Effect of Al Content on the Gas-Phase Dehydration of Glycerol over Silica-Alumina-Supported Silicotungstic Acid Catalysts

The gas-phase dehydration of glycerol to acrolein was carried out over silicotungstic acid (H4SiW12O40 center dot xH(2)O, HSiW) catalysts supported on SiO2, eta-Al2O3, and silica-aluminas with different Al contents. The HSiW catalysts supported on silica-aluminas showed higher glycerol conversions and acrolein yields during the initial 2 h at 315 degrees C than did SiO2- and eta-Al2O3-supported HSiW catalysts. Among the tested catalysts, HSiW/Si0.9Al0.1Ox exhibited the highest space-time yield during the initial 2 h. The loaded HSiW species can change the acid types and suppress the formation of carbonaceous species on Al-rich silica-aluminas. The deactivated HSiW supported on silica-aluminas can be fully regenerated after calcination in air at 500 degrees C. As long as the molar ratio between water and glycerol was in the range of 2-11, the acrolein selectivity increased significantly with increasing water content in the feed, while the surface carbon content decreased owing to the suppression of heavy compounds.