Glycerol hydro-deoxygenation aided by in situ H2 generation via methanol aqueous phase reforming over a Cu–ZnO–Al2O3 catalyst

Abstract

A tandem catalytic cycle of methanol aqueous phase reforming–glycerol hydro-deoxygenation targeted to 1,2-propanediol formation under inert conditions is investigated. The H₂ needed for glycerol hydro-deoxygenation is provided in situ via methanol reforming. The effects of reaction time, temperature, methanol concentration and system pressure were investigated over a Cu : Zn : Al bulk catalyst. The catalytic results showed that 1,2-propanediol selectivity and yield depend on reaction temperature and reaction time combination. Higher methanol concentrations favor glycerol hydro-deoxygenation towards the desired pathway, resulting in a significant increase in 1,2-propanediol selectivity. Under optimum reaction conditions (t = 1 h, T = 250 °C, 36 v/v% C_MeOH + 9 v/v% C_GLY, 1.0 < P_N2 < 3.5 MPa), glycerol was almost fully converted (95.9%), with 79.4% selectivity (76.2% maximum yield) to 1,2-propanediol. Upon catalyst reuse, the Cu : Zn : Al catalyst showed satisfactory stability. An initial loss of activity (35.8%) was observed, which was ascribed to Cu agglomeration; however, catalyst performance was improved and stabilized after the third run, possibly due to Cu re-dispersion. It is proposed that metallic Cu⁰ efficiently catalyzes glycerol hydro-deoxygenation, while methanol reforming is mainly catalyzed by metallic Cu⁰ and facilitated by the interaction of Cu⁰ with ZnO–Al₂O₃ structures.