Necessity of calcination in the preparation of phosphotungstic acid@TiO2 composites. A case study on the facile sol-gel synthesis of nanospheres and their superior performance in catalytic oxi-desulfurization

摘要

Calcination is considered to be a key step in the process of preparation of titanium dioxide based catalysts; however, it consumes a lot of energy. We describe unequivocally here for the first time that high-energy consuming calcination is a surplus process in the preparation of phosphotungstic acid@titanium dioxide (PW12@ TiO2) catalysts with various loadings of phosphotungstic acid (10-40 wt%) for oxidative catalytic reactions. To prove this, a case study on the preparation of PW12@ TiO2 nanospheres via the sol-gel procedure is discussed here. The structure and morphology of the nanospheres were characterized by FT-IR, FT-Raman, BET XRD, ICP and SEM analyses. Oxidative desulfurization of a model oil composed of 350 ppmw(S) dibenzothiophene (DBT) in n-octane was investigated using these nanospheres. The results showed that both calcinated and un-calcinated-PW12@ TiO2 nanospheres exhibited almost parallel yet excellent oxidative desulfurization performances in the model oil. The 350 ppmwS of sulfur content in 20 mL of n-octane was dropped down to 2.4 and 2.6 ppmw(S) within 2 hours at 60 degrees C using 70 mg of calcinated and un-calcinated-PW12@ TiO2 nanospheres with 30 wt% PW12 loading, respectively. The high desulfurization efficiency of the catalyst remained unchanged even after the regeneration of the catalyst ten times. This excellent desulfurization performance makes the as-prepared composite without calcination treatment a promising catalyst in practical oxidative desulfurization processes.