Ammonia slip catalyst filter

Abstract

A catalytic wall-flow filter for treating exhaust gas 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 an inlet end of the substrate and comprises a first SCR composition; the second catalytic layer is disposed within or on a wall of an inlet channel extending from the inlet end of the substrate and comprises a PGM-containing composition; the third catalytic layer is disposed within or on a wall of an outlet channel extending from an outlet end of the substrate and comprises a second SCR composition.

Description

[0001] This invention relates to a catalyst article used as an ammonia leakage catalyst. Specifically, the ammonia leakage catalyst is disposed on a wall-flow filter. The invention also relates to an exhaust gas treatment system incorporating this catalyst article and its applications. This catalyst article is designed to address particulate matter emissions generated by the upstream addition of reducing agents such as ammonia or urea, while maintaining good exhaust gas treatment performance.

[0002] Exhaust gases produced in lean-burn engines and diesel engines are typically oxidized. In a method known as selective catalytic reduction (SCR), NOx is selectively reduced using a catalyst and a reducing agent. This selective catalytic reduction removes NOx... x It is converted into elemental nitrogen (N2) and water. In the SCR method, a gaseous reducing agent (usually anhydrous ammonia, ammonia water, or urea) is added to the exhaust gas stream before the exhaust gas contacts the catalyst. The reducing agent is absorbed onto the catalyst and NO is converted into nitrogen (N2) and water. x It is reduced as the gas passes through or over the catalytic substrate. To make NO... x Maximizing the conversion rate typically requires adding more than the stoichiometric amount of ammonia to the exhaust gas stream. However, releasing excessive ammonia into the atmosphere is harmful to human health and the environment. Furthermore, ammonia is caustic, especially in its aqueous form. Condensation of ammonia and water in the exhaust pipe area downstream of the exhaust catalyst can result in a corrosive mixture that can damage the exhaust system. Therefore, the release of ammonia into the exhaust gas should be eliminated.

[0003] Even the best SCR catalysts cannot achieve maximum NO reduction in systems with non-uniform NH3 distribution. x Reduction. Load, exhaust gas flow rate, and NO x Significant changes in concentration make it difficult to achieve the required 1:1 ammonia:NO ratio for the reaction stoichiometry of NH3. x The average non-reactive oxygen species (ANR) is delivered to the catalyst. Uneven NH3 distribution can lead to incomplete NO deposition in cases of locally low ANR. x The conversion leads to NH3 leakage when ANR is high.

[0004] In many conventional exhaust systems, an ammonia oxidation catalyst (also known as an ammonia leakage catalyst or "ASC") is installed downstream of the SCR catalyst to remove ammonia from the exhaust gas by converting it into nitrogen. Ammonia leakage catalysts are well known in the art. The purpose of an ammonia leakage catalyst is to treat any ammonia that has passed through the upstream SCR catalyst.

[0005] To overcome the difficulty of achieving ideal stoichiometry, ASC technology combines the functions of oxidation catalyst and SCR catalyst on a flow-through (FT) substrate to improve NO2. xReduction is achieved while maintaining low NH3 leakage. ASC allows upstream SCR to operate continuously at higher ANR, thereby compensating for uneven NH3 distribution and promoting NO reduction. x The conversion (on the upstream SCR) is carried out while maintaining low NH3 leakage.

[0006] In ASC (Automatic Smoke Control) systems, oxidation and SCR catalysts can be coated onto the substrate using different design strategies, the most common being the so-called "two-layer ASC" design. The two-layer ASC design is based on the sequential coating of two layers (PGM layer and SCR layer) on the flow channel walls. The functional ASC design converts only a portion of the usable ammonia in the exhaust gas in the oxidation layer. The remaining ammonia fraction is then used as a reducing agent in the SCR layer, ideally allowing the ammonia to be completely converted into water, elemental nitrogen, and as little as possible N2O and NO. x .

[0007] A typical ASC is described in 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 bilayer having a top layer containing the first SCR catalyst and a bottom layer containing platinum on a support 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 this upper layer to Pt, where it can be oxidized to NO. x Then NO x Returning to the SCR layer, it is processed with the stored ammonia to provide N2. In this way, excess leaked ammonia is stored and utilized instead of being released into the atmosphere.

[0008] Another configuration for ASC is described in US20150037233.

[0009] Particulate matter emissions are a well-known problem in diesel engine exhaust treatment systems. These emissions are known to be treated using filters. Known types of filters include diesel particulate filters (DPFs) and catalytic soot filters (CSFs). These filters capture soot from the exhaust gas and can be regenerated by burning off the accumulated soot by increasing the exhaust gas temperature. The conventional substrate used for DPFs or CSFs is a so-called wall-flow filter.

[0010] EP2483537 discloses a four-way catalyst for diesel engine exhaust. As the name suggests, it is used to treat all four main pollutants in the exhaust—CO, HC, NO... x And soot—both are removed in a single component.

