Ultrasmall MoC-MoO₂ Heterojunction Coupled with Nitrogen-Doped Reduced Graphene for Boosting the Deep Oxidative Desulfurization of Fuel Oils

In this study, a MoC-MoO₂@NCrGO-900 composite catalyst comprising two-dimensional nitrogen-doped reduced graphene oxide (NCrGO) and ultrasmall molybdenum carbide-molybdenum dioxide (MoC-MoO₂) heterojunctions was synthesized. The optimized catalyst exhibited an outstanding oxidative desulfurization (ODS) performance. Specifically, a model oil containing 4000 ppm sulfur was completely desulfurized within 30 min, with a desulfurization efficiency of 98.1% being recorded after six consecutive cycles. Moreover, the catalyst demonstrated a broad applicability over a wide range of sulfur concentrations (1000-5000 ppm). The excellent catalytic activity of MoC-MoO₂@NCrGO-900 was attributed to synergy within the MoC-MoO₂ heterojunction structure, the strong electron-donating properties of the NCrGO support, and the uniformly dispersed Mo active sites. Mechanistic studies using radical scavenging experiments and electron paramagnetic resonance spectroscopy revealed that hydroxyl radicals (^·OH) play a dominant role in the oxidation process, with electron transfer between the support and the active centers further enhancing the catalytic efficiency. Overall, this study provides a general and scalable in situ encapsulation strategy for constructing carbon-supported heterojunctions that offer promising prospects for use in practical ODS applications.