Ammonia slip catalyst with in-situ Pt immobilization

Abstract

The present invention includes a substrate having an inlet and an outlet; a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve; and a second coating including a second SCR catalyst, wherein the support includes at least one of a zeolite or a SiO-AlO mixed oxide. The platinum may be immobilized on the support in solution.

Description

[Background technology]

[0001] Hydrocarbon combustion in diesel engines, stationary gas turbines, and other systems produces exhaust gases that must be treated to remove nitrogen oxides (NOx), including NO (nitric oxide) and NO2 (nitrogen dioxide). NOx is known to cause many health problems for people as well as many harmful environmental effects, such as the formation of smog and acid rain. NO in exhaust gases x To mitigate the impact of these on both humans and the environment, it is desirable to remove these undesirable components, preferably by a process that does not produce other harmful or toxic substances.

[0002] Exhaust gases produced by lean-burn and diesel engines are generally oxidizing. NOx must be selectively reduced using a catalyst and a reducing agent in a process known as selective catalytic reduction (SCR), which converts NOx into elemental nitrogen (N2) and water. In the SCR process, a gaseous reducing agent, usually anhydrous ammonia, aqueous ammonia, or urea, is added to the exhaust gas stream before the exhaust gas is contacted with a catalyst. The reducing agent is absorbed on the catalyst, reducing NOx. xis reduced as the gas passes through or over the catalyzed substrate. To maximize NOx conversion, it is often necessary to add more than stoichiometric amounts of ammonia to the gas stream. However, releasing excess ammonia into the atmosphere is harmful to human health and the environment. Furthermore, ammonia is caustic, especially in its aqueous form. Condensation of ammonia and water in the region of the exhaust line downstream of the exhaust catalyst can create a corrosive mixture that can damage the exhaust system. Therefore, it is necessary to eliminate the release of ammonia in the exhaust gas. In many conventional exhaust systems, an ammonia oxidation catalyst (also known as an ammonia slip catalyst or "ASC") is provided downstream of the SCR catalyst to remove ammonia from the exhaust gas by converting it to nitrogen. The use of an ammonia slip catalyst reduces NOx by more than 90% over a typical diesel operating cycle. x Conversion rates can be made possible.

[0003] It is desirable to have a catalyst that provides both NOx removal by SCR and selective ammonia conversion to nitrogen, where the ammonia conversion occurs over a wide range of temperatures during the vehicle's operating cycle, with minimal nitrogen oxide and nitrous oxide by-product formation. Summary of the Invention

[0004] According to some embodiments of the present invention, a catalyst article may include a substrate having an inlet and an outlet; a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve; and a second coating including a second SCR catalyst, wherein the support includes at least one of a molecular sieve or a SiO-AlO mixed oxide. In some embodiments, the platinum is immobilized on the support in solution.

[0005] In some embodiments, the first SCR catalyst molecular sieve comprises a small pore molecular sieve such as AEI, CHA, or a combination thereof. In some embodiments, the first SCR catalyst molecular sieve is essentially free of any transition metals other than Cu and Mn. In some embodiments, the first SCR catalyst molecular sieve contains an additional transition metal in an amount less than about 1 wt. In some embodiments, the first SCR catalyst molecular sieve comprises Cu and Mn in a combined amount of about 0.10 to about 10 wt. % of the Cu and Mn-exchanged molecular sieve. The first SCR catalyst molecular sieve may comprise Cu in an amount of about 0.05 to about 5 wt. % of the Cu and Mn-exchanged molecular sieve. The first SCR catalyst molecular sieve may comprise Mn in an amount of about 0.05 to about 5 wt. % of the Cu and Mn-exchanged molecular sieve. In some embodiments, the first SCR catalyst molecular sieve comprises Cu and Mn in a weight ratio of about 0.1 to about 50.

[0006] In some embodiments, the support comprises a SiO2-Al2O3 mixed oxide, in some embodiments, the SiO2 is present in an amount of from 1% to about 70% by weight, or from about 40% to about 70% by weight of the mixed oxide.

[0007] In some embodiments, the support comprises a molecular sieve. Suitable molecular sieves have a molecular sieve content of at least 50 m 2 / g, at least 70m 2 / g, or at least 100m 2 / g。 In some embodiments, suitable molecular sieves have an average crystallite size of less than about 1 μm, less than about 0.5 μm, or less than about 0.3 μm. In some embodiments, suitable molecular sieves include zeolites having a silica-to-alumina ratio of greater than 100, greater than 300, or greater than 1000. In certain embodiments, the molecular sieve is selected from the group of framework types 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, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON, BEA, MFI, and FER, and mixtures and / or intergrowths thereof. In some embodiments, the molecular sieve is selected from the group of framework types consisting of CHA, LEV, AEI, AFX, ERI, SFW, KFI, DDR, ITE, BEA, MFI, and FER.

[0008] In some embodiments, the second coating completely overlaps the first coating. In some embodiments, the second coating partially overlaps the first coating. In some embodiments, the second coating extends from the inlet end toward the outlet end and covers less than the entire length of the substrate. In some embodiments, the first coating extends from the outlet end toward the inlet end and covers less than the entire length of the substrate. In some embodiments, the second SCR catalyst is located on the inlet side of a coating comprising a blend of platinum on a support and the first SCR catalyst. In some embodiments, the second SCR catalyst is located on the outlet side of a coating comprising a blend of platinum on a support and the first SCR catalyst.

[0009] In some embodiments, the platinum is present in at least one of the following amounts, based on the weight of the platinum support plus the weight of the platinum plus the weight of the first SCR catalyst in the blend: (a) 0.01 to 0.3 wt %, inclusive; (b) 0.03 to 0.2 wt %, inclusive; (c) 0.05 to 0.17 wt %, inclusive; and (d) 0.07 to 0.15 wt %, inclusive. The weight ratio of the first SCR catalyst to the platinum on the support, based on the weight of these components, may be in the range of at least one of: (a) 0:1 to 300:1, inclusive; (b) 3:1 to 300:1, inclusive; (c) 7:1 to 100:1, inclusive; and (d) 10:1 to 50:1, inclusive.

[0010] In some embodiments, the blend further comprises at least one of palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru), or rhodium (Rh).

[0011] In certain embodiments, the second SCR catalyst is a base metal, an oxide of a base metal, a molecular sieve, a metal-exchanged molecular sieve, a mixed oxide, or a mixture thereof. The base metal may be selected from the group consisting of vanadium (V), molybdenum (Mo), tungsten (W), chromium (Cr), cerium (Ce), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu), and mixtures thereof. Such second SCR catalysts may further include at least one base metal promoter.

[0012] When the second SCR catalyst is a molecular sieve or a metal-exchanged molecular sieve, the molecular sieve or metal-exchanged molecular sieve may be small pore, medium pore, large pore, or a mixture thereof. In some embodiments, the second SCR catalyst comprises a molecular sieve selected from the group consisting of aluminosilicate molecular sieves, metal-substituted aluminosilicate molecular sieves, aluminophosphate (AlPO) molecular sieves, metal-substituted aluminophosphate (MeAlPO) molecular sieves, silicoaluminophosphate (SAPO) molecular sieves, and metal-substituted silicoaluminophosphate (MeAPSO) molecular sieves, and mixtures thereof. In some embodiments, the second SCR catalyst comprises a small pore molecular sieve selected from the group of framework types 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, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON, and mixtures thereof and / or intergrowth. In some embodiments, the second SCR catalyst comprises a small pore molecular sieve selected from the group of framework types consisting of CHA, LEV, AEI, AFX, ERI, SFW, KFI, DDR, and ITE. In some embodiments, the second SCR catalyst comprises a medium pore molecular sieve selected from the group of framework types consisting of AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, -PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, SVR, SZR, TER, TON, TUN, UOS, VSV, WEI, and WEN, and mixtures thereof and / or intergrowth.In some embodiments, the second SCR catalyst comprises a large pore molecular sieve selected from the group of framework types 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, and mixtures thereof and / or intergrowth. In certain embodiments, the second SCR catalyst comprises promoted Ce—Zr or promoted MnO 2 .

