COMPOSITE OXIDE, METHOD FOR PRODUCING THE SAME, AND CATALYST FOR EXHAUST GAS PURIFICATION

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A composite oxide and a catalyst for purifying exhaust gas using the same are provided, which oxide has excellent heat resistance, including that a large specific surface area is maintained even when the composite oxide is used in a high temperature environment, and that, even after calcination at 800 °C for 2 hours, no AECeO3 phase is detected and increase in CeO2 crystallite size is inhibited. The composite oxide contains, in terms of oxides, 60 to 98 mass% of a cerium-containing element, the cerium-containing element consisting of Ce and at least one element selected from rare earth elements other than Ce and including Y, Zr, and Si at 85 : 15 to 100 : 0 by mass, 1 to 20 mass% of an alkaline earth metal element, and 1 to 20 mass% aluminum in terms of AI2O3, wherein the composite oxide has properties of exhibiting a specific surface area of not smaller than 40 m2/g as measured by the BET method after calcination at 800 °C for 2 hours, and having no AECeO3 phase and having a CeO2 crystallite size in the (111) plane of not larger than 15 nm, as determined by X-ray diffraction after calcination at 800 °C for 2 hours.