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Computational study on the early stages of the Methanol to Hydrocarbons process

Nastase, Stefan Adrian F. 2019. Computational study on the early stages of the Methanol to Hydrocarbons process. PhD Thesis, Cardiff University.
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Abstract

The Methanol-To-Hydrocarbons (MTH) process is a very important step to produce a wide range of hydrocarbons such as fuel and olefins from various carbon sources. In this thesis, the focus is on understanding the nature of the active sites and reactions occurring in the initial stages of the MTH process by means of state-of-the-art simulation techniques, with the aim of determining the conditions enhancing the conversion rate of methanol and controlling the overall product selectivity. The initial methanol adsorption stage in H-ZSM-5 and H-Y was studied using QM/MM static calculations. Adsorption and methoxylation energies were calculated and shown the H-ZSM-5 sites were achieved a higher adsorption and lower methoxylation energies than those of H-Y. Furthermore, after the formation of the hydrogen bonding network between the reactant and an addition polar molecule, a barrierless Brønsted proton transfer was observed. The nature and adsorption properties of the zeolite active sites were further analysed by using Molecular Dynamics and Metadynamics simulations. Our analysis proved the concerted effect that occurs when having vicinal Brønsted acid sites in the zeolite catalyst and highlighted the improved catalytic activity of such a configuration as opposed to a single acid site. The reactivity of the methoxy groups was analysed with QM/MM simulations, by determining the energy to migrate from one active site or directly form carbene with both pathways proving to be energetically demanding. An additional methanol reaction pathway to dimethyl ether (DME) was simulated with QM/MM methods. The type of active sites and orientation of DME were shown to significantly influence the stability of DME and are projected to further influence the conversion rate of the MTH process. This thesis illustrates the power of complementary computational studies of sorbate reactivity in zeolites, with future work aiming to incorporate these studies into improving different microporous catalytic processes.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 27 February 2020
Last Modified: 25 May 2021 01:39
URI: http://orca.cardiff.ac.uk/id/eprint/130007

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