Patent ID: 8765631

Claim:
A cerium oxide-zirconium oxide based composite oxide comprising a mixture of (1) a cerium-zirconium composite oxide from a melting process and (2) cerium dioxide from a wet process, wherein the cerium-zirconium composite oxide from the melting process in the cerium oxide-zirconium oxide based composite oxide has a crystallite diameter of 102 nm or greater, the cerium dioxide from the wet process in the cerium oxide-zirconium oxide based composite oxide has a crystallite diameter of less than 50 nm; and the cerium oxide-zirconium oxide based composite oxide has a weight ratio of (1):(2) of 20:80 to 99:1; the melting process comprises: mixing a cerium oxide-containing material and a zirconium oxide-containing material to form a mixture, melting the mixture at a temperature at or above the melting point, and cooling the molten material; and the wet process comprises: adding an alkali to a cerium salt-containing solution to form cerium hydroxide, and heating the formed cerium hydroxide.