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The selective oxidation of cyclohexane via the in-situ utilisation of H2O2

Crombie, Caitlin 2020. The selective oxidation of cyclohexane via the in-situ utilisation of H2O2. PhD Thesis, Cardiff University.
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Abstract

Three primary reactions have been investigated within this thesis using heterogeneous catalysis; the direct synthesis of hydrogen peroxide, the oxidation of cyclohexane and the oxidation of benzyl alcohol both via the in-situ production of H2O2. The direct synthesis of H2O2 from molecular H2 and O2 provides a promising alternative to the anthraquinone process currently industrially implemented. Within the literature many additives, halides and acids, have been utilized to increase H2O2 selectivity be reducing the degradation of H2O2 to form H2O. Currently Pd based catalysts are the most advanced showing high activity towards H2O2 synthesis. The alloying of Pd with other metals, especially Au, has then shown increases in activity and selectivity due to electronic and geometric enhancements. In this thesis, a combination of preparation methods and catalyst supports have been investigated as has the alloying of Pd with a range of non-noble metals under ambient temperatures, with obvious financial advantages. The oxidation of cyclohexane via the in-situ production of H2O2 has been investigated. The conditions normally explored for the aerobic oxidation of cyclohexane are high temperatures which are costly and unsuitable for H2O2 synthesis and encourages H2O formation. Hence the use of H2O2 for cyclohexane oxidation allows for better activity at lower temperatures, but the use of commercial H2O2 comes with the added drawbacks of the anthraquinone process. The use of H2O2 generated in-situ would be advantageous by avoiding the transport and handling of concentrated solutions of H2O2. This work explored a variety of reaction conditions to discover the possibility of the oxidation of cyclohexane via the in-situ production of H2O2 under milder conditions than those utilized for the aerobic oxidation. Investigation then continued into catalyst design to increase oxidation product yield. The oxidation of benzyl alcohol via the in-situ production of H2O2 has already been explored in the literature and hence its feasibility had already been demonstrated. In this thesis catalysts design was implemented, focusing on Fenton’s metal, Fe, in combination with Pd due to the known radical mechanism of benzyl alcohol oxidation. Electron Paramagnetic Resonance studies have been utilized to investigate the reaction mechanism and to distinguish the activity differences observed between catalysts.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 12 March 2021
Last Modified: 12 Mar 2021 10:24
URI: http://orca.cardiff.ac.uk/id/eprint/139640

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