Exhaust gas treatment catalyst

Abstract

A catalyst composition suitable for use as a selective catalytic reduction catalyst is described comprising small pore molecular sieve particles having a pore structure and a maximum ring size of 8 tetrahedral atoms and impregnated with a promoter metal, and metal oxide particles dispersed within the small pore molecular sieve particles and outside the pore structure of the small pore molecular sieve particles, wherein the metal oxide particles comprise one or more oxides of a transition metal of Group 3 or Group 4 of the Periodic Table or a lanthanide series element. Also described are methods of making the catalyst, methods of selectively reducing nitrogen oxides, and exhaust gas treatment systems.

Description

TECHNICAL FIELD

[0001] The present invention relates to exhaust gas purification catalysts, methods of making the catalysts, and methods of using the catalysts. More particularly, the present invention relates to selective catalytic reduction catalysts comprising small pore molecular sieves containing a promoter metal.

[0002] BACKGROUND

[0003] Nitrogen oxides (NOx x ) have long been a source of atmospheric pollution. NOx x is contained in exhaust gases from, for example, internal combustion engines (e.g., automobiles and trucks), from combustion facilities (e.g., power plants heated by natural gas, oil, or coal), and from nitric acid production plants.

[0004] Various methods have been used to treat gas mixtures containing NOx x . One type of treatment involves the catalytic reduction of nitrogen oxides. There are two approaches: (1) non-selective reduction, in which carbon monoxide, hydrogen, or a lower hydrocarbon is used as the reducing agent, and (2) selective reduction, in which ammonia or an ammonia precursor is used as the reducing agent. In the selective reduction approach, high removal of nitrogen oxides can be achieved with a small amount of reducing agent.

[0005] The selective reduction approach is known as the SCR process (selective catalytic reduction). The SCR process catalytically reduces nitrogen oxides with ammonia in the presence of atmospheric oxygen to form primarily nitrogen and water vapor:

[0006] 4 NO + 4 NH3+ O2→ 4 N2+ 6 H2O (standard SCR reaction)

[0007] 2 NO2+ 4 NH3→ 3 N2+ 6 H2O (slow SCR reaction)

[0008] NO + NO2+ NH3→ 2 N2+ 3 H2O (fast SCR reaction)

[0009] The catalyst used in the SCR process should ideally be able to maintain good catalytic activity under hydrothermal conditions over a wide range of use temperature conditions, e.g., 200°C to 600°C or higher. Hydrothermal conditions are often encountered in practice, such as during the regeneration of a diesel particulate filter (a component of an exhaust treatment system used to remove particulates).

[0010] Molecular sieves such as zeolites have been used to selectively catalyze the reduction (SCR) of nitrogen oxides with a reductant such as ammonia, urea or a hydrocarbon in the presence of oxygen. Zeolites are crystalline materials having a fairly uniform pore size, on the order of 3 to 10 Angstroms in diameter, depending on the type of zeolite and the type and amount of cations contained in the zeolite lattice. Zeolites having 8-ring pore openings and double-six ring secondary building units, particularly those having cage-like structures, have recently been found to be useful as SCR catalysts. One particular type of zeolite having these properties is chabazite (CHA), which is a small pore zeolite having 8-membered ring pore openings (~3.8 Angstroms) accessible through its three-dimensional pores. The cage-like structure comes from connecting double-six ring building units by 4-rings.

[0011] Metal-promoted zeolite catalysts for the selective catalytic reduction of nitrogen oxides with ammonia are known, including iron-promoted and copper-promoted zeolite catalysts in particular. Iron-promoted zeolite beta has been an effective commercial catalyst for the selective reduction of nitrogen oxides with ammonia. Unfortunately, the activity of many metal-promoted zeolites has been found to begin to decline under severe hydrothermal conditions exhibited during the regeneration of a filter of a diesel particulate filter, for example, at temperatures locally exceeding 700°C. This decline is generally attributed to dealumination of the zeolite and consequent loss of metal-containing active sites within the zeolite.

[0012] Metal-promoted, particularly copper-promoted, aluminosilicate zeolites having the CHA structure type have recently attracted great interest as catalysts for the SCR of nitrogen oxides with nitrogen-containing reductants in lean-burn engines. This is because these materials combine a wide temperature window with excellent hydrothermal durability, as described in U.S. Patent No. 7,601,662. Prior to the discovery of the metal-promoted zeolites described in U.S. Patent No. 7,601,662, although the literature has suggested that many metal-promoted zeolites have been proposed for use as SCR catalysts in the patent and scientific literature, each of the proposed materials suffered from one or both of the following deficiencies: (1) poor conversion of nitrogen oxides at low temperatures, e.g., 350°C and lower temperatures; and (2) poor hydrothermal stability, manifested as a significant decline in catalytic activity in the conversion of nitrogen oxides by SCR. Thus, the invention described in U.S. Patent No. 7,601,662 addresses the pressing, unsolved need to provide a material that achieves both nitrogen oxides conversion at low temperatures and retention of SCR catalytic activity after hydrothermal aging at temperatures exceeding 650°C.

[0013] Although existing catalysts exhibit excellent properties, there remains a need to reduce N2O production during the SCR reaction. Accordingly, there is a need for catalysts having improved NO x conversion efficiency and lower N2O production compared to the prior art.

[0014] SUMMARY

[0015] The present invention relates to a catalyst composition suitable for use as a selective catalytic reduction catalyst comprising an intimate mixture of small pore molecular sieve particles having a pore structure and a maximum ring size of 8 tetrahedral atoms and impregnated with a promoter metal and metal oxide particles comprising one or more oxides of a transition metal of Group 3 or Group 4 of the Periodic Table or a lanthanide series element. It has been found that certain embodiments of the catalyst composition comprising molecular sieve particles having metal oxide particles dispersed therein (but with the metal oxide particles outside the pore structure of the small pore molecular sieve particles) can provide enhanced NO x reduction at low and / or high temperatures as compared to conventional metal promoted molecular sieves that do not contain metal oxide particles or that contain only metal oxides derived from a minimum amount of certain binder materials. The metal oxide is typically present in an amount of about 1 to about 15 weight percent (as oxide) based on the total washcoat layer weight.

[0016] The metal oxide particles typically comprise a metal oxide selected from zirconium oxide, aluminum oxide, cerium dioxide, hafnium dioxide, yttrium oxide, and combinations thereof. In certain embodiments, the metal oxide particles have an average particle size in the range of about 10 nm to about 500 nm and / or a D 10 particle size that is greater than 10 times the pore opening of the molecular sieve. In one embodiment, the metal oxide particles have a D 10 particle size.

[0017] The catalyst composition can include a small pore molecular sieve having d6r units. Exemplary small pore molecular sieves have a structure type selected from AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, LTN, MSO, SAS, SAT, SAV, SFW, and TSC. In one embodiment, the molecular sieve size is SSZ-13.

[0018] The catalyst composition typically includes a promoter metal selected from Cu, Co, Ni, La, Mn, Fe, V, Ag, Ce, Nd, Pr, Ti, Cr, Zn, Zn, Nb, Mo, Hf, Y, W, and combinations thereof. In exemplary embodiments, the promoter metal comprises Cu or Fe or combinations thereof. Typical amounts of the promoter metal are about 1 to about 10 weight percent, such as about 2 to about 5 weight percent, based on the total weight of the molecular sieve.

[0019] In another aspect, the application provides a catalyst article comprising a substrate selected from a flow-through monolith, a wall-flow filter, a foam, or a web, with a catalyst composition according to any embodiment of the present disclosure attached as a washcoat on the substrate. In certain embodiments, the catalyst article of the present application is characterized by at least 10 wt% lower (or at least 15% lower or at least 20% lower or more) N20 production than a catalyst article comprising the same catalyst composition with the same loading but without a washcoat containing metal oxide particles dispersed within the small pore molecular sieve particles.

[0020] In yet another aspect, the application provides a method for selectively reducing nitrogen oxides (NOx) x ) by contacting an exhaust gas stream containing NO x with a catalyst composition or catalyst article according to any embodiment of the present disclosure. In certain embodiments, the amount of N20 produced as a byproduct in the method of the present application is reduced compared to methods carried out with certain conventional catalyst compositions and catalyst articles. For example, in one embodiment, the amount of N20 produced as a byproduct in the method of the present application is reduced compared to the amount of N20 produced in a method using a catalyst article comprising the same catalyst composition with the same loading but without a washcoat containing metal oxide particles dispersed within the small pore molecular sieve particles.

[0021] In yet another aspect, the application provides an exhaust gas treatment system comprising a catalyst composition or catalyst article according to any embodiment of the present disclosure downstream of an engine (e.g., a diesel engine or other lean-burn engine) and an injector that adds reductant to the exhaust stream.

[0022] The application also provides a method of making a catalyst composition, the method comprising:

[0023] dissolving a salt of at least one promoter metal in an aqueous metal oxide sol, wherein the salt of the at least one promoter metal dissociates in the aqueous metal oxide sol to form an aqueous metal salt / metal oxide sol mixture, wherein the metal oxide particles comprise one or more oxides of a transition metal of Group 3 or Group 4 of the Periodic Table or a lanthanide series element;

[0024] treating ammonium- or proton-exchanged small pore molecular sieve particles having a pore structure with a maximum ring size of 8 tetrahedral atoms with the aqueous metal salt / metal oxide sol mixture to impregnate the promoter metal into the pore structure of the small pore molecular sieve; and

[0025] drying and calcining the treated small-pore molecular sieve particles to form a catalyst composition, wherein the catalyst composition comprises small-pore molecular sieve particles impregnated with a promoter metal, and metal oxide particles dispersed within and outside the pore structure of the small-pore molecular sieve particles. The promoter metal and the molecular sieve can be selected as described in any of the embodiments herein.

[0026] The metal oxide sol can include any of the metal oxides noted above for the catalyst composition and can exhibit the same particle size properties described above. In certain embodiments, the metal oxide sol is selected from the group consisting of zirconyl hydroxide sol, nanoscale hydrated zirconia sol, alumina sol (e.g., macrocrystalline, thermally stable boehmite sol), zirconia-yttria sol, zirconia-alumina sol, zirconia-ceria sol, organozirconium sol, and mixtures thereof. Advantageously, the metal oxide particles do not enter the pore structure of the small-pore molecular sieve during the preparation process (i.e., the metal oxide particles are size-excluded outside the pore structure of the molecular sieve).

[0027] The method can further include the steps of mixing the catalyst composition with water to form a washcoat slurry; applying the washcoat slurry to a substrate to form a washcoat layer thereon; and drying and calcining the substrate to form a catalytic article. In certain embodiments, the method includes adding a water-soluble metal oxide compound (e.g., a zirconium compound) to the washcoat slurry to increase its total metal oxide content.

[0028] The present disclosure includes, but is not limited to, the following embodiments.

[0029] Embodiment 1 : A catalyst composition suitable for use as a selective catalytic reduction catalyst, comprising: small-pore molecular sieve particles having a pore structure and a maximum ring size of 8 tetrahedral atoms and impregnated with a promoter metal, and metal oxide particles dispersed within and outside the pore structure of the small-pore molecular sieve particles, wherein the metal oxide particles comprise one or more oxides of a transition metal of Group 3 or Group 4 of the Periodic Table or a lanthanide series element.

[0030] Embodiment 2: The catalyst composition of any preceding or following embodiment, wherein the metal oxide particles comprise a metal oxide selected from the group consisting of zirconium oxide, aluminum oxide, cerium dioxide, hafnium dioxide, yttrium oxide, and combinations thereof.

