This work presents the results of theoretical and experimental characterization of supported (nBuCp)(2)ZrCl2 on organosilanes pre-treated SiO2. Several possibilities are analyzed and considered as an attempt to explain the observed zirconocene loadings, catalyst performance in ethylene polymerization and resulting polymer properties of these supported zirconocenes. The effect of silica pre-treatment with Ph3SiCl, Me3SiCl and Me2HSiCl on the immobilization of (nBuCp)(2)ZrCl2 was modeled. The main considered aspects were the role of the surface concentration of the organosilanes, the presence or absence of residual chlorine and the possibility of interactions between the organosilanes and the zirconocene. All these facts might afford different surface species at the impregnation step prior to the MAO activation during the polymerization reaction.