| 摘要 |
Provided is a composite oxide which is suitable for use as, for example, a promoter for exhaust gas purification catalysts and which has high heat resistance and an excellent ability to absorb and release oxygen at low temperatures. The composite oxide contains Ce and Zr, the proportions of the Ce and the Zr being 30-80 at.% and 20-70 at.%, respectively, relative to the sum of the Ce and the Zr, which is taken as 100 at.%, or further contains a specific element M, the proportions of the Ce, Zr, and element M being 30-80 at.%, excluding 80 at.%, 20-70 at.%, excluding 70 at.%, and 0-15 at.%, excluding 0 at.%, respectively, relative to the sum of the Ce, Zr, and element M, which is taken as 100 at.%. The composite oxide has a phase of a CaF2-type structure or a phase of a structure akin to CaF2, and the ratio of the actual value of the lattice constant of the (311) plane to the theoretical value of the lattice constant is 1.000. The composite oxide has the property of having a total pore volume of 0.30 cc/g or higher after burned at 1,000°C for 5 hours in the air. |
