Electrosynthesis of diphenyl carbonate by homogeneous Pd electrocatalysts using Au nanoparticles on graphene as efficient anodes

Electrochemical carbonylation of phenol (PhOH) with CO (1 atm) to form diphenyl carbonate (DPC) was studied by using a Pd-(in situ NHC) electrocatalyst and graphene-supported Au nanoparticle (Au NPs/GR) anodes. An in situ NHC (N-heterocyclic carbene) was generated from 1,3-di(tert-butyl) imidazoline chloride (SIt-BuHCl) during electrolysis. The Au NPs/GR anodes prepared by impregnation and liquid-phase reduction methods were characterized by using transmission electron microscopy, X- ray diffraction, and inductively coupled plasma spectroscopy. Au NPs on carbon supports with a wide range of particle sizes were prepared by choosing the preparation conditions such as the type of reducing agent, reduction temperature, and the use of a stabilizer. The particle size of Au on the anode influenced the electrosynthesis of DPC by the Pd electrocatalyst. The formation rate and the current efficiency of DPC were high when smaller Au NPs were used as anodes. Cyclic voltammetry studies of the electrochemical system indicated that the oxidation rate of Pd-0 was accelerated at smaller Au NPs. As the electrolysis current increases, the contribution of anodic side-reactions becomes major at large Au particle anodes; as a result, the current efficiency of DPC formation decreases. On the other hand, smaller Au NP anodes efficiently enhanced the DPC formation by the Pd electrocatalyst under severe electrolysis conditions, and relatively high formation rate and current efficiency of DPC were achieved.