Acidic property and gas-phase glycerol-dehydration activity of WO3/Al2O3 catalysts

Abstract

The acidic property of WO3/Al2O3 catalysts loaded with WO3 (5–37 wt%) and their activity for gas-phase glycerol dehydration were investigated. Temperature-programmed desorption of NH3 revealed the formation of weak acid sites (the enthalpy of NH3 desorption; ΔHNH3 <110 kJ mol–1) on WO3/Al2O3. Infrared spectra of adsorbed pyridine indicated that a part of Lewis acid sites of WO3/Al2O3 was converted to Brønsted acid sites by water vapor treatment. The ΔH‡–ΔS‡ relationship for glycerol dehydration over WO3/Al2O3 and H-ZSM-5 indicated a weaker interaction of WO3/Al2O3 catalyst with the reaction intermediate than that of H-ZSM-5. The coke species deposited over WO3/Al2O3 and H-ZSM-5 were confirmed to consist of C3–C4 compounds, acrolein, benzene, toluene, xylene, glycerol, indenes, naphthalenes, and anthracenes (or phenanthrenes); fewer polyaromatic compounds were formed over WO3/Al2O3. For WO3/Al2O3, the weak acid strength of the Brønsted acid sites resulted in high durability for glycerol dehydration.