Catalyst article comprising an ammonia oxidation catalyst

Abstract

A catalyst article for treating an exhaust stream, comprising, in a first coating configuration, a substrate and a coating layer comprising a first catalyst containing a noble metal component and a second catalyst containing a molecular sieve component; or - a substrate, - a first coating layer comprising a first catalyst containing a noble metal component, and - a second coating layer covering at least a portion of the first coating layer and comprising a second catalyst containing a molecular sieve component, in a second coating configuration, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 5.7% or more. It also relates to a process for preparing the catalyst article by using a pore former in a slurry for depositing the coating layer, and a system for treating an exhaust stream containing the catalyst article.

Description

Technical Field

[0001] The present invention relates to selective ammonia oxidation (AMO x ) catalysts, methods for their manufacture, and catalyst systems for treating exhaust gas streams.

Background Art

[0002] Diesel engine exhaust is a heterogeneous mixture containing particulate emissions such as soot, and gaseous emissions containing carbon monoxide (CO), unburned or partially burned hydrocarbons (HC), and nitrogen oxides (collectively referred to as NOx). Catalytic compositions, which are often disposed on one or more monolith substrates, are placed within engine exhaust treatment systems to convert some or all of these exhaust components into harmless compounds. Control of NOx emissions has always been one of the most important topics in exhaust treatment, especially for diesel engines, due to the environmental adverse effects of NOx on ecosystems, humans, animals, and plants.

[0003] To reduce NOx in exhaust gas, various treatment processes have been used, such as catalytic reduction of nitrogen oxides. One typical catalytic reduction process is selective catalytic reduction using ammonia (NH3) or an ammonia precursor as a reducing agent in the presence of oxygen in the atmosphere, which is also referred to as the SCR process. The SCR process is considered excellent because high levels of NOx reduction can be achieved with a small amount of reducing agent. Typically, nitrogen oxides and the reducing agent NH3 react according to the following equations. 4NO + 4NH3 + O2 → 4N2 + 6H2O (standard SCR reaction) 2NO2 + 4NH3 + O2 → 3N2 + 6H2O (slow SCR reaction) NO + NO2 + 2NH3 → 2N2 + 3H2O (fast SCR reaction).

[0004] In the SCR process, typically, a stoichiometrically excessive reducing agent, ammonia or its precursor, is dosed into the exhaust stream to reduce NOx with the highest possible conversion rate. This excessive ammonia can be discharged from the exhaust pipe of an automobile. Another potential scenario where ammonia can be discharged from the exhaust pipe is the desorption of a significant amount of ammonia held on the Lewis and Bronsted acid sites on the surface of the SCR catalyst during the low-temperature part of a typical operating cycle when the operating temperature rises. When the release of ammonia into the air, also known as ammonia slip, occurs, many problems arise. Ammonia slip is harmful to human health and the environment. Ammonia can cause significant eye and throat inflammation when it exceeds 100 ppm and may cause significant skin irritation when it exceeds 400 ppm. The IDLH value of ammonia was known to be 500 ppm in air. In addition, ammonia is corrosive, especially in its aqueous form. The condensation of ammonia and water in the lower-temperature region of the exhaust line downstream of the exhaust catalyst results in a corrosive mixture that damages the exhaust line. Ammonia should be removed before entering the tailpipe.

[0005] An ammonia oxidation (AMOx) catalyst (also known as an ammonia slip catalyst, ASC) installed downstream of the SCR catalyst is generally used to convert the slipped ammonia to N2. Such catalysts are known and generally contain noble metal active species for oxidizing ammonia and usually also contain SCR active species.

[0006] International Publication No. WO 2010 / 062730 (A2) describes a catalyst system for treating an exhaust gas stream containing NOx, comprising at least one monolithic catalyst substrate, a subcoat washcoat layer coated on one end of the monolithic substrate and containing a material composition A effective for catalyzing NH3 oxidation, and a topcoat washcoat layer coated over at least a portion of the subcoat washcoat layer over a length of the monolithic substrate sufficient to cover it and containing a material composition B effective for catalyzing selective catalytic reduction (SCR) of NOx, wherein the material composition B may contain a zeolite or a non-zeolite molecular sieve, the topcoat washcoat layer.

[0007] International Publication No. WO 2017 / 037006 (A1) describes a catalyst for oxidizing ammonia, comprising a washcoat containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms physically mixed with platinum or platinum and rhodium on a refractory metal oxide support. Also described in this patent application is a zoned catalyst for oxidizing ammonia, comprising a first washcoat zone containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms and substantially free of platinum group metals, and a second washcoat zone containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms physically mixed with platinum on a refractory metal oxide support containing a chemical combination including alumina, silica, zirconia, titania, and physical mixtures or atomically doped combinations thereof.

[0008] International Publication No. WO 2020 / 210295 (A1) describes a catalyst comprising an AMOx catalyst and an SCR catalyst, wherein the SCR catalyst is located in a zone upstream of the AMOx catalyst, in a layer above the AMOx catalyst, homogeneously blended with the AMOx catalyst, or any combination thereof. The AMOx catalyst contains a platinum group metal on a support, and the SCR catalyst contains a zeolite-based or non-zeolite-based molecular sieve and optionally a promoter metal.

[0009] U.S. Patent Application Publication No. 2021 / 0299643 (A1) describes a catalyst article comprising a substrate having an inlet and an outlet, a first coating comprising a blend of (1) platinum on a support and (2) a first SCR catalyst, and a second coating comprising a second SCR catalyst, wherein the support comprises at least one of a molecular sieve or a SiO2 - Al2O3 mixed oxide, and the first SCR catalyst comprises a Cu and Mn exchanged molecular sieve.

[0010] The excellent catalytic performance of the AMOx catalyst regarding NH3 conversion at low temperatures, particularly around 250 °C, is important because when the exhaust gas reaches the AMOx catalyst after passing through one or more of the upstream exhaust gas treatment components such as a diesel oxidation catalyst (DOC), a filter, and an SCR catalyst, the exhaust gas temperature decreases to such a temperature.

[0011] The catalytic performance is desirable when the AMOx catalyst has improved catalytic performance for converting the slipped ammonia to N2 at low temperatures. SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a catalyst article comprising an SCR catalyst and a noble metal-based catalyst that can perform better than conventional AMOx catalyst articles for converting the slipped ammonia at low temperatures, particularly around 250 °C.

[0013] This object was achieved by a catalytic article comprising a porous coating layer containing a molecular sieve component on a substrate.

