Ammonia slip catalyst filter

Abstract

A catalytic wall-flow filter for treating exhaust gas is disclosed. The catalytic wall-flow filter comprises at least a first catalyst layer, a second catalyst layer, and a third catalyst layer, wherein the first catalyst layer extends from an inlet end of a substrate and comprises a first SCR composition; the second catalyst layer is provided in or on the wall of an inlet channel and extends from an inlet end of a substrate and comprises a PGM-containing composition; and the third catalyst layer is provided in or on the wall of an outlet channel and extends from an outlet end of a substrate and comprises a second SCR composition.

Description

[0001] The present invention relates to a catalytic article for use as an ammonia slip catalyst. In particular, the ammonia slip catalyst is provided in a wall-flow filter. Furthermore, the present invention relates to an exhaust gas treatment system comprising the catalytic article and the use of the system. The catalytic article is designed to eliminate particulate emissions resulting from the upstream addition of a reducing agent, such as ammonia or urea, while maintaining good exhaust treatment performance.

[0002] Exhaust gases produced by lean-burn and diesel engines are generally oxidizing. NO x is NO x In a process known as selective catalytic reduction (SCR) that converts elemental nitrogen (N2) and water, it is necessary to selectively reduce it with a catalyst and a reducing agent. In the SCR process, a gaseous reducing agent, typically anhydrous ammonia, aqueous ammonia, or urea, is added to the exhaust gas stream before the exhaust gas comes into contact with the catalyst. The reducing agent is absorbed by the catalyst, and as the exhaust gas passes through or over the catalytic substrate, NO x is reduced. NO x To maximize the conversion rate, it is often necessary to add more ammonia than the stoichiometric amount to the exhaust gas stream. However, if excessive ammonia is released into the atmosphere, it will be harmful to human health and the environment. Furthermore, ammonia is corrosive, especially in aqueous solutions. If ammonia and water condense in the exhaust line area downstream of the exhaust catalyst, a corrosive mixture is formed that can damage the exhaust system. Therefore, the release of ammonia from exhaust gases must be eliminated.

[0003] Even with the best SCR catalyst, maximum NO in systems with non-uniform NH3 distribution x The reduction effect cannot be achieved. Load, exhaust flow rate, and NO xSignificant changes in concentration are required for the 1:1 ammonia-NO₂ ratio necessary for the reaction stoichiometry. x It makes it difficult to supply NH3 to the catalyst via the ratio (ANR). Non-uniform NH3 distribution results in incomplete NO when local ANR is low. x It can cause conversion, and if ANR is high, it can cause NH3 slip.

[0004] In many conventional exhaust systems, an ammonia oxidation catalyst (also known as an ammonia slip catalyst or "ASC") is installed downstream of the SCR catalyst to convert and remove ammonia from the exhaust gas into nitrogen. Ammonia slip catalysts are well known in the art. The purpose of an ammonia slip catalyst is to treat all ammonia passing through the upstream SCR catalyst.

[0005] To overcome the difficulties associated with achieving ideal stoichiometry, ASC technology combines oxidation and SCR catalytic functions on a flow-through (FT) substrate to lower NH3 slip while simultaneously NO x Improves reduction. ASC enables the upstream SCR to operate continuously at a higher ANR, compensating for non-uniform NH3 distribution and NO x Increases conversion and simultaneously keeps NH3 slip low.

[0006] In ASC, oxidation catalysts and SCR catalysts can be coated onto the substrate according to various design strategies—one of the most common being the "two-layer ASC" design. The two-layer ASC design is based on sequentially coating two layers (a PGM layer and an SCR layer) on the walls of the through-flow channels. A functional ASC design converts only a portion of the available ammonia in the exhaust gas to the oxidation layer. The remainder of the ammonia, ideally, is converted entirely into just water, elemental nitrogen, and the smallest possible amounts of N2O and NO2. x It is used as a reducing agent for the SCR layer that can be converted.

[0007] A typical ASC is described in International Publication WO2016205509. This document discloses an ASC comprising a combination of platinum on a support with low ammonia storage and a first SCR catalyst. A preferred combination is a double layer having an upper layer comprising the first SCR catalyst and a lower layer comprising platinum on a support that stores low ammonia. In use, some excess ammonia may be stored in the upper SCR catalyst layer. Some of the excess ammonia passes through the Pt and therein NO x It can be oxidized to NO x It passes through the SCR layer again and is treated with the ammonia stored there to provide N2. In this way, excess slip ammonia is not released into the atmosphere but is stored and utilized.

[0008] Another configuration of the ASC is described in U.S. Patent Application Publication US20150037233.

[0009] Particulate emissions are a well-known problem in diesel engine exhaust gas treatment systems. It is known that these emissions can be eliminated using filters. Known filter types include diesel particulate filters (DPF) and catalytic soot filters (CSF). These capture soot from exhaust gases and can be regenerated by burning off the accumulated soot by raising the exhaust gas temperature. Conventional materials for DPFs or CSFs are so-called wall-flow filters.

[0010] European Patent Application Publication EP2483537 discloses a four-way catalyst for diesel exhaust gases. As the name implies, it targets four major emissions (CO, HC, NO) in exhaust gases x , soot) are all removed from a single component.

[0011] European patent application publication EP2567081 discloses a catalytic article for treating an exhaust gas stream containing particulate matter, hydrocarbons, CO, and ammonia. In a first embodiment of this disclosure, the catalytic article comprises a substrate having an inlet end and an outlet end that define the axial length of a first catalytic coating comprising a platinum group metal, wherein the first catalytic coating extends from the outlet end toward the inlet end over a length less than the total axial length of the substrate; and a second catalytic coating comprises a catalyst for the selective catalytic reduction (SCR) of nitrogen oxides, wherein the second catalytic coating extends from the inlet end toward the outlet end over a length less than the total axial length of the substrate and overlaps with a portion of the first catalytic coating.

[0012] European Patent Application Publication EP3277411 and European Patent Application Publication EP3277403 disclose a multi-zone catalytic article, a method for manufacturing a multi-zone catalytic article, and a method for controlling emissions in a diesel engine exhaust gas stream with a multi-zone catalytic article, wherein an emission treatment system of various embodiments effectively treats diesel engine exhaust with a single multi-zone catalytic article.

[0013] European patent application publication EP3357558 discloses a catalyst for purifying exhaust gas of a diesel engine, said catalyst having a plurality of material regions.

[0014] As emission standards become stricter, exhaust system emissions are a problem not only related to particulate emissions but also NO x It is becoming increasingly important to address issues related to species such as NH3 as well.

[0015] Accordingly, the object of the present invention is to provide an ammonia slip catalyst suitable for meeting anticipated future regulations regarding particulate emissions, or at least to solve problems related to particulate emissions in the prior art or to provide a commercially viable alternative thereto.

