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    Hydrogenation of Acetylene over Supported Metal Catalysts: Part 1.—Adsorption of [14C]Acetylene and [14C]Ethylene on Silica Supported Rhodium, Iridium and Palladium and Alumina Supported Palladium
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Al-Ammar, Asad S.; Webb, Geoffrey
    The adsorption of [14C]ethylene and [14C]acetylene on supported palladium, rhodium and iridium catalysts occurs irreversibly at 298 K in two distinct stages; a non-linear primary region, in which the species are predominantly dissociatively adsorbed, and a linear secondary region. Hydrogenation catalysis is associated with the hydrocarbon species adsorbed on the secondary region. From [14C]carbon monoxide adsorptions it is concluded that the hydrocarbon primary region is associated with the metal, whilst the secondary region probably involves the formation of overlayers on the primary adsorbed species. The co-adsorption of ethylene and acetylene shows that, under acetylene hydrogenation conditions, both are adsorbed at separate sites and undergo hydrogenation independently of each other. The relevance of these observations to the selective hydrogenation of acetylene is discussed.
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    Hydrogenation of Acetylene over Supported Metal Catalysts: Part 2.—[14C] Tracer Study of Deactivation Phenomena
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (3), 1978) Asad, S. Al-Ammar; Webb, Geoffrey
    In the hydrogenation of acetylene over Pd + SiO2, Rh + SiO2, Ir + SiO2 and Pd + Al2O3, the activities of the catalysts progressively decrease to a steady state constant activity. This deactivation is irreversible at 298 K and can only be effected by acetylene + hydrogen reaction mixtures; acetylene alone produces no significant deactivation. The selectivity and overall reaction orders are independent of the catalytic activity. Adsorptions of [14C]C2H2 and [14C]C2H4 show that the deactivation is associated with the progressive build up of permanently retained acetylenic species on the catalyst surface. Three types of adsorbed acetylene are recognised. The results are interpreted in terms of the hydrogenation reaction occurring by a hydrogen-transfer mechanism between a dissociatively adsorbed C2Hx species and associatively adsorbed acetylene, which forms an overlayer on the dissociatively adsorbed acetylene. The permanent retention of acetylenic species may be due to surface polymer formation.
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    Heats of Hydrogenation of Large Molecules: Part 2.—Six Unsaturated and Polyunsaturated Fatty Acids
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (01), 1978) Rogers, Donald W.; Hoyte, Otho P. A.; Ho, Rickey Kam C.
    We have determined the heats of hydrogenation of the Cj6 and Cib unsaturated and poly unsaturated fatty acids, palmitoleic, oleic, elaidic, linoleic, linelaidic and linolenic acids. This paper reports and interprets the results in the light of previous experimental measurements and theoretical predictions. Heats of formation follow from Hess’ Law addition to the reliable values of the heats of formation of the hydrogenation products, hexadecanoic (palmitic) and octadecanoic (stearic) acids. Our results are generally in serious disagreement with the scattered experimental data and predictions gleaned from the literature and represent, we think, a significant improvement over them.
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    Hydrogenation of Ethylene on Metal Electrodes: Part 2.—Structure of the Adsorption Layer on Platinum at a Working Condition on Open Circuit
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Fujikawa, Keikichi; Katayama, Akiko; Kita, Hideaki
    The structure of the adsorption layer was studied by the potential sweep method on a platinum electrode in 1 N HC104 solution saturated with a reaction gas of various compositions (mixtures of H2, C2H4 and He). Results show that the structure of the adsorption layer satisfies previous predictions on the rate-determining step and that the open circuit potential is determined by the equilibrium condition of the step, H++e_^H(ads). The large change in the hydrogen peak caused by standing the electrode in the solution is in agreement with the decay of the catalytic activity for the hydrogenation of ethylene.
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    Hydrogenation of Ethylene on Metal Electrodes: Part 2.—Structure of the Adsorption Layer on Platinum at a Working Condition on Open Circuit
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Fujikawa, Keikichi; Katayama, Akiko; Kita, Hideaki
    The structure of the adsorption layer was studied by the potential sweep method on a platinum electrode in 1 N HC104 solution saturated with a reaction gas of various compositions (mixtures of H2, C2H4 and He). Results show that the structure of the adsorption layer satisfies previous predictions on the rate-determining step and that the open circuit potential is determined by the equilibrium condition of the step, H++e_^H(ads). The large change in the hydrogen peak caused by standing the electrode in the solution is in agreement with the decay of the catalytic activity for the hydrogenation of ethylene.
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    Hydrogenation of Ethylene on Metal Electrodes: Part 1.—Reduction of Ethylene with Hydrogen at a Platinum Electrode on Open Circuit
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (3), 1973) Fujikawa, Keikichi; Kita, Hideaki; Miyahara, Koshiro
    Reduction of ethylene with hydrogen was studied at a Pt electrode on open circuit in H2SO4 and HClO4 solutions. The reaction rate and the open circuit potential were followed as a function of the gas composition (C2H4+ H2+ He, 1 atm) and the acid concentration. The rate, v, is independent of the acid concentration and is expressed as v=kHkEPHPE/(kHPH+kEPE), where the k values are constants and PH and PE the partial pressures of H2 and C2H4. The ratio kE/kH is 5–6, which is the same value obtained for the ratio of the diffusion rate constant of C2H4 in solution to that of H2. The rate-determining step is the mass transfer step of H2 or of C2H4 depending on the condition, PH/PE < 5–6 or > 5–6, respectively. This conclusion is supported by the dependence of the open circuit potential on the gas composition. Time variation of the catalytic activity of the activated electrode is discussed in terms of the activity change of the adsorbed hydrogen atom. Newly formed adsorbed hydrogen atoms are reactive, but after remaining on the surface, some of them become stable and have a retarding effect on the reaction.