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Title: Inelastic neutron scattering by adsorbed molecules and catalysts
Author: Gamlen, Philip H.
ISNI:       0000 0001 3487 4636
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1978
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The possibilities of applying cold neutron scattering to the study of sorbed molecules are discussed. Atom-atom pair calculations have been carried out for the interaction of methane and hydrogen molecules with the basal plane of graphite and the results used as a guide to the best scattering law for the sorbed molecule dynamics. As the sorbents used are powders, a method of averaging the two dimensional scattering law over three dimensions has been developed. Neutron time of flight spectra were obtained for methane, ethylene and ammonia adsorbed on Graphon. For the surface coverages studied, 0.6-0.2, methane appears to change from a two dimensional Fickian liquid, to an unidentified phase at the lower surface coverage. The data for ethylene at around one monolayer approaches the two dimensional liquid model, but at higher surface coverages there are significant deviations. Whilst methane and ethylene appear to wet the Graphon surface, ammonia does not seem to do so. The spectra for ammonia show a liquid phase characterised by a diffusion coefficient and activation energy for diffusion, 2.4 kcals/mole, close to those measured for bulk ammonia A solid phase is observed at lower temperatures. Neutron time of flight spectra were obtained for methane absorbed in a lanthanum exchanged Y type zeolite. The spectra show that the methane has lost translational motion but retained rotational freedom. A vibration frequency of 19±1 cm-1 is observed and this is ascribed to a vibration of the methane molecule within the cavity. The sorption of simple molecules on catalytically active surfaces was investigated by beryllium filter spectroscopy. A range of interactions was discovered, varying from the gas like sorption of hydrogen and methane on La-Y, to the dissociative sorption of formic acid on γ alumina. Intermediate behaviour was observed when dichloromethane and acetonitrile were sorbed on La-Y.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available