Transition metal/zeolite scr catalysts

Abstract

A method of converting nitrogen oxides in a gas to nitrogen by contacting the nitrogen oxides with a nitrogenous reducing agent in the presence of a zeolite catalyst containing at least one transition metal, wherein the zeolite is a small pore zeolite containing a maximum ring size of eight tetrahedral atoms, wherein the at least one transition metal is selected from the group consisting of Cr, Mn, Fe, Co, Ce, Ni, Cu, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir and Pt.

1 . A catalyst article comprising a substrate having a catalyst washcoat, the catalyst washcoat comprising
 (a) a first molecular sieve component comprising an aluminosilicate having a CHA framework and containing from 0.01 to 20 weight percent of a metal selected from the group consisting of Cr, Mn, Fe, Co, Ce, Ni, Cu, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir, Pt, and combinations thereof; and   (b) a second molecular sieve component comprising a silicoaluminophosphate having a CHA framework and containing from 0.01 to 20 weight percent of a metal selected from the group consisting of Cr, Mn, Fe, Co, Ce, Ni, Cu, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir, Pt, and combinations thereof.   
     
     
         2 . The catalyst article of  claim 1 , wherein the aluminosilicate is SSZ-13 and the silicoaluminophosphate is SAPO-34. 
     
     
         3 . The catalyst article of  claim 2 , wherein each of the SAPO-34 and the SSZ-13 contains at least one of Cu or Fe. 
     
     
         4 . The catalyst article of  claim 3 , wherein each of the SAPO-34 and the SSZ-13 contains Cu. 
     
     
         5 . The catalyst article of  claim 3 , wherein the SAPO-34 and the SSZ-13 together contain between about 0.5 and about 5 wt. % metal, based on the combined weight of the first and second molecular sieve components. 
     
     
         6 . The catalyst article of  claim 1 , wherein the catalyst washcoat further comprises a metal-containing medium-, large-, or meso-pore zeolite. 
     
     
         7 . The catalyst article of  claim 3 , wherein at least one of said Cu and Fe are added during synthesis of the SAPO-34, the SSZ-13, or both. 
     
     
         8 . The catalyst article of  claim 1 , wherein the substrate is selected from a wall-flow filter, a sintered metal filter, and a partial filter. 
     
     
         9 . The catalyst article of  claim 1 , wherein the substrate is selected from a metal flow-through substrate and a ceramic flow-through substrate. 
     
     
         10 . The catalyst article of  claim 1 , wherein the catalyst washcoat further comprises at least one binder selected from alumina, silica, non-zeolite silica-alumina, natural clay, TiO 2 , ZrO 2 , and SnO 2 . 
     
     
         11 . A catalytic washcoat comprising SAPO-34 and SSZ-13, wherein each of the SAPO-34 and the SSZ-13 contains at least one of Cu or Fe, and further comprising at least one binder selected from alumina, silica, non-zeolite silica-alumina, natural clay, TiO 2 , ZrO 2 , and SnO 2 . 
     
     
         12 . An exhaust system for treatment of an exhaust gas stream comprising NO x  and particulate matter, the exhaust system comprising:
 The catalyst of  claim 1 ; and   an ammonia injector or an ammonia precursor injector positioned upstream of the catalyst;   wherein the catalyst is effective to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively.