Exhaust gas purifying catalyst

Abstract

An exhaust gas purifying catalyst includes two catalyst layers containing a fire resistant inorganic compound carrying a catalyst component in an exhaust gas passage of a base material provided with the exhaust gas passage penetrating through the base material from the exhaust gas introduction port side to discharge port side, wherein each catalyst layer is formed by supporting the catalyst component on a different fire resistant inorganic compound, a catalyst layer extended from the exhaust gas introduction port side to the exhaust gas discharge port side and a catalyst layer extended from the exhaust gas discharge port side to the exhaust gas introduction port side are formed such that the catalyst layers are overlapped on each other and the exhaust gas introduction port side is coated only with one of the catalyst layers and the exhaust gas discharge port side is coated only with the other.

1 . An exhaust gas purifying catalyst in an exhaust gas passage penetrating through a base material from an exhaust gas introduction port side to an exhaust gas discharge port side, the catalyst comprising a first and a second catalyst layer each containing a fire resistant inorganic compound carrying a catalyst component, wherein each catalyst layer is formed by supporting the catalyst component on a different fire resistant inorganic compound, the first catalyst layer extended from the exhaust gas introduction port side to the exhaust gas discharge port side and the second catalyst layer extended from the exhaust gas discharge port side to the exhaust gas introduction port side, the first and second catalyst layers being formed such that the catalyst layers are partly overlapped on each other, the exhaust gas introduction port side is coated only with the first catalyst layer, and the exhaust gas discharge port side is coated only with the second catalyst layer. 
     
     
         2 . The exhaust gas purifying catalyst according to  claim 1 , wherein the exhaust gas passage has a total passage length, the first catalyst layer extending a length of 40% or more to less than 100% of the total passage length from the exhaust gas introduction port side to the exhaust gas discharge port side, and the second catalyst layer extending a length of 40% or more to less than 100% of the total passage length from the exhaust gas discharge port side to the exhaust gas introduction port side such that the first and second catalyst layers are partly overlapped on each other. 
     
     
         3 . The exhaust gas purifying catalyst according to  claim 2 , wherein after the first catalyst layer extending from the exhaust gas introduction port side to the exhaust gas discharge port side is formed, the second catalyst layer extending from the exhaust gas discharge port side to the exhaust gas introduction port side is formed. 
     
     
         4 . The exhaust gas purifying catalyst according to  claim 2 , wherein after the second catalyst layer extending from the exhaust gas discharge port side to the exhaust gas introduction port side is formed, the first catalyst layer extending from the exhaust gas introduction port side to the exhaust gas discharge port side is formed. 
     
     
         5 . The exhaust gas purifying catalyst according to  claim 3 , wherein the first catalyst layer comprises as the catalyst component a precious metal selected from the group consisting of platinum, palladium, rhodium, and platinum/palladium; and the second catalyst layer comprises as the catalyst component a precious metal selected from the group of platinum, palladium, rhodium, rhodium/platinum and rhodium/palladium. 
     
     
         6 . The exhaust gas purifying catalyst according to  claim 3 , wherein the first catalyst layer comprises as the catalyst component a precious metal selected from the group consisting of platinum, palladium, rhodium, rhodium/platinum and rhodium/palladium; and the second catalyst layer comprises as the catalyst component a precious metal selected from the group consisting of platinum, palladium, rhodium and palladium/platinum. 
     
     
         7 . The exhaust gas purifying catalyst according to  claim 2 , wherein the first catalyst layer extends a length of 45% or more to less than 90% of the total passage length from the exhaust gas introduction port side to the exhaust gas discharge port side, and the second catalyst layer extending a length of 45% or more to less than 90% of the total passage length from the exhaust gas discharge port side to the exhaust gas introduction port side such that the first and second catalyst layers are partly overlapped on each other. 
     
     
         8 . The exhaust gas purifying catalyst according to  claim 1 , wherein the base material comprises a material selected from the group consisting of cordierite, metal, silicon carbine, silicon nitride, and aluminum nitride, and mixtures thereof. 
     
     
         9 . The exhaust gas purifying catalyst according to  claim 1 , wherein the catalyst component is selected from the group consisting of nickel, copper, manganese, iron, cobalt, zinc, gold, silver, ruthenium, rhodium, palladium, osmium, iridium, and platinum, and mixtures or combinations thereof. 
     
     
         10 . The exhaust gas purifying catalyst according to  claim 9 , wherein the catalyst component is a mixture of nickel and platinum or palladium. 
     
