Abstract:

High-performance titania-silica(TiO₂-SiO₂) nanocomposites were synthesized with a sol gel method. The composite catalyst was prepared by either in situ synthesis(HPMo-TiO₂-SiO₂-is) or the impregnation method(HPMo/TiO₂-SiO₂) using Keggin-structure phosphomolybdic acid and TiO₂-SiO₂. The structures of these catalysts were characterized by scanning electron micrographs(SEM), Fourier transform infrared spectrum(FT-IR), ultraviolet visible spectroscopy(UV-Vis), Brunauer-Emmett-Teller(BET) and X-ray powder diffraction pattern(XRD). The preservation of the Keggin structure in HPMo-TiO₂-SiO₂-is and HPMo/TiO₂-SiO₂ catalysts was confirmed. The results show that the synthesized catalysts are in nanometer size and the micropores and mesopores coexist. The catalytic oxidation desulfurization reaction was studied over synthesized catalysts with a model oil(n-octane solution of organic sulfur). Reaction conditions are listed as following:model oil/ethanol=10.0 mL/10.0 mL, catalyst 0.15 g, n(O)/n(S)=5, temperature 30~70 ℃ and time=3 h. It is clear that the catalytic properties of the HPMo-TiO₂-SiO₂-is and HPMo/TiO₂-SiO₂ are similar under optimized conditions. The conversion of dibenzothiophene is 96.0% and the content of sulphur is below 10 μg/g. Under the same conditions, the efficiencies of oxidative desulfurization decrease in the order of dibenzothiophene>benzothiophene>thiophene, and the result is influenced by the electron density on the sulfur atoms. The catalytic activity of the recycled HPMo-TiO₂-SiO₂-is catalyst is almost as the same as that of freshly prepared. The HPMo-TiO₂-SiO₂-is and HPMo/TiO₂-SiO₂ catalysts could be recycled and easily separated. These catalysts used herein are an ideal model for oxidation desulfurization of sulfur compounds.

Key words: phosphomolybdic acid, titania-silica nanocomposite, oxidative desulfurization, Sol Gel method, hydrogen peroxide