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Understanding the Effect of Caesium Promotion on the Preparation and Activation of Copper-Based Low-Temperature Water-Gas Shift Catalysts

Farmer, Daniela Maria; (2021) Understanding the Effect of Caesium Promotion on the Preparation and Activation of Copper-Based Low-Temperature Water-Gas Shift Catalysts. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The water-gas shift (WGS) reaction has been extensively researched due to its widespread application. Its purpose is to yield the maximum amount of hydrogen, thermodynamically favoured at low temperatures, making the efficiency and stability of the Cu-based low-temperature shift (LTS) catalyst a necessity. Typically, commercial LTS catalysts are composed of CuO/ZnO/Al2O3 (molar ratio 0.6:0.3:0.1); however, this catalyst formulation is also used for methanol synthesis, making MeOH an undesirable by-product which can cause reactor degradation. Caesium promotion (ca. 1 wt.%) has been reported to inhibit this side reaction but is thought to lead to instability in the catalyst early on, making activation crucial. Initially, alterations to the CuO/ZnO/Al2O3 (molar ratio 0.6:0.3:0.1) coprecipitation method were investigated to determine which conditions afforded catalysts with comparable properties to those employed in industry. This ensured all activation tests were commercially relevant. Understanding how the microstructure of the active Cu0 component in the commercially applicable CuO/ZnO/Al2O3(-Cs2O) catalyst evolves under various H2 partial pressures in the presence/absence of Cs was determined at beamline ID15A, ESRF, where time-resolved 1D XRD and spatially-resolved XRD-CT (X-ray diffraction computed tomography) data were collected for [H2] of 1, 2.5 and 5 %. These were compared to catalysts with higher copper loading (CuO/ZnO/Al2O3(-Cs2O), molar ratio 0.8:0.1:0.1) to elucidate the importance of the zincite support and the effect of the promoter on sintering mechanisms, dislocation character and stacking fault probability. Steam incorporation during activation was also investigated in a commissioned reactor set-up to elucidate possible early onset deactivation mechanisms resulting from the Cs-promoter. The coprecipitation method was scaled-up in order to produce industrially relevant pellets for activation testing, which were then characterised using XRD, Hg porosimetry and mechanical strength testing. This highlighted the effects of phase segregation caused by Cs-incorporation, and the susceptibility of the ZnO support sintering in wet environments.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Understanding the Effect of Caesium Promotion on the Preparation and Activation of Copper-Based Low-Temperature Water-Gas Shift Catalysts
Event: UCL
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
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/10133548
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