Fe–Cu–chloride ionic liquid immobilized SBA-15 for solvent-free oxidation of styrene to benzaldehyde with H2O2

Abstract

Copper, iron–chloride ionic liquids (ILs) were immobilized on SBA-15 via N-methylimidazole grafting with C–Cl in chloropropylsilane pre-anchored on SBA-15, followed by FeCl₃ and CuCl₂ coordination to imidazolium chloride to generate a double metal IL-supported mesoporous composite (SIL-CuFe). The prepared composite exhibited an effective catalytic performance for the solvent-free oxidation of styrene to benzaldehdye (BzH) with H₂O₂ oxidant, offering 51% conversion, a turnover number (TON) of 330.5 mol mol_Fe+Cu⁻¹, and a selectivity of 71% at a reaction temperature of 70 °C. The composite catalyst can be easily recovered and effectively reused without a significant loss in activity and selectivity. The quenching experiments by adding tert-butanol (TBA), 1,4-benzoquinone (p-BQ) and L-histidine (L-HIS) in the reaction system were conducted to identify the type of reactive O species, specifically ˙OH, ˙O₂⁻, and ¹O₂, produced by catalyst activation with H₂O₂ and played a main role in the oxidation. The reaction mechanism of the oxidation process is also proposed.