•Phase-pure monoclinic VO2 (M) was successfully synthesized by hydrothermal or solvent-thermal reduction method.•Intrinsic ODS activity increased with increasing cell volume on different VO2 (M) catalysts.•Phase transition temperature of VO2 (M) to VO2 (R) decreased with increasing cell volume for VO2 (M) catalysts.•VO2 (R) showed lower ODS reaction activation energy (Ea) than VO2 (M).Phase-pure monoclinic VO2 (M) was successfully synthesized by hydrothermal reduction method using oxalic acid as a reductant and solvent-thermal reduction method using methanol as a reductant. Oxidative desulfurization (ODS) activities were investigated and the results revealed that intrinsic ODS activity increased with increasing cell volume for different synthesized VO2 (M) catalysts. DSC measurement gives the evidence that phase transition temperature of monoclinic VO2 (M) to rutile VO2 (R) decreased with increasing cell volume for different VO2 (M) catalysts. Variable-temperature in-situ Raman spectrum also confirmed that phase transition from VO2 (M) to VO2 (R) occurred. Mechanism of ODS reaction on VO2 (M) catalyst was investigated precisely involving temperatures which phase transition occurred. Below the phase-transition temperature VO2 (M) showed higher ODS reaction activation energy, while above the phase-transition temperature VO2 (R) exhibited lower ODS activation energy. This result may be explained by the fact that VO bond length for VO2 (R) (1.93 Å) fits more for the five-member ring formed with the oxidant tert-butyl hydroperoxide (TBHP) during ODS reaction compared with V-O bond length for VO2 (M) (about 2.03 or 1.86 Å).Download high-res image (108KB)Download full-size image

•Linear relationship between oxidative desulfurization activity and the amount of silanol groups on pure mesoporous silcas.•Surface silanol groups act as the active sites of oxidative desulfurization.•Mechanism of surface silanol-mediated oxidative desulfurization of dibenzothiophene.Ordered mesoporous silicas with structures of MCM-41, MCM-48 and SBA-15 were synthesized. Oxidative desulfurization activities of dibenzothiophene and 4,6-dimethyl dibenzothiophene on the mesoporous silicas were investigated using tert-butyl hydroperoxide as an oxidant. Textures and surface properties of the synthesized mesoporous silicas were studied by X-ray diffraction, N2-sorption, FT-IR and NH3-temeprature programmed desorption. The results show that oxidative desulfurization catalytic activities increase with surface area and surface acidity of the mesoporous silicas. Oxidative desulfurization mechanism on MCM-41 was investigated by the addition of surface silanol inhibitor such as acetic acid, water and triethylolamine or silylation of surface silanol groups using trimethylchlorosilane. A hypothetical mechanism based on surface silanol-mediated oxidation desulfurization is proposed. Oxidative desulfurization activities for Mo catalysts supported on MCM-41 were also investigated to identify the difference in oxidative desulfurization mechanism between MoO3 catalysts and pure mesoporous silicas.

A Pd on Ni–B (Pd/Ni–B) bimetallic catalyst was prepared and tested in the hydrodechlorination (HDC) of 4-chlorophenol (4-CP). The catalysts were synthesized by replacement method and treated at different temperatures (298–673 K). The results showed that the one treated at 473 K could achieve complete dechlorination of 200 ppm 4-CP under the pH = 8 within 30 min and keep the high activity in the first four recycles. The introducing of Pd greatly promoted the catalytic HDC efficiency of Ni–B, and the high dispersion of Pd species ensured the high activity of Pd/Ni–B catalysts. The catalytic HDC reaction of 4-CP followed the pseudo-first-order dynamics and the kinetic data was obtained.