US Patent 8713921 Exhaust-gas purification catalytic system

An upper catalyst layer of an upstream catalyst 3 and a downstream catalyst 5 includes an oxygen storage/release material in/on which a catalytic metal is included or loaded. The content of the oxygen storage/release material per 1 L of a substrate in the catalyst layer of the upstream catalyst 3 is larger than that in the catalyst layer of the downstream catalyst 5. The oxygen release amount per a unit amount of the Rh is larger than that for the upper catalyst layer of the upstream catalyst 5. At least part of the oxygen storage/release material included in the downstream catalyst shows a particle size distribution having a peak particle size smaller than that in the upstream catalyst 5.