[0031] Embodiment 3: The catalyst composition of any preceding or following embodiment, wherein the metal oxide particles comprise zirconium oxide.

[0032] Embodiment 4: The catalyst composition of any preceding or following embodiment, wherein the metal oxide particles have an average particle size of from about 10 nm to about 500 nm.

[0033] Embodiment 5: The catalyst composition of any preceding or following embodiment, wherein the metal oxide particles have a D 10 particle size.

[0034] Embodiment 6: The catalyst composition of any preceding or following embodiment, wherein the metal oxide particles have a D 10 particle size.

[0035] Embodiment 7: The catalyst composition of any preceding or following embodiment, wherein the small pore molecular sieve has d6r units.

[0036] Embodiment 8: The catalyst composition of any preceding or following embodiment, wherein the small pore molecular sieve has a structure type selected from the group consisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, LTN, MSO, SAS, SAT, SAV, SFW, and TSC.

[0037] Embodiment 9: The catalyst composition of any preceding or following embodiment, wherein the promoter metal is selected from the group consisting of Cu, Co, Ni, La, Mn, Fe, V, Ag, Ce, Nd, Pr, Ti, Cr, Zn, Zn, Nb, Mo, Hf, Y, W, and combinations thereof.

[0038] Embodiment 10: The catalyst composition of any preceding or following embodiment, wherein the small pore molecular sieve has a CHA structure type.

[0039] Embodiment 11: The catalyst composition of any preceding or following embodiment, wherein the promoter metal comprises Cu or Fe or combinations thereof.

[0040] Embodiment 12: The catalyst composition of any preceding or following embodiment, wherein the promoter metal is present in an amount of about 1 to about 10 wt% based on the total weight of the molecular sieve.

[0041] Embodiment 13: The catalyst composition of any preceding or following embodiment, wherein the promoter metal is present in an amount of about 2 to about 5 wt% based on the total weight of the molecular sieve.

[0042] Embodiment 14: The catalyst composition of any preceding or following embodiment, wherein the metal oxide is present in an amount of about 1 to about 15 wt% based on the total weight of the washcoat as an oxide.

[0043] Embodiment 15: A catalyst article comprising a substrate selected from flow-through bulk material, wall-flow filter, foam or mesh, wherein a catalyst composition according to any of the foregoing or the following embodiments is attached to the substrate as a wash-out coating.

[0044] Implementation Scheme 16: A catalyst article of any of the foregoing or the following embodiments, wherein the wash coating is disposed on a flow-through feed or wall-flow filter.

[0045] Implementation Scheme 17: A catalyst article of any of the foregoing or the following embodiments, wherein the catalyst article is characterized in that the N2O yield is at least 10 weight lower than that of a catalyst article containing the same catalyst composition having the same loading but without a wash coating of metal oxide particles dispersed within the microporous molecular sieve particles.

[0046] Implementation Scheme 18: A selective reduction method for nitrogen oxides (NOx) x The method includes making a substance containing NO... x The exhaust gas stream comes into contact with the catalyst product of any of the aforementioned or described embodiments.

[0047] Implementation Scheme 19: The method of any of the foregoing or the following embodiments, wherein the amount of N2O generated as a byproduct is reduced compared to the amount of N2O generated in a method using a catalyst article comprising the same catalyst composition having the same loading but without a wash coating of metal oxide particles dispersed within the microporous molecular sieve particles.

[0048] Implementation Scheme 20: An exhaust treatment system comprising a catalyst article of any of the foregoing or hereinafter embodiments downstream of an engine and an injector for adding a reducing agent to the exhaust stream.

[0049] Implementation Scheme 21: A method for preparing a catalyst composition, the method comprising:

[0050] A salt of at least one cocatalytic metal is dissolved in an aqueous metal oxide sol, wherein the salt of the at least one cocatalytic metal dissociates in the aqueous metal oxide sol to form an aqueous metal salt / metal oxide sol mixture, wherein the metal oxide particles comprise one or more oxides of transition metals or lanthanides of Group 3 or Group 4 of the periodic table.

[0051] The aqueous metal salt / metal oxide sol mixture is used to treat ammonium or proton-exchanged small-pore molecular sieve particles with a porous structure and a maximum ring size of 8 tetrahedral atoms to impregnate the co-catalyst metal into the pore structure of the small-pore molecular sieve; and

[0052] drying and calcining the treated small pore molecular sieve particles to form a catalyst composition, wherein the catalyst composition comprises small pore molecular sieve particles impregnated with a promoter metal, and metal oxide particles dispersed within the small pore molecular sieve particles and outside the pore structure of the small pore molecular sieve particles.

[0053] Embodiment 22: The method of any preceding or following embodiment, wherein the metal oxide is selected from the group consisting of zirconium oxide, aluminum oxide, cerium dioxide, hafnium dioxide, yttrium oxide, and combinations thereof.

[0054] Embodiment 23: The method of any preceding or following embodiment, wherein the metal oxide comprises zirconium oxide.

[0055] Embodiment 24: The method of any preceding or following embodiment, wherein the metal oxide sol has an average particle size of about 10 nm to about 500 nm.

[0056] Embodiment 25: The method of any preceding or following embodiment, wherein the metal oxide sol has a D 10 particle size that is greater than 10 times the pore opening of the molecular sieve.

[0057] Embodiment 26: The method of any preceding or following embodiment, wherein the metal oxide sol has a D 10 particle size of about 10 nm or greater.

[0058] Embodiment 27: The method of any preceding or following embodiment, wherein the promoter metal is selected from the group consisting of Cu, Co, Ni, La, Mn, Fe, V, Ag, Ce, Nd, Pr, Ti, Cr, Zn, Zn, Nb, Mo, Hf, Y, W, and combinations thereof.

[0059] Embodiment 28: The method of any preceding or following embodiment, wherein the metal oxide sol is selected from the group consisting of zirconium oxide hydroxide sol, nanoscale hydrated zirconium oxide sol, aluminum oxide sol, zirconium oxide-yttrium oxide sol, zirconium oxide-aluminum oxide sol, zirconium oxide-cerium dioxide sol, organic zirconium sol, and mixtures thereof.

[0060] Embodiment 29: The method of any preceding or following embodiment, wherein metal oxide particles do not enter the pore structure of the small pore molecular sieve.

[0061] Embodiment 30: The method of any preceding or following embodiment, wherein the small pore molecular sieve has d6r units.

[0062] Implementation Scheme 31: The method of any of the foregoing or the following implementation schemes, wherein the small-pore molecular sieve has a structural type selected from AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, LTN, MSO, SAS, SAT, SAV, SFW and TSC.

[0063] Implementation Scheme 32: The method of any of the foregoing or the following embodiments, wherein the microporous molecular sieve has a CHA crystal structure.

[0064] Implementation Scheme 33: The method of any of the foregoing or the following embodiments, wherein the co-catalyst metal comprises Cu, Fe or a combination thereof.

[0065] Implementation Scheme 34: A method of any of the foregoing or the following embodiments, further comprising the steps of: mixing the catalyst composition with water to form a wash-coating slurry; applying the wash-coating slurry onto a substrate to form a wash-coating layer thereon; and drying and calcining the substrate to form a catalyst article.

[0066] Implementation Scheme 35: The method of any of the foregoing or the following implementation schemes further includes adding a water-soluble metal oxide compound to the washing slurry to increase its total metal oxide content.

[0067] The appendix is ​​briefly described below. Figure One These and other features, aspects, and advantages of this disclosure will become apparent upon reading the following detailed description. The invention includes any combination of two, three, four, or more of the above embodiments, as well as any combination of two, three, four, or more features or elements set forth in this disclosure, whether or not such features or elements are explicitly combined in the specific embodiments described herein. This disclosure is intended to be interpreted holistically so that any separable features or elements of the disclosed invention in any aspect and embodiment shall be considered composable unless the context clearly specifies otherwise. Brief description of the attached diagram

[0069] Figure 1 The NO catalyst material according to the embodiment x A graph showing the conversion rate and N2O yield versus temperature;

[0070] Figure 2 These are SEM images of the catalyst material according to the embodiments;

[0071] Figure 3 These are SEM images of the catalyst material according to the embodiments;

[0072] Figure 4 The NO catalyst material according to the embodiment x Bar chart of efficiency;

[0073] Figure 5 is a SEM image of a catalyst material according to an embodiment;

[0074] Figures 6A-6D is a collection of SEM images of a catalyst material according to an embodiment;

[0075] Figures 7A-7D is a collection of SEM images of a catalyst material according to an embodiment;

[0076] Figure 8 is a bar graph of NO reduction of a catalyst material according to an embodiment; x

[0077] Figure 9 is a bar graph of NH3 slip, NH3 storage, and N2O production of a catalyst material according to an embodiment;

[0078] Figures 10A-10D is a collection of SEM images of a catalyst material according to an embodiment;

[0079] Figure 11 is a bar graph of NO conversion of a catalyst material according to an embodiment; x

[0080] Figure 12 is a plot of N2O production vs. temperature of a catalyst material according to an embodiment;

[0081] Figure 13 is a bar graph of NO conversion of a catalyst material according to an embodiment compared to a prior art material; x

[0082] Figure 14 is a plot of NO conversion vs. temperature of a catalyst material according to an embodiment compared to a prior art material; x

[0083] Figure 15 is a perspective view of a honeycomb substrate support that can include a catalyst composition according to the present application; and

[0084] Figure 16 shows a schematic diagram of one embodiment of an emissions treatment system in which a catalyst composition of the present application is used.

[0085] DETAILED DESCRIPTION

[0086] Before several exemplary embodiments of the present application are described, it is to be understood that the application is not limited to the details of construction or process steps set forth in the following description. The application is capable of other embodiments and of being practiced or being carried out in various ways.

[0087] ​​​​Government regulations require the use of NO x abatement technologies. NO x xidation (SCR) is an effective and mainstream emission control technology for controlling NO x . In order to comply with government regulations, there is a need for SCR catalysts with improved performance compared to existing Cu-SSZ-13 based benchmark technologies. Provided are catalysts with improved NO x conversion efficiency and lower N2O production in certain embodiments compared to existing Cu-SSZ-13 based benchmark technologies. The catalyst effectively promotes the selective reaction of ammonia with nitrogen oxides in the temperature range of 200 to 600 °C to form nitrogen and H2O.

[0088] Embodiments of the present invention relate to selective catalytic reduction catalysts comprising a small pore molecular sieve and a layer of zirconium oxide. It has been surprisingly found that the modification of a small pore molecular sieve with zirconium oxide results in lower N2O production and improved low to high temperature performance window. In certain embodiments, the present invention provides a catalyst composition in the form of an intimate mixture of small pore molecular sieve particles and metal oxide (e.g., zirconium oxide) particles impregnated with a promoter metal. The metal oxide particles have a size that prevents the metal oxide particles from significantly penetrating into the pore structure of the molecular sieve. Rather, the metal oxide particles provide a surface coating on the molecular sieve particles. The presence of this metal oxide particles has been found to improve low temperature NO x reduction and lower N2O production.

[0089] With respect to the terms used in the present disclosure, the following definitions are provided.

[0090] The term "catalyst" or "catalyst composition" or "catalyst material" as used herein means a material that promotes a reaction.

