Patent ID: 8679411

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 an Rh-including catalyst layer including Rh and provided on a substrate, the Rh-including catalyst layer of the upstream catalyst includes, as oxygen storage/release materials, Rh-doped CeZr-based mixed oxide containing Ce and Zr and also containing Rh dissolved therein, and Rh-loading CeZr-based mixed oxide containing Ce and Zr and loading Rh on a surface thereof, the Rh-including catalyst layer of the downstream catalyst includes, as an oxygen storage/release material, only Rh-doped CeZr-based mixed oxide containing Ce and Zr and also containing Rh dissolved therein, a content of the oxygen storage/release material included per 1 L of the substrate in the Rh-including catalyst layer of the upstream catalyst is smaller than that of the downstream catalyst, and the Rh-doped CeZr-based mixed oxide included as the oxygen storage/release material in the Rh-including catalyst layer of the upstream catalyst shows a particle size distribution having a peak particle size smaller than that of the Rh-doped CeZr-based mixed oxide included as the oxygen storage/release material in the Rh-including catalyst layer of the downstream catalyst.