[0013] Suitable substrates may include cordierite, highly porous cordierite, metal substrates, extruded SCR, filters, or SCRF.

[0014] According to some embodiments of the invention, an exhaust system includes a catalytic article as described herein and a means for introducing a reductant upstream of the catalytic article. The exhaust system may further include a third SCR catalyst providing ≦100% NOx conversion, the third SCR catalyst being a Cu-zeolite SCR catalyst, and disposed in the exhaust gas stream upstream of the catalytic article as described herein.

[0015] According to some embodiments of the present invention, a method for improving NH conversion of an exhaust gas at temperatures of about 300° C. or less includes contacting an exhaust gas containing ammonia with a catalytic article described herein.

[0016] According to some embodiments of the present invention, a method for improving NH conversion of an exhaust gas at temperatures of about 300° C. or less includes contacting an exhaust gas containing ammonia with a catalytic article described herein, the catalytic article having platinum immobilized on a support in solution. In some embodiments, the NH conversion is about 30% to about 100% greater than a catalyst containing a comparable formulation in which the platinum is pre-immobilized on a support.

[0017] According to some embodiments of the present invention, a method for treating an exhaust gas containing ammonia and NOx includes contacting the exhaust gas containing ammonia with a catalytic article described herein. In some embodiments, the weight ratio of ammonia to NOx in the exhaust gas is >1.0 for at least a portion of the operation time of the system. [Brief explanation of the drawings]

[0018] 1-8 are schematic diagrams of catalyst configurations that include a blend of (1) platinum on a support and (2) a first SCR catalyst. The portion of the catalyst that includes a blend of (1) platinum on a support and (2) a first SCR catalyst is referred to as the "blend" in these figures. [Figure 1] A second SCR catalyst is positioned in the exhaust gas stream above the blend, showing a configuration in which the second SCR coats the entire blend. [Figure 2] A second SCR catalyst is positioned in the exhaust gas stream before the blend, with the second SCR covering the entire blend. [Figure 3] A second SCR catalyst is positioned in the exhaust gas stream before the blend, showing a configuration in which the second SCR covers a portion, but not all, of the blend. [Figure 4] A second SCR catalyst is positioned in the exhaust gas stream before the blend, showing a configuration where the blend is not coated. [Figure 5] A second SCR catalyst coats the entire blend, with a portion of the second SCR positioned in the exhaust gas stream after the blend. [Figure 6]1 shows a configuration in which a second SCR catalyst coats a portion of the blend, but not the entire blend, with a portion of the second SCR positioned in the exhaust gas stream after the blend. [Figure 7] The third SCR catalyst is shown as a bottom layer on the substrate, a second layer includes the blend and partially covers the third SCR catalyst, and a third layer includes the second SCR catalyst and is positioned above the blend layer and covers the entire blend layer. [Figure 8] The third SCR catalyst is a bottom layer on a substrate, a second layer includes a blend and partially, but not completely, covers the third SCR catalyst, and a third layer includes the second SCR catalyst and is positioned above the blend layer and partially, but not completely covers the blend layer. [Figure 9] Figure 1 shows NH3 slip, N2O formation, and NOx formation when various ASCs were exposed to a 1 minute pulse of 1000 ppm NH3. [Figure 10] Figure 1 shows the transient NH3 oxidation performance of various ASCs. DETAILED DESCRIPTION OF THE INVENTION

[0019] The catalyst of the present invention relates to an ammonia slip catalyst that can provide improved NH conversion at lower temperatures and can be prepared more cost-effectively. The catalyst article of an embodiment of the present invention includes a substrate having a first coating comprising a blend of (1) platinum on a support and (2) a first SCR catalyst comprising a Cu and Mn-exchanged molecular sieve, where the support comprises a zeolite and / or a SiO-AlO mixed oxide. The catalyst article also includes a second coating comprising the SCR catalyst. In some embodiments, the platinum is immobilized on the support in solution, i.e., in situ. The catalyst and specific configurations are described in further detail below.

[0020] Supported platinum / ammonia oxidation catalysts. Embodiments of the present invention include platinum on a support, which may be included as an ammonia oxidation catalyst in the catalytic articles described herein. Preferably, the support comprises a zeolite and / or a SiO-AlO mixed oxide. In some embodiments, platinum may be immobilized on the support by immobilizing Pt in solution, i.e., in situ.

[0021] The catalytic article of the present invention comprises platinum on a support, the support comprising a zeolite and / or a SiO2-Al2O3 mixed oxide. In some embodiments, platinum is present on the support in an amount of about 0.5% to about 10% by weight of the total weight of platinum and the support, about 1% to about 6% by weight of the total weight of platinum and the support, about 1.5% to about 4% by weight of the total weight of platinum and the support, about 10% by weight of the total weight of platinum and the support, about 0.5% by weight of the total weight of platinum and the support, about 1% by weight of the total weight of platinum and the support, about 2% by weight of the total weight of platinum and the support, about 3% by weight of the total weight of platinum and the support, about 4% by weight of the total weight of platinum and the support, about 5% by weight of the total weight of platinum and the support, about 6% by weight of the total weight of platinum and the support, about 7% by weight of the total weight of platinum and the support, about 8% by weight of the total weight of platinum and the support, about 9% by weight of the total weight of platinum and the support, or about 10% by weight of the total weight of platinum and the support.

[0022] In embodiments in which platinum is supported on a SiO-AlO mixed oxide, the SiO is from about 1% to about 80% by weight of the mixed oxide, from about 1% to about 75% by weight of the mixed oxide, from about 1% to about 70% by weight of the mixed oxide, from about 5% to about 70% by weight of the mixed oxide, from about 10% to about 70% by weight of the mixed oxide, from about 20% to about 70% by weight of the mixed oxide, from about 30% to about 70% by weight of the mixed oxide, from about 40% to about 50% by weight of the mixed oxide, It may be present in an amount of 0% to about 70% by weight, about 50% to about 60% by weight of the mixed oxide, about 1% by weight of the mixed oxide, about 5% by weight of the mixed oxide, about 10% by weight of the mixed oxide, about 20% by weight of the mixed oxide, about 30% by weight of the mixed oxide, about 40% by weight of the mixed oxide, about 50% by weight of the mixed oxide, about 60% by weight of the mixed oxide, about 70% by weight of the mixed oxide, about 75% by weight of the mixed oxide, or about 80% by weight of the mixed oxide.

[0023] In embodiments where platinum is supported on a zeolite, suitable zeolites have a molecular weight of at least about 30 m 2 / g, at least about 40m 2 / g, at least about 50m 2 / g, at least about 60m 2 / g, at least about 70m 2 / g, at least about 80m 2 / g, at least about 90m 2 / g, or at least about 100m 2 / g of external surface area. In some embodiments, suitable zeolites may have an average crystal size of about 2 μm or less to about 1.5 μm or less, about 1 μm or less, about 0.5 μm or less, about 0.3 μm or less, less than about 2 μm, less than about 1.5 μm, less than about 1 μm, less than about 0.5 μm, less than about 0.3 μm, about 0.1 μm to about 2 μm, about 0.3 μm to about 1.5 μm, or about 0.5 μm to about 1 μm. In particular, the particle size may differ significantly from the zeolite crystal size, since the particles may consist of aggregates of many smaller crystals. In some embodiments, suitable zeolites have a silica-to-alumina ratio that is at least 100, at least 200, at least 250, at least 300, at least 400, at least 500, at least 600, at least 750, at least 800, or at least 1000. Zeolites are described in more detail below in the SCR catalyst section. In some embodiments, suitable zeolites for supporting platinum are selected from the group of framework types 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, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON, BEA, MFI, and FER, and mixtures thereof and / or intergrowth. In some embodiments, suitable zeolites for supporting platinum are selected from the group of framework types consisting of CHA, LEV, AEI, AFX, ERI, SFW, KFI, DDR, ITE, BEA, MFI, and FER.

