CATALYSTS FOR TREATING TRANSIENT NOx EMISSIONS

Abstract

A heterogeneous catalyst article having at least one combination of a first molecular sieve having a medium pore, large pore, or meso-pore crystal structure and optionally containing a first metal, and a second molecular sieve having a small pore crystal structure and optionally containing a second metal, and a monolith substrate onto or within which said catalytic component is incorporated, wherein the combination of the first and second molecular sieves is a blend, a plurality of layers, and/or a plurality of zones.

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         41 . A catalyst for use in selective catalytic reduction (SCR), said catalyst comprising one or more zeolites of the MFI structure type, and one or more zeolites of the CHA structure type, wherein at least part of the one or more zeolites of the MFI structure type contains iron (Fe), and wherein at least part of the one or more zeolites of the CHA structure type contains copper (Cu). 
     
     
         42 . The catalyst of  claim 41 , wherein the weight ratio of the one or more zeolites of the MFI structure type relative to the one or more zeolites of the CHA structure type ranges from 0.1 to 1. 
     
     
         43 . The catalyst of  claim 41 , wherein one or more of the zeolites comprise both Al and Si in their respective zeolite frameworks. 
     
     
         44 . The catalyst of  claim 43 , wherein the molar ratio of silica to alumina (SAR) in the one or more zeolites of the CHA structure type ranges from 8 to 150. 
     
     
         45 . The catalyst of  claim 41 , wherein the amount of Fe in the one or more zeolites of the MFI structure type ranges from 0.01 to 20 wt.-% based on the weight of said one or more zeolites. 
     
     
         46 . The catalyst of  claim 41 , wherein the amount of Fe in the one or more zeolites of the MFI structure type ranges from 0.1 to 10 wt.-% based on the weight of said one or more zeolites. 
     
     
         47 . The catalyst of  claim 41 , wherein the amount of Cu in the one or more zeolites of the CHA structure type ranges from 0.01 to 20 wt.-% based on the weight of said one or more zeolites. 
     
     
         48 . The catalyst of  claim 41 , wherein the amount of Cu in the one or more zeolites of the CHA structure type ranges from 0.1 to 10 wt.-% based on the weight of said one or more zeolites. 
     
     
         49 . A catalyst article comprising a honeycomb substrate onto which the catalyst of  claim 41  is provided. 
     
     
         50 . The catalyst article of  claim 49 , wherein the substrate is selected from the group consisting of flow-through substrates and wall-flow substrates. 
     
     
         51 . The catalyst article of  claim 49 , wherein the catalyst comprises a washcoat layer provided on the substrate, the zeolites being contained in one single layer. 
     
     
         52 . An exhaust gas treatment system comprising the SCR catalyst of  claim 41 , an internal combustion engine, and an exhaust gas conduit in fluid communication with the internal combustion engine, wherein said SCR catalyst is present in the exhaust gas conduit, and wherein the internal combustion engine is one of a lean burn engine or a diesel engine. 
     
     
         53 . The exhaust gas treatment system of  claim 52  further comprising at least one of an oxidation catalyst and a diesel particulate filter in said conduit and located upstream from the SCR catalyst. 
     
     
         54 . A process for the treatment of a gas stream comprising NO x , said process comprising conducting a gas stream over a catalyst according to  claim 41 , wherein the gas stream is a diesel exhaust gas stream. 
     
     
         55 . The process for the treatment of a gas stream comprising NO x  according to  claim 54 , wherein the gas stream comprises at least one of ammonia and urea. 
     
     
         56 . The process of  claim 54 , wherein the weight ratio of the one or more zeolites of the MFI structure type relative to the one or more zeolites of the CHA structure type ranges from 0.1 to 1. 
     
     
         57 . The catalyst of  claim 43 , wherein the molar ratio of silica to alumina (SAR) in the one or more zeolites of the CHA structure type ranges from 25 to 50. 
     
     
         58 . The catalyst of  claim 41 , wherein the amount of Fe in the one or more zeolites of the MFI structure type ranges from 0.5 to 5.0 wt.-% based on the weight of said one or more zeolites. 
     
