Metal oxide catalyst for selective catalytic reduction

Abstract

The invention provides a non-vanadium-based metal oxide catalyst composition. The present invention relates to a catalyst composition comprising at least one metal oxide comprising manganese oxide and dispersed on the support, and a support comprising particles of a composite oxide of aluminum and at least one metal selected from cerium, manganese and titanium, aluminum is present in the composite oxide in an amount of from 50 wt% to 80 wt%, calculated as Al2O3, and wherein manganese oxide is present in the metal oxide catalyst composition in an amount of from 2.5 wt% to 10 wt%, calculated as MnO2, based on the total weight of the metal oxide catalyst composition.

Description

Technical Field

[0001] The present invention relates to a non-vanadium-based metal oxide catalyst for selective catalytic reduction, a method for preparing the same, and a method for treating exhaust gas containing nitrogen oxides by selective catalytic reduction. Background Art

[0002] Nitrogen oxides (NOx) are common air pollutants, which are usually contained in exhaust gases from mobile sources such as automobiles and fixed sources such as power plants. Due to the negative environmental impacts of NOx on the ecosystem, humans, animals, and plants, controlling the emissions of NOx has been one of the most important topics in, for example, the field of automobile manufacturing.

[0003] Various treatment methods (such as catalytic reduction of nitrogen oxides) have been used to reduce NOx in exhaust gases. A typical catalytic reduction method is selective catalytic reduction using ammonia (NH3) or an ammonia precursor as a reducing agent in the presence of atmospheric oxygen, which is also known as the SCR method. The SCR method is considered excellent because a high NOx reduction effect can be obtained with a small amount of reducing agent. Generally, nitrogen oxides and the reducing agent NH3 react according to the following equations:

[0004] 4NO + 4NH3 + O2 → 4N2 + 6H2O (standard SCR reaction)

[0005] 2NO2 + 4NH3 + O2 → 3N2 + 6H2O (slow SCR reaction)

[0006] NO + NO2 + 2NH3 → 2N2 + 3H2O (fast SCR reaction).

[0007] A side reaction accompanying selective catalytic reduction is the formation of low-valent nitrogen oxides, especially nitrous oxide (N2O), from the reducing agent NH3 and oxygen.

[0008] The NOx treatment efficacy regarding, for example, NOx conversion and N2O formation depends largely on the catalyst used in the SCR method. Catalysts available for the selective catalytic reduction of NOx (i.e., SCR catalysts) are well known.

[0009] A typical class of SCR catalysts is vanadium-based catalysts, which usually contain vanadium oxide as an active substance on a carrier such as TiO2 and optionally one or more other metal oxides such as WO3 as promoters. However, vanadium-based catalysts do not have desirable thermal durability. Once aged, vanadium-based catalysts will exhibit quite low activity at low temperatures (e.g., below 300 °C). Another disadvantage of vanadium-based catalysts is that V2O5 may escape into the environment, causing environmental problems.

[0010] Another type of SCR catalyst is a zeolite-based catalyst, which typically comprises a small-pore aluminosilicate zeolite exchanged with a transition metal. Zeolite-based catalysts exhibit high activity at low temperatures (e.g., 210 °C), however, they have the drawback of slow response to reductant injection. It is believed that the slow response is due to the acidic sites of the zeolite framework, where the reductant NH3 will be absorbed to saturation before it can be effectively used for NOx reduction.

[0011] Recently, a class of non-vanadium metal oxides has been proposed as an alternative to zeolite-based catalysts and vanadium-based catalysts for SCR. These metal oxide catalysts generally comprise oxides of one or more alkali metal active substances on a carrier, as described in some existing patent applications.

[0012] JP 2003326167A describes an SCR catalyst comprising tungsten oxide or molybdenum oxide on a zirconium-based carrier.

[0013] WO2009001131A describes an SCR catalyst comprising at least one transition metal dispersed on a mixed oxide or composite oxide or a mixture thereof of a carrier material composed of cerium and zirconium.

[0014] CN106824173A describes an SCR catalyst comprising manganese oxide (MnOx) dispersed on a composite oxide of cerium and aluminum (CeO2 - Al2O3) as a carrier. The carrier is prepared by co-precipitation of cerium and aluminum hydroxide followed by calcination.

[0015] It would be desirable to develop a non-vanadium-based metal oxide SCR catalyst with improved NOx treatment efficiency. Summary of the Invention

[0016] One object of the present invention is to provide an SCR catalyst that performs well especially at low temperatures (e.g., below 210 °C).

[0017] Surprisingly, this object is achieved by a non-vanadium-based metal oxide composition comprising manganese (Mn) species dispersed on a carrier comprising particles of a composite oxide of aluminum (Al) and at least one metal selected from cerium (Ce), manganese, and titanium (Ti).

[0018] Another object of the present invention is to provide a method particularly useful for preparing a non-vanadium-based metal oxide composition with improved NOx treatment efficacy.

[0019] This object is achieved by a method comprising impregnating a precursor of the Mn species onto a carrier comprising particles of a composite oxide of aluminum and at least one metal selected from cerium, manganese, and titanium in a water-soluble alcohol solvent.

[0020] Thus, in one aspect, the present invention relates to a non-vanadium-based metal oxide catalyst composition comprising

[0021] - at least one metal oxide comprising manganese oxide, and

[0022] - a support comprising particles of a composite oxide of aluminum and at least one metal selected from cerium, manganese, and titanium, wherein based on the total weight of the composite oxide, aluminum is present in the composite oxide in an amount of 50 wt% to 80 wt% calculated as Al2O3,

[0023] wherein the at least one metal oxide is dispersed on the support, and

[0024] wherein based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of 2.5 wt% to 10 wt% calculated as MnO2.

[0025] In another aspect, the present invention relates to a method for preparing a non-vanadium-based metal oxide catalyst composition as described herein, the method comprising impregnating one or more precursors of at least one metal oxide onto a support, particularly in a water-soluble alcohol solvent, and calcining.

[0026] In yet another aspect, the present invention relates to a method for treating an exhaust gas containing nitrogen oxides by selective catalytic reduction, the method comprising contacting the exhaust gas with the metal oxide catalyst composition as described herein in the presence of a reducing agent.

