Bismat containing a diesel oxidation catalyst

Abstract

The present invention relates to a catalyst comprising a support substrate having a length L extending between ends a and b, and four material zones A, B, C and D, wherein material zone B comprises bismuth.

Description

Technical Field

[0001] The present invention relates to a diesel oxidation catalyst comprising a plurality of catalytic active material zones, wherein one of the material zones contains bismuth.

Background Art

[0002] The exhaust gas of motor vehicles operated in lean combustion engines such as diesel engines contains, in addition to carbon monoxide (CO) and nitrogen oxides (NO X ), components resulting from incomplete combustion of the fuel in the combustion chamber of the cylinder. In addition to residual hydrocarbons (HC), which usually also exist mainly in gaseous form, these include particulate emissions, also referred to as "diesel soot" or "soot particles".

[0003] In order to purify such exhaust gas, certain components must be converted into as harmless compounds as possible, which is only achievable by using a suitable catalyst.

[0004] Hydrocarbons (HC) and carbon monoxide (CO) can be oxidized using a diesel oxidation catalyst (DOC). Conventional diesel oxidation catalysts contain, in particular, platinum and / or palladium on a suitable support oxide, such as aluminum oxide.

[0005] A known method for removing nitrogen oxides from exhaust gas in the presence of oxygen is selective catalytic reduction (SCR) with ammonia on a suitable catalyst. In this method, the nitrogen oxides to be removed from the exhaust gas are converted to nitrogen and water using ammonia.

[0006] Soot particles can be removed very effectively from exhaust gases using diesel particulate filters (DPEs), and wall-flow filters made of ceramic material have proven particularly useful. Particulate filters can also be coated with catalytically active coatings. For example, European Patent No. 1820561(A1) describes a coating for a diesel particulate filter having a catalytic layer that promotes the combustion of filtered soot particles. Diesel particulate filters can also be coated with SCR catalysts, in which case they are simply called SDPFs.

[0007] For the aftertreatment of diesel engine exhaust gases, an exhaust gas aftertreatment system consisting of two or more of the above-mentioned components is used. A key component of such a system is the diesel oxidation catalyst. Its primary purpose is to react carbon monoxide with hydrocarbons, but it also oxidizes nitric oxide (NO) to form nitrogen dioxide (NO2), which is required by components located on the outlet side, such as DPF, SCR, and SDPF.

[0008] Exhaust gas aftertreatment systems that react the aforementioned pollutants over a wide operating window will need to comply with future regulations. In this regard, the development and optimization of diesel oxidation catalysts that react carbon monoxide and hydrocarbons at the lowest possible temperature while simultaneously providing sufficient nitrogen dioxide over the entire operating range is a technical challenge.

[0009] Here, it has been found that a diesel oxidation catalyst having a bismuth-containing material zone arranged in a specific manner on the catalyst satisfies this technical challenge.

[0010] Bismuth-containing diesel oxidation catalysts are known. For example, U.S. Patent No. 5,911,961 describes a catalyst in which platinum and bismuth are supported on titanium dioxide.

[0011] European Patent No. 1927399(A2) discloses a carrier material containing bismuth that supports aluminum oxide and platinum.

[0012] U.S. Patent No. 2003 / 027719 relates to an oxidation catalyst containing palladium and silver, and bismuth as the closest to palladium.

[0013] U.S. Patent 2012 / 302439 discloses a palladium-gold catalyst doped with bismuth and / or manganese.

[0014] International Publication No. 2017 / 064498(A1) discloses an oxidation catalyst containing bismuth or antimony and platinum group metals.

Summary of the Invention

Means for Solving the Problems

[0015] The present invention relates to a catalyst comprising a carrier substrate having a length L extending between ends a and b, and four substance zones A, B, C and D, · Substance zone A extends over a part of the length L from end a, contains platinum and does not contain palladium, does not contain platinum and contains palladium, or contains platinum and palladium, · Substance zone B extends over a part of the length L from end b and contains platinum and bismuth, where L A + L B = L, wherein L A is the length of substance zone A, and L B is the length of substance zone B, · Substance zone C extends over a part of the length L from end a, contains platinum and does not contain palladium, does not contain platinum and contains palladium, or contains platinum and palladium, · Substance zone D extends over a part of the length L from end b, contains platinum and does not contain palladium, does not contain platinum and contains palladium, or contains platinum and palladium, where L C + L D = L, wherein L C is the length of substance zone C, and L D is the length of substance zone D, Material zones C and D are located above material zones A and B.

