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

Sulfur-containing compounds must be removed from raw fuel oils before use and recently, there has been an effort to identify and optimize a more energy efficient method of oil processing. One promising route is electrochemical oxidative desulfurization (ODS), and in this work, we investigate an electrodeposited iron oxide film (FeO(OH)) as a working electrode to catalyze the oxidation of dibenzothiophene (DBT). The FeO(OH) film displays unexpected selectivity for the DBT sulfoxide (DBTO)-departing from the catalytic behavior of gold, which favors the dimerization of DBT. In addition, we observe a morphological change within our FeO(OH) film from γ-FeOOH to γ-Fe₂O₃. This change provides insight to the activity of each structure for ODS as the rate of oxidation increases after the incorporation of γ-Fe₂O₃. Our experimental observations are corroborated with DFT calculations, which suggest that the adsorption energy of DBT on Au is significantly greater than on the FeO(OH), favoring the formation of dimeric and oligomeric products. Calculations also demonstrate that DBT binds preferably in a monodentate configuration but that oxidation occurs via DBT bound via a bidentate configuration. Monodentate binding on γ-FeOOH is significantly stronger than binding on γ-Fe₂O, resulting in easier conversation to bidentate binding on γ-Fe₂O₃.