In the present work Et(IndH(4))(2)ZrCl2 was immobilized on silica previously modified with different chemical compounds, namely VOCl3, SnCl4, Bu3SnH, Me2SiHCl, polymethylhydrosiloxane (PMHS) and such systems were compared to methy-laluminoxane (MAO) pretreated systems. Bu3SnH-modified silica led to the highest zirconocene grafted content. Zr 3d(5/2) binding energy determined by X-ray spectroscopy (XPS) was shown to increase for Et(IndH(4))(2)ZrCl2 supported on silica modified with VOCl3, MAO and Bu3SnH, suggesting the generation of more electron deficient surface species. All systems were shown to be active in ethylene-propylene copolymerization, presenting higher activity than those prepared by grafting the zirconocene on bare silica. Aging test with MAO-mediated systems showed that the catalyst bearing 2.0 wt.% Al/SiO2 kept its catalyst activity at least for 3 months after preparation. (C) 2002 Elsevier Science B.V. All rights reserved.