Dehydration of glycerol over H6P2W18O62/γ-Al2O3 prepared by the supercritical method

Abstract

H₆P₂W₁₈O₆₂/γ-Al₂O₃ catalysts were prepared with different methods: (a) supercritical impregnation; (b) conventional wet impregnation. The obtained catalysts were characterized with XRD, SEM, N₂ adsorption, NH₃-TPD, Pyridine-IR, TG, ICP, and CHNS analyses. The results showed that supercritical CO₂ was helpful in enhancing the dispersity of H₆P₂W₁₈O₆₂ supported on γ-Al₂O₃ and increased the surface area, pore volume and size, the total acid amount, and the proportion of Brønsted acid, and the formation of coke and the leaching of H₆P₂W₁₈O₆₂ were retarded. The main reason is because supercritical carbon dioxide has high solubility and diffusivity, which favors H₆P₂W₁₈O₆₂ dispersion and strengthens the interaction between H₆P₂W₁₈O₆₂ and hydroxyl on γ-Al₂O₃. The performances of two catalysts in glycerol dehydration were evaluated. The conversion of glycerol, selectivity and yield of acrolein, and catalytic stability were significantly enhanced on the H₆P₂W₁₈O₆₂/γ-Al₂O₃ catalyst prepared by supercritical impregnation because greater total acidity is conducive for improving the conversion of glycerol, while a higher ratio of Brønsted acid sites to total acidity is conducive for enhancing the acrolein selectivity.