Study of energy distribution of active sites in heterogeneous Ziegler-Natta catalysts

New method of investigation of active sites non-uniformity was developed. The method is based on mass-spectrometric study of temperature programmed desorption (TPD) products from the catalyst surface at initial stages of olefin gasphase polymerization. The conditions of polymerization allowed to obtain the short macrochains on catalyst surface. Two well-resolved intense maxima in the temperature ranges of 180–210°C and 280–320°C on the TPD curves from SiO2/TiCl4/AlEt2Cl catalyst surface after polymerization were observed in a result of thermal destruction of active Ti-C bonds and the evolution of hydrocarbon molecules of different length (up to 14 monomer units in chain). One may conclude that in this catalyst there are at least two types of active sites varying in the activation energy of thermal destruction of Ti-C bonds. The distribution of active sites over activation energy of Ti-C bond thermal destruction was calculated.