CATALYST DEVICE FOR EXHAUST GAS PURIFICATION AND METHOD OF PURIFYING EXHAUST GAS

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A catalyst device for exhaust gas purification is provided which comprises two or more honeycomb-structure catalysts each comprising a honeycomb structure whose surface has been coated with two or more layers of a catalyst composition. The catalysts are disposed in the passage of the exhaust gas discharged from an internal combustion engine. The exhaust gas is passed through the catalysts to remove hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The catalyst device for exhaust gas purification is characterized in that the honeycomb-structure catalyst (X) located upstream and the honeycomb-structure catalyst (Y) located downstream each contains, in the lower layer, a catalyst composition comprising : an inorganic oxide base containing substantially no rhodium ingredient and having, deposited on the base, at least one of a platinum ingredient and a palladium ingredient; a cerium-containing oxide; and an alkaline-earth metal ingredient. The device is further characterized in that the upper-layer catalyst composition in each of the catalyst (X) and the catalyst (Y) comprises an oxide base and a rhodium ingredient deposited thereon and contains substantially neither a platinum ingredient nor a palladium ingredient, and that the honeycomb-structure catalyst (X) and the honeycomb-structure catalyst (Y) differ in constitution. Also provided is a method of purifying an exhaust gas.