Metallocene catalyst supported on silica-magnesia xerogels for ethylene polymerization

A series of supported metallocene catalysts were prepared by grafting Cp2ZrCl2 on silica-magnesia xerogels, and then they were evaluated for the process of ethylene polymerization. The supports were characterized by a set of complementary techniques including small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N-2 adsorption-desorption. The supported catalysts were characterized by Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared spectroscopy (DRIFTS). The use of silica-magnesia xerogels for immobilization of metallocene yielded systems with higher catalyst activity when compared to the results from metallocene grafted on bare silica. The resulting polymers showed a broader molecular weight distribution than those obtained by homogeneous Cp2ZrCl2 and Cp2ZrCl2/SiO2, which potentially provides a better processing capacity of these alternative polyethylenes. In the case of polyethylene obtained with the system containing 16.0 wt.% Mg/Si, a fiber-like morphology was observed. (C) 2010 Elsevier B.V. All rights reserved.