BR112020006411B1 - COMPOSITIONS OF SCR CATALYST, CATALYST ARTICLE AND EMISSIONS TREATMENT SYSTEM - Google Patents

Abstract

The present invention provides SCR catalyst compositions, catalyst articles and catalyst systems, as well as methods for reducing the amount of NOx present in an engine exhaust gas, particularly in the exhaust of a gasoline engine. The catalyst compositions may particularly comprise a doped ceria substrate, particularly a ceria support doped with at least one niobia component and optionally further doped with an additional material, particularly a basic metal oxide (BMO).

Description

FIELD OF THE INVENTION

[001] The present invention relates, in general, to the field of selective catalytic reduction catalysts and to methods of preparing and using such catalysts to selectively reduce nitrogen oxides.

BACKGROUND OF THE INVENTION

[002] Over time, the harmful components of nitrogen oxides (NOx) led to air pollution. NOx is contained in exhaust gases such as from internal combustion engines (e.g. in cars and trucks), from combustion plants (e.g. power plants heated by natural gas, oil or coal) and from nitric acid production plants.

[003] Various treatment methods have been used for the treatment of gas mixtures containing NOx to decrease air pollution. One type of treatment involves the catalytic reduction of nitrogen oxides. There are two processes: (1) a non-selective reduction process in which carbon monoxide, hydrogen or a lower hydrocarbon is used as the reducing agent; and (2) a selective reduction process in which ammonia or an ammonia precursor is used as a reducing agent. In the selective reduction process, a high degree of nitrogen oxide removal can be achieved with a small amount of reducing agent.

[004] The selective reduction process is called the SCR process (Selective Catalytic Reduction). The SCR process uses catalytic reduction of nitrogen oxides with a reductant (e.g., ammonia) in the presence of atmospheric oxygen, resulting in the formation of predominantly nitrogen and steam: 4NO + 4NH3+O2 → 4N2 + 6H2O (standard SCR reaction) 2NO2 + 4NH3 → 3N2 + 6H2O (slow SCR reaction) NO + NO2 + NH3 → 2N2 + 3H2O ( fast SCR reaction).

[005] Ideally, the catalysts employed in the SCR process should be able to retain good catalytic activity over a wide range of temperature conditions of use, for example, 200 °C to 600 °C or higher, under hydrothermal conditions. SCR catalysts are commonly employed in hydrothermal conditions, such as during regeneration of a soot filter, a component of the exhaust gas treatment system used for particulate removal.

[006] Molecular sieves, such as zeolites, have been used in the selective catalytic reduction of nitrogen oxides with a reductant such as ammonia, urea, or hydrocarbon in the presence of oxygen. Zeolites are crystalline materials with fairly uniform pore sizes that, depending on the type of zeolite and the type and amount of cations included in the zeolite network, range from about 3 to about 10 Angstroms in diameter. Certain zeolites with 8-ring pore openings and secondary building units with six double rings, particularly those with cage-like structures, have been used as SCR catalysts. A specific type of zeolite possessing these properties is chabazite (CHA), which is a small-pore zeolite with pore openings of 8 member rings (~3.8 Angstroms) accessible through its three-dimensional porosity. A cage-like structure results from connecting 6 double ring by 4 ring building units.

[007] Metal-promoted zeolite catalysts are known, also often referred to as ion-exchanged zeolites or copper- and/or iron-supported zeolites, including, but not limited to, copper-promoted and iron-promoted zeolite catalysts, for the selective catalytic reduction of nitrogen oxides with ammonia and can usually be prepared by metal ion exchange processes. For example, iron-promoted beta zeolite has been an effective commercial catalyst for the selective reduction of nitrogen oxides with ammonia.

[008] Metal promoted zeolite catalysts are effective NOx reduction catalysts for use with diesel powered engines and even for use with so-called three-way conversion catalyst (TWC) applications up to a temperature of 900 °C. This, however, presents a temperature limitation, as applications requiring temperatures in excess of 900 °C, such as with aging a contiguous coupled catalyst in a TWC system, are known to destroy zeolite materials.

[009] In the exhaust of a gasoline powered vehicle, there is a moderate amount of ammonia as a result of the excessive reduction of NOx in the TWC catalysts. A catalyst system comprising a TWC catalyst and an SCR catalyst (the so-called TWC + SCR system) is therefore known for the further reduction of NOx by a passive route of NH3-SCR. As noted above, however, zeolite-based SCR catalysts cannot survive typical TWC aging conditions with a temperature inevitably greater than 900°C under frequent lean/rich transitions. Consequently, there remains a need for a non-zeolite-based SCR catalyst component that is resistant to the harsh environments of TWC aging.

SHORT DESCRIPTION OF THE INVENTION

[010] The present invention provides non-zeolitic SCR catalyst compositions, catalyst articles and catalyst systems, as well as methods for reducing the amount of NOx present in an engine exhaust gas, particularly exhaust from a gasoline engine or a lean gasoline direct injection (GDI) engine. The catalyst compositions may particularly comprise a doped ceria substrate, particularly a ceria support doped with at least one niobia component and optionally further doped with an additional material, particularly a basic metal oxide (BMO). Catalyst articles may particularly comprise a catalyst composition as described herein coated onto a catalyst substrate (e.g. a continuous flow filter or wall flow filter) and/or a catalyst composition as described herein in a monolithic form. The catalyst composition may be included in a multi-coated article, wherein the catalyst composition is provided as a first coating with a second coating including a BMO or a platinum group metal (PGM). Catalyst systems may particularly comprise a TWC catalyst combined with a catalyst article, as otherwise described herein.

[011] In one or more embodiments, the present invention may specifically relate to an SCR catalyst. For example, an SCR catalyst composition according to the present invention can comprise a ceria support including a first dopant that is niobium and a second dopant that is a basic metal oxide (BMO). As a further example, an SCR catalyst composition according to the present invention can comprise a ceria support including a first dopant that is niobium and an optional second dopant that is a basic metal oxide (BMO), wherein the ceria support comprises from about 10% to about 95% by weight of ceria and from about 5% to about 90% by weight of an additional metal oxide. In other embodiments, the present SCR catalyst composition may be defined with respect to one or more of the following statements, which may be combined in any number and order.

[012] BMO can be selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, titanium dioxide, tungsten oxide, iron oxide, copper oxide, manganese oxide, nickel oxide, magnesium oxide, barium oxide and combinations thereof.

[013] BMO can be selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, tungsten oxide and combinations thereof.

[014] Niobia may comprise about 0.1 to about 20% by weight of the SCR catalyst composition.

[015] The second dopant may comprise about 0.1 to about 20% by weight of the SCR catalyst composition.

[016] The ceria support may comprise at least 99% by weight of ceria.

[017] The ceria support may comprise about 10% to about 95% by weight of ceria and about 5% to about 90% by weight of an additional metal oxide.

[018] The additional metal oxide that can optionally be combined with the ceria support can be aluminum oxide.

[019] In one or more embodiments, the present invention may specifically relate to a catalyst article. For example, a catalyst article in accordance with the present invention may comprise a catalyst substrate having a plurality of channels adapted for gas flow, each channel having a wall surface in adherence to a catalytic coating comprising a catalyst composition, as otherwise described herein. In other embodiments, the present catalyst article may be defined with respect to one or more of the following statements, which may be combined in any number and order.

[020] The catalyst substrate may be a well comprising a flow barrier filter substrate or a continuous flow substrate.

[021] The catalytic coating may be present on the substrate with a charge of at least about 0.06 g/cm3 (1.0 g/in3).

[022] The catalyst article may further comprise a platinum group metal (PGM).

[023] In one or more embodiments, the present invention may specifically relate to an emissions treatment system for treating an exhaust gas stream. For example, an emissions treatment system in accordance with the present invention may comprise: (i) an engine producing an exhaust gas stream; (ii) a three-way catalytic converter positioned downstream of the engine and in fluid communication with the exhaust stream; and (iii) an SCR catalyst article positioned downstream of the three-way catalyst and in fluid communication with the exhaust stream, the SCR catalyst article comprising a catalyst substrate having a plurality of channels adapted for gas flow, each channel having a wall surface in adherence to a catalytic coating comprising a niobium-doped ceria support. In other embodiments, the present emissions treatment system may be defined with respect to one or more of the following statements, which may be combined in any number and order.

[024] The SCR catalyst article may be substantially free of platinum group metal (PGM).

[025] The SCR catalyst article may include a platinum group metal (PGM).

[026] The PGM may be present on the catalyst substrate with a loading of at least about 17 g/m3 (0.5 g/ft3).

[027] The PGM can be present in the catalyst substrate with a loading from about 17 g/m3 (0.5 g/ft3) to about 707 g/m3 (20 g/ft3).

