A process for conducting a catalytic oxidation reaction, which comprises contacting fluid fuel and an oxidant with a catalyst comprising a support and a catalytically active component supported on said support, wherein at least the part of said support that predominantly supports said active component consists essentially of a composite oxide of alumina and at least one member consisting of the group consisting of lanthanum, neodymium, praseodymium and mixtures thereof, said composite oxide having a specific surface area of at least 10 m.sup.2 /g, said composite oxide containing less than 1% by weight of chromium, strontium and cerium, and said composite oxide being characterized in that it exhibits characteristic peaks corresponding to those of lanthanide-beta-alumina in the X-ray diffraction analysis and said composite oxide being a calcination product of a mixture of an aluminum compound and a member selected from the group consisting of lanthanum compound, neodymium compound, praseodymium compound and mixtures thereof calcined at a temperature of at least 800.degree. C. for time sufficient to convert the mixture into said composite oxide.