[0024] The catalytic article of the present invention may include one or more ammonia oxidation catalysts, also referred to as ammonia slip catalysts ("ASC"). A preferred ammonia oxidation catalyst comprises platinum on a support, as described above, although other or additional ammonia oxidation catalysts may be included in embodiments of the present invention. One or more ammonia oxidation catalysts may be included with or downstream of the SCR catalyst to oxidize excess ammonia and prevent it from being released into the atmosphere. In some embodiments, the ammonia oxidation catalyst may be included on the same substrate as the SCR catalyst or may be blended with the SCR catalyst. In certain embodiments, the ammonia oxidation catalyst material is a catalyst that oxidizes NO x Alternatively, the catalyst may be selected and formulated to promote the oxidation of ammonia instead of forming NO. Generally preferred catalyst materials include platinum, palladium, or a combination thereof. The ammonia oxidation catalyst may include platinum and / or palladium supported on a metal oxide. In some embodiments, the catalyst is disposed on a high surface area support, including, but not limited to, alumina.

[0025] In some embodiments, the ammonia oxidation catalyst comprises a platinum group metal on a siliceous support. The siliceous material may include, for example, materials such as (1) silica, (2) zeolites having a silica-to-alumina ratio of at least 200, and (3) amorphous silica-doped alumina with a SiO2 content of 40% or greater. In some embodiments, the siliceous material may include materials such as zeolites having a silica-to-alumina ratio of at least 200, at least 250, at least 300, at least 400, at least 500, at least 600, at least 750, at least 800, or at least 1000. In some embodiments, the platinum group metal is present in an amount of from about 0.5% to about 10% by weight of the total weight of the platinum group metal and the support, from about 1% to about 6% by weight of the total weight of the platinum group metal and the support, from about 1.5% to about 4% by weight of the total weight of the platinum group metal and the support, about 10% by weight of the total weight of the platinum group metal and the support, about 0.5% by weight of the total weight of the platinum group metal and the support, about 1% by weight of the total weight of the platinum group metal and the support, about 1.5% by weight of the total weight of the platinum group metal and the support, The platinum group metal is present on the support in an amount of about 2 weight percent, about 3 weight percent of the total weight of the platinum group metal and the support, about 4 weight percent of the total weight of the platinum group metal and the support, about 5 weight percent of the total weight of the platinum group metal and the support, about 6 weight percent of the total weight of the platinum group metal and the support, about 7 weight percent of the total weight of the platinum group metal and the support, about 8 weight percent of the total weight of the platinum group metal and the support, about 9 weight percent of the total weight of the platinum group metal and the support, or about 10 weight percent of the total weight of the platinum group metal and the support.

[0026] In some embodiments, the siliceous support may comprise a molecular sieve having a framework type of BEA, CDO, CON, FAU, MEL, MFI, or MWW.

[0027] SCR catalyst The systems of the present invention may include one or more SCR catalysts. In some embodiments, the 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 include the same formulation. In some embodiments, the first SCR catalyst and the second SCR catalyst may include different formulations. In some aspects, the first SCR catalyst includes a Cu and Mn-exchanged molecular sieve, as described in more detail below.

[0028] In some embodiments, the catalyst article can include an SCR catalyst blended with supported platinum. In some embodiments, the catalyst article can include an SCR catalyst blended with supported platinum, the SCR catalyst including a Cu and Mn exchanged molecular sieve. In some embodiments, in addition to the blend, the catalyst article can also include a second coating including an SCR catalyst.

[0029] The selective catalytic reduction composition 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. Exemplary compositions are generally described in U.S. Patent Nos. 4,010,238 and 4,085,193, the entire contents of which are incorporated herein by reference.

[0030] 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 includes 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.

[0031] Metal oxide-based SCR catalyst formulations include titania (e.g., TiO2), ceria (e.g., CeO2), and mixed or composite oxides of cerium and zirconium (e.g., CeO2).x Zr (1-x) 02, where x=0.1 to 0.9, preferably x=0.2 to 0.5).

[0032] When the refractory oxide is titania (e.g., TiO), preferably the concentration of vanadium oxide is 0.5-6 wt. % and / or the concentration of tungsten oxide (e.g., WO) is 5-20 wt. % (e.g., of the metal oxide-based SCR formulation). More preferably, vanadium oxide (e.g., VO) and tungsten oxide (e.g., WO) are supported on titania (e.g., TiO). These catalysts may contain other inorganic materials, such as SiO and ZrO, which act as binders and promoters.

[0033] When the refractory oxide is ceria (e.g., CeO), preferably the concentration of vanadium oxide is 0.1 to 9 wt. % (e.g., of the metal oxide-based SCR formulation) and / or the concentration of tungsten oxide (e.g., WO) is 0.1 to 9 wt. %.

[0034] 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).

[0035] 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.

[0036] When the SCR catalyst is a base metal or mixed base metal oxide, the catalyst article may further comprise at least one base metal promoter. As used herein, "promoter" is understood to mean a substance that, when added to a catalyst, enhances the activity of the catalyst. The base metal promoter may be in the form of a metal, a metal oxide, 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 may preferably be MnO2, Mn2O3, Fe2O3, SnO2, CuO, CoO, CeO2, and mixtures thereof. The at least one base metal catalyst promoter may be added to the catalyst in the form of a salt such as a nitrate or acetate in an aqueous solution. The at least one base metal catalyst promoter and the at least one base metal catalyst, e.g., copper, may be impregnated onto an oxide support material from an aqueous solution, added to a washcoat comprising an oxide support material, or impregnated onto a support pre-coated with a washcoat.

[0037] The selective catalytic reduction composition may comprise or consist essentially of a molecular sieve-based SCR catalyst formulation. The molecular sieve-based SCR catalyst formulation includes a molecular sieve that is optionally a transition metal-exchanged molecular sieve. Preferably, at least one of the SCR catalyst formulations includes a transition metal-exchanged molecular sieve.

[0038] Generally, the molecular sieve-based SCR catalyst formulation may include a molecular sieve having an aluminosilicate framework (e.g., zeolite), an aluminophosphate framework (e.g., AlPO), a silicoaluminophosphate framework (e.g., SAPO), a heteroatom-containing 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 a mixture thereof. The heteroatom (i.e., the 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. Preferably, the heteroatom is a metal (e.g., each of the heteroatom-containing frameworks may be a metal-containing framework).

[0039] The molecular sieve-based SCR catalyst formulation preferably comprises or consists essentially of a molecular sieve having an aluminosilicate framework (e.g., zeolite) or a silicoaluminophosphate framework (e.g., SAPO). Zeolite-based molecular sieves are microporous aluminosilicates having any one of the framework structures listed in the database of zeolite structures published by the International Zeolite Association (IZA). Framework structures include, but are not limited to, CHA, FAU, BEA, MFI, and MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, Y-type zeolite, ultrastable Y-type zeolite, beta zeolite, mordenite, silicalite, X-type zeolite, and ZSM-5.

[0040] When the molecular sieve has an aluminosilicate framework (e.g., the molecular sieve is a zeolite), the molecular sieve typically has a silica-to-alumina molar ratio (SAR) of 5 to 200 (e.g., 10 to 200), 10 to 100 (e.g., 10 to 30 or 20 to 80), e.g., 12 to 40, or 15 to 30. In some embodiments, suitable molecular sieves have a SAR of >200, >600, or >1200. In some embodiments, the molecular sieve has a SAR of about 1500 to about 2100.

