Patent ID: 8713921

Claim:
An exhaust-gas purification catalytic system, comprising an upstream catalyst and a downstream catalyst provided upstream and downstream, respectively, in a flow of exhaust gas in an exhaust passage of an engine, wherein each of the upstream catalyst and the downstream catalyst includes a plurality of catalyst layers stacked on a substrate, the plurality of catalyst layers of each of the upstream catalyst and the downstream catalyst include an upper catalyst layer containing an oxygen storage/release material in/on which a catalytic metal is included or loaded, a content of the oxygen storage/release material per 1 L of the substrate in the upper catalyst layer of the upstream catalyst is larger than that in the upper catalyst layer of the downstream catalyst, an oxygen release amount per a unit amount of a catalytic metal included in or loaded on the oxygen storage/release material for the upper catalyst layer of the downstream catalyst is larger than that for the upper catalyst layer of the upstream catalyst, and at least part of the oxygen storage/release material included in the upper catalyst layer of the downstream catalyst shows a particle size distribution having a peak particle size smaller than that included in the upper catalyst layer of the upstream catalyst.