Comparison of Material Activity and Selectivity in the Electrocatalytic Oxidation of Dibenzothiophene

Due to adverse effects of sulfur-containing compounds present in fuel oils, there is an increasing demand for an efficient and cost-effective method of removing sulfur from oil products, such as oxidative desulfurization. In this work, a set of five materials (gold, glassy carbon, nickel, palladium and platinum) were evaluated as electrochemical catalysts for the oxidation of DBT. Electrolysis at 1.58 V was performed without water present (producing a dimer of DBT) and with the addition of 2 M water (producing DBTO). LC-MS and NMR were used to characterize the oxidation products. It was found that the Faradaic efficiencies ranged from 18.4 – 56.5% for consumption of DBT without water present and there was a correlation between higher rate constants, lower activation energies and more efficient DBT oxidation. After the addition of water, the formation of DBTO was found to have the highest selectivity when catalyzed by gold, with a Faradaic efficiency of 87.9%. The group ten metals demonstrated low Faradaic efficiencies due to the competitive water oxidation taking place. Though there were differences in the observed selectivity for DBT oxidation, all catalysts reduced the concentration of DBT in solution by similar amounts. Of the materials tested, gold served as the most selective for oxidation to DBTO, with the presence of water improving the overall reaction activity.