[0016] According to a first embodiment, a catalytic article for treating exhaust gas is provided, wherein the catalytic article is

[0017] A wall-flow type filter material comprising inlet channels that are opened at the inlet end of the material and closed at the outlet end of the material, wherein the inlet channels are adjacent to outlet channels that are closed at the inlet end of the material and opened at the outlet end of the material.

[0018] A wall-flow filter comprises at least a first catalyst layer, a second catalyst layer, and a third catalyst layer, and

[0019] (i) The first catalyst layer extends from the inlet end of the substrate and comprises a first SCR composition;

[0020] (ii) A second catalyst layer is provided within or on the wall of an inlet channel and extends from the inlet end of the substrate, and comprises a PGM-containing composition, wherein

[0021] When a second catalyst layer is provided on the wall of an inlet channel, the first catalyst layer is provided on the second catalyst layer, and

[0022] If the second catalyst layer is provided within the wall of the inlet channel, the first catalyst layer is provided on the wall of the inlet channel;

[0023] (iii) A third catalyst layer is provided within or on the wall of the discharge channel and extends from the discharge end of the substrate and comprises a second SCR composition;

[0024] g / in of the first and second SCR compositions in the first and third catalyst layers 3 g / ft² in the second catalyst layer relative to the total amount of units 3The ratio of the PGM of the unit is 1.5:8 to 5:8, preferably 2:8 to 4:8, more preferably 2:8 to 3:8.

[0025] The present invention will now be described further. In the following paragraphs, various aspects / embodiments of the present disclosure are defined in greater detail. Each aspect / embodiment defined in this manner may be combined with any other aspects / embodiments or aspects / embodiments unless clearly indicated otherwise. In particular, any feature described as desirable or advantageous may be combined with any other feature described as desirable or advantageous. It is intended that features disclosed in relation to a product may be combined with features disclosed in relation to a method, and vice versa.

[0026] In the following, the terms "ammonia slip catalyst filter" or "ASCF" are used as abbreviations for the structure of the catalyst article as described herein.

[0027] It has recently been noticed that injecting reducing agents (particularly urea / ammonia) into the exhaust gas stream can generate certain aggregated compounds and ammonium salts. These are species formed by the reaction and polymerization of the reducing agents before participating in the SCR reaction. The polymerized material then takes the form of additional fine particulates that can be released into the atmosphere despite strict emission requirements.

[0028] Discussions regarding such polymerized particulate emissions can be found in SAE 2017-01-0915. This document explains that, depending on the urea doser, the design of the decomposition reaction tube (DRT), and operating conditions, solid urea deposits can form in diesel aftertreatment systems due to the incomplete decomposition of injected urea. The formed deposits can increase engine back pressure and degrade NOx treatment performance. Since the formed urea deposits can be further converted into chemically more stable substances when exposed to high-temperature exhaust gases, it is important to understand this conversion process. The authors' experimental results show that 1) below the urea melting temperature (130°C), the formed urea deposits are still primarily urea; 2) in the temperature range of 130 to 190°C, urea is converted into a combination of urea, burette, and CYA; and 3) above the burette melting temperature (190°C), some characteristics of amelides are primarily formed in CYA. At temperatures above 200°C, urea undergoes rapid chemical conversion through urea decomposition, biuret formation, and subsequent biuret decomposition, and is converted into CYA within a short period of time.

[0029] Therefore, when urea and ammonia components polymerize under high-temperature exhaust gas conditions, polymerized particulates can be formed, which may possess a certain degree of thermal stability. While these particulate materials are generally very fine, precisely this type of fine material is now subject to even stricter regulations. Furthermore, since the formation of particulate materials can only occur after a reducing agent is dosed into the exhaust gas treatment system, they generally form after any conventional particulate filter in the system (DPF or CSF) and occur under low-temperature environments (i.e., bottom-down configurations) where regeneration of such filters would have been conventionally difficult.

[0030] The inventors have now discovered that these problems can be solved by providing a catalytic article as described herein. In particular, the article can reduce or eliminate particulate emissions while providing ASC performance comparable to that of a standard through-flow monolith. Furthermore, the inventors [have discovered] N2O and NO of a standard through-flow ASC. x It was found that using a reduced amount of PGM to meet performance requirements is possible and actually desirable. This leads to cost reduction and performance optimization.

[0031] It should be noted that the ASC is often provided as the rear portion of the SCR catalyst article. That is, the through-flow monolith may have a PGM layer on the outlet surface portion and an SCR layer provided along the entire length of the monolith. In other embodiments, the SCR and the dual-layer ASC are provided on separate monoliths but may be arranged immediately in sequence. Performance comparisons at present have been made only for the ASC portion (i.e., not including the upstream SCR-only portion of such combined monoliths). In use, as discussed below, a separate SCR monolith will generally precede the ASCF disclosed herein.

[0032] The present invention relates to catalytic articles. The term "catalytic article" means a structure having catalytic properties as described herein. The catalytic properties are derived from a material contained in or coated on the structure. The articles defined herein include both the coated catalytic substrate described herein and a processed and canned ASCF unit suitable for installation in an automobile. The catalytic article provides a catalyst effective in reducing ammonia slip and particulate emissions when used downstream of an SCR process.

[0033] The present invention relates to a catalytic article for treating exhaust gases. Specifically, the catalytic article may be used to treat exhaust gases derived from combustion processes such as internal combustion engines (whether mobile or stationary), gas turbines for stationary, marine, or locomotive applications, and coal or oil-fired power plants. The article may also be used to treat gases from industrial processes such as refining from refinery heaters and boilers, furnaces, the chemical processing industry, coke ovens, municipal waste power plants, and incinerators. In certain embodiments, the method is used to treat exhaust gases from gas turbines or lean-burn engines. Such treatment is NO x It is performed to remove undesirable components of exhaust gases, such as particulate matter. Other species, such as CO and unburned hydrocarbons (HC), can also be treated by components of the exhaust treatment system.

[0034] Catalytic articles include wall-flow filter substrates. These are very well known in the art. A wall-flow filter has inlet channels that are open at the inlet end of the substrate and closed at the outlet end of the substrate, and the inlet channels are adjacent to outlet channels that are closed at the inlet end of the substrate and open at the outlet end of the substrate. Alternately opening and closing channels mean that, in use, exhaust gas entering through the inlet channels is forced to pass through the walls separating the channels and exit through the open outlet channels. The porosity of the walls and the provision of specific coating areas and layers ensure that the gas is treated while passing through the walls.

[0035] Typical ceramic wall-flow filter substrates are composed of refractory materials such as cordierite or silicon carbide. A common configuration is a multi-channel honeycomb structure having alternating passage ends on the inlet and outlet sides of the honeycomb structure. This configuration creates a checkerboard pattern at both ends.

