Abstract
The catalytic behavior of bifunctional V2O5/MFI catalysts with acid and oxidizing properties was investigated for the gas-phase oxidehydration of glycerol. One of the main reaction products was acrylic acid, produced by dehydration of glycerol to acrolein at an acidic site and subsequent oxidation at a redox site. Comparison of wet impregnation with vanadyl sulfate (VOSO4) and ammonium metavanadate (NH4VO3) showed that VOSO4 impregnation provided the best performance for the conversion of glycerol and selectivity towards acrylic acid. The chemical and structural properties of the catalysts were studied by X-ray diffraction, nitrogen adsorption–desorption isotherms, Raman spectroscopy, temperature programmed ammonia desorption, and X-ray absorption spectroscopy in the XANES region for the K-edge absorption of vanadium. XPS measurements of the fresh and spent catalysts enabled elucidation of the dynamic redox cycles of vanadium oxide during oxidation of acrolein. The presence of vanadium in the zeolite improved the catalyst lifetime, because of the multifunctional ability of the vanadium oxide species to convert acrolein to acrylic acid and act as co-catalyst for the oxidation of coked glycerol products. Qualitative and quantitative analyses of the coke deposited in the spent catalysts were performed using 13C NMR and thermogravimetry, respectively.
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