[0091] The term "catalytic article" as used herein means an element used to promote a desired reaction. For example, a catalytic article can comprise a washcoat containing catalytic species (such as a catalyst composition) on a substrate.

[0092] The term "selective catalytic reduction" (SCR) as used herein means a catalytic process that uses a nitrogen-containing reductant to reduce nitrogen oxides to di-nitrogen (N2).

[0093] The term "washcoat" as used herein has its ordinary meaning in the art, i.e., a thin adherent coating of catalytic material or other material applied to a supporting substrate material (such as a honeycomb-type carrier element) that is porous enough to allow passage of a process gas stream. As understood in the art, a washcoat is obtained from a dispersion of particles in a slurry, which is applied to a substrate, dried and calcined to provide a porous washcoat.

[0094] In one or more embodiments, the selective catalytic reduction catalyst comprises a washcoat including a small pore molecular sieve having a pore structure and a maximum ring size of 8 tetrahedral atoms and containing a promoter metal and a zirconia-containing layer on the small pore molecular sieve containing a promoter metal, wherein the zirconia-containing layer advantageously has zirconia particles having a particle size of about 10 nm to about 500 nm.

[0095] Molecular sieve

[0096] The term "molecular sieve" as used herein refers to framework materials, such as zeolites and other framework materials (e.g., isomorphous materials), which can be used as catalysts in particulate form in combination with one or more promoter metals. Molecular sieves are materials based on a three-dimensional network of oxygen ions containing generally tetrahedral sites and having a substantially uniform pore distribution, with an average pore diameter of no greater than Pore diameter is defined by ring size. The term "zeolite" as used herein refers to one specific example of a molecular sieve that includes silicon and aluminum atoms. According to one or more embodiments, it is recognized that defining a molecular sieve by its structure type is intended to include that structure type and any and all isomorphous framework materials having the same structure type as that zeolite material, such as SAPO, ALPO, and MeAPO materials.

[0097] In more specific embodiments, reference to aluminosilicate zeolite structure types is to limit the material to molecular sieves that do not include phosphorous or other metals substituted in the framework. However, for clarity, "aluminosilicate zeolite" as used herein does not include aluminophosphate materials, such as SAPO, ALPO, and MeAPO materials, and the more general term "zeolite" is intended to include both aluminosilicates and aluminophosphates. Zeolites are crystalline materials having a fairly uniform pore diameter, ranging from about 3 to 10 Angstroms in diameter, depending on the type of zeolite and the type and amount of cations included in the zeolite lattice. Zeolites typically include a silica to alumina (SAR) molar ratio of 2 or greater.

[0098] The term "aluminophosphate" refers to another specific example of a molecular sieve that includes aluminum and phosphate atoms. Aluminophosphates are crystalline materials having a fairly uniform pore diameter.

[0099] Aluminosilicates typically include an open three-dimensional framework structure of corner- sharing TO4 tetrahedra, where T is Al or Si, or optionally P. Cations that balance the charge of the framework are loosely associated with the framework oxygen, and the remaining pore volume is filled with water molecules. The non-framework cations are typically exchangeable, and the water molecules are removable.

[0100] In one or more embodiments, the small pore molecular sieve comprises SiO4 / AlO4 tetrahedra and are linked through shared oxygen atoms to form a three-dimensional network. In other embodiments, the molecular sieve component comprises SiO4 / AlO4 / PO4 tetrahedra. The small pore molecular sieve of one or more embodiments is distinguished primarily by the geometry of the voids formed by the rigid network of (SiO4) / AlO4 or SiO4 / AlO4 / PO4 tetrahedra. In terms of the atoms forming the entrance opening, the entrance to the void is formed by 6, 8, 10, or 12 ring atoms. In one or more embodiments, the molecular sieve comprises a ring size of no greater than 8, including 6 and 8.

[0101] According to one or more embodiments, the molecular sieve can be based on the framework topology used to identify the structure. In general, any structural type of zeolite can be used, such as structural type ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY, AHT, ANA, APC, APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AWO, AWW, BCT, BEA, BEC, BIK, BOG, BPH, BRE, CAN, CAS, SCO, CFI, SGF, CGS, CHA, CHI, CLO, CON, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI, ERI, ESV, ETR, EUO, FAU, FER, FRA, GIS, GIU, GME, GON, GOO, HEU, IFR, IHW, ISV, ITE, ITH, ITW, IWR, IWW, JBW, KFI, LAU, LEV, LIO, LIT, LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, MSO, MTF, MTN, MTT, MTW, MWW, NAB, NAT, NES, NON, NPO, NSI, OBW, OFF, OSI, OSO, OWE, PAR, PAU, PHI, PON, RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAO, SAS, SAT, SAV, SBE, SBS, SBT, SFE, SFF, SFG, SFH, SFN, SFO, SGT, SOD, SOS, SSY, STF, STI, STT, TER, THO, TON, TSC, UEI, UFI, UOZ, USI, UTL, VET, VFI, VNI, VSV, WIE, WEN, YUG, ZON, or combinations thereof.

[0102] In one or more embodiments, the molecular sieve comprises an 8-ring small pore aluminosilicate zeolite. As used herein, "small pore" refers to a pore opening of less than about 5 Angstroms, such as about ~3.8 Angstroms. The term "8-ring" zeolite refers to a zeolite having an 8-ring pore opening and double six-ring secondary building units and having a cage-like structure that is derived by connecting double six-ring units by four rings. Zeolites are constructed from secondary building units (SBUs) and complex building units (CBUs) and exhibit a number of different framework structures. Secondary building units contain up to 16 tetrahedral atoms and are non-chiral. Complex building units need not be non-chiral and are not necessarily used to construct the entire framework. For example, one class of zeolites has single 4-ring (s4r) complex building units in its framework structure. In the 4-ring, the "4" refers to the positions of the tetrahedral silicon and aluminum atoms, and oxygen atoms are located between the tetrahedral atoms. Other complex building units include, for example, single 6-ring (s6r) units, double 4-ring (d4r) units, and double 6-ring (d6r) units. The d4r unit is produced by connecting two s4r units. The d6r unit is produced by connecting two s6r units. In the d6r unit, there are 12 tetrahedral atoms. Zeolite structure types having d6r secondary building units include AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, and WEN.

[0103] In one or more embodiments, the molecular sieve is a small pore molecular sieve having a pore structure and a maximum ring size of 8 tetrahedral atoms. In other embodiments, the small pore molecular sieve comprises d6r units. Thus, in one or more embodiments, the small pore molecular sieve has a structure type selected from the group consisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, LTN, MSO, SAS, SAT, SAV, SFW, TSC, and combinations thereof. In other specific embodiments, the molecular sieve has a structure type selected from the group consisting of CHA, AEI, AFX, ERI, KFI, LEV, and combinations thereof. In still other specific embodiments, the small pore molecular sieve has a structure type selected from the group consisting of CHA, AEI, and AFX. In one or more very specific embodiments, the small pore molecular sieve component has a CHA structure type.

[0104] Zeolite chabazite includes a formula of approximately: (Ca, Na2, K2, Mg) Al2Si4O 12• 6H20 (e.g., hydrous calcium aluminum silicate) zeolite-like naturally occurring framework silicate mineral. Three synthetic forms of zeolite chabazite are described in "Zeolite Molecular Sieves" by D. W. Breck, published by John Wiley & Sons in 1973, which is incorporated herein by reference. The three synthetic forms reported by Breck are zeolite K-G described in J. Chem. Soc, p. 2822 (1956), Barrer et al.; zeolite D described in British Patent No. 868,846 (1961); and zeolite R described in U.S. Patent No. 3,030,181, which are incorporated herein by reference. The synthesis of another synthetic form of zeolite chabazite, SSZ-13, is described in U.S. Patent No. 4,544,538, which is incorporated herein by reference. The synthesis of a synthetic form of molecular sieve having the chabazite crystal structure, silicoaluminophosphate 34 (SAPO-34) is described in U.S. Patent Nos. 4,440,871 and 7,264,789, which are incorporated herein by reference. A method of making another synthetic molecular sieve having the chabazite structure, SAPO-44, is described in U.S. Patent No. 6,162,415, which is incorporated herein by reference.

[0105] In one or more embodiments, the molecular sieve can include all aluminosilicates, borosilicates, gallosilicates, MeAPSOs, and MeAPOs compositions. These include, but are not limited to, SSZ-13, SSZ-62, natural chabazite, zeolite K-G, Linde D, Linde R, LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, ZYT-6, CuSAPO-34, CuSAPO-44, and CuSAPO-47.

[0106] The silica / alumina ratio of the aluminosilicate molecular sieve can vary over a wide range. In one or more embodiments, the molecular sieve has a silica / alumina molar ratio (SAR) of 2 to 300, including 5 to 250; 5 to 200; 5 to 100; and 5 to 50. In one or more specific embodiments, the molecular sieve has a silica / alumina molar ratio (SAR) of 10 to 200, 10 to 100, 10 to 75, 10 to 60, and 10 to 50; 15 to 100, 15 to 75, 15 to 60, and 15 to 50; 20 to 100, 20 to 75, 20 to 60, and 20 to 50.

[0107] In one or more embodiments, the small pore molecular sieve has a CHA structure type and has a silica / alumina ratio of 2 to 300, including 5 to 250, 5 to 200, 5 to 100, and 5 to 50; 10 to 200, 10 to 100, 10 to 75, 10 to 60, and 10 to 50; 15 to 100, 15 to 75, 15 to 60, and 15 to 50; 20 to 100, 20 to 75, 20 to 60, and 20 to 50. In one embodiment, the small pore molecular sieve comprises SSZ-13. In a very specific embodiment, the SSZ-13 has a silica / alumina ratio of 2 to 300, including 5 to 250, 5 to 200, 5 to 100, and 5 to 50; 10 to 200, 10 to 100, 10 to 75, 10 to 60, and 10 to 50; 15 to 100, 15 to 75, 15 to 60, and 15 to 50; 20 to 100, 20 to 75, 20 to 60, and 20 to 50.

[0108] The synthesis of zeolites and related microporous and mesoporous materials varies depending on the structure type of the zeolitic material, but generally involves combining several components (e.g., silica, alumina, phosphorus, alkali metal, organic template, etc.) to form a synthesis gel, which is then hydrothermally crystallized to form the final product. The structure directing agent (SDA) can be in the form of an organic (i.e., tetraethylammonium hydroxide (TEAOH)) or inorganic cation (i.e., Na + or K + ). During the crystallization process, the tetrahedral units organize around the SDA to form the desired framework, and the SDA is typically embedded within the pore structure of the zeolite crystal. In one or more embodiments, crystallization of the molecular sieve material can be obtained by the addition of a structure directing agent / template, a crystal nucleus, or an element. In some cases, crystallization can be performed at temperatures less than 100 °C. Molecular sieves having a CHA structure can be prepared according to various techniques known in the art, for example, U.S. Patent Nos. 4,544,538 (Zones) and 6,709,644 (Zones), which are incorporated herein by reference in their entirety.

[0109] Optionally, the resulting alkali metal zeolite is subjected to NH4 exchange to form an NH4-chabazite. The NH4 ion exchange can be performed according to various techniques known in the art, for example, Bleken, F.; Bjorgen, M.; Palumbo, L.; Bordiga, S.; Svelle, S.; Lillerud, K.-P.; and Olsbye, U. Topics in Catalysis 52, (2009), 218-228.