[028] The catalytic coating may further comprise boehmite.

[029] The ceria support of the catalytic coating of the SCR catalyst article may comprise at least 99% by weight of ceria.

[030] The ceria support of the catalytic coating of the SCR catalyst article may comprise about 10% to about 95% by weight of ceria and about 5% to about 90% by weight of another metal oxide.

[031] The additional metal oxide may be aluminum oxide.

[032] The catalytic coating of the SCR catalyst article may comprise an additional dopant which is a basic metal oxide (BMO).

[033] BMO can be selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, titanium dioxide, tungsten oxide, iron oxide, copper oxide, manganese oxide, nickel oxide, magnesium oxide, barium oxide and combinations thereof.

[034] BMO can be selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, tungsten oxide and combinations thereof.

[035] The catalytic coating comprising the niobia-doped ceria support may be on a first coating layer, and the catalyst substrate of the SCR catalyst article may include a second catalytic coating layer.

[036] The second catalytic coating layer may comprise a base metal oxide (BMO).

[037] The second layer of catalytic coating may comprise a platinum group metal (PGM).

[038] The PGM may be present in the catalyst substrate with a loading of at least about 17 g/m3 (0.5 g/ft3).

[039] The PGM can be present in the catalyst substrate with a loading from about 17 g/m3 (0.5 g/ft3) to about 707 g/m3 (20 g/ft3).

[040] The first coating layer may be a top layer.

[041] The first coating layer may be a bottom layer.

[042] The present application includes, without limitation, the following embodiments.

[043] Embodiment 1: An SCR catalyst composition comprising a ceria support including a first dopant that is niobium and a second dopant that is a basic metal oxide (BMO).

[044] Embodiment 2: An SCR catalyst composition comprising a ceria support including a first dopant that is niobium and an optional second dopant that is a basic metal oxide (BMO), wherein the ceria support comprises about 10% to about 95% by weight of ceria and about 5% to about 90% by weight of another metal oxide.

[045] Embodiment 3: The SCR catalyst composition of any previous embodiment, wherein the BMO is selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, titanium dioxide, tungsten oxide, iron oxide, copper oxide, manganese oxide, nickel oxide, magnesium oxide, barium oxide and combinations thereof.

[046] Embodiment 4: The SCR catalyst composition of any previous embodiment, wherein the BMO is selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, tungsten oxide and combinations thereof.

[047] Embodiment 5: The SCR catalyst composition of any preceding embodiment, wherein niobia comprises about 0.1 to about 20% by weight of the SCR catalyst composition.

[048] Embodiment 6: The SCR catalyst composition of any preceding embodiment, wherein the second dopant comprises about 0.1 to about 20% by weight of the SCR catalyst composition.

[049] Embodiment 7: The SCR catalyst composition of any preceding embodiment, wherein the ceria support comprises at least 99% by weight of ceria.

[050] Embodiment 8: The SCR catalyst composition of any preceding embodiment, wherein the ceria support comprises about 10% to about 95% by weight of ceria and about 5% to about 90% by weight of an additional metal oxide.

[051] Embodiment 9: The SCR catalyst composition of any preceding embodiment, wherein the additional metal oxide is aluminum oxide.

[052] Embodiment 10: A catalyst article comprising a catalyst substrate having a plurality of channels adapted for gas flow, each channel having a wall surface in adherence to a catalytic coating comprising a catalyst composition according to any preceding embodiment.

[053] Embodiment 11: The catalyst article of any preceding embodiment, wherein the catalyst substrate is a well comprising a flow barrier filter substrate or a continuous flow substrate.

[054] Embodiment 12: The catalyst article of any preceding embodiment, wherein the catalytic coating is present on the substrate with a loading of at least about 0.06 g/cm3 (1.0 g/in3).

[055] Embodiment 13: The catalyst article of any preceding embodiment, further comprising a platinum group metal (PGM).

[056] Embodiment 14: An emission treatment system for treating an exhaust gas stream, the emission treatment system comprising: (i) an engine producing an exhaust gas stream; (ii) a three-way catalytic converter positioned downstream of the engine and in fluid communication with the exhaust stream; and (iii) an SCR catalyst article positioned downstream of the three-way catalyst and in fluid communication with the exhaust stream, the SCR catalyst article comprising a catalyst substrate having a plurality of channels adapted for gas flow, each channel having a wall surface in adherence to a catalytic coating comprising a niobium-doped ceria support.

[057] Embodiment 15: The emissions treatment system of any preceding embodiment, wherein the SCR catalyst article is substantially free of platinum group metal (PGM).

[058] Embodiment 16: The emissions treatment system of any preceding embodiment, wherein the SCR catalyst article includes a platinum group metal (PGM).

[059] Embodiment 17: The emissions treatment system of any preceding embodiment, wherein the PGM is present in the catalyst substrate with a loading of at least about 17 g/m3 (0.5 g/ft3).

[060] Embodiment 18: The emissions treatment system of any previous embodiment, wherein the PGM is present in the catalyst substrate with a load of about 17 g/m3 (0.5 g/ft3) to about 707 g/m3 (20 g/ft3).

[061] Embodiment 19: The emissions treatment system of any previous embodiment, wherein the catalytic coating further comprises boehmite.

[062] Embodiment 20: The emissions treatment system of any preceding embodiment, wherein the ceria support of the catalytic coating of the SCR catalyst article comprises at least 99% by weight of ceria.

[063] Embodiment 21: The emissions treatment system of any preceding embodiment, wherein the ceria support of the catalytic coating of the SCR catalyst article comprises about 10% to about 95% by weight of ceria and about 5% to about 90% by weight of another metal oxide.

[064] Embodiment 22: The emissions treatment system of any previous embodiment, wherein the additional metal oxide is aluminum oxide.

[065] Embodiment 23: The emissions treatment system of any preceding embodiment, wherein the catalytic coating of the SCR catalyst article comprises an additional dopant which is a basic metal oxide (BMO).

[066] Embodiment 24: The emissions treatment system of any previous embodiment, wherein the BMO is selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, titanium dioxide, tungsten oxide, iron oxide, copper oxide, manganese oxide, nickel oxide, magnesium oxide, barium oxide and combinations thereof.

[067] Embodiment 25: The emissions treatment system of any previous embodiment, wherein the BMO is selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, tungsten oxide and combinations thereof.

[068] Embodiment 26: The emissions treatment system of any preceding embodiment, wherein the catalytic coating comprising the niobium-doped ceria support is on a first coating layer, and wherein the catalyst substrate of the SCR catalyst article includes a second catalytic coating layer.

[069] Embodiment 27: The emissions treatment system of any preceding embodiment, wherein the second catalytic coating layer comprises a base metal oxide (BMO).

[070] Embodiment 28: The emissions treatment system of any preceding embodiment, wherein the second catalytic coating layer comprises a platinum group metal (PGM).

[071] Embodiment 29: The emissions treatment system of any preceding embodiment, wherein PGM is present in the catalyst substrate with a loading of at least about 17 g/m3 (0.5 g/ft3).

[072] Embodiment 30: The emissions treatment system of any previous embodiment, wherein the PGM is present in the catalyst substrate with a loading of about 17 g/m3 (0.5 g/ft3) to about 707 g/m3 (20 g/ft3).

[073] Embodiment 31: The emissions treatment system of any previous embodiment, wherein the first coating layer is a top layer.

[074] Embodiment 32: The emissions treatment system of any previous embodiment, wherein the first coating layer is a bottom layer.

[075] These and other features, aspects and advantages of the invention will be evident from reading the detailed description below, together with the accompanying drawings, which are briefly described below. The invention includes any combination of two, three, four or more of the aforementioned embodiments, as well as combinations of any two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined in a specific embodiment description herein. This disclosure is intended to be read holistically, so that any separable features or elements of the disclosed invention, in any of its various aspects and embodiments, are to be viewed as intended to be combinable, unless the context clearly indicates otherwise. Other aspects and advantages of the present invention will become apparent from the following.

BRIEF DESCRIPTION OF THE FIGURES

[076] In order to provide an understanding of the embodiments of the invention, reference is made to the accompanying drawings, which are not necessarily drawn to scale, and in which the reference numerals refer to components of exemplary embodiments of the invention. The drawings are exemplary only and should not be construed as limiting the invention.

