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

Abstract

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_x(OH)_y) as a working electrode to catalyze the oxidation of dibenzothiophene (DBT). The FeO_x(OH)_y 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_x(OH)_y 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_x(OH)_y, 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.