Thermal Restructuring of Silica-Grafted TiClx Species and Consequences for Epoxidation Catalysis

Authors

  • Philipp Mania,

    1. Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10 (Switzerland), Fax: (+41) 44-633-1514
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  • Dr. René Verel,

    1. Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10 (Switzerland), Fax: (+41) 44-633-1514
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  • Florian Jenny,

    1. Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10 (Switzerland), Fax: (+41) 44-633-1514
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  • Dr. Ceri Hammond,

    1. Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10 (Switzerland), Fax: (+41) 44-633-1514
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  • Prof. Dr. Ive Hermans

    Corresponding author
    1. Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10 (Switzerland), Fax: (+41) 44-633-1514
    • Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10 (Switzerland), Fax: (+41) 44-633-1514
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Abstract

TiCl4 grafted to dehydrated silica is an industrially applied catalyst for the epoxidation of propylene. As with many heterogeneous catalysts, the precise nature of the surface species is not yet fully known, prohibiting reliable structure–activity correlations. In this study, the speciation and restructuring of site-isolated TiIV Lewis acid centers was carefully investigated by using a variety of techniques. The initially formed [TRIPLE BOND]SiOTiCl3 species were found to restructure upon heating through the transfer of Cl ligands to the silica surface, eventually leading to tripodal ([TRIPLE BOND]SiO)3TiCl species. The superior activity and stability of such tripodal species is demonstrated for catalytic olefin epoxidation under continuous flow conditions.

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