Browsing by Author "Kita, Hideaki"

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Adsorption of hydrogen on a platinum–graphite catalyst. Part 1.—Electron spin resonance measurement in the gas–solid system
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (08), 1978) Katayama, Akiko; Kita, Hideaki
E.s.r. signals from a platinum–graphite catalyst (Pt–graphite) and pure graphite were observed as functions of hydrogen gas pressure, temperature and the amount of platinum. The signals were inferred to be due to conduction charge carriers. The e.s.r. signal of Pt–graphite exhibits behaviour similar to that of pure graphite with respect to the temperature variation of the g∥ value. The signal from pure graphite was not affected by the presence of hydrogen gas. However, the signal from Pt–graphite at g=ge(g value of a free electron) decreased with the amount of platinum and increased with the increment in hydrogen gas pressure, obeying the non-dissociative Langmuir isotherm. Detailed analysis indicated that the adsorption of hydrogen on Pt–graphite causes a change in the number of conduction electrons. Adsorbed hydrogen on Pt–graphite is concluded to be positively polarized in molecular form.
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.
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.
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.