[0016] Material zone A contains platinum and palladium in a weight ratio of 10:1 to 1:5, preferably 3:1 to 1:3.

[0017] Platinum and palladium are preferably present in material zone A at a concentration of 10 to 200 g / ft. 3 For example, 20-180g / ft 3 Or 40-150g / ft 3 It exists in the amount indicated, and the amount stated is the sum of the amounts of platinum and palladium.

[0018] If material zone A contains platinum and palladium, it preferably does not contain bismuth.

[0019] Platinum and palladium in material zone B generally exist on a carrier material. All materials well known to those skilled in the art for this purpose are considered carrier materials. The carrier material has a BET surface area of ​​30 to 250 m². 2 / g, preferably 100-200m 2 The concentration is / g (determined according to DIN66132), and in particular, aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxide, and mixtures or mixed oxides of at least two of these materials.

[0020] Aluminum oxide, cerium / titanium mixed oxide, magnesium / aluminum mixed oxide, and aluminum / silicon mixed oxide are preferred. When aluminum oxide is used, it is particularly preferred to be stabilized with, for example, 1 to 6% by weight, especially 4% by weight, of lanthanum oxide.

[0021] When an aluminum / silicon mixed oxide is used, it has a silicon oxide content of 5-30% by weight, preferably 5-10% by weight.

[0022] Material zone A may be a material for storing hydrocarbons, particularly at a temperature lower than the light-off temperature of material zone A for hydrocarbon oxidation. Such storage materials are zeolites having channels of sufficient size to accommodate hydrocarbons. Preferred zeolites for this purpose are those of structural type BEA.

[0023] Material Zone B contains bismuth, for example, in the form of bismuth oxide (Bi2O3). However, it exists particularly in the form of a composite oxide with aluminum or aluminum and silicon, with a silicon content of 5 to 30% by weight, preferably 5 to 15% by weight, based on the weights of aluminum and silicon oxide. Bismuth is present in an amount of, for example, 1 to 15% by weight, preferably 2 to 7% by weight, based on the composite oxide and calculated as bismuth element.

[0024] According to the present invention, the composite oxide ideally serves as a support material for platinum.

[0025] Based on aluminum and bismuth or a composite oxide of aluminum, silicon, and bismuth, and calculated as a platinum metal, platinum is particularly concentrated at 10-200 g / ft. 3 For example, 20-180g / ft 3 Or 40-150g / ft 3 It exists in that quantity.

[0026] Material zone B preferably does not contain palladium.

[0027] Material Zone L A and L B The combined length corresponds to the length L of the carrier substrate. Material Zone L A In particular, it has a length of 20-80%, preferably 40-60%, of length L. In a preferred embodiment, L A and L B Each extends over 50% of the length L.

[0028] Material zone C contains platinum in a weight ratio of 20:1 to 1:1, preferably 14:1 to 2:1, but does not contain palladium, or contains both platinum and palladium.

[0029] Platinum and palladium are preferably present in 10-200 g / ft 3 For example, 20-180g / ft 3 Or 40-150g / ft 3 The amount present in material zone C is either the amount of platinum if material zone C contains platinum but not palladium, or the sum of the amounts of platinum and palladium if material zone C contains both.

[0030] Platinum and palladium in material zone C generally exist on a carrier material. All materials well known to those skilled in the art for this purpose are considered carrier materials. The carrier material has a BET surface area of ​​30 to 250 m². 2 / g, preferably 100-200m 2 The concentration is / g (determined according to DIN66132), and in particular, aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxide, and mixtures or mixed oxides of at least two of these materials.

[0031] Aluminum oxide, cerium / titanium mixed oxide, magnesium / aluminum mixed oxide, and aluminum / silicon mixed oxide are preferred. When aluminum oxide is used, it is particularly preferred to be stabilized with, for example, 1 to 6% by weight, especially 4% by weight, of lanthanum oxide.

[0032] When using an aluminum / silicon mixed oxide, it has a silicon oxide content of 5-30% by weight, preferably 5-10% by weight.

[0033] Material zone C may be a material for storing hydrocarbons, particularly at a lower temperature than the light-off temperature of material zone A for hydrocarbon oxidation. Such storage materials are zeolites having channels of sufficient size to accommodate hydrocarbons. A preferred zeolite for this purpose is one of structural BEA.

[0034] Material zone D contains platinum in a weight ratio of 20:1 to 1:1, preferably 14:1 to 2:1, but does not contain palladium, or contains both platinum and palladium.

