Bimetallic catalysts for selective ammonia oxidation

Abstract

Catalysts, methods, and systems for treating diesel engine exhaust streams are described. In one or more embodiments, the catalyst comprises a molecular sieve having a silica to alumina ratio (SAR) less than about 30, the molecular sieve including ion-exchanged copper and ion-exchanged platinum. Systems including such catalysts and methods of treating exhaust gas are also provided.

1 .- 20 . (canceled) 
     
     
         21 . A catalyst for oxidizing ammonia to nitrogen and NOx, the catalyst comprising an aluminosilicate molecular sieve having a silica-to-alumina ratio (SAR) less than 30, the molecular sieve comprising ion-exchanged copper and ion-exchanged platinum, wherein the molecular sieve comprises a zeolite having a crystal framework type selected from FAU, MFI, MOR, BEA, HEU, and OFF, and wherein the catalyst is obtainable by a process comprising:
 (a) ion-exchange of copper on the molecular sieve,   (b) calcination of the molecular sieve obtained in (a), and   (c) ion-exchange of platinum on the molecular sieve obtained in (b).   
     
     
         22 . The catalyst of  claim 21 , further comprising an amount of metallic platinum. 
     
     
         23 . The catalyst of  claim 22 , wherein the aluminosilicate molecular sieve comprises a zeolite having a crystal framework type selected from FAU, MFI, MOR and BEA. 
     
     
         24 . The catalyst of  claim 21 , wherein the aluminosilicate molecular sieve comprises a zeolite having a crystal framework type FAU and the zeolite has a SAR less than 10. 
     
     
         25 . The catalyst of  claim 21 , wherein the aluminosilicate molecular sieve comprises a zeolite having a crystal framework type FAU and the zeolite has a SAR less than 6. 
     
     
         26 . The catalyst of  claim 21 , wherein the catalyst is coated on a refractory ceramic support. 
     
     
         27 . The catalyst of  claim 26 , wherein the total loading of the molecular sieve in the substrate is in the range of 18.3 g/1l (0.3 g/in3) and 183 g/1l (3.0 g/in3), based on the total catalyst volume. 
     
     
         28 . The catalyst of  claim 21 , wherein the platinum particle size is in the range of 10-50 nm. 
     
     
         29 . A method for treating emissions produced in the exhaust gas stream of a diesel or lean burn vehicle, the method comprising:
 passing a vehicle's engine exhaust stream through at least a NOx abatement catalyst; and   passing the exhaust stream exiting the NOx abatement catalyst and containing ammonia through an oxidation catalyst according to  claim 21 .   
     
     
         30 . The method of  claim 29 , wherein the NOx abatement catalyst is selected from one or more of an SCR catalyst, a lean NOx trap catalyst, or other catalyst for the destruction of NOx that results in slippage of ammonia from the NOx abatement catalyst. 
     
     
         31 . The method of  claim 29 , wherein the aluminosilicate molecular sieve comprises a zeolite having a crystal framework type FAU and the SAR is less than 10. 
     
     
         32 . The method of  claim 29 , wherein the aluminosilicate molecular sieve comprises a zeolite having a crystal framework type FAU and the SAR is less than 6. 
     
     
         33 . A system for treating an exhaust gas stream comprising:
 an SCR catalyst in communication with the exhaust gas stream;   an ammonia or ammonia precursor injection port in communication with the exhaust gas stream and located upstream from the SCR catalyst; and   the catalyst of  claim 21  in communication with the exhaust gas stream and located downstream from the SCR catalyst.