The research presented in this thesis focuses on the process of direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen. This reaction potentially offers an approach which is greener and more sustainable when compared to the current industrial indirect auto-oxidation process. The work presented herein examines some of the key factors in determining the viability of the process in a water solvent at ambient temperature, conditions which would represent a very economically and environmentally attractive option, if feasible. The first part of this thesis investigates the ways in which changing reaction conditions affects the fundamental reaction processes of the direct synthesis reaction – synthesis of hydrogen peroxide and its subsequent degradation by decomposition and hydrogenation. It was found that moving to a water solvent and ambient temperature results in significantly lower yields and greater degradation comparative to previously used water/methanol solvents and 2°C reactions. The second part of this thesis explores the design of catalysts which are active for the direct synthesis of hydrogen peroxide while limiting degradation activity, to increase the yield in water at ambient temperature. A series of supported metal catalysts of the nominal formulation 0.5 wt. % Pd - 4.5 wt. % ‘base metal’ were prepared and treated with a cyclic oxidative-reductive-oxidative heat treatment. This produced highly stable catalysts with activity for the synthesis of hydrogen peroxide, but low to no activity for both decomposition and hydrogenation pathways. These catalysts also fulfilled a secondary aim of producing economically attractive catalysts due to the low loadings of precious metals used. The third and final part of this thesis studies the implementation of these highly selective catalysts in both gas and gas/liquid phase flow reactors. The production of hydrogen peroxide in a gas phase flow system is shown to be attainable although most likely not a commercially viable option. The direct synthesis of hydrogen peroxide in a gas/liquid flow system is shown to proceed with selectivities greater than those previously reported for different catalysts under similar conditions. Tests also show that hydrogen peroxide can be produced under ‘real world’ conditions of high flow rates, a hard water solvent and a dilute hydrogen in air gas mix. These studies could be used to inform future work on high throughput water cleaning technologies.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:732248 |
| Date | January 2017 |
| Creators | Crole, David Alexander |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/107580/ |
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