[0011] EP2567081 discloses a catalytic article for treating waste gas streams containing particulate matter, hydrocarbons, CO, and ammonia. In a first embodiment of this disclosure, the article comprises: a substrate having an inlet end and an outlet end having defined axial lengths; a first catalyst coating comprising a platinum group metal extending from the outlet end toward the inlet end less than the entire axial length of the substrate; and a second catalyst coating comprising a catalyst for selective catalytic reduction (SCR) of nitrogen oxides extending from the inlet end toward 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 for manufacturing multi-zone catalyst articles, and methods for controlling emissions in diesel engine exhaust gas using multi-zone catalyst articles, wherein the emission treatment systems of various embodiments effectively treat diesel engine exhaust gas using a single multi-zone catalyst article.

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

[0014] As emission standards become increasingly stringent, ensuring the exhaust system's emissions output addresses concerns about particulate matter emissions and other pollutants such as NOx. x The issues surrounding substances such as NH3 are becoming increasingly important.

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

[0016] According to a first aspect, a catalyst article for treating waste gas is provided, the catalyst article comprising:

[0017] A wall-flow filter substrate having inlet channels that open at the inlet end and close at the outlet end, adjacent to an outlet channel that is closed at the inlet end and open at the outlet end.

[0018] The filter comprises at least a first catalyst layer, a second catalyst layer, and a third catalyst layer, wherein:

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

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

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

[0022] When the second catalyst layer is disposed within the wall of the inlet channel, the first catalyst layer is disposed on the wall of the inlet channel; and

[0023] (iii) The third catalyst layer is disposed within or on the wall of the outlet channel extending from the outlet end of the substrate, and contains the second SCR composition;

[0024] The second catalyst layer contains g / ft 3 The calculated PGM content is in the first and third catalyst layers at g / in 3 The ratio of the total amount of the first SCR composition to the total amount of the second SCR composition is 1.5:8 to 5:8, preferably 2:8 to 4:8, and more preferably 2:8 to 3:8.

[0025] This disclosure will now be described further. In the following paragraphs, different aspects / implementations of this disclosure are defined in more detail. Unless expressly stated to the contrary, each aspect / implementation so defined may be combined with any other aspect / implementation or multiple aspects / implementations. In particular, any feature indicated as preferred or advantageous may be combined with one or more other features indicated as preferred or advantageous. Features disclosed relative to a product are contemplated to be combined with those disclosed relative to a method, and vice versa.

[0026] In the following text, the term “ammonia leakage catalyst filter” or “ASCF” is used as an abbreviation for the catalyst product structure described herein.

[0027] Recent observations suggest that injecting reducing agents (especially urea / ammonia) into exhaust gases can lead to the formation of certain aggregated compounds and ammonium salts. These are substances formed through the reaction and polymerization of the reducing agent before it can participate in the SCR reaction. The polymerized materials are then released into the atmosphere as additional fine particulate matter, violating stringent emission requirements.

[0028] A discussion of these particulate emissions from polymerization can be found in SAE 2017-01-0915. It explains that, depending on the urea metering feeder, decomposition reaction tube (DRT) design, and operating conditions, incomplete decomposition of injected urea can lead to the formation of solid urea deposits in diesel aftertreatment systems. These deposits can potentially cause increased engine back pressure and NOx emissions. xTreatment performance deteriorates. The urea deposits formed can further transform into chemically more stable substances upon exposure to hot exhaust gases, making it crucial to understand this transformation 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°C-190°C, urea transforms into a combination of urea, biuret, and CYA; and 3) above the biuret melting temperature (190°C), CYA with some characteristics of cyanuric acid amide is mainly formed. Upon exposure to temperatures above 200°C, urea undergoes rapid chemical transformation through urea decomposition, biuret formation, and subsequent biuret decomposition, transforming 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, which can possess a certain degree of thermal stability. This particulate matter is typically very fine, but it is precisely this fine material that is now subject to increasingly stringent regulation. Furthermore, since particulate matter formation can only occur after the reducing agent is quantitatively added to the exhaust gas treatment system, it typically forms after any conventional particulate filter (DPF or CSF) in the system and at lower temperatures (i.e., under chassis configuration), where routine regeneration of such filters would be difficult.

[0030] The inventors have now discovered that these problems can be solved by providing a catalyst article as described herein. In particular, this article is capable of providing ASC performance comparable to standard flow-through ASCs while reducing or eliminating particulate emissions. Furthermore, the inventors have discovered that, in order to match the N2O and NO emissions of standard flow-through ASCs… x Performance improvements using reduced PGM are possible and, in fact, desirable. This can save costs and optimize performance.

[0031] It should be noted that ASC is typically provided downstream of the SCR catalyst preparation. That is, a flow-through feedstock may have a PGM layer on the outlet surface and an SCR layer along the entire length of the feedstock. In other embodiments, SCR and a dual-layer ASC may be provided on separate feedstocks, but immediately in sequence. This performance comparison is performed only for the ASC portion (i.e., excluding the upstream SCR portion of such a combined feedstock). In use, the ASCF disclosed herein will typically be located before the separate SCR feedstock as described below.

[0032] This invention relates to catalyst articles. A catalyst article is defined herein as a structure having catalytic properties. These catalytic properties derive from materials contained in or coated thereon. Articles as defined herein include both coated catalyst substrates as described herein and treated and canned ASCF units suitable for installation in automobiles. Catalyst articles provide catalysts that are effective in reducing ammonia loss and particulate emissions when used downstream of SCR processes.