[0014] Accordingly, in one aspect, the present invention is a catalytic article for treating an exhaust stream, comprising: - a substrate; - a coating layer comprising a first catalyst containing a noble metal component and a second catalyst containing a molecular sieve component, contained in a first coating configuration; or - a substrate; - a first coating layer comprising a first catalyst containing a noble metal component; - a second coating layer covering at least a portion of the first coating layer and comprising a second catalyst containing a molecular sieve component, contained in a second coating configuration, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 5.7% or more, relating to a catalytic article.

[0015] In a second aspect, the present invention is a process for preparing a catalytic article for treating an exhaust stream, comprising: - applying a slurry comprising a first catalyst containing a noble metal component, a second catalyst containing a molecular sieve component, and a pore former onto a substrate, optionally drying and firing to form a coating layer in a first coating configuration; or -Apply a first slurry containing a first catalyst containing a noble metal component onto a substrate, dry and / or calcine to form a first coating layer, then apply a second slurry containing a second catalyst containing a molecular sieve component and a pore former, optionally dry, and calcine to form a second coating layer in a second coating configuration, including that the pore former is in the form of particles and is used in an amount of at least 15% by weight based on the filling amount of the coating layer in the first coating configuration or the second coating layer in the second coating configuration, related to a process.

[0016] In a third aspect, the present invention is a system for treating an exhaust stream, including a reductant source (e.g., NH3 or its precursor), the catalytic article described herein, and optionally one or more of a diesel oxidation catalyst (DOC), a selective catalytic reduction catalyst (SCR), a three-way conversion catalyst (TWC), a four-way conversion catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), a NOx trap, a hydrocarbon trap catalyst, a sensor, and a mixer, related to a system.

[0017] In a fourth aspect, the present invention is a method for treating an exhaust stream containing nitrogen oxides, including contacting the exhaust stream with the catalytic article described herein in the presence of NH3 as a reductant, or passing the exhaust stream through the system described herein, related to a method.

[0018] Surprisingly, the inventors have found that an AMOx catalytic article having a porous coating containing a molecular sieve component according to the present invention can provide improved NH3 conversion at low temperatures, particularly at about 250 °C, compared to an AMOx catalytic article without the porous coating described herein.

Best Mode for Carrying Out the Invention

[0019] The present invention will be described in detail below in this specification. It should be understood that the present invention can be implemented in many different ways and should not be construed as being limited to the embodiments described herein.

[0020] In this specification, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Terms such as “comprise,” “comprising,” etc. are used interchangeably with “contain,” “containing,” etc. and should be interpreted in a non-limiting, open-ended manner. That is, for example, additional components or elements may be present. Expressions such as “consists of” or “consists essentially of” or cognates thereof may be subsumed within “comprises” or cognates thereof.

[0021] In this specification, the term “inter-particle pores” refers to pores formed during the preparation of the coating layer, including voids generated by the stacking of starting material particles and voids remaining after the pore-forming agent has burned out, and does not include intra-particle pores inherent in the starting material particles.

[0022] In this specification, any reference to “upstream” and “downstream” will be understood to be a relative position with respect to the flow direction of the flow, for example, the flow direction of the exhaust flow.

[0023] As used herein, the term "coating" refers to a film deposited on the surface of the wall of a substrate that defines a channel for the exhaust gas flow to pass through. The coating can consist of a single coating layer or can consist of two or more coating layers. The coating layer can be prepared by repeating the coating step two or more times to achieve a target filling amount, and thus it is understood to include more than one sub-layer having the same chemical composition and catalytic activity. Such a coating layer containing more than one sub-layer having the same chemical composition and catalytic activity is referred to as one coating layer.

[0024] In the context of the coating layer, the term "porosity" as used herein means the ratio of the total cross-sectional area of pores to the total cross-sectional area of the coating layer on a cross-sectional surface perpendicular to the axial direction of the substrate (i.e., the exhaust gas flow channel direction) as measured by SEM.

[0025] As used herein, the term "solid content" is intended to refer to the content of substances that are non-volatile under firing conditions and is expressed, for example, as the ratio of weights measured before and after a firing process at 500 °C for 1 hour.

[0026] According to a first aspect, the present invention is a catalytic article for treating an exhaust gas flow, comprising - a substrate, - a coating layer comprising a first catalyst containing a noble metal component and a second catalyst containing a molecular sieve component, included in a first coating configuration, or - a substrate, - a first coating layer comprising a first catalyst containing a noble metal component, - a second coating layer covering at least a part of the first coating layer and comprising a second catalyst containing a molecular sieve component, included in a second coating configuration, Provided is a catalyst article in which the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 5.7% or more.

[0027] In some specific embodiments, the catalyst article for treating an exhaust stream according to the present invention is or - a substrate, - a first coating layer containing a first catalyst containing a noble metal component, - a second coating layer covering at least a part of the first coating layer and containing a second catalyst containing a molecular sieve component, wherein the second coating layer has interparticle pores with a porosity of 5.7% or more.

[0028] <Substrate> A substrate useful for the catalyst article according to the present invention generally refers to a structure suitable for withstanding the conditions of contact in an exhaust stream, on which a catalyst material is supported in the form of a coating, typically a washcoat. The substrate can have an inlet end and an outlet end defining its axial length, and a plurality of fine parallel gas flow channels extending along the axial length.

[0029] The substrate is usually inert and has conventionally been made from, for example, ceramic or metallic materials and is also known as an "inert substrate". Alternatively, the substrate can be active and can, for example, consist of extrudates containing catalytically active species.

[0030] The substrate can be a monolithic flow-through structure, which has a plurality of fine parallel gas flow channels extending from the inlet end to the outlet end of the substrate. As a result, the flow channels are open to the fluid flow passing therethrough. The flow channels, which are essentially straight paths from the fluid inlet to the fluid outlet, are defined by walls to which a catalytic material is applied as one or more coatings (e.g., washcoat) such that the gas flowing through the flow channels contacts the catalytic material. The flow channels of the monolithic substrate are thin-walled channels and can have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. Such a structure can contain from 60 to over 900 flow channels (or "cells") per square inch of cross-section. For example, the substrate can have 60 to 700 cells per square inch ("cpsi"). The wall thickness of the flow-through substrate can vary, and a typical range is from 2 mils to 0.1 inch.

[0031] The substrate can also be a monolithic wall-flow structure having a plurality of fine parallel gas flow channels extending along the length of the substrate from the inlet end to the outlet end, with alternating flow channels blocked at opposite ends. The flow channels are defined by walls to which a catalytic material is applied as one or more coatings (e.g., washcoat) such that the gas flowing through the flow channels contacts the catalytic material. This configuration requires the gas to flow through the porous walls of the wall-flow substrate to reach the outlet end. The wall-flow substrate can have up to 700 cpsi, for example, 100 to 400 cpsi. The flow channels of the monolithic substrate are thin-walled channels and can have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. The wall thickness of the wall-flow substrate can vary within a typical range of 2 mils to 0.1 inch.

