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Au & Pd surfaces: From capping agents to methane oxidation

Nasrallah, Ali 2020. Au & Pd surfaces: From capping agents to methane oxidation. PhD Thesis, Cardiff University.
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Abstract

This thesis uses Density Functional Theory (DFT) to study the applications of transition metal surfaces in the fields of catalysis and nanoparticle synthesis. Chapter 1 provides the reader with a detailed literature review on methane oxidation, methanol synthesis, and an outlook on the different catalysts that have been used for methane activation. Chapter two then addresses the theoretical background of DFT and the different methods used. The work produced in this thesis is then split into two main sections: Section 1 which encompasses chapters 3 and 4 covers the partial oxidation of methane to methanol on Au and Pd surfaces. By modelling two low index surfaces of Au and Pd, we studied the partial oxidation of methane to methanol using hydrogen peroxide and molecular oxygen as oxidants. We performed a detailed study of the reaction mechanism by modelling the adsorption of intermediary species and the activation energy barriers for each of the steps. The results obtained were then used to explain why the alloy is catalytically superior to the pure metals and the different steps at which the pure surfaces fail to catalyse. Once identified, we then model doped surfaces in order understand how the alloy would tackle the problems associated with the pure metal surfaces. The results obtained show that the Pd surfaces are too active for molecular oxygen to an extent that upon adsorption, the molecule cleaves on the surface with a small barrier to from two oxygen metal-bound atoms. The Au surfaces on the other hand, show an opposite effect with a very endothermic energy of reaction for the displacement of water by molecular oxygen. Upon modelling the doped system, an improved binding of molecular oxygen on the Pd-doped Au surfaces is observed along with a decrease in the affinity of the Au-doped Pd surfaces to molecular oxygen. Section 2 which comprises of chapter 5 discusses the use of capping agents in nanoparticle synthesis. The chapter first describes the importance of the use of capping agents in the stabilisation of nanoparticles in nanoparticle synthesis. Hetero-atom containing ligands provide a main class of capping agents used experimentally and thus using DFT, we study how aminopropanol can be used as a capping agent for the synthesis of Pd nanoparticles. By modelling the adsorption of aminopropanol on Pd surfaces and plotting IR spectra, we rationalise how aminopropanol, a ligand made of two heteroatoms, binds to Pd nanoparticles. Our adsorption energies and IR spectra show that 3-amino-propan-1-ol prefers viii to bind to the Pd surfaces through the amino-group. This was further supported by a comparison of the computed IR and experimental spectra which show strong correlation. Chapter 6 provides general conclusions regarding the significance of the results in all three chapters

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 6 August 2020
Last Modified: 06 Aug 2020 08:28
URI: http://orca.cf.ac.uk/id/eprint/134007

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