Solvent effect on hydrogenolysis of glycerol to 1,2-propanediol over Cu–ZnO catalyst

• The solvent has a significant effect on the glycerol hydrogenolysis over Cu–ZnO.
• The smaller size of Cu nanoparticles contributes to a higher glycerol conversion.
• The lower surface tension is beneficial to improving the glycerol conversion.
• The higher polarity of solvent leads to higher 1,2-propanediol selectivity.

The present work aimed to investigate the effect of solvent on the catalytic performance of glycerol hydrogenolysis to 1,2-propanediol over a Cu–ZnO catalyst prepared by a coprecipitation method. The as-prepared Cu–ZnO particles were spherical in shape with needle-like structure formed by nanoscale particles, and had a specific surface area of 23 m2/g. The solvents used in this work had an obvious influence on the hydrogenolysis of glycerol. Glycerol conversion increased gradually while the selectivity to 1,2-propanediol changed oppositely with water, ethanol and methanol as a solvent, respectively. The mechanism of solvent effect was analyzed in detail through characterizing the physicochemical properties of recovered Cu–ZnO catalyst by NH3-TPD, XRD, SEM and N2O, etc. The larger surface tension of water brought about the serious aggregation of Cu nanoparticles, leading to less active sites and lower glycerol conversion. The catalytic hydrogen transformation from ethanol or methanol to glycerol could also be responsible for the higher glycerol conversion. The higher polarity of water facilitated the removal of 1,2-propanediol from the catalyst surface, contributing to higher selectivity to 1,2-propanediol.