[0032] The term "washcoat" has its ordinary meaning in the art and refers to a thin adhesive coating of a catalyst material or other material applied to a substrate. A washcoat is generally formed by preparing a slurry containing a desired material and processing aids such as a binder having an optionally specific solids content (e.g., 15 - 60 wt%), then applying the slurry onto the substrate, drying it, and firing it to provide a washcoat layer. The washcoat is filled onto the substrate in the form of one or more layers, generally in an amount of 0.1 - 10 g / in 3 , for example, 0.3 - 7 g / in 3 , or 0.5 - 4 g / in 3 .

[0033] <First Catalyst> The first catalyst can be a noble metal-based oxidation catalyst commonly used to catalyze the conversion of NH3 to form N2, which generally contains a noble metal component, preferably a platinum group metal component. The noble metal component can contain one or more selected from ruthenium, rhodium, iridium, palladium, platinum, silver, and gold on the particles of the carrier. Preferably, the noble metal component contains one or more selected from ruthenium, rhodium, iridium, palladium, and platinum, more preferably palladium and platinum, and most preferably platinum on the particles of the carrier.

[0034] In some embodiments, the noble metal component does not substantially contain any platinum group metal (PGM) other than Pt, and in particular does not substantially contain any noble metal other than Pt.

[0035] As used herein, in the context of the noble metal component, the term "does not substantially contain" is intended to mean that no PGM or noble metal other than Pt is intentionally added or used. It will be understood by those skilled in the art that trace amounts of impurity PGM or noble metal from the raw materials cannot be avoided. Trace amounts generally refer to amounts less than 1 wt%, including less than 0.75 wt%, less than 0.5 wt%, less than 0.25 wt%, or less than 0.1 wt%.

[0036] The noble metal can exist in any possible valence state, for example, it can be each metal or metal oxide in the catalytically active form, or, for example, each metal compound, complex, etc., which will be understood to decompose during the calcination or use of the catalyst or otherwise be converted into the catalytically active form.

[0037] Materials useful as supports for noble metals in the first catalyst can be any material suitable for receiving and supporting noble metals, for example, oxides of metals selected from the group consisting of molecular sieves, Ti, Si, W, Al, Ce, Zr, Mg, Ca, Ba, Y, La, Pr, Nb, Mo, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sn, Sm, Eu, Hf, and Bi.

[0038] In particular, the support for the noble metal can be selected from high surface area alumina (for example, γ-alumina having a specific surface area of 50 to 300 m 2 / g), silica, titania, ceria, zirconia, lanthana, barium, yttria, neodymia, praseodymia, titania, europia, samaria, hafnia, and any composites or combinations thereof. Exemplary supports can be composite oxides of silica-alumina, alumina-zirconia, alumina-lanthana, alumina-chromia, alumina-barium, or alumina-ceria.

[0039] It will be understood that when two or more noble metal components are present, they can be supported on the same or different support particles, and the same noble metal component can be supported on one or more types of support particles.

[0040] <The second catalyst> The second catalyst includes a molecular sieve component which can be a zeolitic or non-zeolitic molecular sieve having selective catalytic reduction (SCR) activity. The molecular sieve component useful for the second catalyst is optionally promoted with a metal. As used herein, a molecular sieve generally refers to a framework material based on a three-dimensional network structure of oxygen ions that contains tetrahedral sites and has a substantially uniform pore distribution. The molecular sieves suitable for the purposes of the present invention can be microporous or mesoporous.

[0041] In particular, the molecular sieve component can be an optionally metal-promoted zeolite. As used herein, the term "metal-promoted" in the context of molecular sieves is intended to mean that a metal that can improve any performance of the zeolite is incorporated into and / or on the zeolite.

[0042] Preferably, suitable molecular sieves can include, but are not limited to, aluminosilicate zeolites having a framework type selected from the group consisting of AEI, AEL, AFI, AFT, AFO, AFX, AFR, ATO, BEA, CHA, DDR, EAB, EMT, ERI, EUO, FAU, FER, GME, HEU, JSR, KFI, LEV, LTA, LTL, LTN, MAZ, MEL, MFI, MOR, MOZ, MSO, MTW, MWW, OFF, RTH, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TON, TSC, and WEN. More preferably, the molecular sieve includes zeolites having a framework type selected from the group consisting of AEI, BEA (e.g., beta), CHA (e.g., chabazite, SSZ-13), AFT, AFX, FAU (e.g., zeolite Y), MOR, MFI (e.g., ZSM-5), MOR (e.g., mordenite), and MEL, among which CHA and AEI are particularly preferred.

[0043] When a zeolite is referred to herein with reference to the framework type code generally accepted by the International Zeolite Association (IZA), it is understood that this is intended to include not only the reference materials but also any isotypic framework materials having SCR catalytic activity. Lists of reference materials and isotypic framework materials for each framework type code are available from the IZA database (http: / / www.iza-structure.org / databases / ).

[0044] In some embodiments, the molecular sieve component in the second catalyst can be a metal-promoted zeolite, which zeolite is selected from those described above herein. The promoter metal can be selected from noble metals such as Au and Ag, platinum group metals such as Ru, Rh, Pd, In, and Pt, base metals such as Cr, Zr, Nb, Mo, Fe, Mn, W, V, Al, Ti, Co, Ni, Cu, Zn, Sb, Sn, and Bi, alkaline earth metals such as Ca and Mg, and any combination thereof. The promoter metal is preferably Fe or Cu, or a combination thereof.

[0045] In some exemplary embodiments, the second catalyst comprises a Cu and / or Fe-promoted zeolite having a framework type of AEI, BEA, CHA, AFT, AFX, FAU, FER, KFI, MOR, MFI, MOR, or MEL, particularly a Cu and / or Fe-promoted zeolite having a framework of CHA and AEI.

[0046] The promoter metal can be present in the metal-promoted molecular sieve in an amount of 0.1 to 20 wt%, 0.5 to 15 wt%, 1 to 10 wt%, or 2 to 6 wt% on an oxide basis, based on the total weight of the metal-promoted molecular sieve. In some exemplary embodiments where Cu or Fe is used as the promoter metal, the promoter metal is preferably present in an amount of 0.5 to 15 wt%, or 1 to 15 wt%, or 1 to 10 wt% on an oxide basis, based on the total weight of the metal-promoted molecular sieve.

[0047] The molecular sieve component may have an average crystallite size in the range of 0.1 to 4.0 microns (μm), or 0.5 to 1.5 μm.

[0048] When a molecular sieve having an aluminosilicate framework, such as aluminosilicate zeolite and metal-promoted aluminosilicate zeolite, is used, the aluminosilicate framework preferably has a silica to alumina molar ratio (SAR) in the range of 2 to 200, 5 to 100, 8 to 50, or 10 to 30.

