Enhancing the design of catalysts for the direct synthesis of hydrogen peroxide.

Ward, Ashley 2024. Enhancing the design of catalysts for the direct synthesis of hydrogen peroxide. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis investigates the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen, using supported palladium-based catalysts. The direct synthesis of hydrogen peroxide provides an atom-efficient and environmentally-friendly alternative to the currently industrially adopted anthraquinone oxidation process. However, several issues prevent the industrial adoption of this alternative process, most notably the selectivity towards hydrogen peroxide production of catalysts active for the hydrogenation and decomposition of hydrogen peroxide. Indeed, the major aim of this work is to investigate the design of catalysts with an enhanced catalytic activity and selectivity towards the direct synthesis of hydrogen peroxide. A nitric acid pre-treatment of carbon for use in the preparation of supported gold-palladium catalysts had previously shown to increase catalytic activity and selectivity towards the direct synthesis of hydrogen peroxide, with no such effect on titania supported catalysts. This work investigates the pre-treatment of titania supported palladium-based catalysts with a lower metal loading, demonstrating a metal loading dependency on the de-activation of hydrogenation activity through support pre-treatment. The use of a multi-staged heat treatment on titania supported tin-palladium catalysts has previously shown to increase selectivity towards the direct synthesis reaction, with no such observation made for gold-palladium catalysts. This work investigates a multi-staged heat treatment on nitric acid pre-treated titania supported gold-palladium catalysts, demonstrating a catalyst with no observed hydrogenation activity, able to maintain catalytic activity towards the direct synthesis of hydrogen peroxide over multiple reaction uses. A sol-immobilisation preparation method has previously been demonstrated to produce supported gold-palladium catalysts with a controlled particle size distribution. This work investigates employing a stabiliser-free sol-immobilisation method for the production of alumina supported gold-palladium catalysts, demonstrating comparable catalytic activity and selectivity to polymer-stabilised sol-immobilised prepared catalysts. The modification of titania supported palladium-only catalysts with N-heterocyclic carbene (NHC) ligands has previously shown to enhance catalytic activity towards the direct synthesis of hydrogen peroxide and decrease degradation activity through the electronic modification of palladium species. This work investigates the use of NHCs to modify stabiliser-free sol-immobilised alumina supported gold-palladium catalysts, ultimately demonstrating an NHC-modified gold-palladium catalyst supported on alumina with a substantially enhanced catalytic activity and selectivity towards the direct synthesis of hydrogen peroxide, comparable to that of state-of-the-art catalysts.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	10 October 2024
Last Modified:	10 Oct 2024 11:04
URI:	https://orca.cardiff.ac.uk/id/eprint/172780

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