[0027] In yet another aspect, the present invention relates to a system for treating exhaust gas, particularly exhaust gas from an internal combustion engine, the system comprising a source of reducing agent, the metal oxide catalyst composition as described herein, and optionally one or more of a diesel oxidation catalyst (DOC), a three-way catalyst (TWC), a four-way catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), an ammonia oxidation catalyst (AMOx), a NOx trap, a NOx absorbent catalyst, a hydrocarbon trap catalyst, a sensor, and a mixer.

[0028] The inventors have found that the metal oxide catalyst composition according to the present invention has improved NOx treatment efficacy and can be particularly used for treating exhaust gas from automotive engines, especially heavy-duty diesel engines. The metal oxide catalyst composition according to the present invention exhibits good SCR performance at low temperatures (e.g., below 210 °C) and desirable thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Shows the XRD pattern of the fresh composite oxide support material used in the examples.

[0030] Figure 2 The XRD pattern of the aged composite oxide support material used in the examples is shown. Detailed Description of the Invention

[0031] The present invention will be described in detail below. It should be understood that the present invention can be embodied in many different ways and should not be construed as limited to the embodiments set forth herein.

[0032] As used herein, the singular forms "a / an" and "the" include plural referents unless the context clearly dictates otherwise. The terms "comprising", "including", etc. are used interchangeably with "containing", etc. and are interpreted in a non-limiting, open-ended manner. That is, for example, additional components or elements may be present. The expressions "consisting of", "consisting essentially of", or cognates may be subsumed within "comprising" or cognates.

[0033] As used herein, the term "composite oxide" refers to an oxide material composed of oxides of two or more elements, which can be identified by X-ray diffraction as the respective oxides and crystalline phases. The respective oxides are in close contact, but are not a physical mixture of oxides obtained by physical means (such as by mechanical mixing or blending).

[0034] As used herein, the term "non-vanadium-based" refers to a metal oxide catalyst composition that does not contain any vanadium (e.g., in the form of vanadium oxide) intentionally incorporated into the composition. The terms "non-vanadium-based metal oxide catalyst composition" and "metal oxide catalyst composition" are used interchangeably herein.

[0035] As used herein, the term "catalytic article" is only intended to denote an article of a certain shape having a catalyst function, which is not necessarily a single entity. In other words, a catalytic article can be a single entity or composed of two or more separable entities.

[0036] In a first aspect, the present invention provides a non-vanadium-based metal oxide catalyst composition comprising

[0037] - at least one metal oxide comprising manganese oxide, and

[0038] - a support comprising particles of a composite oxide of aluminum and at least one metal selected from cerium, manganese, and titanium, wherein based on the total weight of the composite oxide, aluminum is present in the composite oxide in an amount of 50 wt% to 80 wt% calculated as Al2O3,

[0039] wherein the at least one metal oxide is dispersed on the support, and

[0040] Based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of 2.5 wt% to 10 wt% calculated as MnO2.

[0041] The at least one metal oxide dispersed on the support may further comprise an oxide of titanium (Ti), iron (Fe), magnesium (Mg), or aluminum (Al), or any combination thereof. Based on the total weight of the metal oxide catalyst composition, each of the oxides of Ti, Fe, Mg, and Al (if present) may be included in the metal oxide catalyst composition according to the invention in an amount not greater than 10 wt%, not greater than 8 wt%, or not greater than 6 wt% calculated as their respective oxides.

[0042] In some embodiments, the at least one metal oxide dispersed on the support consists of manganese oxide, and based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of 2.5 wt% to 10 wt% or 3 wt% to 8 wt% calculated as MnO2.

[0043] In some embodiments, the at least one metal oxide dispersed on the support comprises manganese oxide and titanium oxide, or consists of manganese oxide and titanium oxide. In those embodiments, preferably, based on the total weight of the metal oxide catalyst composition, manganese oxide is present in an amount of 2.5 wt% to 10 wt% or 3 wt% to 8 wt% calculated as MnO2, and titanium oxide is present in an amount of 1 wt% to 6 wt% or 2 wt% to 4 wt% calculated as TiO2. Specifically, manganese oxide and titanium oxide may be present in a weight ratio of 1:1 to 3:1, or 1.2:1 to 2.5:1, or 1.5:1 to 2:1.

[0044] In some embodiments, the at least one metal oxide dispersed on the support comprises manganese oxide and iron oxide, or consists of manganese oxide and iron oxide. In those embodiments, preferably, based on the total weight of the metal oxide catalyst composition, manganese oxide is present in an amount of 2.5 wt% to 10 wt% or 3 wt% to 8 wt% calculated as MnO2, and iron oxide is present in an amount of 1 wt% to 5 wt% or 3 wt% to 5 wt% calculated as Fe2O3. Specifically, manganese oxide and iron oxide may be present in a weight ratio of 1:1 to 2:1 or 1:1 to 1.5:1.

[0045] In some additional embodiments, at least one metal oxide dispersed on a support comprises manganese oxide, titanium oxide, and iron oxide, or consists of manganese oxide, titanium oxide, and iron oxide. In those embodiments, preferably, based on the total weight of the metal oxide catalyst composition, manganese oxide is present in an amount of 2.5 wt% to 10 wt% or 3 wt% to 8 wt% calculated as MnO2, titanium oxide is present in an amount of 1 wt% to 6 wt% or 2 wt% to 4 wt% calculated as TiO2, and iron oxide is present in an amount of 1 wt% to 5 wt% or 3 wt% to 5 wt% calculated as Fe2O3.

[0046] The support is in particulate form, and at least one metal oxide as described herein can be dispersed thereon (also referred to as "supported"). The particles of the composite oxide can have a BET specific surface area of 50 m 2 / g to 200 m 2 / g in the fresh state.

[0047] The particles can be modified with dopants (such as Ti, Si, Zr, La, or Ba). In this case, the support can comprise particles of the composite oxide and dopants. Based on the total weight of the metal oxide catalyst composition, the dopants can be present in an amount of 1 wt% to 10 wt% or 3 wt% to 6 wt% calculated as their respective oxides.

[0048] As used herein, the term "modified" or "modifying" in the context of the support refers to treating the particles of the composite oxide to incorporate dopants onto the particles. In other words, the dopants are not incorporated during the formation of the composite oxide.

