Gas-phase dehydration of glycerol over silica-alumina catalysts

摘要

The gas-phase dehydration of glycerol was conducted over silica-alumina catalysts with different Si/Al molar ratios. For comparison, SiO2 and η-Al2O3 were also examined. A variety of techniques, X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed oxidation (TPO) with mass spectroscopy (MS), infrared spectroscopy (FT-IR) after the adsorption of pyridine or glycerol, solid-state ~(29)Si and ~(27)Al magic-angle spinning nuclear magnetic resonance (MAS/NMR) spectroscopy, Raman spectroscopy, and CHNS analysis, were employed to characterize the catalysts. The initial glycerol conversion at 315 °C was strongly dependent on the total amount of acid sites over the silica-aluminas. The acrolein yield was proportional to the concentration of the Bronsted acid sites, whereas the 1 -hydroxyacetone yield was proportional to the concentration of the Lewis acid sites. Among the tested catalysts, Si_(0.8)Al_(0.2)O_x showed the highest acrolein selectivity during the initial 2 h of the reaction. As long as the molar ratio between water and glycerol was in the range 2-11, the acrolein selectivity increased significantly with the water content of the feed.