The treatment of silica with alkylaluminum compounds, triisobutylaluminum (TIBA) and triethalaluminum (TEA), dramatically enhanced the cocatalytic performances of the [CPh3](+)[B(C6F5)(3)-SiO2](-). We measured the productivity and ethylene-consumption profiles for [CPh3](+)[B(C6F5)(3)-SiO2](+) cocatalysts and Cp2ZrCl2/TIBA. Both of the treated cocatalyst systems improved the average molecular weight of the product when compared with the untreated cocatalyst system. The TIBA-treated cocatalyst provided a narrow molecular weight distribution while the TEA-treated cocatalyst system gave a broad distribution.