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

A tandem catalytic cycle of methanol aqueous phase reforming-glycerol hydro-deoxygenation targeted to 1,2-propanediol formation under inert conditions is investigated. The H-2 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 degrees 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 Cu-0 efficiently catalyzes glycerol hydro- deoxygenation, while methanol reforming is mainly catalyzed by metallic Cu-0 and facilitated by the interaction of Cu-0 with ZnO-Al2O3 structures.