Browsing by Author "Morgan, John A."

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Investigation of the Catalytic Decomposition of Ethyne, Ethene and Butadiene at Low Pressures on Niobium at High Temperatures using Ultra-high Vacuum Techniques
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Morgan, John A.; Robertson, Andrew J. B.
Rates of decomposition of ethyne, ethene and butadiene on niobium wire filaments at high temperatures have been investigated for hydrocarbon pressures between about 100 mN m–2 and 2 µN m–2, using ultra-high vacuum techniques. At high pressures, clean filaments underwent rapid decay of activity to give steady zero-order decomposition rates whose values were independent of the hydrocarbon studied. This phenomenon is discussed in terms of carbon deposition and diffusion of carbon from the surface. At lower pressures, steady first-order rates were observed before very slow decays of activity. Complicating hydrogenation reactions, occurring on the reaction vessel walls, restricted the upper temperatures at which first-order rates could be accurately measured. First-order rates are in reasonable accord with the transition state theory for a mobile transition state. Experiments were performed with carbon, Nb2C and NbC filaments to indicate the possible effects of carbon contamination on niobium. Kinetics on Nb2C and pure Nb were similar. Results for ethyne decomposition on niobium using u.h.v. are compared with some results under conventional high vaccum conditions and differences explained by decarburisation by water vapour. The high pre-exponential terms reported are critically examined and discussed in the light of these findings.
Kinetics of the Decomposition and Hydrogen Reduction of Nitric Oxide on Niobium, Nickel and Platinum Filaments at High Temperatures and Low Pressures
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Morgan, John A.; Robertson, Andrew J. B.
NO decomposition kinetics were studied with ultra-high vacuum techniques on niobium, nickel and platinum wire filaments at high temperatures with pressures between —1 and 100 m-2. Niobium readily decomposed NO with first-order kinetics, nitrogen and oxygen being deposited on the surface, resulting in a progressive loss of filament activity. Nitrogen was desorbed from nickel, which otherwise behaved similarly to niobium. Excess H2 affected the kinetics of NO reaction on these metals mainly by reaction with and subsequent removal of surface contaminants rather than by a direct reaction with NO. Platinum did not observably decompose NO at low pressures except in the presence of excess H2. Above ~1300 K the rate appeared to be determined by H2 atomisation, but at lower temperatures a reaction between H2 and NO may have been occurring. The rate-limiting step for this reaction may be the decomposition of H2 and addition of H atoms to adsorbed NO. The pre-exponential term for this reaction indicated that the transition state was mobile on the surface.