Diesel oxidation catalysts containing bismuth

Abstract

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

Description

[0001] This invention relates to a diesel engine oxidation catalyst comprising multiple catalytically active material regions, one of which contains bismuth.

[0002] Exhaust gases from motor vehicles operated by lean-burn internal combustion engines (such as diesel engines) are deodorized to remove carbon monoxide (CO) and nitrogen oxides (NOx). x In addition to hydrocarbons (HC), these components also include those resulting from the incomplete combustion of fuel in the cylinder's combustion chamber. Besides residual hydrocarbons (HC), which are usually also present primarily in gaseous form, these components also include particulate emissions, also known as "diesel dust" or "particulate matter."

[0003] To clean such exhaust gases, the specified components must be converted into harmless compounds as completely as possible, which is only possible by using a suitable catalyst.

[0004] Diesel engine oxidation catalysts (DOCs) can be used to oxidize hydrocarbons (HC) and carbon monoxide (CO). Conventional diesel engine oxidation catalysts specifically contain platinum and / or palladium on a suitable support oxide such as alumina.

[0005] One known method for removing nitrogen oxides from exhaust gas in the presence of oxygen is selective catalytic reduction (SCR) of ammonia over a suitable catalyst. In this method, ammonia is used to convert the nitrogen oxides to be removed from the exhaust gas into nitrogen and water.

[0006] Diesel particulate filters (DPFs) are highly effective at removing particulate matter from exhaust gases, with wall-flow filters made of ceramic materials proving particularly useful. Particulate filters can also be fitted with a catalytically active coating. For example, EP1820561 A1 describes a coating for a diesel particulate filter with a catalyst layer that aids in the combustion of filtered particulate matter. Diesel particulate filters can also be coated with an SCR catalyst, and are then simply referred to as SDPFs.

[0007] An exhaust aftertreatment system consisting of two or more of the above components is used for exhaust aftertreatment of diesel engines. A key component of such a system is a diesel engine 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 (such as DPF, SCR, and SDPF) arranged on the outflow side.

[0008] Exhaust aftertreatment systems that enable the aforementioned pollutants to react within a wide operating window must comply with future regulations. In this context, the development and optimization of diesel engine oxidation catalysts presents a technical challenge, enabling the reaction of carbon monoxide and hydrocarbons at the lowest possible temperature while simultaneously providing sufficient nitrogen dioxide across the entire operating range.

[0009] It has now been found that diesel engine oxidation catalysts with bismuth-containing material regions arranged in a certain way on the catalyst meet this technical challenge.

[0010] Bismuth-containing diesel engine oxidation catalysts are known. For example, US 5,911,961 describes a catalyst in which platinum and bismuth are supported on titanium dioxide.

[0011] EP 1 927 399 A2 discloses a carrier material comprising alumina and bismuth, which supports platinum.

[0012] US 2003 / 027719 relates to an oxidation catalyst comprising palladium and silver, and bismuth as the nearest neighbor of palladium.

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

[0014] WO 2017 / 064498 A1 discloses an oxidation catalyst containing bismuth or antimony and platinum group metals.

[0015] This invention relates to a catalyst comprising a support substrate having a length L extending between ends a and b, and four material regions A, B, C, and D, wherein

[0016] ● Material region A extends from end a along a portion of length L and contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium;

[0017] ●Material region B extends from end b over a portion of length L and contains platinum and bismuth;

[0018] Where L A + L B = L, where LA is the length of the material region A, and L B The length of material region B;

[0019] ● Material region C extends from end a over a portion of length L and contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium;

[0020] ●The material region D extends from end b over a portion of length L and contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium;

[0021] Where L C + L D = L, where L C Let L be the length of the material region C, and L D Let D be the length of the material region.

[0022] Furthermore, material zones C and D are arranged above material zones A and B.

[0023] Material region A preferably comprises platinum and palladium in a weight ratio particularly of 10:1 to 1:5, preferably 3:1 to 1:3.

[0024] In material region A, platinum and palladium are preferably used at a concentration of 10 g / ft. 3 Up to 200g / ft 3 For example, 20g / ft 3 Up to 180g / ft 3 or 40g / ft 3 Up to 150g / ft 3 The quantity of platinum and palladium is present, wherein the quantity is the sum of the quantities of platinum and palladium.

[0025] If material region A contains platinum and palladium, it preferably does not contain bismuth.

