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, H-2-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 C-2-H in [EMIM][Ac] has a great positive influence on the structure and redox property of [EMIM]PAV([X]) hybrids.