[0041] Typically, the molecular sieve is microporous. Microporous molecular sieves have pores with diameters of less than 2 nm (see, for example, the IUPAC definition of "microporous" [see Pure & Appl. Chem., 66(8), (1994), 1739-1758]).

[0042] The molecular sieve-based SCR catalyst formulation may include a small pore molecular sieve (e.g., a molecular sieve having a maximum ring size of 8 tetrahedral atoms), a medium pore molecular sieve (e.g., a molecular sieve having a maximum ring size of 10 tetrahedral atoms), or a large pore molecular sieve (e.g., a molecular sieve having a maximum ring size of 12 tetrahedral atoms), or a combination of two or more thereof.

[0043] When the molecular sieve is a small pore molecular sieve, 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 mixtures and / or intergrowths of two or more thereof. Preferably, the small pore molecular sieve has a framework structure represented by an 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 an FTC selected from the group consisting of CHA and AEI. The small pore molecular sieve can have a framework structure represented by the CHA part of the FTC. The small pore molecular sieve can have a framework structure represented by the AEI part of the FTC. When the small pore molecular sieve is a zeolite and has a framework represented by the CHA part of the FTC, the zeolite can be chabazite.

[0044] When the molecular sieve is a medium pore molecular sieve, 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, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, -PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, -SVR, SZR, TER, TON, TUN, UOS, VSV, WEI and WEN, or mixtures of two or more thereof and / or intergrowths. Preferably, the medium pore molecular sieve has a framework structure represented by an 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 an FTC selected from the group consisting of FER and MFI, especially MFI. When the medium pore molecular sieve is a zeolite and has a framework represented by the FER or MFI of the FTC, the zeolite may be ferrierite, silicalite, or ZSM-5.

[0045] If the molecular sieve is a large pore molecular sieve, the large pore molecular sieve is 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 The large pore molecular sieve may have a framework structure represented by a framework type code (FTC) selected from the group consisting of: , 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 mixtures and / or intergrowths of two or more thereof. Preferably, the large pore molecular sieve has a framework structure represented by an 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 an FTC selected from the group consisting of BEA, MOR, and MFI. When the large pore molecular sieve is a zeolite and has a framework represented by BEA, FAU, or MOR in the FTC, the zeolite may be beta zeolite, faujasite, zeolite Y, zeolite X, or mordenite.

[0046] The molecular sieve-based SCR catalyst formulation preferably contains a transition metal-exchanged molecular sieve. The metal-exchanged molecular sieve may have at least one metal from Groups VB, VIB, VIIB, VIIIB, IB, or IIB of the periodic table deposited on extraframework sites on the outer surface or within the channels, cavities, or cages of the molecular sieve. The metal may be in one of several forms, including, but not limited to, zerovalent metal atoms or clusters, isolated cations, mononuclear or polynuclear oxycations, or extended 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.

[0047] The transition metal may be present at extra-framework sites on the exterior surface of the molecular sieve, or may be present within the channels, cavities, or cages of the molecular sieve.

[0048] Typically, the transition metal exchanged molecular sieve contains the transition metal in an amount of 0.10 to 10% by weight of the transition metal exchanged molecular sieve, preferably 0.2 to 5% by weight.

[0049] In some embodiments, the metal-exchanged molecular sieve can be a Cu-exchanged small pore molecular sieve having about 0.1 to about 20.0 wt% copper based on the total weight of the catalyst. In some embodiments, the copper is present in an amount of about 0.5 to about 15 wt% copper based on the total weight of the catalyst. In some embodiments, the copper is present in an amount of about 1 to about 9 wt% copper based on the total weight of the catalyst.

[0050] Cu and Mn exchanged molecular sieves The blends of the present invention may include an SCR catalyst comprising a Cu and Mn exchanged molecular sieve. Additionally, in some embodiments, a second SCR catalyst may comprise a Cu and Mn exchanged molecular sieve.

[0051] In some embodiments, the metal-exchanged molecular sieve comprises a molecular sieve having exchanged copper and exchanged manganese. In some embodiments, the molecular sieve is free of, or essentially free of, any additional transition metal. For example, in some embodiments, the molecular sieve contains an additional transition metal (i.e., in addition to the exchanged copper and exchanged manganese) in an amount of less than about 1 wt.%, less than about 0.7 wt.%, less than about 0.5 wt.%, less than about 0.3 wt.%, less than about 0.1 wt.%, less than about 0.07 wt.%, less than about 0.05 wt.%, or less than about 0.01 wt.%, based on the weight of the molecular sieve. In some embodiments, the molecular sieve can be described as bimetallic because it contains two transition metals.

[0052] In some embodiments, the transition metal-exchanged molecular sieve comprises exchanged copper and exchanged manganese in a total amount of about 0.10 to about 10 weight percent of the transition metal-exchanged molecular sieve, about 0.1 to about 7 weight percent of the transition metal-exchanged molecular sieve, about 0.2 to about 7 weight percent of the transition metal-exchanged molecular sieve, about 0.2 to about 5 weight percent of the transition metal-exchanged molecular sieve, about 0.5 to about 6 weight percent of the transition metal-exchanged molecular sieve, about 1 to about 7 weight percent of the transition metal-exchanged molecular sieve, about 1 to about 5 weight percent of the transition metal-exchanged molecular sieve, about 2 to about 5 weight percent of the transition metal-exchanged molecular sieve, about 1.5 to about 3 weight percent of the transition metal-exchanged molecular sieve, about 1.5 to about 4 weight percent of the transition metal-exchanged molecular sieve, or about 2 to about 4 weight percent of the transition metal-exchanged molecular sieve.

[0053] In some embodiments, the transition metal-exchanged molecular sieve of the present invention contains copper by exchange in an amount of about 0.05 to about 7 wt.% of the transition metal-exchanged molecular sieve, about 0.5 to about 5 wt.% of the transition metal-exchanged molecular sieve, about 0.05 to about 5 wt.% of the transition metal-exchanged molecular sieve, about 0.1 to about 4 wt.% of the transition metal-exchanged molecular sieve, about 0.1 to about 3 wt.% of the transition metal-exchanged molecular sieve, about 0.2 to about 3 wt.% of the transition metal-exchanged molecular sieve, about 0.5 to about 2.5 wt.% of the transition metal-exchanged molecular sieve, about 1 to about 4 wt.% of the transition metal-exchanged molecular sieve, or about 1 to about 2 wt.% of the transition metal-exchanged molecular sieve.

[0054] In some embodiments, the transition metal-exchanged molecular sieve of the present invention contains manganese by exchange in an amount of about 0.05 to about 7 wt.% of the transition metal-exchanged molecular sieve, about 0.05 to about 5 wt.% of the transition metal-exchanged molecular sieve, about 0.1 to about 5 wt.% of the transition metal-exchanged molecular sieve, about 0.1 to about 4 wt.% of the transition metal-exchanged molecular sieve, about 0.1 to about 3 wt.% of the transition metal-exchanged molecular sieve, about 0.2 to about 3 wt.% of the transition metal-exchanged molecular sieve, about 0.5 to about 2.5 wt.% of the transition metal-exchanged molecular sieve, or about 1 to about 2 wt.% of the transition metal-exchanged molecular sieve.

[0055] In some embodiments, the transition metal-exchanged molecular sieves of the present invention comprise exchanged copper and exchanged manganese in a weight ratio of about 1:1. In some embodiments, the transition metal-exchanged molecular sieves of the present invention comprise exchanged copper and exchanged manganese in a weight ratio of about 0.1 to about 50, about 0.2 to about 15, or about 0.33 to about 3. In some embodiments, in addition to utilizing the above copper to manganese ratios, the exchange capacity of the molecular sieve, in terms of the ratio of metal ions to exchange sites, should be less than 1, less than 0.75, or less than 0.5. In some embodiments, the transition metal-exchanged molecular sieves have a transition metal to aluminum ratio of less than 1, less than 0.75, or less than 0.5.

