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

• Published in: Journal of catalysis Vol. 292; pp. 188 - 200
• Main Author: Kissin, Yury V.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-08-2012; Elsevier; Elsevier BV
• Subjects: Catalysis; Catalysts; Chemistry; ethylene; Ethylene polymerization; Exact sciences and technology; General and physical chemistry; hydrogen; Kinetics; oxidation; Oxidative addition; phthalates; Polymerization; temperature; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Titanium valence; Ziegler–Natta catalysts; Ethylene polymerization; Titanium valence; Oxidative addition; Ziegler–Natta catalysts; Binary compound; Hydrogen; Ethylene; Silica; Supported catalyst; Solid; Chemical reduction; Alkene; Titanium; Oxidation; Active center; Monomer; Structure; Ziegler Natta catalyst; Experimental data; Hydrocarbon; Polymerization; Transition metal; Heterogeneous catalysis; Valence; Cocatalyst; Silicon oxides; Ziegler-Natta catalysts; Kinetics; Formation mechanism; Ethylenic compound
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.05.012

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► Kinetics of ethylene polymerization with Ziegler–Natta catalysts is studied. ► Temperature, 1-alkenes, H2 and IITi species affect the rate of active center formation. ► Amount of cocatalyst and ethylene concentration do not affect active center formation. ► Rates of active center formation for different IVTi and IIITi-based catalysts are similar. ► Active centers are formed in IVTi (IIITi)→IITi—(ethylene)→IVTi reaction sequence.
The article presents experimental data on the formation rates of active centers in polymerization reactions of ethylene with solid Ti-based Ziegler–Natta catalysts (γ and δ 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 IITi and oxidation addition of alkenes to IITi with the generation of IVTi-based polymerization centers.