[0033] This invention relates to catalyst articles for treating exhaust gases. Specifically, the catalyst articles can be used to treat exhaust gases originating from combustion processes, such as those from internal combustion engines (whether mobile or stationary), gas turbines for stationary, marine, or locomotive applications, and exhaust gases from coal-fired or oil-fired power plants. The articles can also be used to treat gases from industrial processes such as refining, from refinery heaters and boilers, heating furnaces, chemical processing industries, coke ovens, municipal waste treatment plants, and incinerators. In a particular embodiment, the method is used to treat exhaust gases from gas turbines or lean-burn engines. This treatment is performed to remove unwanted 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, adjacent to an outlet channel that is closed at the inlet end of the substrate and open at the outlet end of the substrate. The alternating open and closed channels mean that, in use, exhaust gas entering the inlet channels is forced through the walls separating the channels to exit via the open outlet channels. The porosity of the walls, as well as the arrangement of specific coating areas and layers, ensures 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, with the ends of the channels alternately blocked on the inlet and outlet sides. This configuration creates a checkerboard pattern at both ends.

[0036] The monolithic substrate for wall-flow filters can contain 2.54 cm per square inch. 2 The cross-section may have up to approximately 400 flow channels (or “cells”), although far fewer channels may be used. For example, the carrier may have between 7 cells / square inch and 400 cells / square inch (“cpsi”), particularly between 100 cpsi and 400 cpsi. The cell may have a cross-section that is rectangular, square, circular, elliptical, triangular, hexagonal, or has other polygonal shapes.

[0037] Wall-flow substrates are typically composed of ceramic-like materials such as cordierite, α-alumina, silicon carbide, silicon nitride, zirconium oxide, mullite, spodumene, alumina-silica-magnesium oxide, or zirconium silicate, or of refractory metals such as stainless steel. These materials can withstand the environments encountered when treating waste gas streams, particularly high temperatures. Ceramic wall-flow substrates are typically formed from materials with a porosity of approximately 40 to 70. The term "porosity" as used herein should be understood to refer to the measurement of porosity according to the mercury porosity method of DIN 66133. According to embodiments of the 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 comprises at least a first catalyst layer, a second catalyst layer, and a third catalyst 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 consist of one or more sublayers having the same or different formulations. That is, the first catalyst layer may consist 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 catalyst layers are the only layers and are each provided as a separately applied layer.

[0039] The first catalyst layer extends from the inlet end of the substrate and contains the first SCR composition. Preferably, the first catalyst layer extends for at most 100% of the longitudinal length of the substrate from the inlet end to the outlet end, more preferably 70% to 90% of the longitudinal length. Since the coating method for applying this composition (particularly for thin inner wall coatings) typically involves immersing the substrate in a washcoat, essentially 100% of the coating will extend completely along the interior of the inlet channel until the plug at the outlet end of the channel is blocked. For wall coatings, the washcoat can be applied by drawing the washcoat into the substrate with a strong and short vacuum.

[0040] A preferred coating covering up to 90% of the length will leave a portion of the channel wall adjacent to the plug without any coating. Therefore, an optimal coating covering 70% to 90% of the length provides an inlet region of the inlet channel containing the composition and a composition-free region away from the inlet end. In use, the first catalytic layer will be the first catalytic element of the article that comes into contact with the exhaust gas to be treated.

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

[0042] Preferably, the catalytically active SCR component of the first SCR composition and / or the second SCR composition comprises one or more metal-exchange zeolites, and is preferably composed of them. This does not preclude the presence of additional non-catalytic binders or processing aids, as conventionally used in support coating formation. These will be discussed further below.

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

[0044] Zeolite is a microporous aluminosilicate having any of the framework structures listed in the zeolite structure database published by the International Zeolite Association (LZA). Framework structures include, but are not limited to, those of the CHA, FAU, BEA, MFI, and MOR types. Non-limiting examples of zeolites having these structures include chalcogenide, octahedral zeolite, zeolite Y, ultrastable zeolite Y, β-zeolite, mordenite, silica rock, zeolite X, and ZSM-5. Aluminosilicate zeolites may have a silica / alumina molar ratio (SAR) of at least about 5, preferably at least about 20 (defined as SiO2 / Al2O3), with a range of about 10 to 200 being acceptable.

[0045] Preferably, the metal-exchanged zeolite is a microporous zeolite, preferably having a CHA framework structure. It is preferred that the zeolite is 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% to 5% by weight, most preferably 2% to 4% by weight, based on the weight of the copper-promoted zeolite.

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

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

[0048] Providing a coating "inside the wall" or "on the wall" is well known in the art. This is achieved by carefully tailoring the carrier coating formulation to match the porosity of the filter wall. Therefore, a "thinner" composition with finer materials (especially loaded PGMs) can penetrate into the wall more easily than a "thicker" composition containing coarser materials. Exemplary in-wall and on-wall coatings are provided in the examples. Thus, by adjusting the carrier coating, a coating can be ensured within the porous wall of the article as needed.

[0049] The second catalyst 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. The PGM is preferably provided on a support material. Suitable support materials are known in the art. Preferably, the PGM-containing composition comprises alumina as the PGM support.

