Process of preparing silica-supported catalysts. A support material comprising silica particles impregnated with an alumoxane co-catalyst with at least one-half of the co-catalyst disposed within the internal pore volume of the silica is contacted with a dispersion of a metallocene catalyst in an aromatic solvent. The dispersion and support are mixed at a temperature of about 10° C. or less to enable the metallocene to become reactively supported on and impregnated within the alumoxane-impregnated silica particles. The supported catalyst is recovered from the aromatic solvent and washed with an aromatic hydrocarbon and then a paraffinic hydrocarbon at a temperature of about 10° C. or less. The washed catalyst is dispersed in a viscous mineral oil.