[0049] In some embodiments, the support comprises particles of a composite oxide of aluminum, cerium, and optionally manganese and / or titanium, or consists of particles of a composite oxide of aluminum, cerium, and optionally manganese and / or titanium. Specifically, the support consists of particles of a composite oxide of aluminum and cerium and optionally dopants. The composite oxide of aluminum and cerium can comprise an Al2O3 phase and a CeO2 phase, the crystallite size of the latter being at least 5 nm, preferably at least 9 nm, at least 9.5 nm, or at least 10 nm, as determined by X-ray powder diffraction (XRD) analysis in the fresh state. Based on the total weight of the composite oxide, cerium can be present in the composite oxide in an amount of 20 wt% to 50 wt%, 20 wt% to 40 wt%, or 20 wt% to 30 wt% calculated as CeO2.

[0050] The metal oxide catalyst composition according to the present invention can further comprise a coated metal oxide, such as titanium oxide, alumina, silica, magnesia, zirconia, or any combination thereof. The coated metal oxide can be used to improve the sulfur poisoning resistance of the catalyst or improve the thermal stability of the catalyst.

[0051] As used herein, the term "coating" refers to a component incorporated into a metal oxide catalyst composition by dispersing the component or its precursor onto the surface of the catalyst particles. The coated metal oxide may be in the form of a gas-permeable layer, a partial layer, or discrete islands on the surface of the catalyst particles. The coated metal oxide can be incorporated onto the catalyst by post-treatment or by co-impregnation with the active components.

[0052] Based on the total weight of the metal oxide catalyst composition, the coated metal oxide may be present in the metal oxide catalyst composition in an amount of from 0.5 wt% to 10 wt%, from 1 wt% to 5 wt%, or from 0.8 wt% to 3 wt%.

[0053] In the case where the metal oxide catalyst composition according to the present invention contains titanium in two or more of at least one of the metal oxide, dopant, and coated metal oxide components, based on the total weight of the metal oxide catalyst composition, titanium may be present in a total amount not exceeding 6 wt% calculated as TiO2.

[0054] In some embodiments, the metal oxide catalyst composition according to the present invention contains titanium in only one of the corresponding amounts of at least one of the metal oxide, dopant, and coated metal oxide components as described above.

[0055] In some exemplary embodiments, the metal oxide catalyst composition comprises

[0056] - at least one metal oxide comprising manganese oxide or manganese oxide and titanium oxide, or consisting of manganese oxide or manganese oxide and titanium oxide,

[0057] - a support comprising particles of a composite oxide of aluminum and cerium and an optional dopant, wherein based on the total weight of the composite oxide, cerium is present in the composite oxide in an amount of from 20 wt% to 40 wt% or from 20 wt% to 30 wt% calculated as CeO2,

[0058] wherein the at least one metal oxide is dispersed on the support, and

[0059] wherein based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of from 2.5 wt% to 10 wt% calculated as MnO2.

[0060] In some other exemplary embodiments, the metal oxide catalyst composition comprises

[0061] - at least one metal oxide consisting of manganese oxide or manganese oxide and titanium oxide,

[0062] - A support comprising particles of a composite oxide of aluminum and cerium and optionally a dopant, wherein based on the total weight of the composite oxide, cerium is present in the composite oxide in an amount of 20% to 40% by weight or 20% to 30% by weight calculated as CeO2,

[0063] wherein the at least one metal oxide is dispersed on the support, and

[0064] wherein based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of 3% to 8% by weight calculated as MnO2.

[0065] In some further exemplary embodiments, the metal oxide catalyst composition comprises

[0066] - at least one metal oxide consisting of manganese oxide or manganese oxide and titanium oxide,

[0067] - A support comprising particles of a composite oxide of aluminum and cerium and optionally a dopant, wherein based on the total weight of the composite oxide, cerium is present in the composite oxide in an amount of 20% to 40% by weight or 20% to 30% by weight calculated as CeO2,

[0068] wherein the at least one metal oxide is dispersed on the support,

[0069] wherein based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of 3% to 8% by weight calculated as MnO2, and

[0070] wherein the composite oxide of aluminum and cerium may comprise an Al2O3 phase and a CeO2 phase, the latter having a crystallite size of at least 9 nm, at least 9.5 nm or at least 10 nm, as determined by X-ray powder diffraction (XRD) analysis in the fresh state.

[0071] The metal oxide catalyst composition can be prepared conventionally, for example by impregnating the support with one or more precursors of at least one metal oxide.

[0072] Thus, in a second aspect, the present invention provides a method for preparing a non-vanadium-based metal oxide catalyst composition as described herein, the method comprising the step of impregnating the support with one or more precursors of at least one metal oxide, preferably in a water-soluble alcohol solvent, and then optionally the step of impregnating one or more precursors of a coating metal oxide.

[0073] Specifically, the present invention provides a method for preparing a non-vanadium-based metal oxide catalyst composition as described herein, the method comprising the following steps:

[0074] - In a water-soluble alcohol solvent, impregnate one or more precursors of at least one metal oxide onto the support particles to obtain the loaded particles,

[0075] - Calcinate the loaded particles to obtain the calcined particles, and

[0076] - Optionally, impregnate one or more precursors of the coated metal oxide onto the calcined particles and then calcine.

[0077] Suitable water-soluble alcohols as solvents for impregnating one or more precursors of at least one metal oxide may include, but are not limited to, methanol, ethanol, n-propanol, and isopropanol.

[0078] At least one metal oxide, the support, and the coated metal oxide are as described above for the metal oxide catalyst composition. There is no particular limitation on the precursors of at least one metal oxide and the coated metal oxide. The precursors may be inorganic or organic, soluble salts, complexes, or other compounds of the metal.

[0079] The support may comprise or consist of particles of a composite oxide as described above for the metal oxide catalyst composition in the first aspect. Specifically, the support consists of particles of a composite oxide and optionally dopants such as Ti, Si, Zr, La, or Ba, as described above for the metal oxide catalyst composition.

[0080] In the case where the support consists of particles of a composite oxide modified by a dopant, the modification may also be carried out by a method including: preferably in a water-soluble alcohol solvent, impregnate one or more precursors of the dopant onto the particles of the composite oxide, dry, and optionally calcine.

[0081] Therefore, the method according to the present invention optionally includes the following steps: before impregnating one or more precursors of at least one metal oxide, preferably in a water-soluble alcohol solvent, impregnate one or more precursors of the dopant onto the particles of the composite oxide, dry, and optionally calcine.

