Hydrophobic molybdenum catalysts supported on halloysite nanotubes for highly efficient oxidative desulfurization of fuels in mild conditions

In this work new Mo-containing catalysts based on hydrophobic halloysite clays were applied for oxidative desulfurization in mild conditions. Giving hydrophobic properties made it possible to prevent the aggregation of catalyst particles in excess of the oxidizing agent – hydrogen peroxide, which in turn allowed the process to be carried out under mild conditions. The longer the alkyl substituent and the more hydrophobic the support, the less aggregation of catalyst particles and the lower the oxidation temperature. The obtained materials and catalysts were characterized by low temperature N ₂ adsorption-desorption, high-resolution TEM, XRF, TGA, FT-IR and wetting edge angles techniques. Modifying halloysite clays with alkylsilane, the wetting edge angle increased from 40.5° to 137.6°, while after immobilization with heptamolybdate, it decreased to 59.1, but was higher than the original halloysite clay. The key factors influencing the dibenzothiophene oxidation were investigated. Under selected optimal conditions (C ₈-Hal-Mo 1.0 mass%, 30 min, H ₂O ₂:S 4:1), dibenzothiophene was completely oxidized already at 40 °C. The catalyst could be regenerate and reuse for at least 5 cycles.