The gas-phase dehydration of glycerol was conducted over silica-alumina catalysts with different Si/Al molar ratios. For comparison, SiO(2) and eta-Al(2)O(3) were also examined. A variety of techniques. X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH(3)-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 (22)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 degrees 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. (C) 2011 Elsevier B.V. All rights reserved.