Electrochemical Construction of Hydrogenation System Using Active Hydrogen at Hydrogen Storage Alloy/Gas Interphase

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The information obtained from this work can be summarized as follows.1. Hydrogen diffusion coefficient (Einstein diffusion coefficient) in MmNi_<4.2>Al_<0.5>M_<0.3> (Mm=misch metal, M=Cr, Mn, Fe, Co, Ni) alloys decreases with an increase in atomic radius of M because of enhanced stability of absorbed hydrogen in them. In addition, hydrogen evolution reaction at Mm(B_5)_x (B_5=Ni_<3.6>Mn_<0.4>Al_<0.3>Co_<0.7>,0.8*x*1.12) alloy electrodes proceeds via the Volmer-Tafel mechanism irrespective of x value. An increase in x value depresses the Tafel reaction effectively, leading to promotion of hydrogen absorption in the alloys.2. A new successive system for hydrogenation of stirene was constructed using a two-compartment cell separated by a Pd sheet electrode. The amount of produced ethylbenzene increases linearly after an appropriate induction period and current efficiency for ethylbenzene production is over 90%. The rate of ethylbenzene production increases with an increase in current density for electrolysis of water. The hydrogenation system can be also constructed by using hydrogen storage alloy sheet electrodes prepared by rapid-quenching method.3. The above-mentioned hydrogenation system can be applied to the hydrogenation of alpha-methylstirene, 1-octene, 2-octene and cyclohexene, and the hydrogenation rate increases in the order of cyclohexene<2-octene<alpha-methylstirene<1-octene<stirene. The hydrogenation of acetylene, gaseous unsaturated organic compound, also proceeds and ethane is produced via ethylene.4. Pd black, which is well-known to show high catalytic activity for the hydrogenation, can be deposited three-dimensionally by a reaction of Pd^<2+> with active hydrogen passing through a Pd sheet electrode. The hydrogenation rates of 4-methylstirene and 2-octene using a palladinized Pd sheet electrode increase markedly in comparison with those using a Pd sheet electrode.