[0035] Platinum and palladium are preferably present in 10-200 g / ft 3 For example, 20-180g / ft 3 Or 40-150g / ft 3 The amount present in material zone D is either the amount of platinum if material zone C contains platinum but not palladium, or the sum of the amounts of platinum and palladium if material zone C contains both platinum and palladium.

[0036] Platinum and palladium in material zone D generally exist on a carrier material. All materials well known to those skilled in the art for this purpose are considered carrier materials. The carrier material has a BET surface area of ​​30 to 250 m². 2 / g, preferably 100-200m 2 The concentration is / g (determined according to DIN66132), and in particular, aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxide, and mixtures or mixed oxides of at least two of these materials.

[0037] Aluminum oxide, cerium / titanium mixed oxide, magnesium / aluminum mixed oxide, and aluminum / silicon mixed oxide are preferred. When aluminum oxide is used, it is particularly preferred to be stabilized with, for example, 1 to 6% by weight, especially 4% by weight, of lanthanum oxide.

[0038] When an aluminum / silicon mixed oxide is used, it has a silicon oxide content of 5-30% by weight, preferably 5-10% by weight.

[0039] Material zone D may be a material for storing hydrocarbons, particularly at a lower temperature than the light-off temperature of material zone A for hydrocarbon oxidation. Such storage materials are zeolites having channels of sufficient size to accommodate hydrocarbons. A preferred zeolite for this purpose is one of structural type BEA.

[0040] Material Zone L C and L D The combined length corresponds to the length L of the carrier substrate. Material Zone L C In particular, it has a length of 20-80%, preferably 40-60%, of length L. In a preferred embodiment, L C and L D Each extends over 50% of the length L.

[0041] In one embodiment of the present invention, material zones C and D are identical, that is, they contain the same components in the same amounts. Therefore, in this case, the uniform material zone extends over the entire length L of the carrier substrate and covers material zones A and B.

[0042] In further embodiments of the present invention, material zone A also comprises bismuth and platinum, but preferably does not contain palladium. Similar to material zone B, bismuth is also present in material zone A, for example, in the form of bismuth oxide (Bi2O3), but particularly in the form of a composite oxide with aluminum. In the latter case, bismuth is present in an amount of, for example, 1 to 10% by weight, preferably 2 to 7% by weight, based on the composite oxide and calculated as bismuth element.

[0043] In this embodiment of the present invention, substance zones A and B are, for example, identical, that is, they contain the same components in the same amounts. Therefore, in this case, the uniform substance zone extends over the entire length L of the carrier substrate.

[0044] In a further embodiment of the present invention, the catalyst extends from the end b of the support substrate over a portion of the length L across the material zone D and includes a material zone E that contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium.

[0045] Material zone E contains platinum in a weight ratio of 20:1 to 1:1, preferably 14:1 to 2:1, but does not contain palladium, or contains both platinum and palladium.

[0046] Platinum and palladium are preferably present in 10-200 g / ft 3 For example, 20-180g / ft 3 Or 40-150g / ft 3 The amount present in material zone C is either the amount of platinum if material zone C contains platinum but not palladium, or the sum of the amounts of platinum and palladium if material zone C contains both.

[0047] Platinum, palladium, or platinum and palladium in material zone E generally reside on a carrier material. All materials well known to those skilled in the art for this purpose are considered carrier materials. The carrier material has a BET surface area of ​​30 to 250 m². 2 / g, preferably 100-200m 2 The concentration is / g (determined according to DIN66132), and in particular, aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxide, and mixtures or mixed oxides of at least two of these materials.

[0048] Aluminum oxide, cerium / titanium mixed oxide, magnesium / aluminum mixed oxide, and aluminum / silicon mixed oxide are preferred. When aluminum oxide is used, it is particularly preferred to be stabilized with, for example, 1 to 6% by weight, especially 4% by weight, of lanthanum oxide.

[0049] When an aluminum / silicon mixed oxide is used, it has a silicon oxide content of 5-30% by weight, preferably 5-10% by weight.

[0050] The material zone E preferably extends from end b over 40-60% of the length L.

[0051] In a preferred embodiment of the present invention, substance zones A and B and substance zones C and D are identical in each case; that is, substance zones A and B contain the same components in the same amounts, and substance zones C and D contain the same components in the same amounts.

[0052] In this case, it is preferable that the catalyst contains material zone E.

[0053] The catalyst according to the present invention includes a support, which may be a flow-through substrate or a wall-flow filter.

