one or more of claims 1 to 9, characterized in that it comprises the three-way catalyst A and the catalyst C.

12. Catalyst arrangement according to one or more of claims 1 to 9, characterized in that they in this order the

Three-way catalyst A comprising catalyst B and catalyst C.

13. Catalyst arrangement according to one or more of claims 1 to 12, characterized in that it comprises a catalyst D with an SCR catalytically active material zone Dl.

14. A catalyst arrangement according to claim 13, characterized in that the SCR catalytically active material zone Dl a small-pore

Contains zeolites with a maximum ring size of eight tetrahedral atoms and a transition metal.

15. Catalyst arrangement according to claim 14, characterized in that the zeolite belongs to the framework types AEI, CHA, KFI, ERI, LEV, MER or DDR is exchanged with cobalt, iron, copper or mixtures of two or three of these metals.

16. Catalyst arrangement according to one or more of claims 13 to 15, characterized in that catalyst D comprises an oxidation catalytically active material zone D2.

17. Catalyst arrangement according to claim 16, characterized in that the oxidation-catalytically active material zone D2 up to a

Catalyst inlet temperature of 300 ° C stores nitrogen oxides.

18. A catalyst arrangement according to claim 16 and / or 17, characterized in that the oxidation catalytically active material zone D2 comprises platinum or platinum and palladium, and cerium oxide.

19, catalyst arrangement according to one or more of claims 16 tol8, characterized in that the material zone Dl and the material zone D2 are arranged one behind the other on the support substrate TD, such that material zone Dl points in the direction of the catalyst B or in the direction of the catalyst C.

20. Catalyst arrangement according to one or more of claims 16 to 18, characterized in that material zone D2 is arranged wholly or partly on the material zone Dl.

21. Catalyst arrangement according to one or more of claims 13 to 20, characterized in that adjoining catalyst D catalyst E on a carrier substrate TE, wherein catalyst E a

Nitrous oxide storage catalyst comprises.

22. A method for purifying exhaust gas from lean operated

Otto engines, characterized in that the exhaust gas is passed through a catalyst arrangement according to one or more of claims 1 to 21.

23. The method according to claim 22, characterized in that the catalyst arrangement of the three-way catalyst A and the

Catalysts B and / or C is arranged close to the engine.

24. The method according to claim 22 and / or 23, characterized in that catalyst D and catalyst E is arranged in the underbody of the vehicle.