Recent Advances in New Catalysts for Fuel Oil Desulfurization

To meet the increasingly stringent fuel emission regulations, deep desulfurization of fuel oil is becoming a hot issue in the field of catalysis. However, the requirement of ultra-low sulfur diesel fuel production can hardly be fulfilled economically by conventional hydrodesulfurization. This is because some aromatic sulfur-containing compounds, especially the thiophene compounds, cannot be removed effectively by the conventional method. In view of this, many new alternative desulfurization methods have been developed in recent years. Among these new methods, the oxidative desulfurization is regarded as the most promising one, since it can highly effectively remove the thiophene compounds such as benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene, which is difficult to be reduced by hydrodesulfurization. Furthermore, the oxidative desulfurization can be carried out under mild conditions, making it more applicable industrially. In the oxidative desulfurization of fuel oil, the thiophene compounds are oxidized to their corresponding sulfoxides or sulfones by the suitable oxidants (H2O2, organic peroxide acid, O-2, and air), and the sulfoxides or sulfones will subsequently be removed by adsorption or extraction. The oxidation of thiophene compounds is a key step in the whole process and the organic oxidation reaction is identified to occur in the presence of appropriate catalysts. Therefore, the catalysts play an important role in the oxidative desulfurization. In this review, recent advances in new catalysts for oxidative desulfurization of fuel oil will be addressed, with an emphasis on the innovative and functional materials used to catalyze the process.