Surface science study of model Ziegler-Natta catalysts

The preparation and surface science study of model catalysts for the Ziegler-Natta polymerization are reported. Ultra-thin films of MgCl2 and TiCl4 have been prepared by gas phase deposition on polycrystalline Au foil in UHV conditions and are characterized by XPS. Titanium chloride films can be deposited on both MgCl2 films and clean An at 300 K in a background TiCl4 pressure of 1 x 10(-8)-5 x 10(-7) Torr, in the presence of an electron beam of 1 keV irradiating the substrate. The deposited titanium chloride consists of a TiCl2 multilayer film with one monolayer of TiCl4 chemisorbed at the surface. Upon exposure of AlEt3, the TiCl4 monolayer undergoes reduction and alkylation with the formation of TiCl2Et and TiClEtn species at the film surface, No evidence for TiCl3 formation is observed. These model systems are active catalysts for the Ziegler-Natta polymerization of both ethylene and propylene.