Mesoporous SnO₂-MoO₃ catalyst for diesel oxidative desulfurization: Impact of the SnO₂/MoO₃ ratio on catalytic...

Vehicular SO_x emissions have a huge detrimental impact on public health, catalytic converters, and the environment. Developing strategies to remove sulfur from diesel and thus safeguard the above is imperative. A series of SnO₂-MoO₃ mixed oxides and mono oxides MoO₃ and SnO₂ were prepared by soft template method, calcined at 450 °C and successfully tested in model diesel oxidative desulfurisation (ODS). The impact of the SnO₂/MoO₃ mole ratio (hereinafter denoted as Sn/Mo) on catalytic efficiency was investigated, among other catalytic parameters. The obtained samples were analyzed using X-ray diffraction (XRD), Raman spectrocscopy, scanning electron microscopy (SEM), N₂-physisorption and titration method for acidic properties. The study demonstrates that mixing SnO₂ and MoO₃ improves acidic sites, crystallinity, and morphological properties of pure SnO₂. The addition of MoO₃ increased oxygen vacancies and the surface area of SnO₂. High acidic site densities of 49.3, 47.4, and 46.7 mEqg^-1 were observed for the catalysts with 2:1, 1:1, and 1:2 Sn/Mo mole ratio, respectively. The catalytic efficiency increased with an increase in Sn content with the highest catalytic efficiency of 99.8% for the dibenzothiophene (DBT) oxidation achieved in 30 min for Sn/Mo (2:1) catalyst compared to 92 and 70% for Sn/Mo 1:1 and 1:2 catalysts, respectively. The rate constant for the reaction was 0.057 min^-1, which is eight times that of MoO₃; 0.007 min^-1 and three times that of SnO₂; 0.017 min^-1. The ODS mechanism utilizing the SnO₂-MoO₃ catalyst was proposed. The prepared SnO₂-MoO₃ catalyst demonstrated a high potential for industrial desulfurisation applications.