The application of Cs-exchanged tungstophosphoric acid as an additive in the direct synthesis of hydrogen peroxide and the use of Au-Pd/TS-1 in a one-pot approach to cyclohexanone oxime production

• Main Author: Lewis, Richard J.
• Published: Cardiff University 2016
• Subjects: 547; QD Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.694958

The work presented within this thesis can be separated into two distinct parts. The first investigates the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen using gold-palladium supported catalysts and caesium exchanged tungstophosphoric acid as an acidic additive. The direct synthesis of H2O2 presents an environmentally friendly alternative to the current industrial, anthraquinone process. However for the direct route to be viable a variety of issues must be addressed. Primarily catalytic selectivity towards H2O2 is a major concern for the majority of catalysts active for H2O2 synthesis, with the degradation of H2O2 through hydrogenation or decomposition reported for a number of catalysts within the literature. The use of acid either during catalyst preparation or as part of the reaction solution has previously been shown to improve selectivity towards H2O2. Furthermore acidic supports, including heteropolyacid, have been observed to produce catalysts with greater selectivity than those with a higher isoelectric point and in turn provide higher yields of H2O2. This work investigates the ability of caesium exchanged heteropolyacids to improve catalytic activity towards H2O2 when used in addition to Au-Pd supported catalysts, in particular 2.5 wt. % Au - 2.5 wt. Pd/TiO2. The second part of this work is concerned with the ammoximation of cyclohexanone to cyclohexanone oxime via the in-situ formation of H2O2, in a one-pot style process. The conditions associated with ammoximation of cyclohexanone that is the presence of elevated temperatures and basic conditions, are considered extremely harsh for H2O2 stability. The in-situ generation of H2O2 during the ammoximation of cyclohexanone to cyclohexanone oxime would yield significant reductions in overall costs of the ammoximation reaction. Primarily these costs are associated with the purchasing, transport, storage and dilution of H2O2. This work determines the feasibility of a one-pot ammoximation process via in-situ H2O2 formation. Firstly, reaction conditions are established for this process and following this the role of catalyst design in improving selectivity towards cyclohexanone oxime as well as cyclohexanone conversion for this reaction is studied.