[0082] In the method according to the present invention, the impregnation and calcination operations can be carried out in any conventional manner and conditions known in the art, except that a water-soluble alcohol solvent can be used to impregnate one or more precursors of at least one metal oxide onto the support particles.

[0083] In some embodiments, the impregnation of the dopant and / or the precursors of the coated metal oxide is also carried out in a water-soluble alcohol solvent.

[0084] As is well known in the art, the calcination step in the method according to the present invention can be after the drying step.

[0085] It has been found that, compared with conventional catalysts, the metal oxide catalyst compositions according to the present invention exhibit desirable thermal stability and improved NOx treatment efficacy.

[0086] Without being bound by any theory, it is hypothesized that the thermal stability may be related to the unique microstructure of the composite oxide used as the support in the metal oxide catalyst composition. In addition, it is believed that the improvement in NOx treatment efficacy is related to the unique composition of the included metal oxides and may also be related to the unique microstructure of the composite oxide.

[0087] It has also been surprisingly found that, compared with catalysts prepared in the same manner except that water is used instead of a water-soluble alcohol as the solvent, the catalysts prepared by impregnating one or more precursors of at least one metal oxide onto carrier particles in a water-soluble alcohol solvent exhibit improved NOx conversion.

[0088] In a third aspect, the present invention provides a method for treating exhaust gas containing nitrogen oxides by selective catalytic reduction, the method comprising contacting the exhaust gas with the metal oxide catalyst composition described herein in the presence of a reducing agent.

[0089] The metal oxide catalyst composition can be used in any conventional form in the method for treating exhaust gas, such as as a powder or an extrudate, or as a washcoat on a substrate.

[0090] The metal oxide catalyst composition can be used as a powder, which typically has an average particle size of 1 micrometer (μm) to 100 μm. The particle size of the metal oxide catalyst composition can be adjusted by, for example, grinding and / or sieving.

[0091] The metal oxide catalyst composition can be used as an extrudate, i.e., a shaped body obtained by extrusion. The extrudate can have any suitable structure allowing the exhaust gas flow through, preferably a honeycomb structure. The honeycomb structure can have flow channels as described below for monolithic flow-through and wall-flow structures.

[0092] The metal oxide catalyst composition can be used as a washcoat on a substrate. The substrate generally refers to a structure suitable for withstanding the conditions encountered in the exhaust gas stream, on which the metal oxide catalyst composition in the form of a washcoat is loaded.

[0093] The substrate can be a monolithic flow-through structure having a plurality of fine parallel gas flow channels extending from the inlet face to the outlet face of the substrate, such that the channels are open to the fluid flowing therethrough. The channels having a substantially straight path from their fluid inlet to their fluid outlet are defined by walls, and the catalytic material is applied as a washcoat on these walls such that the gas flowing through the channels contacts the catalytic material.

[0094] Alternatively, the substrate can be a monolithic wall flow structure having a plurality of fine parallel gas flow channels that extend from an inlet face of the substrate to an outlet face, with alternating channels blocked at opposite ends. The channels are defined by walls, and a catalytic material is applied as a washcoat on these walls such that the gas flowing through the 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 face.

[0095] The term "washcoat" has its ordinary meaning in the art and refers to a thin adherent coating of a catalytic or other material applied to a substrate. A washcoat is typically formed by preparing a slurry containing the desired materials and optional processing aids such as a binder having a certain solids content (e.g., 15 wt% to 60 wt%), and then applying the slurry to the substrate, drying, and calcining to provide the washcoat.

[0096] Thus, in a fourth aspect, the present invention provides a catalytic article comprising a metal oxide catalyst composition according to the present invention.

[0097] In a fifth aspect, the present invention provides a system for treating exhaust gas, particularly exhaust gas from an internal combustion engine, the system comprising a source of reductant, a catalytic article as described herein, and optionally one or more of a diesel oxidation catalyst (DOC), a three-way catalyst (TWC), a four-way catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), an ammonia oxidation catalyst (AMOx), a NOx trap, a NOx absorbent catalyst, a hydrocarbon trap catalyst, a sensor, and a mixer.

[0098] The catalytic article according to the present invention can be located downstream of an internal combustion engine (such as a diesel engine, particularly a heavy-duty diesel engine), in a close-coupled position, in a downstream position of the close-coupled position, or in both of the above positions. Preferably, the catalytic article according to the present invention is located downstream of the internal combustion engine, in a close-coupled position.

[0099] Preferably, the exhaust gas treatment system further comprises a diesel oxidation catalyst located downstream of the engine and upstream of the catalytic article according to the present invention. In some embodiments, the exhaust gas treatment system preferably comprises a diesel oxidation catalyst and a catalytic soot filter located upstream of the catalytic article according to the present invention.

[0100] Embodiment

[0101] The following are various embodiments. It should be understood that the embodiments listed below can be combined with all aspects and other embodiments within the scope of the present invention.

[0102] 1. A non-vanadium-based metal oxide catalyst composition comprising

[0103] - at least one metal oxide, said at least one metal oxide comprising manganese oxide, and

[0104] - a support, said support comprising particles of a composite oxide of aluminum and at least one metal selected from cerium, manganese, and titanium, wherein, based on the total weight of the composite oxide, aluminum is present in the composite oxide in an amount of 50 wt% to 80 wt% calculated as Al2O3,

[0105] wherein said at least one metal oxide is dispersed on said support, and

[0106] wherein, based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of 2.5 wt% to 10 wt% calculated as MnO2.

[0107] 2. The non-vanadium-based metal oxide catalyst composition according to embodiment 1, wherein said at least one metal oxide further comprises an oxide of titanium (Ti), iron (Fe), magnesium (Mg), or aluminum (Al), or any combination thereof.

[0108] 3. The non-vanadium-based metal oxide catalyst composition according to embodiment 2, wherein, based on the total weight of the metal oxide catalyst composition, each of the oxides of Ti, Fe, Mg, and Al is present in an amount not greater than 10 wt%, not greater than 8 wt%, or not greater than 6 wt% calculated as their respective oxides.

[0109] 4. The non-vanadium-based metal oxide catalyst composition according to any one of the foregoing embodiments, wherein, based on the total weight of the metal oxide catalyst composition, manganese oxide is present in an amount of 3 wt% to 8 wt% calculated as MnO2.

