Lais, Tahmin;
(2024)
In situ X-ray Spectroscopic Studies of Water-Gas Shift Catalysts.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The research presented in this thesis focuses on the in situ and ex situ studies of catalysts used for water-gas shift reactions. Specifically, Cu-Cr-Fe-based and Cu-Ce-Al-based systems were studied in detail to determine the structural changes during the activation (calcination and reduction) processes to optimise these catalysts for the catalytic reaction. Several methods of analysing the respective XANES data were explored, and their strength and weaknesses were highlighted in the respective work described in the thesis. CuO-Cr2O3-Fe2O3 high-temperature water-gas shift catalysts were investigated in oxidising and non-oxidising atmospheres, using ex situ XRD, Raman, XPS, XAS as well as under in situ HR-XANES and NAP-XPS. It was found that the as-prepared material has a distorted CuO6 environment. During thermal treatment, the Cu(II) ions remain as Cu(II) but undergo a further distortion in their octahedral environment. The results demonstrate that copper ions are in a solid solution and certainly discount any physical mixture of CuO (in any noticeable amounts) along with the solid solution. The reaction atmosphere can stabilise Cr(III) species via migration of chromium into the ferrihydrite matrix. Near-ambient pressure XPS revealed the migration of copper species to the surface. The relevance of varying pre-treatments of the catalysts followed by WGS reaction were subsequently studied by employing in situ XAS. Generally, it was found that under WGS reaction most of the Cr species in the catalysts restructured to form dominantly a phase that is closely similar to the FeCr2O4 spinel phase, irrespective of prior calcination conditions, and metallic copper is observed at ca. 350 C. In situ HR-XANES was also used to understand the role of copper ions interacting with ceria support, specifically CuO/CeO2/Al2O3 under a reducing atmosphere. Detailed analysis provided not only the role of copper ions in promoting Ce(IV) to Ce(III) reduction but also the presence of Ce(IV) interaction with alumina support.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | In situ X-ray Spectroscopic Studies of Water-Gas Shift Catalysts |
| Language: | English |
| Additional information: | Copyright © The Author 2024. 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 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/10193029 |
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