US Patent 7344684 Exhaust emission purifying catalyst device

There is provided an exhaust emission purifying catalyst device which is comprised of a carrier disposed in an exhaust passage and including through holes passed through the carrier in an axial direction (flowing direction), and supporting layers made of fire-resistance inorganic oxide formed on inner surfaces of the through holes. The supporting layers support noble metal and NOx trapping agents which occlude NOx in exhaust gas when the exhaust air-fuel ratio is lean, and emits and reduces the occluded NOx when the exhaust air-fuel ratio is stoichiometric or rich. The amount of the supported noble metal is set to be smaller in an exhaust passage upstream area of the carrier than in an exhaust passage downstream area of the carrier.