[0054] A wall flow filter is a support having channels of length L, which extend parallel to each other between the first and second ends of the wall flow filter, alternately closed at either the first or second end, and separated by a porous wall. A flow-through substrate differs from a wall flow filter in that its channels of length L are open at both ends.

[0055] In its uncoated state, the wall flow filter has a porosity of, for example, 30-80%, specifically 50-75%. In its uncoated state, the average pore size of the wall flow filter is, for example, 5-30 micrometers.

[0056] Generally, the pores in wall flow filters are so-called open pores, meaning they have connections to channels. Furthermore, the pores are generally interconnected with each other. This allows for easy coating of the inner pore surfaces on the one hand, and for easy passage of exhaust gas through the porous walls of the wall flow filter on the other hand.

[0057] Similar to wall flow filters, flow-through substrates are also known to those skilled in the art and are commercially available. They consist of, for example, silicon carbide, aluminum titanate, or cordierite.

[0058] Apart from platinum, palladium, and bismuth, the catalysts according to the present invention generally do not contain any further metals, and in particular do not contain silver, gold, copper, or even iron.

[0059] In a preferred embodiment, the present invention relates to a catalyst comprising a carrier substrate having a length L extending between ends a and b, and four material zones A, B, C, and D. Starting from end a, material zone A extends over 40-60% of length L and contains platinum and palladium in a weight ratio of 3:1-1:3. Starting from end b, material zone B extends over 40-60% of length L and contains a composite oxide of aluminum and bismuth, or platinum supported on a composite oxide of aluminum, silicon and bismuth. Here L A +L B =L, and in the formula, L A L is the length of material zone A, B This is the length of material zone B, Starting from end a, material zone C extends over 40-60% of length L and contains platinum and palladium in a weight ratio of 14:1-2:1. Starting from end b, material zone D extends over 40-60% of length L and contains platinum and palladium in a weight ratio of 14:1-2:1. Here L C +L D =L, and in the formula, L C L is the length of material zone C, D This is the length of material zone D, Material zones C and D are located above material zones A and B.

[0060] In yet another embodiment, the present invention relates to a catalyst comprising a carrier substrate having a length L extending between ends a and b, and five material zones A, B, C, D, and E. Material Zone A and Material Zone B are identical and contain aluminum and bismuth, or platinum supported on a composite oxide of aluminum, silicon and bismuth. Here L A +L B =L, and in the formula, L A L is the length of material zone A, B This is the length of material zone B, • Material zones C and D are identical and contain platinum and palladium in a weight ratio of 14:1 to 2:1. Here L C +L D =L, and in the formula, L C L is the length of material zone C, D This is the length of material zone D, • Material Zone E contains platinum and palladium in a weight ratio of 14:1 to 2:1. Material zones C and D are located above material zones A and B, and material zone E is located above material zone D.

[0061] Material zones A, B, C, D, and E, where applicable, typically exist in the form of coatings on a support.

[0062] The catalyst according to the present invention, in which material zones A, B, C, D and -where applicable-E are present in the form of a coating on a carrier substrate, can be manufactured by methods well known to those skilled in the art, for example, by conventional dip coating methods, or by pump coating or suction coating methods with subsequent heat post-treatment (calcination). Those skilled in the art will recognize that, in the case of wall flow filters, the average pore size and average particle size of the material to be coated can be matched to each other so that they are located on the porous walls forming the channels of the wall flow filter (on-wall coating). The average particle size of the material to be coated can also be selected so that the material is located within the porous walls forming the channels of the wall flow filter, i.e., the inner pore surface is coated (in-wall coating). In this case, the average particle size of the coating material must be small enough to penetrate into the pores of the wall flow filter.

[0063] In another embodiment of the present invention, in which material zones A and B are identical, the carrier substrate is formed from the materials and matrix components of material zones A and B, and material zones C and D exist in the form of coatings on the carrier substrate.

[0064] Those skilled in the art are aware of carrier substrates, flow-through substrates, and wall-flow substrates that contain catalytically active materials in addition to being composed of inert materials such as cordierite. To produce these, a mixture consisting of 10 to 95% by weight of an inert matrix component and 5 to 90% by weight of a catalytically active material is extruded, for example, according to a method known to itself. In this case, all inert materials that are also used to produce catalyst substrates elsewhere can be used as matrix components. These are, for example, silicates, oxides, nitrides, or carbides, and are particularly preferably magnesium aluminum silicate.

