High transition metal loading for ammonia slip catalyst

Abstract

A catalyst comprising a first catalyst coating and a second catalyst coating, wherein the first catalyst coating comprises an ammonia oxidation catalyst, and wherein the second catalyst coating comprises an SCR catalyst comprising a transition metal on a support, wherein a transition metal to Al molar ratio is greater than about 0.43.

Description

High Transition Metal Loading for Ammonia Slip CatalystBACKGROUND OF THE INVENTION

[0001] Hydrocarbon combustion in diesel engines, stationary gas turbines, and other systems generates exhaust gas that must be treated to remove nitrogen oxides (NOx), which comprises NO (nitric oxide) and NO2(nitrogen dioxide), with NO being the majority of the NOx formed. NOXis known to cause a number of health issues in people as well as causing a number of detrimental environmental effects including the formation of smog and acid rain. To mitigate both the human and environmental impact from NOXin exhaust gas, it is desirable to eliminate these undesirable components, preferably by a process that does not generate other noxious or toxic substances.

[0002] Exhaust gas generated in lean-burn and diesel engines is generally oxidative. NOXneeds to be reduced selectively with a catalyst and a reductant in a process known as selective catalytic reduction (SCR) that converts NOXinto elemental nitrogen (N2) and water. In an SCR process, a gaseous reductant, typically anhydrous ammonia, aqueous ammonia, or urea, is added to an exhaust gas stream prior to the exhaust gas contacting the catalyst. The reductant is absorbed onto the catalyst and the NOXis reduced as the gases pass through or over the catalyzed substrate. In order to maximize the conversion of NOX, it is often necessary to add more than a stoichiometric amount of ammonia to the gas stream. However, release of the excess ammonia into the atmosphere would be detrimental to the health of people and to the environment. In addition, ammonia is caustic, especially in its aqueous form. Condensation of ammonia and water in regions of the exhaust line downstream of the exhaust catalysts can result in a corrosive mixture that can damage the exhaust system. Therefore, the release of ammonia in exhaust gas should be eliminated. In many conventional exhaust systems, an ammonia oxidation catalyst (also known as an ammonia slip catalyst or "ASC") is installed downstream of the SCR catalyst to remove ammonia from the exhaust gas by converting it to nitrogen. The use of ammonia slip catalysts can allow for NOXconversions of greater than 90% over a typical diesel driving cycle.

[0003] It would be desirable to have a catalyst that provides for both NOx removal by SCR and for selective ammonia conversion to nitrogen, where ammonia conversion occurs over a wide range of temperatures in a vehicle's driving cycle, and minimal nitrogen oxide and nitrous oxide byproducts are formed.

[0004] Current ammonia slip catalyst formulations typically show an increase in NOx remake and a decrease in NOx conversion after hydrothermal aging. The generation of NOx over the ASC is not ideal and will be an increasingly important factor when considering technologies for future legislation.SUMMARY OF THE INVENTION

[0005] According to some aspects of the present invention, a catalyst comprises a first catalyst coating and a second catalyst coating, wherein the first catalyst coating comprises an ammonia oxidation catalyst, and wherein the second catalyst coating comprises an SCR catalyst comprising a transition metal on a support, wherein the transition metal is present in an amount of greater than about 3.5 wt% of the SCR catalyst.

[0006] According to some aspects of the present invention, a catalyst comprises a first catalyst coating and a second catalyst coating, wherein the first catalyst coating comprises an ammonia oxidation catalyst, and wherein the second catalyst coating comprises an SCR catalyst comprising a transition metal on a support, wherein a transition metal to Al molar ratio is greater than about 0.43. In some aspects, the transition metal to Al molar ratio is greater than about 0.44; greater than about 0.45; greater than about 0.46; about 0.45 to about 0.65; about 0.46 to about 0.65; about 0.45 to about 0.59; or about 0.46 to about 0.59.

[0007] In some aspects, the support comprises a molecular sieve. Examples of suitable molecular sieves may include CHA, AEI, FER, BEA, or combinations thereof. In some aspects, a suitable transition metal may comprise Cu, Fe, or combinations there. In some aspects, the transition metal is present in an amount of greater than about 4 wt% of the SCR catalyst.

[0008] According to some aspects, an ammonia oxidation catalyst comprises a platinum group metal on a support. In some aspects, the ammonia oxidation catalyst comprises a platinum group metal on a support comprising a refractory metal oxide. In some aspects, the ammonia oxidation catalyst comprises a platinum group metal on a support comprising a molecular sieve.

[0009] In certain aspects, the catalyst includes a substrate having an inlet and an outlet relative to a direction of flow of exhaust gas, wherein the first catalyst coating extends from the outletof the substrate toward the inlet, covering less than a full length of the substrate, and the second coating extends the entire length of the substrate, completely overlapping the first coating. In some aspects, a catalyst includes a substrate having an inlet end and an outlet end relative to a direction of flow of exhaust gas, wherein the first catalyst coating extends from the outlet of the substrate toward the inlet, covering less than a full length of the substrate, and the second coating extends from the inlet end towards the outlet end, partially overlapping the first coating.

[0010] In certain aspects, the catalyst provides higher NOx conversion than a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less, when tested as fresh catalysts under equivalent conditions. In certain aspects, the catalyst provides higher NOx conversion than a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less, when tested as hydrothermally aged catalysts under equivalent conditions. In certain aspects, the catalyst provides lower NOx remake than a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less, when tested as hydrothermally aged catalysts under equivalent conditions.

[0011] According to some aspects, a method of reducing emissions for an exhaust steam comprises contacting the exhaust stream with a catalyst article as described herein. In some aspects, the weight ratio of ammonia to NOx in the exhaust gas is >1.0 for at least a portion of an operating time. In some aspects, the weight ratio of ammonia to NOx in the exhaust gas is >2.0 for at least a portion of an operating time. In some aspects, the catalyst provides higher NOx conversion compared to a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less. In some aspects, the catalyst provides lower NOx remake compared to a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less.

[0012] According to some aspects, a system comprises a catalyst as described herein and a means for introducing a nitrogenous reductant upstream of the catalyst.BRI EF DESCRI PTION OF DRAWI NGS

[0013] Figure 1 shows NH3oxidation function of the tested catalysts.

[0014] Figure 2 shows N2O make of the tested catalysts.

[0015] Figure 3 shows NOx remake of the tested catalysts.

[0016] Figure 4 shows NOx conversion of the tested catalysts.

[0017] Figure 5 shows N2O make of the tested catalysts.

