Ammonia loss catalyst filter

Abstract

A catalytic wall flow filter for treating exhaust gases is disclosed. The catalytic wall flow filter includes at least a first catalytic layer, a second catalytic layer, and a third catalytic layer: the first catalytic layer extends from the inlet end of the substrate and includes a first SCR composition; a second catalyst layer disposed within or on a wall of the inlet channel extending from the inlet end of the substrate and comprising a PGM-containing composition; a third catalyst layer is disposed within or on a wall of the outlet channel extending from the outlet end of the substrate and includes a second SCR composition.

Description

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

[0002] The exhaust gases generated in lean burn engines and diesel engines are typically oxidizing. In a process known as selective catalytic reduction (SCR), a catalyst and a reducing agent are required to selectively reduce NOx, which selective catalytic reduction converts NO x to elemental nitrogen (N2) and water. In the SCR process, a gaseous reducing agent (usually anhydrous ammonia, aqueous ammonia, or urea) is added to the exhaust gas stream before the exhaust gas contacts the catalyst. The reducing agent is adsorbed onto the catalyst and NO x is reduced as the gas passes through or over the catalytic substrate. In order to maximize the conversion of NO x , it is generally necessary to add more than a stoichiometric amount of ammonia to the gas stream. However, releasing excess ammonia into the atmosphere is harmful to human health and the environment. In addition, ammonia is caustic, especially in its aqueous form. Condensation of ammonia and water in the exhaust pipe line region downstream of the exhaust gas catalyst can result in a corrosive mixture that can damage the exhaust system. Therefore, the release of ammonia in the exhaust gas should be eliminated.

[0003] Even the best SCR catalysts will not achieve maximum NO x reduction in a system with a non-uniform NH3 distribution. Significant variations in loading, exhaust gas flow rate, and NO x concentration make it difficult to deliver NH3 to the catalyst at the 1:1 ammonia:NO x ratio (ANR) required by the reaction stoichiometry. A non-uniform NH3 distribution can result in incomplete NO x conversion in cases of low local ANR and ammonia slip in cases of high ANR.

[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 remove ammonia from the exhaust gas by converting it to nitrogen. Ammonia slip catalysts are well known in the art. The purpose of the ammonia slip catalyst is to treat any ammonia passing through the upstream SCR catalyst.

[0005] To overcome the difficulties of achieving the ideal stoichiometry, ASC technology combines oxidation catalyst and SCR catalyst functions on a flow through (FT) substrate to improve NO xReduce while maintaining low NH3 slip. The ASC allows the upstream SCR to operate continuously at a higher ANR, thereby compensating for the non-uniform NH3 distribution and promoting NO x conversion (on the upstream SCR), while maintaining low NH3 slip.

[0006] In the ASC, the oxidation catalyst and the SCR catalyst can be coated on the substrate according to different design strategies. The most common one is the so-called "double-layer ASC" design. The double-layer ASC design is based on the sequential coating of two layers (PGM layer and SCR layer) on the wall of the flow channel. The functional ASC design will convert only a part of the available ammonia in the exhaust gas in the oxidation layer. Then, the remaining ammonia fraction will be used as a reducing agent in the SCR layer, ideally allowing the complete conversion of ammonia into water, elemental nitrogen and as little N2O and NO as possible x 。

[0007] A typical ASC is described in WO2016205509. This document discloses an ASC that comprises a combination of platinum on a carrier with low ammonia storage and a first SCR catalyst. The preferred combination is a double layer having a top layer comprising the first SCR catalyst and a bottom layer comprising platinum on a carrier with low ammonia storage. In use, some excess ammonia can be stored in the upper SCR catalyst layer. Some of this excess ammonia can pass through the upper layer to the Pt where it can be oxidized to NO x 。Then NO x returns to the SCR layer where it is treated with the stored ammonia to provide N2. In this way, the excess slip ammonia is stored and utilized rather than being emitted into the atmosphere.

[0008] Another configuration of the ASC is described in US20150037233.

[0009] Particulate emissions are a well-known problem in diesel engine exhaust gas treatment systems. It is known to treat these emissions by using filters. Known types of filters include diesel particulate filters (DPF) and catalytic soot filters (CSF). These filters capture soot from the exhaust gas and can be regenerated by raising the exhaust gas temperature to burn off the accumulated soot. A conventional substrate for DPF or CSF is the so-called wall-flow filter.

[0010] EP2483537 discloses a four-way catalyst for diesel engine exhaust gas. As the name implies, all four major emissions in the exhaust gas - CO, HC, NO x and soot - are removed in a single component.

[0011] EP2567081 discloses a catalytic article for treating an exhaust gas stream containing particulate matter, hydrocarbons, CO, and ammonia. In a first embodiment of the present disclosure, the article comprises: a substrate having an inlet end and an outlet end defining an axial length; a first catalyst coating containing a platinum group metal, the first catalyst coating extending from the outlet end towards the inlet end less than the entire axial length of the substrate; and a second catalyst coating containing a catalyst for selective catalytic reduction (SCR) of nitrogen oxides, the second catalyst coating extending from the inlet end towards the outlet end less than the entire axial length of the substrate and overlapping a portion of the first catalyst coating.

[0012] EP3277411 and EP3277403 disclose multi-zone catalyst articles, methods of making multi-zone catalyst articles, and methods of controlling emissions in a diesel engine exhaust gas stream using a multi-zone catalyst article, wherein the emissions treatment systems of various embodiments effectively treat diesel engine exhaust gas with a single multi-zone catalyst article.

[0013] EP3357558 discloses a catalyst for purifying diesel engine exhaust gas, the catalyst having several material zones.

[0014] As emission standards become increasingly stringent, it becomes increasingly important to ensure that the emissions output of the exhaust system addresses issues related to particulate emissions and substances such as NO x and NH3.

