Exhaust gas purifying catalyst and production method thereof

Abstract

An exhaust gas purifying catalyst including: a plurality of first compounds 5 which have precious metal particles 3 supported thereon and are formed into a particle shape; and second compounds 7 which are arranged among the plurality of first compounds 5 and separate the first compounds 5 from one another, wherein pore volumes of the precious metal particles 3, the first compounds 5 and the second compounds 7 are 0.24 to 0.8 cm 3 /g.

1 . An exhaust gas purifying catalyst, comprising:
 a honeycomb carrier; and   a catalyst layer provided on the honeycomb carrier, the catalyst layer comprising:
 precious metal particles; 
 a plurality of first compounds on which the precious metal particles are supported; and 
 second compounds which cover the plurality of first compounds on which the precious metal particles are supported and separate the first compounds from one another, 
   wherein a pore volume of the catalyst layer is within a range of 0.24 to 0.8 cm 3 /g.   
     
     
         2 . The exhaust gas purifying catalyst according to  claim 1 , wherein the first compounds are an oxide containing Ce. 
     
     
         3 . The exhaust gas purifying catalyst according to  claim 1 , wherein the first compounds contain CeO 2.    
     
     
         4 . The exhaust gas purifying catalyst according to  claim 1 , wherein the first compounds contain a composite oxide of Ce and Zr. 
     
     
         5 . The exhaust gas purifying catalyst according to  claim 1 , wherein the second compounds comprises Al 2 O 3 . 
     
     
         6 . The exhaust gas purifying catalyst according to  claim 1 , wherein the second compounds are an oxide containing at least either of Al and Zr. 
     
     
         7 . The exhaust gas purifying catalyst according to  claim 1 , wherein both of the first compounds and the second compounds are formed into a particle shape, and an average particle diameter of the second compounds is 10 to 100 nm. 
     
     
         8 . The exhaust gas purifying catalyst according to  claim 1 , wherein the precious metal particles comprises at least one selected from the group consisting of Pt, Pd and Rh. 
     
     
         9 . The exhaust gas purifying catalyst according to  claim 1 , wherein the pore volume of the first compounds is within a range of 0.18 to 0.38 cm 3 /g. 
     
     
         10 . The exhaust gas purifying catalyst according to  claim 1 , wherein the first compounds are composed of CeO 2  that occupies 74 to 80% and ZrO 2  that occupies 20 to 26%. 
     
     
         11 . The exhaust gas purifying catalyst according to  claim 1 , wherein the first compounds are composed of ZrO 2  that occupies 95 to 99% and La 2 O 3  that occupies 1 to 5%. 
     
     
         12 . The exhaust gas purifying catalyst according to  claim 1 , wherein a pore volume of a precursor of the second compounds after being calcined is within a range of 0.8 to 1.0 cm 3 /g. 
     
     
         13 . The exhaust gas purifying catalyst according to  claim 5 , wherein the alumina comprises CeO 2  that occupies 5 to 15% and ZrO 2  that occupies 3 to 7%. 
     
     
         14 . The exhaust gas purifying catalyst according to  claim 1 , wherein an aspect ratio of the precursor of the second compounds is within a range of 0.5 to 10. 
     
     
         15 . The exhaust gas purifying catalyst according to  claim 1 ,
 wherein the second compounds comprise Al 2 O 3  derived from boehmite of which an aspect ratio is within a range of 0.5 to 10.   
     
     
         16 . The exhaust gas purifying catalyst according to  claim 1 , wherein a degree of dispersion of the precious metal particles in powder of the exhaust gas purifying catalyst is within a range of 35 to 80%. 
     
     
         17 . The exhaust gas purifying catalyst according to  claim 1 , wherein a degree of dispersion of the precious metal particles supported on the first compounds is within a range of 50 to 100%.