[077] Figure 1 is a perspective view of a honeycomb substrate vehicle that may comprise a selective reduction catalyst (SCR) substrate coating (washcoat) composition according to the present invention;

[078] Figure 2 is a partial cross-sectional view enlarged in relation to Figure 1 and taken along a plane parallel to the end faces of the substrate vehicle of Figure 1 representing a monolithic continuous flow substrate, showing an enlarged view of a plurality of gas flow passages shown in Figure 1;

[079] Figure 3 is a sectional view of an enlarged section in relation to Figure 1, in which the honeycomb substrate vehicle in Figure 1 represents a monolith of flow barrier filter substrate;

[080] Figure 4 is a partial cross-sectional view of a substrate with a plurality of layers of different substrate-coated catalytic articles (washcoated) thereon in a non-overlapping configuration;

[081] Figure 5 is a partial cross-sectional view of a substrate with a plurality of layers of different substrate-coated catalytic articles thereon, wherein a substrate coating layer partially overlaps a second substrate coating layer;

[082] Figure 6 is a partial cross-sectional view of a substrate with a plurality of layers of different substrate-coated catalytic articles thereon, wherein a substrate coating layer completely overlaps a second substrate coating layer; It is

[083] Figure 7 is a schematic of an emissions treatment system in which an SCR catalyst composition of the present invention is used.

DETAILED DESCRIPTION

[084] The present invention will now be described in more detail hereinafter. This invention can, however, be embodied in a number of different ways and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. As used in this specification and in the claims, the singular forms "a", "an", "the" and "the" include plural referents, unless the context clearly indicates otherwise.

[085] The present invention generally provides catalysts, catalyst articles and catalyst systems comprising these catalyst articles. In particular, these articles and systems comprise an SCR catalyst composition, which is effective for the selective reduction of nitrogen oxides in the presence of a reductant and a catalyst. The catalyst is particularly configured to remain stable even under high temperature conditions - for example, aging at temperatures in excess of 900 °C.

[086] The following terms shall, for the purposes of this application, have the respective meanings set forth below.

[087] As used herein, the term "selective catalytic reduction" (SCR) refers to the catalytic process of reducing nitrogen oxides to dinitrogen (N2) using a nitrogenous reductant (eg, ammonia, urea, and the like).

[088] As used herein, the term "catalyst" or "catalyst composition" refers to a material that promotes a reaction.

[089] As used herein, the terms "upstream" and "downstream" refer to relative directions according to the flow of an engine exhaust gas stream from an engine towards an exhaust pipe, with the engine in an upstream location and the exhaust pipe and any pollution abatement articles, such as filters and catalytic converters, being downstream of the engine.

[090] As used herein, the term "stream" broadly refers to any combination of flowing gas that may contain solid or liquid particulate matter. The term "gaseous stream" or "exhaust gas stream" means a stream of gaseous constituents, such as the exhaust from a lean combustion engine, which may contain entrained non-gaseous components such as liquid droplets, solid particulates, and the like. The exhaust gas stream from a lean combustion engine typically further comprises products of combustion, products of incomplete combustion, nitrogen oxides, combustible and/or carbonaceous particulate matter (soot), and unreacted oxygen and nitrogen.

[091] As used herein, the term "substrate" refers to the monolithic material on which the catalyst composition is placed, typically in the form of a substrate coating containing a plurality of particles containing a catalytic composition thereon. A substrate coating is formed by preparing a slurry containing a certain solid content (e.g., 10-80% by weight) of particles in a liquid carrier, which is then coated onto a substrate and dried to provide a substrate coating layer.

[092] As used herein, the term "substrate coating" has its usual meaning in the art of a thin, adherent coating of a catalytic or other material applied to a substrate material, such as a honeycomb-type carrier member, that is porous enough to allow the passage of the gas stream to be treated.

[093] As used herein, the term "catalyst article" refers to an element that is used to promote a desired reaction. For example, a catalyst article can comprise a substrate coating containing catalytic compositions on a substrate.

[094] The term “reduce” means to decrease the quantity and “reduction” means a decrease in quantity, caused by any means.

[095] A catalyst composition according to the present invention is particularly configured for use as a selective catalytic reduction (SCR) catalyst. The catalyst composition, in particular, may comprise a support formed from at least one metal oxide, the support including at least one first dopant. In preferred embodiments, the support is formed of at least ceria and the dopant is at least niobia (Nb2O5).

[096] Niobia is preferably present in the catalyst composition in an amount of about 0.1% to about 20% by weight, about 0.1% to about 15% by weight, about 0.1 to about 10% by weight, or about 0.1 to about 8% by weight. In some embodiments, niobia can be present in an amount of from about 1% to about 10% by weight, about 1.5% to about 8% by weight, or about 2% to about 6% by weight. The above amounts are based on the total weight of the catalyst composition.

[097] In addition to niobia, the catalyst composition may include a second dopant. In preferred embodiments, the second dopant can be particularly a basic metal oxide (BMO). Non-limiting examples of BMOs that can be used as a second dopant include lanthanum oxide (La2O3), praseodymium oxide (Pr6O11), neodymium oxide (Nd2O3), yttrium oxide (Y2O3), titanium dioxide (TiO2), tungsten oxide (W2O5), iron oxide (Fe2O3), copper oxide (CuO), manganese oxide (MnO2 ), nickel oxide (NiO), magnesium oxide (MgO) and barium oxide (BaO). Any combination of two or more BMOs can also be used as the second dopant. As such, the catalyst composition can be characterized as including one dopant, two dopants, three dopants, four dopants, and so on. In one or more embodiments, a specific BMO (including but not limited to the foregoing listing) may be deleted. In certain embodiments, preferred BMOs may include La2O3, Pr6O11, Nd2O3, Y2O3, TiO2, W2O5, Fe2O3, NiO, and combinations thereof. In other embodiments, preferred BMOs may include La2O3, Pr6O11, Nd2O3, Y2O3, W2O5, and combinations thereof.

[098] The dopant(s) included, in addition to niobia, may be present separately in an amount of about 0.1% to about 20% by weight, about 0.1% to about 10% by weight, or about 0.1 to about 8% by weight. In some embodiments, the included dopant(s), other than niobia, may be present separately in an amount of from about 1% to about 10% by weight, about 1.5% to about 8% by weight, or about 2% to about 6% by weight. The above amounts are based on the total weight of the catalyst composition.

[099] The total amount of dopants (i.e., niobia plus one or more additional dopants) included in the catalyst composition can be from about 1% to about 40%, about 1% to about 30%, about 1.5% to about 20%, or about 2% to about 10% by weight. The above amounts are based on the total weight of the catalyst composition.

[0100] The support component of the catalyst composition may comprise wholly or substantially wholly ceria. For example, the support can comprise at least 99% by weight of ceria and thus comprise substantially only ceria. Comprising "completely ceria" may indicate that the support component comprises at least 99.9% by weight of ceria. Comprising "substantially just ceria" or "substantially completely ceria" may indicate that the support component comprises at least 99% ceria by weight.

[0101] In some embodiments, the support may comprise ceria and at least one additional metal oxide. For example, the support can comprise about 10% to about 95% by weight of ceria and about 5% to about 90% by weight of at least one additional metal oxide. In some embodiments, the support can comprise about 20% to about 80% by weight of ceria and about 80% to about 20% by weight of at least one additional metal oxide. In other embodiments, the support can comprise about 50% to about 95% by weight of ceria and about 5% to about 50% by weight of at least one additional metal oxide. The above amounts are based on the total weight of the catalyst composition support component.

[0102] Non-limiting examples of metal oxides that can be included in the support, in addition to ceria, include aluminum oxide (Al2O3), lanthanum oxide (La2O3), neodymium oxide (Nd2O3) and yttrium oxide (Y2O3). In a preferred example, the support component of the catalyst composition comprises ceria and aluminum oxide.

[0103] The catalyst composition can be prepared by any suitable method for combining a metal oxide dopant with a metal oxide support. In particular, the support component formed by ceria (alone or in combination with at least one additional metal oxide) can be impregnated with niobia (alone or in combination with at least one additional dopant) which is in the form of a metal solution. For example, any of the following metal compounds can be supplied in solution for impregnation of the corresponding metal oxide: niobium (V) ammonium oxalate (ANO); La(NO3)3; Pr(NO3)3; Nd(NO3)3; Y(NO3)3; Ti(OC2H5)4; (NH4)6H2Wi2θ4o^H2θ; Fe(NOa)3-H2O; Cu(NO3)2-2.5H2O;Mn(NO3)2^6H2O; Ni(NO3>6H2O; Mg(NO3)2; and Ba(OAc)2. Metal oxides can be impregnated onto the support component using a wet-wet impregnation technique. Wet-wet impregnation techniques, also called capillary impregnation or dry impregnation, are commonly used for the synthesis of heterogeneous materials, i.e., catalysts. Typically, an active metal precursor is dissolved in an aqueous or organic solution, and then the active metal-containing solution is added to a support of catalyst that contains the same pore volume as the volume of the solution that was added. The metal can be supplied in the form of any soluble salt of the same, such as an acetate, nitrate, halide, metal oxalate or the like. Capillary action draws the solution into the pores of the support. The solution added in excess of the pore volume of the support causes the transport of the solution to change from a capillary action process to a diffusion process, which is much slower.

