Modelling approaches to p-Xylene catalysis

Thomas, Harry 2024. Modelling approaches to p-Xylene catalysis. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The oxidation of p-Xylene to terephthalic acid is of significant commercial value as the product, terephthalic acid, is used in the production of the polymer polyethylene terephthalate. The commercial oxidation of p-Xylene uses a cobalt / manganese / bromide catalyst, where the oxidation proceeds through a redox cascade process; however, the structure of the cobalt and manganese catalyst species still remains poorly understood, despite the importance of the catalytic process. To better understand the structures of the cobalt and manganese catalysts present under the commercial operating conditions, a computational, density functional theory study is performed. Structural thermodynamics studies of the catalysts suggest that the most thermodynamically stable structures are the octahedrallycoordinated, mononuclear, [Mn(OAc)2(HOAc)2], [Mn(OAc)3(H2O)1], [Co(OAc)2(HOAc)2], and [Mn(OAc)3] for Mn(II), Mn(III), Co(II), and Co(III), respectively. First principles molecular dynamics studies of the manganese and cobalt catalysts in aqueous acetic acid show a low number of water molecules (0 – 1) coordinate under the commercial operating conditions; additional calculations performed with the HBr moiety included, show bromide does not coordinate to the manganese catalyst. Redox potential studies of the investigated catalysts show all steps in the p-Xylene redox cascade are thermodynamically favourable with the exception of the oxidation of bromide by the Mn(III) catalyst; the feasibility of this oxidation step could be explained by the formation of brominated Mn(III) complexes or positively charged complexes, which calculations suggest to be more redox active. Our results give a more complete understanding of the structural properties of the Co/Mn/Br catalyst, as well as the involved reaction mechanism in the p-Xylene redox cascade.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	20 January 2025
Last Modified:	20 Jan 2025 15:38
URI:	https://orca.cardiff.ac.uk/id/eprint/175382

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