[0056] The catalysts of the present invention can be prepared by any suitable means known in the art, including, for example, one-pot, pre-fixing, and spray drying.

[0057] Generally, the selective catalytic reduction catalyst is 0.5 to 4.0 g in -3 , preferably 1.0 to 3.0 4.0 g in -3 The selective catalytic reduction composition comprises a total concentration of

[0058] The SCR catalyst composition may comprise a mixture of a metal oxide-based SCR catalyst formulation and a molecular sieve-based SCR catalyst formulation: (a) the metal oxide-based SCR catalyst formulation may comprise or consist essentially of an oxide of vanadium (e.g., VO), and optionally an oxide of tungsten (e.g., WO), supported on titania (e.g., TiO), and (b) the molecular sieve-based SCR catalyst formulation may comprise a transition metal-exchanged molecular sieve.

[0059] The exhaust system of embodiments of the present invention may include an SCR catalyst positioned downstream of an injector for introducing ammonia or a compound decomposable into ammonia into the exhaust gas. The SCR catalyst may be positioned immediately downstream of the injector for injecting ammonia or a compound decomposable into ammonia (e.g., no intervening catalyst is present between the injector and the SCR catalyst).

[0060] blend Embodiments of the invention may include a blend of (1) platinum on a support and (2) an SCR catalyst comprising a Cu and Mn-exchanged molecular sieve. In some embodiments, within the blend, the weight ratio of the SCR catalyst to platinum on a support is from about 3:1 to about 300:1, from about 3:1 to about 250:1, from about 3:1 to about 200:1, from about 4:1 to about 150:1, from about 5:1 to about 100:1, from about 6:1 to about 90:1, from about 7:1 to about 80:1, from about 7:1 to about 100:1, from about 8:1 to about 70:1, from about 9:1 to about 60:1, or from about 10:1 to about 200:1. 1 to about 50:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 15:1, about 20:1, about 25:1, about 30:1, about 40:1, about 50:1, about 75:1, about 100:1, about 125:1, about 150:1, about 175:1, about 200:1, about 225:1, about 250:1, about 275:1, or about 300:1.

[0061] The term "active component loading" refers to the weight of the platinum support plus the weight of the platinum plus the weight of the first SCR catalyst in the blend. In some embodiments, the platinum is present in an active ingredient loading of about 0.01 wt % to about 0.25 wt %, inclusive, about 0.04 wt % to about 0.2 wt %, inclusive, about 0.07 wt % to about 0.17 wt %, inclusive, about 0.05 wt % to about 0.15 wt %, inclusive, about 0.01 wt %, about 0.02 wt %, about 0.03 wt %, about 0.04 wt %, about 0.05 wt %, about 0.06 wt %, about 0.07 wt %, about 0.08 wt %, about 0.1 wt %, about 0.12 wt %, about 0.15 wt %, about 0.17 wt %, about 0.2 wt %, about 0.22 wt %, or about 0.25 wt %.

[0062] In some embodiments, the blend comprising platinum on a support and an SCR catalyst further comprises at least one of palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru), or rhodium (Rh).

[0063] Base material The catalyst of the present invention may further comprise a flow-through substrate or a filter substrate, respectively. In one embodiment, the catalyst may be coated onto the flow-through substrate or the filter substrate, preferably deposited onto the flow-through substrate or the filter substrate using a washcoat procedure.

[0064] The combination of an SCR catalyst and a filter is known as a selective catalytic reduction filter (SCRF catalyst). SCRF catalysts are single-substrate devices that combine the functions of an SCR and a particulate filter and are suitable for embodiments of the present invention, as desired. References to and references to SCR catalysts throughout this application are understood to also include SCRF catalysts, where applicable. In the case of an SCRF, the selective catalytic reduction composition is generally disposed within the walls of a wall-flow filter substrate monolith. Additionally, the selective catalytic reduction composition may be disposed on the walls of the inlet channels and / or on the walls of the outlet channels.

[0065] The flow-through substrate or filter substrate is a substrate that can contain catalyst / adsorbent components. The substrate is preferably a ceramic substrate or a metal substrate. The ceramic substrate may be made of any suitable refractory material, such as alumina, silica, titania, ceria, zirconia, magnesia, zeolite, silicon nitride, silicon carbide, zirconium silicate, magnesium silicate, aluminosilicates, metalloaluminosilicates (such as cordierite and spodumene), or a mixture or mixed oxide of any two or more thereof. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0066] The metal substrate may be made of any suitable metal, particularly heat-resistant metals and metal alloys such as titanium and stainless steel, and ferritic alloys containing iron, nickel, chromium, and / or aluminum in addition to other trace metals.

[0067] The flow-through substrate is preferably a honeycomb structure with many small, parallel, thin-walled channels that are axially continuous through the substrate and extend entirely from the inlet or 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 elliptical. The flow-through substrate may also be highly porous, allowing the catalyst to penetrate the substrate wall.

[0068] The filter substrate is preferably a wall-flow monolith filter. The channels of the wall-flow filter are alternately blocked, allowing the exhaust gas flow to enter a channel through an inlet, then flow through the channel walls and exit the filter through a different channel leading to an outlet. Thus, particulate matter in the exhaust gas flow is trapped within the filter.

[0069] The catalyst / sorbent may be added to the flow-through or filter substrate by any known means, such as a washcoat procedure.

[0070] composition Embodiments of the present invention relate to a catalyst article having a first coating and a second coating, where the first coating comprises a blend of (1) platinum on a support and (2) a first SCR catalyst comprising a Cu and Mn-exchanged molecular sieve, and the second coating comprises a second SCR catalyst. The catalyst article can be prepared in a variety of configurations. In some embodiments, the coatings are positioned so that the exhaust gas contacts the second coating before contacting the first coating. In some embodiments, the second SCR catalyst is located on the inlet side of the blend. In some embodiments, the SCR catalyst is located on the outlet side of the blend.

[0071] In a first configuration, the catalyst can include a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve, and a second coating including a second SCR catalyst, the second coating being a layer above the first coating and covering all of the first coating. Figure 1 shows an example of this configuration, where a second SCR is positioned in the exhaust gas stream above the blend and covers the entire blend.

[0072] In a second configuration, the catalyst can include a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve, and a second coating including a second SCR catalyst, where the first coating extends from the outlet end toward the inlet end and covers less than the entire length of the substrate, and the second coating extends the entire length of the substrate and completely overlaps the first coating. Figure 2 shows an example of this configuration, where the second SCR is positioned in the exhaust gas stream before the blend and completely overlaps the blend.

[0073] In a third configuration, the catalyst can include a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve, and a second coating including a second SCR catalyst, where the first coating extends from the outlet end toward the inlet end and covers less than the entire length of the substrate, and the second coating extends from the inlet end toward the outlet end and partially overlaps the first coating. The second SCR catalyst can overlap the first coating by an amount of about 10% to about 95%, inclusive, preferably about 50% to about 95%, inclusive. Figure 3 shows an example of this configuration, where a second SCR is positioned in the exhaust gas stream before the blend, and the second SCR covers some, but not all, of the blend. In Figure 3, the second SCR covers about 40% of the blend.

[0074] In a fourth configuration, the catalyst can include a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve, and a second coating including a second SCR catalyst, where the first coating extends from the outlet end toward the inlet end and covers less than the entire length of the substrate, and the second coating extends from the inlet end toward the outlet end and does not overlap the first coating. There may be a space between the first and second coatings, the first and second coatings may be in contact but not overlap, or there may be slight, trace overlap between the first and second coatings. Figure 4 shows an example of this configuration, where the second SCR is positioned in the exhaust gas stream before the blend and is in contact with but not overlapping the blend.

