The uses of metal-free carbonaceous catalysts for efficient sulfur (S) removal from fuel through oxidative desulfurization, especially using stable oxygen (O₂), are limited and challenging due to their low O₂ activation efficiency. Instead, a considerable amount of research in this area has been dedicated to less green peroxides-assisted oxidation because of the easier activation of peroxides than O₂ by various metal/metal-free catalysts. In this study, a carbonaceous metal-free catalyst from petroleum coke, a waste from the oil refinery process, was synthesized. The surface of the petroleum coke was modified by doping with the heteroatom boron (B) through a solvent-free mechanochemical approach. B-doping induced defects were hypothesized to generate an electron redistribution over the adjacent carbon atoms in the petroleum coke and provide active sites for the O₂ activation to a superoxide radical during the aerobic oxidative desulfurization of the refractory sulfur compound dibenzothiophene (DBT). The B loading in petroleum coke was positively correlated with the DBT conversion as well as the defect concentration as measured by Raman spectroscopy. The active species were identified to be the sites of B-C, B-O, and BCO₂ atoms using X-ray photoelectron spectroscopy. Thermal treatment of B-doped petroleum coke at 900 ^oC led to increased B-C interaction and defects concentration producing 68% DBT conversion compared to only 28% conversion after treatment at 600 ^oC (reaction at 110 ^oC for 3 h). Increasing the reaction time to 5 h resulted in a further increase in the DBT conversion to 96% for the catalyst produced at 900 ^oC. Nearly 42% DBT conversion was observed at 120 ^oC and 3 h with no catalyst. This auto-oxidation has not been considered in many of the earlier metal-free catalyzed DBT oxidative desulfurization studies. The kinetic analysis suggested a pseudo-first-order reaction.

Ahmed Magdy Abdelaziz Ahmed

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