[0050] Preferably, the second catalyst layer extends for at most 100% of the longitudinal length of the substrate from the inlet end to the outlet end, more 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 catalyst layer, a preferred coating of at most 90% of its length will leave a portion of the channel wall adjacent to the plug uncoated. Therefore, a preferred coating of 40% to 70% of its length provides an inlet region of the inlet channel containing the composition and a region of the inlet channel away from the inlet end that does not contain the composition.

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

[0052] The third catalyst layer is disposed within or on the wall of the outlet channel extending from the outlet end of the substrate, and comprises the second SCR composition. As described above, the second SCR composition may be selected from the same material as the first SCR composition. Preferably, the second SCR composition is copper-promoted CHA zeolite.

[0053] The third catalyst layer extends from the outlet end of the substrate. Preferably, the third catalyst layer extends for at most 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%, more preferably 30% to 70%, and most preferably 40% to 60%. In embodiments where it does not 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 embodiments where they overlap, the third layer can be longer, such as 60% to 90% of the length. Since the coating method of applying this composition typically involves immersing the substrate in a carrier coating, essentially 100% of the coating will extend completely along the interior of the outlet channel until the plug at the inlet end of the channel blocks it. A preferred coating of at most 90% of the length will leave a portion of the channel wall adjacent to the plug without any coating. Thus, the most preferred coating of 70% to 90% of the length provides an outlet area of ​​the outlet channel containing the composition and a composition-free area away from the outlet end. In use, the third catalytic layer will be the final catalytic element of the product that comes into contact with the waste gas to be treated.

[0054] When the in-wall catalyst composition is applied, the carrier coating can be applied to all the pores of the wall. Therefore, if both the second and third catalyst compositions are disposed in the wall, there can be considerable overlap in the positions of the catalyst compositions. Nevertheless, it is still possible to determine from which side the composition was applied. This is not only because the inlet channel will include the second composition up to the inlet opening, but also because the third composition cannot be coated that far, considering the plug blocking the inlet end of the outlet channel. Conversely, the outlet channel will include the third composition up to the outlet opening, and the second composition cannot be coated that far, considering the plug blocking the outlet end of the inlet channel. Therefore, even when both the second and third compositions are disposed in the wall, there will still be an in-wall region for SCR only at the 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 disposed within the wall of the inlet channel, and the third catalyst layer is disposed on the wall of the outlet channel. According to another preferred embodiment, the third catalyst composition is disposed within the wall, and the second catalyst layer is disposed within 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 catalyst layers. In some embodiments, the second and third catalyst layers are preferably adjacent but do not overlap.

[0056] Preferably, the compositions forming the first and third layers are free of any PGM components. Preferably, the compositions forming the second layer are free of any SCR components. However, it should be understood that a small amount of seepage may occur between the layers when coating a porous wall-flow filter.

[0057] When describing the loading of the support coating in a catalyst article, it is usually provided in g / ft. 3 The calculated PGM loading. This is an assessment of the metal itself in the applied layer. In contrast, the carrier coating loading of SCR materials is typically much higher, expressed in g / in. 3 Given. Unlike PGM, such values ​​for SCR materials typically include all elements of the carrier coating, including, for example, binders. Therefore, the SCR compositions described herein comprise both the zeolite component and any binder. Preferably, the SCR composition is therefore synonymous with the first and third catalyst layers.

[0058] In conventional ASC (i.e., the PGM-containing end portion of the combined SCR / ASC), in g / ft 3 The total load of PGM is calculated in g / in 3 The ratio of the total loading of the SCR compositions is generally greater than 1:1, and more generally greater than 5:4. The inventors have found that when they formulate ASCFs with the same catalytic loading, there is an excessive amount of NO. x It forms with N2O. Not wanting to be bound by theory, we believe the exhaust gases in the new configuration are exposed to the PGM material to a much greater extent. That is, although in a flow-through ASC, the exhaust gases only encounter the PGM as they pass through the catalyst material layer, the ASCF configuration forces all exhaust gases to pass directly through the PGM-containing composition.

[0059] Therefore, the inventors sought to solve these problems and achieved an optimized relative loading of catalyst material in each layer. In the second catalyst layer, the loading is expressed as g / ft. 3 The calculated PGM content is in the first and third catalyst layers at g / in 3 The ratio of the total amount of the first SCR composition to the total amount of the second SCR composition is 1.5:8 to 5:8, preferably 2:8 to 4:8, preferably 4.5:16 to 7:16, and more preferably 4.5:16 to 6:16. Preferably, the second catalyst layer contains g / ft 3 The calculated PGM content is in the first and third catalyst layers at g / in 3 The total ratio of the first SCR composition to the second SCR composition is approximately 5:16.

[0060] Given the basic understanding of ASCs, it is surprising that this structure can also function in a three-layer configuration as disclosed herein. Specifically, the SCR layer of a conventional ASC functions only when in use due to the amount of ammonia captured in the SCR layer. Surprisingly, sufficient ammonia can permeate through the first and second layers to reach the third catalytic layer, and then neutralize any NO formed when the exhaust gas comes into contact with the PGM in the second catalytic layer. xSCR was performed. Nevertheless, performance data showed that this does indeed occur, and comparative examples demonstrated that in the absence of an outlet-end SCR composition, the exhaust gas exhibited undesirably high levels of NO. x And N2O—presumably the result of contact with PGM as the final layer before leaving the product.