     
         11 . The exhaust gas purifying catalyst according to  claim 1 , wherein the fire resistant inorganic compound is one or more types of compounds selected from the group consisting of alumina, silica alumina, zeolite, titanium oxide, silica, ceria, and zirconia, and the composite oxides thereof, and mixtures or combinations thereof, and the fire resistant inorganic compound of the first catalyst layer and the second catalyst layer differ in composition and/or type. 
     
     
         12 . The exhaust gas purifying catalyst according to  claim 1 , wherein the fire resistant inorganic compound is a powder having an average particle diameter of 2 to 10 microns (μm). 
     
     
         13 . An exhaust gas purifying system comprising
 a base material having a total exhaust passage length extending from an exhaust gas introduction port side to an exhaust gas discharge port side,   a first catalyst layer comprising a first fire resistant inorganic compound carrying a catalyst component, the first catalyst layer extending from the exhaust gas introduction port side to the exhaust gas discharge port side, and   a second catalyst layer comprising a second fire resistant inorganic compound carrying a catalyst component, the second catalyst layer extending from the exhaust gas discharge port side to the exhaust gas introduction port side, and   wherein the exhaust gas introduction port side is coated only with the first catalyst layer in a portion ‘B’ of the total exhaust passage length, and the exhaust gas discharge port side is coated only with the second catalyst layer in a portion ‘C’ of the total passage length, and the first and second catalyst layers are partly overlapped on each other in a portion ‘A’ extending a length of 20% or more to less than 90% of the total passage length.   
     
     
         14 . The exhaust gas purifying system according to  claim 13 , wherein the portion ‘A’ extends a length of 30% or more to less than 80% of the total passage length. 
     
     
         15 . The exhaust gas purifying system according to  claim 13 , wherein a ratio of the portion ‘B’ to the portion ‘C’ is from about 1:1 to about 1:5, such that the portions ‘B’ and ‘C’ overlap to form the portion ‘A’. 
     
     
         16 . The exhaust gas purifying system according to  claim 13 , wherein the base material comprises a material from the group consisting of cordierite, metal, silicon carbine, silicon nitride, and aluminum nitride, and mixtures thereof. 
     
     
         17 . The exhaust gas purifying system according to  claim 13 , wherein the catalyst component is selected from the group consisting of nickel, copper, manganese, iron, cobalt, zinc, gold, silver, ruthenium, rhodium, palladium, osmium, iridium, and platinum, and mixtures or combinations thereof, and the catalyst components of the first catalyst layer and the second catalyst layer are the same or are different. 
     
     
         18 . The exhaust gas purifying system according to  claim 13 , wherein the first and second fire resistant inorganic compounds are one or more types of compounds selected from the group consisting of alumina, silica alumina, zeolite, titanium oxide, silica, ceria, and zirconia, and the composite oxides thereof, and mixtures or combinations thereof, and the first and second fire resistant inorganic compounds differ in composition and/or type. 
     
     
         19 . A method of making an exhaust gas purifying system comprising
 preparing a base material having a plurality of exhaust gas passages and a total exhaust passage length extending from an exhaust gas introduction port side to an exhaust gas discharge port side, the base material comprising a material from the group consisting of cordierite, metal, silicon carbine, silicon nitride, and aluminum nitride, and mixtures thereof,   immersing the base material in a first catalyst slurry at a length of 40% or more to less than 100% of the total passage length from the exhaust gas introduction port side to the exhaust gas discharge port side, the first catalyst slurry comprising a first fire resistant inorganic compound carrying a catalyst component, followed by drying and calcining to form a first catalyst layer on the base material, and   immersing the base material in a second catalyst slurry at a length of 40% or more to less than 100% of the total passage length from the exhaust gas discharge port side to the exhaust gas introduction port side, the second catalyst slurry comprising a second fire resistant inorganic compound carrying a catalyst component, followed by drying and calcining to form a second catalyst layer on the base material,   wherein the exhaust gas introduction port side is coated only with the first catalyst layer in a portion ‘B’ of the total exhaust passage length, and the exhaust gas discharge port side is coated only with the second catalyst layer in a portion ‘C’ of the total passage length, and the first and second catalyst layers are partly overlapped on each other in a portion ‘A’ extending a length of 20% or more to less than 90% of the total passage length.   
     
     
         20 . The method of making an exhaust gas purifying system of  claim 19 , wherein the first catalyst slurry and the second catalyst slurry further comprise alkali metals, alkali earth metals, or rare earth elements.