[0104] In some embodiments, the support component and the dopant(s) are in the form of a co-precipitant. For example, metal precursor compounds for the support component (eg, ceria) and at least one dopant (eg, niobia) can be combined in solution and a precipitating agent can be added. For example, a pH adjusting agent can be used as the precipitating agent. The precipitating agent can be effective to co-precipitate the metal species from solution. As such, the niobium, alone or in combination with at least one additional dopant, is mixed with the ceria (or ceria combined with another base metal oxide) and simultaneously formed into a unitary body. It is thus understood that a co-precipitant, due to the mixture of materials that arise during co-precipitation, may exhibit different properties from a material in which the dopant(s) is(are) impregnated into a previously formed support component.

[0105] After impregnation of the support component with the solution of metal precursors (active), the catalyst composition is dried, such as by heat treatment at elevated temperature (for example, 100-150 °C) for a period of time (for example, 1 to 3 hours) and then calcined to remove volatile components from the solution, depositing the metal on the surface of the molecular sieves and converting the metal into a more catalytically active oxide form. The concentration profile of the impregnated material depends on the mass transfer conditions within the pores during impregnation and drying.

[0106] The temperature during calcination of the catalyst composition is less than about 800 °C. In some embodiments, the calcination temperature ranges from about 300°C to about 700°C, about 300°C to about 500°C, about 350°C to about 500°C, about 400°C to about 500°C, or from about 425°C to about 475°C for a period of time. In some embodiments, the calcination temperature is less than about 700°C, about 600°C, about 500°C, about 450°C, about 400°C, or about 350°C, with a lower limit of 300°C. In some embodiments, the time period for calcination ranges from about 1 hour to about 16 hours, about 1 to about 10 hours, or from 3 hours to about 6 hours (i.e., less than about 16 hours, about 15 hours, about 14 hours, about 13 hours, about 12 hours, about 11 hours, about 10 hours, about 9 hours, about 8 hours, about 7 hours, about 6 hours, about 5 hours, about 4 hours, about 3 hours, about 2 hours, or about 1 hour with a lower limit of about 10 minutes).

[0107] To achieve the desired level of dopant being ion exchanged or impregnated, the above process can be repeated more than once. The resulting material can be stored as a dry powder or slurry.

[0108] The catalyst composition can be used in a catalyst article in which the catalyst composition can be provided on a catalyst substrate. According to one or more embodiments, the substrate for the SCR catalyst composition can be constructed of any material typically used to prepare automotive catalysts and will typically comprise a metal or ceramic honeycomb structure. The substrate typically provides a plurality of wall surfaces to which a substrate coating of the SCR catalyst composition is applied and adhered, thereby acting as a vehicle for the catalyst composition.

[0109] Exemplary metallic substrates include heat-resistant metals and metal alloys, such as titanium and stainless steel, as well as other alloys in which iron is a substantial or major component. These alloys may contain one or more of nickel, chromium and/or aluminum, and the total amount of these metals may advantageously comprise at least 15% by weight of the alloy, for example 10 to 25% by weight of chromium, 3 to 8% by weight of aluminum and up to 20% by weight of nickel. The alloys may also contain small amounts or trace amounts of one or more other metals, such as manganese, copper, vanadium, titanium and the like. Metal surface or carriers can be oxidized at high temperatures, for example 1000°C and above, to form an oxide layer on the surface of the substrate, improving the corrosion resistance of the alloy and facilitating the adhesion of the substrate coating layer to the metal surface.

[0110] The ceramic materials used to construct the substrate may include any suitable refractory material, for example, cordierite, mullite, α-cordierite alumina, silicon carbide, silicon nitride, aluminum titanate, zircon mullite, spodumene, magnesium alumina-silica, zircon silicate, sillimanite, magnesium silicates, zircon, petalite, α alumina, aluminosilicates and similar.

[0111] Any suitable substrate may be employed, such as a monolithic continuous flow substrate having a plurality of thin parallel gas flow passages extending from an inlet to an outlet face of the substrate such that the passages are open to fluid flow. The passages, which are essentially straight paths from the inlet to the exit, are defined by walls on which the catalytic material is coated like a substrate coating, so that gases flowing through the passages come into contact with the catalytic material. The flow passages of the monolithic substrate are thin-walled channels which may be of any suitable cross-sectional shape such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular and the like. Such structures may contain from about 9 to about 186 or more gas inlet openings (i.e., "cells") per square centimeter (60 to about 1200 or more gas inlet openings, i.e., "cells", per square inch of cross section (cpsi)), most usually from about 46 to 93 cells/cm2 (300 to 600 cpsi). The wall thickness of continuous flow substrates can vary, with a typical range being between 0.0508 and 2.54 mm (0.002 and 0.1 inches). A representative commercially available continuous flow substrate is a cordierite substrate having 62 cells/cm2 (400 cpsi) and a wall thickness of 6 mil or 93 cells/cm2 (600 cpsi) and a wall thickness of 4 mil. However, it will be understood that the invention is not limited to a specific substrate type, material or geometry.

[0112] In alternative embodiments, the substrate may be a flow barrier substrate, where each passageway is blocked at one end of the substrate body with a non-porous plug, with alternate passageways blocked at opposite end faces. This requires the gas to flow through the porous walls of the flow barrier substrate to reach the outlet. Such monolithic substrates can contain up to about 10 8 or more cells/cm2 (700 or more cpsi), such as about 15 to 62 cells/cm2 (100 to 400 cpsi), and more typically about 31 to about 47 cells/cm2 (200 to about 300 cpsi). The cross-sectional shape of the cells can be varied as described above. Flow barrier substrates typically have a wall thickness between 0.0508 and 2.54 mm (0.002 and 0.1 inches). A representative commercially available flux barrier substrate is constructed from a porous cordierite, an example of which has 31 cells/cm2 (200 cpsi) and 10 mil wall thickness or 46.5 cells/cm2 (300 cpsi) at 8 mil wall thickness and wall porosity between 45 and 65%. Other ceramic materials such as aluminum titanate, silicon carbide and silicon nitride are also used in flow barrier filter substrates. However, it will be understood that the invention is not limited to a particular substrate type, material or geometry. Note that when the substrate is a flow barrier substrate, the SCR catalyst composition can permeate the pore structure of the porous walls (i.e. partially or completely occlude the pore openings) in addition to being placed on the surface of the walls. Figures 1 and 2 illustrate an exemplary substrate (2) in the form of a flow-through substrate coated with a substrate coating composition as described herein. Referring to Figure 1, the exemplary substrate (2) has a cylindrical shape and a cylindrical outer surface (4), an upstream end face (6) and a corresponding downstream end face (8), which is identical to the end face (6). The substrate (2) has a plurality of thin parallel gas flow passages (10) formed therein. As seen in Figure 2, the flow passages (10) are formed by walls (12) and extend through the vehicle (2) from the upstream end face (6) to the downstream end face (8), the passages (10) being unobstructed to allow the flow of a fluid, e.g. a stream of gas, longitudinally through the vehicle (2) through gas flow passages (10) thereof. As most easily seen in Figure 2, the walls (12) are dimensioned and configured so that the gas flow passages (10) have a substantially regular polygonal shape. As shown, the substrate coating composition can be applied in multiple distinct layers, if desired. In the illustrated embodiment, the substrate coating consists of both a discrete bottom substrate coating layer (14) adhered to the walls (12) of the vehicle element, and a second discrete top substrate coating layer (16) coated over the bottom substrate coating layer (14). The present invention may be practiced with one or more (e.g., 2, 3, or 4) layers of substrate coating and is not limited to the illustrated two-layer embodiment.

[0113] Figure 3 illustrates an exemplary substrate (2) in the form of a flux barrier filter substrate coated with a substrate coating composition as described herein. As seen in Figure 3, the exemplary substrate (2) has a plurality of passageways (52). The passages are tubularly enclosed by the inner walls (53) of the filter substrate. The substrate has an inlet end (54) and an outlet end (56). Alternating passages are plugged at the inlet end with inlet plugs (58) and at the outlet end with outlet plugs (60) to form opposing checkerboard patterns at the inlet (54) and outlet (56). A gas stream (62) enters the uncapped channel inlet (64), is stopped by the outlet plug (60) and diffuses through the channel walls (53) (which are porous) to the outlet side (66). Gas cannot pass back to the inlet side of the walls due to the inlet plugs (58). The porous flow barrier filter used in this invention is catalyzed by the fact that the wall of said element has in it or contains in it one or more catalytic materials. The catalytic materials may be present on the inlet side of the element wall alone, on the outlet side alone, on both the inlet and outlet sides, or the wall itself may be filled with all or part of the catalytic material. This invention includes the use of one or more layers of catalytic material that are within the wall or on the inlet and/or outlet walls of the element.

