Gas-phase dehydration of glycerol over silica–alumina catalysts

Abstract

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 29Si and 27Al 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 Brønsted acid sites, whereas the 1-hydroxyacetone yield was proportional to the concentration of the Lewis acid sites. Among the tested catalysts, Si0.8Al0.2Ox showed the highest acrolein selectivity during the initial 2h 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.