Molecular Modelling of Methyl Ester-Promoted Dimethyl Ether Formation from Methanol

: Enhancing Routes to Renewable Fuels in MFI Zeolite through Reactivity and Dynamics

Abstract

The methanol to hydrocarbon reaction, catalysed by MFI-type zeolites, offers a
promising route for producing renewable fuels, crucial in the global effort to
transition away from fossil fuels amidst the increasingly damaging effects of
climate change. Recently, methyl esters have been found to promote the formation of dimethyl ether, the first stage of the methanol to hydrocarbon reaction, but the reason(s) for the promotional effect remain unclear. The diffusion of species toward, or away from, Brønsted acid sites, adsorption at such sites, and changes in reaction mechanisms could all factor in the increased formation of dimethyl ether. It is difficult to carry out experiments that shed light on these processes as they occur within the complex internal porous structures of zeolites. As such, computational techniques have been developed to investigate diffusion, adsorption, and reaction mechanisms in zeolites.
In this thesis, we initially investigate the competing diffusion of promoters and
methanol using molecular dynamics simulations, observing novel diffusion behaviour and potential bottlenecks to diffusion that could lead to molecular traffic control effects increasing catalytic activity. Through the use of the novel enhanced sampling method interactive molecular dynamics in virtual reality, we investigate the potential bottleneck, finding further evidence of molecular traffic control effects, and provide a portfolio of systems relevant to materials chemistry and catalysis for future study. Finally, we explore the competing associative and dissociative mechanisms for the formation of dimethyl ether in the absence, and presence, of promoters using a multilevel quantum mechanical method. We observe more exothermic pathways with reduced barriers for this reaction in the presence of the promoters and find significant correlation to the promoters adsorption and catalytic efficiency. We summarise the findings of these studies and provide a number of routes for further exploration.

Date of Award	1 Oct 2024
Original language	English
Awarding Institution	University of Bristol
Sponsors	BP
Supervisor	Neil L Allan (Supervisor) & Adrian J Mulholland (Supervisor)