[0114] For example, in one embodiment, a catalytic article comprises a catalytic material having multiple layers, each layer having a different catalyst composition. The bottom layer (e.g., layer (14) of Figure 2) may comprise an SCR catalyst composition as described herein, and the top layer (e.g., layer (16) of Figure 2) may comprise an additional catalyst composition. Alternatively, the top layer (16) can comprise an SCR catalyst composition and the bottom layer (14) can comprise an additional catalyst composition. It is understood from Figure 2 that the backsheet (14) and topsheet (16) may each extend fully from a front or leading edge of the substrate to a rear or trailing edge of the substrate.

[0115] In some embodiments, the additional catalyst composition may comprise a platinum group metal (PGM). In particular, palladium and/or rhodium can be used; however, other PGMs may also (or alternatively) be used. Furthermore, if desired, a specific PGM can be expressly excluded from the present invention. When present, a PGM can be present in a load of at least about 17 g/m3 (0.5 g/ft3), for example, with a maximum load of about 707 g/m3 (20 g/ft3). Therefore, when present, a PGM can be present in an amount of up to about 707 g/m3 (20 g/ft3). In certain embodiments, the total PGM loading can be from about 17 g/m3 (0.5 g/ft3) to about 707 g/m3 (20 g/ft3), about 35 g/m3 (1 g/ft3) to about 354 g/m3 (10 g/ft3), or about 70 g/m3 (2 g/ft3) to about 354 g/m3 (10 g/ft3) ). In certain embodiments, it may be desirable for a catalyst composition and/or catalyst article of the present invention to be substantially free of a PGM. To that end, a catalyst composition can be "substantially free" of a PGM if it includes less than 0.1% by weight of PGM or less than 0.01% by weight of PGM. Likewise, a catalyst article can be "substantially free" of PGM if it has a PGM loading of less than 3.54 g/m3 (0.1 g/ft3) or less than 0.36 g/m3 (0.01 g/ft3). Preferably, "substantially free" can mean only a trace amount present. In some embodiments, a catalyst composition or catalyst article can be completely free of PGM, if desired.

[0116] In further embodiments, another catalyst composition used in a multilayer catalytic coating can be an ammonia oxidation catalyst (AMOx). AMOx catalysts are taught, for example, in the publication U.S. At the. 2011/0271664, the disclosure of which is incorporated herein by reference. An ammonia oxidation catalyst (AMOx) can be a supported precious metal component that is effective for removing ammonia from an exhaust gas stream. Precious metal can include ruthenium, rhodium, iridium, palladium, platinum, silver or gold. For example, the precious metal component includes physical mixtures or combinations of chemically or atomically doped precious metals. The precious metal component, for example, includes platinum. The platinum can be present in an amount from about 0.008% to about 2% by weight based on the AMOx catalyst.

[0117] In some embodiments, the substrate may be coated with at least two layers contained in separate substrate coating slurries in an axially zoned configuration. For example, the same substrate can be coated with a one layer substrate coating slurry and a another layer substrate coating slurry, each layer being different. The two separate substrate coating compositions may include separate catalyst compositions and may be substantially non-overlapping. For example, referring to Figure 4, a first substrate coating zone (102) including a substrate coating of a first catalyst composition and a second substrate coating zone (103) including a substrate coating of a different second catalyst composition can be located side by side along the length of the substrate (100). The first substrate coating zone (102) of specific embodiments extends from the front or leading end (100a) of the substrate (100) across the range from about 5% to about 95%, from about 5% to about 75%, from about 5% to about 50%, or from about 10% to about 35% of the length of the substrate (100). The second substrate coating zone (103) extends from the trailing or trailing end (100b) of the substrate (100) from about 5% to about 95%, from about 5% to about 75%, from about 5% to about 50%, or from about 10% to about 35% of the total axial length of the substrate (100). The at least two-component catalyst compositions within a treatment system as described in the present invention can be zoned on the same substrate. The first substrate coating zone (102) may be an SCR catalyst composition as described herein, and therefore may be coated near the leading or leading end (100a) of the substrate (100). Therefore, the second substrate coating zone (103) may be formed by a different catalyst composition which is thus coated near the rear or outlet (100b) of the substrate (100). In another embodiment, the second substrate coating zone (103) may represent the SCR catalyst composition of the present invention, and the first substrate coating zone (102) may comprise the other, different catalyst composition.

[0118] In some embodiments, as seen in Figure 5, a substrate (100) may be coated with a first coating layer (106) that extends from the leading or front end (100a) of the substrate (100) to the trailing or trailing end (100b) of the substrate (100) and a second coating layer (107) that is coated over the first coating layer (106) near the leading or front end (100a) of the substrate (100) and extends through only a partial length of the substrate (100) (i.e., it ends before reaching the trailing or trailing end (100b) of the substrate (100)). In some embodiments, the first coating layer (106) may comprise the SCR catalyst composition and the second coating layer (107) may comprise an additional catalyst composition. In another embodiment, the second coating layer can comprise the SCR catalyst composition and the second coating layer can comprise the additional catalyst composition.

[0119] In some embodiments, as seen in Figure 6, a substrate (100) may be coated with a first coating layer (115) close to the trailing or trailing end (100b) of the substrate (100) and extending only partially along the length of the substrate (100) (i.e., ending before reaching the leading or leading end (100a) of the substrate (100)). The substrate (100) may be coated with a second coating layer (114). As seen in Figure 6, the second coating layer (114) extends from the leading or leading end (100a) of the substrate (100) to the trailing or trailing end (100b) of the substrate (100) (and therefore is completely coated over the first coating layer (115)). In some embodiments, the first coating layer (115) may comprise the SCR catalyst composition and the second coating layer (114) may comprise additional catalyst composition. In another embodiment, the second coating layer (114) may comprise the SCR catalyst composition and the first coating layer (115) may comprise the SCR catalyst composition. It is understood that the above embodiments given as examples and other combinations of catalytic coatings are included.

[0120] When describing the amount of substrate coating or catalyst metal components or other components of the composition, it is convenient to use units of component weight per unit volume of catalyst substrate. Therefore, the units, grams per cubic inch (“g/in3”) and grams per cubic foot (“g/ft3”), are used here to mean the weight of a component per volume of substrate, including the volume of substrate voids. Other weight-by-volume units, such as g/L, are also sometimes used. The total loading of the SCR catalyst composition on the catalyst substrate, such as a monolithic continuous flow substrate, is typically from about 0.006 to about 0.40 g/cm3 (0.1 to about 6 g/in3), and more typically from about 0.06 to about 0.31 g/cm3 (1 to about 5 g/in3). In some embodiments, the SCR catalyst composition can be present in a loading amount of up to about 707 g/m3 (20 g/ft3). Note that these weights per unit volume are typically calculated by weighing the catalyst substrate before and after treatment with the catalyst substrate coating composition and, as the treatment process involves drying and calcining the catalyst substrate at high temperature, these weights represent an essentially solvent-free catalyst coating, as essentially all of the water in the substrate coating slurry has been removed.

[0121] The aforementioned SCR catalyst composition (typically in powder or particulate form) is mixed with water to form a slurry for the purpose of coating a catalyst substrate such as a honeycomb substrate. In addition to the catalyst particles, the slurry may optionally contain a binder (such as alumina, silica and/or titania), zirconium acetate, water-soluble or water-dispersible stabilizers (for example, barium acetate), promoters (for example, lanthanum nitrate)), associative thickeners and/or surfactants (including anionic, cationic, nonionic or amphoteric surfactants) and/or other similar materials known to be useful in substrate coatings.

[0122] When present, the binder is typically used in an amount of from about 0.003 g/cm3 (0.05 g/in3) to about 0.06 g/cm3 (1 g/in3). When alumina is used as a binder, it can be, for example, boehmite, pseudo-boehmite, gamma-alumina, delta/theta alumina, silica-alumina, zirconia-alumina or combinations thereof.

[0123] The slurry can be milled to improve the mixing of the particles and the formation of a homogeneous material. Grinding can be carried out in a ball mill, continuous mill or other similar equipment, and the solids content of the slurry can be, for example, about 10 to 80% by weight, more particularly about 30 to 40% by weight. In one embodiment, the post-milling slurry is characterized by a D90 particle size of from about 5 to about 40 microns, preferably 5 to about 30 microns, more preferably from about 5 to about 10 microns. The D90 is defined as the particle size at which 90% of the particles have a finer particle size.

