Importance

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Abstract

Provided is a composite oxide which is suitable as a co-catalyst for an exhaust gas purifying catalyst or the like, has high heat resistance, and has an excellent oxygen absorbing and desorbing capability at low temperatures. The composite oxide contains Ce and Zr, wherein the Ce content is 30 to 80 at % and the Zr content is 20 to 70 at %, based on the total of Ce and Zr being 100 at %, or further contains particular element M, wherein the Ce content is not less than 30 at % and less than 80 at %, the Zr content is not less than 20 at % and less than 70 at %, and the content of element M is more than 0 at % and not more than 15 at %, based on the total of Ce, Zr, and element M being 100 at %; wherein the composite oxide has CaF₂-type or CaF₂-like structure phase, wherein the ratio of an actual lattice parameter in the (311) plane to the theoretical is 1.000, and wherein the composite oxide has a property of exhibiting a total pore volume of not less than 0.30 cc/g after calcination at 1000° C. for 5 hours in the atmosphere.

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First Claim