[0049] The second catalyst may optionally contain a further component having SCR activity, such as a vanadium-based SCR catalyst containing vanadium species on a refractory metal oxide support such as alumina, silica, zirconia, titania, ceria, and combinations thereof. Vanadium-based SCR catalysts are well-known and are widely commercially used in mobile exhaust treatment applications. For example, typical vanadium-based SCR catalyst compositions are described in U.S. Patent Nos. 4,010,238 and 4,085,193, the entire contents of which are incorporated herein by reference. Particularly in mobile applications, an exemplary vanadium-based SCR catalyst composition commercially used contains 5 to 20 wt% of WO3 and 0.5 to 6 wt% of V2O5 supported on TiO2 particles. These vanadium-based SCR catalysts may contain further inorganic materials such as SiO2 and ZrO2.

[0050] <Coating configuration> In the catalyst article according to the present invention, the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 5.7% or more, or 7.0% or more, preferably 8.0% or more, particularly 9.0% or more. More preferably, the coating layer in the first coating configuration or the second coating layer in the second coating configuration has interparticle pores with a porosity of 25% or less, preferably 20% or less, particularly 15% or less.

[0051] In particular, the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity in the range of 5.7% to 25%, or 7.0% to 20%, or 8.0% to 15%, or 9.0% or 15%.

[0052] As used herein, interparticle pores particularly refer to pores having a pore diameter in the range of less than 50 microns (μm), preferably in the range of 5 to 30 microns (μm), more preferably in the range of 8 to 20 μm, as measured by scanning electron microscopy (SEM). The pore diameter of the pores refers to the diameter determined by SEM assuming that the pore shape is a perfect circle.

[0053] In some embodiments, the catalyst article according to the present invention has a first coating configuration and includes a coating layer (hereinafter also referred to as "coating layer containing the first catalyst and the second catalyst") containing a first catalyst containing a noble metal component and a second catalyst containing a molecular sieve component. In other words, the first catalyst and the second catalyst are not separated into separate layers but are physically blended in a single coating layer.

[0054] In embodiments where the catalyst article according to the present invention has a first coating configuration, the coating layer containing the first catalyst and the second catalyst can be disposed along the gas flow channel extending over the entire axial length of the substrate, i.e., from the inlet end to the outlet end. Alternatively, the coating layer containing the first catalyst and the second catalyst can extend along the gas flow channel from the outlet end towards the inlet end over a partial axial length of the substrate, for example, less than 30% to 100% (including 40%, 50%, 60%, 70%, 80%, or 90%) of the length of the substrate. In the latter case, another coating layer, for example, another SCR catalyst coating layer, can be disposed upstream, i.e., from the inlet end to the outlet end over a partial length of the substrate.

[0055] The first catalyst and the second catalyst can be included in the coating layer containing the first catalyst and the second catalyst at a weight ratio in the range of 1:15 to 2:1, preferably 1:10 to 1:1, more preferably 1:8 to 1:2.

[0056] In some other embodiments, the catalyst article according to the present invention has a second coating configuration and includes: i) a first coating layer (hereinafter also referred to as the "first coating layer") containing a first catalyst containing a noble metal component; and ii) a second coating layer (hereinafter also referred to as the "second coating layer") covering at least a part of the first coating layer and containing a second catalyst containing a molecular sieve component.

[0057] In the embodiment where the catalyst article has a second coating configuration, the second coating layer is directly above the first coating layer and can cover a part or the whole of the first coating layer.

[0058] For example, in some specific embodiments, the catalyst article has a second coating configuration and includes: i) a first coating layer containing a first catalyst containing a noble metal component; and ii) a second coating layer containing a second catalyst containing a molecular sieve component. Both the first and second coating layers extend along the gas flow channel over the entire axial length of the substrate, and the second coating layer is directly above the first coating layer.

[0059] In some other specific embodiments, the catalyst article has a second coating configuration and includes: i) a first coating layer containing a first catalyst containing a noble metal component; and ii) a second coating layer containing a second catalyst containing a molecular sieve component. The first coating layer extends along the gas flow channel over the entire axial length of the substrate, and the second coating layer is directly above the first coating layer and extends along the gas flow channel from the inlet end or the outlet end over a partial axial length of the substrate, for example, less than 30% to 100% (including 40%, 50%, 60%, 70%, 80%, or 90%) of the length of the substrate.

[0060] In some further specific embodiments, the catalyst article has a second coating configuration and includes: i) a first coating layer including a first catalyst containing a noble metal component; and ii) a second coating layer including a second catalyst containing a molecular sieve component. The first coating layer extends along the gas flow channel from an inlet end or an outlet end over a partial axial length of the substrate, for example, less than 30% to 100% (including 40%, 50%, 60%, 70%, 80%, or 90%) of the length of the substrate. The second coating layer is directly above the first coating layer and extends along the gas flow channel over the entire axial length of the substrate.

[0061] In some further specific embodiments, the catalyst article has a second coating configuration and includes: i) a first coating layer including a first catalyst containing a noble metal component; and ii) a second coating layer including a second catalyst containing a molecular sieve component. The first coating layer and the second coating layer each extend along the gas flow channel from an outlet end and an inlet end over a partial axial length of the substrate, for example, less than 30% to 100% (including 40%, 50%, 60%, 70%, 80%, or 90%) of the length of the substrate. The second coating layer is directly above the first coating layer.

[0062] Optionally, the catalyst article having the second coating configuration may further include a third coating layer adjacent to or overlapping the second coating layer. The third coating layer is, for example, another SCR catalyst coating layer different from the second coating layer and may or may not have the porosity described herein.

[0063] Thus, in certain embodiments, the catalyst article has a second coating configuration and includes: i) a first coating layer including a first catalyst containing a noble metal component; ii) a second coating layer including a second catalyst containing a molecular sieve component; and iii) a third SCR catalyst coating layer. The first coating layer extends along the gas flow channel over the entire axial length of the substrate. The second and third coating layers are located directly above the first coating layer and extend from both ends along the gas flow channel over a partial axial length of the substrate. For example, the second coating layer extends from the inlet end, and the third coating layer extends from the outlet end, both along the gas flow channel over a partial axial length of the substrate.

[0064] In the above embodiments where the catalyst article has a second coating configuration, the first catalyst and the second catalyst may be included in a weight ratio in the range of 1:15 to 2:1, preferably 1:10 to 1:1, more preferably 1:8 to 1:2.

[0065] It will be understood that the catalyst articles having the second coating configuration described herein may, without limitation, include a single substrate piece or two or more substrate pieces. For example, a catalyst article as described in the above "some other specific embodiments" may include two substrate pieces, one piece carrying a part of the first coating layer and the second coating layer, and the other piece carrying the remaining part of the first coating layer.

