Patent ID: 7169734

Claim:
A method of producing an exhaust gas purifying catalyst adapted to adsorb nitrogen oxides in exhaust gas which is in a lean region, and to reduce the adsorbed nitrogen oxides in exhaust gas which is in a range including a rich region and a stoichiometric region, said exhaust gas purifying catalyst including a monolithic substrate; a first catalytic layer formed on said monolithic substrate, said first catalytic layer containing at least one noble metal selected from the group consisting of rhodium, platinum and palladium, a compound of at least one metal selected from the group consisting of alkali metal, alkaline earth metal and rare earth metal, and alumina; and a second catalytic layer formed on said first catalytic layer and containing rhodium, at least one noble metal selected from the group consisting of platinum and palladium, a compound of at least one metal selected from the group consisting of alkali metal, alkaline earth metal and rare earth metal, and alumina, a content of the compound of at least one metal in said second catalytic layer being larger than that in said first catalytic layer, said method comprising: preparing a first powder by causing the at least one noble metal selected from the group consisting of rhodium, platinum and palladium to be carried on alumina; preparing a first aqueous solution of the compound of at least one metal selected from the group consisting of alkali metal, alkaline earth metal and rare earth metal; forming a first mixture of the first powder and the first aqueous solution; grinding the first mixture to form a first slurry; coating the first slurry on the monolithic substrate to form the first catalytic layer; preparing a second powder by causing rhodium to be carried on alumina; preparing a third powder by causing at least one noble metal selected from the group consisting of platinum and palladium to be carried on alumina; preparing a second aqueous solution of the compound of at least one metal selected from the group consisting of alkali metal, alkaline earth metal and rare earth metal; forming a second mixture of the second powder, the third powder and the second aqueous solution; grinding the second mixture to form a second slurry; and coating the second slurry on the first catalytic layer formed on the monolithic substrate to form the second catalytic layer.