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

[0016] According to a first aspect, there is provided a catalyst article for exhaust gas treatment, the catalyst article comprising:

[0017] 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, the inlet channels being adjacent to outlet channels that are closed at the inlet end of the substrate and open at an outlet end of the substrate, the wall-flow filter

[0018] comprising at least a first catalytic layer, a second catalytic layer, and a third catalytic layer, wherein:

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

[0020] (ii) The second catalytic layer is disposed within or on the walls of the inlet channels extending from the inlet end of the substrate and contains a PGM-containing composition, wherein:

[0021] When the second catalytic layer is disposed on the wall of the inlet passage, the first catalytic layer is disposed on the second catalytic layer, and

[0022] when the second catalytic layer is disposed within the wall of the inlet passage, the first catalytic layer is disposed on the wall of the inlet passage; and

[0023] (iii) A third catalytic layer is disposed within or on the wall of an outlet passage extending from the outlet end of the substrate and comprises a second SCR composition;

[0024] wherein the ratio of the PGM in the second catalytic layer in g / ft 3 to the total amount of the first SCR composition and the second SCR composition in the first catalytic layer and the third catalytic layer in g / in 3 is from 1.5:8 to 5:8, preferably from 2:8 to 4:8, and more preferably from 2:8 to 3:8.

[0025] The present disclosure will now be further described. In the following paragraphs, different aspects / embodiments of the present disclosure are defined in more detail. Unless there is an express and contrary indication, each aspect / embodiment so defined can be combined with any other aspect / embodiment or aspects / embodiments. In particular, any feature indicated as being preferred or advantageous can be combined with any other one or more features indicated as being preferred or advantageous. It is contemplated that features disclosed with respect to the product can be combined with those disclosed with respect to the method, and vice versa.

[0026] Hereinafter, the term "ammonia slip catalyst filter" or "ASCF" is used as a shorthand for the catalyst article structure described herein.

[0027] It has recently been observed that injecting a reducing agent (especially urea / ammonia) into an exhaust gas stream can result in the formation of certain agglomerated compounds and ammonium salts. These are substances formed by the reaction and polymerization of the reducing agent before the reducing agent can participate in the SCR reaction. The polymerized material is then released into the atmosphere in the form of additional fine particulate matter, which violates strict emission requirements.

[0028] A discussion of these polymerized particulate emissions can be found in SAE 2017-01-0915. It is explained here that depending on the urea doser, decomposition reaction tube (DRT) design, and operating conditions, incomplete decomposition of the injected urea can lead to the formation of solid urea deposits in the diesel aftertreatment system. The deposits formed may cause an increase in engine back pressure and NO xProcessing performance degradation. The formed urea deposits can be further transformed into chemically more stable substances when exposed to hot exhaust gases, so understanding this transformation process is crucial. The experimental results of the authors show that: 1) below the urea melting temperature (130 °C), the formed urea deposits are still mainly urea; 2) in the temperature range of 130 °C - 190 °C, urea is transformed into a combination of urea, biuret, and CYA; and 3) above the biuret melting temperature (190 °C), CYA with some characteristics of melamine amide is mainly formed. When exposed to temperatures above 200 °C, urea undergoes rapid chemical transformation through urea decomposition, biuret formation, and subsequent biuret decomposition, and is transformed into CYA within a short time.

[0029] Therefore, the polymerization of urea and ammonia components under hot exhaust gas conditions can lead to the formation of polymeric particulate matter, and this can have a certain thermal stability. This particulate matter is usually very fine, but it is precisely this fine material that is now subject to increasingly strict regulations. In addition, since the formation of particulate matter can only occur after the reducing agent is quantitatively added to the exhaust gas treatment system, it usually forms after any conventional particulate filter (DPF or CSF) in the system and in a lower temperature environment (i.e., underfloor configuration), and the conventional regeneration of such filters in this environment is difficult.

[0030] The present inventors have now found that these problems can be solved by providing a catalyst article as described herein. In particular, the article is capable of providing ASC performance comparable to that of a standard flow-through monolith while reducing or avoiding particulate emissions. In addition, the present inventors have found that in order to match the N2O and NO x performance of a standard flow-through ASC, it is possible and actually desirable to use a reduced amount of PGM. This can save costs and optimize performance.

[0031] It should be noted that the ASC is usually provided at the rear of the SCR catalyst article. That is, the flow-through monolith can be provided with a PGM layer on the outlet surface portion and an SCR layer along the entire length of the monolith. In other embodiments, the SCR and double-layer ASC can be provided on separate monoliths but arranged immediately in sequence. This performance comparison is only carried out for the ASC portion (i.e., not including the upstream only SCR portion of such a combined monolith). In use, the ASCF disclosed herein will generally be located before a separate SCR monolith as described below.

[0032] The present invention relates to catalyst articles. A catalyst article is a structure having catalytic properties as described herein. The catalytic properties are derived from materials contained within or coated onto the structure. Articles as defined herein include both coated catalytic substrates as described herein and treated and canned ASCF units suitable for installation in motor vehicles. The catalyst article provides a catalyst that is effective in reducing ammonia slip and particulate emissions when used downstream of an SCR process.

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

[0034] The catalyst article includes a wall flow filter substrate. These components are well known in the art. The 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 these 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. The alternately open and closed channels mean that, in use, the exhaust gas entering the inlet channels is forced to pass through the walls separating the channels to exit via the open outlet channels. The porosity of the walls and the arrangement of specific coated areas and layers ensure that the gas is treated as it passes 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, and the ends of the alternately channeled sides on the inlet and outlet sides of the honeycomb structure are blocked. This configuration forms a checkerboard pattern at both ends.

[0036] The monolithic substrate for the wall flow filter can contain up to about 400 flow channels (or "cells") per square inch ((2.54 cm) 2 ) cross-section, although far fewer channels can be used. For example, the carrier can have 7 cells per square inch to 400 cells per square inch ("cpsi"), particularly 100 cpsi to 400 cpsi. The cells can have the following cross-sections: rectangular, square, circular, oval, triangular, hexagonal, or having other polygonal shapes.

[0037] A wall-flow substrate is typically composed of a ceramic-like material such as cordierite, α-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or zirconium silicate, or is composed of a refractory metal such as stainless steel. Such materials are capable of withstanding the environment encountered when treating an exhaust gas stream, particularly high temperatures. A ceramic wall-flow substrate is typically formed from a material having a porosity of about 40 to 70. As used herein, the term "porosity" should be understood to be determined according to the mercury porosimetry method of DIN 66133. According to an embodiment of the present invention, the wall-flow substrate particularly has a porosity in the range of 38 to 75.

