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

Abstract

There is an increasing demand for efficient methods to remove 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 dibenzothiophene (DBT). Bulk electrolysis performed without water present produced DBT dimer, while the addition of 2 M water produced dibenzothiophene sulfoxide (DBTO), both more polar than DBT. LC-MS and NMR were used to characterize the oxidation products. Faradaic efficiencies ranged from 18.4%–56.5% for DBT consumption without water present, and there was a correlation between higher rate constants, lower activation energies, and more efficient DBT oxidation. With water present, selectivity for DBTO formation was highest using gold with a Faradaic efficiency of 87.9%. Group ten metals demonstrated low Faradaic efficiencies due to competitive water oxidation. Though there were differences in the observed selectivity for DBT oxidation, all catalysts reduced the concentration of DBT in solution by similar amounts. Our findings indicate that the overall percent conversion does not give a complete picture of catalytic activity. Of the materials tested, gold was the most selective for oxidation to DBTO, with the presence of water improving the overall reaction activity.

Controlling Product Selectivity in Oxidative Desulfurization Using an Electrodeposited Iron Film

“…Thierry et al studied the properties of several Fe-based films and observed the major Raman peak for ϒ-Fe2O3 to be between 650-740 cm -1 , stating also that a broad Raman band at 1425 cm -1 is characteristic of that film. 13 Finally, the transition from an oxyhydroxide to an oxide is also consistent with previously established behavior of a Fe film undergoing OER, where a progressively higher fraction of oxide phases (such as Fe2O3) relative to hydrated phases (such as FeOOH) was observed as oxidation occurred. 34 To investigate the electrocatalytic activity of the Fe film pre-and post-activation, Koutecky-Levich analysis was performed on a newly deposited Fe film, as well as on an Fe film which had undergone three hours of electrolysis.…”

“…For the Fe film electrodeposited on the Au RDE, cyclic voltammetry was first performed to establish whether it was capable of DBT oxidation. An oxidation peak was observed at 1.55 V vs SCE, which is in good agreement with the potential for DBT oxidation on other known electrocatalysts, 13 including Au (Figure S1). We next carried out bulk electrolysis of DBT using the Fe film.…”

“…9 Over the first hour of oxidation, the Au electrode exhibited a high rate of DBTO conversion, which is consistent with our previous report (Figure 1). 13 Beyond one hour of electrolysis, however, DBTO production increased at a slower rate throughout the remainder of the 48 hours.…”

“…Our previous work established several parameters for an effective ODS electrocatalyst, which include a low energy barrier and high rate for DBT oxidation, as well as a high activation energy for water oxidation. 13 Water oxidation is a competing reaction in the system, as H 2 O is present in the reaction as an oxygen source for the conversion of DBT to its sulfoxide (DBTO).…”

Controlling product selectivity in oxidative desulfurization using an electrodeposited iron oxide film

“…6 Typically, the oxidation is facilitated by a combination of a catalyst and a chemical oxidant. Herein, we focus on electrochemical ODS, 7 which has been shown to successfully remove up to 99.9% of sulfurcontaining compounds such as DBT, 8 and demonstrates a possibility of larger-scale applications in fuel processing. DBT is often used as a model sulfur-containing compound for ODS because it is poorly targeted by conventional desulfurization techniques.…”