[0018] Figure 6 shows NH3conversion of catalyst C and D

[0019] Figure 7 shows NOx remake of catalyst C and D

[0020] Figure 8 shows NOx conversion of catalyst C and D

[0021] Figure 9 shows NH3conversion of catalyst E, F, G and H

[0022] Figure 10 shows NOx conversion of catalyst E, F, G and H

[0023] Figure 11 shows NOx conversion of catalyst E, F, G and H

[0024] Figure 12 shows NH3conversion and NOx make of catalyst J and I

[0025] Figure 13 shows NH3conversion of catalyst K and L

[0026] Figure 14 shows NOx make of catalyst K and L

[0027] Figure 15 shows NOx conversion and N2O make of catalyst K and L

[0028] Figure 16 shows NH3conversion of catalyst M, N and O

[0029] Figure 17 shows NOx make of catalyst M, N and O

[0030] Figure 18 shows NOx conversion and N2O make of catalyst M, N and O

[0031] Figure 19 shows NH3conversion of catalyst P and Q

[0032] Figure 20 shows NOx make of catalyst P and QDETAILED DESCRI PTION OF THE I NVENTION

[0033] Catalysts, catalyst articles, systems, and methods of the present invention relate to ammonia slip catalysts formulated to provide improved NOx conversion and decreased NOx remake with minimal impact to NH3oxidative function. Catalyst articles of the present invention may include a substrate having a first coating comprising an ammonia oxidation component and a second coating comprising a selective catalytic reduction ("SCR") component, wherein the SCR catalyst has a high transition metal content.

[0034] It has surprisingly been found that including a high transition metal content in a second coating of an ammonia slip catalyst substantially boosts NOx conversion performance of catalysts when tested fresh while having a minimal impact to NH3oxidation function. Further, after hydrothermal aging, the high transition metal content substantially decreases NOx remake and boosts NOx conversion, with minimal impact to NH3oxidation function. When tested on engine, the high transition metal content has shown to substantially improve NOx conversion function at high ammonia to NOx ratios ("ANRs"), such as ANR > 2, with minimal impact on selectivity. Such benefits are surprising as the opposite trend is observed in SCR catalysts where high transition metal content results in worse NOx conversion due to over-oxidation of NH3.

[0035] The catalysts, catalyst articles, and specific configurations are described in further detail below.

[0036] SCR Catalyst with High Transition Metal Content

[0037] Catalyst articles of the present invention may include a second coating comprising an SCR catalyst. In some embodiments, the SCR catalyst comprises a support, such as a molecular sieve, with a transition metal. As described herein, it has been found that an SCR catalyst comprising a support with high transition metal loading provides unexpected benefits.

[0038] In certain embodiments, the SCR catalyst comprises a transition metal on a support. In some embodiments the support comprises a molecular sieve. In some embodiments, the support comprises a metal oxide. In certain embodiments, the SCR catalyst comprises CuCHA, FeCHA, CuAEI, FeAEI, CuFER, FeFER, CuBEA, or FeBEA.

[0039] In some embodiments, a high transition metal content may be defined by a transition metal to Al molar ratio. As used herein, a high transition metal content may be considered a transition metal to Al molar ratio higher than the traditional molar ratios of 0.35 to 0.4. In some embodiments, the SCR catalyst comprises a transition metal to Al molar ratio of about 0.40 to about 0.65; about 0.41 to about 0.65; about 0.42 to about 0.65; about 0.43 to about 0.65; about 0.44 to about 0.65; about 0.45 to about 0.64; about 0.45 to about 0.63; about 0.45 to about 0.62; about 0.45 to about 0.62; about 0.46 to about 0.61; about 0.47 to about 0.60; about 0.48 to about 0.59; about 0.45 to about 0.59; about 0.46 to about 0.59; about 0.45; about 0.46; about 0.47; about 0.48; about 0.49; about 0.50; about 0.51; about 0.52; about 0.53; about 0.54; about 0.55; about 0.56; about 0.57; about 0.58; about 0.59; about 0.60; about 0.61; about 0.62; about 0.63; about 0.64; about 0.65; greater than about 0.40, greater than about 0.41; greater than about 0.42; greater than about 0.43; greater than about 0.44; greater than about 0.45; greater than about 0.46; greater than about 0.47; or greater than about 0.50. In some embodiments, the transition metal is Cu and therefore this ratio is a Cu:AI molar ratio. In some embodiments, the transition metal is Fe and therefore this ratio is a Fe:AI molar ratio.

[0040] In some embodiments, a high transition metal content may be defined by transition metal weight percent of the SCR catalyst. In some embodiments, the SCR catalyst comprises a transition metal in an amount of greater than about 4 wt%; greater than about 4.1 wt%; greater than about 4.2 wt%; greater than about 4.3 wt%; greater than about 4.4 wt%; greater than about 4.5 wt%; greater than about 4.6 wt%; greater than about 4.7 wt%; greater than about 4.8 wt%; about 4 wt%; about 4.1 wt%; about 4.2 wt%; about 4.3 wt%; about 4.4 wt%; about 4.5wt%; about 4.6 wt%; about 4.7 wt%; about 4.8 wt%; about 4.9 wt%; about 5 wt%; about 5.1 wt%; about 5.2 wt%; about 5.3 wt%; about 5.4 wt%; about 5.5 wt%; about 3.5 wt% to about 5.8 wt%; about 3.6 wt% to about 5.8 wt%; about 3.7 wt% to about 5.8 wt%; about 3.8 wt% to about5.8 wt%; about 3.9 wt% to about 5.7 wt%; about 4 wt% to about 5.6 wt%; about 4.1 wt% to about 5.5 wt%; about 4.2 wt% to about 5.4 wt%; about 4.3 wt% to about 5.3 wt%; about 4.4 wt% to about 5.2 wt%; about 4.5 wt% to about 5.1 wt%; about 4.6 wt% to about 5 wt%; or about 4.7 wt% to about 4.9 wt%, where the wt% is relative to the SCR catalyst. In some embodiments, the transition metal is Cu and therefore these weight percentages are weight percent of Cu in the SCR catalyst. In a preferred embodiment, the SCR catalyst comprises a transition metal in an amount of between 3.5 wt% and 7 wt%, preferably between 4 wt% and6.8 wt%, e.g. between 4.1 wt% and 6.5 wt% or from 4.2 wt% to 6.2 wt%, where the wt% is relative to the SCR catalyst.

[0041] The SCR catalyst may comprise, or consist essentially of, a metal oxide based SCR catalyst formulation, a base metal based SCR catalyst formulation, a molecular sieve based SCR catalyst formulation, a metal exchanged molecular sieve, or mixtures thereof. Such SCR catalyst formulations are known in the art. Typical compositions are generally described in U.S. Pat. Nos. 4,010,238 and 4,085,193, the entire contents of which are incorporated herein by reference. Preferably, the SCR catalyst comprises a metal exchanged molecular sieve.

[0042] In some embodiments, the selective catalytic reduction composition may comprise, or consist essentially of, a molecular sieve based SCR catalyst. The molecular sieve based SCR catalyst comprises a molecular sieve, which is optionally a transition metal exchanged molecular sieve.

