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

Abstract

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 ppmw_S 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 °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.