[0036] The monolith material used in wall-flow filters is 2.54 cm square inches. 2 It may contain up to about 400 flow passages (or "cells") per unit, but may use much fewer. For example, a carrier may have 7 to 400 cells per square inch ("cpsi"), specifically 100 to 400 cells. Cells may have a cross-section in the shape of a rectangle, square, circle, ellipse, triangle, hexagon, or other polygon.

[0037] Wall-type substrates are generally composed of ceramic-like materials such as cordierite, alpha-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia, or zirconium silicate, or refractory metals such as stainless steel. These materials can withstand the environment faced when processing exhaust streams, particularly high temperatures. Ceramic wall-type substrates are generally formed from materials having a porosity of about 40 to 70. As used in this context, the term "porosity" is understood to be determined according to the mercury porosity measurement method in accordance with DIN 66133. According to embodiments of the present invention, the wall-type substrate has a porosity in the range of 38 to 75.

[0038] The wall-flow filter of the present invention comprises at least a first catalyst layer, a second catalyst layer, and a third catalyst layer. It is preferable that these be the only layers present in the catalyst article. Nevertheless, it should be understood that other conventional layers may be present, or that the first, second, and third layers themselves may consist of one or more sublayers having the same or different formulations. That is, the first catalyst layer may consist of two layers comprising SCR catalysts to form a single SCR catalyst formulation or to provide two layers of different SCR catalyst formulations. In the most preferred embodiment, the three catalyst layers are the only layers present and are each provided as a single applied layer.

[0039] The first catalyst layer extends from the inlet end of the substrate and comprises the first SCR composition. Preferably, the first catalyst layer extends up to 100% of the longitudinal length extending from the inlet end of the substrate to the outlet end, preferably 70 to 90% of the longitudinal length. Since a coating method for applying this composition, particularly a coating method for coating on a thin wall, typically involves immersing the substrate in a washcoat, substantially 100% coating will extend completely along the interior of the inlet channel to a plug blocking the outlet end of the channel. In the case of a coating on the wall, this can be applied by applying a strong, short vacuum to draw the washcoat into the substrate.

[0040] A preferred coating of up to 90% of the length will leave a portion of the wall at the end of the channel adjacent to the plug without any coating thereon. Accordingly, a most preferred coating of 70 to 90% of the length provides an inlet region of the inlet channel where the composition is provided, and a distal region from the inlet end where the composition is not provided. In use, the first catalyst layer will be the first catalytic element of the article that the exhaust gas to be treated comes into contact with.

[0041] In some preferred embodiments, the second catalyst layer and the third catalyst layer do not overlap and extend together for 100% of the longitudinal length extending from the discharge end to the inlet end of the substrate. These embodiments have been found to achieve excellent conversion rates while minimizing back pressure. In these embodiments, preferably, the second catalyst layer is provided within the wall of the inlet channel, and the third catalyst layer is provided within the wall of the discharge channel.

[0042] Preferably, the catalytically active SCR component of the first and / or second SCR composition comprises one or more metal exchange zeolites, and preferably consists of one or more metal exchange zeolites. This does not exclude the presence of additional non-catalytic binders or treatment aids typically used in washcoat formation. This is discussed further below.

[0043] Preferably, the first SCR composition comprises a copper-promoting zeolite, an iron-promoting zeolite, a manganese-promoting zeolite, or a combination thereof. The total amount of Cu, Mn, and Fe is preferably present in an amount of 0.1 to 5 weight percent, most preferably 1 to 3 weight percent, of the promoting zeolite. The second SCR composition may be independently selected from the same materials as those presented herein in the case of the first SCR composition.

[0044] Zeolites comprise microporous aluminosilicates having any one of the framework structures listed in the Database of Zeolite Structures published by the International Zeolite Association (IZA). Framework structures include, but are not limited to, types of CHA, FAU, BEA, MFI, and MOR. Non-limiting examples of zeolites having these structures include cabasite, sporesite, zeolite Y, ultra-stable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5. Aluminosilicate zeolites may have a silica / alumina molar ratio (SAR: defined as SiO2 / Al2O3) of at least about 5, preferably at least about 20, with a useful range of about 10 to 200.

[0045] The metal exchange zeolite is preferably a small-pore zeolite having a CHA framework structure. The zeolite is preferably exchanged with Cu and / or Mn. The zeolite is preferably copper-promoted and has a CHA framework. Preferably, copper is present in an amount of 0.1 to 5 weight%, most preferably 2 to 4 weight%, of the copper-promoted zeolite.

[0046] A second catalyst layer is provided within or on the wall of an inlet channel, extends from the inlet end of the substrate, and comprises a PGM-containing composition. That is, the second catalyst layer extends from the inlet end, just like the first catalyst layer.

[0047] When in use, the second catalyst layer will be a second catalytic element of the article that the exhaust gas to be treated comes into contact with. This is achieved by providing the second catalyst layer on the wall of the inlet channel and the first catalyst layer on the second catalyst layer, or by providing the second catalyst layer inside the wall of the inlet channel and the first catalyst layer on the wall of the inlet channel.

[0048] It is well known in the art to provide a coating “inside the wall” or “on the wall.” This is achieved by carefully adjusting the washcoat formulation to the porosity of the filter wall. Thus, a “thin” composition containing finer materials (especially supported PGMs) can penetrate the wall more easily than a “thick” composition containing coarser materials. Exemplary coatings inside the wall and on the wall are provided in the examples. Thus, by adapting the washcoat material, it can be ensured that the coating is provided as desired on the porous wall of the article.

[0049] The second catalyst layer comprises a PGM-containing composition. Suitable PGMs include Pd, Pt, and Rh. Preferably, the PGM-containing composition contains Pt, and preferably contains only PGM. It is desirable for the PGM to be provided on a carrier. Suitable carrier materials are well known in the art. Preferably, the PGM-containing composition comprises alumina as a carrier for the PGM.

[0050] Preferably, the second catalyst layer extends up to 100% of the longitudinal length extending from the inlet end to the outlet end of the substrate, preferably 25 to 90% of the longitudinal length, more preferably 35 to 80%, even more preferably 40 to 70%, and most preferably 45 to 65%. In the first catalyst layer, a preferred coating of up to 90% of the length will leave a portion of the wall at the end of the channel adjacent to the plug without any coating thereon. Thus, a preferred coating of 40 to 70% of the length provides an inlet region of the inlet channel where the composition is provided, and a distal region from the inlet end where the composition is not provided.

[0051] When in use, the second catalyst layer will be the second catalytic element of the article that the exhaust gas to be treated comes into contact with. It is preferable that the first catalyst layer be provided with at least the same length as the second catalyst layer, preferably at least 5% to 10% longer (relative to the total length of the article). This ensures that the exhaust gas comes into contact with the first catalyst layer before the second catalyst layer.

