Electrocatalytic hydrogenation of aromatic compounds in ionic liquid solutions over WS2-on-glassy carbon and Raney nickel cathodes

In order to assess the potential application of electrocatalytic hydrogenation to petroleum fractions, as an alternative to high-pressure hydrotreating, we studied the conversion of a series of model compounds. Naphthalene, 1-methyl naphthalene, quinoline, carbazole, and dibenzothiophene were reacted in a flow cell over sulfur-resistant tungsten disulfide/glassy carbon electrodes. Raney nickel was used as a reference catalytic electrode material. The reactants were dissolved in a solution of ionic liquid and water, to provide high solubility of reactant, high conductivity, and protons for electrochemical hydrogenation. Both quinoline and carbazole were hydrogenated on WS2/glassy carbon cathodes in the presence of thiophene, but the initial current efficiencies were less than 10%. Conversion of naphthalene was detected, but the initial current efficiency was only 1.8%. Conversion of 1-methyl naphthalene and dibenzothiophene was not detected over this electrode material. Raney nickel gave higher conversion rates and current efficiencies for quinoline, carbazole, and naphthalene, but only traces of product from 1-methylnaphthalene were detected. These results indicate that current efficiency and sustained conversion rates for alkylaromatics and heteroaromatics must be improved considerably in order for electrocatalytic hydrogenation to compete with conventional hydrotreating.