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Surfaces of Pd-based alloys as catalysts for CO2 activation and hydrogenation to methanol

Kowalec, Igor 2023. Surfaces of Pd-based alloys as catalysts for CO2 activation and hydrogenation to methanol. PhD Thesis, Cardiff University.
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This thesis investigates the active sites and reactions involved in CO2 hydrogenation to methanol on the promising Pd-based catalysts. Using state-of-the-art simulation techniques, the study aims to identify catalyst features enhancing CO2 activation via the formate mechanism and develop descriptors for high-throughput computational analysis of Pd-alloy surfaces. The mechanism of CO2 hydrogenation to methanol on low-index Pd facets is explored in detail using density functional theory calculations. The rate-determining step involves HCOOH to H2COOH conversion; however, the Gibbs free energy analysis reveals that the reaction on Pd surfaces is limited at the initial hydrogenation of CO2 to formate. Further, hydrogen adsorption on Pd (111) and Pd (100) surfaces is analysed, considering an exhaustive number of configurations at coverages of up to 2 monolayers. We predict that subsurface hydrogen is present on Pd surfaces at hydrogen coverages expected at reaction conditions relevant for CO2 hydrogenation. Initial stages of CO2 hydrogenation are modelled on low-index metallic Cu, Pd, Zn and alloy CuPd and PdZn surfaces. CuPd (110) surface shows a CO2 hydrogenation barrier similar to that on Pd (100) but inhibits CO2 dissociation linked to lower selectivity of CO2 hydrogenation to methanol. Moreover, the CuPd (110) surface shows a significantly stronger hydrogen adsorption as compared to Cu surfaces. The PdZn surfaces show lower activation energy barriers for CO2 hydrogenation than Pd facets, but CO2 chemisorption constitutes most of the barrier, suggesting an Eley-Rideal mechanism of CO2 hydrogenation on PdZn surfaces. The observed reaction energy barriers correlate with the characteristics of the monodentate formate intermediate. Overall, this thesis aims to understand the behaviour of CO2 and hydrogen on Pd-based catalysts, illustrating the power of simulation in explaining experimental observations and facilitating rational catalyst design to address climate change in the transportation sector.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 18 December 2023
Last Modified: 18 Dec 2023 11:34

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