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

[0062] Preferably, at least two, and more preferably all three, catalyst layers extend for 70% to 90% of the longitudinal length. It is understood that when all three layers extend to such a length, there will be overlap between them. In embodiments where all three layers extend to this length, there is therefore a portion of the inlet channel wall without the first or second catalyst layer (and of course, without the third catalyst layer) and a portion of the outlet channel wall without the third catalyst layer (and of course, without the first or second catalyst layer). This configuration facilitates layer formation, avoids accumulation at the ends that may occur when attempting full-channel coating, and also helps ensure that the gas to be treated contacts the first catalyst layer first and the third catalyst layer last.

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

[0064] Compositions containing SCR and PGM may include additional components. These may include, for example, fillers, binders, stabilizers, rheology modifiers, and other additives. In some embodiments, the support coating includes pore-forming agents such as graphite, cellulose, starch, polyacrylate, and polyethylene. 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 catalyst's contact surface area, or increasing the catalyst's adhesion to the substrate. Typically, the only additional component will be the binder. Preferably, the additional component forms less than 25% by weight of the layer, preferably less than 15% by weight, most preferably less than 10% by weight, with the balance being either SCR or supported PGM. The particle size of the binder will vary depending on whether the associated coating is an in-wall or on-wall coating. Typical alumina binders for in-wall applications have a D90 of less than 7 μm, measured by laser diffraction.

[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 coated onto 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 inventors have conceived of two methods for forming catalyst articles. According to one aspect, a method is provided for manufacturing a catalyst article in the following steps: applying a support coating to an outlet channel to form a third coating, followed by calcination; applying a support coating to an inlet channel to form a second coating, followed by calcination; and applying a support coating to an inlet channel to form a first coating, followed by calcination. In each calcination step, a preceding drying step is typically present.

[0067] According to a more preferred embodiment, a method for manufacturing a catalyst article is provided in the following steps, involving fewer calcinations: applying a support coating to an inlet channel to form a second coating, followed by calcination; applying a support coating to an outlet channel to form a third coating, followed by drying; and applying a support coating to an inlet channel to form a first coating, followed by calcination. Typically, a preceding drying step is present in each calcination step. Avoiding the calcination step reduces energy and process costs.

[0068] Preferably, the catalyst article includes a device for electrically heating the catalyst article. Such devices are well known in the art and typically rely on resistance heating to increase the operating temperature of the catalyst article in use. This method can be used for in-situ regeneration of the catalyst article to remove accumulated particulate deposits, although reaching the desired temperature incurs associated energy costs. Other regeneration methods are known, such as increasing the exhaust gas temperature through engine management or hydrocarbon metering.

[0069] According to another aspect, an exhaust gas treatment system is provided, which includes the catalyst article described herein. Therefore, the system implicitly includes an initial manifold for receiving, for example, exhaust gas from an engine, and an outlet for discharging the treated exhaust gas into the environment. In use, the catalyst article is capable of treating any ammonia leaked from upstream components to produce N2 without forming and releasing excess NO. x Or it may produce excessive amounts of N2O.

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

[0071] Providing CSF upstream of the catalytic converter product (ASCF) prevents soot accumulation on the ASCF. This is desirable because the large amount of material accumulation in the end-of-system components is difficult to handle due to the relatively low temperatures. This makes raising the ASCF temperature require more energy, as this would lead to soot accumulation. In contrast, the accumulation of urea / ammonia-derived particles is relatively low, allowing regeneration to be performed 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, this catalyst is the last catalyst encountered by the exhaust gas before it is released into the atmosphere. This means that the catalyst can be suitably used as an ammonia leakage catalyst while simultaneously preventing the release of particulate matter from urea / ammonia into the atmosphere.

[0074] According to another aspect, a fuel combustion and exhaust gas treatment system is provided, 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, a vehicle including the fuel combustion and exhaust gas treatment system described herein is provided, preferably wherein at least the catalyst article described herein is located under the chassis and / or encounters exhaust gases at temperatures of 200°C to 450°C, preferably 270°C to 350°C, during normal use. Because the catalyst article is preferably located at the end of the exhaust system, it is provided under the chassis. This presents a challenge, as the temperature here promotes the formation rather than the destruction of reductant-derived particulate matter; therefore, ASCF is a solution for meeting emission standards.

[0076] According to another aspect, a method for treating waste gas is provided, the method comprising passing the waste gas through the catalyst article or the waste gas treatment system described herein.

[0077] The invention will now be further described with reference to 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 The configuration of the components of the exhaust gas treatment system downstream of the engine is shown.

[0081] Figure 4 The graphs show the comparison of NH3 conversion, N2O and NOx production of flow-through ASC and ASCF at different PGM:SCR loading ratios (NH3 only - 500ppm SCAT SV = 90k).