[0043] In general, the molecular sieve based SCR catalyst formulation may comprise a molecular sieve having an aluminosilicate framework (e.g. zeolite), an aluminophosphate framework (e.g. AlPO), a silicoaluminophosphate framework (e.g. SAPO), a heteroatomcontaining aluminosilicate framework, a heteroatom-containing aluminophosphate framework (e.g. MeAlPO, where Me is a metal), or a heteroatom-containing silicoaluminophosphate framework (e.g. MeAPSO, where Me is a metal), or mixtures thereof. The heteroatom (i.e. in a heteroatom-containing framework) may be selected from the group consisting of boron (B), gallium (Ga), titanium (Ti), zirconium (Zr), zinc (Zn), iron (Fe), vanadium (V) and combinations of any two or more thereof. It is preferred that the heteroatom is a metal (e.g. each of the above heteroatom-containing frameworks may be a metal-containing framework).

[0044] It is preferable that the molecular sieve based SCR catalyst formulation comprises, or consist essentially of, a molecular sieve having an aluminosilicate framework (e.g. zeolite) or a silicoaluminophosphate framework (e.g. SAPO). A zeolitic molecular sieve is a microporous aluminosilicate having any one of the framework structures listed in the Database of Zeolite Structures published by the International Zeolite Association (IZA). The framework structures include, but are not limited to those of the CHA, FAU, BEA, MFI, MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5.

[0045] When the molecular sieve has an aluminosilicate framework (e.g. the molecular sieve is a zeolite), then typically the molecular sieve has a silica to alumina molar ratio (SAR) of from 5 to 200 (e.g. 10 to 200), 10 to 100 (e.g. 10 to 30 or 20 to 80), such as 12 to 40, or 15 to 30. In some embodiments, a suitable molecular sieve has a SAR of > 200; > 600; or > 1200. In some embodiments, the molecular sieve has a SAR of from about 1500 to about 2100.

[0046] Typically, the molecular sieve is microporous. A microporous molecular sieve has pores with a diameter of less than 2 nm (e.g. in accordance with the IUPAC definition of "microporous" [see Pure & Appl. Chem., 66(8), (1994), 1739-1758)]).

[0047] The molecular sieve based SCR catalyst may comprise a small pore molecular sieve (e.g. a molecular sieve having a maximum ring size of eight tetrahedral atoms), a medium pore molecular sieve (e.g. a molecular sieve having a maximum ring size of ten tetrahedral atoms) or a large pore molecular sieve (e.g. a molecular sieve having a maximum ring size of twelve tetrahedral atoms) or a combination of two or more thereof.

[0048] When the molecular sieve is a small pore molecular sieve, then the small pore molecular sieve may have a framework structure represented by a Framework Type Code (FTC) selected from the group consisting of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, LTA, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SFW, SIV, THO, TSC, UEI, UFI, VNI, YUG and ZON, or a mixture and / or an intergrowth of two or more thereof. Preferably, the small pore molecular sieve has a framework structure represented by a FTC selected from the group consisting of CHA, LEV, AEI, AFX, EM, ERI, LTA, SFW, KFI, DDR and ITE. More preferably, the small pore molecular sieve has a framework structure represented by a FTC selected from the group consisting of CHA and AEL The small pore molecular sieve may have a framework structure represented by the FTC CHA. The small pore molecular sieve may have a framework structure represented by the FTC AELWhen the small pore molecular sieve is a zeolite and has a framework represented by the FTC CHA, then the zeolite may be chabazite.

[0049] When the molecular sieve is a medium pore molecular sieve, then the medium pore molecular sieve may have a framework structure represented by a Framework Type Code (FTC) selected from the group consisting of AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, ELIO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, N ES, OBW, -PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, -SVR, SZR, TER, TON, TU N, UOS, VSV, WEI and WEN, or a mixture and / or an intergrowth of two or more thereof. Preferably, the medium pore molecular sieve has a framework structure represented by a FTC selected from the group consisting of FER, MEL, MFI, and STT. More preferably, the medium pore molecular sieve has a framework structure represented by a FTC selected from the group consisting of FER and MFI, particularly MFL When the medium pore molecular sieve is a zeolite and has a framework represented by the FTC FER or MFI, then the zeolite may be ferrierite, silicalite, or ZSM-5.

[0050] When the molecular sieve is a large pore molecular sieve, then the large pore molecular sieve may have a framework structure represented by a Framework Type Code (FTC) selected from the group consisting of AFI, AFR, AFS, AFY, ASV, ATO, ATS, BEA, BEC, BOG, BPH, BSV, CAN, CON, CZP, DFO, EMT, EON, EZT, FAU, GME, GON, IFR, ISV, ITG, IWR, IWS, IWV, IWW, JSR, LTF, LTL, MAZ, MEI, MOR, MOZ, MSE, MTW, NPO, OFF, OKO, OSI, -RON, RWY, SAF, SAO, SBE, SBS, SBT, SEW, SFE, SFO, SFS, SFV, SOF, SOS, STO, SSF, SSY, USI, UWY, and VET, or a mixture and / or an intergrowth of two or more thereof. Preferably, the large pore molecular sieve has a framework structure represented by a FTC selected from the group consisting of AFI, BEA, MAZ, MOR, and OFF. More preferably, the large pore molecular sieve has a framework structure represented by a FTC selected from the group consisting of BEA, MOR and MFL When the large pore molecular sieve is a zeolite and has a framework represented by the FTC BEA, FAU or MOR, then the zeolite may be a beta zeolite, faujasite, zeolite Y, zeolite X or mordenite.

[0051] The molecular sieve based SCR catalyst preferably comprises a transition metal exchanged molecular sieve. A metal exchanged molecular sieve can have at least one metal from one of the groups VB, VIB, VI I B, VI 11 B, IB, or 11 B of the periodic table deposited onto extraframework sites on the external surface or within the channels, cavities, or cages of the molecular sieves. Metals may be in one of several forms, including, but not limited to, zero valent metal atoms or clusters, isolated cations, mononuclear or polynuclear oxycations, or asextended metal oxides. The transition metal may be selected from the group consisting of cobalt, copper, iron, manganese, nickel, palladium, platinum, ruthenium, rhenium, and combinations thereof.

[0052] The transition metal may be present on an extra-framework site on the external surface of the molecular sieve or within a channel, cavity or cage of the molecular sieve.

[0053] The selective catalytic reduction composition may comprise, or consist essentially of, a metal oxide based SCR catalyst formulation. The metal oxide based SCR catalyst formulation comprises vanadium or tungsten or a mixture thereof supported on a refractory oxide. The refractory oxide may be selected from the group consisting of alumina, silica, titania, zirconia, ceria and combinations thereof.

[0054] The metal oxide based SCR catalyst formulation may comprise, or consist essentially of, an oxide of vanadium (e.g. V2O5) and / or an oxide of tungsten (e.g. WO3) supported on a refractory oxide selected from the group consisting of titania (e.g. TiO2), ceria (e.g. CeO2), and a mixed or composite oxide of cerium and zirconium (e.g. CexZr(l x)O2, wherein x = 0.1 to 0.9, preferably x = 0.2 to 0.5).

