Production of propylene glycol (1,2-propanediol) by the hydrogenolysis of glycerol in a fixed-bed downflow tubular reactor over a highly effective Cu–Zn bifunctional catalyst: effect of an acidic/basic support†
In this study, different acidic (V2O5, ZrO2, and TiO2) and basic (CaO and MgO) oxide-supported copper–zinc bimetallic catalysts were prepared by a deposition–precipitation method, and they were evaluated for the vapor-phase hydrogenolysis of glycerol to propylene glycol at 0.1 MPa and at 220 °C. The catalysts were thoroughly characterized by different techniques such as BET, XRD, H2-TPR, NH3 and CO2 TPD, N2O adsorptive decomposition, TEM, XPS, FE-SEM and TGA. Among all the supported catalysts, the Cu–Zn/MgO catalyst was found to be the most selective to propylene glycol. High copper-metal dispersion (∼5%), surface area (∼23 m2 g−1), the highest basicity (0.25 mmol CO2 g cat−1) and the availability of partially reduced copper species (Cu2O, CuO and Cu0) were the primary reasons for the higher propylene glycol selectivity. At optimum reaction conditions, i.e., at 220 °C, 0.72 MPa and a weight hourly space velocity (WHSV) of 0.073 h−1, ∼98.5% conversion of glycerol with ∼89% selectivity to propylene glycol was obtained over the Cu–Zn/MgO catalyst. This catalyst was also found to be stable for a long period of time (84 h) without much deactivation and without decrease in the selectivity to propylene glycol.