Farooq, Danial;
(2025)
Exploring structural evolution of Mn-doped Co Fischer-Tropsch catalysts via X-ray scattering computed tomography.
Doctoral thesis (Ph.D), UCL (University College London).
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Danial Farooq - Thesis.pdf - Accepted Version Access restricted to UCL open access staff until 1 March 2026. Download (18MB) |
Abstract
Fischer-Tropsch (FT) catalysts enable the production of long-chain hydrocarbons from syngas, contributing to the development of carbon-neutral fuel and chemicals. Recently, manganese (Mn)-doped cobalt (Co) FT catalysts have demonstrated increased selectivity towards commercially valuable alcohols and olefins. X-ray diffraction/scattering computed tomography (XRSCT) provided 2D images of passivated catalysts post-reaction, after 150 and 300 hours on stream under industrially relevant conditions, revealing the spatial variation of Co phases and the influence of Mn loading. A wax product coating throughout the extrudate preserved the state of the Co/Mn species, enabling post-reaction analysis without extensive post-treatment. The 3 % Mn loading exhibited an optimum equilibrium between hexagonal close-packed (HCP) Co and Co₂C phases, which resulted in maximum oxygenate selectivity. It was thought that MnO particles promoted Co carburisation, which enhanced oxygenate selectivity. Co₂C formed after carburisation under CO and preferentially reduced to Co HCP, where lower loadings of Mn (1.5 – 3 wt. % Mn) exhibited higher weight percentages of both phases. In situ XRD and PDF experiments were used to observe the reduction of the catalysts. Low Mn loadings promoted reduction, but higher loadings inhibited it. A theoretical model of FCC/HCP Co stacking faults was developed, and the fit of experimental XRD data was improved. The stacking fault analysis enabled a more accurate analysis of the presence of FCC/HCP Co phases, where it was found that extrinsically faulted FCC led to HCP formation followed by Co₂C. This study underscores the significance of examining catalysts under industrially relevant reaction times and employing spatially resolved techniques to analyse catalytic pellets and understand structure-function relationships. It emphasises the role of HCP domains in promoting Co₂C formation and increasing olefin and oxygenate selectivity. Further research is needed to investigate the exact role of Mn in promoting Co carburisation and its impact on Co active sites.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Exploring structural evolution of Mn-doped Co Fischer-Tropsch catalysts via X-ray scattering computed tomography |
| Language: | English |
| Additional information: | Copyright © The Author 2025. 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/10204601 |
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