[0055] When the refractory oxide is titania (e.g. TiO2), then preferably the concentration of the oxide of vanadium is from 0.5 to 6 wt% (e.g. of the metal oxide based SCR formulation) and / or the concentration of the oxide of tungsten (e.g. WO3) is from 5 to 20 wt%. More preferably, the oxide of vanadium (e.g. V2Os) and the oxide of tungsten (e.g. WO3) are supported on titania (e.g. TiO2). These catalysts may contain other inorganic materials such as SiO2and ZrO2acting as binders and promoters.

[0056] When the refractory oxide is ceria (e.g. CeO2), then preferably the concentration of the oxide of vanadium is from 0.1 to 9 wt% (e.g. of the metal oxide based SCR formulation) and / or the concentration of the oxide of tungsten (e.g. WO3) is from 0.1 to 9 wt%.

[0057] The metal oxide based SCR catalyst formulation may comprise, or consist essentially of, an oxide of vanadium (e.g. V2O5) and optionally an oxide of tungsten (e.g. WO3), supported on titania (e.g. TiO2).

[0058] The selective catalytic reduction composition may comprise, or consist essentially of, a base metal based SCR catalyst formulation. Suitable base metals may include vanadium (V), molybdenum (Mo) and tungsten (W), chromium (Cr), cerium (Ce), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu), and mixtures thereof.

[0059] When the SCR catalyst is a base metal or mixed base metal oxide, the catalyst article can further comprise at least one base metal promoter. As used herein, a "promoter" is understood to mean a substance that when added into a catalyst, increases the activity of the catalyst. The base metal promoter can be in the form of a metal, an oxide of the metal, or a mixture thereof. The at least one base metal catalyst promoter may be selected from neodymium (Nd), barium (Ba), cerium (Ce), lanthanum (La), praseodymium (Pr), magnesium (Mg), calcium (Ca), manganese (Mn), zinc (Zn), niobium (Nb), zirconium (Zr), molybdenum (Mo), tin (Sn), tantalum (Ta), strontium (Sr) and oxides thereof. The at least one base metal catalyst promoter can preferably be MnO2, Mn2O3, Fe2O3, SnO2, CuO, CoO, CeO2and mixtures thereof. The at least one base metal catalyst promoter may be added to the catalyst in the form of a salt in an aqueous solution, such as a nitrate or an acetate. The at least one base metal catalyst promoter and at least one base metal catalyst, e.g., copper, may be impregnated from an aqueous solution onto the oxide support material(s), may be added into a washcoat comprising the oxide support material(s), or may be impregnated into a support previously coated with the washcoat.

[0060] Catalyst articles and systems of the present invention may include one or more SCR catalyst. In some embodiments, a catalyst article may include a first SCR catalyst and a second SCR catalyst. In some embodiments, the first SCR catalyst and the second SCR catalyst may comprise the same formulation as each other. In some embodiments, the first SCR catalyst and the second SCR catalyst may comprise different formulations than each other.

[0061] Ammonia Oxidation Catalyst

[0062] Catalyst articles of the present invention may include a first coating comprising an ammonia oxidation catalyst. An ammonia oxidation catalyst may be formulated to oxidize excess ammonia and prevent it from being released to the atmosphere. The ammonia contained in an exhaust gas stream is reacted with oxygen over the ammonia oxidation component to form N2over a catalyst.

[0063] According to some embodiments, the ammonia oxidation catalyst may include a supported platinum group metal component which is effective to remove ammonia from the exhaust gas stream. In some embodiments, the platinum group metal component includes platinum, palladium, ruthenium, rhodium, iridium, osmium, or combinations thereof. In some embodiments, the platinum metal component comprises platinum and / or palladium. In some embodiments, the platinum group metal component comprises platinum. In some embodiments, the platinum group metal component comprises palladium.

[0064] According to some embodiments, the platinum group metal component is supported on a high surface area refractory metal oxide support. Examples of suitable high surface area refractory metal oxides include, but are not limited to, alumina, silica, titania, ceria, and zirconia, as well as physical mixtures, chemical combinations and / or atomically-doped combinations thereof. In some embodiments, the refractory metal oxide may contain a mixed oxide such as silica-alumina, amorphous or crystalline aluminosilicates, alumina-zirconia, alumina-lanthana, alumina-chromia, alumina-baria, alumina-ceria, and the like. An exemplary refractory metal oxide comprises high surface area y-alumina having a specific surface area of about 50 to about 300 m2 / g.

[0065] In some embodiments, the ammonia oxidation catalyst may include a zeolitic or non- zeolitic molecular sieve, which may have any one of the framework structures as described in the SCR Catalyst section above. The framework structures include, but are not limited to those of the CHA, AEI, FER, FAU, BEA, MFI, and MOR types. A suitable molecular sieve may comprise a small pore molecular sieve (e.g. a molecular sieve having a maximum ring size of eight tetrahedral atoms), a medium pore molecular sieve (e.g. a molecular sieve having a maximum ring size of ten tetrahedral atoms), a large pore molecular sieve (e.g. a molecular sieve having a maximum ring size of twelve tetrahedral atoms), or a combination of two or more thereof.

[0066] In some embodiments, a platinum group metal may be supported by the molecular sieve, being distributed on the external surface or in the channels, cavities, or cages of the molecular sieve. In some embodiments, a molecular sieve component may be physically mixed with an oxide-supported platinum metal group component.

[0067] In some embodiments, a platinum group metal is present on the support in an amount of about 0.03 wt% to about 2.5 wt%; about 0.01 wt% to about 5 wt%; about 0.02 to about 4.5 wt%; about 0.03 wt% to about 4 wt%; about 0.03 to about 3.5 wt%; about 0.03 to about 3 wt%; about 0.01 wt% to about 10 wt%; about 0.05 wt% to about 10 wt%; about 0.1 wt% to about 10 wt%; about 0.3 wt% to about 10 wt%; about 0.5 wt% to about 10 wt%; about 1 wt% to about 6 wt%; about 1.5 wt% to about 4 wt%; about 10 wt%; about 0.01 wt%; about 0.02 wt%; about 0.03 wt%; about 0.04 wt%; about 0.05 wt%; about 0.07 wt%; about 0.1 wt%; about 0.2 wt%; about 0.3 wt%; about 0.4 wt%; about 0.5 wt%; about 1 wt%; about 2 wt%; about 2.5 wt%; about 3 wt%; about 4 wt%; about 5 wt%; about 6 wt%; about 7 wt%; about 8 wt%; about 9 wt%; or about 10 wt%, wherein the wt% is of the total weight of the platinum group metal and the support.

[0068] In some embodiments, the first coating may include an ammonia oxidation catalyst blended with an SCR catalyst. The SCR catalyst may consist of any one of the SCR catalysts described in the preceding section. In some embodiments, the first coating consists of a physical mixture of an oxide-supported platinum group metal and an SCR catalyst. In some embodiments, a platinum group metal may be distributed on the external surface or in the channels, cavities, or cages of the SCR catalyst.