[0110] 5. The non-vanadium-based metal oxide catalyst composition according to any one of the foregoing embodiments, wherein said at least one metal oxide further comprises titanium oxide, and based on the total weight of the catalyst composition, the titanium oxide is preferably present in an amount of 1 wt% to 6 wt% or 2 wt% to 4 wt% calculated as TiO2.

[0111] 6. The non-vanadium-based metal oxide catalyst composition according to any one of the foregoing embodiments, wherein said at least one metal oxide further comprises iron oxide, and based on the total weight of the metal oxide catalyst composition, the iron oxide is preferably present in an amount of 1 wt% to 5 wt% or 3 wt% to 5 wt% calculated as Fe2O3.

[0112] 7. The non-vanadium-based metal oxide catalyst composition according to any one of the foregoing embodiments, wherein the support comprises particles of the composite oxide and a dopant selected from Ti, Si, Zr, La, and Ba, and based on the total weight of the metal oxide catalyst composition, the dopant is preferably present in an amount of 1 wt% to 10 wt% or 3 wt% to 6 wt% in terms of their respective oxides.

[0113] 8. The non-vanadium-based metal oxide catalyst composition according to any one of the foregoing embodiments, wherein the support comprises particles of a composite oxide of aluminum, cerium, and optionally manganese and / or titanium.

[0114] 9. The non-vanadium-based metal oxide catalyst composition according to embodiment 7, wherein the support consists of particles of a composite oxide of aluminum and cerium and optionally the dopant.

[0115] 10. The non-vanadium-based metal oxide catalyst composition according to embodiment 8 or 9, wherein based on the total weight of the composite oxide, cerium is present in the composite oxide in an amount of 20 wt% to 50 wt%, 20 wt% to 40 wt%, or 20 wt% to 30 wt% in terms of CeO2.

[0116] 11. The non-vanadium-based metal oxide catalyst composition according to embodiment 10, wherein the composite oxide of aluminum and cerium comprises an Al2O3 phase and a CeO2 phase, and the crystallite size of the latter is at least 5 nm, preferably at least 9 nm, at least 9.5 nm, or at least 10 nm, as determined by XRD analysis in the fresh state.

[0117] 12. The non-vanadium-based metal oxide catalyst composition according to any one of the foregoing embodiments, further comprising a coating metal oxide, such as titanium oxide, aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, or any combination thereof.

[0118] 13. A method for preparing the non-vanadium-based metal oxide catalyst composition according to any one of the foregoing embodiments, the method comprising the step of impregnating one or more precursors of the at least one metal oxide onto the support, and then optionally the step of impregnating one or more precursors of the coating metal oxide.

[0119] 14. The method according to embodiment 13, wherein the impregnating of one or more precursors of the at least one metal oxide onto the support is carried out in a water-soluble alcohol solvent.

[0120] 15. The method according to embodiment 13 or 14, wherein the water-soluble alcohol solvent is selected from methanol, ethanol, n-propanol, and isopropanol.

[0121] 16. The method according to any one of embodiments 13 to 15, the method further comprising the steps of: before impregnating one or more precursors of the at least one metal oxide, preferably in a water-soluble alcohol solvent, impregnating one or more precursors of the dopant onto the particles of the composite oxide.

[0122] 17. A method for treating exhaust gas containing nitrogen oxides by selective catalytic reduction, the method comprising contacting the exhaust gas with a metal oxide catalyst composition according to any one of embodiments 1 to 12 in the presence of a reducing agent.

[0123] 18. The method according to embodiment 17, wherein the exhaust gas is from an internal combustion engine, such as a diesel engine, especially a heavy-duty diesel engine.

[0124] 19. A catalytic article comprising a metal oxide catalyst composition according to any one of embodiments 1 to 12, the metal oxide catalyst composition being in the form of, for example, a powder or an extrudate, or a washcoat on a substrate.

[0125] 20. The catalytic article according to embodiment 19, wherein the substrate is a monolithic flow-through structure or a monolithic wall-flow structure.

[0126] 21. A system for treating exhaust gas, especially exhaust gas from an internal combustion engine, the system comprising a source of reducing agent, a catalytic article according to embodiment 19 or 20, and optionally one or more of a diesel oxidation catalyst (DOC), a three-way catalyst (TWC), a four-way catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), an ammonia oxidation catalyst (AMOx), a NOx trap, a NOx absorbent catalyst, a hydrocarbon trap catalyst, a sensor, and a mixer.

[0127] 22. The system according to embodiment 21, wherein the catalytic article is located downstream of an internal combustion engine such as a diesel engine, especially a heavy-duty diesel engine, in a close-coupled position, in a downstream position of the close-coupled position, or in both positions, preferably in a close-coupled position.

[0128] The present invention will be further illustrated by the following examples, which illustrate particularly advantageous embodiments. Although the examples are provided to illustrate the present invention, they are not intended to limit the present invention.

[0129] Example

[0130] I. Preparation Examples

[0131] Example 1 - Preparation of Vanadium-based Metal Oxide Catalyst (3V@8W-TiO2)

[0132] Dissolve 0.1909 g of ammonium metatungstate in 30 ml of deionized water and stir evenly. Add 2 g of TiO₂ in anatase form thereto and stir for 1 hour. Transfer the resulting solution to a rotary evaporator and dry at 60 °C. Then calcine the resulting product in a muffle furnace at a heating rate of 2 °C / minute at 500 °C for 3 hours to provide a WO₃-modified TiO₂ support.

[0133] Dissolve 0.0867 g of NH₄VO₃ in a solution of 0.5 g of oxalic acid in 30 ml of deionized water. Then add the WO₃-modified TiO₂ support obtained above to the solution and stir for 1 hour. Transfer the mixed solution to a rotary evaporator and dry at 60 °C. Then calcine the resulting product in a muffle furnace at a heating rate of 2 °C / minute at 500 °C for 3 hours.