     
         59 . The catalyst of  claim 41 , wherein the amount of Cu in the one or more zeolites of the CHA structure type ranges from 2.0 to 4.0 wt.-% based on the weight of said one or more zeolites. 
     
     
         60 . A catalytic combination comprising:
 a first molecular sieve having a first framework structure containing a first metal, said first framework structure selected from the group consisting of AEL, AFI, AFO, AFR, ATO, iron isomorphous BEA, BEA, GME, HEU, MFI, MWW, OFF, and a meso-pore crystal structure; and   a second molecular sieve having a second framework structure containing a second metal, said second framework structure 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, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG and ZON,   wherein said first and second metals are selected from the group consisting of Cr, Mn, Fe, Co, Ce, Ni, Cu, Zn, Ga, Mo, Ru, Rh, Pd, Pt, Ag, In, Sn, Re, and Ir.   
     
     
         61 . The catalytic combination of  claim 60 , wherein said first molecular sieve contains about 0.01 to about 20 weight percent of said first metal, and said second molecular sieve contains about 0.01 to about 20 weight percent of said second metal. 
     
     
         62 . The catalytic combination of  claim 60 , wherein said second metal is copper, said second molecular sieve has a CHA framework structure and contains about 0.5 to about 5 weight percent copper, said first metal is iron, and said first molecular sieve has either an iron isomorphous BEA framework structure having a silica-to-ferric oxide ratio of about 50 to about 200 or a pre-aged BEA framework structure containing 0.5 to 5.0 weight percent iron. 
     
     
         63 . The catalytic combination of  claim 62 , wherein said second molecular sieve has a silica-to-alumina ratio of about 8 to about 150. 
     
     
         64 . The catalytic combination of  claim 62 , wherein said second molecular sieve contains about 2.0 to about 4.0 weight percent copper. 
     
     
         65 . The catalytic combination of  claim 62 , wherein said second molecular sieve is SSZ-13. 
     
     
         66 . The catalytic combination of  claim 65 , wherein said catalytic combination comprises a weight ratio of said first molecular sieve to said second molecular sieve of about 0.1 to about 1.0. 
     
     
         67 . The catalytic combination of  claim 66 , wherein said first molecular sieve has an iron isomorphous BEA framework structure and said weight ratio is about 0.2 to about 0.6. 
     
     
         68 . A heterogeneous catalyst article comprising:
 said catalytic combination of  claim 60 ; and   a monolith substrate, wherein said catalytic combination is incorporated onto or within said monolith substrate,   wherein said catalytic combination is in a form selected from the group consisting of a blend, a plurality of layers, and a plurality of zones and wherein said second molecular sieve comprises a majority of said combination based on the combined weight of said first and second molecular sieves.   
     
     
         69 . A method for treating a diesel exhaust gas stream comprising contacting a feed exhaust gas stream over or through the heterogeneous catalyst article of  claim 68  in the presence of a nitrogenous reductant at a temperature of about 150° C. to about 750° C. to produce a treated exhaust gas stream, wherein said feed exhaust gas stream has a first concentration of NO x , said treated exhaust gas stream has a second concentration of NO x  and said second concentration of NO x  is less than said first concentration of NO x . 
     
     
         70 . The method of  claim 69 , wherein:
 said first molecular sieve has either an iron isomorphous BEA framework structure having a silica-to-ferric oxide ratio of about 50 to about 200 or a pre-aged BEA framework structure containing 0.5 to 5.0 weight percent iron;   said second molecular sieve has a CHA framework structure having a silica-to-alumina ratio of about 8 to about 150 and contains about 0.5 to about 5 weight percent copper;   said combination comprises said first molecular sieve and said second molecular sieve in a weight ratio of about 0.25 to about 0.50;   said temperature is about 175° C. to about 400° C.; and   said feed exhaust gas stream contacts said heterogeneous catalyst article at a gas hourly space velocity of about 10,000/hour to about 200,000/hour.