[0038] The wall-flow filter of the present invention includes at least a first catalytic layer, a second catalytic layer, and a third catalytic layer. Preferably, these are the only layers in the catalyst article. However, it should be understood that other conventional layers may be present, or the first, second, and third layers themselves may be composed of one or more sub-layers having the same or different formulations. That is, the first catalytic layer may be composed of two layers containing an SCR catalyst, or a single SCR catalyst formulation may be constructed, or two different SCR catalyst formulations may be provided. In the most preferred embodiment, the three catalytic layers are the only layers and are each provided as a separately applied layer.

[0039] The first catalytic layer extends from the inlet end of the substrate and contains a first SCR composition. Preferably, the first catalytic layer extends up to 100% of the longitudinal length of the substrate from the inlet end to the outlet end, preferably 70% to 90% of the longitudinal length. Since the coating method for applying such a composition (particularly for thin inner wall coatings) typically involves dipping the substrate into a washcoat, substantially 100% of the coating will extend completely along the interior of the inlet channels until the plugs that block the outlet ends of the channels. For wall coatings, the washcoat can be applied by pulling it into the substrate by applying a strong and short vacuum.

[0040] A preferred coating that occupies up to 90% of the length will leave a portion of the wall at the channel end adjacent to the plug without any coating. Thus, a most preferred coating that occupies 70% to 90% of the length provides an inlet region of the inlet channels provided with the composition and a region free of the composition away from the inlet end. In use, the first catalytic layer will be the first catalytic element of the article that contacts the exhaust gas to be treated.

[0041] In some preferred embodiments, the second catalytic layer and the third catalytic layer do not overlap and together extend 100% of the longitudinal length of the substrate from the outlet end to the inlet end. It has been found that these embodiments achieve good conversion while minimizing back pressure. In these embodiments, preferably, the second catalytic layer is disposed within the walls of the inlet channels, and the third catalytic layer is disposed within the walls of the outlet channels.

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

[0043] Preferably, the first SCR composition comprises a copper-promoted zeolite, an iron-promoted zeolite, a manganese-promoted zeolite, or a combination thereof. The total amount of Cu, Mn, and Fe is preferably present in an amount of 0.1 wt% to 5 wt%, most preferably 1 wt% to 3 wt%, based on the weight of the promoted zeolite. The second SCR composition can independently be selected from the same materials listed herein for the first SCR composition.

[0044] The zeolite is a microporous aluminosilicate having any of the framework structures listed in the Zeolite Structure Database published by the International Zeolite Association (LZA). The framework structures include, but are not limited to, those of the CHA, FAU, BEA, MFI, MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5. The aluminosilicate zeolite can 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] Preferably, the metal-exchanged zeolite is a small-pore zeolite, preferably having a CHA framework structure. The zeolite is preferably exchanged with Cu and / or Mn. Preferably, the zeolite is copper-promoted and has a CHA framework. Preferably, copper is present in an amount of 0.1 wt% to 5 wt%, most preferably 2 wt% to 4 wt%, based on the weight of the copper-promoted zeolite.

[0046] The second catalytic layer is disposed within or on the walls of the inlet channels extending from the inlet end of the substrate and comprises a PGM-containing composition. That is, like the first catalytic layer, the second catalytic layer extends from the inlet end.

[0047] In use, the second catalytic layer will be the second catalytic element of the article in contact with the exhaust gas to be treated. This is achieved by providing the second catalytic layer on the walls of the inlet channels and the first catalytic layer on the second catalytic layer, or by providing the second catalytic layer within the walls of the inlet channels and the first catalytic layer on the walls of the inlet channels.

[0048] Providing a coating “within the wall” or “on the wall” is well known in the art. This is achieved by carefully adjusting the carrier coating formulation to match the porosity of the filter wall. Thus, a “thinner” composition with finer materials (especially supported PGM) can penetrate into the wall more easily than a “thicker” composition containing coarser materials. Exemplary within-wall and on-wall coatings are provided in the examples. Thus, by adjusting the carrier coating, it is ensured that the coating is provided within the porous wall of the article as required.

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

[0050] Preferably, the second catalytic layer extends for at most 100% of the longitudinal length of the substrate extending from the inlet end to the outlet end, preferably 25% to 90% of the longitudinal length, more preferably 35% to 80%, more preferably 40% to 70%, and most preferably 45% to 65%. For the first catalytic layer, a preferred coating that occupies at most 90% of the length will leave a portion of the wall at the channel end adjacent to the plug without any coating. Thus, a preferred coating that occupies 40% to 70% of the length provides an inlet region of the inlet channel with the composition and a region without the composition away from the inlet end.

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

[0052] The third catalytic layer is provided within or on the wall of the outlet channel extending from the outlet end of the substrate and comprises a second SCR composition. As described above, the second SCR composition can 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 catalytic layer extends from the outlet end of the substrate. Preferably, the third catalytic layer extends up to 100% of the longitudinal length of the substrate from the outlet end to the inlet end, preferably 20% to 90% of the longitudinal length, more preferably 30% to 80%, preferably 30% to 70%, and most preferably 40% to 60%. In embodiments where there is no overlap with the second catalytic layer, preferably the lengths are complementary (i.e., the second layer is 40% to 70% and the third layer is 60% to 30%). In embodiments with overlap, the third layer can be longer, such as 60% to 90% of the length. Since the coating method of applying such a composition typically involves dipping the substrate into the washcoat, substantially 100% of the coating will extend completely along the interior of the outlet channel until the plug blocking the inlet end of the channel. A preferred coating that is up to 90% of the length will leave a portion of the wall at the channel end adjacent to the plug without any coating. Thus, the most preferred coating that is 70% to 90% of the length provides an outlet region of the outlet channel with the composition and a region without the composition away from the outlet end. In use, the third catalytic layer will be the last catalytic element of the article in contact with the exhaust gas to be treated.

