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

Abstract

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.