[0124] The slurry is then coated onto the catalyst substrate using an art-known substrate coating technique. In one embodiment, the catalyst substrate is dipped one or more times into the slurry or otherwise coated with the slurry. Thereafter, the coated substrate is dried at an elevated temperature (e.g., 100 to 150°C) for a period of time (e.g., about 10 minutes to about 3 hours) and then calcined by heating, e.g., less than 700°C, typically for about 10 minutes to about 8 hours.

[0125] The temperature during calcination of the coated catalyst substrate is less than about 700 °C. In some embodiments, the calcination temperature ranges from about 300°C to about 700°C, about 300°C to about 500°C, about 350°C to about 500°C, about 400°C to about 500°C, or from about 450°C to about 500°C for a period of time. In some embodiments, the calcination temperature is less than about 700°C, about 600°C, about 500°C, about 450°C, about 400°C, or about 350°C with a lower limit of 300°C. In some embodiments, the time period for calcination ranges from about 10 minutes to about 8 hours, about 1 to about 6 hours, or from 3 hours to about 6 hours (i.e., less than 8 hours, 7 hours, 6 hours, 5 hours, 4 hours, 3 hours, 2 hours, or 1 hour with a lower limit of about 10 minutes).

[0126] After drying and calcination, the final coating layer of the substrate coating can be seen as essentially solvent-free. After calcination, catalyst loading can be determined by calculating the difference in coated and uncoated substrate weights. As will be apparent to those skilled in the art, catalyst loading can be modified by altering the rheology of the slurry. Furthermore, the coating/drying/calcining process to generate a substrate coating can be repeated as needed to build the coating to the desired filler level or thickness, which means that more than one layer of substrate coating can be applied. For example, in some embodiments, the catalyst composition can be applied as a single layer or in multiple layers. In one embodiment, the catalyst is applied in a single layer (eg, only layer (14) of Figure 2). In another embodiment, the catalyst composition is applied in several layers (eg layers (14) and (16) of Figure 2). The catalyst composition described herein (e.g. a support comprising ceria (and, optionally, additional support materials) which is doped with niobia and, optionally, one or more additional dopants) can be provided as a bottom coat layer or a top coat layer in combination with a coat layer formed by a different catalyst composition.

[0127] In some embodiments, the calcined coated substrate is aged. Aging can be conducted under a variety of conditions and, as used herein, "aging" is understood to encompass a range of conditions (eg, temperature, time and atmosphere). Exemplary aging protocols involve subjecting the calcined coated substrate to a temperature of 650°C for about 50 hours at 10% steam, 750°C for about 5 hours at 10% steam, or a temperature of 800°C for about 16 hours at 10% steam. However, these protocols are not intended to be limiting and the temperature may be lower or higher (e.g., including but not limited to temperatures of 400°C and higher, e.g., 400°C to 900°C, 600°C to 900°C, or 650°C to 900°C); the time can be shorter or longer (for example, including, but not limited to, times from about 1 hour to about 50 hours or about 2 hours to about 25 hours); and the atmosphere can be modified (e.g., to have different amounts of vapor and/or other constituents present therein).

[0128] The present invention also provides an emissions treatment system that incorporates the SCR catalyst composition described herein. The SCR catalyst composition of the present invention is typically used in an integrated emissions treatment system comprising one or more additional components for treating exhaust emissions, for example exhaust emissions from a gasoline engine. For example, the emissions treatment system may comprise a TWC in a contiguous coupled configuration with a catalyst article comprising an SCR catalyst composition as described herein.

[0129] An example of an emissions treatment system is illustrated in Figure 7, which represents a schematic representation of an emissions treatment system (32). As shown, an exhaust stream containing gaseous pollutants is carried through the exhaust pipe (36) of an engine (34) to a TWC (38) and then in the pipe (40) to a selective catalytic reduction (SCR) component (42), which is coated with the substrate coating catalyst composition of the present invention. While there may be sufficient nitrogenous reducing agent in the exhaust exiting the TWC, in some embodiments, an injector (44) for introducing a nitrogenous reducing agent into the exhaust stream can be located upstream of the SCR catalyst component (42), if desired. The nitrogenous reducing agent introduced into the exhaust gas stream promotes the reduction of NOx to N2 and water as the gas is exposed to the catalyst composition. Examples of reductants include ammonia, hydrazine or any suitable ammonia precursor such as urea ((NH2)2CO), ammonium carbonate, ammonium carbamate, ammonium hydrogencarbonate or ammonium formate. In one embodiment, the nitrogenous reducing agent can be added using a reductant injector, which adds ammonia precursor to the exhaust gas stream upstream of the SCR component (46).

[0130] The present invention can be particularly beneficial, as it is possible to reduce ammonia emissions from an engine exhaust. While ammonia (or other nitrogenous reducing agent) is typically added to an SCR treatment system, the present invention benefits from the ability to provide SCR treatment of a gasoline engine or lean GDI engine without the need to add nitrogenous reducing agent. Thus, any residual ammonia in the exhaust can react substantially during the SCR catalytic reaction, and the total amount of ammonia (or other nitrogenous reducing agent), which would otherwise be depleted from the system, can be reduced or eliminated.

EXAMPLES

[0131] Aspects of the present invention are more fully illustrated by the following examples, which are presented to illustrate certain aspects of the present invention and are not to be construed as limiting the same.

EXAMPLE 1

[0132] Niobium (V) ammonium oxalate (ANO, 23.2% Nb2O5) was dissolved in deionized water. The ANO aqueous solution was impregnated onto a powder support by the incipient moisture technique to achieve the desired Nb2O5 loading (2%, 5%, 10% or 20% by weight). The powder support was formed by: ceria alone; aluminum oxide alone, zirconium oxide and lanthanum oxide mixed together; mixed zirconium oxide, cerium oxide, yttrium oxide and lanthanum oxide; or mixed cerium oxide and aluminum oxide. The wet impregnated powder was dried at 120 °C and calcined at 550 °C for 2 hours in air. Sample compositions (1A to 1J) are summarized in Table 1.TABLE 1

EXAMPLE 2

[0133] Example compositions 2A-2L were prepared by doping a second basic metal oxide (in an amount of 5% by weight) over the composition of Example 1A by the incipient moisture impregnation technique. The precursors used for the formation of the other base metal oxide dopants were the following: La2O3: La(NO3)3 aq.; Pr6O11: aq. Pr(NO3)3; Nd2O3: aq. Nd(NO3)3; Y2O3: aq. Y(NO3)3; TiO2: Ti(OC2H5)4; W2O5: (NH4)6H2Wi2θ4o^xH2θ; Fe2O3: Fe(NOs)3-xH2O; CuO:Cu(NO3>2.5H2O; MnO2: Mn(NO3)2-6H2O; NiO: Ni(NO3)2-6H2O; MgO: Mg(NO3)2; BaO: Ba(OAc)2. These precursors were dissolved in deionized water for moisture impregnation, except for 2E, where ethanol was used as solvent for the precursor Ti(OC2H5)4. The wet impregnated powder was dried at 120 °C and calcined at 550 °C for 2 hours in air The sample compositions are summarized in Table 2.TABLE 2

EXAMPLE 3

[0134] The Nb2O5-doped powders prepared in Example 1 and Example 2 were individually dispersed in deionized water to give a solid percentage of approximately 30%. The slurry was milled and then dried while stirring. The dried paste was calcined at 700°C for 2 hours. The resulting powder was ground and sieved to collect 250-500 µm size particles for testing in a high throughput reactor.

[0135] Aging was carried out at 850 °C for 5 hours under lean/rich cyclic conditions in the presence of 10% steam. The lean/rich aging cycle included 5 minutes of air, 5 minutes of N2, 5 minutes of 4% H2 balanced with N2, and 5 minutes of N2. This cycle was repeated until the desired aging duration was reached.

