Browsing by Author "Taylor, Duncan"

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Acidic Properties of Mixed Tin-i-Antimony Oxide Catalysts
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Irving, Elizabeth A.; Taylor, Duncan
Mixed oxides of tin and antimony have been used as catalysts in a static system and outgassed both at room temperature and at 698 K in a study of the approximately zero order stages of the isomerization of 3,3-dimethylbut-1-ene (373 K), cyclopropane (411 K), but-1-ene (293 K) and cis-but-2-ene (293 K) and of the dehydration of isopropanol (343 and 408 K). With catalysts outgassed at room temperature, weakly acidic sites are present, and all the reactions probably occur by a carbonium ion type of mechanism with Brönsted acid sites as a source of protons. Rates increase to a maximum as the antimony content increases from zero to ≈ 50 atomic %, and then decline with further increase in the antimony content. Outgassing of the catalysts at 698 K increased the rate of isomerization of 3,3-dimethylbut-1-ene, but for cyclopropane and isopropanol decreased rates were observed due to poisoning by the propene product. For but-1-ene and cis-but-2-ene, the higher temperature outgassing procedure changed the rate against catalyst composition pattern considerably in that only catalysts with less than 50 % Sb were active, and a mechanism involving an allyl intermediate is proposed. Catalyst activity could be poisoned by treatment with bases or with sodium acetate. It is concluded on the basis of a proposed correlation between rates and acidity, that the catalyst composition corresponding to maximum acidity is different from that for maximum selective oxidation activity.
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.
Dehydrogenation and isomerization of n-butenes on mixed tin + antimony oxide catalysts
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (06), 1978) Irvine, Elizabeth A.; Taylor, Duncan
The dehydrogenation and concurrent isomerization of the three n-butenes have been investigated at 474 K on a range of mixed tin + antimony oxide catalysts outgassed at 698 K. The initial approximately zero order reaction rates were used as a measure of catalytic activity to construct patterns of activity as a function of catalyst composition. Comparison of the patterns with those for the isomerization of 3,3-dimethylbut-1-ene and for the selective oxidation of propene on the same catalysts indicate that dehydrogenation of but-1-ene involves a π-allyl intermediate, while isomerization occurs through carbonium ion formation. For the cis- and trans-isomers, it is suggested that both reactions occur via a common allyl (but not π-allyl) type of intermediate.