[0026] Platinum and palladium in material region B are typically present on a support material. All materials used for this purpose, as are familiar to those skilled in the art, are considered support materials. Their BET surface area is 30 m². 2 / g to 250m 2 / g, preferably 100m 2 / g to 200m 2 / g (as determined according to DIN 66132), and in particular alumina, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxides, and mixtures or mixed oxides of at least two of these materials.

[0027] Preferred materials include alumina, cerium / titanium mixed oxides, magnesium / aluminum mixed oxides, and aluminum / silicon mixed oxides. If alumina is used, it is particularly preferred to stabilize it with, for example, 1% to 6% by weight, especially 4% by weight, lanthanum oxide.

[0028] When using aluminum / silicon mixed oxide, it particularly has a silicon oxide content of 5% to 30% by weight, preferably 5% to 10% by weight.

[0029] Material zone A can be a material for storing hydrocarbons, particularly below the ignition temperature of material zone A used for hydrocarbon oxidation. Such storage materials are, in particular, zeolites whose channels are large enough to accommodate hydrocarbons. Preferred zeolites for this purpose are those with a structural type of BEA.

[0030] Material region B contains bismuth, for example in the form of bismuth oxide (Bi₂O₃); however, it is particularly present in the form of a composite oxide with aluminum or with aluminum and silicon, wherein the silicon content is, for example, 5% to 30% by weight, preferably 5% to 15% by weight, based on the weight of aluminum and silicon oxide. Based on the composite oxide and calculated as elemental bismuth, bismuth is present, for example, in an amount of 1% to 15% by weight, preferably 2% to 7% by weight.

[0031] According to the present invention, composite oxides are ideally used as carrier materials for platinum.

[0032] Based on aluminum and bismuth or aluminum, silicon and bismuth complex oxides and calculated in platinum metal, with platinum specifically calculated at 10 g / ft. 3 Up to 200g / ft 3 For example, 20g / ft 3 Up to 180g / ft 3 or 40g / ft 3 Up to 150g / ft 3 The quantity exists.

[0033] Material region B preferably does not contain palladium.

[0034] Material area L A and L B The length of the material region L corresponds to the length L of the carrier substrate. A Specifically, it has a length of 20% to 80%, preferably 40% to 60%, of the length L. In a preferred embodiment, L A and L B Each extends at 50% of the length L.

[0035] Material region C preferably contains platinum but not palladium, or contains platinum and palladium in a weight ratio particularly of 20:1 to 1:1, preferably 14:1 to 2:1.

[0036] Platinum and palladium are preferably in a concentration of 10 g / ft 3 Up to 200g / ft 3 For example, 20g / ft 3 Up to 180g / ft 3 or 40g / ft 3 Up to 150g / ft 3 The amount of platinum present in material region C is either the amount of platinum in material region C containing platinum but not palladium, or the sum of the amounts of platinum and palladium in material region C containing both platinum and palladium.

[0037] Platinum and palladium in material region C are typically present on a support material. All materials used for this purpose, as are familiar to those skilled in the art, are considered support materials. Their BET surface area is 30 m². 2 / g to 250m 2 / g, preferably 100m 2 / g to 200m 2 / g (as determined according to DIN 66132), and in particular alumina, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxides, and mixtures or mixed oxides of at least two of these materials.

[0038] Preferred materials include alumina, cerium / titanium mixed oxides, magnesium / aluminum mixed oxides, and aluminum / silicon mixed oxides. If alumina is used, it is particularly preferred to stabilize it with, for example, 1% to 6% by weight, especially 4% by weight, lanthanum oxide.

[0039] When using aluminum / silicon mixed oxide, it particularly has a silicon oxide content of 5% to 30% by weight, preferably 5% to 10% by weight.

[0040] Material zone C can be a material for storing hydrocarbons, particularly at a temperature below the ignition temperature of material zone A, which is used for the oxidation of hydrocarbons. Such storage materials are especially zeolites with sufficiently large channels to accommodate hydrocarbons. Preferred zeolites for this purpose are those with a structural type of BEA.

[0041] Material region D preferably contains platinum but not palladium, or contains platinum and palladium in a weight ratio particularly of 20:1 to 1:1, preferably 14:1 to 2:1.

