Defective silicotungstic acid-loaded magnetic floral N-doped carbon microspheres for ultra-fast oxidative desulfurization of high sulfur liquid fuels

Highly active Keggin-type silicotungstic acid (SiW12) with oxygen vacancy (Ov) defects was encapsulated into the magnetic floral N-doped carbon microspheres (gamma-Fe2O3@NC-300) through the facile one-step air pyrolysis of the precursor comprising core-shell Fe3O4@polydopamine (Fe3O4@PDA) and SiW12 to prepare gamma-Fe2O3@NC@SiW12-300. The fabricated catalysts were systematically characterized and subsequently employed for the oxidation desulfurization (ODS) of the model fuel. The magnetic floral gamma-Fe2O3@NC@SiW12-300 catalyst exhibited nearly perfect catalytic activity, which under mild conditions could remove 100% amount of 4000 ppm DBT in model fuel within 20 min (0.03 g catalysts and n(H2O2)/n(S) of 2). The catalyst activity is mainly attributed to the high activity SiW12 with the Ov defect and its outstanding dispersibility in gamma-Fe2O3@NC, along with the high number of exposed active sites. A selected catalyst, gamma-Fe2O3@NC@SiW12-300, showed a noticeable turnover frequency (TOF) (110.07 h-1) and lower activation energy (38.79 kJ mol-1) in oxidative desulfurization (ODS) with good recyclability. HO radical was found to be the active species involved in ODS as confirmed by the EPR and scavenger experiments. Additionally, the fabricated catalyst can be conveniently separated and recycled within an externally applied magnetic field. The magnetic floral gamma-Fe2O3@NC@SiW12-300 with oxygen vacancies shows a high desulfurization rate, high TOF, and low Ea in ODS, and its HO radical oxidation desulfurization mechanism is proposed.