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UBC Theses and Dissertations

Palladium membrane reactor as a tool to resolve hydrogenation reaction pathways Huang, Aoxue


Heterogeneous hydrogenation is an important industrial process widely used in fine chemical syntheses, pharmaceutical, food, and biofuel production. Hydrogenation is performed by combining reactants (H2 gas and substrates) in one reactor, where both react on the same catalyst surface. This combination of reactants complicates understanding the catalytic process because several competing processes will occur on the same catalyst surface. The electrocatalytic palladium membrane reactor (ePMR) is a unique hydrogenation reactor that separates the hydrogen activation from the hydrogenation process. This reactor not only enables hydrogenation to be performed at ambient temperatures and pressures but also provides fine-tuning of the amount of hydrogen supplied (fugacity) by tuning the applied current. This thesis presents a series of work related to the heterogeneous catalytic processes in the ePMR. This thesis first presents the study of electrochemical processes of the palladium electrode. A customized temperature-programmed desorption (TPD) instrument was built to characterize the palladium films electrochemically saturated with absorbed hydrogen (PdHx for x > 0.6). The electrolyte choice is found to affect hydrogen sorption and desorption kinetics on the palladium surface due to the specific adsorption of the anion. The thesis then presents the advantages of ePMR to study the reaction pathway of hydrogenation. The conventional thermochemical hydrogenation process requires high temperatures and pressure, which may lead to morphology change of the catalysts. It also complicates the understanding of hydrogenation because multiple catalytic processes occur on the same catalyst surface. The ePMR enables the hydrogenation at ambient conditions and separates the catalytic process. The hydrogenation pathway of benzaldehyde is successfully resolved on the palladium nanocubes by combining the ePMR and well-defined nanocubes. Finally, the use of ePMR for hydrogen peroxide production is demonstrated. Hydrogen peroxide is a crucial chemical for various applications. The production of hydrogen peroxide is a carbon-intensive process that requires the hydrogenation and oxidation of an intermediate molecule. The direct hydrogenation of oxygen can simplify the infrastructure and decrease the capital cost of the process but is risky for using the mixture of hydrogen and oxygen. The ePMR can supply high-fugacity hydrogen in-situ and overcome these disadvantages.

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