[0065] In another embodiment of the present invention, a carrier substrate composed of a corrugated sheet of an inert material is used. Such a carrier substrate is known to those skilled in the art as a "corrugated substrate." Suitable inert materials are, for example, fibrous materials having an average fiber diameter of 50 to 250 μm and an average fiber length of 2 to 30 mm. Preferably, the fibrous material is heat-resistant and consists of silicon dioxide, particularly glass fibers.

[0066] In the manufacture of such carrier substrates, for example, the aforementioned sheets of fibrous material are corrugated in known ways, and the individual corrugated sheets are made into cylindrical monolithic structures having channels extending through the body. Preferably, monolithic structures having a transverse corrugated structure are formed by stacking several corrugated sheets as parallel layers having corrugations of different orientations between the layers. In one embodiment, non-corrugated (i.e., flat) sheets can be placed between the corrugated sheets.

[0067] Substrates made from corrugated sheets can be directly coated with substances A and B, but preferably, they are first coated with an inert material, such as titanium dioxide, and only afterward coated with a catalytic substance.

[0068] When the catalyst according to the present invention contains aluminum and bismuth, or a composite oxide of aluminum, silicon, and bismuth, the composite oxide can be obtained, for example, by contacting aluminum oxide or silicon-stabilized aluminum oxide with an aqueous solution of bismuth salt, followed by drying and calcination. The contact between aluminum oxide or silicon-stabilized aluminum oxide and the aqueous solution of bismuth salt can be advantageously carried out by spraying the aqueous solution of bismuth salt onto aluminum oxide in a mixer. Suitable mixers are well known to those skilled in the art. For example, a powder mixer or apparatus for spray drying is suitable.

[0069] The catalyst according to the present invention is perfectly suited as a diesel oxidation catalyst, which efficiently reacts carbon monoxide with hydrocarbons even at low temperatures, while also forming sufficient nitrogen dioxide for catalysts positioned on the outlet side, such as particulate filters and SCR catalysts. In particular, the catalyst according to the present invention has been shown to produce more nitrogen dioxide than a comparative catalyst that is otherwise identical but does not contain bismuth in material zone B.

[0070] Accordingly, the present invention also relates to a method for purifying exhaust gases of a motor vehicle operating with a lean-burn engine, the method characterized in that the exhaust gases are passed over the catalyst described above, wherein the exhaust gases enter the catalyst at end a and exit the catalyst at end b.

[0071] The present invention also relates to an exhaust gas system having the above-mentioned catalyst at end b, to which one or more further catalysts selected from a series consisting of a diesel particulate filter, a diesel particulate filter coated with an SCR catalyst, a diesel particulate filter coated with a coating that reduces soot ignition temperature, and an SCR catalyst disposed on a flow-through substrate are connected.

[0072] The optional and / or preferred embodiments described above for material zones A, B, C, D and E, where applicable, also apply to the methods and exhaust gas systems according to the present invention.

[0073] In the exhaust gas system according to the present invention, the SCR catalyst is, in principle, located upstream of the particulate filter or flow-through substrate, and therefore, regardless of its upstream location, it can be selected from all catalysts active in the SCR reaction between nitrogen oxides and ammonia, particularly those conventionally known to those skilled in the art of automotive exhaust gas catalysts. This includes mixed oxide type catalysts and zeolite-based catalysts—particularly transition metal exchange zeolite-based catalysts.

[0074] In embodiments of the present invention, an SCR catalyst containing a porous zeolite having a maximum ring size of eight tetrahedral atoms and a transition metal is used. Such SCR catalysts are described, for example, in International Publication Nos. 2008 / 106519(A1), 2008 / 118434(A1), and 2008 / 132452(A2).

[0075] Furthermore, zeolites with large and medium pores can also be used, and those with a BEA structure should be given particular consideration. Therefore, iron-BEA and copper-BEA are relevant.

[0076] Particularly preferred zeolites are those of the BEA, AEI, AFX, CHA, KFI, ERI, LEV, MER, or DDR structural type, and cobalt, iron, and copper are particularly preferably replaced with a mixture of two or three of these metals.

[0077] The term zeolite also includes molecular sieves, which are sometimes called “zeolite-like” compounds. Molecular sieves are preferred if they belong to one of the aforementioned structural types. Examples include silica aluminum phosphate zeolite, known by the term “SAPO,” and aluminum phosphate zeolite, known by the term “AIPO.”

[0078] These are also particularly preferable if they are replaced with cobalt, iron, copper, or mixtures of two or three of these metals.

[0079] Preferred zeolites also have a SAR (silica-to-alumina ratio) value of 2 to 100, particularly 5 to 50.

