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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