Preparation of MoO2/g-C3N4 composites with a high surface area and its application in deep desulfurization from model oil

Highlights: • X-MoO₂/g-C₃N₄ were synthesized by calcination of a mixture of (NH₄)₆Mo₇O₂₄·4H₂O and g-C₃N₄. • X-MoO₂/g-C₃N₄ exhibits excellent activity in the oxidative desulfurization system. • Surface area of MoO₂/g-C₃N₄ is improved through MoO₂ dispersed on g-C₃N₄. • The 3%-MoO₂/g-C₃N₄ exhibits high desulfurization activity and stability for sulfide. • The desulfurization rate can attach to 96% and still reached 93.2% after 6 recycles. A series of catalysts of composition X-MoO₂/g-C₃N₄ (X = 0, 0.5, 1, 3, 5 wt.%) were successfully synthesized by calcination of a mixture of (NH₄)₆Mo₇O₂₄·4H₂O and g-C₃N₄. Oxidative desulfurization experiments were conducted using X-MoO₂/g-C₃N₄ as a catalyst, H₂O₂ as an oxidant, and ionic liquids (ILs) as extraction agents. Catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and Brunauer-Emmett-Teller analysis (BET). Characterization results suggested that MoO₂ was present in the catalyst and its crystallinity improved with increased Mo-loading. The catalysts had a larger specific surface area due to the presence of MoO₂ dispersed on g-C₃N₄. Experimental results showed that 3%-MoO₂/g-C₃N₄ had the highest catalytic activity among all the catalysts tested. A desulfurization rate of 96.0% was achieved under optimal conditions. Through gas chromatography-mass spectrometry (GC–MS) analysis, it was shown that dibenzothoiphene sulfone was the sole product of the oxidation desulfurization reaction. An apparent activation energy of 61.1 kJ/mol was estimated based on Arrhenius equation. The activity of 3%-MoO₂/g-C₃N₄ slightly decreased after six runs. A possible mechanism for the reaction has been proposed.