Razi University

Refractory sulfur compounds such as dibenzothiophene (DBT) in petroleum fuels pose a major challenge in the production of clean fuels meeting stringent environmental standards. Conventional hydrodesulfurization (HDS) processes, due to their severe operating conditions and limited efficiency in removing these compounds, require alternative methods. In this study, a cobalt-loaded titanium dioxide (Co/TiO?) photocatalyst with different weight percentages (5, 10, 15, and 20 wt%) was synthesized via the impregnation method, and its performance was evaluated in the photocatalytic oxidative desulfurization (PODS) of a model fuel containing DBT. The samples were irradiated with visible light at a power of 52 W and wavelengths in the range of 550–700 nm. The synthesized samples were characterized using XRD, FESEM, EDX-MAP, BET, FTIR, UV-Vis DRS, and PL techniques. Optimization of operational parameters, including oxidant-to-sulfur molar ratio (O/S), catalyst dosage, and reaction time, was carried out using response surface methodology (RSM) with a Box-Behnken design (BBD). The results demonstrated that cobalt loading reduced the band gap energy and shifted the absorption edge toward the visible region, thereby overcoming the inherent limitation of TiO? in ultraviolet absorption. Furthermore, PL analysis confirmed a significant reduction in the electron-hole recombination rate. The 10 wt% Co/TiO? sample exhibited the best performance with a removal efficiency of 91.3%. The RSM model showed high accuracy with a coefficient of determination (R²) of 0.96. The optimal conditions were determined as O/S molar ratio of 6, catalyst dosage of 3.75 g/L, and reaction time of 62 minutes, achieving a predicted removal efficiency of 92.14% and an experimental efficiency of 93.08%. Overall, the 10% Co/TiO? photocatalyst, activated under visible light, with reduced charge recombination and mild operating conditions (ambient temperature, atmospheric pressure, no hydrogen requirement), represents an efficient and green approach for the production of low-sulfur fuels. Keywords: Photocatalytic Oxidative Desulfurization, Dibenzothiophene, Co/TiO? Photocatalyst, Response Surface Methodology, Clean Fuel