[0082] Figure 5 The graphs show the comparison of NH3 conversion, N2O and NOx production between flow-through ASC and ASCF at different PGM:SCR loading ratios (NOx emphasis:

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

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

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

[0086] Figures 8 to 10 It shows when Figures 7A to 7C Test data when comparing the implementation plan with the standard.

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

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

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

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

[0091] In operation, exhaust gas entering catalyst product 1 through inlet face 20 enters inlet channel 5, passes through porous wall 15, enters outlet channel 10, and exits product 1. This route is indicated by large arrows. The gas sequentially passes through the first catalyst layer, the second catalyst layer, and the third catalyst layer (35, 50, 55). Ammonia is stored in the first and third catalyst layers (35, 55) until it can be used for SCR reaction to decompose NO generated on the second catalyst layer 50. x Particulate matter from ammonia / urea accumulates in inlet channel 5 instead of being released into the atmosphere. If necessary, the particulate matter can be burned to reduce excessive accumulation, and this can be assisted if necessary, but local resistance heating is performed using electrical components (not shown).

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

[0093] A second catalyst layer 50 is disposed on the wall 40 of the inlet channel 5. A first catalyst layer 35 is disposed on the second catalyst layer 50, and because the first catalyst layer is slightly longer, it is disposed to overlap a small portion of the wall 40 of the inlet channel 5. A third catalyst layer 55 is disposed in the porous wall 10, although it may alternatively be disposed on the surface 60 of the outlet channel 10.

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

[0095] The invention will now be further described in conjunction with the following non-limiting embodiments.

[0096] The exemplary catalyst products are produced and tested as described below.

[0097] Engine testing

[0098] This embodiment of the invention uses a 10.5-inch × 6.0-inch wall-flow filter substrate. A 10.5-inch × 4.0-inch reference filter is used, but coated with a carrier coating of the same total mass (g) as the coated filter (which varies depending on the filter, as described below).

[0099] SCR "In-Wall" Coating – "Coating 1" :

[0100] A spray-dried Cu (3.3 wt%) chabazite (SAR 20) slurry was milled to a target particle size distribution characterized by D90 = 3.8 μm–3.9 μm and stirred overnight. The milled slurry was adjusted to a target pH of 9.9–10.2 by adding an aqueous tetraethylammonium hydroxide solution 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%), characterized by a particle size distribution of D90 = 3.0 μm–5.0 μm, was added under high-speed stirring until a target of 11 wt% relative to the calcined weight of Cu chabazite was achieved. The carrier coating with the above composition was stirred overnight and then readjusted to pH 9.9–10.2 by adding an aqueous tetraethylammonium hydroxide solution. The pH-adjusted carrier coating was stirred for 30 minutes and coated from the tail end of a suitable DPF until a value of 0.8 g / in was achieved. 3 The target carrier coating load, relative to the volume of ASCF bricks.

[0101] The bricks were dried at 110°C for 30 minutes and then calcined at 500°C for 2 hours.

[0102] PGM "Interior Wall" Coating – "Coating 2" :

[0103] Succinic acid was dissolved in deionized water to achieve the target of 40 g / ft. 3 The solution was stirred for 5 minutes. Platinum nitrate (IV) was then slowly added to the solution until the target concentration of 0.5 g / ft was reached. 3 Platinum was added, and the mixture was stirred for 5 minutes. Finally, low-particle-size alumina PO (pre-ground to a target particle size distribution characterized by D90 = 4.8 μm-5.0 μm) was added in slurry form to achieve the target of 0.06 g / in. 3 The carrier coating having the above composition is stirred for 3 hours and coated from the front end of the DPF intermediately processed containing the calcined SCR "coating 1" (as described above), then dried at 115°C for 30 minutes and calcined at 500°C for 2 hours.

[0104] All of the above targets refer to the final load relative to the volumetric gauge of the ASCF brick.

[0105] SCR Porous Wall Coating – "Coating 3" :

[0106] A slurry of spray-dried Cu (3.3 wt%) chabazite (SAR 20) was milled to a target particle size distribution characterized by D90 = 3.8 μm–3.9 μm and stirred overnight. The slurry was transferred to a cooling tank, and colloidal alumina hydroxide (boehmite) was added under high-speed stirring to reach a target of 18 wt% relative to the weight of calcined Cu chabazite. The mixture was stirred for 30 minutes, and then a cellulose pore-forming agent (Arbocel UFC100) was added under high-speed stirring to reach a target of 54 wt% relative to the weight of calcined Cu chabazite. The mixture was stirred for 30 minutes, and then a cellulose thickener was added under high-speed stirring to reach a target of 0.2 wt% relative to the total weight of the wet carrier coating. The mixture was stirred at high speed for 30 minutes, and then the carrier coating was stored in a sealed container for 2 days. The carrier coating was then stirred at high speed for 3 minutes and coated from the tip of an intermediate-processed DPF containing calcined SCR "Coating 1" and calcined PGM "Coating 2" (as described above) to reach 0.8 g / in. 3 The target carrier coating loading is calculated relative to the volume of the finished catalyst. The bricks were dried at 110°C for 45 minutes and then calcined at 500°C for 2 hours.

[0107] SCAT test

[0108] The test is performed using the SCAT test. This type of test does not include any other upstream or downstream catalyst, 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 enrichment conditions", or for "NOx enrichment conditions". X The "emphasis" conditions are 350ppm CO / 500ppm NH3 / 500ppm NO.