[0042] Platinum and palladium are preferably in a concentration of 10 g / ft 3 Up to 200g / ft 3 For example, 20g / ft 3 Up to 180g / ft 3 or 40g / ft 3 Up to 150g / ft 3 The amount of platinum present in material region D is either the amount of platinum in material region C containing platinum but not palladium, or the sum of the amounts of platinum and palladium in material region C containing both platinum and palladium.

[0043] Platinum and palladium in material region D are typically present on a support material. All materials used for this purpose, as are familiar to those skilled in the art, are considered support materials. Their BET surface area is 30 m². 2 / g to 250m 2 / g, preferably 100m 2 / g to 200m 2 / g (as determined according to DIN 66132), and in particular alumina, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxides, and mixtures or mixed oxides of at least two of these materials.

[0044] Preferred materials include alumina, cerium / titanium mixed oxides, magnesium / aluminum mixed oxides, and aluminum / silicon mixed oxides. If alumina is used, it is particularly preferred to stabilize it with, for example, 1% to 6% by weight, especially 4% by weight, lanthanum oxide.

[0045] When using aluminum / silicon mixed oxide, it particularly has a silicon oxide content of 5% to 30% by weight, preferably 5% to 10% by weight.

[0046] Material zone D can be a material for storing hydrocarbons, particularly at a temperature below the ignition temperature of material zone A, which is used for the oxidation of hydrocarbons. Such storage materials, especially zeolites with sufficiently large channels to accommodate hydrocarbons, are preferred. Preferred zeolites for this purpose are those with a structural type of BEA.

[0047] Material area L C and L D The length of the material region L corresponds to the length L of the carrier substrate. C Specifically, it has a length of 20% to 80%, preferably 40% to 60%, of the length L. In a preferred embodiment, L C and L D Each extends at 50% of the length L.

[0048] In one embodiment of the invention, material regions C and D are identical, i.e., they contain the same amount of the same components. In this case, the uniform material region thus extends along the entire length L of the carrier substrate and covers material regions A and B.

[0049] In another embodiment of the invention, material region A further comprises bismuth and platinum, and preferably does not contain palladium. Bismuth is also present in material region A, for example in the form of bismuth oxide (Bi₂O₃), but particularly in the form of a complex oxide with aluminum. In the latter case, based on the complex oxide and calculated as elemental bismuth, bismuth is present, for example, in an amount of 1% to 10% by weight, preferably 2% to 7% by weight.

[0050] In this embodiment of the invention, material regions A and B are, for example, identical, i.e., they contain the same amount of the same component. In this case, the uniform material region thus extends along the entire length L of the carrier substrate.

[0051] In another embodiment of the invention, the catalyst includes a material region E that begins at end b of the support substrate, extends over a portion of length L in the material region D, and comprises platinum but not palladium, comprises palladium but not platinum, or comprises both platinum and palladium.

[0052] Material region E preferably contains platinum but not palladium, or contains platinum and palladium in a weight ratio particularly of 20:1 to 1:1, preferably 14:1 to 2:1.

[0053] Platinum and palladium are preferably in a concentration of 10 g / ft 3 Up to 200g / ft 3 For example, 20g / ft 3 Up to 180g / ft 3 or 40g / ft 3 Up to 150g / ft 3 The amount of platinum present in material region C is either the amount of platinum in material region C containing platinum but not palladium, or the sum of the amounts of platinum and palladium in material region C containing both platinum and palladium.

[0054] Platinum, palladium, or platinum and palladium in material region E are typically present on a support material. All materials used for this purpose that are familiar to those skilled in the art are considered support materials. Their BET surface area is 30 m². 2 / g to 250m 2 / g, preferably 100m 2 / g to 200m 2 / g (as determined according to DIN 66132), and in particular alumina, silicon oxide, magnesium oxide, titanium oxide, cerium / titanium mixed oxides, and mixtures or mixed oxides of at least two of these materials.

[0055] Preferred materials include alumina, cerium / titanium mixed oxides, magnesium / aluminum mixed oxides, and aluminum / silicon mixed oxides. If alumina is used, it is particularly preferred to stabilize it with, for example, 1% to 6% by weight, especially 4% by weight, lanthanum oxide.

[0056] When using aluminum / silicon mixed oxide, it particularly has a silicon oxide content of 5% to 30% by weight, preferably 5% to 10% by weight.

[0057] The material region E preferably extends from the end b over 40% to 60% of the length L.

[0058] In a preferred embodiment of the invention, material regions A and B, as well as material regions C and D, are identical in each case, i.e., material regions A and B contain the same amount of the same component, and material regions C and D contain the same amount of the same component.