[0080] Zeolites or molecular sieves contain transition metals as metal oxides, i.e., as Fe2O3 or CuO, in particular in amounts of 1 to 10% by weight, especially 2 to 5% by weight.

[0081] A preferred embodiment of the present invention contains, as an SCR catalyst, a beta-type (BEA), chabazite-type (CHA), AEI, AFX, or levin-type (LEV) zeolite or molecular sieve replaced with copper, iron, or copper and iron. The corresponding zeolites or molecular sieves are known by the names ZSM-5, Beta, SSZ-13, SSZ-62, Nu-3, ZK-20, LZ-132, SAPO-34, SAPO-35, AlPO-34, and AlPO-35, for example, see U.S. Patents No. 6,709,644 and No. 8,617,474.

[0082] In one embodiment of the exhaust gas system according to the present invention, an injection device for a reducing agent is placed upstream of the SCR catalyst.

[0083] The injection device can be freely selected by those skilled in the art, and suitable devices can be found in the literature (see, for example, T. Mayer, Feststoff-SCR-System auf Basis von Ammoniumcarbamat, Dissertation, TU Kaiserslautern, 2005 and European Patent No. 1561919(A1)). Ammonia can be injected into the exhaust gas stream via the injection device, either in itself or in the form of compounds formed from ammonia under ambient conditions. Examples of suitable compounds include aqueous solutions of urea or ammonium formate, and solid ammonium carbamate. Typically, a reducing agent or its precursor is kept readily available in an accompanying container connected to the injection device. [Brief explanation of the drawing]

[0084] [Figure 1] This figure shows an embodiment of the catalyst according to the present invention. [Figure 2] This figure shows an embodiment of the catalyst according to the present invention. [Figure 3] This figure shows the NO2 / NOx ratio [%] of K1 and VK1 after catalyst, measured on an engine test bench during the NEDC cycle. [Figure 4]This figure shows the NO2 / NOX ratio [%] of K2 and VK2 after catalyst, measured on an engine test bench during the NEDC cycle. [Modes for carrying out the invention]

[0085] Figures 1 and 2 show embodiments of the catalyst according to the present invention, which have the following meanings. (1) Carrier substrate (2) Material Zone A (3) Material Zone B (4) Material Zone C (5) Material Zone D (6) Material Zone E A and B show the two ends of the carrier substrate, and the arrows indicate the direction of exhaust gas flow when the catalyst is used as intended.

[0086] Figure 1 shows a catalyst according to the present invention having material zones A, B, C, and D, where all material zones have the same length, i.e., 50% of the length of the support substrate.

[0087] Figure 2 shows a catalyst according to the present invention having material zones A, B, C, D, and E, where A and B and C and D are identical.

[0088] Example 1 a) Starting from its first end, a commercially available flow-through substrate made of cordierite is supported over 50% of its length on 72.65 g / l aluminum oxide stabilized with lanthanum oxide at a weight ratio of 65 g / ft². 3 It was coated with platinum and palladium, as well as 40 g / l of β-zeolite. b) Starting from its second end, the flow-through substrate obtained according to a) is supported over 50% of its length on 100 g / l aluminum oxide doped with 3 wt% bismuth oxide at a rate of 65 g / ft 3 It was coated with platinum and 40 g / l of β-zeolite. The flow-through substrate obtained according to c) and b) was supported over its entire length on 60 g / l aluminum oxide stabilized with lanthanum oxide, at a weight ratio of 25 g / ft² at 14:1. 3 It was coated with platinum and palladium.

[0089] The total amount of platinum and palladium catalyst packed is 90 g / ft 3 That is the case.

[0090] In the catalyst K1 obtained in this manner according to the present invention, material zones C and D are identical, and an adhesion layer is formed along the entire length of the flow-through substrate on material zones A and B.

[0091] Comparative Example 1 a) A commercially available flow-through substrate made of cordierite is supported over its entire length on 72.65 g / l aluminum oxide stabilized with lanthanum oxide at a weight ratio of 65 g / ft². 3 It was coated with platinum and palladium, as well as 40 g / l of β-zeolite. The flow-through substrate obtained according to b)a) was supported over its entire length on 60 g / l aluminum oxide stabilized with lanthanum oxide, at a weight ratio of 25 g / ft² at 14:1. 3 It was coated with platinum and palladium.

[0092] The total amount of platinum and palladium catalyst packed is 90 g / ft 3 That is the case.

[0093] In the comparative catalyst VK1 obtained in this manner, material zones A and B, and C and D are identical. Catalyst VK1 does not contain any bismuth.