[0109] All embodiments used a 1-inch × 5.53-inch wall-flow filter substrate. The air velocity was the same in all tests.

[0110] An exemplary ASCF is manufactured having: an SCR carrier coating (0.8 g / in) on the wall of the inlet channel. 3 ); an in-wall composition containing PGM (Pt on alumina with different loadings) applied from the inlet side; and an in-wall SCR carrier coating (0.8 g / in) in the outlet channel. 3 The contrast filter has an overlying SCR layer (2.4 g / in). 3 ) and containing 3g / ft 3 The lower layer of Pt contains a PGM layer. The PGM coating is applied to the back 50% of the brick.

[0111] PGM level is 1g / ft 3 0.75g / ft 3 0.5g / ft 3 and 0.25g / ft 3 This gives the results discussed in this paper regarding SCR materials (1.6 g / in). 3 The ratios are 10:16, 7.5:16, 5:16, and 2.5:16. Here, the SCR material is a binder for the copper-exchanged zeolite and the carrier coating. In comparison, the standard ASC ratio in the examples is 30:24. This is representative of a conventional configuration.

[0112] In further SCAT testing, the results showed that for 1 g / ft 3 0.75g / ft 3 0.5g / ft 3 The conversion rates of Pt and NH3 are comparable, but for 0.25 g / ft 3 For Pt, the conversion rate is much worse. For 0.5 g / ft 3 The Pt and N2O yields are essentially the same as in the standard flow-through, but for those embodiments with higher Pt loadings, the yields are much lower.

[0113] When compared with standard ASC on the FT, the ASCF catalyst showed improved filtration efficiency in preliminary measurements. In particular, when the ASCF catalyst was used instead of standard ASC on the FT, PN10 emissions were reduced by 70%–90%.

[0114] Therefore, Pt 0.5g / ft 3 Nearly the value (with 1.6 g / in) 3 The optimal point (SCR pairing) is where the oxidation performance matches the SCR performance—the NH3 conversion is sufficient without excessive N2O generation, while the filtration performance addresses the reductant-derived particulate matter. Ideally, this ratio should be observed to be around 5:16.

[0115] exist Figure 4 In the text, for NH3 conversion rate, the lines at 300℃ from top to bottom are: standard, 1 g / ft 3 0.75g / ft 3 0.5g / ft 3 and 0.25g / ft 3 For N2O production, the peak values ​​from top to bottom are: 1 g / ft. 3 Standard, 0.75g / ft 3 0.5g / ft 3 and 0.25g / ft 3 For NOx production, the lines at 400℃ from top to bottom are: 1g, 0.75g, 0.5g, 0.25g, and standard.

[0116] As illustrated in these embodiments, a three-layer ASCF has been developed to transform the ASC concept from a flow-through approach to a filter substrate. Compared to standard two-layer ASCs, the three-layer ASCF approach broadens the range of feasible coating designs while significantly reducing particulate emissions. In particular, the use of a three-layer ASCF allows for different combinations of in-wall and top-wall coatings, enabling fine-tuning of ASC activity, back pressure, and filtration efficiency.

[0117] Subsequent testing using engine test data demonstrated that the same benefits could be achieved under real-world operating conditions. In this case, the ASCF or SCR / ASC brick was located downstream of another SCR flow-through brick (VSCR in this case). More information is shown in Figure 6. Here, the standard ASCF was coated with the same mass (grams) of SCR catalyst and PGM catalyst as the standard flow-through SCR / ASC, while the “lower PGM” variant had only half the amount of PGM but the same amount of SCR carrier coating. Steady-state (SS) engine test data were obtained at three different temperatures (270°C, 320°C, and 370°C), where the low PGM variant performed significantly better in terms of secondary emissions, while still being comparable to the SCR / ASC reference in terms of NH3 conversion—providing a better balance between NH3 conversion and secondary emissions for the low PGM variant.

[0118] In each set of results, the left column represents the standard SCR / ASC ratio, the middle column represents ASCF with SCR and PGM levels comparable to the standard SCR / ASC ratio, and the right column represents PGM levels half that of the middle column (total 0.5 g / ft). 3 PGM and 1.6g / in 3 (SCR).

[0119] Figure 6A The ASCF of this invention demonstrates that it achieves sufficiently good NH3 leakage control. Figure 6B This indicates an improvement in the reduced N2O production level. Figure 6C This indicates a decrease in NO x Improved production levels. The SS numbers in each chart reflect the test temperature under steady-state conditions.

[0120] Figures 7A to 7C For the same components, use with Figure 1 and Figure 2 Same reference numerals as shown in the attached figures.

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

[0122] Figure 7B and Figure 7CThis embodiment is in which the second catalyst layer 50 does not overlap with the third catalyst layer 55. These two layers (50, 55) are provided as an inner-wall carrier coating and together coat the catalyst article 1 along a total length 45. Figure 7B In this structure, the second catalyst layer 50 comprises approximately 25% of the total length 45, and the third catalyst layer 55 comprises approximately 75% of the total length 45. Figure 7C In the process, the second catalyst layer 50 is approximately 50% of the total length 45, and the third catalyst layer 55 is approximately 50% of the total length 45.

