Sustainable production of acrolein: Acidic binary metal oxide catalysts for gas-phase dehydration of glycerol

Acidic binary metal oxide catalysts, including SnO2–TiO2, SnO2–ZrO2, TiO2–Al2O3, SiO2–TiO2, ZrO2–SiO2, ZnO–TiO2 and TiO2–ZrO2, were prepared and employed to catalyze the dehydration reaction of glycerol (GL) at 315 °C. Correlation of the catalyst acidities with their catalytic performance demonstrated that the strongly acidic sites at −8.2 < H0 ≤ −3.0 were efficient for the selective production of acrolein (AC) from aqueous GL (10 mol% or 36.2 wt% GL). Micropores in the catalyst textures showed a negative effect on AC selectivity, probably by inducing secondary reactions of AC. The highest AC selectivity obtained over these binary oxide catalysts was in the range between 45 mol% and 52 mol%. A direct use of the anhydrous GL, instead of the aqueous GL, for the dehydration reaction produced much lower AC selectivity but larger amount of heavier products. Among all the catalysts investigated, 10 mol% TiO2–Al2O3 calcined at 600 °C and 50 mol% TiO2–ZrO2 calcined at 550 °C exhibited the best catalytic performance for AC production from aqueous GL. The appropriate reaction temperature range for the production of AC was also reported by using this 50 mol% TiO2–ZrO2 as a representative catalyst.