[0110] Promoter metal

[0111] As used herein, "promoted" means a component that is intentionally added to the molecular sieve, as opposed to an impurity that is inherent in the molecular sieve. Thus, the promoter is intentionally added to increase the activity of the catalyst as compared to a catalyst without the intentional addition of the promoter. To facilitate the SCR of nitrogen oxides, in one or more embodiments, a suitable metal is exchanged into the molecular sieve component. Accordingly, the molecular sieve of one or more embodiments can be subsequently ion-exchanged with one or more promoter metals, such as copper (Cu), cobalt (Co), nickel (Ni), lanthanum (La), manganese (Mn), iron (Fe), vanadium (V), silver (Ag), and cerium (Ce), neodymium (Nd), praseodymium (Pr), titanium (Ti), chromium (Cr), zinc (Zn), tin (Sn), niobium (Nb), molybdenum (Mo), hafnium (Hf), yttrium (Y), and tungsten (W). In specific embodiments, the molecular sieve component is promoted with Cu, Fe, and combinations thereof. In very specific embodiments, the molecular sieve component is promoted with Cu.

[0112] The promoter metal content of the molecular sieve component, on an oxide basis, is at least about 0.1 wt% in one or more embodiments. In one or more embodiments, the promoter metal is present in an amount of from about 1 to about 10 wt%, including from about 2 to about 5 wt%, in each case based on the total weight of the molecular sieve. In one or more specific embodiments, the promoter metal comprises Cu, and the Cu content, calculated as CuO, is at most about 10 wt%, including 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, and 0.1 wt% (on an oxide basis), in each case based on the total weight of the calcined molecular sieve component, and reported on a volatile-free basis. In specific embodiments, the Cu content, calculated as CuO, is from about 2 to about 5 wt%.

[0113] Metal oxide on the surface of the molecular sieve

[0114] According to one or more embodiments, the catalyst composition includes a molecular sieve containing a promoter metal and a metal oxide on the surface of the molecular sieve. The metal oxide is intimately mixed with the molecular sieve to provide a dispersed phase of the metal oxide within the molecular sieve material. In certain embodiments, the metal oxide is relatively uniformly dispersed throughout the molecular sieve material. However, in some embodiments, at least a portion of the metal oxide can be present in an enriched region of the washcoat surface containing the catalyst composition of the present invention, generally due to the amount of water-soluble zirconium compound (or other metal oxide compound) that migrates to the surface of the washcoat and decomposes / oxidizes in air during the substrate coating process.

[0115] For ease of reference, the present disclosure is largely focused on zirconium oxide (and related zirconium precursors). However, other metal oxides can be used without departing from the invention, such as metal oxides comprising one or more oxides of transition metals of Group 3 or Group 4 of the Periodic Table or lanthanides. Specific examples include zirconium oxide, aluminum oxide, cerium dioxide, hafnium dioxide, yttrium oxide, and combinations thereof, although minor amounts of other metal oxides can also be present. In certain embodiments, the primary (greater than 50 wt% of the total metal oxide weight) metal oxide is zirconium oxide, aluminum oxide, cerium dioxide, hafnium dioxide, yttrium oxide, or combinations thereof. In certain advantageous embodiments, the metal oxide is primarily zirconium oxide, including composites of zirconium oxide with other metal oxides such as cerium dioxide, aluminum oxide, hafnium dioxide, or yttrium oxide. In other embodiments, the metal oxide is aluminum oxide, such as a large crystal boehmite material, such as a boehmite having a crystallite size of about 20 nm or greater.

[0116] In certain embodiments, the metal oxide content of the catalyst composition is provided at least in part by a mixture of a metal oxide sol containing metal oxide microparticles or nanoparticles and the molecular sieve. Unlike the use of water-soluble precursors that are later calcined to the oxide form, the introduction of the relatively insoluble form of the metal oxide material helps prevent the migration of the promoter metal within the catalyst composition, which can be detrimental to high temperature NO x Reduction is detrimental. Thus, the benefits of increased metal oxide content (reduced N2O production and enhanced low temperature NO x Reduction) can be realized without adversely affecting high temperature performance.

[0117] For example, in some embodiments, zirconium oxide is introduced using an aqueous zirconium oxide sol. As used herein, the term "aqueous zirconium oxide sol" refers to a colloidal suspension of small solid particles of zirconium oxide or hydrated zirconium oxide in a continuous liquid (water) medium. In one or more embodiments, the aqueous zirconium oxide sol is selected from the group consisting of zirconyl hydroxide sols, nanoscale hydrated zirconium oxide sols, zirconium oxide-yttrium oxide sols, zirconium oxide-aluminum oxide sols, zirconium oxide-cerium dioxide sols, organic zirconium sols, and mixtures thereof. As described herein, aqueous aluminum oxide sols, such as large crystal boehmite sols, can also be used in certain embodiments.

[0118] In some embodiments, the aqueous zirconia sol can include one or more promoter metals in the form of an aqueous metal salt. In other words, the molecular sieve can be impregnated with a promoter metal and mixed with the metal oxide particles in the same processing step. As used herein, "promoted" refers to a component that is intentionally added to the aqueous zirconia sol, as opposed to an impurity that is inherent in the aqueous zirconia sol. Thus, the promoter is intentionally added to increase the activity of the aqueous zirconia sol compared to an aqueous zirconia sol without the intentional addition of the promoter. In one or more embodiments, the aqueous zirconia sol includes a promoter metal selected from lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), copper (Cu), manganese (Mn), iron (Fe), nickel (Ni), titanium (Ti), chromium (Cr), zinc (Zn), tin (Sn), vanadium (V), niobium (Nb), molybdenum (Mo), hafnium (Hf), tungsten (W), yttrium (Y), and combinations thereof.

[0119] In one or more embodiments, the zirconia sol (or other metal oxide sol) referred to herein has particles of zirconia (or other metal oxide) having an average particle size of about 10 nm to about 500 nm, including about 10 nm to about 400 nm, about 10 nm to about 300 nm, and about 10 nm to about 250 nm. As used herein, the term "average particle size" refers to the average diameter of the zirconia particles (or other metal oxide particles) as measured by a CILAS 1064 laser particle size analyzer according to the manufacturer's recommended liquid mode method having a measurement range of 0.04 to 500 microns. The particle size of the nanoscale sol components can be measured using a CILAS 1064 laser particle size analyzer according to the manufacturer's recommended liquid mode method having a measurement range of 0.04 to 500 microns. For particles <40 nanometers, such particle size can be measured using a Malvern Zetasizer Nano ZS, which is a high performance dual angle particle and molecular size analyzer with "NIBS" optics using dynamic light scattering for enhanced detection of aggregates and measurement of small or dilute samples and samples at very low or high concentrations.

[0120] In one or more embodiments, the molecular sieve and the zirconia (or other metal oxide) particles have an average or median particle size distribution ratio of greater than about 10: 1, including greater than about 100: 1, greater than about 1000: 1, greater than about 10,000: 1. As used herein, the terms "average particle size distribution ratio" and "median particle size distribution ratio" refer to the D50 of the molecular sieve particles divided by the D50 of the zirconia (or other metal oxide) particles. 50 (50% = value).

[0121] Without intending to be bound by theory, it is believed that the zirconia (or other metal oxide) should advantageously contain nanoscale particles having a size such that D 10greater than 10 times (10x) the pore opening of the small pore molecular sieve such that the particles do not penetrate the pores of the small pore molecular sieve. In one or more embodiments, the zirconium oxide particles (and / or the zirconium oxide particles in the starting zirconium oxide sol) have a D 10 Particle size. Reference to D 10 Particle size refers to a particle size distribution having 10 weight percent of the particles having a diameter below a given threshold. In certain embodiments, the zirconium oxide particles have a D 10 value.

[0122] Surprisingly, it has been found that the presence of zirconium oxide reduces N2O production. In one or more embodiments, for certain catalyst articles of the present application, the N2O production is reduced by greater than about 10 weight percent, including greater than about 15%, greater than about 20%, greater than about 25%, greater than about 30%, greater than about 35%, and greater than about 40% compared to a catalyst article comprising a washcoat including the same small pore molecular sieve / promoter metal (at the same catalyst and promoter metal loadings) but which does not contain a zirconium oxide-containing layer. Exemplary test conditions for determining N2O production can be found in Example 3.

[0123] In one or more embodiments, the zirconium oxide (or other metal oxide) is present in an amount of about 1 to about 20 weight percent, including about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, and about 15 weight percent, in each case based on the total weight of the washcoat. As used herein, the term "total weight of the washcoat" refers to the weight of all components in the washcoat after the washcoat has been dried and calcined, including the molecular sieve, the promoter metal, and the zirconium oxide. In certain embodiments, the zirconium oxide (or other metal oxide) is present in an amount of at least about 5 weight percent, at least about 6%, at least about 7%, at least about 8%, at least about 9%, or at least about 10% based on the total weight of the washcoat.

[0124] In certain embodiments, the metal oxide content is supplemented by using a water soluble metal oxide precursor added to the washcoat slurry during the washcoating process. In one embodiment, the metal oxide is provided entirely in this manner, although it is advantageous for at least some of the metal oxide content to originate from a relatively insoluble source as described above. As described in the examples, the use of a large amount of water soluble metal oxide precursor can facilitate undesirable co-catalyst metal migration within the washcoat layer. It is therefore desirable to minimize the contribution of the water soluble metal oxide precursor to the total metal oxide content and / or to calcine the metal co-catalyzed molecular sieve material prior to contact with the water soluble metal oxide precursor (e.g., calcination in air at a temperature of at least about 3000C to minimize co-catalyst metal solubility.

[0125] The washcoat slurry is typically prepared using a large amount of water, and thus an aqueous washcoat slurry is typically used as well. Zirconium compounds that migrate to the surface of the washcoat layer are soluble in water, and thus must also be soluble in the slurry. In one or more embodiments, the zirconium compound is at least 15 wt% soluble in water, including at least about 20% soluble, at least about 30% soluble, at least about 40% soluble, at least about 50% soluble, at least about 60% soluble, at least about 70% soluble, at least about 80% soluble, and at least about 90% soluble. In other embodiments, the zirconium compound has a water solubility of from about 15 to about 100% soluble, including from about 15 to about 85%, from about 20 to about 100%, from about 20 to about 85%, from about 30 to about 100%, from about 30 to about 85%, from about 40 to about 100%, from about 40 to about 85%, from about 50 to about 100%, and from about 50 to about 85% soluble. Reference to solubility in wt% refers to the percentage of the zirconium compound that dissolves in the aqueous washcoat composition at room temperature (250C) and 1 atm.

[0126] As used herein, "water soluble zirconium oxide component," "water soluble zirconium compound," and the like refer to the corresponding water soluble zirconium containing compound, complex, precursor, and the like that decomposes, oxidizes, or otherwise transforms into a catalytically active form, typically a metal or metal oxide (i.e., zirconium oxide), upon calcination or use of the catalyst. As described above, other water soluble precursors of metal oxides can be used in place of the zirconium compound.

[0127] In one or more embodiments, a salt, such as NH4NO3or NH4OAc, is added to the aqueous washcoat composition containing the zirconium compound to increase the ionic strength. The pH is then adjusted / controlled, for example, to a pH of ~4-5, to ensure that the zirconium compound, such as a zirconyl salt, for example, zirconyl acetate, is soluble in water and migrates during the drying process.