[0052] A third catalyst layer is provided within or on the wall of the discharge channel and extends from the discharge end of the substrate and comprises a second SCR composition. As mentioned above, the second SCR composition may be selected from the same materials as the first SCR composition. Preferably, the second SCR composition is a copper-promoted CHA zeolite.

[0053] The third catalyst layer extends from the discharge end of the substrate. Preferably, the third catalyst layer extends to 100% of the longitudinal length extending from the inlet end to the discharge end of the substrate, preferably 20 to 90% of the longitudinal length, more preferably 30 to 80%, even more preferably 30 to 70%, and most preferably 40 to 60%. In an embodiment without overlap with the second catalyst layer, the lengths are preferably complementary (i.e., the second layer is 40 to 70% and the third layer is 60 to 30%). In an embodiment with overlap, the third layer may be longer, such as 60 to 90% of the length. Since a coating method for applying this composition typically involves immersing the substrate in a washcoat, substantially 100% of the coating will extend completely along the interior of the discharge channel to the plug blocking the inlet end of the channel. A preferred coating of up to 90% of the length will leave a portion of the wall at the end of the channel adjacent to the plug without any coating thereon. Accordingly, a most preferred coating of 70 to 90% of the length provides an exhaust region of the exhaust channel where the composition is provided, and a distal region from the exhaust end where the composition is not provided. In use, the third catalyst layer will be the final catalytic element of the article that the exhaust gas to be treated comes into contact with.

[0054] When the catalyst composition is applied inside the wall, the washcoat can be coated into all the pores of the wall. Therefore, if both the second and third catalyst compositions are provided inside the wall, there may be substantial overlap in the locations of the catalyst compositions. Nevertheless, it is still possible to determine which composition has been applied. This is not merely because the inlet channel will contain the second composition up to the immediate entrance of the inlet, while the third composition cannot be coated up to that point, in terms of the plug blocking the inlet end of the outlet channel. Conversely, the outlet channel will contain the third composition up to the immediate entrance of the outlet, while the second composition cannot be coated up to that point, in terms of the plug blocking the outlet end of the inlet channel. Therefore, even if both the second and third compositions are provided inside the wall, there will still exist an area where only the SCR is inside the wall at the immediate outlet of the outlet channel.

[0055] In a preferred embodiment, the third catalyst composition is provided on the wall. Preferably, the second catalyst layer is provided within the wall of the inlet channel, and the third catalyst layer is provided on the wall of the outlet channel. According to another preferred embodiment, with the second catalyst layer provided within the wall of the inlet channel, the third catalyst composition is provided within the wall. In this case, if there is overlap, there is close contact between the particles of the second catalyst layer and the particles of the third catalyst layer. In some embodiments, it is preferable that the second catalyst layer and the third catalyst layer are in contact but do not overlap.

[0056] Preferably, the composition forming the first and third layers does not contain PGM components. Preferably, the composition forming the second layer does not contain SCR components. Nevertheless, it should be understood that when coating a porous wall-flow filter, there may be a small amount of leakage between the layers.

[0057] When explaining the washcoat loading amount in catalytic articles, the PGM loading amount is given in g / ft² 3 It is common to provide it in units. This is an evaluation of the metal itself within the applied layer. In contrast, the washcoat loading of SCR materials, which is generally much higher, is g / in 3 It is provided as a unit. Unlike in the case of PGM, these values ​​of the SCR material generally include all elements of the washcoat, for example, including the binder. Accordingly, the SCR composition herein includes both the zeolite component and any binder. Accordingly, it is preferable that the SCR composition be synonymous with the first and third catalyst layers.

[0058] In conventional ASC (i.e., the PGM-containing end portion of the combined SCR / ASC), g / in of the SCR composition 3 g / ft of PGM relative to the total loading of the unit 3 The ratio of the total loading amounts of the units is typically greater than 1:1, more generally greater than 5:4. The inventors found that when ASCF was prepared with a catalyst composition of the same loading amount, excessive NO x It was discovered that N2O formation occurs. When examined without being bound by theory, it was believed that exhaust gases of the new configuration are exposed to the PGM material much more. That is, in the penetrating flow ASC, exhaust gases encounter the PGM only when penetrating through a layer of catalytic material, whereas in the case of the ASCF configuration, all exhaust gases are forced to penetrate directly into the PGM-containing composition.

[0059] Accordingly, the inventors sought to solve these related problems and succeeded in optimizing the relative loading amount of the catalytic material in the layers. g / in of the first and second SCR compositions in the first and third catalyst layers 3 g / ft² in the second catalyst layer relative to the total amount of units 3The ratio of the PGM units is 1.5:8 to 5:8, preferably 2:8 to 4:8, preferably 4.5:16 to 7:16, more preferably 4.5:16 to 6:16. Preferably, the g / in of the first and second SCR compositions in the first and third catalyst layers. 3 g / ft² in the second catalyst layer relative to the total amount of units 3 The ratio of the PGM of the unit is 5:16.

[0060] Given the basic understanding of ASCs, it is surprising that this structure can operate with a three-layer configuration as disclosed herein. In particular, the SCR layer of a conventional ASC functions solely due to the amount of ammonia trapped in the SCR layer during use. After sufficient ammonia penetrates through the first and second layers to the third catalyst layer, any NO formed upon contact between the exhaust gas and the PGM of the second catalyst layer x It is surprising that SCR can be performed. Nevertheless, performance demonstrates that this occurs, and comparative examples show that in the absence of the exhaust end SCR composition, the exhaust gas produces undesirably high levels of NO x It shows that it has N2O – this is likely the result of contacting the PGM as the final layer before leaving the item.

[0061] Preferably, the weight ratio of the catalytically active composition in the first and third catalyst layers is 2:3 to 3:2, preferably about 1:1. That is, it is desirable that the first catalyst layer and the third catalyst layer be provided in similar amounts. In practice, from a manufacturing perspective, it is particularly desirable that the first catalyst layer and the third catalyst layer have substantially the same composition.

[0062] Preferably, at least two of the first, second, and third catalyst layers, preferably all three, extend to 70 to 90% of the longitudinal length. As will be understood, if all three extend to this length, there will be overlap between all three layers. Thus, in an embodiment where all three layers extend to this range of length, there is a portion of the inlet channel wall where the first or second catalyst layer is not provided (and of course, the third catalyst layer is not provided either), and a portion of the exhaust channel wall where the third catalyst layer is not provided (and of course, neither the first nor the second catalyst layer is provided either). This configuration facilitates layer formation, facilitates avoiding accumulation at plug-type ends that may occur when attempting to coat the entire channel, and also helps ensure that the exhaust gas to be treated contacts the first catalyst layer first and finally the third catalyst layer.

