Development and optimization of a sustainable polyoxometalate-kaolinite-based catalyst for efficient desulfurization...

The oxidative desulfurization of dibenzothiophene in model and real fuel has been investigated by developing an environmentally sustainable catalyst H₄SiW₁₂O₄₀@f-kaolinite. The catalyst was synthesized by modifying kaolinite clay with (3-aminopropyl)triethoxysilane (f-kaolinite) followed by immobilizing silicotungstic acid hydrate (H₄SiW₁₂O₄₀) onto its surface. The successful synthesis of the catalyst was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, UV-visible spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The influence of variables i.e., catalyst dosage, temperature, and oxidant concentration on the conversion of dibenzothiophene was optimized by Box-Behnken design. The highest sulfur reduction (from 1000 to 78.3 ppm, with a conversion rate of 92.17%) was achieved at 70 °C, using a catalyst dosage of 70 mg and 8 mL of H₂O₂ in a model fuel. ANOVA analysis indicated that the quadratic model (R ² = 0.99) was well-fitted for dibenzothiophene conversion, with a p-value of 0.2302 suggesting no statistically significant lack of fit compared to pure error. Furthermore, the H₄SiW₁₂O₄₀@f-kaolinite demonstrated a reduction of dibenzothiophene concentration from 354 ppm to 224 ppm in a real fuel oil sample. The heterogeneous nanocatalyst showed remarkable stability, maintaining its elemental structure after five cycles without significant efficiency loss, promoting environmental sustainability.