[0054] When applying the in-wall catalyst composition, the washcoat can be coated into all the pores of the wall. Thus, if both the second and third catalyst compositions are provided in the wall, there can be a significant overlap in the positions of the catalyst compositions. Nevertheless, it is still possible to determine from which side the composition has been applied. This is not only because the inlet channel will include the second composition up to the inlet mouth, and considering that the plug blocks the inlet end of the outlet channel, the third composition cannot be coated so far. Conversely, the outlet channel will include the third composition up to the outlet mouth, and considering that the plug blocks the outlet end of the inlet channel, the second composition cannot be coated so far. Thus, even when both the second and third compositions are provided in the wall, there will still be an in-wall region with only SCR at the outlet of the outlet channel.

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

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

[0057] When describing the washcoat loading in a catalyst article, the PGM loading is typically provided in g / ft 3 terms. This is an assessment of the metal itself in the applied layer. In contrast, the washcoat loading of SCR materials is typically much higher and is given in g / in 3 terms. Unlike PGM, such values for SCR materials typically include all elements of the washcoat, including, for example, binders. Thus, the SCR compositions herein include both the zeolite component and any binder. Preferably, the SCR composition is thus synonymous with the first and third catalytic layers.

[0058] In a conventional ASC (i.e., the PGM-containing end portion of a combined SCR / ASC), the ratio of the total PGM loading in g / ft 3 terms to the total SCR composition loading in g / in 3 terms is generally higher than 1:1, and more generally higher than 5:4. The inventors have found that when they formulated an ASCF with catalytic compositions of the same loading, there was an excessive formation of NO x and N2O. Without wishing to be bound by theory, we believe that the extent of exposure of the exhaust gas to the PGM material in the new configuration is much greater. That is, in a flow-through ASC, the exhaust gas only encounters the PGM as they pass through the catalyst material layer, but providing an ASCF configuration forces all of the exhaust gas directly through the PGM-containing composition.

[0059] Accordingly, the inventors sought to address these issues and achieved an optimized relative loading of the catalyst material in each layer. The ratio of the PGM in the second catalytic layer in g / ft 3 terms to the total amount of the first and second SCR compositions in the first and third catalytic layers in g / in 3 terms is from 1.5:8 to 5:8, preferably 2:8 to 4:8, preferably 4.5:16 to 7:16, preferably 4.5:16 to 6:16. Preferably, the ratio of the PGM in the second catalytic layer in g / ft 3 terms to the total amount of the first and second SCR compositions in the first and third catalytic layers in g / in 3 terms is about 5:16.

[0060] Given the basic understanding of an ASC, it is surprising that this structure can also function in a three-layer configuration as disclosed herein. In particular, the SCR layer of a conventional ASC only functions during use due to the amount of ammonia trapped in the SCR layer. Surprisingly, sufficient ammonia can permeate through the first and second layers to reach the third catalytic layer and then react with any NO xPerform SCR. Nevertheless, the performance indicates that this does occur, and the comparative examples demonstrate that in the absence of the exit-end SCR composition, the exhaust gas has an undesirably high level of NO x and N2O - presumably as a result of contacting the PGM as the last layer before exiting the article.

[0061] Preferably, the weight ratio of the catalytically active components in the first catalytic layer and the third catalytic layer is from 2:3 to 3:2, and preferably about 1:1. That is, it is preferred to provide the first catalytic layer and the third catalytic layer in similar amounts. In fact, from a manufacturing perspective, it is particularly preferred that the first catalytic layer and the third catalytic layer also have substantially the same composition.

[0062] Preferably, at least two of the first catalytic layer, the second catalytic layer, and the third catalytic layer, preferably all three catalytic layers, extend 70% to 90% of the longitudinal length. It will be appreciated that when all three layers extend to such a length, there will be an overlap between all three layers. In embodiments where all three layers extend to this length range, there is thus a portion of the inlet channel wall that is not provided with the first catalytic layer or the second catalytic layer (and of course not the third catalytic layer) and a portion of the outlet channel wall that is not provided with the third catalytic layer (and of course not the first catalytic layer or the second catalytic layer). This configuration facilitates the formation of the layers, avoids accumulation at the blocked ends that may occur when attempting full-channel coating, and also helps to ensure that the gas to be treated first contacts the first catalytic layer and finally contacts the third catalytic layer.

[0063] In embodiments where the second catalytic layer and the third catalytic layer do not overlap, preferably the first catalytic layer extends 70% to 90% of the longitudinal length, the second catalytic layer extends 30% to 60% of the longitudinal length, and the third catalytic layer extends 70% to 40% of the longitudinal length.

[0064] The SCR- and PGM-containing composition may comprise additional components. For example, components such as fillers, binders, stabilizers, rheology modifiers, and other additives. In certain embodiments, the washcoat comprises a pore former, such as graphite, cellulose, starch, polyacrylates, and polyethylene, among others. These additional components do not necessarily catalyze the desired reaction, but rather improve the effectiveness of the catalytic material, for example, by increasing its operating temperature range, increasing the contact surface area of the catalyst, increasing the adhesion of the catalyst to the substrate, etc. Typically, the only additional component will be the binder. Preferably, the additional components form less than 25 wt%, preferably less than 15 wt%, and most preferably less than 10 wt% of the layer, with the balance being SCR or supported PGM, respectively. The particle size of the binder particles will vary depending on whether the relevant coating is an in-wall coating or an on-wall coating. By laser diffraction measurement, a typical alumina binder for in-wall applications has a D90 of less than 7 μm.

[0065] The techniques for applying the first and second layers are well known in the art and include applying a carrier coating to the surface to be coated. After the layers are applied to the article, they are typically calcined to fix the layers. Calcination is well known in the art and can be carried out in air at a temperature of about 500 °C.

[0066] The present inventors envision two methods for forming the catalyst article. According to one aspect, a method for manufacturing a catalyst article in the following steps is provided so that: a carrier coating is applied to the outlet channels to form a third coating and then calcined; a carrier coating is applied to the inlet channels to form a second coating and then calcined; a carrier coating is applied to the inlet channels to form a first coating and then calcined. In each calcination step, there is typically a preceding drying step.