[0066] Any possible variations including two or more substrate pieces are contemplated and may be included in the present invention.

[0067] In any embodiment according to the present invention, the noble metal component is present in a total amount of 0.01 to 20 g / ft 3 , preferably 0.5 to 10 g / ft 3 , more preferably 1.5 to 5 g / ft 3 based on the volume of the substrate, calculated as each noble metal.

[0068] Additionally or alternatively, the molecular sieve component may be present in an amount of 0.5 to 6.0 g / in 3 , preferably 1.0 to 4.0 g / in 3 , more preferably 1.5 to 3.0 g / in 3 based on the volume of the substrate.

[0069] Any of the coating layers described herein may also contain one or more other components in addition to the catalyst. The other components may be non-catalytically active components, such as processing aids useful in the preparation of the catalytic article, such as stabilizers, surfactants, and binders.

[0070] The other components may also be catalytically active. For example, when the catalytic article according to the invention comprises a first coating layer and a second coating layer as described herein, the first coating layer may further comprise a zeolite or non-zeolite molecular sieve component. Suitable molecular sieves may be selected from the molecular sieve components described for the second catalyst.

[0071] The catalytic article according to the invention can be prepared by a conventional washcoating process. The washcoating process generally involves applying one or more slurries containing each catalyst onto a substrate. For the purposes of the present invention, the pore former in particulate form is used in one or more slurries to provide interparticle pores at a desired porosity in the resulting coating layer. The pore former is included in the slurry from which the coating layer in the first coating configuration having the desired porosity or the second coating layer in the second coating configuration is obtained upon firing.

[0072] Accordingly, in a second aspect, the present invention is a process for preparing a catalytic article for treating an exhaust stream, comprising: - applying a slurry comprising a first catalyst containing a noble metal component, a second catalyst containing a molecular sieve component, and a pore former onto a substrate, optionally drying, and firing to form a coating layer in a first coating configuration. or - applying a first slurry containing a first catalyst containing a noble metal component onto a substrate, drying and / or firing to form a first coating layer, and then applying a second slurry containing a second catalyst containing a molecular sieve component and a pore former, optionally drying, firing to form a second coating layer in the first coating configuration, including providing a process in which the pore former is in particulate form and is used in an amount of at least 15% by weight, respectively, based on the loading of the coating layer in the first coating configuration or the second coating layer in the second coating configuration.

[0073] The substrate for supporting the coating layer in the first coating configuration or the first coating layer in the second coating configuration can be a blank substrate or can be contemplated to be optionally coated with any suitable bottom coating layer. The blank substrate is intended to mean a substrate that does not carry a coating layer before the coating layer in the first coating configuration or the first coating layer in the second coating configuration is applied thereon.

[0074] The pore former is preferably used in an amount of at least 18% by weight or at least 20% by weight, respectively, based on the loading of the coating layer in the first coating configuration or the second coating layer in the second coating configuration. In particular, the pore former can be used in an amount of 50% by weight or less, or 40% by weight or less, respectively, based on the loading of the coating layer in the first coating configuration or the second coating layer in the second coating configuration.

[0075] In particular, the pore former can be used in an amount of 18% to 50% by weight, or 20% to 40% by weight, respectively, based on the loading of the coating layer in the first coating configuration or the second coating layer in the second coating configuration.

[0076] The pore former can be organic or inorganic material particles that can be burned out during the firing step to provide a coating layer, leaving voids. For example, the pore former can be selected from organic materials such as natural and synthetic polymers, organic low molecular weight compounds, inorganic salts and carbon materials, cellulose-containing natural materials, and any combination thereof.

[0077] Suitable natural and synthetic polymers as pore formers include, but are not limited to, polyether polyols such as polyethylene glycol and its alkyl cap derivatives, styrene homopolymers or copolymers such as polystyrene, poly(meth)acrylic acid and its ester derivatives such as polymethyl methacrylate, cellulose, ether and ester derivatives of cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, and any combination thereof.

[0078] Suitable organic low molecular weight compounds as pore formers include, but are not limited to, benzoic acid and its derivatives, carbamide (urea), sugar crystals, and any combination thereof.

[0079] Suitable inorganic salts as pore formers include, but are not limited to, ammonium bicarbonate, magnesium carbonate, and any combination thereof.

[0080] Suitable carbon materials as pore formers include, but are not limited to, carbon black, carbon fiber, graphite, and any combination thereof.

[0081] Suitable cellulose-containing natural materials as pore formers can be granulated products from dry plants, such as sunflower, cotton, rice, wheat, sorghum, pampas grass, sugarcane, corn, bamboo, and any combination thereof, but are not limited thereto. The granulated products can be obtained from various parts of plants such as leaves, bark, straw, roots, husks, and any combination thereof.

[0082] The pore former can be particles having various shapes, including but not limited to spheres, tablets, cylinders, or fibers. Preferably, the pore former has an average particle size D in the range of 15 to 25 μm, preferably 17 to 21 μm. 50 It has.

[0083] The steps of preparing and applying the slurry, drying and firing the coated slurry can be carried out by conventional methods for the washcoating process without any particular limitations. Generally, a slurry for washcoating can be prepared by suspending finely divided particles of the catalyst in a suitable vehicle (e.g., water), to which an accelerator, a stabilizer, and / or a surfactant can be added in the form of a solution in water or a water-miscible vehicle. The slurry can be milled / micronized such that substantially all solids have an average particle size in the range of less than 10 microns, e.g., 0.1 to 8 microns. Milling / micronization can be achieved in a ball mill, a continuous attritor mill, or other similar equipment. The suspension or slurry generally has a pH of less than 2 to 9 and can be adjusted by adding inorganic or organic acids and / or bases as necessary. The solid content of the slurry can be, for example, 15 to 60 wt%. The resulting slurry can be applied to the substrate by dipping the substrate into the slurry or otherwise coating the substrate such that a catalyst coating layer of the desired loading is deposited on the substrate. Thereafter, the coated substrate can optionally be dried at a temperature in the range of 100 to 300 °C. Firing is generally carried out by heating at a temperature in the range of 350 to 650 °C for a certain period of time, e.g., 1 to 3 hours. Drying and firing are typically carried out in air. The processes of coating, drying, and firing can be repeated as necessary to achieve the final desired weight measurement of the coating layer on the support. The loading of the coating layer can be determined by calculating the difference in weight before and after applying the coating layer. The pore former, if used, can be incorporated into the slurry at any time during the preparation of the slurry, e.g., after milling / micronization.

[0084] The catalyst article according to the present invention can be used to treat the exhaust stream from an automotive combustion engine, particularly a diesel engine.

