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 . An exhaust system for treatment of an exhaust gas stream comprising NO x  and particulate matter, the exhaust system comprising:
 an SCR catalyst substrate containing a catalyst comprising a transition metal-containing silicoaluminophosphate, aluminophosphate, metal-substituted silicoaluminophosphate, or metal-substituted aluminophosphate having a CHA framework structure; and   an ammonia injector or an ammonia precursor injector positioned upstream of the SCR catalyst substrate;   wherein the catalyst is effective to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively; and   wherein the transition metal is selected from Cr, Mn, Fe, Co, Ce, Ni, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir, Pt, and combinations thereof.   
     
     
         2 . The exhaust system of  claim 1 , wherein the catalyst comprises an Fe-containing silicoaluminophosphate. 
     
     
         3 . The exhaust system of  claim 2 , wherein the catalyst comprises Fe-SAPO-34. 
     
     
         4 . The exhaust system of  claim 3 , wherein the catalyst contains a binder selected from the group consisting of alumina, silica, (non-zeolite) silica-alumina, naturally occurring clays, TiO 2 , ZrO 2 , and SnO 2 . 
     
     
         5 . The exhaust system of  claim 4 , wherein the binder comprises ZrO 2 . 
     
     
         6 . The exhaust system of  claim 3 , wherein the Fe-SAPO-34 contains between about 0.5 wt. % and about 5 wt. % Fe. 
     
     
         7 . The exhaust system of  claim 6 , wherein the Fe-SAPO-34 contains about 3 wt. % Fe. 
     
     
         8 . The exhaust system of  claim 3 , wherein the Fe-SAPO-34 is combined with a metal-containing zeolite SCR catalyst selected from small pore aluminosilicate zeolites, Beta zeolite, zeolite Y, and ZSM-5. 
     
     
         9 . The exhaust system of  claim 1 , further comprising means for metering urea flowing into the system. 
     
     
         10 . The exhaust system of  claim 1 , further comprising a second substrate interposed between the ammonia injector or ammonia precursor injector and the SCR catalyst substrate. 
     
     
         11 . The exhaust system of  claim 10 , wherein the second substrate is selected from a honeycomb flow through substrate, a wall flow substrate, or a honeycomb wall flow substrate. 
     
     
         12 . The exhaust system of  claim 1 , further comprising an oxidation catalyst upstream of the ammonia injector or ammonia precursor injector. 
     
     
         13 . The exhaust system of  claim 1 , wherein the catalyst comprises a transition metal loaded on a metal-substituted silicoaluminophosphate. 
     
     
         14 . The exhaust system of  claim 13 , wherein the metal-substituted silicoaluminophosphate is substituted with one or more of As, B, Be, Co, Fe, Ga, Ge, Li, Mg, Mn, Zn and Zr. 
     
     
         15 . The exhaust system of  claim 14 , wherein the metal-substituted silicoaluminophosphate is substituted with Zr. 
     
     
         16 . The exhaust system of  claim 13 , wherein the metal-substituted silicoaluminophosphate comprises metal-substituted SAPO-34 and the transition metal comprises Fe. 
     
     
         17 . The exhaust system of  claim 16 , wherein the metal-substituted SAPO-34 is substituted with one or more of As, B, Be, Co, Fe, Ga, Ge, Li, Mg, Mn, Zn and Zr. 
     
     
         18 . The exhaust system of  claim 17 , wherein the SAPO-34 is substituted with Zr. 
     
     
         19 . The exhaust system of  claim 1 , wherein the substrate is a filtering substrate. 
     
     
         20 . The exhaust system of  claim 19 , wherein the filtering substrate is a wall-flow filter. 
     
     
         21 . The exhaust system of  claim 1 , wherein the substrate is a flow-through substrate. 
     
     
         22 . The exhaust system of  claim 1 , wherein the substrate comprises a washcoat of the catalyst. 
     
     
         23 . The exhaust system of  claim 1 , wherein the catalyst is combined with a metal-containing small pore zeolite. 
     
     
         24 . An exhaust system for treatment of an exhaust gas stream comprising NO x  and particulate matter, the exhaust system comprising:
 a SCR catalyst substrate containing a catalyst comprising an Fe-loaded silicoaluminophosphate having a CHA framework structure and an Fe-loading so that the catalyst is effective to selectively reduce nitrogen oxides with ammonia in the presence of oxygen in an exhaust gas stream at low temperature; and   an ammonia injector or an ammonia precursor injector positioned upstream of the SCR catalyst substrate for injecting ammonia or an ammonia precursor;   wherein the catalyst is effective to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively.   
     
     
         25 . An exhaust system for treatment of an exhaust gas stream comprising NO x  and particulate matter, the exhaust system comprising:
 an SCR catalyst substrate containing a catalyst comprising a transition metal loaded on at least one of AlPO-34, [Al—As—O]-CHA, [Al—Co—P—O]-CHA, |Co|[Be—P—O]-CHA, |Co 3  (C 6 N 4 H 24 ) 3  (H 2 O) 9 |[Be 18 P 18 O 72 ]-CHA, [Co—Al—P—O]-CHA, [Mg—Al—P—O]-CHA, [Si—O]-CHA, [Zn—Al—P—O]-CHA, [Zn—As—O]-CHA, CoAPO-44, CoAPO-47, DAF-5, GaPO-34, LZ-218, MeAPO-47, MeAPSO-47, (Ni(deta) 2 )-UT-6, SAPO-34, SAPO-47, UiO-21, and ZYT-6; and   an ammonia injector or an ammonia precursor injector positioned upstream of the SCR catalyst substrate;   wherein the catalyst is effective to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively; and   wherein the transition metal is selected from Cr, Mn, Fe, Co, Ce, Ni, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir, Pt, and combinations thereof.   
     
     
         26 . An exhaust system for treatment of an exhaust gas stream comprising NO x  and particulate matter, the exhaust system comprising an SCR catalyst substrate containing a catalyst comprising a transition metal-containing silicoaluminophosphate having a CHA framework structure,
 wherein the transition metal is selected from Cr, Mn, Fe, Co, Ce, Ni, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir, Pt, and combinations thereof.   
     
     
         27 . The exhaust system of  claim 26 , wherein the transition metal is Fe. 
     
     
         28 . The exhaust system of  claim 27 , wherein the Fe-containing silicoaluminophosphate comprises Fe-SAPO-34. 
     
     
         29 . The exhaust system of  claim 28 , wherein the Fe-SAPO-34 contains between about 0.5 wt. % and about 5 wt. % Fe. 
     
     
         30 . The exhaust system of  claim 29 , wherein the Fe-SAPO-34 contains about 3 wt. % Fe. 
     
     
         31 . A catalyst article comprising
 a catalyst substrate containing a catalyst comprising a transition metal-containing silicoaluminophosphate, aluminophosphate, metal-substituted silicoaluminophosphate, or metal-substituted aluminophosphate having a CHA framework structure;   wherein the catalyst is effective to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively; and   wherein the transition metal is selected from Cr, Mn, Fe, Co, Ce, Ni, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir, Pt, and combinations thereof.   
     
     
         32 . The catalyst article of  claim 31 , wherein the transition metal is Fe. 
     
     
         33 . The catalyst article of  claim 31 , wherein the catalyst comprises a transition metal-containing SAPO-34. 
     
     
         34 . The catalyst article of  claim 31 , wherein the catalyst comprises Fe-SAPO-34.