[0069] Substrate

[0070] Catalyst articles of the present invention may each further comprise a flow-through substrate or filter substrate. In one embodiment, the catalyst may be coated onto the flow- through or filter substrate, and preferably deposited on the flow-through or filter substrate using a washcoat procedure.

[0071] The combination of an SCR catalyst and a filter is known as a selective catalytic reduction filter (SCRF catalyst). An SCRF catalyst is a single-substrate device that combines the functionality of an SCR and particulate filter, and is suitable for embodiments of the present invention as desired. Description of and references to the SCR catalyst throughout this application are understood to include the SCRF catalyst as well, where applicable.

[0072] The flow-through or filter substrate is a substrate that is capable of containing catalyst / adsorber components. The substrate is preferably a ceramic substrate or a metallic substrate. The ceramic substrate may be made of any suitable refractory material, e.g., alumina, silica, titania, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicates, magnesium silicates, aluminosilicates, metallo aluminosilicates (such as cordierite and spudomene), or a mixture or mixed oxide of any two or more thereof. Cordierite, a magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0073] The metallic substrates may be made of any suitable metal, and in particular heat- resistant metals and metal alloys such as titanium and stainless steel as well as ferritic alloys containing iron, nickel, chromium, and / or aluminum in addition to other trace metals.

[0074] The flow-through substrate is preferably a flow-through monolith having a honeycomb structure with many small, parallel thin-walled channels running axially through the substrate and extending throughout from an inlet or an outlet of the substrate. The channel cross-section of the substrate may be any shape, but is preferably square, sinusoidal, triangular, rectangular, hexagonal, trapezoidal, circular, or oval. The flow-through substrate may also be high porosity which allows the catalyst to penetrate into the substrate walls.

[0075] The filter substrate is preferably a wall-flow monolith filter. The channels of a wall-flow filter are alternately blocked, which allow the exhaust gas stream to enter a channel from the inlet, then flow through the channel walls, and exit the filter from a different channel leading to the outlet. Particulates in the exhaust gas stream are thus trapped in the filter.

[0076] The catalyst / adsorber may be added to the flow-through or filter substrate by any known means, such as a washcoat procedure.

[0077] Configurations

[0078] Embodiments of the present invention may include a first coating comprising an ammonia oxidation catalyst and a second coating comprising an SCR catalyst. Such coatings may be formulated as described in the relevant sections above. Catalytic articles may be prepared with various configurations. In some embodiments, the coatings are arranged such that the exhaust gas contacts the second coating before contacting the first coating.

[0079] In a first configuration, a catalyst can comprise a first coating comprising an ammonia oxidation catalyst and a second coating comprising an SCR catalyst, where the second coating is located in a layer over the first coating and the second coating covers all of the first coating.

[0080] In a second configuration, a catalyst can comprise a first coating comprising an ammonia oxidation catalyst and a second coating comprising an SCR catalyst, where the first coating extends from the outlet end toward the inlet end, covering less than a full length of the substrate, and the second coating extends the entire length of the substrate, completely overlapping the first coating.

[0081] In a third configuration, a catalyst can comprise a first coating comprising an ammonia oxidation catalyst and a second coating comprising an SCR catalyst, where the first coating extends from the outlet end toward the inlet end, covering less than a full length of the substrate, and the second coating extends from the inlet end towards the outlet end, partially overlapping the first coating. The second coating can overlap the first coating by an amount from about 10% to about 95%, inclusive, preferably about 50% to about 95%, inclusive.

[0082] In a fourth configuration, a catalyst can comprise a first coating comprising an ammonia oxidation catalyst and a second coating comprising an SCR catalyst, where the first coating extends from the outlet end toward the inlet end, covering less than a full length of the substrate, and the second coating extends from the inlet end towards the outlet end, without overlapping the first coating. There may be a space between the first coating and the secondcoating, the first coating and the second coating may meet but not overlap, or there may be a slight and insubstantial overlap of the first and second coating.

[0083] In a fifth configuration, a catalyst can comprise a first coating comprising an ammonia oxidation catalyst and a second coating comprising a second SCR catalyst, where the first coating extends from the inlet end toward the outlet end, covering less than a full length of the substrate, and the second coating extends the entire length of the substrate, completely overlapping the first coating.

[0084] In a sixth configuration, a catalyst can comprise a first coating comprising an ammonia oxidation catalyst and a second coating comprising an SCR catalyst, where the first coating extends from the inlet end toward the outlet end, covering less than a full length of the substrate, and the second coating extends from the outlet end toward the inlet end, covering less than the full length of the substrate, and partially overlapping the first coating. The second coating can overlap the first coating by an amount from about 10% to about 95%, inclusive, preferably about 50% to about 95% inclusive.

[0085] In a further configuration, a catalyst can comprise a first coating comprising an ammonia oxidation catalyst, a second coating comprising an SCR catalyst and a third coating comprising a second SCR catalyst. The second SCR catalyst can comprise SCR catalyst a transition metal- loaded zeolite, e.g., a transition metal-loaded zeolite selected from CuCHA, FeCHA, CuAEI, FeAEI, CuFER, FeFER, CuBEA, or FeBEA. In a preferred embodiment, the second SCR catalyst can comprise a CuAEI and / or CuCHA zeolite. The second SCR catalyst can comprise a transition metal in an amount of less than about 4.5 wt%, preferably less than about 4 wt%, preferably less than about 3.5 wt% of the second SCR catalyst. Put another way, the second SCR catalyst can comprise a transition metal to Al molar ratio is less than about 0.42, e.g. less than about 0.40, preferably in a ratio of between 0.35 to 0.4.The second SCR catalyst can comprise a zeolite with a silica to alumina molar ratio (SAR) of from 5 to 200 (e.g. 10 to 200), 10 to 100 (e.g. 10 to 30 or 20 to 80), such as 12 to 40, or 15 to 30. In some embodiments, the zeolite of the second SCR catalyst has a SAR of > 200; > 600; or > 1200. In some embodiments, the zeolite of the second SCR catalyst has a SAR of from about 1500 to about 2100.

[0086] Reductant / Urea Injector

[0087] Systems of some embodiments of the present invention may include a means for introducing a nitrogenous reductant into the exhaust system upstream of the ammonia slip catalyst. It may be preferred that the means for introducing a nitrogenous reductant into the exhaust system is directly upstream of the ammonia slip catalyst (e.g. there is no intervening catalyst between the means for introducing a nitrogenous reductant and the ammonia slip catalyst).

[0088] The reductant is added to the flowing exhaust gas by any suitable means for introducing the reductant into the exhaust gas. Suitable means include an injector, sprayer, or feeder. Such means are well known in the art.

[0089] The nitrogenous reductant for use in the system can be ammonia per se, hydrazine, or an ammonia precursor selected from the group consisting of urea, ammonium carbonate, ammonium carbamate, ammonium hydrogen carbonate, and ammonium formate. Urea is particularly preferred.

[0090] The exhaust system may also comprise a means for controlling the introduction of reductant into the exhaust gas in order to reduce NOx therein. Preferred control means may include an electronic control unit, optionally an engine control unit, and may additionally comprise a NOx sensor located downstream of the NO reduction catalyst.

[0091] Method of Using

[0092] A method of reducing emissions from an exhaust stream may include contacting the exhaust stream with a catalytic article as described herein. In some embodiments, a method of improving NH3conversion in an exhaust gas may include contacting an exhaust gas comprising ammonia with a catalytic article as described herein. In some embodiments, a method of treating exhaust gas comprising ammonia and NOx may include contacting an exhaust gas comprising ammonia with a catalytic article as described herein. In some embodiments, the weight ratio of ammonia to NOx (ANR) in the exhaust gas is >1.0 for at least a portion of the operating time of the system.

[0093] Benefits

[0094] Catalysts, catalyst articles, systems, and methods of the present invention may provide improved catalytic activity and selectivity. Catalyst articles which include a substrate having a first coating comprising an ammonia oxidation catalyst and a second coating comprising an SCR catalyst, wherein the SCR catalyst has a high transition metal content, have surprisingly been found to provide improved NOx conversion and decreased NOx remake with minimal impact toNH3oxidative function. In some embodiments, a high transition metal content may be defined based on the transition metal to aluminum ratio and / or the weight percent of transition metal in the SCR catalyst.

[0095] Typically, ammonia slip catalysts may include a second coating having an SCR catalyst with a transition metal content based on a desired range of transition metal to Al molar ratio. In some cases, use of higher transition metal to Al molar ratios may be beneficial at low temperature but may be detrimental to high temperature SCR function. Therefore, a transition metal to Al molar ratio range may be based on SCR activity to minimize NH3oxidation instead of SCR reaction at high temperatures. Traditionally, such transition metal to Al molar ratio may be about 0.35 to about 0.4.

[0096] However, it has been discovered that ammonia slip catalysts of the present invention, having a second coating with a higher transition metal content than traditionally used, may provide surprising benefits. In some embodiments, a catalyst article of the present invention may provide a substantial boost to NOx conversion performance of fresh catalysts with minimal impact to NH3oxidation function. After hydrothermal aging, catalyst articles of the present invention provide substantially decreased NOx remake and boost NOx conversion, with minimal impact to NH3oxidation function. It has also been found that catalyst articles of the present invention provide substantially improved NH3oxidation function at high ammonia to NOx ratios with minimal impact on selectivity. These benefits are unexpected because in the absence of an oxidation layer / component, the presence of a high molar ratio of transition metakAI would result in increased NOx remake due to increased oxidation of NH3by the transition metal SCR catalyst.

[0097] In some embodiments, a catalyst as described herein provides higher NOx conversion than a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less, when tested as fresh catalysts under equivalent conditions.

[0098] In one example, a fresh catalyst with Cu:AI of about 0.59 provides 8% better NOx conversion than a catalyst with Cu:AI of about 0.42 at 400°C, 500ppm NH3+ 500ppm NO inlet, 180k SV.

[0099] In one example, a catalyst hydrothermally aged at 750°C for 16hrs with Cu:AI of about 0.59 has about 8% lower NOx remake than a catalyst with Cu:AI of about 0.42 at 400°C, 500ppm NH3only inlet, 180k SV.

[0100] In one example, a catalyst hydrothermally aged at 750°C for 16hrs with Cu:AI of about 0.59 provides 18% better NOx conversion than a catalyst with Cu:AI of about 0.42 at 400°C, 500ppm NH3+ 500ppm NO inlet, 180k SV.

[0101] Terms

[0102] As used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly indicates otherwise. Thus, for example, reference to "a catalyst" includes a mixture of two or more catalysts, and the like.

[0103] The term "ammonia slip", means the amount of unreacted ammonia that passes through the SCR catalyst.

[0104] The term "support" means the material to which a catalyst is fixed.

[0105] The term "calcine", or "calcination", means heating the material in air or oxygen. This definition is consistent with the IUPAC definition of calcination. (IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http: / / goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351 / goldbook.) Calcination is performed to decompose a metal salt and promote the exchange of metal ions within the catalyst and also to adhere the catalyst to a substrate. The temperatures used in calcination depend upon the components in the material to be calcined and generally are between about 400 °C to about 900 °C for approximately 1 to 8 hours. In some cases, calcination can be performed up to a temperature of about 1200 °C. In applications involving the processes described herein, calcinations are generally performed at temperatures from about 400 °C to about 700 °C for approximately 1 to 8 hours, preferably at temperatures from about 400 °C to about 650 °C for approximately 1 to 4 hours.

[0106] When a range, or ranges, for various numerical elements are provided, the range, or ranges, can include the values, unless otherwise specified.

[0107] The term "N2selectivity" means the percent conversion of ammonia into nitrogen.

[0108] The terms "diesel oxidation catalyst" (DOC), "diesel exotherm catalyst" (DEC), "NOx absorber", "SCR / PNA" (selective catalytic reduction / passive NOx adsorber), "cold-start catalyst" (CSC) and "three-way catalyst" (TWC) are well known terms in the art used to describe various types of catalysts used to treat exhaust gases from combustion processes.

[0109] The term "platinum group metal" or "PGM" refers to platinum, palladium, ruthenium, rhodium, osmium and iridium. The platinum group metals are preferably platinum, palladium, ruthenium or rhodium.

[0110] The terms "downstream" and "upstream" describe the orientation of a catalyst or substrate where the flow of exhaust gas is from the inlet end to the outlet end of the substrate or article.

[0111] The following examples merely illustrate the invention; the skilled person will recognize many variations that are within the spirit of the invention and scope of the claims.

[0112] EXAMPLES

[0113] Example 1

[0114] Three catalyst articles were prepared and tested to measure the impact of transition metal content on NH3conversion, N2O make, NOx make, NOx conversion, and N2O slip.

[0115] Flow-through honeycomb cores (4.66 inches by 3.0 inches, 400 cpsi, 4 mil wall thickness) were coated with an oxidation catalyst slurry containing platinum nitrate and alumina support to form a bottom layer. They were dried at 100°C and calcined at 500°C. The oxidation catalyst layer washcoat loading was 0.35 g / in3.

[0116] Two top layer catalysts were prepared to give catalyst articles A and B, as follows.

[0117] SCR catalyst slurries were prepared by mixing a copper ion-exchanged aluminosilicateCHA and binder. Each SCR catalyst slurry was coated over the oxidation catalyst layer so that the bottom layer is completely covered. It was dried at 100°C calcined at 500°C. SCR layer was coated at the same loading of 2.4gin-3.

[0118] Catalyst A contained a normal copper:AI ratio of 0.42, which is 3.3 wt% Cu.

