Nb-Doped g‑C₃N₄: A Highly Efficient and Stable Catalyst for Oxidative Desulfurization

This study reports the synthesis and application of niobium-doped graphitic carbon nitride as a high-performance catalyst for oxidative desulfurization (ODS) of fuels. The 10-NbCN material, prepared via pyrolysis, exhibits Nb species that are highly dispersed at the atomic level within the g-C₃N₄ framework, as confirmed by XRD, FTIR, and TEM. Under optimized conditions (60 °C, O/S = 20:1, 4 g L^-1 catalyst), 96% removal of dibenzothiophene (DBT) is achieved within 120 min, outperforming pure g-C₃N₄ and Nb₂O₅. Kinetic studies reveal pseudo-first-order behavior with an activation energy of 41.2 kJ mol^-1. Remarkably, quinoline enhances DBT conversion even at high concentrations, indicating an unusual tolerance to nitrogen-containing compounds typically known to inhibit ODS systems. Evaluation in real diesel confirms that 10-NbCN selectively removes sulfur compounds while preserving the hydrocarbon matrix. EPR and DFT results suggest that Nb sites efficiently activate H₂O₂, promoting the generation of reactive oxygen species. The catalyst demonstrates outstanding stability over six cycles with negligible Nb leaching, supported by the preservation of Nb-N coordination under oxidative conditions. These findings highlight Nb-g-C₃N₄ as a robust and N-tolerant catalyst for ultralow sulfur fuel production.