| abstract |
1. A complex oxide containing more than 0 parts by weight, but not more than 20 parts by weight of silicon, in terms of SiO, for a total of 100 parts by weight of rare earth metals, including cerium, in terms of oxides; that when measuring temperature-programmed reduction (TPR) in an atmosphere of 10% hydrogen-90% argon at 50-900 ° C at a rate of temperature increase of 10 ° C / min, followed by oxidative treatment at 500 ° C for 0.5 hours, then measure the temperature-programmed recovery conduct again, its calculated degree of reduction at 400 ° C and below is at least 1.5% .2. The composite oxide according to claim 1, characterized in that after repeating said measurements of temperature-programmed reduction and oxidative treatment three times, its specific surface according to the BET method is at least 20 m / g. The composite oxide according to claim 1 or 2, wherein the rare earth metals include cerium and rare earth metals other than cerium, including yttrium, in a weight ratio of 85:15 to 99: 1, in terms of oxides. The composite oxide according to claim 1 or 2, containing 2-20 parts by weight of silicon, calculated on SiO, for a total of 100 parts by weight of rare earth metals, including cerium, in terms of oxides. The composite oxide according to claim 1 or 2, wherein said reduction ratio at 400 ° C. or lower is at least 2.0%. The composite oxide of claim 2, wherein said BET specific surface area is at least 25 m / g. A method for producing a complex oxide, comprising: step (a1), in which a cerium solution is prepared in which at least 90 mol% of cerium ions are even |