Supported metallocenes produced by a non-hydrolytic sol-gel process: Application in ethylene polymerization

Abstract

The immobilization of Cp2ZrCl2 was performed by entrapment within the binary oxides SiO2-CrO3, SiO2-MoO3 and SiO2-WO3 using a non-hydrolytic sol-gel route. Catalyst performance was evaluated in ethylene polymerization. The highest catalyst activity was found with a lower metal chloride:Si ratio and catalyst bearing W moieties. The catalyst and oxide matrices were characterized by complementary techniques (nitrogen porosimetry, small angle X-ray scattering, Fourier Transform infrared spectroscopy, X-ray photoelectron spectroscopy, and differential pulse voltammetry). The interaction between the binary oxide support and the immobilized metallocene reduced the electron density on the Zr centers, enabling the activation reaction to occur with lower concentrations of the methylaluminoxane (MAO) co-catalyst (Al/Zr = 500). The catalytic activity showed a direct relationship with the size and shape of the mass fractal. The results demonstrate that the entrapping method allows for the generation of a catalyst system in which part of the activation process may be attributed to the support.