[0136] The catalytic performance was evaluated in a high-efficiency reactor at À = 1.00 +/- 0.05 with an oscillating feed of one second of lean gas and one second of rich gas. Lean gas at λ = 1.05: 0.7% CO, 0.22% H2, 1.8% O2, 1500 ppm C1 C3H6, 750 ppm C1 C3H8, 750 ppm C1 iso-C10H22, 750 ppm NO, 750 ppm NH3, 14% CO2, 10% H2O and N2 balance. Gas rich in λ = 0.95: 2.0% CO, 0.7% H2, 0.71% O2, 1500 ppm C1 C3H6, 750 ppm C1 C3H8, 750 ppm C1 iso-C10H22, 750 ppm NO, 750 ppm NH3, 14% CO2, 10% H2O and N2 balance. The sample amount is 100 mg for each coating at a flow rate of 70 L/h. Activities were measured at constant temperatures from 250 to 550 °C at 25 °C intervals. The results are shown in Table 3. TABLE 3

[0137] Under the powder test conditions, 5% Nb2O5/CeO2 (Example 1A) provided 30.5-54.4% NOx conversions at 350-550 °C. In comparison, Y-alumina (Example 1B), lanthania-stabilized zirconia (Example 1C), and ceria-zirconia (Example 1D), as supports for 5% Nb2O5, exhibited poor NOx performance. Mixed ceria-alumina composites (Examples 1E-G), especially with a ceria content greater than or equal to 50%, provided better NOx activities compared to 5% Nb2O5/CeO2. For example, Example 1G gave NOx conversions of 65.6% and 43.3% at 450 °C and 550 °C, respectively. The performance improvement is presumably attributable to the stabilizing effect of the alumina on the ceria, which can make the ceria component more resistant to aging at high temperatures. The 2-20% Nb2O5/CeO2 composites (Examples 1A, 1H-J) were all active in reducing NOx, with a preferred Nb2O5 loading of 5-10%. Second base metal oxide dopants (Examples 2A-L) were selected with a loading of 5% by weight. In general, lanthanide oxides, eg La2O3, Pr6O11, Nd2O3 and Y2O3, are compatible with the 5% Nb2O5/CeO2 composite. The materials doped with Nd2O3 and Y2O3 actually provided better NOx conversions at 350-450 °C. Fe2O3, CuO, MnO2 and NiO dopants (Example 2G-2J) provided lower NOx conversions because these transition metal oxides had ammonia non-selective oxidative activity. The alkaline earth metal oxides, such as MgO and BaO (Examples 2K and 2L), were detrimental to SCR activity.

EXAMPLE 4

[0138] A conventional TWC catalyst with a three-layer substrate coating architecture was prepared in accordance with Example 1 of U.S. Pat. At the. 7,758,834, which is incorporated herein by reference. In particular, the first layer was formed from 10% barium stabilized gamma alumina, lanthanum oxide, strontium oxide, zirconium oxide, neodymium oxide, a composite of cerium and zirconium oxide with approximately 30% ceria and palladium content in concentrations of 64%, 6.4%, 6.4%, 2.6%, 6.4%, 12.8% and 1.1%, respectively, based on the calcined weight of the catalyst. Palladium (2.47.103 g/m3 or 70 g/ft3) in the form of palladium nitrate solutions was impregnated by the planetary mixer (P-blender) onto the stabilized alumina to form a wet powder while obtaining incipient moisture. The other components, such as promoters and stabilizers, were introduced as their soluble salts using water as the slurry vehicle. The aqueous slurry was formed by combining all of the above components and milled to a particle size of 90% less than 9 microns and coated onto the cordierite vehicle. After coating, the vehicle plus the first layer were calcined at a temperature of 550 °C for at least 2 hours. The second layer was formed by 26.1% by weight of stabilized gamma alumina, 0.7% by weight of a mixture of zirconium oxide and alumina oxide as binders, 69.3% by weight of a composite of cerium and zirconium oxide with approximately 30% ceria content and 0.9% by weight of rhodium, based on the calcined weight of the catalyst. The catalyst was prepared by impregnating rhodium (4.94,102 g/m3 or 14 g/ft3) in the form of rhodium nitrate by P-blender on stabilized alumina and cerium zirconium composite separately with a ratio distribution of 30/70. The rhodium-alumina and rhodium-ceria-zirconia powders were each added to a basic solution containing monoethanolamine (MEA) about three times the weight of rhodium and mixed for 10 minutes. Zirconium hydroxide was added at 0.7% by weight of the total solid into the rhodium-alumina-containing slurry. Each slurry was then acidified to bring a pH range of about 4 to 5 for milling. The aqueous slurry was individually milled to a particle size of 90% less than 9 microns before blending. The resulting slurry with a solids content of about 28% can be briefly re-milled or homogenized to ensure the particle size is 90% less than 9 microns. After that, it was coated on the first layer. The resulting vehicle plus the first layer and second layer were calcined at 450 °C for not less than 2 hours. After cooling, the third layer was coated onto the second layer. The third layer was formed from gamma-alumina doped with 10% baria-10% lanthania-7% neodymium, strontium, mixed cerium-zirconium oxide, zirconia and palladium at concentrations of 65.6%, 6.7%, 24.6, 0.8% and 2.4%, based on the final calcined weight of the third layer. The aqueous paste containing palladium (4,10,103 g/m3 or 116 g/ft3) was produced in the same way as the paste for the first layer. The aqueous slurry was milled to a particle size of less than 9 microns and coated onto the second layer. After coating, the vehicle plus the first layer and the second layer were calcined at a temperature of 550 °C for 2 hours.

[0139] The catalyst prepared as described above was coated onto a 4.66”x 2.87” cylinder cordierite monolith substrate with a cell density of 93 cells/cm2 (600 cpsi) and a wall thickness of 3.5 mil (about 100 μm). The total PGM loading was 7.06.103 g/m3 (200 g/ft3) with a Pd/Rh ratio of 186/14.

EXAMPLE 5

[0140] A catalyst article was prepared using an SCR catalyst composition comprising 5% Nb2O5/CeO2. The substrate coating was formed from 73.5% by weight of the composition of Example 1A (5% Nb2Oδ/CeO2), 24.5% by weight of a Y-Al2O3 stabilized with 4% La2O3 and 2% by weight of a boehmite binder, based on the calcined weight of the catalyst article. The slurry was milled to reduce average particle size and then coated onto 4.66" x 2.87" cylinder cordierite monolith substrates with a cell density of 93 cells/cm2 (600 cpsi) and a wall thickness of 3.5 mil to achieve the target substrate coating load of 1.50.10-1 g/cm3 (2.45 g/in3). The coated catalysts were quickly dried in a continuous flow dryer at 200°C and calcined at 550°C for 2 hours.

EXAMPLE 6

[0141] A catalyst article was prepared using an SCR catalyst composition comprising 5% Nb2O5 / 70% CeO2 - 30% Al2O3. The substrate coating was formed from 98% by weight of the composition of Example 1E (5% Nb2O5/70% CeO2-30% Al2O3) and 2% by weight of a boehmite binder, based on the calcined weight of the catalyst. The slurry was milled to reduce average particle size and then coated onto 4.66" x 2.87" cylinder cordierite monolith substrates with a cell density of 93 cells/cm2 (600 cpsi) and a wall thickness of 3.5 mil to achieve the target substrate coating load of 1.50.10-1 g/cm3 (2.45 g/in3). The coated catalysts were quickly dried in a continuous flow dryer at 200°C and calcined at 550°C for 2 hours.

EXAMPLE 7

[0142] A catalyst article was prepared using a PGM-free catalyst comprising a two-layer substrate coating architecture. The bottom layer, with a substrate coating load of 7.63.10-2 g/cm3 (1.25 g/in3), contained Fe2O3 in the form of Fe(NO3^xH2O and a composite of CeO2 and Al2O3 (50% CeO2-50% Al2O3) at concentrations of 5% and 95%, respectively, based on the calcined weight of the catalyst. The top layer, with a substrate coating load of 1 ,50.10 -1 g/cm3 (2.45 g/in3), contained 73.5% by weight of the catalyst composition of Example 1A (5% Nb2O5/CeO2), 24.5% by weight of a Y-Al2O3 stabilized with 4% La2O3, and 2% by weight of a boehmite binder, based on the calcined weight of the catalyst. The slurries were milled to reduce average particle size and then coated onto 4.66” x 2.87” cylinder cordierite monolith substrates having a cell density of 93 cells/cm2 (600 cpsi) and a wall thickness of 3.5 mil, to achieve the target loading of the substrate coating.

EXAMPLE 8 - COMPARATIVE

[0143] A catalyst article was prepared using a downstream SCR catalyst based on Cu-CHA for passive reactions of NH3-SCR. The substrate coating was formed from 95% by weight Cu-SSZ-13 (2.4% CuO) and 5% by weight ZrO2 as an aqueous solution of ZrO(OAc)2, based on the calcined weight of the catalyst. The slurry was milled to reduce average particle size and then coated onto 4.66" x 2.87" cylinder cordierite monolith substrates with a cell density of 93 cells/cm2 (600 cpsi) and a wall thickness of 3.5 mil to achieve the target substrate coating load of 1.67.10-1 g/cm3 (2.73 g/in3). The coated catalysts were quickly dried in a continuous flow dryer at 200°C and calcined at 550°C for 2 hours.

