Abstract: A zirconium- and cerium-based mixed oxide having good thermal stability and oxidation-reduction performance, in particular, is provided. The mixed oxide which comprises zirconium and cerium is characterized in (1) that cubic phase purity of a zirconia- and ceria-based solid solution is not less than 95% by volume of the crystal phase thereof and (2) that the cubic phase purity is not less than 75% by volume even after two repetitions of the step of subjecting the mixed oxide to heat treatment at 1,000° C. and then cooling the same to room temperature. A method of producing the mixed oxide is also provided which comprises admixing basic zirconium sulfate with a cerium ion-containing solution and then adding a base to the resulting mixed solution to thereby causing formation of a precipitate.

Abstract: Mixed oxides excellent in thermal stability of specific surface area and in oxidation-reduction performance are provided on an industrial scale. Catalyst materials useful in exhaust gas purification are also provided. The invention is concerned with mixed oxides containing cerium, zirconium and sulfur, namely cerium- and zirconium-based mixed oxides having the composition: 50 to 79% by weight as cerium oxide, 20 to 49% by weight as zirconium oxide, and 1 to 5% by weight as sulfate (SO.sub.4). The invention also relates to a method of producing cerium- and zirconium-based mixed oxides which comprises mixing a cerous-alkali metal sulfate double salt with a zirconium ion-containing solution and then adding a base to the mixed solution to thereby cause formation of a precipitate. The invention further relates to catalyst materials for exhaust gas purification which comprise a mixed oxide containing cerium, zirconium and sulfur, namely a cerium- and zirconium-based mixed oxide containing sulfur in an amount of 0.