Silica gels modified by MgO, LiOH, and NaOH, i.e., SiO2/MgO, SiO2/LiOH, SiO2/NaOH, respectively, were examined as solid supports in the ethylene and propylene polymerization reactions using dimethylsilylene-bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride (SHIZ) as the catalyst and i-Bu3Al as the co-catalyst. All three were found to be equally effective for the former reaction, whereas activity was discrete for the latter reaction, with the order being SiO2/MgO > SiO2/LiOH > SiO2/NaOH. For the SiO2/MgO combination which showed the highest performance, BET and STEM studies indicated that Mg was evenly distributed in the silica gel. Acid-base measurements of all three solids indicated that SiO2/MgO had strongly acidic sites whereas the other two did not, and in addition, SiO2/NaOH had strongly basic sites whereas the remaining two had only weakly basic spots. These results suggested that the presence of weakly nucleophilic anionic sites is essential for high reactivity and that strongly acidic sites enhance the reactivity. (C) 2009 Elsevier B.V. All rights reserved.