[0085] Thus, in a third aspect, the present invention relates to a system for treating an exhaust stream, particularly an exhaust stream resulting from a diesel engine, the system comprising a source of reducing agent (e.g., NH3 or a precursor thereof) and a catalyst article as obtained from a process as described in the first aspect above or as described in the second aspect above.

[0086] The system for treating the exhaust stream may further comprise one or more exhaust stream treatment elements. Conventional exhaust stream treatment elements include, but are not limited to, a diesel oxidation catalyst (DOC), a selective catalytic reduction catalyst (SCR), a three-way conversion catalyst (TWC), a four-way conversion catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), NOx trap, hydrocarbon trap catalyst, sensors and mixers.

[0087] In some embodiments, the system for treating the exhaust stream further comprises a diesel oxidation catalyst (DOC) and a selective catalytic reduction (SCR) catalyst located downstream of the engine and upstream of the catalyst article. Preferably, the system for treating the exhaust stream further comprises a diesel oxidation catalyst (DOC), a catalytic soot filter (CSF), and a selective catalytic reduction (SCR) catalyst located upstream of the catalyst article.

[0088] In a fourth aspect, the present invention relates to a method for treating an exhaust stream containing nitrogen oxides, the method comprising contacting the exhaust stream with the catalyst article as described in the first aspect in the presence of NH3 as a reducing agent, or passing the exhaust stream through the system as described in the third aspect. This method is particularly useful for treating exhaust streams resulting from diesel engines.

[0089] Embodiments Various embodiments are listed below. It will be understood that the embodiments listed below may be combined with all aspects and other embodiments in accordance with the scope of the present invention. 1. A catalyst article for treating an exhaust stream, - a substrate, - a coating layer comprising a first catalyst containing a noble metal component and a second catalyst containing a molecular sieve component, comprising in a first coating configuration, or - a substrate, - a first coating layer comprising a first catalyst containing a noble metal component, - a second coating layer covering at least a portion of the first coating layer and comprising a second catalyst containing a molecular sieve component, comprising in a second coating configuration, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 5.7% or more, a catalyst article. 2. The catalyst article according to embodiment 1, wherein the molecular sieve is optionally selected from metal-promoted zeolites. 3. The molecular sieve component is selected from aluminosilicate zeolites having a framework type selected from the group consisting of AEI, AEL, AFI, AFT, AFO, AFX, AFR, ATO, BEA, CHA, DDR, EAB, EMT, ERI, EUO, FAU, FER, GME, HEU, JSR, KFI, LEV, LTA, LTL, LTN, MAZ, MEL, MFI, MOR, MOZ, MSO, MTW, MWW, OFF, RTH, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TON, TSC, and WEN, preferably AEI, BEA, CHA, AFT, AFX, FAU, MOR, MFI, MOR, and MEL, more preferably CHA and AEI, the catalyst article according to embodiment 1 or 2. 4. The catalyst article according to any one of embodiments 1 to 4, wherein the molecular sieve component has an average crystallite size in the range of 0.1 to 4 microns. 5. The catalyst article according to embodiment 4, wherein the molecular sieve component has an average crystallite size in the range of 0.5 to 1.5 microns. 6. The catalyst article according to any one of embodiments 1 to 5, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 7.0% or more. 7. The catalyst article according to embodiment 6, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 8.0% or more. 8. The catalyst article according to embodiment 7, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 9.0% or more. 9. The catalyst article according to any one of embodiments 1 to 8, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 25% or less. 10. The catalyst article according to embodiment 9, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 20% or less. 11. The catalyst article according to embodiment 10, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 15% or less. 12. The catalyst article according to any one of embodiments 1 to 11, wherein the substrate has an inlet end and an outlet end defining its axial length, and a plurality of fine parallel gas flow channels extending along the axial length, such as a flow-through substrate or a wall-flow substrate, preferably a flow-through substrate. 13. The catalyst article according to any one of embodiments 1 to 12, having a second coating configuration, wherein the second coating layer is directly above the first coating layer and covers part or all of the first coating layer. 14. The catalyst article according to embodiment 12, having a second coating configuration in which both the first coating layer and the second coating layer extend along a gas flow channel over the entire axial length of the substrate. 15. The catalyst article according to embodiment 14, wherein the second coating layer is directly above the first coating layer. 16. A process for preparing a catalyst article for treating an exhaust stream, - applying a slurry comprising a first catalyst containing a noble metal component, a second catalyst containing a molecular sieve component, and a pore former onto a substrate, optionally drying and firing to form a coating layer in a first coating configuration; or - applying a first slurry comprising a first catalyst containing a noble metal component onto a substrate, drying and / or firing to form a first coating layer, and then applying a second slurry comprising a second catalyst containing a molecular sieve component and a pore former, optionally drying and firing to form a second coating layer in a first coating configuration, wherein the pore former is in particulate form and is used in an amount of at least 15 wt% based on the loading of the coating layer in the first coating configuration or the second coating layer in the second coating configuration, respectively. 17. The process according to embodiment 16, wherein the catalyst article for treating an exhaust stream according to any of embodiments 1 to 15 is prepared. 18. The process according to embodiment 16 or 17, wherein the pore former is used in an amount of at least 18 wt% based on the loading of the coating layer in the first coating configuration or the second coating layer in the second coating configuration, respectively. 19. The process according to embodiment 18, wherein the pore former is used in an amount of at least 20 wt% based on the loading of the coating layer in the first coating configuration or the second coating layer in the second coating configuration, respectively. 20. The process according to any one of embodiments 16 to 19, wherein the pore-forming agent is used in an amount of 50% by weight or less, respectively, based on the filling amount of the coating layer in the first coating configuration or the second coating layer in the second coating configuration. 21. The process according to embodiment 20, wherein the pore-forming agent is used in an amount of 40% by weight or less, respectively, based on the filling amount of the coating layer in the first coating configuration or the second coating layer in the second coating configuration. 22. The process according to any one of embodiments 16 to 21, wherein the pore-forming agent is selected from organic materials such as natural and synthetic polymers, organic low-molecular compounds, inorganic materials such as inorganic salts and carbon materials, cellulose-containing natural materials, and any combination thereof. 23. The process according to embodiment 22, wherein the pore-forming agent is selected from polyether polyols such as polyethylene glycol and its alkyl cap derivatives, styrene homopolymers or copolymers such as polystyrene, poly(meth)acrylic acid and its ester derivatives such as polymethyl methacrylate, cellulose, ether and ester derivatives of cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, and any combination thereof. 24. The pore-forming agent has an average particle size D in the range of 15 to 25 μm 50 The process according to any one of embodiments 16 to 23. 25. The pore-forming agent has an average particle size D in the range of 17 to 21 μm 50 The process according to embodiment 24. 26. A system for treating an exhaust stream, comprising a reducing agent source (e.g., NH3 or its precursor), a catalyst article according to any one of embodiments 1 to 10 or a catalyst article obtained from the process according to any one of embodiments 11 to 17, and optionally one or more of a diesel oxidation catalyst (DOC), a selective catalytic reduction catalyst (SCR), a three-way conversion catalyst (TWC), a four-way conversion catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), a NOx trap, a hydrocarbon trap catalyst, a sensor, and a mixer. 27. A system according to embodiment 26, wherein the exhaust stream originates from an internal combustion engine, particularly a diesel engine. 28. A method for treating an exhaust stream containing nitrogen oxides, the method comprising contacting the exhaust stream with a catalyst article according to any of embodiments 1 - 15 or a catalyst article obtained from a process according to any of embodiments 16 - 25 in the presence of NH3 as a reducing agent, or passing the exhaust stream through a system according to embodiment 26 or 27.

