PREPARATION OF A MODEL ZIEGLER-NATTA CATALYST SURFACE SCIENCE STUDIES OF MAGNESIUM-CHLORIDE THIN-FILM DEPOSITED ON GOLD AND ITS INTERACTION WITH TITANIUM CHLORIDE

The preparation and surface science study of a magnesium chloride/titanium chloride system, grown in the form of a thin film on an inert substrate under ultra-high vacuum conditions is reported. The aim of the authors is to build a model catalyst for the Ziegler-Natta polymerization of ethylene and propylene. Magnesium chloride and titanium chloride are deposited on a gold polycrystalline foil from the gas phase. The deposited films are characterized by AES, TPD of n-C6H14 and film sublimation. Auger uptake experiments show that the MgCl2 film grows by a layer-by-layer mechanism on the polycrystalline substrate. The deposition of MgCl2 on the Au substrate can be followed by TPD of n-C6H14 up to the completion of the first monolayer. It is not possible to grow TiCl4 films on a MgCl2 film at room temperature, because of its high vapor pressure. The chemical interaction of TiCl4 with an ordered MgCl2 surface is too weak to allow the growth of a TiCl4 monolayer around 300 K. The bombardment of the MgCl2 thin film with Ar ions did not produce a surface capable to adsorb TiCl4 at room temperature.