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Hydrocarbon Pool Mechanisms in zeolite catalysts studied by Kerr-gated Raman Spectroscopy

Campbell, Emma Jane; (2022) Hydrocarbon Pool Mechanisms in zeolite catalysts studied by Kerr-gated Raman Spectroscopy. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Hydrocarbon pools (HCP) are thought to be an integral part of some zeolite-catalysed hydrocarbon conversion mechanisms. The composition of a HCP can vary due to reaction conditions and to zeolite properties, i.e., topology and acidity. The HCP composition and behaviour control the activity and selectivity of the reaction, and therefore a full understanding of the speciation in these reactions is necessary for future reaction developments to improve efficiency. In this thesis, Kerr-gated Raman Spectroscopy is applied under operando conditions using a visible wavelength laser (400 nm) to identify HCP intermediates during catalytic conversion of methanol, and biomass derived model-compounds. In this work the application of the Kerr-gate is vital for removing the inherent emission signals from zeolite samples which typically dominate Raman spectra. In Chapter 3, this technique is used to unravel the Methanol-to-Olefins (MTO) reaction. The first part of this chapter identifies the role of polyenes during the initial stages of catalyst deactivation in small pore zeolites, while the second part interrogates how calcium affects the HCP and therefore the reaction mechanism. Chapter 4 focuses on furan conversion, as a model compound for biomass to study Catalytic Fast Pyrolysis (CFP). This reaction is followed by Raman and UV-Vis spectroscopy during temperature ramping, allowing the changes that lead to aromatics and olefins production on four zeolites (ZSM-5, beta, Zeolite Y and ferrierite) to be followed and understood. Only in ZSM-5 is benzofuran observed to form on the zeolite, an intermediate linked with higher aromatic formation. Chapter 5 continues the study of converting model compounds of biomass using ZSM-5 only, but changing the chemical feed to acetic acid, acetaldehyde, and hydrogenated furan. Finally, in Chapter 6, the results from a UV-Raman study of the MTO and CFP reactions are shown, demonstrating the usefulness of probing samples with different incident wavelengths to capitalize on resonance enhancement.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Hydrocarbon Pool Mechanisms in zeolite catalysts studied by Kerr-gated Raman Spectroscopy
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/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 BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL
URI: https://discovery.ucl.ac.uk/id/eprint/10144324
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