[0090] The present invention will be further illustrated by the following examples, which describe particularly advantageous embodiments. The examples are provided to illustrate the present invention, but are not intended to limit it.

Examples

[0091] Comparative Example 1 Preparation of AMOx slurry An aqueous solution of 4.5 g of tetraamineplatinum(II) hydroxide (H 14 N4O2Pt, 12.6% Pt) was diluted in water and then filled by incipient wetness impregnation into 250 g of an Al2O3 - SiO2 composite oxide powder support (98.5 wt% Al2O3 and 1.5 wt% SiO2) under constant stirring to ensure a uniform distribution, providing a slurry having a solid content of 42 wt%. Then, the slurry was adjusted to a pH of about 4.0 and then ground to a particle size of D 90 of 7 μm.

[0092] Preparation of SCR slurry containing Cu - CHA 78.7 g of an aqueous zirconia binder having a solids content of 30.0 wt% (calculated as ZrO2) was added dropwise to 160 g of DI water with stirring. After thorough mixing, 510.7 g of Cu-CHA powder having a solids content of 88.6 wt%, a Cu content of 5.0% (calculated as CuO based on the solids content), and a SAR of 17 (SiO2 / Al2O3 ratio) was slowly added while stirring at 400 rpm for 12 hours, and the resulting slurry was measured with a Sympatec particle size analyzer and milled to a particle size D of 6 μm. 90 Next, 79.3 g of an alumina sol having a solids content of 30 wt% was added while stirring at 400 rpm. Before coating, the final solids content was adjusted to 37 wt% with DI H2O.

[0093] Coating of the coating layer onto the substrate A ceramic flow-through monolith core (1 inch × 3 inches, 600 cpsi / 3 mil) as the substrate was first coated with an AMOx coating layer by immersing it in the AMOx slurry. Excess slurry was carefully blown off using compressed air, followed by drying in flowing air at 250 °C for a short time, and then firing in a muffle furnace at 550 °C (ramp 4 °C / min) for 1 hour. After cooling to 250 °C, the coated substrate was weighed to determine the AMOx catalyst loading. The loading of the AMOx coating layer was 0.5 g / in 3 (30 g / L), and the Pt loading was 2.0 g / ft 3 . Thereafter, the SCR coating layer was applied using the same process as described above for the AMOx coating layer, and the loading of the SCR coating layer was 2.2 g / in 3 (135 g / L), and the Cu-CHA loading was 2.0 g / in 3 .

[0094] Comparative Example 2 The SCR slurry containing Cu-CHA was measured with a Sympatec particle size analyzer, and D 50It further contained 25.0 g of polymethyl methacrylate (PMMA, SUNPMMA-S200 from SUNJIN Chemical), which was added to the SCR slurry after the addition of the alumina sol was completed and uniformly stirred, and the process described in Comparative Example 1 was repeated except for this.

[0095] Comparative Example 3 The process described in Comparative Example 2 was repeated except that the SCR slurry containing Cu-CHA contained 50.0 g of polymethyl methacrylate.

[0096] Comparative Example 4 The process described in Comparative Example 2 was repeated except that the SCR slurry containing Cu-CHA contained 65.0 g of polymethyl methacrylate (PMMA).

[0097] Example 1 The process described in Comparative Example 2 was repeated except that the SCR slurry containing Cu-CHA contained 100.0 g of polymethyl methacrylate (PMMA).

[0098] Example 2 The process described in Comparative Example 2 was repeated except that the SCR slurry containing Cu-CHA contained 150.0 g of polymethyl methacrylate (PMMA).

[0099] Example 3 The process described in Comparative Example 2 was repeated except that the SCR slurry containing Cu-CHA contained 200.0 g of polymethyl methacrylate (PMMA).

[0100] Example 4 The process described in Comparative Example 2 was repeated except that the SCR slurry containing Cu-CHA contained 250.0 g of polymethyl methacrylate (PMMA).

[0101] Comparative Example 5 The process described in Comparative Example 1 was repeated, except that 461.9 of Cu-AEI powder having a solid content of 98.0 wt%, a Cu content of 5.0% (calculated as CuO based on the solid content), and a SAR (SiO2 / Al2O3 ratio) of 16 was used instead of the Cu-CHA powder.

[0102] Example 5 The process described in Comparative Example 5 was repeated, except that the SCR slurry containing Cu-AEI further contained 100.0 g of polymethyl methacrylate (PMMA), which was added to the SCR slurry after the addition of the alumina sol was completed and stirred uniformly.

[0103] Measurement of Porosity Each fresh sample obtained from the above examples and comparative examples was measured for porosity using a scanning electron microscope / energy dispersive X-ray spectroscopy (SEM / DES, Supra 55 from Zeiss company). Photographs were taken from a cross-section perpendicular to the axial direction of the substrate, and the total cross-sectional area of the SCR coating layer and the total cross-sectional area of the pores in the SCR coating layer were determined. The porosity was calculated according to the following formula. Porosity = (Ap / Ac) × 100% In the formula, Ap is the total cross-sectional area of the pores in the SCR coating layer, Ac is the total cross-sectional area of the SCR coating layer.

[0104] The total cross-sectional area of the pores can be obtained by automatically measuring and summing the areas of each pore cross-section observed from the cross-section photograph by SEM / DES. Also, the total cross-sectional area of the SCR coating layer can be obtained in the same way. The average of the measured values of three photographs was reported as the porosity result.

[0105] Performance Test All catalytic performance tests were carried out on a flow reactor using simulated diesel exhaust with the composition shown below as the feed gas for the aged samples prepared from the fresh samples from the above examples and comparative examples by aging at 650 °C for 50 hours in 10 vol% water / air. Before the test, the aged samples were pretreated in N2 at 550 °C for 0.5 hours and cooled to 250 °C.