[0134] Example 2 - Preparation of Non-vanadium-based Metal Oxide Catalyst with Alumina Support (MnCeTi@Al)

[0135] First, prepare a certain amount of γ-Al₂O₃ support in a 25 ml crucible. Dissolve the calculated amounts of Ce(NO₃)₃·6H₂O and Mn(NO₃)₂·4H₂O in 1.44 ml of absolute ethanol in a 5 ml beaker under ultrasound for 10 seconds. Then add the calculated amount of tetrabutyl titanate to the solution. Then add this solution to the crucible with the γ-Al₂O₃ support under stirring to reach the initial wetting state. Dry the mixture in the crucible in an oven at 80 °C for 2 hours and calcine at a heating rate of 2 °C / minute at 500 °C for 3 hours. Let the calcined powder cool naturally to room temperature to obtain the catalyst. The formulations of different samples are listed in Table 1 below.

[0136] Table 1

[0137] <![CDATA[Sample Name * > <![CDATA[Ce(NO3)3·6H2O, g]]> <![CDATA[Mn(NO3)3·4H2O, g]]> Tetrabutyl titanate, ml Support, g 10% MnCeTi@Al 0.1262 0.0952 0.072 0.9 20% MnCeTi@Al 0.2524 0.1904 0.144 0.8 30% MnCeTi@Al 0.3786 0.2856 0.216 0.7

[0138] * % refers to the total amount (wt%) of Mn, Ce, and Ti calculated as their respective oxides based on the total weight of the catalyst.

[0139] Example 3 - Preparation of Non-vanadium-based Metal Oxide Catalysts (Mn@AlCe, MnTi@AlCe)

[0140] Put a certain amount of a composite oxide of aluminum and cerium (AlCe10, AlCe20, AlCe30, or AlCe50) as a support into a crucible. Dissolve the calculated amount of Mn(NO₃)₂·4H₂O in 1.44 ml of absolute ethanol in a 5 ml beaker under ultrasound for 10 seconds. When titanium is also to be loaded, add the calculated amount of tetrabutyl titanate to the above solution. Thus, a solution for impregnation is provided.

[0141] The solution for impregnation was added to the crucible with the support under stirring to reach the initial wetting state. The mixture in the crucible was dried in an oven at 80 °C for 2 h. The dried powder was heated to 500 °C at a rate of 2 °C / min and held for 3 h to obtain the calcined powder. The calcined powder was naturally cooled to room temperature to obtain the catalyst. The formulations of different samples are listed in Table 2 below.

[0142] Example 4 - Preparation of Non-vanadium-based Metal Oxide Catalyst in Water (7Mn@AlCe20(H2O))

[0143] The catalyst sample was prepared in the same manner as described in Example 3, except that the same amount of deionized water was used instead of absolute ethanol.

[0144] Example 5 - Preparation of Non-vanadium-based Metal Oxide Catalyst with Ti-modified Support (8Mn@Ti-AlCe20)

[0145] A certain amount of the composite oxide of aluminum and cerium (AlCe20) as the support was placed in a crucible. The calculated amount of tetrabutyl titanate was dissolved in 1.44 ml of absolute ethanol under ultrasound until transparent. Then this solution was added to the crucible with AlCe20 under stirring to reach the initial wetting state. The mixture in the crucible was dried in an oven at 80 °C for 2 h to obtain the Ti-modified AlCe20 support. Then, the calculated amount of Mn(NO3)2·4H2O was dissolved in 1.44 ml of absolute ethanol in a 5 ml beaker under ultrasound for 10 s. Then this solution was added to the crucible with the support under stirring to reach the initial wetting state. The powder was heated to 500 °C at a rate of 2 °C / min and held for 3 h to obtain the calcined powder. The calcined powder was naturally cooled to room temperature to obtain the catalyst. The formulation of the sample is also listed in Table 2 below.

[0146] Table 2

[0147]

[0148]

[0149] * The numbers before Mn and Ti represent their amounts (wt%) calculated as the respective oxides based on the total weight of the catalyst; the number after Ce represents its amount (wt%) calculated as CeO2 based on the weight of the composite oxide of Al and Ce.

[0150] ** “(H2O)” refers to the solvent used for synthesis

[0151] Example 6 - Preparation of Non-vanadium-based Metal Oxide Catalysts (5Fe6.5Mn3.3Ti@AlCe20, 5Fe7Mn@AlCe20) Preparation

[0152] Put a certain amount of AlCe20 as the carrier into a crucible. Under ultrasonic conditions, dissolve the calculated amounts of Mn(NO3)2·4H2O and Fe(NO3)3·9H2O in 1.44 ml of absolute ethanol in a 5 ml beaker for 10 seconds. When titanium is also to be loaded, add the calculated amount of tetrabutyl titanate to the above solution. Thus, a solution for impregnation is provided.

[0153] Add the solution for impregnation to the crucible with the AlCe20 carrier under stirring to reach the initial wetting state. Dry the mixture in the crucible in an oven at 80 °C for 2 hours. Heat the dried powder to 500 °C at a rate of 2 °C / min and hold for 3 hours to obtain the calcined powder. Then cool the calcined powder naturally to room temperature to obtain the catalyst. The formulations of different samples are listed in Table 3 below.

[0154] Table 3

[0155]

[0156] * The numbers before Fe, Mn, and Ti represent their amounts (wt%) calculated as their respective oxides based on the total weight of the catalyst; the number after Ce represents its amount (wt%) calculated as CeO2 based on the weight of the composite oxide of Al and Ce.

[0157] Example 7 - Preparation of TiO2-coated Metal Oxide Catalysts (TiO2-coated 7Mn@AlCe20, Al2O3-coated 7Mn@AlCe20)

[0158] First, prepare 1 g of catalyst 7Mn@AlCe20 in the same manner as described in Example 1.

[0159] Under ultrasonic conditions, dissolve a certain amount of diisopropyl bis(triethanolamine) titanate (M = 466.4) or aluminum isopropoxide in 1.44 ml of absolute ethanol until transparent. Then add this solution to the crucible with catalyst 7Mn@AlCe20 under stirring to reach the initial wetting state. Dry the mixture in the crucible in an oven at 80 °C for 2 hours. Heat the dried powder to 500 °C at a rate of 2 °C / min and hold for 3 hours to obtain the calcined powder. Then cool the calcined powder naturally to room temperature to obtain the catalyst with a coating. The formulations of different samples are listed in Table 4 below.