[0119] Catalyst B contained an increased copper:AI ratio of 0.50, which is 4.0 wt% Cu.

[0120] The catalyst articles were tested in 500 ppm NH3, 500 ppm NO, and 350 ppm CO, at 180k SV. Each catalyst was tested fresh, hydrothermally aged at 650°C for 50 hours, and hydrothermally aged at 750°C for 16 hours.

[0121] As shown in Figure 1, increasing transition metal content has a minimal effect on the NH3oxidation function of the catalyst for both fresh and aged versions.

[0122] As shown in Figure 2, increasing transition metal content decreases N2O make after hydrothermal aging.

[0123] As shown in Figure 3, increasing transition metal content decreases NOx remake after hydrothermal aging.

[0124] As shown in Figure 4, the high-transition-metal content catalyst has the highest NOx conversion after hydrothermal aging. This may be surprising as it does not follow a trend as expected for transition metal zeolite SCR catalysts.

[0125] As shown in Figure 5, increasing transition metal content has minimal effect on N2O make in the ANR = 1 exhaust gas.

[0126] Example 2

[0127] A flow-through honeycomb core (4.66 inches by 3.0 inches, 400 cpsi, 4 mil wall thickness) was coated with a first oxidation catalysts from both inlet and outlet and coated approximately 50% respectively, to form a bottom layer and then coated with a second SCR catalysts (front and rear) to form a top layer over the bottom layer to give Catalyst C.

[0128] The catalyst of the bottom layer was a standard ASC bottom layer washcoat slurry containing aqueous salts (as nitrates) of platinum, an alumina support and a binder with a homogeneous platinum loading of 2gft-3. The washcoat slurry was applied to the honeycomb core as a bottom catalyst layer and the coated core dried and calcined.

[0129] The catalyst of the top layers comprised copper ion-exchanged aluminosilicate zeolite CHA and binder washcoat. This washcoat was coated over the bottom catalyst layer so that the bottom layer is completely covered, then were dried and calcined.

[0130] Catalysts C & D were prepared. Catalyst C uses a copper loading of 3.75wt% (Cu:AI 0.42). Catalyst D uses a copper loading of 4.3wt% (Cu:AI 0.48). 1x3" cores were cut from the prepared catalyst of Catalyst C and Catalyst D and aged at 650°C for lOOhours in an atmosphere of 10% water in air before being tested for NH3conversion and N2selectivity using a temperature ramp in 500ppm NH3at 180k SV (8% O2, 5% water and N2balance). Where applicable (Figure 8) was tested under same gas mix with 500ppm NO.

[0131] Catalysts C and D exhibit similar NH3conversion activity (Figure 6) but crucially sample D results in a lower NOx remake (Figure 7). This is summarised in Table 1.

[0132] Under SCR conditions (Figure 8) Catalyst D showed improved NOx conversion overCatalyst C.Tohfe 7 Summary of catalytic activity and NOx remake of catalyst C and D

[0133] Example 3

[0134] A flow-through honeycomb core (4.66 inches by 3.0 inches, 400 cpsi, 4 mil wall thickness) was coated with a first oxidation catalysts from both inlet and outlet and coated approximately 50% respectively, to form a bottom layer and then coated with a second SCR catalysts (front and rear) to form a top layer over the bottom layer to give Catalyst E.

[0135] The catalyst of the bottom layer was a standard ASC bottom layer washcoat slurry containing aqueous salts (as nitrates) of platinum, an alumina support and a binder with a homogeneous platinum loading of 2gft-3. The washcoat slurry was applied to the honeycomb core as a bottom catalyst layer and the coated core dried and calcined.

[0136] The catalyst of the top layers comprised copper ion-exchanged aluminosilicate zeolite CHA and binder washcoat. This washcoat was coated over the bottom catalyst layer so that the bottom layer is completely covered, then were dried and calcined.

[0137] Catalysts E, F, G and H were prepared. Catalyst E uses a copper loading of 4.0wt% (Cu:AI 0.28). Catalyst F uses a copper loading of 5.0wt% (Cu:AI 0.48). Catalyst G uses a copper loading of 6.0wt% (Cu:AI 0.42). Catalyst H uses a copper loading of 6.85wt% (Cu:AI 0.48). 1x3" cores were cut from the prepared catalyst of Catalysts E, F, G & F and aged at 650°C for lOOhours in an atmosphere of 10% water in air before being tested for NH3conversion and N2selectivity using a temperature ramp in 500ppm NH3at 180k SV (8% O2, 5% water and N2balance). Where applicable (Figure 11) was tested under same gas mix with 500ppm NO and 500ppm NH3.

[0138] Catalysts E, F, G and H exhibit similar NH3 conversion activity (Figure 9) but crucially sample NOXremake is in the order: Catalyst E > Catalyst F > Catalyst G > Catalyst H (Figure 10). This is summarised in Table 2.

[0139] Under SCR test conditions (Figure 11) Catalyst H showed best NOx conversion in order Catalyst H > Catalyst G > Catalyst F and Catalyst E.FaNe .? Summary of catalytic activity and NOx remake of catalyst E, G H

[0140] Example 4

[0141] A flow-through honeycomb core (5.66 inches by 3.0 inches, 600 cpsi, 3.5 mil wall thickness) was coated with a first oxidation catalysts from outlet and coated approximately 66% respectively, to form a bottom layer and then coated with a second SCR catalysts from outlet (approx. 66%) to form a top layer over the bottom layer to give Catalyst J.

[0142] The catalyst of the bottom layer was a standard ASC bottom layer washcoat slurry containing aqueous salts (as nitrates) of platinum, an alumina support and a binder with a platinum loading of 1.5gft-3. The washcoat slurry was applied to the honeycomb core as a bottom catalyst layer and the coated core dried and calcined.

[0143] The catalyst of the top layers comprised copper ion-exchanged aluminosilicate zeolite CHA and binder washcoat. This washcoat was coated over the bottom catalyst layer so that the bottom layer is completely covered, then were dried and calcined.

[0144] Catalysts J and I were prepared. Catalyst J uses a copper loading of 4.0wt% (Cu:AI 0.5). Catalyst I uses a copper loading of 3.3wt% (Cu:AI 0.42).

[0145] 1x1.5" cores were cut from the prepared catalyst of Catalyst I and Catalyst J and aged for 650°C for lOOhours in an atmosphere of 10% water in air under forceflow conditions beforebeing tested for NH3conversion and N2selectivity at various temperatures under steady state conditions in 500ppm NH3at 200k SV (10 % 02, 7 % Water, 8% CO and N2 balance).

[0146] Catalyst I and J exhibit similar NH3 conversion activity but crucially sample J results in a lower NOx make (Figure 12). This is summarised in Table 3.

[0147] Example 5

[0148] Two catalyst articles were prepared and tested to measure the impact of transition metal content on NH3conversion, N2O make, and NOXmake, NOXconversion and N2O slip.

