Useful cracking catalysts and catalyst supports comprising silica supported on alumina are prepared by compositing particles of silica or silica precursor with particles of porous alumina and subjecting the resulting composite to high temperature steaming in a non-reducing environment at a temperature of at least about 500.degree. C. for a time sufficient to disperse at least a portion of the silica over the alumina surface. The silica wets, spreads out and reactions with the surface hydroxyul groups of the alumina. The supported silica on alumina composites that can be made from this process may exhibit properties of both bulk silica and bulk alumina at the same time, bulk silica and alumina whose exterior surface only has been modified with silica as wells as composites exhibiting surface properties different from both bulk silica and bulk alumina.