[0075] In a fifth configuration, the catalyst can include a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve, and a second coating including a second SCR catalyst, where the first coating extends from the inlet end toward the outlet end and covers less than the entire length of the substrate, and the second coating extends the entire length of the substrate and completely overlaps the first coating. Figure 5 shows an example of this configuration, where the second SCR covers the entire blend and a portion of the second SCR is positioned in the exhaust gas stream after the blend.

[0076] In a sixth configuration, the catalyst can include a first coating including a blend of (1) platinum on a support and (2) a first SCR catalyst including a Cu and Mn-exchanged molecular sieve, and a second coating including a second SCR catalyst, where the first coating extends from the inlet end toward the outlet end and covers less than the entire length of the substrate, and the second coating extends from the outlet end toward the inlet end and covers less than the entire length of the substrate and partially overlaps the first coating. The second SCR catalyst can overlap the blend by an amount of about 10% to about 95%, inclusive, preferably about 50% to about 95%, inclusive. Figure 6 shows an example of this configuration, where the second SCR covers a portion of the blend but not the entire blend, with a portion of the second SCR positioned in the exhaust gas stream after the blend. In Figure 6, the second SCR covers about 95% of the blend.

[0077] In a seventh configuration, the catalyst can include a first layer containing a third SCR catalyst. The first layer can be partially, but not completely, coated with a coating containing a blend of (1) platinum on a support and (2) a first SCR catalyst containing a Cu and Mn-exchanged molecular sieve. The blend can cover the third SCR catalyst in an amount of about 10% to about 95%, inclusive, preferably about 50% to about 95%, inclusive. The blend can be coated with a coating containing a second SCR catalyst, with the second SCR catalyst coating covering the entire blend coating. Figure 7 shows an example of this configuration, where the third SCR catalyst is the bottom layer on a substrate, a second layer containing the blend partially coating the third SCR catalyst, and a third layer containing the second SCR catalyst positioned on top of the second layer and covering the entire blend layer.

[0078] In an eighth configuration, the catalyst may include a first layer containing a third SCR catalyst. The first layer may be partially, but not completely, coated with a coating containing a blend of (1) platinum on a support and (2) a first SCR catalyst containing a Cu and Mn-exchanged molecular sieve. The blend may cover the third SCR catalyst in an amount of about 10% to about 95%, inclusive, preferably about 50% to about 95%, inclusive. The blend may be covered with a coating containing a second SCR catalyst, the second SCR catalyst coating partially, but not completely, covering the blend coating, and a portion of the second SCR catalyst coating is also located downstream of the blend and also covering a portion of the third SCR catalyst downstream of the blend coating. The second SCR catalyst may cover the third SCR catalyst in an amount of about 10% to about 95%, inclusive, preferably about 50% to about 95%, inclusive. Figure 8 shows an example of this configuration, where a third SCR catalyst is a bottom layer on a substrate, a second layer includes a blend and partially but not completely covers the third SCR catalyst, and a third layer includes a second SCR catalyst and is positioned on top of the second layer, partially but not completely covering the blend layer. In Figure 8, the blend layer covers approximately 60% of the first layer, and the layer with the second SCR catalyst covers approximately 20% of the first layer. The term "covering" refers to the portion of a layer that is in direct contact with another layer.

[0079] Reductant / Urea Injector The 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 preferable that the means for introducing the nitrogenous reductant into the exhaust system is immediately upstream of the ammonia slip catalyst (e.g., there is no intervening catalyst between the means for introducing the nitrogenous reductant and the ammonia slip catalyst).

[0080] 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, atomizer, or feeder. Such means are well known in the art.

[0081] The nitrogen-based reductant for use in the system may be ammonia itself, hydrazine, or an ammonia precursor selected from the group consisting of urea, ammonium carbonate, ammonium carbamate, ammonium bicarbonate, and ammonium formate, with urea being particularly preferred.

[0082] The exhaust system may also include means for controlling the introduction of a reductant into the exhaust gas to reduce NOx. Preferred control means may include an electronic control unit, optionally an engine control unit, and may further include a NOx sensor located downstream of the NOx reduction catalyst.

[0083] Manufacturing method The catalyst articles of some embodiments of the present invention can be prepared by any suitable means known in the art. In the case of catalyst articles comprising platinum on a support, such platinum can be immobilized on the support in solution, i.e., in situ, without the need for a separate pre-immobilization process. To prepare a coating comprising a blend of (1) platinum on a support and (2) an SCR catalyst comprising a Cu and Mn-exchanged molecular sieve, the following steps may be taken: The support material is combined with water and mixed into a batch. Adding an organic acid to act as a reducing agent for the platinum and / or create a reducing environment during the subsequent calcination step. Examples of suitable organic acids include citric acid, succinic acid, oxalic acid, ascorbic acid, acetic acid, formic acid, and combinations thereof. Add platinum nitrate to the batch in an amount such that the molar ratio of organic acid to platinum is 20:1 to 1:1, 10:1 to 1:1, or 5:1 to 1:1. ·Combining platinum batches with SCR batches. Adjust the rheology and % solids of the combined batch, coat and bake in air at 500-550°C.

[0084] How to use A method for reducing emissions from an exhaust stream can include contacting the exhaust stream with a catalytic article described herein. In some embodiments, a method for improving NH conversion of an exhaust gas at temperatures of about 300° C. or less can include contacting an exhaust gas containing ammonia with a catalytic article described herein. In some embodiments, a method for treating an exhaust gas containing ammonia and NOx can include contacting an exhaust gas containing ammonia with a catalytic article described herein. In some embodiments, the ammonia to NOx weight ratio (ANR) in the exhaust gas is >1.0 for at least a portion of the system's operating time.

[0085] effect The catalytic articles of the present invention can provide improved catalytic activity and selectivity. While ammonia slip catalysts comprising a layer having a blend of (1) a platinum group metal on a support and (2) an SCR catalyst have provided improvements in both NO formation and NO regeneration, certain of these catalysts may exhibit drawbacks and / or limitations. In particular, when such catalysts require the platinum group metal to be pre-immobilized on a support, such catalysts involve additional costs associated with the pre-immobilization step and may exhibit lower NH conversion at low temperatures (e.g., below 300°C) and under difficult conditions (e.g., high NH slip and / or high space velocity).

[0086] Surprisingly, it has been discovered that the catalytic articles of the present invention can minimize or mitigate such aforementioned drawbacks and limitations. For example, by immobilizing the platinum group metal on the support in solution, i.e., in situ, the additional costs associated with a pre-immobilization step are eliminated. In addition, such catalytic articles exhibit improved NH conversion at low temperatures (e.g., below 300°C) and under difficult conditions (e.g., high NH slip and / or high space velocity).

[0087] In some embodiments, a catalytic article of the present invention having a platinum group metal immobilized on a support in solution may provide comparable or improved activity for NH conversion at temperatures up to about 300° C. compared to an otherwise comparable catalytic article having a platinum group metal pre-immobilized on a support. In some embodiments, a catalyst article of the invention having a platinum group metal immobilized on a support in solution may have improved activity for NH conversion at temperatures of about 300° C. or less, compared to an otherwise equivalent catalyst article having a platinum group metal pre-immobilized on a support, with the catalyst article of the invention exhibiting an improvement in NH conversion at temperatures of about 300° C. or less of about 30% to about 100%, about 35% to about 95%, about 40% to about 90%, about 45% to about 85%, about 50% to about 80%, about 55% to about 75%, about 30% to about 50%, about 35% to about 55%, about 40% to about 60%, about 50% to about 70%, about 60% to about 80%, about 70% to about 90%, about 80% to about 100%, greater than 30%, greater than 40%, greater than 50%, greater than 60%, greater than 70%, greater than 80%, or greater than 90%.

