Gas-phase dehydration of glycerol over ZSM-5 catalysts

Abstract

The effect of the SiO2/Al2O3 ratios in ZSM-5 on the gas-phase dehydration of glycerol was examined over Na-ZSM-5 and H-ZSM-5. H-ZSM-5 with a SiO2/Al2O3 ratio of 150 showed the highest glycerol dehydration activity at 315 C among the various ZSM-5 catalysts. H-ZSM-5 with a SiO2/Al2O3 ratio of 30 showed less catalytic activity than H-ZSM-5 with a SiO2/Al2O3 ratio of 150. Several characterization techniques: X-ray diffraction (XRD), the temperature-programmed desorption of ammonia or water (NH3-TPD, H2O-TPD) with mass spectroscopy, temperature-programmed oxidation (TPO) with mass spectroscopy, infrared spectroscopy (FT-IR) after pyridine adsorption, and CHNS analysis were employed. The amount of acid sites and the acid strength decreased with increasing SiO2/Al2O3 ratio in the case of H-ZSM-5. The amount of adsorbed H2O and its binding strength also decreased with increasing SiO2/Al2O3 ratio in the case of H-ZSM-5. Na-ZSM-5, having moderate Lewis acid sites, showed the least catalytic activity, which may be due to its weak acid strength for this reaction and strong adsorption of H2O on the active sites. As long as the molar ratio between water and glycerol was in the range from 2 to 11, there was no noticeable difference in the glycerol conversion but the acrolein yield increased with increasing fraction of water in the feed. (C) 2009 Elsevier Inc. All rights reserved.