[0067] According to a more preferred embodiment, since it involves fewer calcination steps, a method for manufacturing a catalyst article in the following steps is provided so that: a carrier coating is applied to the inlet channels to form a second coating and then calcined; a carrier coating is applied to the outlet channels to form a third coating and then dried; a carrier coating is applied to the inlet channels to form a first coating and then calcined. In each calcination step, there is typically a preceding drying step. Avoiding the calcination step reduces the energy cost and process cost.

[0068] Preferably, the catalyst article includes means for electrically heating the catalyst article. Such means are well known in the art and typically rely on resistive heating to increase the operating temperature of the catalyst article in use. The method can be used for in-situ regeneration of the catalyst article to remove accumulated particulate deposits, although there is an associated energy cost to reach the desired temperature. Other regeneration methods are known, such as raising the temperature of the exhaust gas by engine management or hydrocarbon metering.

[0069] According to another aspect, an exhaust gas treatment system is provided that includes the catalyst article described herein. Thus, the system implicitly includes an inlet manifold for receiving exhaust gas, for example from an engine, and an outlet for discharging the treated exhaust gas to the environment. In use, the catalyst article is capable of treating any ammonia leaking from upstream components to produce N2 without forming and releasing excessive amounts of NO x or producing excessive amounts of N2O.

[0070] Preferably, the exhaust gas treatment system sequentially includes a catalytic soot filter (CSF) or a diesel particulate filter (DPF), a device for injecting a nitrogen-containing reducing agent, an SCR catalyst article, and the catalyst article described herein. Preferably, the system further includes a diesel oxidation catalyst (DOC) upstream of the CSF. All of these components, as well as their formulations and compositions, are well known in the art. The upstream devices for injecting the nitrogen-containing reducing agent and the SCR catalyst article are the cause of potential ammonia leakage (and thus ASCF) and particulate matter formation from the reducing agent. Since this particulate matter from the reducing agent is generated downstream of the CSF (or DPF), no other filter body can retain it.

[0071] Providing the CSF upstream of the catalyst article (ASCF) prevents soot accumulation on the ASCF. This is desirable because the accumulation of a large amount of material in the end components of the system is difficult to handle due to the relatively low temperature. This makes it consume more energy to raise the temperature of the ASCF because soot accumulation will occur in this way. In contrast, the accumulation of urea / ammonia-derived particles is relatively low, enabling regeneration to be carried out only occasionally as needed.

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

[0073] Preferably, the catalyst article is, in use, the last catalyst article that the exhaust gas encounters before being discharged into the atmosphere. This means that the article can be suitably used as an ammonia slip catalyst and at the same time prevent the release of particulate matter derived from urea / ammonia into the atmosphere.

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

[0075] According to another aspect, there is provided a vehicle including the fuel combustion and exhaust gas treatment system described herein, preferably wherein at least the catalyst article described herein is located in an under-chassis position and / or encounters exhaust gas at a temperature of 200 °C to 450 °C, preferably 270 °C to 350 °C, during normal use. Since the catalyst article is preferably at the end of the exhaust system, the article is provided in an under-chassis position. This poses a challenge because the temperature here promotes the formation rather than the destruction of particulate matter derived from the reducing agent, and thus the ASCF is the solution to meet the emission standards.

[0076] According to another aspect, a method of treating exhaust gas is provided that includes passing the exhaust gas through the catalyst article described herein or the exhaust gas treatment system described herein.

[0077] The present invention will now be further described in conjunction with the following figures. Wherein:

[0078] Figure 1 A schematic cross-section of a portion of the catalyst article described herein is shown.

[0079] Figure 2 A schematic cross-section of a portion of the catalyst article described herein is shown.

[0080] Figure 3 A configuration of components of an exhaust gas treatment system downstream of an engine is shown.

[0081] Figure 4 A graph showing NH3 conversion, N2O, and NOx production of a comparative flow-through ASC and ASCF at different PGM:SCR loading ratios (only NH3 - 500 ppm SCAT SV = 90k).

[0082] Figure 5 A graph showing NH3 conversion, N2O, and NOx production of a comparative flow-through ASC and ASCF at different PGM:SCR loading ratios (NOx focus:

[0083] 500 ppm NH3 and 500 ppm NO, SCAT SV = 90k).

[0084] Figure 6 shows engine test data as described below.

[0085] Figures 7A to 7C Three preferred embodiments of the present invention are shown.

[0086] Figures 8 to 10 Shows when Figures 7A to 7C The test data when the embodiment is compared with a standard.

[0087] Figure 1 A schematic portion of the catalyst article 1 as described herein is shown. In particular, the portion shown focuses 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 opens at the inlet face 20 of the catalyst article 1 and is plugged with a plug 25 at the outlet face 30 of the catalyst article 1. The outlet channel 10 opens at the outlet face 30 of the catalyst article 1 and is plugged with a plug 25 at the inlet face 20 of the catalyst article 1.

[0088] A first catalytic layer 35 is provided on a first wall surface 40 of the inlet passage 5. The first catalytic layer 35 is provided as a washcoat and contains an SCR composition such as a Cu-CHA washcoat composition, as well as conventional binders and processing aids. The first catalytic layer 35 extends from the inlet face 20 for at least 70% of the total length 45 of the catalyst article 1.

[0089] A second catalytic layer 50 is provided in the porous wall 15. The second catalytic layer 50 is provided as a washcoat and contains a PGM-containing composition such as Pt supported on alumina, as well as conventional binders and processing aids. The second catalytic layer 50 extends from the inlet face 20 for at least 70% of the total length 45 of the catalyst article 1. The second catalytic layer 50 is preferably slightly shorter than the first catalytic layer 35.

[0090] A third catalytic layer 55 is provided on a second wall surface 60 of the outlet passage 10. The third catalytic layer 55 is provided as a washcoat and contains an SCR composition such as a Cu-CHA washcoat composition, as well as conventional binders and processing aids. The third catalytic layer 55 extends from the outlet face 30 for at least 70% of the total length 45 of the catalyst article 1.