[0128] In one or more embodiments, the zirconium compound is selected from the group consisting of ionic zirconium salts, covalently bonded organozirconium complexes, covalently bonded organooxozirconium compounds, and mixtures thereof. As used herein, the term "organozirconium salt, compound or complex" means Zr having any anionic organic ligand covalently bonded to form a complex 4+ which can also include polymeric species. In one or more embodiments, the water soluble zirconium compound is selected from the group consisting of zirconium acetate, zirconium citrate, zirconium tartrate, zirconium lactate, zirconium adipate, and mixtures thereof. As used herein, the term "organooxozirconium salt, compound or complex" means ZrO having any anionic organic ligand ionically bonded to form a complex 2+ which can also include polymeric species. In one or more embodiments, the water soluble zirconium compound is selected from the group consisting of zirconium nitrate, zirconium chloride, zirconium sulfate, zirconyl nitrate, zirconyl chloride, zirconyl sulfate, zirconyl acetate, zirconyl citrate, zirconyl tartrate, zirconyl lactate, zirconyl adipate, and mixtures thereof.

[0129] Particle shape and size

[0130] The catalyst according to embodiments of the present application can be provided in the form of a powder or a spray material from a separation technique including decanting, filtering, centrifuging or spraying.

[0131] In general, the powder or spray material can be shaped without any other compounds, for example by suitable compacting, to obtain a molded article of the desired geometry, for example a wafer, a cylinder, a sphere, etc.

[0132] For example, the powder or spray material is mixed with or coated with a suitable modifier known in the art. For example, modifiers such as silica, alumina, zeolite or refractory binders (e.g. zirconium precursors) can be used. The powder or spray material, optionally after mixing with or coating with a suitable modifier, is formed into a slurry, for example with water, which is deposited on a suitable refractory support, for example a flow-through honeycomb substrate support or a wall-flow honeycomb substrate support.

[0133] The catalyst according to embodiments of the present application can also be provided in the form of an extrudate, a pellet, a wafer or any other suitable shaped particle for use as a packed bed of particulate catalyst or as a shaped piece, such as a plate, a saddle, a tube, etc.

[0134] SCR activity

[0135] In one or more embodiments, the coated substrate comprising the selective catalytic reduction catalyst of one or more embodiments exhibits an aged NOx conversion at 200°C of at least 50% measured at a GHSV of 80,000 h -1 x ​Conversion. In particular embodiments, the catalyst exhibits an aged NOx conversion at 450°C of at least 70% measured at a gas hourly space velocity of 80,000 h"1 -1 Conversion. In particular embodiments, the catalyst exhibits an aged NOx conversion at 450°C of at least 70% measured at a gas hourly space velocity of 80,000 h"1 x Conversion. In particular embodiments, the catalyst exhibits an aged NOx conversion at 450°C of at least 70% measured at a gas hourly space velocity of 80,000 h"1 -1 Conversion. In particular embodiments, the catalyst exhibits an aged NOx conversion at 450°C of at least 70% measured at a gas hourly space velocity of 80,000 h"1 x Conversion. In particular embodiments, the catalyst exhibits an aged NOx conversion at 450°C of at least 70% measured at a gas hourly space velocity of 80,000 h"1 x Conversion. In particular embodiments, the catalyst exhibits an aged NOx conversion at 450°C of at least 70% measured at a gas hourly space velocity of 80,000 h"1 -1 Conversion. In particular embodiments, the catalyst exhibits an aged NOx conversion at 450°C of at least 70% measured at a gas hourly space velocity of 80,000 h"1

[0136] SCR activity measurements have been demonstrated in the literature, see, for example, PCT Application Publication No. WO 2008 / 106519.

[0137] Further, according to one or more embodiments, the catalyst is effective in reducing N2O production.

[0138] Substrate

[0139] In one or more embodiments, the catalyst composition can be applied to a substrate as a washcoat. As used herein, the term "substrate" refers to a monolith onto which the catalyst is typically placed in the form of a washcoat. The washcoat is formed by preparing a slurry containing a certain catalyst solids content (e.g., 30-90 wt%) in a liquid carrier, which is then applied to the substrate and dried to provide the washcoat layer.

[0140] In one or more embodiments, the substrate is selected from one or more of flow-through honeycomb monoliths, wall-flow filters, foams, or meshes, and the catalyst is applied to the substrate as a washcoat.

[0141] According to one or more embodiments, the substrate for the catalyst composition can be constructed of any material commonly used to make automotive catalysts and typically comprises a metallic or ceramic honeycomb structure. The substrate typically provides a plurality of wall surfaces onto which the catalyst composition is applied and adhered, thereby serving as a support for the catalyst composition.

[0142] Exemplary metallic substrates include heat resistant metals and metal alloys, such as titanium and stainless steel, and other alloys having iron as an essential or major component. Such alloys can contain one or more of nickel, chromium, and / or aluminum, and the total amount of these metals can advantageously comprise at least 15 wt% of the alloy, for example, 10-25 wt% chromium, 3-8 wt% aluminum, and up to 20 wt% nickel. The alloy can also contain small or trace amounts of one or more other metals, such as manganese, copper, vanadium, titanium, and the like. The surface or metallic support can be oxidized at high temperatures, for example, 1000°C and above, to form an oxide layer on the surface of the substrate to improve the corrosion resistance of the alloy and promote adhesion of the washcoat layer to the metallic surface.

[0143] Ceramic materials used to construct the substrate can include any suitable refractory material, such as cordierite, mullite, cordierite-alpha alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alpha alumina, alumino-silicate, and the like.

[0144] Any suitable substrate can be used, such as a monolithic flow-through type substrate having a plurality of fine, parallel gas flow channels extending from an inlet face of the substrate to an outlet face to open the channels to fluid flow. The channels, which are substantially straight paths from the inlet to the outlet, are defined by walls, and the catalytic material is coated as a washcoat on the walls to contact the gas flowing through the channels with the catalytic material. The flow channels of the monolithic substrate are thin-walled channels, which can have any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, and the like. Such structures can contain from about 60 to about 1200 or more gas inlets (i.e., "pores") per square inch of cross section (cpsi), more typically from about 300 to 600 cpsi. The wall thickness of the flow-through type substrate can vary, typically ranging between 0.002 and 0.1 inches. Representative commercially available flow-through type substrates are cordierite substrates having 400 cpsi and a wall thickness of 6 mil or 600 cpsi and a wall thickness of 4 mil. However, it is to be understood that the present application is not limited to a particular substrate type, material, or geometry.

[0145] In alternative embodiments, the substrate can be a wall-flow substrate, in which each channel is closed at one end of the substrate body by a non-porous plug, with adjacent channels closed at the opposite end face. This requires the gas to flow through the porous walls of the wall-flow substrate to reach the outlet. Such monolithic substrates can contain up to about 700 or more cpsi, such as about 100 to 400 cpsi, more typically about 200 to about 300 cpsi. The cross-sectional shape of the pores can vary as described above. Wall-flow substrates typically have a wall thickness of 0.002 to 0.1 inches. Representative commercially available wall-flow substrates are composed of porous cordierite, one example of which has 200 cpsi and a 10 mil wall thickness, or 300 cpsi and an 8 mil wall thickness, and a wall porosity of 45-65%. Other ceramic materials, such as aluminum titanate, silicon carbide and silicon nitride are also used as wall-flow filter substrates. However, it is to be understood that the present application is not limited to a particular substrate type, material or geometry. It is noted that where the substrate is a wall-flow substrate, the DOC composition can be infiltrated into the pore structure of the porous wall in addition to being located on the wall surface (i.e., partially or completely plugging the pore openings).

[0146] Figure 15 An exemplary substrate 2 in the form of a honeycomb monolith coated with a catalyst composition as described herein is shown. 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 identical to end face 6. The substrate 2 has a plurality of fine, parallel gas flow channels 10 formed therein. In the case of a flow-through monolith, the channels 10 are typically open to allow fluid, such as a gas stream, to flow longitudinally through the support 2 via the gas flow channels 10. Alternatively, the substrate 2 can be in the form of a wall-flow filter as discussed in detail above. In such embodiments, each gas flow channel 10 is plugged at the inlet or outlet end and the channel wall is porous to allow gas to pass from one gas flow channel into an adjacent gas flow channel, as is understood in the art. If desired, the catalyst composition can be applied in a plurality of discrete layers. The present application can be practiced with one or more (e.g., 2, 3 or 4) washcoats.

[0147] To coat a substrate with the catalyst of one or more embodiments, the substrate is vertically immersed in a portion of the catalyst slurry such that the top of the substrate is just above the surface of the slurry. The slurry thereby contacts the inlet face of each honeycomb wall, but is prevented from contacting the outlet face of each wall. The sample is left in the slurry for about 30 seconds. The substrate is removed from the slurry and excess slurry is removed from the substrate by first allowing it to drain from the channels, then by blowing compressed air across the substrate (against the direction of slurry penetration), and then by pulling a vacuum from the direction of slurry penetration. By using this technique, in the case of a wall-flow substrate, the catalyst slurry penetrates the substrate wall, but does not plug the pores to the extent that excessive back pressure builds up in the final substrate. As used herein, the term "penetration" when used to describe the dispersion of catalyst slurry on a substrate means that the catalyst composition is dispersed throughout the substrate wall and thereby at least partially plugs the pores in the wall.

[0148] The coated substrate is typically dried at about 100°C and calcined at higher temperatures, e.g., 300 to 450°C. After calcination, the catalyst loading can be determined by calculating the coated and uncoated weight of the substrate. It will be apparent to those skilled in the art that the catalyst loading can be varied by varying the solids content of the coating slurry. Alternatively, repeated dipping of the substrate in the coating slurry can be performed, followed by removal of excess slurry as described above.

[0149] Preparation of catalyst

[0150] According to one or more embodiments, a method for the synthesis of a selective catalytic reduction catalyst is provided. More particularly, the catalyst comprises a small pore molecular sieve having a pore structure with a maximum ring size of 8 tetrahedral atoms and containing a promoter metal, and a zirconia-containing layer on the small pore molecular sieve containing the promoter metal, wherein the zirconia-containing layer generally has zirconia particles having an average particle size of about 10 nm to about 500 nm.

[0151] For ease of reference, the above description focuses on the use of a zirconia sol. However, it is to be understood that other metal oxide sols can be used without departing from the present invention. In one embodiment, the catalyst can be prepared by dissolving a metal salt (e.g., a nitrate or acetate salt) in an aqueous zirconia sol (e.g., but not limited to colloidal zirconia hydroxide). In one or more embodiments, the metal salt is a salt of at least one metal selected from the group consisting of La, Ce, Nd, Pr, Cu, Mn, Fe, Ni, Ti, Cr, Zn, Sn, V, Nb, Mo, Hf, Y, and W. The metal salt dissolves and dissociates in the aqueous zirconia sol to form a soluble aqueous metal salt / zirconia sol mixture. Exemplary metal salts include copper (II) nitrate, copper (II) acetate, iron (III) nitrate, and iron (III) acetate. The aqueous zirconia sol has zirconia particles having an average particle size of about 10 nm to about 500 nm. The aqueous metal salt (i.e., promoter metal salt) / zirconia sol mixture is formed having an incipient wetness concentration of about 50 to 100%. In one or more embodiments, higher incipient wetness, particularly approaching 100%, is desired.

