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Effect of precious metal particle size and support type on catalytic activity as revealed by X-ray methods

Decarolis, Donato; (2019) Effect of precious metal particle size and support type on catalytic activity as revealed by X-ray methods. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

For supported nanoparticulate catalysts, the effect of their properties, such as size and interaction with support, on a catalytic process is still in debate. This is partially caused by the limited control that typical nanoparticle preparation methods offer which may lead to the presence of nanoparticles possessing a range of sizes and shapes, leading to a lack of clarity in the correlation between properties and catalysis. The work presented in this thesis focuses on producing size-selected monometallic supported nanoparticles and their detailed characterisation, both ex situ and in situ (under reaction conditions) mainly through the application of the technique of X-ray absorption spectroscopy (XAFS). Chapter 3 of this thesis focuses on understanding the mechanism of formation of Au nanoparticles produced by reverse micelle encapsulation, through a combination of various techniques (transmission electron microscopy, dynamic light scattering, UV-vis, combined small angle X-ray scattering/XAFS). From the combined data, it is possible to rationalise the synthesis process, which can be divided into three steps: fast reduction of Au (III) species to Au (I), slow reduction and agglomeration of Au atoms in sub-nanometric clusters and a final agglomeration to form the nanoparticles. Chapter 4 and 5 focus on the application of monometallic nanoparticles to the catalytic hydrogenation of 1,3-butadiene, used as a model reaction, using in situ XAFS to correlate size and support effect with their catalytic activities. For Au nanoparticles (chapter 4) it appears that a restructuring process takes places under reaction conditions. Depending on the sample, this process can be favourable (Au/SiO2) or detrimental (Au/Al2O3) and is highly dependent on particle size. For Pd nanoparticles (chapter 5) it was possible to identify the active species necessary (Pd0), and detrimental (PdH and PdC) for the selective hydrogenation of 1,3-butadiene in Pd as well as the role of support and size in promoting the presence of each phase.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Effect of precious metal particle size and support type on catalytic activity as revealed by X-ray methods
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10066557
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