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 - 50 . (canceled) 
     
     
         51 . A method of selective catalytic reduction (SCR) of NOx in exhaust gas, said method comprising: contacting exhaust gas with a microporous crystalline material comprising SAPO-34. 
     
     
         52 . The method of  claim 51 , wherein said crystalline material comprises iron and/or copper. 
     
     
         53 . The method of  claim 51 , wherein said contacting step is performed in the presence of ammonia or urea. 
     
     
         54 . The method of  claim 52 , wherein said iron comprises at least 0.10 weight percent of the total weight of said material. 
     
     
         55 . The method of  claim 52 , wherein said copper comprises at least 1.0 weight percent of the total weight of said material. 
     
     
         56 . The method of  claim 51 , further comprising providing an article comprising said microporous crystalline material, wherein said article is in the form of a honeycombed-shaped body. 
     
     
         57 . The method of  claim 56 , wherein the honeycombed-shaped body or structural piece is formed by extruding a mixture comprising the SAPO-34 molecular sieve. 
     
     
         58 . The method of  claim 56 , wherein the honeycombed-shaped body or structural piece is formed by coating or depositing a mixture comprising the SAPO-34 molecular sieve on a preformed substrate. 
     
     
         59 . The method of  claim 53 , wherein said SAPO-34 contains at least one transition metal, selected from the group consisting of Fe, Cu, and combinations thereof, said transition metal having a concentration of about 0.5 to about 5 wt % of said SAPO-34 and said transition metal, and wherein said contacting occurs at a temperature of about 150° C. to about 750° C. 
     
     
         60 . A method of converting NOx in an exhaust gas to nitrogen, said method comprising: contacting said NOx with a nitrogenous reductant at a temperature of about 150° C. to about 750° C. and in the presence of a catalyst comprising SAPO-34 and at least one transition metal, selected from the group consisting of Fe, Cu, and combinations thereof, said transition metal having a concentration of about 0.5 to about 5 wt % of said SAPO-34 and said transition metal. 
     
     
         61 . The method of  claim 60 , wherein the nitrogenous reductant is ammonia per se, hydrazine or an ammonia precursor selected from the group consisting of urea ((NH 2 ) 2 CO), ammonium carbonate, ammonium carbamate, ammonium hydrogen carbonate and ammonium formate. 
     
     
         62 . The method of  claim 61 , wherein addition of nitrogenous reductant is controlled so that NH 3  at said catalyst inlet is about 60% to 200% of theoretical ammonia calculated at 1:1 NH 3 /NO and 4:3 NH 3 /NO 2 . 
     
     
         63 . The method of  claim 60 , further comprising
 oxidizing nitrogen monoxide in said exhaust gas to form nitrogen dioxide using an oxidation catalyst located upstream of said catalyst, said oxidation catalyst being adapted to yield a resulting gas stream having a ratio of NO to NO 2  of about 4:1 to about 1:3 by volume; and   mixing said resulting gas stream with said nitrogenous reductant upstream of said catalyst.   
     
     
         64 . The method of  claim 60 , wherein said exhaust gas is derived from a combustion process. 
     
     
         65 . The method of  claim 64 , wherein said combustion process is the combustion of fuel in a vehicular lean burn internal combustion engine.