[0063] In an embodiment where the second and third catalyst layers do not overlap, it is preferable that the first catalyst layer extends for 70 to 90% of the longitudinal length, the second catalyst layer extends for 30 to 60% of the longitudinal length, and the third catalyst layer extends for 70 to 40% of the longitudinal length.

[0064] Compositions containing SCR and PGM may include additional components. For example, components such as fillers, binders, stabilizers, flow modifiers, and other additives. The catalyst composition includes pore-forming agents, such as graphite, cellulose, starch, polyacrylate, and polyethylene. These additional components do not necessarily catalyze the desired reaction, but instead improve the effectiveness of the catalytic material by, for example, increasing its operating temperature range, increasing the contact surface area of ​​the catalyst, increasing the adhesion of the catalyst to the substrate, etc. Generally, the only additional component is the binder. Preferably, the additional components each form a layer of less than 25 wt%, preferably less than 15 wt%, and most preferably less than 10 wt%, where the remainder is SCR or supported PGM. The particle size of the binder particles will vary depending on whether the relevant coating is applied inside the wall or on the wall. A typical alumina binder applied inside the wall has a D90 of less than 7 μm when measured by laser diffraction.

[0065] Techniques for applying the first and second layers are well known in the art and include applying a washcoat to the surface to be coated. After the layers are coated onto the article, they are generally calcined to fix the layers. Calcination is well known in the art and can be performed in air at a temperature of about 500°C.

[0066] The inventors have devised two approaches for forming a catalytic article. According to one embodiment, a method for manufacturing a catalytic article is provided, in order, by applying a washcoat to an outlet channel to form a third coating and then calcining; applying a washcoat to an inlet channel to form a second coating and then calcining; and applying a washcoat to an inlet channel to form a first coating and then calcining. There will generally be a drying step preceding each calcination step.

[0067] According to a more preferred embodiment as it involves less calcination, a method for manufacturing a catalyst article is provided in the following steps: applying a washcoat to an inlet channel to form a second coating and then calcining; applying a washcoat to an outlet channel to form a third coating and then drying; and applying a washcoat to an inlet channel to form a first coating and then calcining. There will generally be a drying step preceding each calcination step. Eliminating the calcination step reduces energy costs and process costs.

[0068] Preferably, the catalyst article includes means for electrically heating the catalyst article. Such means are well known in the art and generally rely on resistance heating to raise the operating temperature of the catalyst article in use. This approach can be used to regenerate the catalyst article on-site to remove accumulated particulate deposits, although there are associated energy costs to achieve the required temperature. Other regeneration approaches are also known, such as raising the temperature of exhaust gases through engine maintenance or hydrocarbon dosing.

[0069] According to a further embodiment, an exhaust gas treatment system comprising the catalytic article described herein is provided. Accordingly, the system implicitly comprises an initial manifold receiving exhaust gas, e.g., exhaust gas from an engine, and an outlet for discharging the treated exhaust gas into the environment. In use, the catalytic article treats ammonia sloughed off from an upstream component to produce N2, while excessive NO x It can be produced without forming and releasing N2O or generating an excessive amount.

[0070] Preferably, the exhaust gas treatment system comprises, in sequence, a catalytic soot filter (CSF) or a diesel particulate filter (DPF), means for injecting a nitrogen reducing agent, an SCR catalyst article, and the catalyst article described herein. Preferably, the system further comprises a diesel oxidation catalyst (DOC) upstream of the CSF. These components and their formulations and compositions are all well known in the art. The means for injecting the nitrogen reducing agent upstream and the SCR catalyst article are the cause of the potential ammonia slippage (and thus ASCF) and the formation of reducing agent-derived particulate matter. Since this reducing agent-derived particulate matter is generated downstream of the CSF (or DPF), there is no filter body to retain it.

[0071] Providing CSF upstream of the catalytic component (ASCF) prevents soot from accumulating on the ASCF. This is desirable because it is difficult to handle large accumulations of material due to the relatively low temperature at the system end components. This requires more energy to be concentrated to raise the temperature of the ASCF in the event of soot accumulation. In contrast, the accumulation of urea / ammonia-derived particles is relatively small, so regeneration can be performed infrequently as needed.

[0072] The nitrogen reducing agent provided by the means for injecting the nitrogen reducing agent may be an ammonia precursor selected from the group consisting of ammonia itself, hydrazine, or urea ((NH2)2CO), ammonium carbonate, ammonium carbamate, ammonium bicarbonate, and ammonium formate. Ammonia and urea are the most preferred alternatives. Preferably, the means for injecting the nitrogen reducing agent further comprises a reservoir containing urea.

[0073] Preferably, the catalyst article is the last catalyst article encountered before the exhaust gas is released into the atmosphere during use. This means that the article can suitably function as an ammonia slip catalyst while simultaneously preventing the release of urea / ammonia-derived particulate matter into the atmosphere.

[0074] According to another embodiment, a fuel combustion and exhaust treatment system comprising the engine and exhaust gas treatment system described herein is provided. Preferably, the engine is a diesel or lean-burn engine.

[0075] According to another embodiment, a vehicle comprising a fuel combustion and exhaust treatment system as described herein is provided, wherein at least the catalyst article described herein is preferably located below the floor and / or, during normal use, is preferably exposed to exhaust gas at a temperature of 200 to 450°C, preferably 270 to 350°C. The catalyst article is installed below the floor of the vehicle because it is desirable for the catalyst article to be located at the end of the exhaust system. Since this results in a problem where the temperature promotes the formation of particulate matter derived from the reducing agent but does not promote its destruction, ASCF is a solution for meeting emission standards.

[0076] According to another embodiment, an exhaust gas treatment method is provided, comprising the step of passing exhaust gas through a catalytic article described herein or an exhaust gas treatment system described herein.

[0077] The present invention will now be further described in the following drawings.

[0078] FIG. 1 shows a schematic cross-section of a portion of the catalyst article described herein.

[0079] FIG. 2 shows a schematic cross-section of a portion of the catalyst article described herein.

[0080] Figure 3 shows the configuration of the components of the exhaust gas treatment system downstream of the engine.

[0081] Figure 4 is a chart showing NH3 conversion, N2O, and NOx generation in the case of through-flow ASC compared to ASCF, with different ratios of PGM to SCR loading amounts (NH3 only - 500 ppm SCAT SV = 90 k).

[0082] Figure 5 is a chart showing NH3 conversion, N2O, and NOx generation in the case of through-flow ASC compared to ASCF with different ratios of PGM to SCR loading amounts (NOx-localized: 500 ppm NH3 and 500 ppm NO, SCAT SV=90 k).

[0083] Figure 6 shows the engine test data discussed below.

[0084] FIGS. 7a to 7c illustrate three preferred embodiments of the present invention.

[0085] FIGS. 8 to 10 show test data when the embodiments of FIGS. 7a to 7c are compared with a standard.