[0059] In this case, it is preferable if the catalyst contains material region E.

[0060] The catalyst according to the invention comprises a support body. This can be a flow-through substrate or a wall-flow filter.

[0061] A wall-flow filter is a carrier body comprising channels of length L that extend parallel between a first end and a second end of the filter, closing alternately at either end and separated by porous walls. A key difference between a flow-through substrate and a wall-flow filter is that the channels of length L are open at both ends.

[0062] In their uncoated state, wall-flow filters have a porosity of, for example, 30% to 80%, particularly 50% to 75%. In their uncoated state, their average pore size is, for example, 5 micrometers to 30 micrometers.

[0063] Generally, the pores in a wall-flow filter are so-called open pores, meaning they are connected to the channels. Furthermore, the pores are usually interconnected. This allows for easy coating of the inner pore surface and facilitates the passage of exhaust gas through the porous walls of the wall-flow filter.

[0064] Similar to wall-flow filters, flow-through substrates are known to those skilled in the art and are commercially available. They are composed of, for example, silicon carbide, aluminum titanate, or cordierite.

[0065] In addition to platinum, palladium and bismuth, the catalysts according to the invention generally do not contain any other metals, particularly not silver, gold, copper or even iron.

[0066] In a preferred embodiment, the present invention relates to a catalyst comprising a support substrate having a length L extending between ends a and b, and four material regions A, B, C, and D, wherein

[0067] ●Starting from end a, the material region A extends over 40% to 60% of the length L and contains platinum and palladium in a weight ratio of 3:1 to 1:3;

[0068] ●Starting from end b, the material region B extends over 40% to 60% of the length L and contains platinum loaded on aluminum and bismuth or a composite oxide of aluminum, silicon and bismuth;

[0069] Where L A + L B = L, where L A Let L be the length of the material region A, and L B The length of material region B;

[0070] ●Starting from end a, the material region C extends over 40% to 60% of the length L and contains platinum and palladium in a weight ratio of 14:1 to 2:1;

[0071] ●Starting from end b, the material region D extends over 40% to 60% of the length L and contains platinum and palladium in a weight ratio of 14:1 to 2:1;

[0072] Where L C + L D = L, where L C Let L be the length of the material region C, and L D Let D be the length of the material region.

[0073] Furthermore, material zones C and D are arranged above material zones A and B.

[0074] In yet another preferred embodiment, the present invention relates to a catalyst comprising a support substrate having a length L extending between ends a and b, and five material regions A, B, C, D, and E, wherein

[0075] ● Material region A and material region B are identical and contain platinum loaded on aluminum and bismuth or a composite oxide of aluminum, silicon and bismuth;

[0076] Where L A + L B = L, where L A Let L be the length of the material region A, and L B The length of material region B;

[0077] ● Material region C and material region D are identical and contain platinum and palladium in a weight ratio of 14:1 to 2:1;

[0078] Where L C + L D = L, where L C Let L be the length of the material region C, and L D Let D be the length of the material region; and

[0079] ●Material zone E contains platinum and palladium in a weight ratio of 14:1 to 2:1;

[0080] Furthermore, material zones C and D are arranged above material zones A and B, and material zone E is arranged above material zone D.

[0081] Material zones A, B, C, D and (if applicable) E are typically present on the load-bearing body in the form of a coating.

[0082] The catalyst according to the invention (in which material regions A, B, C, D and (if applicable) E are present in the form of a coating on a carrier substrate) can be prepared by methods familiar to those skilled in the art, such as conventional dip coating methods or pump coating and suction coating methods with subsequent heat post-treatment (calcination). Those skilled in the art know that, in the case of wall-flow filters, their average pore size and the average particle size of the material to be coated can be matched to each other, such that they are disposed on a porous wall that forms the channels of the wall-flow filter (wall coating). The average particle size of the material to be coated can also be selected such that it is located within the porous wall forming the channels of the wall-flow filter; that is, coating the inner pore surface (inner 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.

[0083] In another embodiment of the invention, material regions A and B are identical, the carrier substrate is formed of the material and matrix components of material regions A and B, and material regions C and D exist on the carrier substrate in the form of a coating.

