The Application of X-Ray Absorption Spectroscopy to Study the Titanium Environment on MgCl2 Supported Ziegler Natta Catalysts

As a problem in structural chemistry the aim to characterise the catalytic site on MgCl2 based TiCl4 Ziegler Natta catalysts presents substantial difficulties. Problems centre on the instability of Ti complexes in air, and the consequent need for in-situ studies, and the dilution and dispersion of active material. The potential of x-ray absorption spectroscopy (XAS) opposite some of these difficulties makes it well suited to characterise catalyst structure. The technique uses fine structure at core level absorption edges to derive information on chemical state and near neighbour bonding round elements of specific interest. At the absorption edge information comes from transitions which occur to the valence band. For higher x-ray energies absorption fine structure (EXAFS/XANES) results from back scattering of the photo-electron by neighbouring atoms. Since XAS is concerned with local order information can be derived from amorphous systems independent of dispersion. Also, using x-rays, material is accessible in pores, at interfaces or in-situ under working environments including liquids. Taking advantage of these possibilities, using XAS at the Daresbury Synchrotron Radiation Source, we have been able to study the Ti environment in MgCl2 supported TiCl4 Ziegler Natta catalysts made by milling and precipitation. The results of the first stages of this work are presented in this paper.