[0086] FIG. 1 shows a schematic portion of a catalyst article (1) as described herein. In particular, the illustrated portion is concentrated on a single inlet channel (5) and a corresponding single outlet channel (10). The inlet channel (5) is separated from the outlet channel (10) by a porous wall (15). The inlet channel (5) is open at the inlet side (20) of the catalyst article (1) and is blocked by a plug (25) at the outlet side (30) of the catalyst article (1). The outlet channel (10) is open at the outlet side (30) of the catalyst article (1) and is blocked by a plug (25) at the inlet side (20) of the catalyst article (1).

[0087] A first catalyst layer (35) is provided on a first wall surface (40) on an inlet channel (5). The first catalyst layer (35) is provided as a washcoat and comprises an SCR composition, such as a Cu-CHA washcoat composition, together with a conventional binder and a treatment aid. The first catalyst layer (35) extends from the inlet surface (20) to at least 70% of the total length (45) of the catalyst article (1).

[0088] A second catalyst layer (50) is provided within the porous wall (15). The second catalyst layer (50) is provided as a washcoat and comprises a PGM-containing composition, such as Pt supported on alumina, together with a conventional binder and processing aid. The second catalyst layer (50) extends from the inlet surface (20) to at least 70% of the total length (45) of the catalyst article (1). It is preferable that the second catalyst layer (50) be slightly shorter than the first catalyst layer (35).

[0089] A third catalyst layer (55) is provided on a second wall surface (60) on the discharge channel (10). The third catalyst layer (55) is provided as a washcoat and comprises an SCR composition, such as a Cu-CHA washcoat composition, together with a conventional binder and a treatment aid. The third catalyst layer (55) extends from the discharge surface (30) to at least 70% of the total length (45) of the catalyst article (1).

[0090] When in use, exhaust gas entering the catalytic article (1) through the inlet surface (20) passes through the inlet channel (5), through the porous wall (15), and through the exhaust channel (10) to exit the article (1). This path is indicated by a large arrow. The exhaust gas passes through the first, second, and third catalyst layers (35, 50, 55) in sequence. Ammonia is stored in the first and third catalyst layers (35, 55) until it can be used to perform an SCR reaction to decompose the NOx generated on the second catalyst layer (50). Particulate matter from the ammonia / urea is not released into the atmosphere but accumulates within the inlet channel (5). The particulate matter can be burned to reduce excessive accumulation if necessary, which may be assisted if necessary, but can be done by local resistance heating using an electric element (not shown).

[0091] FIG. 2 illustrates an alternative configuration of the first, second, and third catalyst layers (35, 50, 55) within the catalyst article (1). All reference numerals refer to the same components, and all configuration details are kept the same.

[0092] A second catalyst layer (50) is provided on the wall (40) of the inlet channel (5). A first catalyst layer (35) is provided on the second catalyst layer (50) and, because it is slightly longer, is provided overlapping a small portion of the wall (40) of the inlet channel (5). A third catalyst layer (55) is provided within the porous wall (10), but may instead be provided on the surface (60) of the outlet channel (10).

[0093] FIG. 3 illustrates an exhaust gas treatment system comprising a diesel oxidation catalyst (DOC) (70) downstream of an engine (65), followed by a catalytic soot filter (CSF) (75), followed by means for injecting a nitrogen reducing agent (80), followed by an SCR (85), and finally a catalytic article (1) as described herein, namely an ASCF. The CSF (75) may be a diesel particulate filter (DPF). It is preferable to have the CSF (75) or DPF upstream of the catalytic article (1) because it is difficult to regenerate these components and the accumulation of soot on the catalytic article (1) (prevented by the CSF (75) or DPF) would result in unacceptable back pressure. The difficulty in regenerating the catalytic article (1) is the accumulation of soot, which is exacerbated by a system shutdown location (e.g., under the bottom) where low temperatures are insufficient.

[0094] Examples

[0095] The present invention will now be described further in relation to the following non-limiting embodiments.

[0096] An exemplary catalyst article was manufactured and tested as described below.

[0097] Engine test

[0098] The embodiment of the present invention used a wall-flow filter substrate of 10.5" x 6.0". A reference filter was used that was coated with a total washcoat mass (g) identical to that on the coated filter (which varies depending on the filter as discussed below), but of 10.5" x 4.0".

[0099] SCR "Inside Wall" Coating - "Coating 1":

[0100] A slurry of spray-dried Cu (3.3 wt%) cabazer (SAR 20) was milled to a target particle size distribution characterized by D90 = 3.8 to 3.9 μm and stirred overnight. An aqueous tetraethylammonium hydroxide solution was added to the ground slurry to adjust the pH to a target of 9.9 to 10.2 and stirred for 5 minutes. Finally, a low-particle-size mixed oxide comprising Al2O3 (91.2 wt%) / La2O3 (4.8 wt%) / Nd2O3 (4.1 wt%), having a particle size distribution characterized by D90 = 3.0 to 5.0 μm, was added under high-speed stirring to reach a target of 11 wt% relative to the weight of the calcined Cu cabazer. The washcoat having the above composition was stirred overnight, and then an aqueous tetraethylammonium hydroxide solution was added to readjust the pH to 9.9 to 10.2. Stir the pH-adjusted washcoat for 30 minutes, then coat from the downstream end of a suitable DPF at 0.8 g / in based on the volume of ASCF brick. 3 Coated up to the target washcoat loading amount.

[0101] The block was dried at 110°C for 30 minutes and calcined at 500°C for 2 hours.

[0102] PGM "Inside Wall" Coating - "Coating 2":

[0103] Target 40 g / ft of succinic acid in deionized water 3 After dissolving up to, the solution was stirred for 5 minutes. To this solution, 0.5 g / ft³ of platinum(IV) nitrate was added. 3 The platinum was slowly added up to the target value, and the mixture was stirred for 5 minutes. Finally, low-particle-size alumina P0 (pre-ground to a target particle size distribution characterized by D90 = 4.8 to 5.0 μm) was added as a slurry at 0.06 g / in 3Added up to the target amount. A washcoat having the above composition was stirred for 3 hours, coated from the front of an intermediately treated DPF containing calcined SCR "coating 1" (described above), dried at 115°C for 30 minutes, and calcined at 500°C for 2 hours.

[0104] All of the above goals refer to the final loading amount based on the volume of the ASCF brick.