[0160] Example 8 - Preparation of SiO2-coated Metal Oxide Catalyst (SiO2-coated 7Mn@AlCe20)

[0161] 1 g of the catalyst 7Mn@ / AlCe20 prepared in the same manner as described in Example 1 was dispersed in 100 ml of deionized water, and then adjusted to pH 8 with ammonium hydroxide. When the solution was heated at 70 °C, a certain amount of tetraethyl orthosilicate was added under strong stirring for 1 hour. After that, the formed precipitate was separated and washed with 1 L of deionized water until the pH was 7. The wet mixture was dried in an oven at 80 °C for 2 hours. The dried powder was heated to 500 °C at a rate of 2 °C / min and held for 3 hours to obtain the calcined powder. Then the calcined powder was naturally cooled to room temperature to obtain the catalyst with a coating. The formulations of different samples are also listed in Table 4 below.

[0162] Table 4

[0163]

[0164]

[0165] * The ratios in parentheses refer to molar ratios

[0166] Example 9 - Preparation of MgO-coated Metal Oxide Catalyst (MgO-coated 7Mn@AlCe20)

[0167] First, 1 g of the catalyst 7Mn@AlCe20 was prepared in the same manner as described in Example 1. 0.1908 g of Mg(NO3)2·4H2O was dissolved in 1.44 ml of absolute ethanol in a 5 ml beaker under ultrasound for 10 seconds. This solution was added to the crucible with the catalyst 7Mn@AlCe20 under stirring to reach the initial wetting state. The mixture in the crucible was dried in an oven at 80 °C for 2 hours. The dried powder was heated to 500 °C at a rate of 2 °C / min and held for 3 hours to obtain the calcined powder. The calcined powder was naturally cooled to room temperature to obtain the catalyst.

[0168] Example 10 - Preparation of Non-vanadium-based Metal Oxide Catalyst Based on Composite Oxide of Al and Ce with High Ce Content (10Mn@AlCe52)

[0169] The composite oxide of Al and Ce was prepared according to Example 1 in CN106824173A. The obtained composite oxide AlCe52 was impregnated with Mn(NO3)2·4H2O in the same manner as described in Example 3.

[0170] II. SCR Performance Measurement

[0171] II.1 General Procedures

[0172] The SCR performance measurement was carried out using a fixed-bed quartz flow reactor (inner diameter = 4 mm). The reactor was filled with 0.15 g of catalyst sample of 40 mesh - 60 mesh (about 250 μm to 400 μm) and cordierite particles as diluents to a total length of 32 mm. The measurement was carried out in the temperature range of 90 °C to 480 °C.

[0173] The gas feed consisted of 500 vppm NO, 500 vppm NH3, 10 vol% O2, 5 vol% H2O, 5 vol% CO2 and the balance N2. The total flow rate was controlled at 475 mL / min, corresponding to a gas hourly space velocity (GHSV) of 150 000 h -1 -1. The GHSV calculated by the catalyst volume was fixed by cordierite so that the volume of all catalysts was the same.

[0174] The gas concentrations of NO, NO2, NH3, H2O and N2O were simultaneously monitored by an FTIR spectrometer (Thermo Fisher). The SCR catalytic activity was recorded after the reaction system reached a steady state. The NO conversion was calculated according to the following formula:

[0175]

[0176] where [NO] in and [NO] out represent the inlet and outlet NO concentrations, respectively.

[0177] Catalyst aging conditions: Air with 10% H2O, 650 °C for 50 hours.

[0178] Sulfation conditions: 0.15 g of 40 mesh - 60 mesh catalyst was filled into a fixed-bed quartz flow reactor (inner diameter = 4 mm). The sulfation process was carried out at a temperature of 300 °C. The gas feed consisted of 40 vppm SO2, 10 vol% O2, 5 vol% H2O, 5 vol% CO2 and the balance N2. The total flow rate was controlled at 235 mL·min -1 -1, corresponding to a gas hourly space velocity (GHSV) of 75,000 h -1 -1.

[0179] Desulfation conditions: The desulfation process was carried out at a temperature of 600 °C for 3 hours with 475 mL / min N2 as the balance gas. The total flow rate was controlled at 475 mL·min -1 -1, corresponding to a gas hourly space velocity (GHSV) of 150,000 h -1 -1.

[0180] II.2 Test Results

[0181] The test results are summarized in the following table.

[0182] Summary of NO Conversion Rates of Aged Samples in Table 5

[0183]

[0184]

[0185] As can be seen from the results, at temperatures of 210 °C or lower, the catalyst according to the present invention exhibits a higher NO conversion rate than conventional vanadium-based catalysts and catalysts having a composition other than according to the present invention.

[0186] Comparison of NO Conversion Rates between Fresh and Aged Samples in Table 6

[0187]

[0188]

[0189] Comparison of N2O Formation between Fresh and Aged Samples in Table 7

[0190]

[0191] As can be seen from the results, the catalyst according to the present invention has a desired thermal stability and does not exhibit a significant decrease in activity during aging. The coated catalyst even exhibits improved activity during aging.

[0192] NO Conversion Rates during Sulfidation and Desulfurization at 210°C in Table 8

[0193] Sample After Sulfidation, % After Desulfurization, % 6.5Mn3.3Ti@AlCe20 0.60 n.a. 5Fe6.5Mn3.3Ti@AlCe20 8.10 n.a. 7Mn@AlCe20 5.87 15.68 5Fe7Mn@AlCe20 17.91 n.a. <![CDATA[7Mn@AlCe20 coated with TiO2 (Mn:Ti = 2:1)]]> 5.78 18.72 <![CDATA[7Mn@AlCe20 (Mn:Al = 3:1) coated with Al2O3]]> 6.83 12.18 MgO-coated 7Mn@AlCe20 5.19 17.78

[0194] III. Characterization of Composite Oxide as Support

[0195] The composite oxide used as the support in the above catalyst was characterized by XRD. The patterns of each sample are shown in Figure 1 and Figure 2 , where the d value indicated for each sample corresponds to 2θ = 28.5°. The composite oxide and the CeO2 microcrystal size of each sample obtained from the XRD pattern are summarized in Table 9 below.

[0196] The surface area of the composite oxide was also characterized by the BET method, and the pore volume and pore diameter were characterized by the BJH method. The measurement results are summarized in Table 9 below.

[0197] Table 9

[0198]

[0199] *Aging: Air containing 10% H2O, aged at 650 °C for 50 hours

[0200] The composite oxides used as carriers all show an increased crystallite size upon aging. The less the crystallite size increases, the higher the stability exhibited by the composite oxide. It can be seen that the composite oxide having at least 50% aluminum (calculated as Al2O3) used in the catalyst according to the present invention exhibits higher hydrothermal stability than the composite oxide AlCe52.

