To provide a perovskite-type composite oxide which has stable quality in which a solid solution of Pd is formed at a high rate, a method for producing the perovskite-type composite oxide, and a catalyst composition containing the perovskite-type composite oxide, the perovskite-type composite oxide is produced by formulating materials in accordance with each atomic ratio of a perovskite-type composite oxide represented by the following general formula (1):



        A_xB_(1-y)Pd_yO_3+δ     (1)



wherein A represents at least one element selected from rare earth elements and alkaline earth metals; B represents at least one element selected from transition elements (excluding rare earth elements, and Pd), Al and Si; x represents an atomic ratio satisfying the following condition: 1 < x; y represents an atomic ratio satisfying the following condition: 0 < y ≤ 0.5; and δ represents an oxygen excess.

A first heat-resistant filter medium is disposed in an exhaust pathway of an internal combustion engine. The first heat-resistant filter medium traps hydrocarbon compounds and carbon-containing particulates included in a flow of exhaust gas in a dispersive manner to bring the respective particulates and hydrocarbon compounds in contact with oxygen included in the exhaust gas. The trapped hydrocarbon compounds and the trapped carbon-containing particulates are subjected to combustion with the exhaust gas having a filter inflow temperature lower than a combustible temperature of the carbon-containing particulates. A second heat-resistant filter medium is further disposed downstream of the first heat-resistant filter medium to trap the remaining carbon-containing particulates, which have not been trapped by the first heat-resistant filter medium but have passed through the first heat-resistant filter medium. This arrangement desirably enhances the reduction rate of the particulates. Since most of the particulates are trapped by the first filter medium, the second filter medium can keep the high reduction rate of the particulates over a long time period.

An exhaust gas purifying catalyst is formed of a first powder formed of porous particles supporting rhodium (Rh), and a second powder formed of porous particles supporting platinum (Pt) and a nitrogen oxides (NOx)-adsorbing material. The second powder and the first. powder are present in a mixed state. In this catalyst, Rh is supported apart from Pt and the NOx adsorbent, so that reduction of the oxidizing performance of Pt is prevented, and so that the problems of poor compatibility between Rh and the NOx adsorbent is eliminated.

The catalyst therefore maintains high NOx removing rate not only during an initial period but also after the endurance test.

An exhaust gas purifying catalyst is formed of a first powder formed of porous particles supporting rhodium (Rh), and a second powder formed of porous particles supporting platinum (Pt) and a nitrogen oxides (NOx)-adsorbing material. The second powder and the first. powder are present in a mixed state. In this catalyst, Rh is supported apart from Pt and the NOx adsorbent, so that reduction of the oxidizing performance of Pt is prevented, and so that the problems of poor compatibility between Rh and the NOx adsorbent is eliminated.

The catalyst therefore maintains high NOx removing rate not only during an initial period but also after the endurance test.

An NO_x storage member including at least one member selected from the group consisting of alkali metals, alkaline-earth metals and rare-earth elements, and at least one noble metal selected from the group consisting of Pt, Pd and Rh are loaded on a support including a porous oxide including TiO₂ at least and ZrO₂ on which Rh is loaded in advance.

H₂, which is generated by Rh/ZrO₂, inhibits the sulfur poisoning, and the support, which includes TiO₂ at least, secures the initial NO_x purifying capability, thereby further inhibiting the sulfur poisoning. Accordingly, it is possible to inhibit the NO_x storage member from the sulfur poisoning, and to maintain a high NO_x conversion even after a durability test.