[0106] Feed gas: 100,000 h -1 space velocity, 500 ppm NH3 in 10% O2, 8% CO2, 7% H2O, and the balance N2.

[0107] The feed gas was purged into the reactor until a steady state of NH3 slip was reached, and then the amount of NH3 slip ([NH3] out ) was recorded, and the NH3 conversion rate was calculated according to the following formula. Conversion rate NH3 = ([NH3] in - [NH3] out ) / [NH3] in × 100%.

[0108]

Table 1

[0109] As shown in the above table, the catalyst article according to the present invention shows an improved NH3 conversion rate compared to the conventional catalyst article without pores (Examples 1 to 4 vs. Comparative Example 1, Example 5 vs. Comparative Example 5).

[0110] Moreover, surprisingly, the inventors have also found that the performance of the catalyst article does not mathematically scale with the porosity. In other words, the catalyst article does not necessarily perform well as the porosity increases. Catalyst articles with porosities of 5% and 13% show even lower NH3 conversion rates than the conventional catalyst article with zero porosity (Comparative Examples 2 and 4 vs. Comparative Example 3), but it can be seen that the catalyst article with a porosity of 10% performs better than the conventional catalyst article with zero porosity.

Claims

**Claim 1** A catalyst article for treating an exhaust stream, comprising: - a substrate; - a coating layer comprising a first catalyst containing a noble metal component and a second catalyst containing a molecular sieve component, either included in a first coating configuration; or - a substrate; - a first coating layer comprising a first catalyst containing a noble metal component; - a second coating layer covering at least a portion of the first coating layer and comprising a second catalyst containing a molecular sieve component, included in a second coating configuration; wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 5.7% or more, a catalyst article. **Claim 2** The catalyst article according to claim 1, wherein the molecular sieve is optionally selected from metal-promoted zeolites. **Claim 3** The catalyst article according to claim 1 or 2, wherein the molecular sieve component is selected from aluminosilicate zeolites having a framework type selected from the group consisting of AEI, AEL, AFI, AFT, AFO, AFX, AFR, ATO, BEA, CHA, DDR, EAB, EMT, ERI, EUO, FAU, FER, GME, HEU, JSR, KFI, LEV, LTA, LTL, LTN, MAZ, MEL, MFI, MOR, MOZ, MSO, MTW, MWW, OFF, RTH, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TON, TSC, and WEN, preferably AEI, BEA, CHA, AFT, AFX, FAU, MOR, MFI, MOR, and MEL, more preferably CHA and AEI. **Claim 4** The catalyst article according to any one of claims 1 to 3, wherein the molecular sieve component has an average crystallite size in the range of 0.1 to 4 microns or 0.5 to 1.5 microns. **Claim 5** The catalyst article according to any one of claims 1 to 4, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration each has interparticle pores with a porosity of 7.0% or more, preferably 8.0% or more, particularly 9.0% or more. **Claim 6** The catalyst article according to any one of claims 1 to 5, wherein the coating layer in the first coating configuration or the second coating layer in the second coating configuration has interparticle pores with a porosity of 25% or less, preferably 20% or less, particularly 15% or less.

7. The catalyst article according to any one of claims 1 to 6, wherein the substrate has an inlet end and an outlet end defining its axial length, and a plurality of fine parallel gas flow channels extending along the axial length, such as a flow-through substrate or a wall-flow substrate, preferably a flow-through substrate.

8. The catalyst article according to any one of claims 1 to 7, wherein the second coating layer has the second coating configuration, is directly above the first coating layer, and covers part or all of the first coating layer.

9. The catalyst article according to claim 7, wherein both the first coating layer and the second coating layer have the second coating configuration and extend along the gas flow channels over the entire axial length of the substrate.

10. The catalyst article according to claim 9, wherein the second coating layer is directly above the first coating layer.

11. A process for preparing a catalyst article for treating an exhaust stream, - applying a slurry containing a first catalyst containing a noble metal component, a second catalyst containing a molecular sieve component, and a pore former onto a substrate, optionally drying and firing to form a coating layer in a first coating configuration, or - applying a first slurry containing a first catalyst containing a noble metal component onto a substrate, drying and / or firing to form a first coating layer, and then applying a second slurry containing a second catalyst containing a molecular sieve component and a pore former, optionally drying and firing to form a second coating layer in a first coating configuration, wherein the pore former is in particulate form and is used in an amount of at least 15% by weight based on the filling amount of the coating layer in the first coating configuration or the second coating layer in the second coating configuration.

12. The process according to claim 11, wherein a catalyst article for treating an exhaust stream according to any one of claims 1 to 10 is prepared.

13. The process according to claim 11 or 12, wherein the pore-forming agent is used in an amount of at least 18% by weight or at least 20% by weight, respectively, based on the filling amount of the coating layer in the first coating configuration or the second coating layer in the second coating configuration.

14. The process according to any one of claims 11 to 13, wherein the pore-forming agent is used in an amount of 50% by weight or less or 40% by weight or less, respectively, based on the filling amount of the coating layer in the first coating configuration or the second coating layer in the second coating configuration.

15. The process according to any one of claims 11 to 14, wherein the pore-forming agent is selected from organic materials such as natural and synthetic polymers, organic low-molecular solid compounds, inorganic materials such as inorganic salts and carbon materials, cellulose-containing natural materials, and any combination thereof.

16. The process according to claim 15, wherein the pore-forming agent is selected from polyether polyols such as polyethylene glycol and its alkyl cap derivatives, styrene homopolymers or copolymers such as polystyrene, poly(meth)acrylic acid and its ester derivatives such as polymethyl methacrylate, cellulose, ether and ester derivatives of cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, and any combination thereof.

17. The pore former has an average particle size D in the range of 15 to 25 μm, preferably 17 to 21 μm ５０ The process according to any one of claims 11 to 16, having this property.

18. A system for treating an exhaust stream, comprising a reductant source (e.g., NH ３ or a precursor thereof), a catalyst article obtained from the catalyst article according to any one of claims 1 to 10 or the process according to any one of claims 11 to 17, and optionally, one or more of a diesel oxidation catalyst (DOC), a selective catalytic reduction catalyst (SCR), a three-way conversion catalyst (TWC), a four-way conversion catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), a NOx trap, a hydrocarbon trap catalyst, a sensor, and a mixer.

19. The system according to claim 18, wherein the exhaust stream originates from an internal combustion engine, particularly a diesel engine.

20. A method for treating an exhaust stream containing nitrogen oxides, in the presence of NH as a reducing agent ３ contacting the exhaust stream with a catalyst article according to any one of claims 1 to 10 or a catalyst article obtained from the process according to any one of claims 11 to 17, or passing the exhaust stream through a system according to claim 18 or 19.

Images