[0088] In some embodiments, high external surface area zeolites (>50 m 2 The catalyst article of the present invention having platinum on a support comprising a high external surface area zeolite (>50 m / g) or SiO2-Al2O3 mixed oxide is 2 / g) or a catalyst article that is otherwise equivalent, having a platinum group metal immobilized on a support other than a SiO2-Al2O3 mixed oxide, may provide comparable or improved activity for NH3 conversion at temperatures up to about 300°C. In some embodiments, high external surface area zeolites (>50 m 2 The catalyst article of the present invention having platinum on a support comprising a high external surface area zeolite (>50 m / g) or SiO2-Al2O3 mixed oxide is 2%. / g) or a catalyst article that is otherwise equivalent, having a platinum group metal immobilized on a support other than a SiO.sub.2-Al.sub.2O.sub.3 mixed oxide, the catalyst article of the present invention may provide comparable or improved activity for NH.sub.3 conversion at temperatures of about 300.degree. C. or less, compared to an otherwise equivalent catalyst article having a platinum group metal immobilized on a support other than a SiO.sub.2-Al.sub.2O.sub.3 mixed oxide, the catalyst article of the present invention exhibiting an improvement in NH.sub.3 conversion at temperatures of about 300.degree. C. or less of about 30% to about 100%, about 35% to about 95%, about 40% to about 90%, about 45% to about 85%, about 50% to about 80%, about 55% to about 75%, about 30% to about 50%, about 35% to about 55%, about 40% to about 60%, about 50% to about 70%, about 60% to about 80%, about 70% to about 90%, about 80% to about 100%, greater than 30%, greater than 40%, greater than 50%, greater than 60%, greater than 70%, greater than 80%, or greater than 90%.

[0089] Furthermore, it has been surprisingly discovered that additional benefits are obtained when Cu and Mn exchanged molecular sieves are used as part of the blend. Specifically, the use of Cu and Mn exchanged molecular sieves in the blend provides the benefit of improved NH conversion while maintaining the benefits associated with Cu-zeolites for NO formation and NO regeneration. Furthermore, adjusting the amount and / or ratio of Mn and Cu loading provides an advantage in tuning catalytic activity versus selectivity.

[0090] term As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a catalyst" includes a mixture of two or more catalysts, and the like.

[0091] The term "ammonia slip" refers to the amount of unreacted ammonia that passes through the SCR catalyst.

[0092] The term "support" means the material on which the catalyst is fixed.

[0093] The term "calcining" (or "calcination") means heating a substance in air or oxygen. This definition is consistent with the IUPAC definition of calcination. (IUPAC Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"), prepared by A.D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML online modified version: http: / / goldbook.iupac.org (2006-), constructed by M. Nic, J. Jirat, B. Kosata; updates prepared by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351 / goldbook.) Calcination is performed to decompose metal salts, promote exchange of metal ions within the catalyst, and also to adhere the catalyst to the substrate. The temperature used for calcination depends on the components in the material being calcined, and is generally from about 400°C to about 900°C for about 1 to 8 hours. In some cases, calcination can be carried out at temperatures up to about 1200°C. For applications involving the processes described herein, calcination is generally carried out at temperatures from about 400°C to about 700°C for about 1 to 8 hours, preferably from about 400°C to about 650°C for about 1 to 4 hours.

[0094] Where a range or ranges for various numerical elements are specified, unless otherwise specified, the values ​​can be inclusive of the range or ranges.

[0095] The term "N2 selectivity" refers to the conversion of ammonia to nitrogen.

[0096] The terms "diesel oxidation catalyst" (DOC), "diesel exothermic catalyst" (DEC), "NOx absorber", "SCR / PNA" (selective catalytic reduction / passive NOx absorber), "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 the combustion process.

[0097] The term "platinum group metal" or "PGM" refers to platinum, palladium, ruthenium, rhodium, osmium, and iridium. The platinum group metal is preferably platinum, palladium, ruthenium, or rhodium.

[0098] The terms "downstream" and "upstream" describe the orientation of the catalyst or substrate in the direction of exhaust gas flow from the inlet end to the outlet end of the support or article.

[0099] The following examples are merely illustrative of the present invention, and those skilled in the art will recognize many variations that are within the spirit and scope of the claims.

[0100] Example Example 1 In-situ blended catalysts were prepared containing platinum on a support blended with an SCR catalyst. Various catalysts were prepared using different supports, as shown in Table 1 below.

[0101] To prepare the in-situ blended catalysts, in-situ platinum immobilization was used, i.e., the platinum precursor was immobilized on the support in solution, so no separate pre-immobilization process was required, as described below. The support material is combined with water and mixed into a batch. Adding an organic acid to act as a reducing agent for the platinum and / or create a reducing environment during the subsequent calcination step. Examples of suitable organic acids include citric acid, succinic acid, oxalic acid, ascorbic acid, acetic acid, formic acid, and combinations thereof. Add platinum nitrate to the batch in an amount such that the molar ratio of organic acid to platinum is 20:1 to 1:1, 10:1 to 1:1, or 5:1 to 1:1. ·Combining platinum batches with SCR batches. Adjust the rheology and % solids of the combined batch, coat and bake in air at 500-550°C.

[0102] [Table 1] * NOTE: For oxides, total BET surface area is used; for zeolites, t-Plot external surface area is used.

[0103] The following catalysts were prepared: Reference ASC: As a reference example, a two-layer formulation was used with Pt on an alumina bottom layer and an SCR top layer.

[0104] A bottom layer was applied to a ceramic substrate using a washcoat containing 0.17 wt. % Pt on a blend of alumina and exposed zeolite. The washcoat was applied to the ceramic substrate, and then vacuum was used to draw the washcoat down onto the substrate. The article was dried and calcined at about 500°C for about 1 hour. The Pt loading on the article was 3 g / ft. 3 It was.

[0105] A second washcoat containing Cu-CHA was used to apply a top layer to the bottom-coated substrate, and then a vacuum was used to draw the washcoat down onto the substrate. The article was dried and calcined at about 500°C for about 1 hour. The CuCHA loading in the top layer was 1.8 g / in. 3 It was.

[0106] Pre-immobilized Pt-zeolite blend ASC: A washcoat containing a blend of 4 wt. % Pt and Cu-CHA on ZSM-5 (an MFI framework with an SAR of 2000) was used to apply the bottom layer to a ceramic substrate. The washcoat was applied to the ceramic substrate, and then negative pressure was used to draw the washcoat down onto the substrate. The article was dried and calcined at about 500°C for about 1 hour. The loadings of Pt, zeolite, and CuCHA on the article were each 3 g / ft. 3 , 0.045g / in 3 , and 0.9 g / in 3 It was.

[0107] A second washcoat containing Cu-CHA was used to apply a top layer to the bottom-coated substrate, and then a vacuum was used to stretch the washcoat over the substrate to a distance of approximately 50% of the substrate's length. The article was dried and calcined at approximately 500°C for approximately 1 hour. The CuCHA loading in the top layer was 1.8 g / in. 3 It was.

[0108] In-situ blended ASC: Using the procedure described above, two-layer formulations were prepared with an in-situ immobilized Pt-support blend with a Cu-CHA bottom layer and an SCR top layer with various support materials for Pt.

[0109] The bottom layer contained 3.5 wt. % Pt on the support listed in Table 1. The loadings of Pt, support material, and CuCHA on the article were each 3 g / ft 3 , 0.05g / in 3 , and 0.9 g / in 3 It was.

[0110] A second washcoat containing Cu-CHA was used to apply a top layer to the bottom-coated substrate, and then a vacuum was used to draw the washcoat down onto the substrate. The article was dried and calcined at about 500°C for about 1 hour. The CuCHA loading in the top layer was 1.8 g / in. 3 It was.

