Sustainable production of acrolein: Gas-phase dehydration of glycerol over Nb 2O 5 catalyst

Abstract

Gas-phase dehydration of glycerol to produce acrolein was investigated at 315 °C over Nb 2O 5 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 Nb 2O 5 catalysts that exhibit significantly higher fractions of strong acid sites at − 8.2 ⩽ H 0 ⩽ − 3.0 ( H 0 being the Hammett acidity function) than the crystallized Nb 2O 5 samples obtained by calcination at or above 500 °C. Glycerol conversion and acrolein selectivity of the Nb 2O 5 catalysts were dependent of the fraction of strong acid sites ( − 8.2 ⩽ H 0 ⩽ − 3.0 ). The amorphous catalyst prepared by the calcination at 400 °C, having the highest fraction of acid sites at − 8.2 ⩽ H 0 ⩽ − 3.0 , showed the highest mass specific activity and acrolein selectivity (51 mol%). The other samples, having a higher fraction of either stronger ( H 0 ⩽ − 8.2 ) or weaker acid sites ( − 3.0 ⩽ H 0 ⩽ 6.8 ), were less effective for glycerol dehydration and formation of the desired acrolein.