AVS 46th International Symposium
    Applied Surface Science Division Tuesday Sessions
       Session AS-TuA

Paper AS-TuA9
Surface Science Studies of Model Ziegler-Natta Polymerization Catalysts

Tuesday, October 26, 1999, 4:40 pm, Room 6A

Session: Modeling in Applied Surface Science
Presenter: S.H. Kim, University of California at Berkeley
Authors: G.A. Somorjai, University of California at Berkeley
S.H. Kim, University of California at Berkeley
Correspondent: Click to Email
Model Ziegler-Natta catalysts of titanium chloride, supported on Au and MgCl@sub 2@, have been synthesized using chemical vapor deposition (CVD) methods in a ultra-high vacuum (UHV) chamber and tested for polymerization of ethylene and propylene with triethylaluminum, AlEt@sub 3@, as a co-catalyst in a high-pressure reaction cell. The deposition kinetics, chemical composition, surface sites, and activation of model catalysts are investigated using Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). TiCl@sub 4@ does not chemisorb on either Au or MgCl@sub 2@ to form a film stable at room temperature in UHV. The titanium chloride films supported on Au (TiCl@sub x@/Au) are produced by electron beam irradiation onto the substrate during the TiCl@sub 4@ exposure. Electrons induce the ionization and dissociation of TiCl@sub 4@, producing active species that can be deposited on Au at both 100K and 300K. The deposition temperature alters the stoichiometry and structure of TiCl@sub x@/Au due to difference in deposition kinetics. The titanium chloride films supported on magnesium chloride (TiCl@sub x@/MgCl@sub 2@/Au) are prepared by reaction of TiCl@sub 4@ with Mg on Au. Two deposition sequences, co-deposition of gas-phase Mg and TiCl@sub 4@ and deposition of TiCl@sub 4@ on a Mg film, are used. Regardless of deposition sequence, the uppermost layers of the TiCl@sub x@/MgCl@sub 2@/Au films are mostly composed of titanium chloride, though the distribution of titanium chloride in the film changes with deposition sequence. For these model catalysts before and after the AlEt@sub 3@ treatment, desorption behaviors of organic molecules are studied to differentiate various adsorption sites on the surface. Identification of active sites for polymerization will be attempted from the comparison of the distribution of surface sites with polymerization activity.