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

Article abstract of DOI:10.1016/j.jcat.2007.06.016

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 (H₀ 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). The amorphous catalyst prepared by the calcination at 400 °C, having the highest fraction of acid sites at - 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 ≤ - 8.2) or weaker acid sites (- 3.0 ≤ H₀ ≤ 6.8), were less effective for glycerol dehydration and formation of the desired acrolein.