[0111] The prepared catalyst was tested under the following conditions: -Aging conditions: 650℃, 10% H2O in air, 50 hours Test conditions: 1 minute, 1000 ppm NH3 pulse, 10% O2, 4.5% H2O, 4.5% CO2, balance N2; SV = 120,000 h -1

[0112] Figure 9 shows a summary of NH3 slip, N2O formation, and NOx formation when various ASCs were exposed to a 1-minute pulse of 1000 ppm NH3. All catalysts were 3The Pt loadings were comparable, with the CuCHA overlayer at the same loading. Compared to the reference ASC, all blended ASCs (both pre-loaded Pt-zeolite and in-situ Pt support blends) showed clear advantages in terms of lower NO and NO formation. However, NH conversion efficiency was highly dependent on the choice of Pt support material. Compared to the pre-loaded Pt-zeolite blended ASCs, the in-situ blended ASCs with alumina, silica-alumina, or silica-titania as the Pt support all showed similar or improved NH conversion. Samples with pure siliceous materials (fumed silica, silica gel, and siliceous zeolite) as the Pt support generally had the poorest NH conversion, with the exception of nano-zeolite, which showed the highest NH conversion activity among all the blended ASCs tested.

[0113] Example 2 Reference ASC: As a reference example, a two-layer formulation was used with Pt on an alumina bottom layer and an SCR top layer.

[0114] A bottom layer was applied to a ceramic substrate using a washcoat containing 0.17 wt. % Pt on a blend of alumina and exposed zeolite. The washcoat was applied to the ceramic substrate, and then vacuum was used to draw the washcoat down onto the substrate. The article was dried and calcined at about 500°C for about 1 hour. The Pt loading on the article was 3 g / ft. 3 It was.

[0115] A second washcoat containing Cu-CHA was used to apply a top layer to the bottom-coated substrate, and then a vacuum was used to draw the washcoat down onto the substrate. The article was dried and calcined at about 500°C for about 0.5 hours. The CuCHA loading in the top layer was 1.8 g / in. 3 It was.

[0116] Pt-zeolite blend ASC: A bottom layer was applied to a ceramic substrate using a washcoat containing a blend of 3.5 wt. % Pt on ZSM-5 (an MFI framework with an SAR of 400) and one of Cu-CHA, Cu-AEI, MnCu-CHA, or MnCuAEI. The washcoat was applied to the ceramic substrate, and then vacuum was used to draw the washcoat down onto the substrate. The article was dried and calcined at about 500°C for about 0.5 hours. The loadings of Pt and SCR on the article were each 3 g / ft. 3 , 0.045g / in 3 , and 0.9 g / in 3 It was.

[0117] A second washcoat containing Cu-CHA was used to apply a top layer to the bottom-coated substrate, and then a vacuum was used to stretch the washcoat over the substrate to a distance of approximately 50% of the substrate's length. The article was dried and calcined at approximately 500°C for approximately 0.5 hours. The CuCHA loading in the top layer was 1.8 g / in. 3 It was.

[0118] The formulations were labeled as follows: -ASC-1:Pt.Z+Cu.CHA blend bottom layer -ASC-2:Pt.Z + Cu.AEI blend bottom layer -ASC-3:Pt.Z+MnCu.CHA blend bottom layer -ASC-4:Pt.Z+MnCu.AEI blend bottom layer

[0119] The prepared catalyst was tested under the following conditions: -Aging conditions: 650℃, 10% H2O in air, 50 hours Test conditions: 1 minute, 1000 ppm NH3 pulse, 10% O2, 4.5% H2O, 4.5% CO2, balance N2; SV = 120,000 h -1

[0120] As shown in Figure 10, when comparing Pt-zeolite blend ASCs with either Cu zeolite or MnCu zeolite, the catalysts with MnCu zeolite generally exhibited higher NH conversion, which was comparable to or greater than that of the reference ASC. NO formation in the blend ASCs containing MnCu zeolite was significantly lower than that of the reference ASC. With regard to NO regeneration, all Pt-zeolite blend ASCs exhibited comparable results, much lower than that of the reference ASC. In summary, CuMn zeolite offers the advantage of improved NH conversion while maintaining the advantages associated with Cu-zeolite for NO formation and NO regeneration. Furthermore, adjusting the amount and / or ratio of Mn and Cu loadings can be effective in tuning catalyst activity versus selectivity.

Claims

1. 1. A catalytic article comprising: a substrate having an inlet and an outlet; a first coating comprising a blend of (1) platinum on a support and (2) a first SCR catalyst; a second coating comprising a second SCR catalyst; The carrier is a molecular sieve or SiO ２ -Al ２ O ３ mixed oxides, The catalyst article, wherein the first SCR catalyst comprises a Cu and Mn exchanged molecular sieve.

2. The catalytic article of claim 1 , wherein the first SCR catalyst molecular sieve comprises a small pore molecular sieve.

3. The catalytic article of claim 1 , wherein the first SCR catalyst molecular sieve comprises AEI, CHA, or a combination thereof.

4. 10. The catalytic article of claim 1, wherein the first SCR catalyst molecular sieve is essentially free of any transition metals other than Cu and Mn.

5. 10. The catalyst article of claim 1, wherein the first SCR catalyst molecular sieve comprises Cu and Mn in a combined amount of 0.10 to 10 wt. % of the Cu and Mn exchanged molecular sieve.

6. 10. The catalyst article of claim 1, wherein the first SCR catalyst molecular sieve comprises Cu in an amount of 0.05 to 5 wt. % of the Cu and Mn exchanged molecular sieve.

7. 10. The catalyst article of claim 1, wherein the first SCR catalyst molecular sieve comprises Mn in an amount of 0.05 to 5 wt. % of the Cu and Mn exchanged molecular sieve.

8. 10. The catalytic article of claim 1, wherein the first SCR catalyst molecular sieve comprises Cu and Mn in a weight ratio of 0.1-50.

9. The catalytic article of claim 1 , wherein the platinum is immobilized on the support in solution.

10. The support is SiO ２ -Al ２ O ３ The catalytic article of claim 1 comprising a mixed oxide.

11. SiO ２ 11. The catalytic article of claim 10, wherein is present in an amount of from 1% to 70% by weight of said mixed oxide.

12. The catalytic article of claim 1 , wherein the support comprises a molecular sieve.

13. The molecular sieve is at least 50 m ２ 13. The catalyst article of claim 12, comprising an external surface area of ​​0.15 wt. / g.

14. 13. The catalytic article of claim 12, wherein the molecular sieve is selected from the group of framework types consisting of CHA, LEV, AEI, AFX, ERI, SFW, KFI, DDR, ITE, BEA, MFI, and FER.

15. 10. The catalyst article of claim 1, wherein the platinum is present in an amount of 0.01 to 0.3 wt. %, based on the weight of the support for platinum in the blend plus the weight of platinum plus the weight of the first SCR catalyst.

16. 10. The catalytic article of claim 1, wherein the weight ratio of the first SCR catalyst to platinum on the support is in the range of 0:1 to 300:1 based on the weight of these components.

17. The catalytic article of claim 1 , wherein the blend further comprises at least one of palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru), or rhodium (Rh).

18. 10. The catalytic article of claim 1, wherein the second SCR catalyst comprises a small pore molecular sieve selected from the group of framework types consisting of CHA, LEV, AEI, AFX, ERI, SFW, KFI, DDR, and ITE.

19. the second SCR catalyst comprises at least one base metal promoter, the at least one base metal promoter being selected from the group consisting of (i) Ce and Zr or (ii) MnO ２ 2. The catalytic article of claim 1, wherein:

20. 10. An exhaust system comprising the catalyst article of claim 1, means for introducing a reductant upstream of the catalyst article, and a third SCR catalyst, the catalyst article being disposed downstream of the third SCR catalyst.

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