[0105] Coating on SCR porous walls - "Coating 3":

[0106] A slurry of spray-dried Cu (3.3 wt%) cabazer (SAR 20) was milled to a target particle size distribution characterized by D90 = 3.8 to 3.9 μm and stirred overnight. The slurry was transferred to a cooling tank, and colloidal aluminum oxide hydroxide (boehmite) was added under high-speed stirring up to a target of 18 wt% relative to the calcined weight of Cu cabazer. The mixture was stirred for 30 minutes, then a cellulose pore-forming agent (Arbocel UFC100) was added under high-speed stirring up to a target of 54 wt% relative to the calcined weight of Cu cabazer. The mixture was stirred for 30 minutes, then a cellulose thickener was added under high-speed stirring up to a target of 0.2 wt% relative to the total weight of the wet washcoat. The mixture was stirred at high speed for 30 minutes, then the washcoat was stored in a sealed container for 2 days. Then, the washcoat is stirred at high speed for 3 minutes and coated from the upstream of the intermediate-treated DPF containing calcined SCR "Coating 1" and calcined PGM "Coating 2" (described above), at 0.8 g / in based on the volume of the final catalyst. 3 The brick was coated up to the target washcoat loading amount. The brick was dried at 110°C for 45 minutes and calcined at 500°C for 2 hours.

[0107] SCAT test

[0108] The test was performed using the SCAT test. This type of test does not involve any other catalysts upstream or downstream, but under specific operating conditions—namely, “NH3-rich conditions” of 350 ppm CO / 500 ppm NH3 / 0 ppm NOx, or “NOx x In the case of “uneven conditions,” a gas composition representing 350 ppm CO / 500 ppm NH3 / 500 ppm NO - is artificially provided to the core.

[0109] All embodiments used a 1" x 5.53" wall-flow filter substrate. The space velocity was the same in all tests.

[0110] Example ASCFs are SCR washcoat (0.8 g / in²) on the wall of the inlet channel. 3 ); PGM-containing wall composition applied from the inlet side (Pt on alumina with various loading amounts); and SCR washcoat (0.8 g / in 3 It was manufactured to have ). For comparison, the through-flow filter has an SCR layer (2.4 g / in) placed on top. 3 ) and, 3 g / ft 3 A PGM-containing layer having Pt was prepared underneath. A PGM coating was applied to 50% of the back surface of the brick.

[0111] The PGM level is 1 g / ft 3 , 0.75 g / ft 3 , 0.5 g / ft 3 , and 0.25 g / ft 3 was. As a result, the SCR material (1.6 g / in²) discussed in this institution 3 The ratios with ) are given as 10:16, 7.5:16, 5:16, and 2.5:16. Here, the SCR materials are the binder of the washcoat layer and the copper exchange zeolite. These are compared with a standard ASC having a ratio of 30:24 in the examples. This represents a conventional configuration.

[0112] The results of the additional SCAT test showed an NH3 conversion rate of Pt 1 g / ft 3 , 0.75 g / ft 3 , 0.5 g / ft 3 It was similar at 0.25 g / ft 3 It shows that it was much worse at Pt 0.5 g / ft 3 In the case of, the amount of N2O generated was substantially the same as in the standard through-flow method, but in the example with a higher Pt loading amount, it was much worse.

[0113] The ASCF catalyst showed improved filtration efficiency in preliminary measurements compared to standard ASC in FT. In particular, when the ASCF catalyst was used instead of standard ASC in FT, PN10 emissions were 70 to 90% lower.

[0114] Therefore, Pt 0.5 g / ft 3 (1.6 g / in 3 Values ​​around (paired with SCR) provide a sweet spot where oxidation performance matches SCR performance, NH3 conversion is sufficient without excessive N2O, and at the same time, filtration performance treats particulate matter derived from the reducing agent. This is ideally observed at a ratio of 5:16 and near this ratio.

[0115] In Fig. 4, for the NH3 conversion, the lines at 300°C are, in order from top to bottom, Std, 1, 0.75, 0.5, and 0.25 g / ft². 3 For N2O formation, the peaks of the lines are in order from top to bottom: 1, STD, 0.75, 0.5, and 0.25 g / ft. 3 It is. In the case of NOx generation, the lines at 400℃ are 1 g, 0.75 g, 0.5 g, 0.25 g, and STD in order from top to bottom.

[0116] As shown in these embodiments, a 3-layer ASCF was developed with the goal of transitioning the ASC concept from a through-flow to a filter substrate. The 3-layer ASCF approach expands the variety of feasible coating designs compared to standard 2-layer ASCs, while also significantly reducing the emission of particulate matter. In particular, the use of a 3-layer ASCF allows for the utilization of various combinations of coatings within the walls and coatings on the walls, thereby enabling precise control of ASC activity, back pressure, and filtration efficiency.

[0117] Using engine test data, tests were conducted to demonstrate that the same benefits can be obtained under actual operating conditions. In this case, one of the ASCF or SCR / ASC bricks is located downstream of another SCR through-flow brick (in this case, VSCR). Additional information is shown in Fig. 6. Here, the standard ASCF is coated with the same mass (grams) of SCR catalyst and PGM catalyst as the standard through-flow SCR / ASC, whereas the "low-PGM" variant has only half the amount of PGM but the same amount of SCR washcoat. Steady-state (SS) engine test data were performed at three different temperatures (270, 320, and 370°C), where the low-PGM variant is significantly superior for secondary emissions while still matching the SCR / ASC standard in terms of NH3 conversion—this provides a better balance between NH3 conversion and secondary emissions for the low-PGM variant.

[0118] In each result cluster, the left column represents the conventional SCR / ASC, the middle column represents the ASCF equipped with SCR and PGM comparable to the conventional SCR / ASC, and the right column represents one with PGM at half the level of the middle column (PGM 0.5 g / ft² 3 , total SCR amount 1.6 g / in 3 )am.

[0119] Figure 6a shows that the ASCF of the present invention achieves sufficiently excellent NH3-slip control. Figure 6b shows that the reduction in N2O generation levels is improved. Figure 6c shows NO x It shows that the reduction in generation levels has improved. The SS numbers in each chart represent the test temperature under steady conditions.

[0120] FIGS. 7a to 7c use the same reference numerals as FIGS. 1 and FIG. 2 for identical component parts.

[0121] FIG. 7a is an embodiment similar to FIG. 2, but with a shorter length in which the second catalyst layer (50) extends to about 50% of the total length (45) of the catalyst article (1). The first catalyst layer extends to about 80% of the total length (45) of the catalyst article (1). In FIG. 7a, the PGM layer is coated as a porous coating on the wall in an attempt to prevent / minimize close contact with SCR catalyst particles (which are dispersed within the wall volume and then fundamentally separated from the PGM on the wall).

[0122] FIGS. 7b and 7c are embodiments in which the second catalyst layer (50) does not overlap with the third catalyst layer (55). These layers (50, 55) are both provided as a wall-in washcoat and together coat the total length (45) of the catalyst article (1). In FIG. 7b, the second catalyst layer (50) is about 25% of the total length (45), and the third catalyst layer (55) is about 75% of the total length (45). In FIG. 7c, the second catalyst layer (50) is about 50% of the total length (45), and the third catalyst layer (55) is about 50% of the total length (45).

