Sustainable production of acrolein: Gas-phase dehydration of glycerol over Nb2O5 catalyst

Gas-phase dehydration of glycerol to produce acrolein was investigated at 315 °C over Nb2O5 catalysts calcined in the temperature range of 350–700 °C. The catalysts were characterized by nitrogen physisorption, TG-DTA, XRD, and n-butylamine titration using Hammett indicators to gain insight into the effect of calcination temperature on catalyst texture, crystal structure, and acidity. Calcination at 350 and 400 °C produced amorphous Nb2O5 catalysts that exhibit significantly higher fractions of strong acid sites at −8.2⩽H0⩽−3.0−8.2⩽H0⩽−3.0 (H0H0 being the Hammett acidity function) than the crystallized Nb2O5 samples obtained by calcination at or above 500 °C. Glycerol conversion and acrolein selectivity of the Nb2O5 catalysts were dependent of the fraction of strong acid sites (−8.2⩽H0⩽−3.0−8.2⩽H0⩽−3.0). The amorphous catalyst prepared by the calcination at 400 °C, having the highest fraction of acid sites at −8.2⩽H0⩽−3.0−8.2⩽H0⩽−3.0, showed the highest mass specific activity and acrolein selectivity (51 mol%). The other samples, having a higher fraction of either stronger (H0⩽−8.2H0⩽−8.2) or weaker acid sites (−3.0⩽H0⩽6.8−3.0⩽H0⩽6.8), were less effective for glycerol dehydration and formation of the desired acrolein.