Oxidative desulfurization performance of a polyoxometalate-based protic ionic liquid catalyst

Abstract

The development of efficient and sustainable catalytic systems for ultra-deep desulfurization is important for producing cleaner fuels and reducing sulfur emissions. In this study, we describe a polyoxometalate-based protic ionic liquid (POM-PIL) hybrid, (DBUH)₃PW₁₂O₄₀, formed by combining a Brønsted acidic (DBUH)⁺ cation with a redox-active Keggin-type PW₁₂O₄₀³⁻ anion. The hybrid benefits from both components: the polyoxometalate cluster offers strong redox activity, while the PIL improves polarity and proton transfer, together enabling efficient oxidative desulfurization (ODS) under mild conditions. Using H₂O₂ as the oxidant and acetonitrile as the extractant, a DBT removal efficiency of 96.95% was achieved within 50 min at 40 °C with an O/S molar ratio of 6, a catalyst dosage of 80 mg, and 1.5 mL of acetonitrile, demonstrating efficient desulfurization performance under mild conditions compared with many previously reported POM-based ODS catalysts. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) analyses confirm that the Keggin framework remains intact and that hydrogen-bond interactions exist between (DBUH)⁺ and PW₁₂O₄₀³⁻. Radical-quenching experiments show that hydroxyl radicals (˙OH) play the main role in DBT oxidation, and density functional theory (DFT) calculations indicate that a charge-assisted N⁺–H⋯S interaction helps concentrate DBT molecules near the catalyst. The hybrid maintains 88.16% of its initial activity after seven cycles, demonstrating good structural stability and recyclability.