Combined slip catalyst and hydrocarbon exotherm catalyst

Abstract

A catalyst comprising: (a) a first layer comprising an oxidizing catalyst having an effective PGM loading such that oxidation of hydrocarbons generates sufficient heat to regenerate soot, wherein said effective amount of PGM is greater than about 10 g/ft 3 ; and (b) a second layer adjacent to said first layer and comprising a reducing catalyst to selectively reduce NOx.

What is claimed is: 
     
         1 . A catalyst comprising:
 a first layer comprising an oxidizing catalyst having an effective PGM loading such that oxidation of hydrocarbons generates sufficient heat to regenerate soot, wherein said effective amount of PGM is greater than about 10 g/ft 3 ; and   a second layer adjacent to said first layer and comprising a reducing catalyst to selectively reduce NOx.   
     
     
         2 . The catalyst of  claim 1 , wherein said effective amount of PGM is greater than about 15 g/ft 3 . 
     
     
         3 . The catalyst of  claim 2 , wherein said effective amount of PGM is about 15 g/ft3 to about 70 g/ft3. 
     
     
         4 . The catalyst of  claim 3 , wherein said effective amount of PGM is no less than about 20 g/ft3. 
     
     
         5 . The catalyst of  claim 1 , wherein said PGM is selected from the group consisting of Pt and Pd and combinations thereof. 
     
     
         6 . The catalyst of  claim 5 , wherein said PGM is a combination of Pt and Pd. 
     
     
         7 . The catalyst of  claim 1 , wherein said catalyst has a HC light-off temperature of less than 350° C. in an atmosphere of 12% O2, 200 ppm NH3, 200 ppm CO, 1000 ppm C10H22, 4.5% H2O, 4.5% CO2, and the balance N2. 
     
     
         8 . The catalyst of  claim 7 , wherein said HC light-off temperature is no greater than about 325° C. 
     
     
         9 . The catalyst of  claim 1 , wherein said SCR catalyst is a molecular sieve loaded with a transition metal. 
     
     
         10 . The catalyst of  claim 9 , wherein said transition metal is selected from Cu, Fe and combinations thereof. 
     
     
         11 . The catalyst of  claim 10 , wherein said molecular sieve is a SAPO, CHA or a beta zeolite. 
     
     
         12 . The catalyst of  claim 1 , further comprising a substrate upon which said first layer is disposed. 
     
     
         13 . The catalyst of  claim 12 , wherein said second layer overlays said first layer. 
     
     
         14 . The catalyst of  claim 12 , wherein said first layer is upstream of said second layer. 
     
     
         15 . A method of generating heat for soot removal and reducing NH3 slip in an exhaust system, said method comprising:
 injecting nitrogenous reductant into an exhaust flow having NOx   reducing said NOx using said nitrogenous reductant in the presence of an SCR catalyst to form a NOx-reduced gas stream, which, at least intermittently, contains slip nitrogenous reductant;   injecting HC into said NOx-reduced gas stream to form a HC-enriched gas stream; and   contacting said HC-enriched gas stream with a combined catalyst to form a heated gas stream, said combined catalyst comprising a first layer having an oxidization catalyst to oxidize at least a portion of said HC to heat said heated gas stream, and a second layer having an SCR catalyst to reduce at least a portion of NOx in said heated gas stream.   
     
     
         16 . The method of  claim 15 , wherein said heated gas stream is heated to at least 400° C. 
     
     
         17 . The method of  claim 15 , wherein said HC-enriched gas stream is less than 350° C. 
     
     
         18 . The method of  claim 15 , wherein said first layer is loaded with greater than about 15 g/ft 3  PGM.