[0152] Subsequently, the ammonium or proton exchanged molecular sieve is impregnated with the metal salt / zirconia-based sol mixture. Impregnation can be performed in various mixers known in the art for mixing powders with solutions or dispersions, such as a ribbon mixer or planetary mixer equipped with a nozzle for spraying liquid into the mixer. The impregnated material is dried and calcined in air to form a catalyst comprising a metal exchanged / promoted molecular sieve having a zirconia-containing layer. Calcination of the impregnated material can be performed using various techniques known in the art, including tray calcination, calcination in a rotary kiln, or by using a fluidized bed calciner. Rapid drying and calcination in a single step, for example using a fluidized bed calciner, is preferred in certain embodiments because such a process provides short residence times and uniform drying / calcination on a particle level.

[0153] Without being bound by theory, it is believed that upon drying and calcination, the metal from the metal salt enters the pores of the small pore molecular sieve, migrates to the Brønsted acid sites via a concentration gradient effect in the presence or absence of H2O vapor, and then acts as a promoter metal, while the particles of zirconia (or other metal oxide) do not enter the pore structure of the molecular sieve. Rather, the zirconia forms a rich layer (zirconia-containing layer) on the small pore molecular sieve and / or between the particles to bind them together to form a zeolite particle agglomerate promoted with metal.

[0154] In one or more embodiments, at least one binder compound is added to the aqueous washcoat formulation after the addition and dispersion of the molecular sieve powder, the particles of which are enriched with zirconia. The washcoat including the binder is then applied to a substrate, dried and calcined to produce the final catalyst material. Such additional binder can be selected from any binder known in the art. In one or more embodiments, the additional binder can be a titania, alumina, zirconia, or silica binder known to those skilled in the art. For example, without limitation, the binder can be selected from titanium oxychloride (TiOCl2), titanyl sulfate (TiOSO4), aluminum trihydrate (Al(OH)3), boehmite (AlO(OH)), aluminum nitrate Al(NO3)3, SiO2 sol (e.g., commercially available 1034A) and zirconia compounds.

[0155] Method and exhaust treatment system for reducing NO x x and NO2

[0156] In general, the above-described molecular sieve material having a zirconia-containing layer can be used as a molecular sieve, adsorbent, catalyst, catalyst support, or binder thereof. In one or more embodiments, the material is used as a catalyst.

[0157] Another aspect of the present invention relates to a method for catalyzing a chemical reaction, wherein a catalyst of one or more embodiments is used to catalyze the chemical reaction, wherein the catalyst is used as a catalytically active material.

[0158] The catalyst is particularly suitable for use with nitrogen oxides (NOx). x Selective reduction (SCR) of NH3; a catalyst for the oxidation of NH3, especially for the oxidation of NH3 escaping from diesel engine systems.

[0159] One or more implementations provide selective reduction of nitrogen oxides (NOx). x The method includes, in one or more embodiments, making a NO-containing... x The exhaust gas stream contacts the catalyst of one or more embodiments. In particular, the selective reduction of nitrogen oxides uses a selective catalytic reduction catalyst of an embodiment of the present invention, which comprises a wash coating comprising a microporous molecular sieve having a porous structure with a maximum ring size of 8 tetrahedral atoms and containing a cocatalyst metal, and a zirconium oxide (or other metal oxide) layer on the microporous molecular sieve containing the cocatalyst metal, as a catalytically active material in the reaction in the presence of ammonia or urea.

[0160] Ammonia is the reducing agent chosen for stationary power plants, while urea is the reducing agent chosen for mobile SCR systems. Typically, SCR systems are integrated into the vehicle's exhaust treatment system and generally also contain the following main components: a selective catalytic reduction catalyst according to an embodiment of the invention, comprising a wash coating comprising a porous molecular sieve having a porous structure with a maximum ring size of 8 tetrahedral atoms and containing a co-catalyst metal, and a zirconium oxide (or other metal oxide) layer on the porous molecular sieve containing the co-catalyst metal; and an injector located upstream of the SCR catalyst for injecting a reducing agent, such as ammonia or an ammonia precursor (e.g., urea). In a specific embodiment, the system may include a urea storage tank; a urea pump; a urea metering system; a urea injector / nozzle; and respective control units.

[0161] In other embodiments, the SCR catalyst according to one or more embodiments is used as the SCR catalyst in the exhaust treatment system of a lean-burn gasoline direct injection (GDI) engine. In such cases, the SCR catalyst according to one or more embodiments acts as a passive ammonia-SCR catalyst and is capable of effectively storing ammonia at temperatures of 400°C and higher.

[0162] As used herein, the term "stream" refers broadly to any combination of flowing gas that can contain solid or liquid particulate matter. The term "gaseous stream" or "exhaust stream" refers to a stream of gaseous components, such as the exhaust of a lean-burn engine (i.e., an engine that burns fuel in the presence of excess oxygen), which can contain entrained non-gaseous components, such as liquid droplets, solid particulates, etc. Exhaust streams of lean-burn engines typically further comprise combustion products, products of incomplete combustion, nitrogen oxides, combustible and / or carbonaceous particulate matter (soot), and unreacted oxygen and nitrogen.

[0163] The term nitrogen oxide, NOx, as used in embodiments of the present invention refers to oxides of nitrogen, in particular dinitrogen monoxide (N2O), nitric oxide (NO), dinitrogen trioxide (N2O3), nitrogen dioxide (NO2), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5), and nitric oxide (NO3). x The term nitrogen oxide, NOx, as used in embodiments of the present invention refers to oxides of nitrogen, in particular dinitrogen monoxide (N2O), nitric oxide (NO), dinitrogen trioxide (N2O3), nitrogen dioxide (NO2), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5), and nitric oxide (NO3).

[0164] Another aspect of the present invention relates to an exhaust treatment system. In one or more embodiments, the exhaust treatment system comprises an exhaust stream optionally containing a reductant, such as ammonia, urea, and / or a hydrocarbon, and in particular embodiments, ammonia and / or urea, and a selective catalytic reduction catalyst according to one or more embodiments (which comprises a washcoat layer comprising a small pore molecular sieve having a pore structure and a maximum ring size of 8 tetrahedral atoms and containing a promoter metal and a layer comprising zirconium oxide (or other metal oxide) on the small pore molecular sieve containing the promoter metal). The catalyst is effective to destroy at least a portion of the ammonia in the exhaust stream.

[0165] In one or more embodiments, the catalyst can be disposed on a substrate, such as a filter. A catalyzed or un-catalyzed filter can be upstream or downstream of the catalyst. In one or more embodiments, the system can further comprise a diesel oxidation catalyst. In particular embodiments, the diesel oxidation catalyst is upstream of the catalyst. In other particular embodiments, the diesel oxidation catalyst and catalyzed filter are upstream of the catalyst.

[0166] In particular embodiments, the exhaust is passed from the engine to a downstream location in the exhaust system, and in more particular embodiments, contains NOx x at which a reductant, such as urea, is added and the exhaust stream with the added reductant is passed to the catalyst.

[0167] For example, catalyzed filters, diesel oxidation catalysts, and reductants are described in WO 2008 / 106519, which is incorporated herein by reference. In particular embodiments, the filter comprises a wall-flow filter substrate in which the channels are alternately plugged so that a gaseous stream entering the channels from one direction (the inlet direction) flows through the channel walls and exits the channels from the other direction (the outlet direction).

[0168] An ammonia oxidation catalyst (AMOx) can be provided downstream of the catalyst(s) of one or more embodiments to remove any ammonia that escapes from the system. In particular embodiments, the AMOx catalyst can comprise a platinum group metal, such as platinum, palladium, rhodium, or combinations thereof.

[0169] Such an AMOx catalyst can be used in an exhaust treatment system that includes an SCR catalyst. As discussed in commonly assigned U.S. Patent No. 5,516,497 (the entire contents of which are incorporated herein by reference), a gaseous stream containing oxygen, nitrogen oxides, and ammonia can be passed sequentially through first and second catalysts, the first catalyst promoting reduction of nitrogen oxides and the second catalyst promoting oxidation or other decomposition of excess ammonia. As described in U.S. Patent No. 5,516,497, the first catalyst can be an SCR catalyst comprising a zeolite and the second catalyst can be an AMOx catalyst comprising a zeolite.

[0170] The AMOx and / or SCR catalyst compositions can be coated on a flow-through or a wall-flow filter. If a wall-flow substrate is used, the resulting system is capable of removing particulate matter along with gaseous pollutants. The wall-flow filter substrate can be made of materials known in the art, such as cordierite, aluminum titanate, or silicon carbide. It is understood that the loading of the catalytic composition on a wall-flow substrate depends on the substrate properties, such as porosity and wall thickness, and is generally lower than the loading on a flow-through substrate.

[0171] An exemplary exhaust treatment system is shown in Figure 16 which depicts a schematic of an exhaust treatment system 32. As shown, an exhaust stream containing gaseous pollutants and particulate matter is conveyed from an engine 34 (e.g., a diesel engine, a lean-burn GDI engine, or other lean-burn engine) via an exhaust pipe 36 to a diesel oxidation catalyst (DOC) 38 to a catalyzed soot filter (CSF) to a selective reduction catalyst (SRC) coated with the washcoat composition of the present application. In the DOC 38, unburned gaseous and non-volatile hydrocarbons (i.e., SOF) and carbon monoxide are largely combusted to form carbon dioxide and water. In addition, NO x A certain proportion of the NO of the component can be oxidized to NO2in the DOC.

[0172] The exhaust stream is then conveyed via an exhaust pipe 40 to a catalyzed soot filter (CSF) 42, which traps particulate matter present in the exhaust stream. The CSF 42 is optionally catalyzed passive or active soot regeneration. The CSF 42 can optionally include the SCR composition of the present application to convert NOx present in the exhaust.

[0173] After removal of particulate matter by the CSF 42, the exhaust stream is conveyed via an exhaust pipe 44 to a downstream selective catalytic reduction assembly 46 of the present application for further treatment and / or conversion of NOx The exhaust gas is passed through the SCR assembly 46 at a flow rate that allows sufficient time for the catalyst composition to reduce the NOx content of the exhaust gas at a given temperature. The SCR assembly 46 can be optionally included in the emission treatment system when the CSF 42 already includes an SCR catalyst composition. An injector 50 for introducing a nitrogenous reductant into the exhaust gas stream is located upstream of the SRC 46. The nitrogenous reductant introduced into the exhaust gas stream facilitates the reduction of NOx to N2and water when the gas is exposed to the catalyst composition. If the CSF 42 also contains an SCR catalyst, the injector 50 can be moved to a position upstream of the CSF.

[0174] The application will now be described with reference to the following examples. Before describing several exemplary embodiments of the application, it is to be understood that the application is not limited to the details of construction or process steps set forth in the following description. The application is capable of other embodiments and of being practiced or being carried out in various ways. Example

[0175] Example 1 - 10% Zr02 with zirconyl acetate added to slurry

[0176] Cu exchanged CHA (3.25 wt% CuO, SAR 28) was dispersed in water and recirculated through an in-line homogenizer @ 50 Hz to break up large agglomerates to D90 < 14 pm. Zirconyl acetate binder was then added to achieve a total binder loading of 10 wt% on the calcined washcoat basis. The final pH of the resulting slurry was approximately 4.0. The mixture was then coated onto a cordierite substrate, dried and calcined to 450°C to form an active catalytic washcoat. A forced fan heated oven was used to promote flow-through the part to achieve drying. As zirconyl acetate is very soluble, it moves through the washcoat during drying and forms an enrichment layer on the surface of the CHA. After coating, drying and calcination, the final washcoat composition was 2.9% CuO, 87.1% CHA and 10% Zr02.