EXAMPLE 9

[0144] A catalyst article was prepared using an ultra-low PGM catalyst comprising a two-layer substrate coating architecture. The bottom layer, with a substrate coating load of 9.95 x 10-2 g/cm3 (1.63 g/in3), was formed from 73.5% by weight of the catalyst composition of Example 1A (5% Nb2O5/CeO2), 24.5% by weight of a Y-Al2O3 stabilized with 4% La2O3, and 2% by weight of a boehmite binder, based on calcined weight of the catalyst. The top layer, with a substrate coating load of 1,31.10 -1 g/cm3 (2.15 g/in3), was formed from 0.054% by weight of Rh in the form of an aqueous solution of Rh(NO3)3, 37.2% by weight of a Y-Al2O3 stabilized with 4% La2O3, 30.2% by weight of a composite of CeO2 and ZrO2 (with a content of 40% of CeO2), 30.2% by weight of ZrO2 stabilized with 10% La2O3, and 2.3% by weight of a boehmite binder, based on the calcined weight of the catalyst. The slurries were milled to reduce average particle size and then coated onto 4.66" x 2.87" cylinder cordierite monolith substrates having a cell density of 93 cells/cm2 (600 cpsi) and a wall thickness of 3.5 mil to achieve the target loading of the substrate coating. The coated catalysts were quickly dried in a continuous flow dryer at 200°C and calcined at 550°C for 2 hours.

EXAMPLE 10 - COMPARATIVE

[0145] A catalyst article was prepared using an ultra-low PGM catalyst comprising a two-layer substrate coating architecture. The bottom layer was exclusively Y-Al 2 O 3 with a substrate coating load of 9.95 × 10 -2 g/cm 3 (1.63 g/in 3 ). The top layer, with a substrate coating load of 1,31.10-1 g/cm3 (2.15 g/in3), contained 0.054 wt% Rh in the form of an aqueous solution of Rh(NO3)3, 37.2 wt% of a y-Al2O3 stabilized with 4% La2O3, 30.2 wt% of a composite of CeO2 and ZrO2 (with a content of 40% Ce O2), 30.2% by weight of ZrO2 stabilized with 10% La2O3, and 2.3% by weight of a boehmite binder, based on the calcined weight of the catalyst. The slurries were milled to reduce average particle size and then coated onto 4.66" x 2.87" cylinder cordierite monolith substrates having a cell density of 93 cells/cm2 (600 cpsi) and a wall thickness of 3.5 mil to achieve the target loading of the substrate coating. The coated catalysts were quickly dried in a continuous flow dryer at 200°C and calcined at 550°C for 2 hours.

EXAMPLE 11

[0146] The monolithic catalysts prepared in Examples 4 to 10 were mounted individually in steel converter cans and aged in a gasoline engine exhaust line under fuel-cut aging cycles to simulate a contiguous coupled system with an upstream TWC catalyst (Example 4) and downstream SCR catalysts (Examples 5 to 10). The upstream TWC catalyst (Example 4) was aged at a maximum bed temperature of 950 °C for 50 hours. The downstream catalysts (Examples 5-10) were aged at a maximum bed temperature of 920 °C for 50 hours. Aged catalysts were tested in a PZEV vehicle equipped with a 1.8 L gasoline engine, operating US FTP-75 driving cycles following certified procedures. All emission control systems contained Example 4 in a first contiguous coupling position (CC1) as the upstream TWC universal catalyst and one of the remaining catalysts (Examples 5-10) in a second contiguous coupling position (CC2). The total amounts of nitrogen oxides, hydrocarbons and carbon monoxide in the tailpipe were measured by collecting three bags and weighted averages were calculated. Table 4 provides the tailpipe emissions of NOx, NMHC and CO from the catalyst systems in the FTP-75 tests.TABLE 4

[0147] Compared to System D containing the SCR downstream catalyst based on Cu-CHA (Comparative Example 8), Systems AC containing the downstream SCR catalysts based on Nb2O3 (Examples 5-7) provided at least 22 mg/mile less NOx in the tailpipe. The main reason is that Cu-CHA, as a component of zeolite-based SCR, is not stable to the aging of TWC at a temperature higher than 900°C. Improvements were also observed in NMHC and CO, especially in System C with Example 7, which comprised an additional layer of Fe2O3-based substrate coating for oxidation activities. System E used Example 9 as the downstream catalyst, which contained an upper layer of TWC with a relatively low level of PGM, in addition to a lower layer of Nb2O3-based SCR. System E delivered 15 mg/mile of NOx, 23 mg/mile of NMHC and 104 mg/mile of CO in the tailpipe. System F used Comparative Example 10 as the downstream catalyst, which contained the same top layer of TWC with the same relatively low level of PGM and a bottom layer of Nb2O3 free alumina. System F delivered 20 mg/mile of NOx in the tailpipe, which represents 33% more NOx emissions compared to System E. These findings indicate that the disclosed Nb2O3-based SCR composites can be formulated in conjunction with PGM-based components for improved NOx conversion.

[0148] Various modifications and other embodiments of the subject matter disclosed herein will be reminiscent of one skilled in the art to which this subject matter belongs, having the benefit of the teachings presented in the foregoing descriptions and associated drawings. Therefore, it is to be understood that the present invention is not to be limited to the specific embodiments described herein and that modifications and other embodiments are to be included within the scope of the appended claims. Although specific terms are used here, they are used in a generic and descriptive sense only and are not intended to be limiting.

Claims (15)

1. SCR CATALYST COMPOSITION, characterized in that it comprises a ceria support including a first dopant that is niobium and an optional second dopant that is a basic metal oxide (BMO), wherein the ceria support comprises 20% to 80% by weight of ceria and 20% to 80% by weight of an additional metal oxide, wherein the additional metal oxide is aluminum oxide. 2. COMPOSITION, according to claim 1, characterized in that BMO is selected from the group consisting of lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide, titanium dioxide, tungsten oxide, iron oxide, copper oxide, manganese oxide, nickel oxide, magnesium oxide, barium oxide and combinations thereof. 3. COMPOSITION according to any one of claims 1 to 2, characterized in that niobia comprises 0.1 to 20% by weight of the SCR catalyst composition. COMPOSITION according to any one of claims 1 to 2, characterized in that the second dopant comprises 0.1 to 20% by weight of the SCR catalyst composition. 5. COMPOSITION according to Claim 1, characterized in that the ceria support comprises at least 99% by weight of ceria. 6. CATALYST ARTICLE, characterized in that it comprises a catalyst substrate (2) having a plurality of channels adapted for gas flow (10), each channel having a wall surface (12) in adherence to a catalytic coating comprising a catalyst composition, as defined in any one of claims 1 to 5. 7. ARTICLE according to claim 6, characterized in that the catalyst substrate (2) is a well comprising a flow barrier filter substrate or a continuous flow substrate. 8. ARTICLE according to claim 6, characterized in that the catalytic coating is present on the substrate (2) with a charge of at least 0.06 g/cm3 (1.0 g/in3). 9. ARTICLE, according to claim 6, characterized in that it also comprises a platinum group metal (PGM). 10. EMISSIONS TREATMENT SYSTEM (32), for treating an exhaust gas stream, characterized in that the emissions treatment system (32) comprises: i) an engine (34) that produces an exhaust gas stream; ii) a three-way catalytic converter (38) positioned downstream of the engine (34) and in fluid communication with the exhaust stream; and iii) an SCR catalyst article (42) positioned downstream of the three-way catalyst (38) and in fluid communication with the exhaust stream, the SCR catalyst article (42) comprising a catalyst substrate (2) having a plurality of channels adapted for gas flow (10), each channel having a wall surface (12) in adherence to a catalytic coating comprising the catalyst composition as defined in any one of claims 1 to 5. 11. SYSTEM (32) according to claim 10, characterized in that the SCR catalyst article (42) is free of platinum group metal (PGM). SYSTEM (32) according to claim 10, characterized in that the SCR catalyst article (42) includes a platinum group metal (PGM), wherein the PGM is present in the catalyst substrate (2) with a loading of at least 17 g/m3 (0.5 g/ft3). 13. SYSTEM (32) according to any one of claims 10 to 12, characterized in that the catalytic coating of the SCR catalyst article (42) comprises an additional dopant which is a basic metal oxide (BMO). 14. SYSTEM (32) according to any one of claims 10 to 13, characterized in that the catalytic coating comprising the niobium-doped ceria support is on a first coating layer (106) and wherein the catalyst substrate (2) of the SCR catalyst article (42) includes a second catalytic coating layer (107), wherein the second catalytic coating layer (107) comprises a basic metal oxide (BMO). 15. SYSTEM (32) according to claim 14, characterized in that the second catalytic coating layer (107) comprises a platinum group metal (PGM).