Exhaust emission control device for an internal combustion engine

Abstract

A three-way catalyst ( 30 ) comprises a microporous catalyst element ( 30 a ) having a micropore group whose average pore opening size is smaller than molecular size of HC in a washcoat and a macroporous catalyst element ( 30 b ) having a macropore group whose average pore opening size is larger than the molecular size of HC in a washcoat.

1 . An exhaust emission control device for an internal combustion engine, comprising: 
 a three-way catalyst located in an exhaust channel of an internal combustion engine, wherein:    said three-way catalyst comprises one or more catalyst elements and has two or more pore groups different in average pore opening size in a washcoat.    
     
     
         2 . The exhaust emission control device for an internal combustion engine according to  claim 1 , wherein: 
 said three-way catalyst comprises a microporous catalyst element having a micropore group whose average pore opening size is smaller than prescribed size in a washcoat and a macroporous catalyst element having a macropore group whose average pore opening size is larger than said prescribed size in a washcoat.    
     
     
         3 . The exhaust emission control device for an internal combustion engine according to  claim 2 , wherein: 
 said three-way catalyst comprises a microporous catalyst element having a micropore group whose average pore opening size is smaller than molecular size of HC in a washcoat and a macroporous catalyst element having a macropore group whose average pore opening size is larger than the molecular size of HC in a washcoat.    
     
     
         4 . The exhaust emission control device for an internal combustion engine according to  claim 2 , wherein: 
 said microporous catalyst element and said macroporous catalyst element are arranged in series with each other, facing in a direction of an exhaust flow.    
     
     
         5 . The exhaust emission control device for an internal combustion engine according to  claim 4 , wherein: 
 said microporous catalyst element is disposed on the upstream side of the exhaust flow, and said macroporous catalyst element on the downstream side of the exhaust flow.    
     
     
         6 . The exhaust emission control device for an internal combustion engine according to  claim 2 , wherein: 
 said microporous catalyst element and said macroporous catalyst element are arranged in layers.    
     
     
         7 . The exhaust emission control device for an internal combustion engine according to  claim 6 , wherein: 
 said microporous catalyst element is disposed on a surface layer side, and said macroporous catalyst element on an internal layer side.    
     
     
         8 . The exhaust emission control device for an internal combustion engine according to  claim 1 , further comprising: 
 air-fuel ratio modulating means for periodically modulating an air-fuel ratio of an exhaust emission that flows into said three-way catalyst between a lean air-fuel ratio and a rich air-fuel ratio.