[0091] In use, the exhaust gas entering the catalyst article 1 through the inlet face 20 enters the inlet passage 5, passes through the porous wall 15, enters the outlet passage 10 and exits the article 1. This route is shown by the large arrows. The gas passes successively through the first catalytic layer, the second catalytic layer and the third catalytic layer (35, 50, 55). Ammonia is stored on the first catalytic layer and the third catalytic layer (35, 55) until it is available for the SCR reaction to decompose NO generated on the second catalytic layer 50. x Particulate matter from ammonia / urea accumulates in the inlet passage 5 rather than being released into the atmosphere. If necessary, the particulate matter can be combusted to reduce excessive accumulation, and if necessary, this can be assisted, but local resistance heating is carried out using electrical components (not shown).

[0092] Figure 2 An alternative configuration of the first catalytic layer, the second catalytic layer and the third catalytic layer (35, 50, 55) in the catalyst article 1 is shown. All reference numerals represent the same components, and all compositional details remain the same.

[0093] The second catalytic layer 50 is provided on the wall 40 of the inlet passage 5. The first catalytic layer 35 is provided on the second catalytic layer 50 and, since the first catalytic layer is slightly longer, is provided to overlap a small portion of the wall 40 of the inlet passage 5. The third catalytic layer 55 is provided in the porous wall 10, although it can alternatively be provided on the surface 60 of the outlet passage 10.

[0094] Figure 3An exhaust gas treatment system is shown that includes, downstream of an engine 65, a diesel oxidation catalyst (DOC) 70, followed by a catalytic soot filter (CSF) 75, followed by a device 80 for injecting a nitrogen-containing reductant, followed by an SCR 85, and finally a catalyst article 1 as described herein, i.e., an ASCF. The CSF 75 can be a diesel particulate filter (DPF). It is desirable to have the CSF 75 or DPF upstream of the catalyst article 1 because it is difficult to regenerate such a component, and the accumulation of soot on the catalyst article 1 (prevented by the CSF 75 or DPF) can result in unacceptable backpressure. The difficulty in regenerating the catalyst article 1 lies in soot accumulation, and this difficulty is exacerbated by the end-of-system location (e.g., under the chassis), where lower temperatures are insufficient. Example

[0095] The present invention will now be further described in connection with the following non-limiting examples.

[0096] Exemplary catalyst articles were produced and tested as described below.

[0097] Engine test

[0098] Embodiments of the present invention use a 10.5-inch by 6.0-inch wall-flow filter substrate. A 10.5-inch by 4.0-inch reference filter is used, but coated with the same total mass (g) of washcoat (varying as described below for the filter) as on the coated filter.

[0099] SCR "in-wall" coating – "Coating 1" :

[0100] A slurry of spray-dried Cu(3.3 wt%) chabazite (SAR 20) is milled to a target particle size distribution characterized by D90 = 3.8 μm - 3.9 μm and stirred overnight. The milled slurry is adjusted to a target pH of 9.9 - 10.2 by adding an aqueous solution of tetraethylammonium hydroxide and stirred for 5 minutes. Finally, a low-particle-size mixed oxide containing Al2O3 (91.2 wt%) / La2O3 (4.8 wt%) / Nd2O3 (4.1 wt%), with a particle size distribution characterized by D90 = 3.0 μm - 5.0 μm, is added with high-speed stirring until a target of 11 wt% is reached, based on the calcined weight of the Cu chabazite. The washcoat having the above composition is stirred overnight and then re-adjusted to pH 9.9 - 10.2 by adding an aqueous solution of tetraethylammonium hydroxide. The pH-adjusted washcoat is stirred for 30 minutes and coated from the back end of a suitable DPF until a target washcoat loading of 0.8 g / in 3 is reached, based on the volume of the ASCF brick.

[0101] Dry the bricks at 110 °C for 30 minutes and calcine them at 500 °C for 2 hours.

[0102] PGM "in-wall" coating – "Coating 2" :

[0103] Dissolve succinic acid in deionized water to a target of 40 g / ft 3 , and stir the solution for 5 minutes. Slowly add platinum(IV) nitrate to the solution to a target of 0.5 g / ft 3 platinum, and stir the mixture for 5 minutes. Finally, add low-grit alumina P0 (pre-ground to a target particle size distribution characterized by D90 = 4.8 μm - 5.0 μm) in slurry form to a target of 0.06 g / in 3 . Stir the washcoat with the above composition for 3 hours and coat it from the front end of an intermediate-processed DPF containing the calcined SCR "washcoat 1" (as described above), then dry it at 115 °C for 30 minutes and calcine it at 500 °C for 2 hours.

[0104] All of the above targets refer to the final loading amount based on the volume of the ASC F brick.

[0105] SCR coating on porous wall – "Coating 3" :

[0106] Grind the slurry of spray-dried Cu(3.3 wt%) chabazite (SAR 20) to a target particle size distribution characterized by D90 = 3.8 μm - 3.9 μm and stir it overnight. Transfer the slurry to a cooling tank and add colloidal aluminum hydroxide (boehmite) under high-speed stirring to a target of 18 wt%, based on the calcined weight of the Cu chabazite. Stir the mixture for 30 minutes, then add a cellulose pore former (Arbocel UFC100) under high-speed stirring to a target of 54 wt%, based on the calcined weight of the Cu chabazite. Stir the mixture for 30 minutes, then add a cellulose thickener under high-speed stirring to a target of 0.2 wt%, based on the total weight of the wet washcoat. Stir the mixture at high speed for 30 minutes, then store the washcoat in a sealed container for 2 days. Then stir the washcoat at high speed for 3 minutes and coat it from the front end of an intermediate-processed DPF containing the calcined SCR "washcoat 1" and the calcined PGM "washcoat 2" (as described above) to a target washcoat loading of 0.8 g / in 3 based on the volume of the finished catalyst. Dry the bricks at 110 °C for 45 minutes and then calcine them at 500 °C for 2 hours.

[0107] SCAT test

[0108] Test with SCAT - test. This type of test does not include any other catalysts upstream or downstream, but artificially provides the core with a gas composition representative of specific operating conditions, i.e., 350 ppm CO / 500 ppm NH3 / 0 ppm NOx for "NH3 - rich conditions", or 350 ppm CO / 500 ppm NH3 / 500 ppm NO for "NO X focus" conditions.

