Journal Articles (before-1995)

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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.
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    Catalytic Decomposition of Formic Acid on Sodium Tungsten Bronzes
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Moody, S. S.; Taylor, Duncan
    The kinetics of the catalytic decomposition of formic acid on sodium tungsten bronzes, NaxWO3 with x in the range 0.11–0.85, and on tungstic oxide have been investigated manometrically in a static system at 150–250°C with acid pressures of 25–30 Torr. The decomposition products were CO2, CO, H2O and H2, the mole ratios CO2 : CO and H2 : CO2 being determined with a mass spectrometer. Initial (zero order) rates were used in conjunction with the ratios CO2: CO to estimate the relative dehydration and dehydrogenation activities of the catalysts as a function of sodium content. Electrical conductivity measurements (a.c. and d.c.) were carried out on the catalysts under reaction conditions. By use of Fuchs' model of the bronze structure, in which clustering, in contrast to random distribution of sodium ions is postulated, the catalytic activity of the bronzes is interpreted in terms of geometric rather than electronic factors: dehydration of formic acid involves adsorption on adjacent sodium and oxygen vacancies, while dehydrogenation requires adsorption on a sodium cluster site. The marked change from dehydration to dehydrogenation activity, which occurs when the x-value increases beyond ∼ 0.7, is related to the reported ordering of the residual sodium vacancies which occurs near x= 0.75.