Exhaust system including paticulate filter with oxidation zone capable of generating no2 under lean conditions

Abstract

Systems and methods of the present invention related to an exhaust gas purification system comprising: (a) a particulate filter including an inlet and an outlet with an axial length L therebetween, wherein the filter includes an oxidation catalyst capable of generating NO2 under lean burn conditions; (b) an injector for injecting ammonia or a compound decomposable to ammonia into the exhaust gas, located downstream of the filter; and (c) a downstream catalyst comprising a selective catalytic reduction (SCR) catalyst, located downstream of the injector.

1 . A system for treating exhaust gas from a lean-burn combustion engine comprising:
 a. a particulate filter including an inlet and an outlet with an axial length L therebetween, wherein the filter includes an oxidation catalyst capable of generating NO 2  under lean burn conditions;   b. an injector for injecting ammonia or a compound decomposable to ammonia into the exhaust gas, located downstream of the filter; and   c. a downstream catalyst comprising a selective catalytic reduction (SCR) catalyst, located downstream of the injector.   
     
     
         2 . The system of  claim 1 , wherein the oxidation catalyst is coated on the outlet of the filter. 
     
     
         3 . The system of  claim 1 , wherein the oxidation catalyst comprises one or more platinum group metals. 
     
     
         4 . The system of  claim 1 , wherein the oxidation catalyst comprises platinum, palladium, or combinations thereof. 
     
     
         5 . The system of  claim 1 , wherein the oxidation catalyst is coated extending from the outlet end for at least 50% of L. 
     
     
         6 . The system of  claim 1 , wherein the filter further comprises a three-way catalyst (TWC) or a lean NO x  trap (LNT) catalyst. 
     
     
         7 . The system of  claim 6 , wherein the TWC or the LNT catalyst is coated on the inlet of the filter. 
     
     
         8 . The system of  claim 7 , wherein the TWC or the LNT catalyst is coated extending from the inlet for at least 50% of L. 
     
     
         9 . The system of  claim 8 , wherein the oxidation catalyst and the TWC or the LNT catalyst compositions overlap by at most 80% of L. 
     
     
         10 . The system of  claim 1 , wherein the SCR catalyst comprises a metal oxide based SCR catalyst formulation, a molecular sieve based SCR catalyst formulation, or mixtures thereof. 
     
     
         11 . The system of  claim 1 , wherein the exhaust gas entering the downstream catalyst has a NO 2 :NO x  ratio of more than 10%. 
     
     
         12 . The system of  claim 1 , wherein the lean-burn combustion engine is a lean-burn gasoline engine. 
     
     
         13 . The system of  claim 12 , wherein the gasoline engine is a direct-injection gasoline engine. 
     
     
         14 . The system of  claim 12 , wherein the particulate filter is a gasoline particulate filter (GPF). 
     
     
         15 . The system of  claim 1 , further comprising an upstream catalyst located upstream of the filter, the upstream catalyst comprising a second three-way catalyst, a NO x  storage catalyst, a three-way NO x  trap (TWLNT) catalyst, or combinations thereof. 
     
     
         16 . The system of  claim 15 , wherein the upstream catalyst is coated onto an electrically-heated catalyst (EHC). 
     
     
         17 . A method of purifying exhaust gas from a lean burn combustion engine, comprising:
 a. passing the exhaust gas through a particulate filter including an inlet and an outlet with an axial length L therebetween, wherein the filter includes an oxidation catalyst capable of generating NO 2  under lean burn conditions;   b. adding ammonia or a compound decomposable into ammonia into the exhaust gas by an injector, located downstream of the filter; and   c. passing the exhaust gas through a downstream catalyst comprising a selective reduction catalyst, located downstream of the injector.   
     
     
         18 . The method of  claim 17 , wherein the oxidation catalyst is coated on the outlet of the filter. 
     
     
         19 . (canceled) 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . The method of  claim 17 , wherein the filter further comprises a three-way catalyst (TWC) or a lean NO x  trap (LNT) catalyst. 
     
     
         23 . The system of  claim 22 , wherein the TWC or the LNT catalyst is coated on the inlet of the filter. 
     
     
         24 - 32 . (canceled)