[0109] All examples use a 1 - inch × 5.53 - inch wall - flow filter substrate. The space velocity is the same in all tests.

[0110] Exemplary ASCFs were fabricated to have: an SCR washcoat on the walls in the inlet channels (0.8 g / in 3 ); a PGM - containing in - wall composition (Pt on alumina with different loadings) applied from the inlet side; and an in - wall SCR washcoat in the outlet channels (0.8 g / in 3 ). The comparative flow - through filter was provided with an overlying SCR layer (2.4 g / in 3 ) and a lower PGM - containing layer with 3 g / ft 3 Pt. The PGM coating was applied to the rear 50% of the bricks.

[0111] The PGM levels were 1 g / ft 3 , 0.75 g / ft 3 , 0.5 g / ft 3 and 0.25 g / ft 3 . This gives ratios to the SCR material (1.6 g / in 3 ) as discussed herein of 10:16, 7.5:16, 5:16 and 2.5:16. The SCR material here is the copper - exchanged zeolite and the binder of the washcoat. In contrast, the ratio for the standard ASC in the examples is 30:24. This is representative of the traditional configuration.

[0112] In further SCAT tests, the results showed that for 1 g / ft 3 , 0.75 g / ft 3 , 0.5 g / ft 3 of Pt, the NH3 conversion was comparable, but for 0.25 g / ft 3 of Pt, the conversion was much worse. For 0.5 g / ft 3 of Pt, the N2O production was substantially the same as that of the standard flow - through, but for those examples with higher Pt loadings, the production was much worse.

[0113] When compared to a standard ASC on a FT, the ASCF catalyst shows improved filtration efficiency in preliminary measurements. In particular, when using the ASCF catalyst instead of the standard ASC on a FT, PN10 emissions are reduced by 70% - 90%.

[0114] Therefore, Pt 0.5 g / ft 3 near values (paired with SCR of 1.6 g / in 3 provide the optimum point where the oxidation performance matches the SCR performance - NH3 conversion is sufficient and there is no excessive N2O generation, while the filtration performance addresses reductant-derived particulate matter. Ideally, a ratio of around 5:16 should be observed.

[0115] At Figure 4 for NH3 conversion, the lines at 300 °C from top to bottom are: standard, 1 g / ft 3 , 0.75 g / ft 3 , 0.5 g / ft 3 and 0.25 g / ft 3 . For N2O production, the line peaks from top to bottom are: 1 g / ft 3 , standard, 0.75 g / ft 3 , 0.5 g / ft 3 and 0.25 g / ft 3 . For NOx production, the lines at 400 °C from top to bottom are: 1 g, 0.75 g, 0.5 g, 0.25 g and standard.

[0116] As shown in these examples, a three-layer ASCF has been developed with the aim of transforming the ASC concept from a flow-through type to a filter substrate. When compared to a standard two-layer ASC, the three-layer ASCF approach broadens the variety of viable coating designs while also significantly reducing particulate emissions. In particular, the use of the three-layer ASCF allows for different combinations of in-wall and on-wall coatings, thereby enabling fine control of ASC activity, backpressure, and filtration efficiency.

[0117] Subsequent tests using engine test data indicate that the same benefits can be achieved under real-world use conditions. In this case, the ASCF or SCR / ASC brick is located downstream of another SCR flow-through brick (in this case, the VSCR). More information is shown in Figure 6. Here, the standard ASCF is coated with the same mass (grams) of SCR catalyst and PGM catalyst as the standard flow-through SCR / ASC, while the "lower PGM" variant has only half the amount of PGM but the same amount of SCR washcoat. Steady-state (SS) engine test data was conducted at three different temperatures (270 °C, 320 °C, 370 °C), where the lower PGM variant performed much better in terms of secondary emissions while still being comparable to the SCR / ASC reference in terms of NH3 conversion - this provides a better balance between NH3 conversion and secondary emissions for the lower PGM variant.

[0118] In each set of results, the left column is the conventional SCR / ASC, the middle column is the ASCF with SCR and PGM levels comparable to the conventional SCR / ASC, and the right column has half the PGM level of the middle column (0.5 g / ft 3 of PGM and 1.6 g / in 3 of SCR).

[0119] Figure 6A Shows that the ASCF of the present invention achieves good enough NH3 slip control. Figure 6B Indicates an improvement in the reduced N2O production level. Figure 6C Indicates an improvement in the reduced NO x production level. The SS numbers in each graph reflect the test temperature at steady state.

[0120] Figures 7A to 7C For the same component parts, the same reference numerals are used as in Figure 1 and Figure 2 the same.

[0121] Figure 7A Similar to Figure 2 , but this is an embodiment in which the second catalytic layer 50 has a shorter length, approximately 50% of the total length 45 of the extended catalyst article 1. The first catalytic layer extends approximately 80% of the total length 45 of the extended catalyst article 1. In Figure 7A the PGM layer is coated as a porous coating on the walls, attempting to prevent / minimize close contact with SCR catalyst particles (which are dispersed within the wall volume and then substantially isolated from the PGM on the walls)

[0122] Figure 7B and Figure 7CAn embodiment in which the second catalytic layer 50 does not overlap with the third catalytic layer 55. These two layers (50, 55) are provided as a wall-mounted carrier coating and together coat the entire length 45 of the catalyst article 1. In Figure 7B , the second catalytic layer 50 is about 25% of the total length 45, and the third catalytic layer 55 is about 75% of the total length 45. In Figure 7C , the second catalytic layer 50 is about 50% of the total length 45, and the third catalytic layer 55 is about 50% of the total length 45.

[0123] As supported in embodiments 7B and 7C, avoiding the overlap between these layers avoids the close contact between the platinum group metal and the SCR catalyst.

[0124] Figure 8 Showing a comparison of embodiments 7A - 7C with a comparative example, in which the second catalytic layer 50 is about 70% of the total length 45 (inside the wall), and the third catalytic layer 55 is about 80% of the total length 45 (inside the wall). The provision of these overlapping wall coatings means that there is an overlap of the platinum group metal and the SCR catalyst inside the wall. The columns from left to right are: comparative example, embodiment 7C, 7B, and 7A.

