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Heterogeneous nanoalloyed precious metal catalysts

Howe, Alexander 2018. Heterogeneous nanoalloyed precious metal catalysts. PhD Thesis, Cardiff University.
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Abstract

Hydrogen peroxide is a commodity chemical that is currently produced industrially using a complex and relatively inefficient process. The direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen therefore represents a more environmentally friendly, atom efficient alternative. The aim of this thesis is to explore the preparation of highly active catalysts for the direct synthesis of hydrogen peroxide. Chapter 3 investigates microwave assisted solvothermal methods as a possible preparation protocol for catalysts for the direct synthesis of hydrogen peroxide. It was found that mono- and bimetallic supported catalysts could be readily prepared in a one pot method, with the use of a microwave reactor greatly increase the speed and ease of catalyst preparation in comparison to conventional heating. PdAu/TiO2 and PdX/TiO2 catalysts, where X= Sn, Ni or In catalysts were explored, given their high activity for hydrogen peroxide synthesis when prepared by other methods. Preparation parameters such as solvent choice, the presence of stabilisers and metal loadings were all investigated with their regard to catalyst activity. Chapter 4 focuses on the development of PdAu/TiO2 catalysts using the sol immobilisation preparation technique. The protocol is commonly used as a recipe in literature to prepare catalysts, with little thought given to the nature of the preparation. Herein, factors such as preparation temperature, choice of reductant and the presence of stabilisers are considered in producing active catalysts. The optimised catalysts were found to be highly active for hydrogen peroxide synthesis but entirely inactive towards the non-productive hydrogen peroxide hydrogenation pathway, indicating that they are highly selective towards hydrogen peroxide. The catalysts were found to contain a unique agglomerated chain nanostructure, which was in part responsible for the high selectivity of the catalyst. Chapter 5 investigates the preparation of PdAu/C catalysts for the direct synthesis of hydrogen peroxide. Catalysts prepared by wet impregnation and sol immobilisation, supported on various commercial carbons, were evaluated for their activity, finding that the choice of carbon support material greatly defines activity of the final catalyst. In the case of catalysts prepared by impregnation, the nanostructuring, oxidation state and surface composition of the PdAu nanoparticles varies wildly between catalyst, making identification of the factors important in preparing active catalysts difficult. In comparison, preparing using the sol immobilisation method yields catalysts containing nanoparticles of the same size, oxidation state and surface composition. In this case, the activity of the catalysts was found to correlate with the oxygen surface concentration of the support material.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 25 June 2019
Last Modified: 27 Jun 2019 09:17
URI: http://orca.cf.ac.uk/id/eprint/123711

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