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Molecular Transport and Reactivity in Confinement

Le, TN; (2016) Molecular Transport and Reactivity in Confinement. Doctoral thesis , UCL (University College London). Green open access

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Abstract

For decades, tremendous efforts have been made through extensive experimental, theoretical and molecular simulated approaches to study numerous extraordinary phenomenon occur at sub-surface environments. As parts of such expedition, the works presented in this thesis employ (1) molecular dynamics (MD) simulations to investigate different structural and dynamic properties of confined fluids and (2) reactive ensemble Monte Carlo (RxMC) to explore thermodynamic properties of carbon dioxide methanation at nano-confinement. At the beginning, a series of studies by MD were conducted to examine the adsorption, structures and diffusion of (1) pure hydrocarbon and (2) mixtures of different hydrocarbons and carbon dioxide in silica pores at sub-, near-, and super-critical conditions. At equilibrium, pronounced layering was observed for propane near the pore surface. Counterintuitively, simulated MD results, in agreement with experimental quasielastic incoherent neutron scattering data, reveal that pure propane confined in silica meso-pore yields higher selfdiffusivity at higher loading, isothermally. In the case of binary mixture, CO2 preferential adsorption on the pore surface is likely to attenuate the surface adsorption of hydrocarbon, lower the activation energy for hydrocarbon diffusivity, and consequently enhance hydrocarbon mobility at low CO2 loading. At high CO2 loading, hydrocarbon diffusivity is hindered by molecular crowding. Hence, the non-monotonic change in hydrocarbon selfdiffusion coefficients as functions of CO2 concentration displays local maxima. On the other hand, results obtained from RxMC simulations show strong dependency of the confined reaction equilibrium conversions 2 and equilibrium constants Kp on the pore size, pore chemistry and pore morphology. Conditions that facilitate the preferential adsorption of water on the pore walls (e.g., small pore width, high hydrophobicity of pore substrate, and rough pore surface) yield high 2 and Kp, with the possibility of changing significantly the equilibrium composition of the reactive system with respect to bulk observations.

Type: Thesis (Doctoral)
Title: Molecular Transport and Reactivity in Confinement
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Keywords: Molecular Simulations, Interfacial Interactions
UCL classification: UCL > Provost and Vice Provost Offices
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/1532188
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