Sol–Gel Synthesis and Characterisation of Nanoscopic FeF3-MgF2 Heterogeneous Catalysts with Bi-Acidic Properties

Authors

  • Ying Guo,

    1. Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin (Germany), Fax: (+49) 30-20937468
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  • Dr. Piotr Gaczyński,

    1. Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Hans-Sommer-Straße 10, 38106, Braunschweig (Germany)
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  • Prof. Dr. Klaus-Dieter Becker,

    1. Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Hans-Sommer-Straße 10, 38106, Braunschweig (Germany)
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  • Prof. Dr. Erhard Kemnitz

    Corresponding author
    1. Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin (Germany), Fax: (+49) 30-20937468
    • Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin (Germany), Fax: (+49) 30-20937468
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Abstract

Nanoscopic metal fluorides with surface hydroxy groups are of broad interest in heterogeneous catalysis. With both Lewis and Brønsted acid sites on the surface, these catalysts can be applied to a wide range of reactions. Having previously synthesised AlF3- and MgF2-based catalysts, we report a new transition metal fluoride with bi-acidity. A pre-dehydration procedure was developed to introduce hydroxy groups to a Lewis acid, FeF3. Subsequently, ternary nanoscopic FeF3-MgF2 with enhanced porosity was prepared through a one-step fluorination. The interaction between MgF2 and FeF3 was elucidated. Surface characterisation revealed a remarkable increase in the surface area of FeF3-MgF2 compared with FeF3. More importantly, medium–strong Lewis and Brønsted acid sites were detected on the FeF3-MgF2 surface. In line with its bi-acidity, FeF3-MgF2 was highly active in the model reaction, the isomerisation of citronellal to isopulegol. Finally, we discuss how the porosity and surface acidity jointly determine the activity of FeF3-MgF2. Our study demonstrates the feasibility of ternary FeF3-MgF2 and opens new possibilities to synthesise bi-acidic fluoride catalysts.

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