[0123] As supported in the embodiments of FIG. 7b and FIG. 7c, avoiding overlap between these layers prevents close contact between the platinum group metal and the SCR catalyst.

[0124] FIG. 8 shows a comparison of the embodiments of FIG. 7a through 7c to a comparative example in which the second catalyst layer (50) is about 70% of the total length (45) (inside the wall) and the third catalyst layer (55) is about 80% of the total length (45) (inside the wall). Providing such overlapping inside-wall coatings means that there is an overlap of the platinum group metal and the SCR catalyst within the wall. The columns from left to right are FIG. 7c, FIG. 7b, and FIG. 7a, respectively, which were compared. FIG. 8 shows that the lowest back pressure was achieved in the case of the embodiment of FIG. 7c (62) and the embodiment of FIG. 7b (63).

[0125] Figure 9 shows the NH3 conversion at various temperatures. In the case of the embodiment of Figure 7c, the performance is consistently the highest. The embodiment of Figure 7b shows the worst performance. The columns from left to right are Figures 7c, 7b, and 7a, which were compared, respectively.

[0126] Figure 10 shows NH3, N2O, and NOx emissions at various temperatures and ANR ratios. The columns from left to right for each set of conditions are Figures 7c, 7b, and 7a, respectively, which were compared.

[0127] As used herein, the term “comprising” may be replaced with the definitions “essentially composed of” or “consisting of.” The term “comprising” is intended to imply that while the named element is essential, other elements may be added to still form a configuration within the scope of the claims. The term “essentially composed of” limits the scope of the claims to specific materials or steps, and limits them to materials or steps that do not substantially affect the basic and novel feature(s) of the claimed invention. The term “consisting of” prevents any claim of including materials other than those mentioned, with the exception of impurities ordinarily associated with said materials.

[0128] The foregoing detailed description is provided for illustrative and illustrative purposes only and is not intended to limit the scope of the appended claims. Many variations of the currently preferred embodiments exemplified herein will be apparent to those skilled in the art and fall within the scope of the appended claims and their equivalents.

[0129] To avoid doubt, the full contents of all documents recognized by this institution are incorporated herein by reference.

Claims

Claim 1 A catalytic article for exhaust gas treatment comprises a wall-flow filter substrate having inlet channels that are open at an inlet end of the substrate and closed at an outlet end of the substrate, wherein the inlet channels are adjacent to outlet channels that are closed at an inlet end of the substrate and open at an outlet end of the substrate, and the wall-flow filter comprises at least a first catalyst layer, a second catalyst layer, and a third catalyst layer, wherein (i) the first catalyst layer extends from an inlet end of the substrate and comprises a first SCR composition; and (ii) the second catalyst layer is provided in or on the walls of the inlet channels and extends from an inlet end of the substrate and comprises a PGM-containing composition, wherein, where the second catalyst layer is provided on the walls of the inlet channels, the first catalyst layer is provided on the second catalyst layer, and where the second catalyst layer is provided in the walls of the inlet channels, the first catalyst layer is provided on the walls of the inlet channels; (iii) The third catalyst layer is provided in or on the walls of the discharge channels and extends from the discharge end of the substrate and comprises a second SCR composition; and g / in of the first and second SCR compositions in the first and third catalyst layers 3 g / ft² of the second catalyst layer relative to the total amount of units 3 A catalyst article for exhaust gas treatment, wherein the ratio of the above PGM of the unit is 1.5:8 to 5:

8. Claim 2 A catalyst article for exhaust gas treatment according to claim 1, wherein the second catalyst layer is provided within the walls of the inlet channels and / or the third catalyst layer is provided on the walls of the outlet channels. Claim 3 An exhaust gas treatment catalyst article according to claim 1, wherein (i) the first catalyst layer extends for up to 100% of the longitudinal length extending from the inlet end to the outlet end of the substrate, or for 70 to 90% of the longitudinal length; and / or (ii) the second catalyst layer extends for up to 100% of the longitudinal length extending from the inlet end to the outlet end of the substrate, or for 25 to 90% of the longitudinal length, or for 40 to 70% of the longitudinal length; and / or (iii) the third catalyst layer extends for up to 100% of the longitudinal length extending from the outlet end to the inlet end of the substrate, or for 20 to 90% of the longitudinal length, or for 30 to 60% of the longitudinal length, or for 70 to 90% of the longitudinal length. Claim 4 A catalyst article for exhaust gas treatment according to claim 3, wherein at least two of the first, second, and third catalyst layers extend to 70 to 90% of the longitudinal length. Claim 5 A catalyst article for exhaust gas treatment according to claim 1, wherein the second catalyst layer and the third catalyst layer do not overlap and extend together for 100% of the longitudinal length extending from the discharge end to the inlet end of the substrate, and the second catalyst layer is provided within the walls of the inlet channels and the third catalyst layer is provided within the walls of the discharge channels. Claim 6 In claim 1, the g / in of the first and second SCR compositions in the first and third catalyst layers. 3 g / ft² of the second catalyst layer relative to the total amount of units 3 A catalyst article for exhaust gas treatment, wherein the ratio of the above PGM of the unit is 5:

16. Claim 7 In claim 1, the above PGM-containing composition is a catalyst article for exhaust gas treatment containing Pt. Claim 8 A catalyst article for exhaust gas treatment according to claim 1, wherein the PGM-containing composition comprises alumina as a carrier for the PGM. Claim 9 A catalyst article for exhaust gas treatment according to claim 1, wherein the catalytically active SCR component of the first and / or second SCR composition comprises one or more metal exchange zeolites. Claim 10 In claim 9, the metal exchange zeolite is a small-pore zeolite having a CHA framework structure, and the zeolite is a catalyst article for exhaust gas treatment that is exchanged with Cu and / or Mn. Claim 11 A catalyst article for exhaust gas treatment according to claim 1, wherein the weight ratio of the first SCR composition and the second SCR composition in the first and third catalyst layers is 2:3 to 3:

2. Claim 12 A catalyst article for exhaust gas treatment according to claim 1, further comprising means for electrically heating the catalyst article. Claim 13 An exhaust gas treatment system comprising a catalytic article according to paragraph 1. Claim 14 An exhaust gas treatment system according to claim 13, comprising a catalytic soot filter (CSF), means for injecting a nitrogen reducing agent, an SCR catalyst article, and a catalyst article according to claim 1 in this order. Claim 15 A fuel combustion and exhaust treatment system including an exhaust gas treatment system and an engine according to paragraph 13 or 14. Claim 16 A vehicle comprising a fuel combustion and exhaust treatment system according to claim 15, wherein at least a catalytic article according to claim 1 is located below the floor and / or encounters exhaust gas at a temperature of 270 to 350°C during normal use. Claim 17 A method for treating exhaust gas, comprising the step of passing exhaust gas through a catalytic article according to claim 1.

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