Selective Oxidation of Methacrolein to Methacrylic Acid over Sb-Doped (NH₄)H₃PMo₁₁VO₄₀

Selective oxidation of methacrolein (MAL) to methacrylic acid (MAA) is a pivotal step in the industrial production of methyl methacrylate (MMA). In this study, a series of Keggin-type ammonium phosphomolybdovanadate heteropoly acid (NH4HPAV) catalysts with modification of Sb component were systematically investigated for their catalytic performance in MAL partial oxidation to MAA. Comprehensive physicochemical characterizations including XRD, FT-IR, Raman spectroscopy, NH3-TPD, chemical titration, H2-TPR, and XPS were employed to elucidate the structural and functional impact of Sb incorporation. The results indicated that the introduced Sb partially substituted protons in the secondary structure, leading to a decrease of surface Bro̷nsted acid sites and significant modulation of the redox behavior of molybdenum species. In addition, the incorporation of Sb component would also improve the MAL adsorption and MAA desorption abilities on the catalyst surface. A strong linear relationship was observed between the MAL conversion and reduction capacity of the molybdenum species, highlighting the critical role of redox properties enhanced by Sb. The optimized Sb-modified catalyst exhibited a 23.6% increase in MAL conversion, compared to the unmodified catalyst while maintaining comparable MAA selectivity.