Modeling the Stabilization of Surface Defects by Donors in Ziegler-Natta Catalyst Support

We describe a concept for modeling structural defects in crystalline magnesium dichloride used as a support in the Ziegler-Natta polymerization catalysis. The defects are systematically generated into the catalytically relevant (104) and (110) MgCl2 surfaces and stabilized by methanol, selected as a model electron donor. Periodic quantum chemical calculations indicate a strong effect of surface site coordination on the relative stabilities of both ideal and defect surfaces, favoring sites with five-coordinate magnesiums. Saturation of the surfaces by the donor completely reverses the stability order in comparison to the plain surfaces, ending up favoring four-coordinate magnesium atoms. The approach can be readily expanded to include more complex donors as well as titanium chlorides.