[0084] Carrier substrates, flow-through substrates, and wall-flow substrates that not only consist of inert materials such as cordierite but also additionally contain catalytically active materials are known to those skilled in the art. To prepare them, a mixture consisting of, for example, 10% to 95% by weight of an inert matrix component and 5% to 90% by weight of a catalytically active material is extruded according to methods known per se. In this case, all inert materials also used in the production of catalyst substrates can be used as the matrix component. These are, for example, silicates, oxides, nitrides, or carbides, with magnesium aluminum silicate being particularly preferred.

[0085] In another embodiment of the invention, a carrier substrate made of a corrugated sheet of an inert material is used. Such a carrier substrate is referred to by those skilled in the art as a "corrugated substrate." Suitable inert materials are, for example, fibrous materials having an average fiber diameter of 50µm to 250µm and an average fiber length of 2mm to 30mm. Preferably, the fibrous material is heat-resistant and consists of silica, particularly glass fiber.

[0086] To produce such carrier substrates, sheets of the aforementioned fibrous material are corrugated, for example, in a known manner, and individual corrugated sheets are formed into a monolithically constructed body in the shape of columns, with channels running through the body. Preferably, a monolithically constructed body with a transverse corrugated structure is formed by stacking multiple corrugated sheets into parallel layers, wherein the corrugation orientation differs between the layers. In one embodiment, non-corrugated (i.e., flat) sheets may be arranged between the corrugated sheets.

[0087] The substrate made of corrugated sheet can be directly coated with materials A and B, but they are preferably first coated with an inert material, such as titanium dioxide, and then coated only with a catalytic material.

[0088] If the catalyst according to the invention comprises an aluminum and bismuth or a composite oxide of aluminum, silicon, and bismuth, the composite oxide can be obtained, for example, by contacting alumina or silicon-stabilized alumina with an aqueous solution of a bismuth salt and subsequently drying and calcining. Contacting the alumina or silicon-stabilized alumina with the aqueous solution of the bismuth salt can advantageously be achieved by spraying the alumina with the aqueous solution of the bismuth salt in a mixer. Suitable mixers are known to those skilled in the art. For example, a powder mixer or an apparatus for spray drying is suitable.

[0089] The catalyst according to the invention is well-suited as an oxidation catalyst for diesel engines, effectively reacting carbon monoxide and hydrocarbons even at low temperatures, but it also produces sufficient nitrogen dioxide for catalysts arranged on the outflow side (such as particulate filters and SCR catalysts). In particular, it has been shown that the catalyst according to the invention produces more nitrogen dioxide than a comparative catalyst that is otherwise identical but contains no bismuth in material region B.

[0090] Therefore, the present invention also relates to a method for purifying exhaust gas from a motor vehicle operating with a lean-burn engine, characterized in that the exhaust gas is passed through the catalyst described above, wherein the exhaust gas enters the catalyst at end a and exits the catalyst at end b.

[0091] The present invention also relates to an exhaust gas system comprising the above-mentioned catalyst, wherein one or more additional catalysts are connected at its end b, the additional catalysts being 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 the ignition temperature of soot, and an SCR catalyst located on a flow-through substrate.

[0092] The optional and / or preferred embodiments described above for material zones A, B, C, D and (if applicable) E are also similarly applicable to the method according to the invention and the exhaust gas system according to the invention.

[0093] In the exhaust gas system according to the invention, the SCR catalyst can, in principle, be selected from all catalysts active in the SCR reaction of nitrogen oxides and ammonia, regardless of whether it is located upstream of the particulate filter or the flow-through substrate, particularly those catalysts known conventionally to those skilled in the art of automotive exhaust catalysis. This includes mixed oxide type catalysts, as well as zeolite-based catalysts, specifically transition metal exchange-based zeolite catalysts.

[0094] In embodiments of the invention, an SCR catalyst is used, which comprises a small-pore zeolite with a maximum ring size of eight tetrahedral atoms and a transition metal. Such SCR catalysts are described, for example, in WO2008 / 106519 A1, WO2008 / 118434 A1 and WO2008 / 132452 A2.

[0095] In addition, macroporous and mesoporous zeolites can also be used, especially those with BEA structure types. Therefore, iron-BEA and copper-BEA are of interest.

[0096] Particularly preferred zeolites are those with structural types BEA, AEI, AFX, CHA, KFI, ERI, LEV, MER, or DDR, and are particularly preferred to be replaced with cobalt, iron, copper, or a mixture of two or three of these metals.