[0201] Although the present invention has been described herein with reference to specific embodiments and examples, it is to be understood that these embodiments and examples are illustrative only of the principles and applications of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the compositions and methods of the invention without departing from the spirit and scope of the invention. Accordingly, the invention is intended to embrace modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. A non-vanadium-based metal oxide catalyst composition comprising - at least one metal oxide, said at least one metal oxide comprising manganese oxide, and - a support, said support comprising particles of a composite oxide of aluminum and at least one metal selected from the group consisting of cerium, manganese, and titanium, wherein based on the total weight of the composite oxide, aluminum is present in the composite oxide in an amount of 50 wt% to 80 wt% calculated as Al2O3, wherein said at least one metal oxide is dispersed on said support, and wherein based on the total weight of the metal oxide catalyst composition, manganese oxide is present in the metal oxide catalyst composition in an amount of 2.5 wt% to 10 wt% calculated as MnO2.

2. The non-vanadium-based metal oxide catalyst composition according to claim 1, wherein said at least one metal oxide further comprises an oxide of titanium (Ti), iron (Fe), magnesium (Mg), or aluminum (Al), or any combination thereof.

3. The non-vanadium-based metal oxide catalyst composition according to claim 2, wherein based on the total weight of the metal oxide catalyst composition, each of the oxides of Ti, Fe, Mg, and Al is present in an amount not greater than 10 wt%, not greater than 8 wt%, or not greater than 6 wt% calculated as their respective oxides.

4. The non-vanadium-based metal oxide catalyst composition according to any one of the preceding claims, wherein based on the total weight of the metal oxide catalyst composition, manganese oxide is present in an amount of 3 wt% to 8 wt% calculated as MnO2.

5. The non-vanadium-based metal oxide catalyst composition according to any one of the preceding claims, wherein said at least one metal oxide further comprises titanium oxide, and based on the total weight of the catalyst composition, the titanium oxide is preferably present in an amount of 1 wt% to 6 wt% or 2 wt% to 4 wt% calculated as TiO2.

6. The non-vanadium-based metal oxide catalyst composition according to any one of the preceding claims, wherein said at least one metal oxide further comprises iron oxide, and based on the total weight of the metal oxide catalyst composition, the iron oxide is preferably present in an amount of 1 wt% to 5 wt% or 3 wt% to 5 wt% calculated as Fe2O3.

7. The non-vanadium-based metal oxide catalyst composition according to any one of the preceding claims, wherein the support comprises particles of the composite oxide and a dopant selected from Ti, Si, Zr, La, and Ba, and based on the total weight of the metal oxide catalyst composition, the dopant is preferably present in an amount of 1 wt% to 10 wt% or 3 wt% to 6 wt% calculated as their respective oxides.

8. The non-vanadium-based metal oxide catalyst composition according to any one of the preceding claims, wherein the support comprises particles of a composite oxide of aluminum, cerium, and optionally manganese and / or titanium.

9. The non-vanadium-based metal oxide catalyst composition according to claim 7, wherein the support consists of particles of a composite oxide of aluminum and cerium and optionally said dopant.

10. The non-vanadium-based metal oxide catalyst composition according to claim 8 or 9, wherein, based on the total weight of the composite oxide, cerium is present in the composite oxide in an amount of 20% to 50% by weight, 20% to 40% by weight, or 20% to 30% by weight calculated as CeO2.

11. The non-vanadium-based metal oxide catalyst composition according to claim 10, wherein the composite oxide of aluminum and cerium comprises an Al2O3 phase and a CeO2 phase, and the crystallite size of the latter is at least 5 nm, preferably at least 9 nm, at least 9.5 nm, or at least 10 nm, as determined by XRD analysis in the fresh state.

12. The non-vanadium-based metal oxide catalyst composition according to any one of the preceding claims, further comprising a coated metal oxide, such as titanium oxide, aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, or any combination thereof.

13. A method for preparing the non-vanadium-based metal oxide catalyst composition according to any one of the preceding claims, the method comprising the step of impregnating one or more precursors of the at least one metal oxide onto the carrier, and then optionally the step of impregnating one or more precursors of the coated metal oxide.

14. The method according to claim 13, wherein the impregnating of one or more precursors of the at least one metal oxide onto the carrier is carried out in a water-soluble alcohol solvent.

15. The method according to claim 13 or 14, wherein the water-soluble alcohol solvent is selected from methanol, ethanol, n-propanol, and isopropanol.

16. The method according to any one of claims 13 to 15, the method further comprising the steps of: Before the impregnating of one or more precursors of the at least one metal oxide, preferably in a water-soluble alcohol solvent, one or more precursors of a dopant are impregnated onto the particles of the composite oxide.

17. A method for treating an exhaust gas containing nitrogen oxides by selective catalytic reduction, the method comprising contacting the exhaust gas with the metal oxide catalyst composition according to any one of claims 1 to 12 in the presence of a reducing agent.

18. The method according to claim 17, wherein the exhaust gas is derived from an internal combustion engine, such as a diesel engine, especially a heavy-duty diesel engine.

19. A catalytic article, the catalytic article comprising the metal oxide catalyst composition according to any one of claims 1 to 12, the metal oxide catalyst composition being in the form of, for example, a powder or an extrudate, or a washcoat on a substrate.

20. The catalytic article according to claim 19, wherein the substrate is a monolithic flow-through structure or a monolithic wall-flow structure.

21. A system for treating exhaust gas, especially exhaust gas from an internal combustion engine, the system comprising a source of reducing agent, the catalytic article according to claim 19 or 20, and optionally one or more of a diesel oxidation catalyst (DOC), a three-way catalyst (TWC), a four-way catalyst (FWC), a non-catalytic or catalytic soot filter (CSF), an ammonia oxidation catalyst (AMOx), a NOx trap, a NOx absorbent catalyst, a hydrocarbon trap catalyst, a sensor, and a mixer.

22. The system according to claim 21, wherein the catalytic article is located downstream of an internal combustion engine, such as a diesel engine, particularly a heavy-duty diesel engine, in a close-coupled position, in a downstream position of the close-coupled position, or in both positions, preferably in the close-coupled position.

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