An investigation of some organic-based photochemical systems for hydrogen production

• Main Author: Buckthorpe, Kevin E.
• Published: University of Sussex 1991
• Subjects: 546
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549665

This project has involved the identification of photochemical and photo-thermolytic reaction cycles for the conversion and storage of solar energy in the form of chemical potential, using the photochemistry of simple organic ketones for the production of hydrogen from alcohols. Several approaches have been investigated which involved; (i) transfer of hydrogen from hydroxyalkyl radicals to aromatic compounds, (ii) photolysis of diphenylhydroxymethyl radicals and (iii) the thermolytic decomposition of pinacols. Irradiation of suitable benzophenone solutions with a 1kW Hg~Xe U.V.lamp generated hydrogen as a photolysis product (by excitation of the diphenylhydroxymethyl radical) and demonstrated that this can be achieved without employing dye lasers for specific photoexcitations. An attempt was made to improve the efficiency of hydrogen production in this system by the photochemical generation of hydroxy alkyl radicals in zeolite channels. Pyrolysis of pinacols under flash vacuum and static thermolysis conditions produced hydrogen and a ketone product. This decomposition is essentially the reverse of a photolytic reduction of the ketone, from which the pinacol may originally be formed, and therefore provides a completed photo-thermolytic cycle for the production of hydrogen from an organic solvent. Two mechanistic routes were proposed for the pinacol decomposition a six-centred molecular process and a mechanism involving free radical intermediates. Experimental evidence and UMINDO calculations were found to support the free radical route