[0177] Reference is made to Figure 1 The SCR conversion is relatively constant at the low temperature end 200-300°C and slightly higher at the high temperature end in the 10% Zr02scenario (relative to the same washcoat prepared with only 5% Zr02).

[0178] The zirconyl acetate solution also contained an excess of acetic acid (acetic acid / Zr02molar ratio ~ 1.6) for stability purposes, so more CuO became soluble and migrated to the surface, which explains the selectivity change observed between 450-600°C, where the performance of the 10% Zr02decreased, as it is known that free CuO (ex- exchanged sites) oxidizes NH3 to actually form more NOx relative to those that have already been reduced.

[0179] As Figure 1The ZrO2 enrichment on the washcoat surface is responsible for the reduced N2O production at all temperatures (200-6000C) as shown in Figure 1. This experiment shows the correlation between the zirconia concentration in the washcoat and the N2O production, with higher zirconia amounts resulting in reduced N2O production.

[0180] Example 2 - 5% zirconyl acetate + higher slurry conductivity

[0181] To investigate the effect of more soluble Zr, one slurry batch was made in the same manner as in Example 1, but with only 5 wt% ZrO2 added as zirconyl acetate. After the zirconyl acetate was added, the slurry was split into two samples, labeled Sample 1 and Sample 2. Sample 1 was not further modified, and thus had the same composition as one of the compositions of Example 1.

[0182] To Sample 2, 0.1% ammonium nitrate (NH4NO3) was added to increase the conductivity (as measured using Cole Parmer Item #EW-19601-04). The conductivity was increased from 870 μS / cm to 2200 μS / cm, and the final pH of both slurries was 4.4 (see Table 1).

[0183] Table 1: Solubility of Cu and Zr in aqueous liquid phase of wash coated slurry after centrifugation

[0184]

[0185] The same method as in Example 1 was used, and then the mixture was coated onto a cordierite substrate, dried and calcined to 4500C to form an active catalytic washcoat. A forced fan heated oven was used to promote flow-through the part to achieve drying. Table 1 indicates that the Zr solubility of Sample 2 was 2x higher than Sample 1. Solubility was measured by taking a slurry sample, adding it to a centrifuge tube and subjecting it to 7800 rpm for 2 hours using a Thermo Electron Corporation IEC CL40R centrifuge. The resulting clear water-white to blue supernatant (depending on how much Cu 2+ was soluble) was analyzed using Inductively Coupled Plasma (ICP) to determine the ppm concentration in the liquid phase, and the % soluble fraction of a given element in the liquid phase was calculated based on the slurry solids content and the elemental composition of the washcoat. Table 1 and Table 2 (see Example 3) demonstrate that the solubility of Zr needs to be greater than 15% to as high as 100% soluble in the slurry phase to promote the migration of soluble species (i.e., zirconium compounds) to the surface of the washcoat during the drying process.

[0186] Figure 2 and 3 are scanning electron microscope (SEM) images of Sample 1 and Sample 2, respectively, focused on a portion of the washcoat in a corner of the coated substrate cell. Figure 2 (Example 1) and Figure 3(Example 2) The EDS table results all show higher Zr and Cu element concentrations on the surface. However Figure 3 show visible enrichment bands containing higher Cu and Zr, which directly correlates to the amount of each element soluble in the aqueous slurry phase as confirmed in Table 1.

[0187] Figure 4 is a bar graph comparing Sample 2 and Sample 1 for NOx efficiency for each sample when used in a specific emissions treatment system (results reported as two measurements for each sample and their average). Figure 4 indicates that Sample 2 (higher Zr and Cu on the surface, Figure 3 ) has improved performance compared to Sample 1 ( Figure 2 ). The system results include the use of the same / standardized (constant) DOC as the first catalyst in the system (6.5"φ x 8"L with 70 g / ft 3 of PGM), the second and third catalysts in the system are 8"φ x 6"L 400 / 4.5 coated with Cu / CHA (SCR) slurry, and the fourth catalyst in the system is the same / standardized (constant) catalyzed soot filter (CSF) measured as 8"φ x 10"L. The entire system is used for a medium duty application where low temperature performance is important. The system was aged at 750°C (measured at the diesel oxidation catalyst (DOC) outlet) using a 6.7L engine prior to testing. Efficiency was measured using the EPA75 test cycle and reported as weighted modal data DOC to SCR outlet without any regeneration steps. The temperature at which the data was generated was between 180 and 220°C, with data recorded at an average of approximately 200°C.

[0188] This example demonstrates that the presence of soluble zirconium species in the washcoat results in more zirconium migration to the washcoat surface, which can improve low temperature NO X reduction. However, as described above, the increase in soluble zirconium species in the outer washcoat is also accompanied by an increased copper concentration in the same region, which can be attributed to increased copper migration during the washcoating process. Copper migration is thus detrimental to high temperature NO x conversion.

[0189] Example 3 - 8% Zr02 / 3.25% CuO / CHA

[0190] Step 1 : Dissolve 1.7 kilograms of Cu(II) nitrate crystals in 3.6 kilograms of a commercially available nitric acid based zirconia sol with a 15 wt% Zr02content by mixing at room temperature.

[0191] Step 2: The solution from Step 1 was impregnated onto 18.8 kilograms of spray-dried NH4 / CHA powder and then simultaneously dried / calcined. The product of this step, 3% Zr02 / 3.25% CuO / CHA powder, is shown in the scanning electron microscope (SEM) image at 10,000X magnification in Figure 5 Figure 1. This SEM image shows that the zirconium particles (lighter colored material) are present around and interspersed among the zeolite particles (darker, larger particles).

[0192] Step 3: The calcined powder from Step 2 was then dispersed in water and recirculated through an in-line homogenizer @ 50 Hz to break up large agglomerates to a D90 < 14 μm. An additional 5 wt% zirconyl acetate was added as a binder to achieve a total Zr02loading of approximately 8 wt% based on washcoat after calcination. The final pH of the resulting slurry was 3.8.

[0193] The mixture was then coated onto a cordierite substrate, dried and calcined to 450°C to form an active catalytic coating. A forced fan heating oven was used to promote flow-through the part to achieve drying. After coating, drying and calcination, the final washcoat composition was 3.1% CuO, 89.1% CHA and 7.8% Zr02, and is labeled as Sample 3 in Table 2. Table 2 shows that Sample 3 contained low Cu and Zr solubility due to the pre- preparation step which included a rapid drying / calcination of the 3% Zr02 / 3.25% CuO / CHA powder preparation step. This rapid drying and calcination in air created a rapid concentration gradient in < 1.5 seconds which created a driving force to move Cu 2+ towards the Brønsted acid sites.

[0194] Sample 4 was prepared by dispersing a Cu-exchanged CHA (3.25 wt% CuO, SAR 28) in water and recirculating through an in-line homogenizer @ 50 Hz to break up large agglomerates to a D 90 <14 μm. An additional zirconyl acetate binder was then added to achieve a total binder loading of 5 wt% based on the calcined washcoat. The final pH of the resulting slurry was approximately 4.3. The mixture was then coated onto a cordierite substrate, dried and calcined to 450°C to form an active catalytic coating. The final composition of Sample 4 was 3.1% CuO / 5.0% Zr02 / 91.9% CHA. Sample 4 contained higher soluble Cu and Zr in the slurry phase compared to Sample 3.

[0195] Table 2: Solubility of Cu and Zr in aqueous liquid phase of wash coated slurry after centrifugation

[0196]

[0197] Figures 6A-6Dis a collection of scanning electron microscope (SEM) images of the material of Sample 4. The upper left frame (6A) is an SEM micrograph showing the washcoat distribution within the unit cell at 50X magnification. In a counterclockwise direction, the lower left frame (6B) shows the Cu distribution in the washcoat, as delineated using electron dispersive spectroscopy (EDS), and indicates that Cu is uniformly distributed throughout the washcoat, with slight enrichment at the washcoat surface. Continuing in a counterclockwise direction, the micrograph in the lower right corner (6C) shows the Zr distribution by EDS. There is a distinct band of Zr enrichment at the washcoat surface, which correlates with the Zr solubility in Table 2. In the upper right corner is another SEM micrograph at 10,000X (6D), which focuses on the Zr-enriched layer on the surface, which is approximately 1-3 μm thick. Figures 6A-5D confirm the ZrO2enrichment on the washcoat surface as also observed for Examples 1 and 2.

[0198] Figures 7A-7D is a collection of scanning electron microscope (SEM) images of the material of Sample 3. These figures confirm that the sample with reduced amounts of soluble Cu and Zr did not form any enrichment layers; however, note the layering and particle-to-particle bonding by nano-ZrO2, and that the washcoat also appears more porous. The upper left frame (7A) shows the washcoat distribution within the unit cell at 50X magnification. Continuing in a counterclockwise direction, the lower left frame (7B) confirms that Cu is uniformly distributed throughout the washcoat. In the lower right corner (7C), Zr is shown to be distributed throughout the washcoat, with areas of higher concentration (brighter areas), as in the other samples, but they are more prevalent as the Zr concentration increases. No enrichment of Zr on the washcoat surface was noted. Concluding with the upper right corner (7D), Zr is clearly visible on the surface of some particles and forms bridges between particles. The washcoat also appears more porous. The CHA fines are believed to have been bonded together by the larger particles during the rapid drying / calcination step during the ZrO2 / Cu / CHA composite powder preparation step. The zirconyl acetate added during the slurry preparation / washcoat manufacturing step further bonded the particles together during the washcoat substrate drying and calcination steps, resulting in the final 7.8% ZrO2 / 3.1% CuO, 89.1% CHA washcoat.

[0199] Table 3 summarizes the reactor gas composition and test procedures.

[0200] Table 3: SCR CAEF

[0201]

[0202] Figure 8 is a graph showing the NOxconversion of the material of Sample 3 compared to Sample 4 (which contains Zr enrichment on the washcoat surface) at 200, 250, and 525°C. xReduced stick plots. These samples were first aged at 700°C for 4 hours in 10% steam and air. They were subsequently tested in the reactor according to Table 3. Figure 8 Demonstration of NO reduction at 200°C and 250°C x Reduced slightly, NO x Conversion is significantly higher at 525°C. Sample 3 exhibits a wider performance window (higher zirconium loading, use of less soluble zirconium species), indicating improved Cu 2+ Exchange to Brønsted acid sites and benefit of a heat fixation step prior to incorporation of 3% Zr02 / 3.25% CuO / CHA powder to produce a final washcoat with composition 7.8% Zr02 / 3.1% CuO / 89.1% CHA on a N400 / 4 substrate.

[0203] Figure 9 are stick plots showing NH3slip, NH3storage and N2O production at different temperatures for the material of Example 3. Figure 9 Demonstration of further reduction of N2O for the material of sample 3 compared to the material of sample 4. This can be explained as follows: sample 3 contains a higher Zr02concentration (8% vs 5% for sample 4), is enriched at the particle level, soluble Cu and Zr in the slurry phase are reduced, and Cu 2+ is more efficiently exchanged to Brønsted acid sites. This example shows that the benefit of increased zirconia concentration in the washcoat (e.g. reduced N2O production at low temperature and improved NO x reduction) can be achieved by reducing the dependency on soluble zirconium species, without causing undesirable copper migration.