[0094] Example 2 a) Starting from its first end, a commercially available flow-through substrate made of cordierite is supported on cerium titanate at a weight ratio of 1:3, over 50% of its length, at a rate of 40 g / ft. 3 It was coated with platinum and palladium. b) Starting from its second end, the flow-through substrate obtained according to a) is supported over 50% of its length on 100 g / l aluminum oxide doped with 3 wt% bismuth oxide at a rate of 65 g / ft 3 It was coated with platinum and 40 g / l of β-zeolite. c) Starting from its first end, the flow-through substrate obtained according to b) is supported over 50% of its length on 62.28 g / l aluminum oxide at a weight ratio of 70 g / ft 3 It was coated with platinum and palladium, as well as 25 g / l of β-zeolite. d) Starting from its second end, the flow-through substrate obtained according to c) is supported over 50% of its length on 60 g / l aluminum oxide stabilized with lanthanum oxide, at a weight ratio of 25 g / ft² at 14:1. 3 It was coated with platinum and palladium.

[0095] The total amount of platinum and palladium catalyst packed is 100 g / ft 3 That is the case.

[0096] The catalyst obtained in this manner according to the present invention will be referred to as K2 below.

[0097] Comparative Example 2 a) A commercially available flow-through substrate made of cordierite is supported over its entire length on cerium titanate at a weight ratio of 1:3, at 40 g / ft. 3 It was coated with platinum and palladium. The flow-through substrate obtained according to b)a) was supported over its entire length on 62.28 g / l aluminum oxide at a weight ratio of 70 g / ft² in a 2:1 ratio. 3 It was coated with platinum and palladium, as well as 25 g / l of β-zeolite.

[0098] The total amount of platinum and palladium catalyst packed is 110 g / ft 3 That is the case.

[0099] In the comparative catalyst VK2 obtained in this manner, material zones A and B, and C and D are identical. Catalyst VK2 does not contain any bismuth.

[0100] Example 3 a) A commercially available flow-through substrate made of cordierite is supported along its entire length on 25 g / l aluminum oxide doped with 3 wt% bismuth oxide, at a rate of 25 g / ft 3 It was coated with platinum. The flow-through substrate obtained according to b)a) was supported over its entire length on 110 g / l aluminum oxide at a weight ratio of 40 g / ft² in a 2:1 ratio. 3 It was coated with platinum and palladium. c) Starting from its second end, the flow-through substrate obtained according to b) is supported over 50% of its length on 50 g / l silicon oxide stabilized with silicon oxide at a weight ratio of 50 g / ft 3 It was coated with platinum and palladium.

[0101] The total amount of platinum and palladium catalyst packed is 90 g / ft 3 That is the case.

[0102] The catalyst obtained in this manner according to the present invention will be referred to as K3 below. Substance zones A and B, and C and D are identical, and substance zones A and B contain bismuth. In addition, substance zone D supports substance zone E as a further substance zone.

[0103] Comparative Experiment 1 Figure 3 shows the NO2 / NO2 ratio of K1 and VK1 after catalyst, measured on an engine test bench during the NEDC cycle. X The ratio [%] is shown. The black curve shows the results for VK1, and the gray curve shows the results for K1. The gray curve for K1 shows higher NO2 / NO2 ratios, especially in cycles between approximately 1125 seconds and 1500 seconds. X Shows the ratio.

[0104] Comparative Experiment 2 Figure 4 shows the NO2 / NO2 ratio of K2 and VK2 after catalyst, measured on an engine test bench during the NEDC cycle. X The ratio [%] is shown. The black curve shows the results for VK2, and the gray curve shows the results for K2. The gray curve indicates a higher NO2 / NO X Shows the ratio.

Claims

1. A diesel oxidation catalyst comprising a carrier substrate having a length L extending between ends a and b, and four material zones A, B, C, and D, - Material zone A extends from end a over a portion of length L and contains platinum but does not contain palladium, contains palladium but does not contain platinum, or contains platinum and palladium. Material Zone A does not contain any bismuth. - Material zone B extends from end b over a portion of length L and contains platinum and bismuth. Here L Ａ +L Ｂ = L, and in the formula, L Ａ L is the length of material zone A, Ｂ This is the length of material zone B, - Material zone C extends from end a over a portion of length L and contains platinum but does not contain palladium, contains palladium but does not contain platinum, or contains platinum and palladium. - Material zone D extends from end b over a portion of length L and contains platinum but does not contain palladium, contains palladium but does not contain platinum, or contains platinum and palladium. Here L Ｃ +L Ｄ = L, and in the formula, L Ｃ L is the length of material zone C, Ｄ This is the length of material zone D, Material zones C and D are located above material zones A and B. Substance zone B contains bismuth in the form of bismuth oxide (Bi ２ O ３ ), or in the form of aluminum or a composite oxide of aluminum and silicon, The bismuth in the aforementioned composite oxide is present in an amount of 1 to 15% by weight, calculated based on the aforementioned composite oxide and as bismuth element, together with aluminum or aluminum and silicon. The exhaust gas is intended to enter the diesel oxidation catalyst at end a and exit the diesel oxidation catalyst at end b. Diesel oxidation catalyst.

