Exhaust gas purification system

Abstract

An upstream catalyst ( 3 ) and a downstream catalyst ( 4 ) are disposed upstream of a particulate filter ( 5 ) in an exhaust passage of a diesel engine. The downstream catalyst ( 4 ) has a larger amount of support material for supporting catalytic metal than the upstream catalyst ( 3 ). This enhances the efficiency of oxidation reactions of HC in the catalysts to raise the temperature of exhaust gas flowing into the filter ( 5 ).

1 . An exhaust gas purification system for a diesel engine in which a filter for trapping particulates in exhaust gas from the engine is disposed in an exhaust passage of the engine and a catalyst for oxidizing HC in exhaust gas is disposed upstream of the filter in the exhaust passage, wherein 
 the catalyst comprises a catalytic layer which is formed on the wall surfaces of each cell of a honeycomb support and contains catalytic metal, active alumina and an oxygen storage component both serving as a support material which supports the catalytic metal, and    part of the catalyst downstream in the direction of flow of the exhaust gas is larger than part of the catalyst upstream in the direction of flow of the exhaust gas in terms of the amount of the support material per unit area of the wall surfaces of the cells of the honeycomb support.    
   
   
       2 . The exhaust gas purification system of  claim 1 , wherein the catalyst is an oxidation catalyst.  
   
   
       3 . The exhaust gas purification system of  claim 1 , wherein the catalyst is a lean-NOx catalyst.