[0097] The term zeolite here also includes molecular sieves, sometimes referred to as "zeolite-like" compounds. Molecular sieves belonging to one of the above structural types are preferred. Examples include silica-alumina phosphate zeolite with the term "SAPO" and aluminum phosphate zeolite with the term "AlPO".

[0098] These materials are also particularly preferred when they are replaced with cobalt, iron, copper, or a mixture of two or three of these metals.

[0099] Preferred zeolites are those with an SAR value (silica to alumina ratio) of 2 to 100, specifically 5 to 50.

[0100] Zeolites or molecular sieves contain transition metals, specifically in the form of metal oxides, i.e., for example, Fe2O3 or CuO, in amounts of 1% to 10% by weight and especially 2% to 5% by weight.

[0101] Preferred embodiments of the present invention contain β-type (BEA), chamazolithic (CHA), AEI, AFX, or intercalated zeolite (LEV) zeolites or molecular sieves as SCR catalysts for exchange with copper, iron, or copper and iron. The corresponding zeolites or molecular sieves are known, for example, as ZSM-5, Beta, SSZ-13, SSZ-62, Nu-3, ZK-20, LZ-132, SAPO-34, SAPO-35, AlPO-34, and AlPO-35; see, for example, US 6,709,644 and US 8,617,474.

[0102] In one embodiment of the exhaust gas system according to the invention, the injection device for the reducing agent is located upstream of the SCR catalyst.

[0103] The injection device can be freely selected by those skilled in the art, and suitable devices can be obtained from the literature (see, for example, T. Mayer, Feststoff-SCR-System auf Basis von Ammoniumcarbamat, Dissertation, TU Kaiserslautern, 2005 and EP 1 561 919 A1). Ammonia can be injected into the exhaust gas stream either on its own or in the form of a compound that forms ammonia under ambient conditions via the injection device. Examples of suitable compounds are aqueous solutions of urea or ammonium formate, as well as solid ammonium carbamate. Typically, a reducing agent or its precursor remains available in an accompanying container connected to the injection device.

[0104] Figure 1 and Figure 2 An embodiment of the catalyst according to the present invention is shown, which has the following meaning:

[0105] (1) Carrier substrate

[0106] (2) Material Zone A

[0107] (3) Material Zone B

[0108] (4) Material Zone C

[0109] (5) Material Zone D

[0110] (6) Material Zone E

[0111] a and b represent the two ends of the carrier substrate, and the arrows indicate the direction of exhaust gas flow when the catalyst is used as intended.

[0112] Figure 1 A catalyst having material regions A, B, C and D according to the invention is shown, wherein all material regions have the same length, i.e. 50% of the length of the support substrate.

[0113] Figure 2 A catalyst having material regions A, B, C, D and E according to the present invention is shown, wherein A and B, as well as C and D, are each identical.

[0114] Figure 3 Showing the NO2 / NOx ratios of K1 and VK1 as [%] after the catalyst was measured on the engine test bench during the NEDC cycle.

[0115] Figure 4 Showing the NO2 / NOx ratios of K2 and VK2 as [%] after the catalyst was measured on the engine test bench during the NEDC cycle.

[0116] Example 1

[0117] a) Starting from its first end, a commercially available flowable substrate made of cordierite is applied at 65 g / ft along 50% of its length. 3 The platinum and palladium were loaded in a weight ratio of 2:1 onto 72.65 g / l of lanthanum oxide-stabilized alumina and coated with 40 g / l of β-zeolite.

[0118] b) Starting from its second end, apply 65 g / ft of the flow-through substrate obtained in a) over 50% of its length. 3 The loading was coated with platinum on 100 g / L alumina doped with 3 wt% bismuth oxide and coated with 40 g / L β-zeolite.

[0119] c) Apply 25 g / ft of the flow-through substrate obtained according to b) along its entire length. 3 The platinum and palladium coatings on lanthanum oxide-stabilized alumina were loaded at a weight ratio of 14:1 on 60 g / L alumina.

[0120] The total loading of the catalyst containing platinum and palladium is 90 g / ft. 3 .

[0121] In the catalyst K1 obtained thereby according to the invention, material regions C and D are identical and an adhesive layer is formed on material regions A and B over the entire length of the flow-through substrate.

[0122] Comparative Example 1

[0123] a) Using commercially available circulating substrate made of cordierite along its entire length at 65 g / ft 3 The platinum and palladium were loaded in a weight ratio of 2:1 onto 72.65 g / l of lanthanum oxide-stabilized alumina and coated with 40 g / l of β-zeolite.

