. The electrocatalytic hydrogenation (ECH) of phenanthrene, anthracene, and naphthalene has been investigated under constant current at Raney nickel electrodes in a mixed aqueous organic medium. The influence of various parameters on the efficiency of the process determined by the current efficiency (a measure of the competition between hydrogenation and hydrogen evolution, the only two electrochemical processes occumng), the extent of hydrogenation (yield of octahydro-derivatives), and the conversion rate was studied with phenanthrene. The best conditions were ethylene glycol or propylene glycol as cosolvent containing between 1.5 to 5% of water, a neutral or slightly acidic medium containing boric acid (0.1 M) as buffer (initial pH of 2.6, final pH of 6.0-6.2), sodium chloride or tetrabutylamonium chloride as supporting electrolyte, a temperature of 80°C, and a current density of 42 to 84 m~/ c r n~. The most active electrodes (consisting of Raney Ni particles dispersed in a nickel matrix and surrounded by a layer of porous nickel) were obtained by leaching the dispersed alloy particles at 75°C for 7 h in 30% aqueous sodium hydroxide. The electrohydrogenation stopped at derivatives with a single aromatic ring, namely the octahydrophenanthrenes, octahydroanthracenes, and tetralin. In a non-buffered medium, tetrahydrophenanthrene could be obtained with selectivities of 80% or better.
The hydrogen evolution reaction was studied at composite‐coated Raney nickel electrodes in aqueous and aqueous methanolic solutions containing
1MKOH
at 25°C, using ac impedance and steady‐state polarization techniques. In aqueous solutions, the experimental results were analyzed by the constant‐phase element (CPE) and the porous electrode models, and the resulting parameters were compared. In aqueous methanolic solutions it was found that the experimental data could be well approximated by both the fractal and the porous models. The kinetic parameters obtained in the different media were compared to those obtained on polycrystalline nickel.
975trocatalyst may be due to the combined effects of the Raney type Pt-Cr-Cu alloy and of the base metal oxide. A shortterm stability test indicated nearly stable performance for 20 h after little loss of performance in the first 10 h of cell operation. REFERENCES 1.
ABSTRACTThe hydrogen evolution reaction (HER) has been studied at Raney nickel electrodes in the absence and presence of several organic compounds. A poisoning effect of nonreducible organic substrates on the kinetics of the HER was studied. It was found that only pyridine had a strong inhibiting effect on the HER. A compound having one reducible double bond, trans-cinnamic acid, was used as a model in a study of the mechanism of the electrocatalytic hydrogenation (ECH) reaction and its influence on the HER. It was established that the HER proceeds via the Volmer-Hyrovsky reaction mechanism, and the slowest step is the Heyrovsky reaction. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 155.198.30.43 Downloaded on 2015-03-16 to IP
. The electrocatalytic hydrogenation (ECH) of various ketones was investigated at codeposited Raney metal electrodes in aqueous methanol. The influence of different parameters (pH, supporting electrolyte, and water percentage) on the ECH of cyclohexanone and acetophenone was studied. The relative ease of electrohydrogenation of a variety of monoketones was determined in competitive electrolyses. The ECH of a-and P-diketones was carried out and different products were obtained selectively by the right choice of catalytic material and electrolysis conditions. The diastereoselectivity of the formation of diols was also determined.
The influence of preoxidizing the surface of polycrystalline copper electrodes on the efficiency of the controlled potential electrochemical reduction of nitrobenzene and azobenzene to aniline in basic aqueous methanol has been investigated. Electrodes electrochemically preoxidized to CU(OH)~ or to CuzO gave high yields of aniline (90-100%) with high current efficiencies (88-99%) for the electrohydrogenation of nitrobenzene compared to electrodes preoxidized by air (7-29% of aniline, 64-74% current efficiency). For the electrohydrogenation of azobenzene, copper electrodes preoxidized to CuzO were found to be more active (average yield of aniline of 28%, average current efficiency of 55%) than electrodes preoxidized to CU(OH)~ (3-1 1% of aniline, 42-53% current efficiency), and electrodes preoxidized by air were inactive (the electrohydrogenation stopped at hydrazobenzene). The improvement of activity induced by preoxidation of the copper surface is linked to the increase of the surface area.
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