SiO2-Supported DMDAAC-Modified Heteropoly Acid as Highly Active and Stability Catalysts for Methacrolein Oxidation

In view of the drawbacks of small specific surface area, poor thermal stability, and easy decomposition, CsPAV was modified by the organic ammonium source dimethyl diallyl ammonium chloride (DMDAAC). A series of (DMDAAC)CsPAV/SiO2 catalysts with different (DMDAAC)CsPAV loadings were prepared by an impregnation method. When DMDAAC-modified CsPAV was supported on SiO2, it exhibited a high specific surface area and more active sites. The catalytic performance of (DMDAAC)CsPAV/SiO2 was investigated by methacrolein (MAL) oxidation to methacrylic acid (MAA). The performance of the catalyst was characterized by FT-IR, XRD, TG, NH3-TPD, NMR, and XPS. There was an interaction between SiO2 and (DMDAAC)CsPAV, and the NH4+ crystalline salt was formed in the process of calcination from DMDAAC. The interaction between the formed NH4+ and SiO2 carrier prevented the decomposition of CsPAV. (DMDAAC)CsPAV/SiO2 showed high stability, and the catalytic performance was stable in the long-term evaluation test. Under the optimum conditions, the conversion of MAL was 80.8%, and the selectivity to MAA was 89.1% for 50(DMDAAC)CsPAV/SiO2.