[0124] b) Apply 25 g / ft of the flow-through substrate obtained according to a) along its entire length. 3 The platinum and palladium coatings on lanthanum oxide-stabilized alumina were loaded at a weight ratio of 14:1 on 60 g / L alumina.

[0125] The total loading of the catalyst containing platinum and palladium is 90 g / ft. 3 .

[0126] In the comparative catalyst VK1 thus obtained, material regions A and B, as well as C and D, are identical. Catalyst VK1 does not contain any bismuth.

[0127] Example 2

[0128] a) Starting from its first end, a commercially available circulating substrate made of cordierite is applied at 40 g / ft along 50% of its length. 3 Platinum and palladium coating loaded on cerium titanium oxide in a weight ratio of 1:3.

[0129] b) Starting from its second end, apply 65 g / ft of the flow-through substrate obtained in a) over 50% of its length. 3 The loading was coated with platinum on 100 g / L alumina doped with 3 wt% bismuth oxide and coated with 40 g / L β-zeolite.

[0130] c) Starting from its first end, apply 70 g / ft of the flow-through substrate obtained according to b) over 50% of its length. 3 Platinum and palladium coatings with a weight ratio of 2:1 were applied to 62.28 g / L alumina and 25 g / L β-zeolite.

[0131] d) Starting from its second end, apply 25 g / ft of the flow-through substrate obtained according to c) over 50% of its length. 3 Platinum and palladium were coated on lanthanum oxide-stabilized alumina at a weight ratio of 14:1 at 60 g / L.

[0132] The total loading of the catalyst containing platinum and palladium is 100 g / ft. 3 .

[0133] The catalyst obtained thus according to the invention is referred to hereinafter as K2.

[0134] Comparative Example 2

[0135] a) Apply 40 g / ft of commercially available circulating substrate made of cordierite along its entire length. 3 Platinum and palladium coating loaded on cerium titanium oxide in a weight ratio of 1:3.

[0136] b) Apply 70 g / ft of the flow-through substrate obtained according to a) along its entire length. 3 Platinum and palladium coatings with a weight ratio of 2:1 were applied to 62.28 g / L alumina and 25 g / L β-zeolite.

[0137] The total loading of the catalyst containing platinum and palladium is 110 g / ft. 3 .

[0138] In the comparative catalyst VK2 thus obtained, material regions A and B, as well as C and D, are identical. Catalyst VK2 does not contain any bismuth.

[0139] Example 3

[0140] a) Apply 25 g / ft of commercially available circulating substrate made of cordierite along its entire length. 3 The loading was on a platinum-coated alumina doped with 3% by weight bismuth oxide at a density of 25 g / L.

[0141] b) Apply 40 g / ft of the flow-through substrate obtained according to a) along its entire length. 3 Platinum and palladium coatings were loaded onto 110 g / L alumina at a weight ratio of 2:1.

[0142] c) Starting from its second end, apply 50 g / ft of the flow-through substrate obtained according to b) along 50% of its length. 3 Platinum and palladium are coated on silicon-stabilized alumina at a weight ratio of 12:1 in 50 g / L.

[0143] The total loading of the catalyst containing platinum and palladium is 90 g / ft. 3 .

[0144] The catalyst obtained thus according to the invention is referred to hereinafter as K3. Material regions A and B, as well as C and D, are each identical therein, wherein material regions A and B contain bismuth. Furthermore, material region D supports material region E as another material region.

[0145] Comparative Experiment 1

[0146] Figure 3 The NO2 / NOx ratios of K1 and VK1, expressed as [%], are shown after the catalyst was measured on an engine test bench during the NEDC cycle. The black curve shows the results for VK1, and the gray curve shows the results for K1. The gray curve for K1 shows a higher NO2 / NOx ratio, especially in the cycle between approximately 1125 seconds and 1500 seconds.

[0147] Comparative Experiment 2

[0148] Figure 4 The NO2 / NOx ratios of K2 and VK2, expressed as a percentage (%), are shown after the catalyst was measured on an engine test bench during the NEDC cycle. The black curve shows the result for VK2, and the gray curve shows the result for K2. The gray curve indicates a higher NO2 / NOx ratio.

