Direct conversion of glycerol to n-propanol over a tandem catalytic dehydration–hydrogenation system

Abstract

The direct dehydration–hydrogenation of glycerol to n-propanol over a tandem catalytic system containing HZSM-5 (Si/Al ∼13) and supported Ni catalysts was studied under atmospheric H₂. Complete glycerol conversion to acrolein and propionaldehyde (>82% selectivity) was optimized for dehydration in the first bed (HZSM-5) at 300 °C. Ni/MgO, Ni/SiO₂, Ni/Mg–Al-LDH, Ni/TiO₂, and Ni/Al₂O₃ (20 wt% Ni loading) were used as hydrogenation catalysts in the second bed at 175 °C. Without the interference of glycerol from the first bed, the acrolein and propionaldehyde produced were hydrogenated to n-propanol (∼90% selectivity). Nevertheless, propanoic acid was observed as a minor product from water reduction by propionaldehyde. The cause of deactivation was investigated for the second beds (Ni/SiO₂), where the formation of high MW products was evidenced. While the catalysts can be simply regenerated by calcining in air at 450 °C, HZSM-5¦20Ni/Al₂O₃ with high Ni dispersion provides a higher stability and n-propanol yield (>73%) compared to other tandem catalysts.