Novel catalyst for selective NOx reduction using hydrocarbons

Abstract

This invention discloses a catalyst and process for removing nitrogen oxides from exhaust streams under lean burn conditions using hydrocarbons as the reductant. Catalysts consists of two phases, a metal exchanged molecular sieve and a stabilizing metal oxide associated with the molecular sieve.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A two phase catalyst comprising a molecular sieve having a pore size not less than about 4 Å supported transition metal and a stabilizing oxide.  
     
     
         2 . The two phase catalyst of  claim 1 , wherein the molecular sieve is a zeolite of one or more of zeolite Y, zeolite beta, mordenite, ferrierite, ZSM-5, and ZSM-12.  
     
     
         3 . The two phase catalyst of  claim 2 , wherein the transition metal is one or more of Cu, Co, Fe and Mo and the stabilizing oxide is one or more of the oxides of Ce, Zr, Mo, V and Nb.  
     
     
         4 . The two phase catalyst of  claim 1 , wherein the two phases are a physical mixture.  
     
     
         5 . The two phase catalyst of  claim 1 , wherein the zeolite is impregnated with the stabilizing oxide.  
     
     
         6 . A two phase catalyst comprising a zeolite supported transition metal and a stabilizing oxide.  
     
     
         7 . The two phase catalyst of  claim 6 , wherein the zeolite has a pore size not less than about 4 Å.  
     
     
         8 . The two phase catalyst of  claim 6 , wherein the zeolite has a pore size in the range of from about 4 Å to about 8 Å.  
     
     
         9 . The two phase catalyst of  claim 6 , wherein the zeolite is one or more of zeolite beta, mordenite, ferrierite, ZSM-5, ZSM-12, and zeolite Y.  
     
     
         10 . The two phase catalyst of  claim 7 , wherein the transition metal is one or more of Cu, Co, Fe and Mo.  
     
     
         11 . The two phase catalyst of  claim 7 , wherein the stabilizing oxide is one or more of the rare earth oxides, zirconium oxide, molybdenum oxide, vanadium oxide and niobium oxide.  
     
     
         12 . The two phase catalyst of  claim 10 , wherein the stabilizing oxide one or more of the oxides of Ce, Zr, Mo, V and Nb.  
     
     
         13 . The two phase catalyst of  claim 12 , wherein the transition metal includes Cu and the stabilizing oxide includes CeO 2 .  
     
     
         14 . The two phase catalyst of  claim 13 , wherein the zeolite has both Al and Si and the Si to Al ratio is between about 238 and about 17.  
     
     
         15 . The two phase catalyst of  claim 6 , wherein the two phases are a physical mixture.  
     
     
         16 . The two phase catalyst of  claim 6 , wherein the stabilizing oxide is impregnated on the zeolite.  
     
     
         17 . A method of remediating the concentration of nitrogen oxides (NO x ) in the exhaust from lean burn combustion in the presence of water comprising contacting the exhaust containing water and NO x  with one or more of an alkane or alkene reductant or mixtures thereof at a temperature of not greater than about 600° C. with a two part catalyst comprising a molecular sieve having a pore size not less than about 4 Å supported transition metal and a stabilizing oxide.  
     
     
         18 . The method of  claim 17 , wherein the molecular sieve is a zeolite.  
     
     
         19 . The catalyst of  claim 18 , wherein the zeolite has a pore size in the range of from about 4 Å to about 8 Å.  
     
     
         20 . The method of  claim 18 , wherein the zeolite is one or more of zeolite beta, mordenite, ferrierite, ZSM-5, ZSM-12, and zeolite Y.  
     
     
         21 . The method of  claim 17 , wherein the transition metal is one or more of Cu, Co, Fe and Mo.  
     
     
         22 . The method of  claim 17 , wherein the stabilizing oxide is one or more of the rare earth oxides, zirconium oxide, molybdenum oxide, vanadium oxide and niobium oxide.  
     
     
         23 . The method of  claim 18 , wherein the stabilizing oxide is one or more of the oxides of Ce, Zr, Mo, V and Nb and the transition metal is one or more of Cu, Co, Fe and Mo.  
     
     
         24 . The method of  claim 23 , wherein the transition metal includes Cu and the stabilizing oxide includes CeO 2 .  
     
     
         25 . The method of  claim 24 , wherein the zeolite has both Al and Si and the Si to Al ratio is between about 238 and about 17.  
     
     
         26 . The method of  claim 17 , wherein the reductant is a C 1  to C 16  hydrocarbon.  
     
     
         27 . The method of  claim 17 , wherein nitrogen oxides are present in a concentration of the exhaust gas of not less than about 100 ppm.  
     
     
         28 . The method of  claim 17 , wherein nitrogen oxides are present in a concentration of the exhaust gas in the range of from about 100 ppm to about 2000 ppm.  
     
     
         29 . The method of  claim 27 , wherein the exhaust contacting the catalyst is at a temperature less than about 500° C.  
     
     
         30 . The method of  claim 27 , wherein the exhaust contacting the catalyst is at a temperature less than about 350° C. and has water present in the exhaust at a concentration of not less than about 10% by volume.