Exhaust gas purifying catalyst and method of producing same

Abstract

An exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine of an automotive vehicle. The exhaust gas purifying catalyst comprises a substrate on which a catalytic coat layer containing a catalyst component is formed. The catalytic coat layer is formed by coating a slurry containing the catalyst component on a surface of the substrate. A crack-preventing coat layer is formed on an upper-most surface of the catalytic coat layer. The crack-preventing coat layer has a thickness of not larger than 50 μm.

What is claimed is:  
     
         1 . An exhaust gas purifying catalyst comprising: 
 a substrate;    a catalytic coat layer containing a catalyst component, formed on said substrate, said catalytic coat layer being formed by coating a slurry containing the catalyst component on a surface of said substrate; and    a crack-preventing coat layer formed on an upper-most surface of said catalytic coat layer, said crack-preventing coat layer having a thickness of not larger than 50 μm.    
     
     
         2 . An exhaust gas purifying catalyst as claimed in    claim 1   , wherein said crack-preventing coat layer containing particle materials having an average particle size ranging from 3 to 7 μm.  
     
     
         3 . An exhaust gas purifying catalyst as claimed in    claim 1   , wherein said crack-preventing coat layer is formed by coating a slurry on the upper-most surface of said catalytic coat layer, wherein the slurry for said crack-preventing coat layer has an ion content of not higher than 50 ppm.  
     
     
         4 . An exhaust gas purifying catalyst as claimed in    claim 1   , wherein said substrate is a monolithic substrate.  
     
     
         5 . An exhaust gas purifying catalyst as claimed in    claim 4   , wherein said monolithic substrate is one selected from the group consisting of ceramic honeycomb-type monolithic substrate and a metallic honeycomb-type monolithic substrate.  
     
     
         6 . A method of producing an exhaust gas purifying catalyst, comprising: 
 coating a substrate with a first slurry containing a catalytic component;    drying and firing the first slurry on said substrate to form a first catalytic coat layer on said substrate;    coating a second slurry containing a catalytic component, on an upper-most surface of said catalytic coat layer, said second slurry containing particle materials having an average particle size ranging from 3 to 7 μm; and    drying and firing the second slurry on the first catalytic coat layer to form a second catalytic coat layer having a thickness of not larger than 50 μm.    
     
     
         7 . A method as claimed in    claim 6   , wherein said second slurry contains alumina.  
     
     
         8 . A method as claimed in    claim 6   , wherein said second slurry contains porous substance.  
     
     
         9 . A method of producing an exhaust gas purifying catalyst, comprising: 
 preparing a slurry including a catalyst component and water which containing anion other than OH −  in a content of not larger than 50 ppm and cation other than H +  in a content of not larger than 50 ppm;    coating a substrate with the slurry; and    drying and firing the slurry on said substrate to form a catalytic coat layer on said substrate.