Dibenzothiophene oxidation in a model diesel fuel using CuO/GC catalysts and H2O2 in the presence of acetic acid under acidic condition

•Cu2+/(Cu2+ + Cu+) ratio is well correlated with dibenzothiophene (DBT) conversion.•DBT oxidation and adsorption are coupled in the oxidative desulfurization process.•Low pH value favored significantly the DBT oxidation.•Acetic acid promoted DBT oxidation in acidic condition.

A series of CuO supported on graphite carbon catalysts (noted as Cu/GC) was prepared with impregnation method and CuO loading varied from 1 wt% to 5, 10 and 15 wt%. Textural properties, crystalline structure, phase composition, copper oxidation states, and morphology of the Cu/GC catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy. Surface acidity was measured by using temperature-programmed desorption of ammonia (TPD-NH3). Surface Cu2+ ions, H2O2 oxidant, acetic acid promoter, and acidic media were all crucial for oxidative desulfurization (ODS) of a model diesel fuel. Both XRD and XPS results confirmed that Cu2+ and Cu+ coexisted on the carbon surface and the Cu2+/(Cu2+ + Cu+) ratio increased with increasing of copper oxide loading. The copper speciation result is in good correlation with the catalytic activity, indicating that surface Cu2+ ions are the active catalytic sites. Acetic acid reacted with H2O2 to form surface peroxyacetic species that coordinated with Cu2+ on the Cu/GC catalysts in acidic media and promoted the ODS activity. Low pH condition favored significantly dibenzothiophene (DBT) oxidation. Under the optimal operation condition (pH = 0, reaction temperature 70 °C, and catalyst loading 0.3 g with H2O2-glacial acetic acid), DBT concentration in oil was reduced from an initial value of 300 ppm to 78 ppm, 9 ppm, 3 ppm and 0 ppm after ODS treatment using Cu/GC catalysts loading with 1, 5, 10, and 15 wt% of CuO, respectively.

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