Browsing by Author "Kemball, C."

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Adsorption of neopentane on tungsten and palladium films
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (5), 1972) Ross, J. R. H.; Roberts, M. W.; Kemball, C.
The adsorption of neopentane has been studied on tungsten and on palladium films; allied experiments were carried out with methane (W, Pd) and with propane (W). The evolution of hydrogen from each gas/metal system was studied as a function of time and temperature; reaction with gas phase deuterium was used to determine how many of the hydrogen atoms in the surface phase were exchangeable, either rapidly or by slower processes. Rapid dissociative chemisorption, involving the cleavage of an average of 3 or 4 C—H bonds occurred with neopentane or propane on tungsten. Neopentane was chemisorbed on palladium at room temperature but dissociation of methane was not observed below ∼373 K; the extent of the dissociation of both hydrocarbons was smaller than on tungsten. Further breakdown of the surface species, accompanied by evolution of hydrogen, occurred with all systems on raising the temperature. Evidence for C—C bond rupture was obtained from the hydrogenolysis of neopentane at higher temperatures.
Effect of Adsorbed Hydrocarbon on the Catalytic Exchange of n-Butane and Deuterium on Tungsten Films
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (6), 1972) Arroyo, Antonio Cortes; Kemball, C.
The exchange of n-butane with deuterium is catalyzed by tungsten films at temperatures below 250 K; the reaction involves mainly simple exchange with no evidence of self-poisoning. The adsorption of butane on tungsten at temperatures from 273 to 423 K gives strongly adsorbed hydrocarbon species which reduce the rate of the subsequent exchange at 273 K by factors of from 10 to 2000, the effect increasing with the adsorption temperature. Only a fraction of these adsorbed species is easily rehydrogenated. Some results for comparison arc obtained with adsorbed but-l-ene, neopentane or methane.
Hydrogenolysis of Saturated Hydrocarbons on Evaporated Platinum Films
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (11), 1972) Dowie, R. S.; Whan, D. A.; Kemball, C.
The reactions of ethane, propane, n-butane, isobutanc and neopentane have been examined in the presence of deuterium on platinum films. Details of the products of exchange, hydrogenolysis and, where possible, isomerization are reported. The kinetic behaviour of the hydrogenolysis reaction showed a trend in that reactions of ethane were acccleratory, those of propane maintained a constant rate and those of molecules with four or more carbon atoms decelerated with time. The retardation in rates was much more marked with branched chain than with linear hydrocarbons. The results are discussed in terms of the nature of the adsorbed species accumulating on the surface, species possessing some carbonium ion character being likely precursors to the material responsible for the observed poisoning. Little additional mechanistic information was obtained from an analysis of the deuterium contents of the various molecules as exchange was fast compared to hydrogenolysis or isomerization, leading to rapid isotopic equilibration. A fragmentation correction scheme taking into account the influence of molecular composition on bond rupture has also been developed for analysis of the mass spectral data.