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

[0124] Figure 8 The comparison between embodiments 7A-7C and comparative examples is shown, in which the second catalyst layer 50 is approximately 70% of the total length 45 (inside the wall), and the third catalyst layer 55 is approximately 80% of the total length 45 (inside the wall). The provision of these overlapping in-wall coatings means that the platinum group metals and the SCR catalyst overlap within the wall. The columns from left to right are: comparative example, embodiments 7C, 7B, and 7A.

[0125] Figure 8 Display for Figure 7C (62) and Figure 7B The implementation scheme of (63) achieves the lowest back pressure.

[0126] Figure 9 The conversion rate of NH3 is shown at different temperatures. Figure 7C The performance of the implementation scheme is always the highest. Figure 7B The implementation scheme has the worst performance. The columns from left to right are: Comparative Example, Implementation Scheme 7C, 7B, and 7A.

[0127] Figure 10 The outputs of NH3, N2O, and NOx are shown at different temperatures and ANR ratios. The columns from left to right for each group of conditions are: Comparative Example, Implementation Scheme 7C, 7B, and 7A.

[0128] As used herein, the term "comprising" may be replaced by the definition "consistently consisting of" or "components of". The term "comprising" is intended to indicate that the stated element is necessary, but other elements may be added and still form a construction within the scope of the claims. The term "consistently consisting of" limits the scope of the claims to the specified materials or steps and those that do not materially affect the essential and novel features of the invention protected by the claims. The term "components of" limits the claims to exclude materials other than those listed, except for impurities typically associated with them.

[0129] The detailed description above has been provided 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 skilled in the art and remain within the scope of the appended claims and their equivalents.

[0130] To avoid any doubt, the full text of all recognized references is incorporated herein by reference.

Claims

1. A catalyst article for treating waste gas, said catalyst article comprising: A wall-flow filter substrate having an inlet channel that opens at an inlet end and closes at an outlet end, the inlet channel being adjacent to an outlet channel that is closed at the inlet end and open at the outlet end. The wall-flow filter includes at least a first catalyst layer, a second catalyst layer, and a third catalyst layer, wherein: (i) The first catalyst layer extends from the inlet end of the substrate and comprises a first SCR composition; (ii) The second catalyst layer is disposed within or on the wall of the inlet channel extending from the inlet end of the substrate, and comprises a PGM-containing composition, wherein: When the second catalyst layer is disposed on the wall of the inlet channel, the first catalyst layer is disposed on the second catalyst layer, and When the second catalyst layer is disposed within the wall of the inlet channel, the first catalyst layer is disposed on the wall of the inlet channel; and (iii) The third catalyst layer is disposed within or on the wall of the outlet channel extending from the outlet end of the substrate, and comprises a second SCR composition; The second catalyst layer contains g / ft 3 The calculated PGM in the first catalyst layer and the third catalyst layer at a ratio of g / in 3 The total ratio of the first SCR composition to the second SCR composition is between 1.5:8 and 5:

8.

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

3. The catalyst article according to claim 1 or claim 2, wherein: (i) The first catalyst layer extends at most 100% of the longitudinal length of the substrate from the inlet end to the outlet end; and / or (ii) The second catalyst layer extends at most 100% of the longitudinal length of the substrate from the inlet end to the outlet end; and / or (iii) The third catalyst layer extends from the outlet end to the inlet end of the substrate for at most 100% of its longitudinal length.

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

5. The catalyst article according to claim 1 or claim 2, wherein the second catalyst layer and the third catalyst layer do not overlap and together extend 100% of the longitudinal length of the substrate from the outlet end to the inlet end.

6. The catalyst article according to claim 1 or claim 2, wherein the second catalyst layer contains g / ft 3 The calculated PGM in the first catalyst layer and the third catalyst layer at a ratio of g / in 3 The total amount of the first SCR composition and the second SCR composition is calculated to be approximately 5:

16.

7. The catalyst article according to claim 1 or claim 2, wherein the PGM-containing composition contains Pt.

8. The catalyst article according to claim 1 or claim 2, wherein the PGM-containing composition comprises alumina as a carrier of the PGM.

9. The catalyst product according to claim 1 or claim 2, wherein the catalytically active SCR component of the first SCR composition and / or the second SCR composition comprises one or more metal-exchanged zeolites.

10. The catalyst product according to claim 9, wherein the metal-exchange zeolite is a microporous zeolite.

11. The catalyst article according to claim 1 or claim 2, wherein the weight ratio of the first SCR composition to the second SCR composition in the first catalyst layer and the third catalyst layer is 2:3 to 3:

2.

12. The catalyst article according to claim 1 or claim 2, further comprising means for electrically heating the catalyst article.

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

14. The waste gas treatment system according to claim 13, wherein the waste gas treatment system comprises, in sequence, a catalytic fly ash filter (CSF), a device for injecting a nitrogen-containing reducing agent, an SCR catalyst product, and a catalyst product according to any one of claims 1 to 12.

15. A fuel combustion and exhaust gas treatment system, the fuel combustion and exhaust gas treatment system comprising an engine and an 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.

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

Images