Toward a Unified Model Explaining Heterogeneous Ziegler-Natta Catalysis

Abstract

We propose a model for MgCl 2 -supported Ziegler-Natta catalysts, which is capable to reconcile the discrepancies emerging in the last 20 years, in which attempts have been made to rationalize experimental data by molecular models. We show that step defects on the thermodynamically more stable (104) facet of MgCl 2 can lead to sites for strong TiCl 4 adsorption. The corresponding Ti-active site is stereoeselective, and its stereoselectivity can be enhanced by coordination of Al-alkyls or Lewis bases in the close proximity. The surface energy of the step defected (104) MgCl 2 facet is clearly lower than that of the well accepted (110) facet.