Redox diverse Co+2/Co+3 species embedded 3D nanoconfined silica walls as an efficient catalyst for fast oxidative desulfurization of fuel oil

Sulfur contamination in fuel oils poses significant environmental and health risks, necessitating the development of an efficient and sustainable desulfurization method. Traditional methods, being energy and cost-intensive, drive a growing interest in catalytic oxidative desulfurization (ODS) as a greener alternative. However, the effectiveness of ODS largely depends on the dispersion rate of active sites within the catalyst. Herein, we developed a highly dispersive, redox-active Co/KIT-6 catalyst via surge encapsulation of cobalt species within the nanoconfined channels of as-synthesized KIT-6 (TCK) using the solid impregnation calcination (SIC) method. This approach significantly enhanced the stability and dispersion rate of cobalt species by exploiting the confined spaces between the P123 template and the silanol-enriched silica walls of TCK, creating a highly active Co-Si-O structure. Characterization reveals that up to 7 wt% cobalt species were smoothly dispersed in TCK channels, while severe aggregation and structural deterioration were observed in the template-free counterpart (Co7TFK) sample at similar loadings. Our ODS findings reveal that Co7TCK demonstrates higher activity than Co7TCK catalyst, achieving 99.7 % conversion of dibenzothiophene (DBT) at room temperature in 15 min within 0.055 g catalyst dosage with high reaction rate (0.332 min⁻¹), turnover frequency (197.5 h⁻¹) and turnover number (33.2). Kinetic and thermodynamic data suggest that DBT oxidation over Co7TCK is endothermic, non-spontaneous and follows pseudo-first-order kinetics with an activation energy of 33.51 kJ/mol. Additionally, the Co7TCK catalyst exhibited excellent stability and recyclability over multiple cycles, underscoring its potential for industrial applications.