No abstract

Electrodes consisting of particles of a transition metal entrapped and dispersed in a reticulated vitreous carbon (RVC) matrix were prepared in situ by stirring the particles in the presence of an RVC cathode. Such electrodes were used for the electrocatalytic hydrogenolysis (ECHsis) of 4-phenoxyphenol, a compound representative of the 4-O-5 type linkage in lignins. The electrolyses were carried out under galvanostatic control in aqueous 1 M NaOH. Raney nickel, nickel boride, and transition metals supported on activated charcoal or alumina were used as catalytic powders. The extent and efficiency of the ECHsis of 4-phenoxyphenol was found to depend on the catalyst and on the temperature.Key words: electrocatalytic hydrogenation, electrocatalytic hydrogenolysis, 4-phenoxyphenol, Raney nickel, palladium on charcoal, palladium on alumina.

The electrocatalytic hydrogenolysis of pentachlorophenol (PCP) was carried out under galvanostatic control, in an aqueous 1 M NaOH solution in which PCP is fully soluble, and on particles of palladium or rhodium supported on alumina (Pd(5%)/Al2O3 or Rh(5%)/Al2O3) and entrapped in a reticulated vitreous carbon (RVC) electrode. On Pd/Al2O3 and at 75 °C, the conversion was complete (>99%) after 16 mol of electrons per mol of substrate (16 F mol-1) were consumed, and phenol was the sole product formed in 98% yield (61% current efficiency). On Rh/Al2O3 and 25 °C, 100% conversion was reached after 24 F mol-1, and cyclohexanol was obtained in 98% yield with some 2% of cyclohexanone (62% current efficiency). The ease of electrocatalytic hyrogenolysis was found to increase in the following order:  PCP < 2,6-dichlorophenol < 4-chlorophenol.

No abstract

No abstract