The Co-Operative Redox Enhancement Effect: Origin, mechanism and scope

Daniel, Isaac 2024. The Co-Operative Redox Enhancement Effect: Origin, mechanism and scope. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Catalysis will be profoundly important as the chemical industry transitions towards cleaner practices. The progression of fundamental knowledge is vital to ensure this transition is effective and sustainable. In recent years, multimetallic systems have come to the forefront of catalytic science as a way of enhancing reaction rates and tuning selectivity. However, our understanding of the operation of these systems still needs to be improved. The research presented herein is centred on a new multimetallic catalytic effect termed Co-Operative Redox Enhancement, or CORE. This describes a process whereby two distinct active sites catalyse two separate halfreactions, resulting in significant activity increases. In this work, the CORE effect is investigated and expanded in depth, using the oxidative dehydrogenation of 5- hydroxymethylfurfural as the model reaction. This transformation is a key step in the formation of a bioplastic precursor, 5-furan-2-dicarboxylic acid. Carbon-supported Au and Pd catalysts are used to perform a detailed set of thermochemical reactions that provide evidence in support of the CORE mechanism. In a critical demonstration using a physical mixture of Au/C and Pd/C, the amount of a relatively inactive Pd/C catalyst is shown to indirectly dictate the overall reaction rate, underlining the co-operativity between two separated active sites. Through analysis of the model reaction at a range of temperatures, the coupling between two physically separated monometallic catalysts is shown to affect activation energy and reaction selectivity. A detailed kinetic model is derived based on the CORE mechanism, which can predict the molar ratio of Au/Pd required to achieve maximum activity. Accurate alignment between the kinetic model and experimental results provides further support for the CORE system from an entirely new perspective. Finally, the close relationship between electro- and thermocatalysis is leveraged to define a clear origin for CORE. By analysis of alternative catalysts, namely carbonsupported Pt and Ir, CORE is demonstrated to be an inherently general effect for bimetallic catalytic systems, providing a defined set of conditions are met. In sum, the understanding gained from this work lays a foundation for the CORE effect to be incredibly impactful in catalysis and have wide-reaching applications.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	29 May 2024
Last Modified:	29 May 2024 15:51
URI:	https://orca.cardiff.ac.uk/id/eprint/169261

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