Kaolin supported heteropoly acid catalysts for methacrolein oxidation: Insights into the carrier acidity effect on active components

The application of heteropoly acid catalyst in methacrolein (MAL) oxidation reaction is limited for its poor thermal stability and few active centers. Here, the supported catalyst of P-Mo-V heteropoly acid (CsNH4KPMoV) active components supported on kaolin were prepared, and were characterized by FT-IR, TG/DTA, XRD, N2-adsorption and desorption, NH3-TPD, TPO-MS and XPS. The results show that kaolin was weak acidity and the negative charge on the surface of kaolin promoted the reduction of V5+ species to V4+(VO2+) active species. There was a strong electron interaction between kaolin and HPVA, and chemical adsorption occurred by DFT calculations. Under optimal conditions, higher MAL conversion (81.8%) and Methacrylic acid (MAA) selectivity (88.2%) were obtained by 50CsNH4KPMoV/kaolin catalyst. The Keggin structure was maintained and the acid strength and acidity did not decrease after the catalyst was used continuously for 100 h. There was no carbon deposition in the reaction process.