Molybdovanadophosphoric Heteropolyacid-Catalyzed Aerobic Oxidation of Methacrolein: The Crucial Role of Ionic Liquid as a Modifier

[EMIM]PAV_[X] (X = Ac, NO₃, BF₄) was synthesized by a facile method using imidazolium-based ionic liquids ([EMIM][X], X = Ac, NO₃, BF₄) as the modifying reagent. Characterization by FT-IR, XRD, SEM, TG/DTA, H₂-TPR and XPS demonstrated that [EMIM]PAV_[Ac] has uniform rod-like morphology, better redox property and higher amount of NH₄⁺ composite, which therefore provides a high selectivity of 98% in the oxidative transformation of methacrolein (MAL) to methacrylic acid (MAA) as a catalyst. Theoretical calculations suggested the relatively strong H-bond basicity of C₂−H in [EMIM][Ac] has a great positive influence on the structure and redox property of [EMIM]PAV_[X] hybrids. Graphic Abstract: [Figure not available: see fulltext.]