Active centers in Ziegler-Natta catalysts: Formation kinetics and structure

作者：Kissin Yury V^*

来源：Journal of Catalysis, 2012, 292: 188-200.

DOI：10.1016/j.jcat.2012.05.012

• Ziegler-Natta catalysts
• Ethylene polymerization
• Titanium valence
• Oxidative addition

The article presents experimental data on the formation rates of active centers in polymerization reactions of ethylene with solid Ti-based Ziegler-Natta catalysts (gamma and delta forms of TiCl3, TiCl2) and five types of supported catalysts, TiCl4/MgCl2/SiO2, TiCl3/MgCl2/SiO2 and TiCl4/MgCl2/diisobutyl phthalate. Effects of the following factors on the center formation are discussed: reaction temperature, monomer concentration, the amount of cocatalyst, the initial valence state of Ti atoms in the catalyst, pre-reactions of catalysts with cocatalysts, the presence of molecular hydrogen, effects of 1-alkenes in ethylene polymerization reactions. A combination of the results produces the basis for the formation mechanism of active centers in Ziegler-Natta catalysts, which involves reduction of numerous Ti species on the catalyst surface to Ti-II and oxidation addition of alkenes to Ti-II with the generation of Ti-IV-based polymerization centers.

• 出版日期2012-8