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Computational investigations to understand the coking thermodynamics and intrinsic chemistry of methane steam reforming on Ni

Yadavalli, Sai Sharath; (2023) Computational investigations to understand the coking thermodynamics and intrinsic chemistry of methane steam reforming on Ni. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Efficient production of hydrogen is of paramount importance to meet the global energy demands of the 21st century. Methane Steam Reforming (MSR) is a major contributor to hydrogen production at the industrial scale. In chemical industries, Ni is the preferred choice as a catalyst for the MSR reaction due to its high activity and low price. However, it is highly susceptible to coking at steam reforming conditions. Ni catalyst deactivation (due to “coking”) in MSR is a critical industrial challenge that requires imminent solutions. In this contribution, we have employed Density Functional Theory (DFT) calculations, microkinetic (MK) models, and Kinetic Monte Carlo (KMC) simulations to gain a fundamental understanding of the coking thermodynamics and intrinsic chemistry of MSR. At first, we performed a detailed screening study to identify a suitable DFT functional for the MSR-graphene system (“graphene” is a model for coke at the molecular level). The DFT predictions were systematically compared to experimental binding energies of MSR species and graphene (obtained from the literature). Subsequently, we developed a first-principles-based KMC model for the methane cracking reaction on Ni(111) to understand the coke morphology and identify conditions of coking. The thermodynamic stabilities of large-body carbon-based configurations were captured under the cluster expansion (CE) framework of KMC. Upon completion of the aforementioned study, we performed CE-based KMC simulations to elucidate the role of potassium in MSR. The MSR reaction was modelled on the clean Ni(111) and potassium-doped (with different loadings) Ni(111) surfaces. The effect of potassium on MSR kinetics was thoroughly investigated. Finally, we formulated an ab-initio MK model for the methane cracking and C-C coupling reactions to understand the coking mechanism on Ni(111). The MK model identifies favourable coking pathways and rate limiting/inhibiting events. These investigations pave the way for identifying next-generation Ni-based catalysts that are resistant to poisoning.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Computational investigations to understand the coking thermodynamics and intrinsic chemistry of methane steam reforming on Ni
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2023. 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 Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10183762
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