A semi-empirical study on ziegler natta catalyst: Concerning the interaction EtInd2ZrCl2/MAO/SiO2

FERREIRA, M.L.; BRANDA, M. MARTA; JUAN, A.; DAMIANI, D.E.

JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL

ELSEVIER SCIENCE BV

Año: 1997 vol. 122 p. 51 - 60

1381-1169

A modified extended Huckel method (EHMO), which includes core-core repulsion terms, was used to study a propylene polymerization heterogeneous catalyst by modeling the adsorption of the ansa-metallocene ethylen-bisindenylzirconium dichloride (C2H5(C9H6)2ZrCl2 from now on EtInd2ZrCl2) 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°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 modeled at 200°C while it inhibits that process at 600°C.