Patent ID: 8043992

Claim:
A particulate inorganic mixed oxide comprising: aluminum; zirconium; cerium; lanthanum; and an additional element selected from the group consisting of neodymium and praseodymium, wherein a content of aluminum in the inorganic mixed oxide is 60 to 90 at %, in terms of element content, relative to a total amount of elements which form cations in the inorganic mixed oxide, a content of cerium in the inorganic mixed oxide is 0.4 to 50 at %, in terms of element content, relative to a total amount of zirconium and cerium in the inorganic mixed oxide, a content of a total amount of lanthanum and the additional element is 1 to 12 at %, in terms of element content, relative to the total amount of the elements which form cations in the inorganic mixed oxide, at least 80% of primary particles of the inorganic mixed oxide have a particle diameter of 100 nm or less, at least a part of the primary particles have an enriched surface region where a content of the additional element is locally increased in a surface layer portion thereof, and an amount of the additional element in the enriched surface region is 0.1 to 0.95% by mass, in terms of oxide, relative to a whole amount of the inorganic mixed oxide.