Catalytic converter for automotive pollution control, and process for making catalytic converter

Abstract

A catalytic converter for cleaning exhaust gas includes a heat-resistant support, and a coating formed on the support. The coating includes at least one kind of catalytically active substance and a zirconium oxide. The zirconium oxide has a pre-aging specific surface area I and a post-aging specific surface area A, wherein the aging is performed in an atmosphere of 1,000° C. for 5 hours, and wherein A/I≧0.4 and I≧40m 2 /g.

1 . A catalytic converter for cleaning exhaust gas comprising: 
 a heat-resistant support; and    a coating formed on the support, the coating including at least one kind of catalytically active substance and a zirconium oxide;    wherein the zirconium oxide having a pre-aging specific surface area I and a post-aging specific surface area A, the aging being performed in an atmosphere of 1,000° C. for 5 hours; and    wherein A/I≧0.4 and I≧40m 2 /g.    
     
     
         2 . The catalytic converter according to  claim 1 , wherein the zirconium oxide is a zirconium complex oxide represented by the following formula,  
       Zr 1−(x+y) Ce x R y Oxide  
       where R represents a rare earth element other than Ce or an alkaline earth metal, the zirconium complex oxide meeting 0.12≦x≦0.25 and 0.02≦y≦0.15 in said formula.  
     
     
         3 . The catalytic converter according to  claim 1 , wherein the catalytically active substance is selected from a group consisting of Pt, Rh and Pd.  
     
     
         4 . The catalytic converter according to  claim 1 , wherein the coating further comprises an oxygen-storing oxide.  
     
     
         5 . The catalytic converter according to  claim 4 , wherein the oxygen-storing oxide is a cerium complex oxide.  
     
     
         6 . The catalytic converter according to  claim 1 , wherein the coating further comprises at least one heat-resistant inorganic oxide selected from a group consisting of alumina, silica, titania and magnesia.  
     
     
         7 . The catalytic converter according to  claim 1 , wherein the heat-resistant support has a honeycomb structure.  
     
     
         8 . A process for making a catalytic converter for cleaning exhaust gas, comprising the steps of: 
 performing preliminary baking of a zirconium oxide for causing a decrease in specific surface area of the zirconium oxide; and    coating the preliminarily baked zirconium oxide on a heat-resistant support together with at least one kind of catalytically active substance.    
     
     
         9 . The process according to  claim 8 , wherein the preliminary baking step is performed at a temperature of not lower than 700° C.  
     
     
         10 . The process according to  claim 8 , wherein the preliminarily baked zirconium complex oxide is first treated to support the catalytically active substance and then coated on the heat-resistant support.  
     
     
         11 . The process according to  claim 8 , wherein the zirconium oxide is a zirconium complex oxide represented by the following formula,  
       Zr 1−(x+y) Ce x R y Oxide  
       where R represents a rare earth element other than Ce or an alkaline earth metal, the zirconium complex oxide meeting 0.12≦x≦0.25 and 0.02≦y≦0.15 in said formula.  
     
     
         12 . The process according to  claim 8 , wherein the catalytically active substance is selected from a group consisting of Pt, Rh and Pd.