[0149] The catalysts were prepared as in Example 1.

[0150] Catalyst K contained a normal copper:AI ratio of 0.42, which is 3.3 wt% Cu.

[0151] Catalyst L contained an increased copper:AI ratio of 0.59, which is 4.7 wt% Cu.

[0152] The catalyst articles were tested in 500ppm NH3, 500ppm NO (where applicable, Figure 15), and 350ppm CO, at 180k SV. Each catalyst was tested after hydrothermal ageing at 750°C for 16 hours.

[0153] As shown in Figure 13, increasing transition metal content has a minimal effect on the NH3oxidation function however showed decreased NOXremake after hydrothermal ageing (Figure 14).

[0154] As shown in Figure 15, the high transition metal content catalyst has the highest NOXconversion particularly at high temperatures. This may be surprising as it does not follow a trend as expected for transition metal zeolite SCR catalysts. The increasing transition metal content has minimal effect on N2O make.

[0155] Example 6

[0156] Three catalyst articles were prepared and tested to measure the impact of transition metal content on NH3conversion, N2O make, and NOXmake, NOXconversion and N2O slip.

[0157] The catalysts were prepared as in Example 1.

[0158] Catalyst M contained an increased copper:AI ratio of 0.55, which is 5.4 wt% Cu.

[0159] Catalyst N contained an increased copper:AI ratio of 0.49, which is 4.75 wt% Cu.

[0160] Catalyst O contained a normal copper:AI ratio of 0.41, which is 4.0 wt% Cu.

[0161] The catalyst articles were tested in 500ppm NH3, 500ppm NO (where applicable, Figure18), and 350ppm CO, at 180k SV. Each catalyst was tested after hydrothermal ageing at 750°C for 16 hours.

[0162] As shown in Figure 16, increasing transition metal content has minimal effect on the NH3oxidation function of the catalyst whereas increasing transition metal content decreases NOx remake after hydrothermal ageing (Figure 17).

[0163] As shown in Figure 18, increasing transition metal content increases the NOx conversion of the catalyst. This may be surprising as it does not follow a trend as expected for transition metal zeolite SCR catalysts. The increasing transition metal content has minimal effect on N2O make.

[0164] Example 7

[0165] Two catalyst articles were prepared and tested to measure the impact of transition metal content on NH3conversion, N2O make, and NOXmake.

[0166] Flow-through honeycomb cores (4.66 inches by 3.0 inches, 400cpsi, 4 mil wall thickness) were coated with an oxidation catalyst slurry containing platinum nitrate, alumina support, bare molecular sieve and a binder as described in WO2019116268A1. They were dried at 100°C and calcined at 500aC. The oxidation catalyst layer washcoat loading was 1.0 g in-3.

[0167] Two top layer catalysts were prepared as in Example 1.

[0168] Catalyst P contained an increased copper:AI ratio of 0.50, which is 4.0 wt% Cu.

[0169] Catalyst Q contained a normal copper:AI ratio of 0.42, which is 3.3 wt% Cu.

[0170] The catalyst articles were tested in 500ppm NH3and 350pppm CO at 180k SV. Each catalyst was tested after hydrothermal ageing at 650°C for 100 hours.

[0171] As shown in Figure 19, increasing transition metal content has a small effect on the NH3oxidation function of the catalyst whilst demonstrating decreased NOXremake (Figure 20).

Claims

Claims1. A catalyst comprising a first catalyst coating and a second catalyst coating, a. wherein the first catalyst coating comprises an ammonia oxidation catalyst, and b. wherein the second catalyst coating comprises an SCR catalyst comprising a transition metal on a support, wherein the transition metal is present in an amount of greater than about 3.5 wt% of the SCR catalyst.

2. A catalyst comprising a first catalyst coating and a second catalyst coating, a. wherein the first catalyst coating comprises an ammonia oxidation catalyst, and b. wherein the second catalyst coating comprises an SCR catalyst comprising a transition metal on a support, wherein a transition metal to Al molar ratio is greater than about 0.43.

3. A catalyst of any of the preceding claims, wherein the transition metal to Al molar ratio is greater than about 0.44; greater than about 0.45; greater than about 0.46; about 0.45 to about 0.65; about 0.46 to about 0.65; about 0.45 to about 0.59; or about 0.46 to about 0.59.

4. A catalyst of any of the preceding claims, wherein the support comprises a molecular sieve.

5. A catalyst of claim 4, wherein the molecular sieve comprises CHA, AEI, FER, BEA, or combinations thereof.

6. A catalyst of any of the preceding claims, wherein the transition metal comprises Cu, Fe, or combinations thereof.

7. A catalyst of any of the preceding claims, wherein the transition metal is present in an amount of greater than about 4 wt% of the SCR catalyst.

8. The catalyst of any of the preceding claims, wherein the ammonia oxidation catalyst comprises a platinum group metal on a support.

9. The catalyst of any of the preceding claims, wherein the ammonia oxidation catalyst comprises a platinum group metal on a support comprising a refractory metal oxide.

10. The catalyst of any of the preceding claims, wherein the ammonia oxidation catalyst comprises a platinum group metal on a support comprising a molecular sieve.

11. The catalyst of any of the preceding claims, comprising a substrate having an inlet and an outlet relative to a direction of flow of exhaust gas, wherein the first catalyst coating extends from the outlet of the substrate toward the inlet, covering less than a full length of the substrate, and thesecond coating extends the entire length of the substrate, completely overlapping the first coating.

12. The catalyst of any of the preceding claims, comprising a substrate having an inlet end and an outlet end relative to a direction of flow of exhaust gas, wherein the first catalyst coating extends from the outlet of the substrate toward the inlet, covering less than a full length of the substrate, and the second coating extends from the inlet end towards the outlet end, partially overlapping the first coating.

13. A catalyst of any of the preceding claims, wherein the catalyst provides higher NOx conversion than a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less, when tested as fresh catalysts under equivalent conditions.

14. A catalyst of any of the preceding claims, wherein the catalyst provides higher NOx conversion than a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less, when tested as hydrothermally aged catalysts under equivalent conditions.

15. A catalyst of any of the preceding claims, wherein the catalyst provides lower NOx remake than a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less, when tested as hydrothermally aged catalysts under equivalent conditions.

16. A method of reducing emissions for an exhaust stream, comprising contacting the exhaust stream with a catalyst article of any of the preceding claims.

17. The method of claim 16, wherein the weight ratio of ammonia to NOx in the exhaust gas is >1.0 for at least a portion of an operating time.

18. The method of claims 16-17, wherein the catalyst provides higher NOx conversion compared to a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less.

19. The method of claims 16-18, wherein the catalyst provides lower NOx remake compared to a catalyst which is equivalent except has a transition metal to Al ratio of 0.4 or less.

20. A system comprising a catalyst of any of claims 1-13 and a means for introducing a nitrogenous reductant upstream of the catalyst.

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