Two-Step Conversion of Biomass-Derived Glucose with High Concentration over Cu-Cr Catalysts

The conversion of highly concentrated glucose was conducted over a Cu-Cr catalyst with a base in two steps for the first time. Reaction parameters such as reaction time, temperature, and H-2 pressure were optimized in each step. On the basis of these results, the corresponding reaction route was proposed. At the low-temperature step, and without a base, glucose was hydrogenated into sorbitol or isomerized and hydrogenated into mannitol. While in the presence of a base, the direct decomposition of glucose was observed because of base-catalyzed retro-aldol condensation. At the high-temperature step, it was found that the addition of a base greatly restrained the formation of oligosaccharides. Compared with CaCO3, Ba(OH)(2), KOH, and NaOH, Ca(OH)(2) exhibited the best promotion, indicating that the conversion of glucose was relative to not only the concentration of OH- but also the metal ionic radius and electric charge. The addition of a base had no obvious effect on the stability of Cu-Cr catalyst. In the recycling, the catalyst exhibited reasonable recyclability because of the partial deactivation originating from the migration of Cr onto Cu sites and the coverage of carbon species, as shown by X-ray photoelectron spectroscopy measurements.