The kinetics of the cathodic reduction of ethylene on platinum and ruthenium in aqueous acid and alkali solutions are reported. The reduction proceeds according to the stoichiometric equations C2H4+2H++2e -+ C2Hs (acid) or C2H4+2H20+2e + CzH6+20H-(alkali). Tafel slopes, reaction orders in hydrogen ion and ethylene together with temperature effects have been determined by steady state potentiostatic techniques combined with chromatographic analysis.
The kinetics and mechanism of the cathodic reduction of ethylene on gold, tungsten and a number of other materials is reported. Tafel slopes, reaction orders and isotope effects indicate a rate determining step (r.d.s,) between adsorbed ethylene and adsorbed hydrogen. Contrasts between the catalytic behaviour of platinum (reported previously) and gold are discussed and attributed to the different pH dependencies of the potential of zero charge values (P.z.c.) of these metals. Catalytic efficiencies of the several materials are reviewed in the light of theories of catalysis.
The kinetics of the cathodic reduction of acetylene on platinized platinum in aqueous acid solutions are reported. The products are both ethylene and ethane. Tafel slopes, the reaction order in hydrogen ion and the enthalpy of activation have been determined by steady-state potentiostatic techniques combined with chromatographic analysis. The observed parameters in the reduction are compared and constrasted with those of ethylene reduction reported previously. Tafel slopes, the potential dependence of the products, a limiting current and the pH effects are interpreted in terms of a r.d.s. between a strongly adsorbed organic species and adsorbed hydrogen.A detailed study of the electro-reduction of ethylene on platinum and ruthenium and on gold, tungsten and other substrates in aqueous solutions has been reported previously. The reduction of acetylene has been investigated under similar conditions on platinized platinum only. A number of contrasts have emerged.
EXPERIMENTAL
MATERIALS A N D EQUIPMENTThese have been described e1sewhere.l The acetylene (B.O.C.) was washed free of acetone in a train of Drechsel bottles before entry into the cell. The platinum (99.99 %, Koch-Light) was platinized with 1 % chloroplatinic acid solution. The electrodes used
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