[0204] Example 4: 5% nanoceria / zirconia on 3.25% CuO / CHA

[0205] First 3.8 kg of 3.25% CuO / CHA were dispersed in 6.2 kg of water, then recirculated through an in-line homogenizer @ 50 Hz to break up large agglomerates to achieve a D 90 <20 μm particle size distribution. To this mixture, 794 g of (Ce 45 Nd5Zr 50 )02aqueous dispersion was added to the mixture and recirculation through the homogenizer was continued until the particle size distribution had a D90< 14 μm. The final slurry had a pH of 4.6.

[0206] The mixture was then coated onto a cordierite substrate, dried and calcined to 450°C to form an active catalytic washcoat. A forced fan heated oven was used to promote flow through the part to achieve drying. After coating, drying and calcination, the final washcoat composition was 2.25% Ce02, 0.25% Nd203, 2.51% Zr02, 3.09% CuO and 91.91% CHA and is labeled as Sample 5 in Table 5.

[0207] Sample 6 was prepared by dispersing Cu exchanged CHA (3.25 wt% CuO, SAR 28) in water, recirculated through an in-line homogenizer at 50 Hz to break up large agglomerates into D 90 <14 μm. Zirconyl acetate binder was then added to achieve a total binder loading of 5 wt% based on the calcined washcoat. The final pH of the resulting slurry was approximately 4.3. The mixture was then coated onto a cordierite substrate, dried and calcined to 450°C to form an active catalytic washcoat. The final composition of Sample 6 was 3.1% CuO / 5.0% Zr02 / 91.9% CHA.

[0208] Table 4: Aqueous dispersion of <1 pm Zr02 particles doped with Ce02 and Nd203

[0209] Trial Nano-CeO2 / Nd2O3 / ZrO2 Units ZrO2+ HfO2 (bal.) 50.1 %, as oxide CeO2 44.9 %, as oxide Nd2O3 5.0 %, as oxide Solid content 25.2 % of dispersion pH 4.96

[0210] Table 5: Solubility of Cu and Zr in aqueous liquid phase of wash coated slurry after centrifugation

[0211]

[0212] Figures 10A-10D is a collection of scanning electron microscope (SEM) images of the material of Sample 5. The upper left frame (10A) is a SEM micrograph showing the washcoat distribution within a number of unit substrate cells at 25X magnification. Clockwise, the lower left frame (10B) shows the Ce distribution in the washcoat as mapped using electron dispersive spectroscopy (EDS) and it indicates that Ce is uniformly distributed throughout the washcoat. Zr and Nd are also both well dispersed based on the sol composition as specified in Table 4. Continuing clockwise, the micrograph in the lower right corner (10C) shows that Cu is uniformly distributed throughout the washcoat and finally, the micrograph in the upper right corner (10D) indicates that porosity in the washcoat is evident once magnified to 500X.

[0213] Referring to Figure 11 Sample 5 had a slight improvement in SCR conversion at 200-250°C, but was slightly less than Sample 6 at temperatures from 250-600°C. Figure 12Sample 5 was shown to be slightly less than sample 6 in terms of N20 production. While not wishing to be bound by theory, it is suspected that the oxidizing properties of Ce02 are at least partially responsible for this result. However, the use of ceria-zirconia composites is believed to have improved quality in oxidizing carbon soot during regeneration, thereby minimizing zeolite fouling. Additionally, metal oxide composites incorporating higher amounts of zirconia than ceria can achieve the desired reduction in N20 production.

[0214] Example 5: 6% Zr02 on 3.25% CuO / CHA

[0215] One kilogram of Cu(II) nitrate crystals were dissolved in 4.5 kilograms of a commercially available nitric acid based zirconia sol having a 15 weight percent Zr02content (ZSL-15N available from Daiichi Kigenso Kagaku Kogyo Co., Ltd) by mixing at room temperature. The resulting solution was impregnated onto 9 kilograms of spray dried NH4 / CHA powder in a blender, followed by simultaneous drying / calcination. The product of this step was a 6% Zr02 / 3.25% CuO / CHA powder. This calcined powder was then dispersed in water and recirculated through an in-line homogenizer @ 50 Hz to break up large agglomerates to a D90 < 14 μm. This rapid drying and calcination in air creates a rapid concentration gradient, not wishing to be bound by theory, which is believed to create a driving force to move Cu 2+ towards the Br0nsted acid sites.

[0216] Figure 13 A powder reactor temperature scan is shown comparing the standard 3.25% ion exchanged Cu / CHA material with the 6% Zr02 / 3.25% CuO / CHA made in this example, the left y-axis provides % conversion of NOx, and the right y-axis provides N20 production in ppm. In this graph, the triangles refer to NOx conversion for the zirconia modified material, the squares refer to NOx conversion for the comparative Cu / CHA material, the circles refer to N20 production for the zirconia modified material, and the diamonds refer to N20 production for the comparative Cu / CHA material. As shown, the zirconia modified CHA material provides improved NOx conversion at low temperature and slightly elevated N20 production at low temperature. The high temperature NOx performance of the two materials is about the same, with the zirconia modified material providing improved N20 production at higher temperatures.

[0217] Example 6: 6% Al203 on 3.25% CuO / CHA

[0218] 1.7 kg of Cu(II) nitrate crystals were dissolved in 5.4 kg of a commercially available nitrate-based alumina sol (available from Sasol's Dispal 23N4-20, a large-crystal boehmite material) with a 20 wt% Al2O3 content at room temperature. The solution was sprayed onto CHA powder in a mixer, and the resulting solution was then impregnated onto 18.2 kg of spray-dried NH4 / CHA powder, followed by simultaneous drying / calcination. The product of this step was a 6% Al2 / O3 / 3.25% CuO / CHA powder. The calcined powder was then dispersed in water and circulated through an online homogenizer at 50 Hz to break down large agglomerates to D90 < 14 μm. This rapid drying and calcination in air generated a rapid concentration gradient within < 1.5 seconds, unconstrained by theory, which is believed to generate a driving force for Cu... 2+ It moves toward the Brønsted acid site.

[0219] The catalyst materials of Examples 5 and 6 were hydrothermally aged at 800°C for 6 hours in the presence of 10% H₂O, and their NOx conversion performance was compared with that of unmodified CuO / CHA material aged under the same conditions. The results are listed below. Figure 14 In the figure, CuO / CHA materials without zirconium oxide or alumina sol are represented by rhombuses. The catalyst material of Example 5 (6% ZrO2 / 3.25% CuO / CHA) is represented by a triangle, and the catalyst material of Example 6 (6% Al2 / O3 / 3.25% CuO / CHA) is represented by a square. As shown in the figure, CHA materials modified with zirconium oxide or alumina perform better than unmodified materials at higher temperatures.

[0220] Example 7: 8% Zr02 / 2% Y203 on 4.4% CuO / CHA

[0221] 0.5 kg of a commercially available 60 / 40 ZrO2 / Y2O3 mixed sol was dispersed in 41 kg of DI water containing 0.17 kg of 90% acetic acid. 2.2 kg of a commercially available nitrate-based zirconium oxide sol (available from Daiichi Kigenso Kagaku Kogyo Co., Ltd., ZSL-15N) with a ZrO2 content of 15 wt% was added to the dispersion prepared in the previous step by mixing at room temperature. 5.4 kg of spray-dried 4.91% CuO / CHA was added to the resulting dispersion to produce 8% ZrO2 / 2% Y2O3 / 4.40% CuO / CHA. The product mixture from the previous step was then recycled through an online homogenizer at 50 Hz to break down large agglomerates to D90 < 14 μm. The resulting slurry was then applied to a 400 / 4 cordierite substrate, dried, and calcined at 450°C to achieve a dry weight gain of 2.75 g / cubic inch.

[0222] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the materials and methods discussed herein (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein unless otherwise indicated herein or otherwise apparent from context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended to illuminate the application and is not intended to otherwise limit the scope of the application unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential.

[0223] References throughout this specification to "one implementation", "certain implementations", "one or more implementations" or "implementation" mean that a particular element, structure, material, or characteristic described in connection with the implementation is included in at least one implementation of the application. The appearances of the phrases "in one or more implementations", "in certain implementations", "in one implementation", or "in an implementation" in various places in the specification are not necessarily all referring to the same implementation of the application. Furthermore, a particular element, structure, material, or characteristic can be combined in any suitable manner in one or more implementations.

[0224] While the application has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and in some instances some features of the application will be employed without a corresponding use of other features. Accordingly, it is intended that the application should not be limited to any particular embodiments described herein and that the application can be carried out with other modifications as well.

Claims

1. A method for preparing a catalyst composition for the selective reduction of nitrogen oxides, the method comprising: A salt of at least one cocatalytic metal is dissolved in an aqueous metal oxide sol, wherein the salt of the at least one cocatalytic metal dissociates in the aqueous metal oxide sol to form an aqueous metal salt / metal oxide sol mixture, wherein the metal oxide particles comprise one or more oxides of transition metals or aluminum or lanthanides from Group 3 or Group 4 of the periodic table. The aqueous metal salt / metal oxide sol mixture is used to treat ammonium or proton-exchanged small-pore molecular sieve particles with a porous structure and a maximum ring size of 8 tetrahedral atoms to impregnate the co-catalyst metal into the pore structure of the small-pore molecular sieve; and Drying and calcining microporous molecular sieve particles to form a catalyst composition, wherein the catalyst composition comprises microporous molecular sieve particles impregnated with a co-catalyst metal, and metal oxide particles dispersed within the microporous molecular sieve particles and outside the pore structure of the microporous molecular sieve particles.

2. The method of claim 1, wherein the metal oxide is selected from zirconium oxide, aluminum oxide, cerium dioxide, hafnium dioxide, yttrium oxide, and combinations thereof.

3. The method of claim 1, wherein the metal oxide comprises zirconium oxide.

4. The method of claim 1, wherein the metal oxide sol has an average particle size of 10 nm to 500 nm.

5. The method of claim 1, wherein the metal oxide sol has a D that is 10 times larger than the pore opening of the molecular sieve. 10 granularity.

6. The method of claim 1, wherein the metal oxide sol has a density of 10 nm or greater. 10 granularity.

7. The method of any one of claims 1 to 6, wherein the co-catalyst metal is selected from Cu, Co, Ni, La, Mn, Fe, V, Ag, Ce, Nd, Pr, Ti, Cr, Zn, Sn, Nb, Mo, Hf, Y, W, and combinations thereof.

8. The method of any one of claims 1 to 6, wherein the metal oxide sol is selected from zirconium hydroxide sol, nano-sized hydrated zirconium oxide sol, alumina sol, zirconium oxide-yttrium oxide sol, zirconium oxide-alumina sol, zirconium oxide-cerium dioxide sol, organozirconium sol, and mixtures thereof.

9. The method of any one of claims 1 to 6, wherein the microporous molecular sieve has d6r units.

10. The method of any one of claims 1 to 6, wherein the microporous molecular sieve has a structural type selected from AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, LTN, MSO, SAS, SAT, SAV, SFW and TSC.

11. The method of any one of claims 1 to 6, wherein the microporous molecular sieve has a CHA crystal structure.

12. The method of any one of claims 1 to 6, wherein the co-catalyst metal comprises Cu, Fe, or a combination thereof.

13. The method of any one of claims 1 to 6, further comprising the steps of: mixing the catalyst composition with water to form a wash-coating slurry; applying the wash-coating slurry onto a substrate to form a wash-coating layer thereon; and drying and calcining the substrate to form a catalyst article.

14. The method of claim 13, further comprising adding a water-soluble metal oxide compound to the washing slurry to increase its total metal oxide content.

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