| abstract |
[PROBLEMS] To maintain a high specific surface area even when used in a high-temperature environment, and to detect an AECeO 3 phase that deteriorates performance after baking at 800 ° C. for 2 hours, and to suppress an increase in the crystallite diameter of CeO 2. The present invention provides a composite oxide having excellent heat resistance, such as a catalyst, and an exhaust gas purification catalyst using the same. The composite oxide of the present invention comprises a rare earth metal element containing Y, Zr and Si in an amount of 60 to 98% by mass in terms of oxide, an alkaline earth metal element in an amount of 1 to 20% by mass in terms of oxide, and Al is 1 to 20% by mass in terms of Al 2 O 3 , and the rare earth metal element including Y, Zr and Si is Ce, and at least one of the rare earth metal element including Y and not including Ce, Zr and Si. The specific surface area according to the BET method after baking at 800 ° C. for 2 hours is 40 m 2 / g or more in a mass ratio in terms of oxide, in the range of 85:15 to 100: 0, and after baking at 800 ° C. for 2 hours, No AECeO 3 phase is detected by X-ray diffraction, and the CeO 2 crystallite diameter in the (111) plane is 15 nm or less. [Selection figure] None |