2. The diesel oxidation catalyst according to claim 1, characterized in that material zone A contains platinum and palladium.

3. The diesel oxidation catalyst according to claim 1, characterized in that the composite oxide consisting of bismuth and aluminum or bismuth, aluminum and silicon is a platinum support material.

4. The diesel oxidation catalyst according to any one of claims 1 to 3, characterized in that material zone B does not contain any palladium.

5. The diesel oxidation catalyst according to any one of claims 1 to 4, characterized in that material zone C contains platinum but does not contain palladium, or contains platinum and palladium.

6. The diesel oxidation catalyst according to any one of claims 1 to 5, characterized in that material zone D contains platinum but does not contain palladium, or contains platinum and palladium.

7. A diesel oxidation catalyst according to any one of claims 1 to 6, characterized in that material zones C and D are the same.

8. The diesel oxidation catalyst according to any one of claims 1 to 7, characterized in that the diesel oxidation catalyst extends from the end b of the carrier substrate over a portion of the length L spanning the material zone D, and includes a material zone E that contains platinum but not palladium, contains palladium but not platinum, or contains platinum and palladium.

9. The diesel oxidation catalyst comprises a carrier substrate having a length L extending between ends a and b, and four material zones A, B, C, and D. Starting from end a, material zone A extends over 40-60% of length L and contains platinum and palladium in a weight ratio of 3:1 to 1:

3. Starting from end b, material zone B extends over 40-60% of length L and contains a composite oxide of aluminum and bismuth, or platinum supported on a composite oxide of aluminum, silicon and bismuth. Here L Ａ +L Ｂ = L, and in the formula, L Ａ L is the length of material zone A, Ｂ This is the length of material zone B, Starting from end a, material zone C extends over 40-60% of length L and contains platinum and palladium in a weight ratio of 14:1 to 2:

1. Starting from end b, material zone D extends over 40-60% of length L and contains platinum and palladium in a weight ratio of 14:1 to 2:

1. Here L Ｃ +L Ｄ = L, and in the formula, L Ｃ L is the length of material zone C, Ｄ This is the length of material zone D, The diesel oxidation catalyst according to claim 1, wherein material zones C and D are located above material zones A and B.

10. A diesel oxidation catalyst comprising a carrier substrate having a length L extending between ends a and b, and five material zones A, B, C, D and E, Material zone A extends from end a over a portion of length L, Material zone B extends from end b over a portion of length L, • Material zone C extends from end a over a portion of length L, • Material zone D extends from end b over a portion of length L, Material Zone A and Material Zone B are identical and contain aluminum and bismuth, or platinum supported on a composite oxide of aluminum, silicon and bismuth. Here L Ａ +L Ｂ = L, and in the formula, L Ａ L is the length of material zone A, Ｂ This is the length of material zone B, Material Zone C and Material Zone D are identical and contain platinum and palladium in a weight ratio of 14:1 to 2:

1. Here L Ｃ +L Ｄ = L, and in the formula, L Ｃ L is the length of material zone C, Ｄ This is the length of material zone D, - Material Zone E contains platinum and palladium in a weight ratio of 14:1 to 2:

1. Material zones C and D are located above material zones A and B, and material zone E is located above material zone D. A diesel oxidation catalyst in which exhaust gas is intended to enter the diesel oxidation catalyst at end a and exit the diesel oxidation catalyst at end b.

11. A method for purifying exhaust gas from a motor vehicle operating with a lean-burn engine, wherein the exhaust gas is passed over a diesel oxidation catalyst according to any one of claims 1 to 10, characterized in that the exhaust gas enters the diesel oxidation catalyst at end a and exits the diesel oxidation catalyst at end b.

12. It is an exhaust gas system, a) Diesel oxidation catalyst according to any one of claims 1 to 10 and b) Exhaust gas system including SCR catalyst.

Images