Claims

1. A catalyst comprising a support substrate having a length L extending between ends a and b, and four material regions A, B, C, and D, wherein ● Material region A extends from end a along a portion of length L and contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium; ●Material region B extends from end b over a portion of length L and contains platinum and bismuth; where L A + L B = L, where L A is the length of material region A and L B is the length of material region B; ● Material region C extends from end a over a portion of length L and contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium; ●The material region D extends from end b over a portion of length L and contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium; where L C + L D = L, where L C is the length of material region C and L D is the length of material region D; Furthermore, material zones C and D are arranged above material zones A and B. Material region B contains bismuth in the form of bismuth oxide (Bi₂O₃) or in the form of a composite oxide with aluminum or with aluminum and silicon. Material region B does not contain any palladium. Based on the composite oxide and calculated using elemental bismuth, the bismuth in the composite oxide exists in an amount of 1% to 15% by weight with aluminum or with aluminum and silicon. The exhaust gas is intended to enter the diesel engine oxidation catalyst at end a and exit the diesel engine oxidation catalyst at end b.

2. The catalyst according to claim 1, characterized in that, Material region A contains platinum and palladium.

3. The catalyst according to claim 1, characterized in that, Material region A does not contain any bismuth.

4. The catalyst according to claim 1, characterized in that, The composite oxide, composed of bismuth and aluminum or bismuth, aluminum, and silicon, is the carrier material for the platinum.

5. The catalyst according to claim 1, characterized in that, Material region C contains platinum but not palladium, or contains both platinum and palladium.

6. The catalyst according to claim 1, characterized in that, Material region D contains platinum but not palladium, or contains both platinum and palladium.

7. The catalyst according to claim 1, characterized in that, Material regions C and D are the same.

8. The catalyst according to claim 1, characterized in that, Material region A contains bismuth and platinum but not palladium.

9. The catalyst according to claim 8, characterized in that, Material regions A and B are the same.

10. The catalyst according to claim 9, characterized in that, Material regions A and B, as well as material regions C and D, are all the same.

11. The catalyst according to any one of claims 1 to 10, characterized in that, It includes a material region E that begins at end b of the carrier substrate, extends over a portion of length L on the material region D, and contains platinum but not palladium, contains palladium but not platinum, or contains both platinum and palladium.

12. The catalyst according to claim 1, characterized in that, The catalyst comprises a support substrate having a length L extending between ends a and b, and four material regions A, B, C, and D, wherein ●Starting from end a, the material region A extends over 40% to 60% of the length L and contains platinum and palladium in a weight ratio of 3:1 to 1:3; ●Starting from end b, the material region B extends over 40% to 60% of the length L and contains platinum loaded on aluminum and bismuth or a composite oxide of aluminum, silicon and bismuth; Where L A + L B = L, where L A Let L be the length of the material region A, and L B The length of material region B; ●Starting from end a, the material region C extends over 40% to 60% of the length L and contains platinum and palladium in a weight ratio of 14:1 to 2:1; ●Starting from end b, the material region D extends over 40% to 60% of the length L and contains platinum and palladium in a weight ratio of 14:1 to 2:1; Where L C + L D = L, where L C Let L be the length of the material region C, and L D Let D be the length of the material region. Furthermore, material zones C and D are arranged above material zones A and B.

13. The catalyst according to claim 1, characterized in that, It includes a carrier substrate having a length L extending between ends a and b, and five material regions A, B, C, D, and E, wherein ● Material region A and material region B are identical and contain platinum loaded on aluminum and bismuth or a composite oxide of aluminum, silicon and bismuth; Where L A + L B = L, where L A Let L be the length of the material region A, and L B The length of material region B; ● Material region C and material region D are identical and contain platinum and palladium in a weight ratio of 14:1 to 2:1; Where L C + L D = L, where L C Let L be the length of the material region C, and L D Let D be the length of the material region; and ● Material zone E contains platinum and palladium in a weight ratio of 14:1 to 2:1; Furthermore, material zones C and D are arranged above material zones A and B, and material zone E is arranged above material zone D.

14. A method for purifying exhaust gas from a motor vehicle operating with a lean-burn engine, characterized in that, The exhaust gas is passed through a catalyst according to any one of claims 1 to 13, wherein the exhaust gas enters the catalyst at end a and exits the catalyst at end b.

15. An exhaust gas system, the exhaust gas system comprising: a) The catalyst according to any one of claims 1 to 13, and b) SCR catalyst.

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