[0125] Figure 8 Showing that for Figure 7C (62) and Figure 7B the embodiments of (63) obtain the lowest back pressure.

[0126] Figure 9 Showing the NH3 conversion rate at different temperatures. Figure 7C The performance of the embodiments of is always the highest. Figure 7B The embodiments of have the worst performance. The columns from left to right are: comparative example, embodiment 7C, 7B, and 7A.

[0127] Figure 10 Showing the NH3, N2O, and NOx outputs at different temperatures and ANR ratios. The columns from left to right for each set of conditions are: comparative example, embodiment 7C, 7B, and 7A.

[0128] As used herein, the term "comprising" may be replaced with the definitions "consisting essentially of" or "consisting of". The term "including" is intended to mean that the stated element is essential, but other elements may be added and still form a construction within the scope of the claim. The term "consisting essentially of" limits the scope of the claim to the specified materials or steps and those materials or steps that do not substantially affect the basic and novel features of the invention protected by the claim. The term "consisting of" limits the claim to the exclusion of materials other than those listed, except for impurities normally associated therewith.

[0129] The foregoing detailed description has been presented by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

[0130] For the avoidance of doubt, the entire contents of all documents recognized herein are hereby incorporated by reference.

Claims

1. A catalyst article for waste gas treatment, the catalyst article comprising: 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, the inlet channels being adjacent to outlet channels that are closed at the inlet end of the substrate and open at the outlet end of the substrate; the wall - flow filter comprising at least a first catalytic layer, a second catalytic layer, and a third catalytic layer, wherein: (i) the first catalytic layer extends from the inlet end of the substrate and contains a first SCR composition; (ii) the second catalytic layer is disposed within or on the walls of the inlet channels extending from the inlet end of the substrate and contains a PGM - containing composition, wherein: when the second catalytic layer is disposed on the walls of the inlet channels, the first catalytic layer is disposed on the second catalytic layer, and when the second catalytic layer is disposed within the walls of the inlet channels, the first catalytic layer is disposed on the walls of the inlet channels; and (iii) the third catalytic layer is disposed within or on the walls of the outlet channels extending from the outlet end of the substrate and contains a second SCR composition; wherein the ratio of the PGM in the second catalytic layer in g / ft 3 to the total amount of the first SCR composition and the second SCR composition in the first catalytic layer and the third catalytic layer in g / in 3 is from 1.5:8 to 5:8, preferably from 2:8 to 4:8, and more preferably from 2:8 to 3:

8.

2. The catalyst article according to claim 1, wherein the second catalytic layer is disposed within the walls of the inlet channels, and / or the third catalytic layer is disposed on the walls of the outlet channels.

3. The catalyst article according to claim 1 or claim 2, wherein: (i) the first catalytic layer extends up to 100% of the longitudinal length of the substrate extending from the inlet end to the outlet end, preferably 70% to 90% of the longitudinal length; and / or (ii) the second catalytic layer extends up to 100% of the longitudinal length of the substrate extending from the inlet end to the outlet end, preferably 25% to 90% of the longitudinal length, more preferably 40% to 70% of the longitudinal length; and / or (iii) the third catalytic layer extends up to 100% of the longitudinal length of the substrate extending from the outlet end to the inlet end, preferably 20% to 90% of the longitudinal length, more preferably 30% to 60% of the longitudinal length, preferably 70% to 90% of the longitudinal length.

4. The catalyst article according to claim 3, wherein at least two of the first catalytic layer, the second catalytic layer, and the third catalytic layer, preferably all three catalytic layers, extend 70% to 90% of the longitudinal length.

5. The catalyst article according to any one of the preceding claims, wherein the second catalytic layer and the third catalytic layer do not overlap and together extend 100% of the longitudinal length of the substrate extending from the outlet end to the inlet end, preferably wherein the second catalytic layer is disposed within the walls of the inlet channels and wherein the third catalytic layer is disposed within the walls of the outlet channels.

6. The catalyst article according to any one of the preceding claims, wherein the ratio of the PGM in the second catalytic layer in g / ft 3 to the total amount of the first SCR composition and the second SCR composition in the first catalytic layer and the third catalytic layer in g / in 3 is about 5:

16.

7. The catalyst article according to any one of the preceding claims, wherein the PGM - containing composition contains Pt, preferably as the sole PGM.

8. The catalyst article according to any one of the preceding claims, wherein the PGM-containing composition comprises alumina as a support for the PGM.

9. The catalyst article according to any one of the preceding claims, wherein the catalytically active SCR component of the first SCR composition and / or the second SCR composition comprises and preferably consists of one or more metal-exchanged zeolites.

10. The catalyst article according to claim 9, wherein the metal-exchanged zeolite is a small-pore zeolite, preferably having a CHA framework structure, preferably wherein the zeolite is exchanged with Cu and / or Mn.

11. The catalyst article according to any one of the preceding claims, wherein the weight ratio of the first SCR composition and the second SCR composition in the first catalytic layer and the third catalytic layer is from 2:3 to 3:2, and preferably about 1:

1.

12. The catalyst article according to any one of the preceding claims, further comprising means for electrically heating the catalyst article.

13. An exhaust gas treatment system comprising the catalyst article according to any one of claims 1 to 12.

14. The exhaust gas treatment system according to claim 13, which sequentially comprises a catalytic soot filter (CSF), means for injecting a nitrogen-containing reducing agent, an SCR catalyst article, and the catalyst article according to any one of claims 1 to 11, preferably wherein the system further comprises a diesel oxidation catalyst (DOC) upstream of the CSF.

15. A fuel combustion and exhaust gas treatment system comprising an engine and the exhaust gas treatment system according to claim 13 or claim 14.

16. A vehicle comprising the fuel combustion and exhaust gas treatment system according to claim 15, preferably wherein at least the catalyst article according to any one of claims 1 to 12 is located in an under-chassis position and / or is exposed to exhaust gases having a temperature of 270 °C to 350 °C during normal use.

17. A method for treating exhaust gas, the method comprising passing the exhaust gas through the catalyst article according to any one of claims 1 to 12, or the exhaust gas treatment system according to claim 13 or claim 14.

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