A semi-empirical study on Ziegler Natta catalyst: Concerning the interaction EtInd(2)ZrCl(2)/MAO/SiO2

A modified extended Huckel method (EHMO), which includes core-core repulsion terms, was used to study a propylene polymerization heterogeneous catalyst by modelling the adsorption of the ansa-metallocene ethylen-bisindenylzirconium dichloride (C2H5(C9H6)(2)ZrCl2 from now on EtInd(2)ZrCl(2)) on SiO2 surfaces. The adsorption was considered to occur at two faces of SiO2 (with geminal and isolated OH's) and at two different temperatures for SiO2 pretreatment (200 and 600 degrees C). Taking into account that the interaction with Al compounds is considered as a way to improve the catalyst performance, specially with methylaluminoxane (MAO), a local model of aluminoxane (AlO) was added to Si-O bond with the subsequent metallocene adsorption. The results show that AlO improves the zirconocene adsorption on SiO2 modelled at 200 degrees C while it inhibits that process at 600 degrees C.