Highly selective oxidation of monosaccharides to sugar acids by nickel-embedded carbon nanotubes under mild conditions

Abstract

The preparation of inexpensive, high-performance non-noble metal catalysts for selective oxidation of biomass-derived monosaccharides to high value-added chemicals is challenging but in high demand. Herein, we successfully synthesized a nickel-embedded carbon nanotube (Ni-NCNT) catalyst to selectively convert the monosaccharides into sugar acids under mild condition. The Ni-NCNT catalyst was highly reactive towards glucose and xylose oxidation, reaching 90.8% yield of gluconic acid and 88.4% yield of xylonic acid under the optimal condition. Theoretical calculations revealed that the intrinsic reaction mechanism of xylose oxidation involves the activation of the oxidant, adsorption of xylose, dissociation of the formyl C–H bond in xylose, formation of chemisorbed xylonic acid, and desorption of xylonic acid. The dissociation of the formyl C–H bond and the formation of adsorbed xylonic acid are key steps in the oxidation of xylose. The OH−, instead of O2, acted as a direct oxidant and was crucial for the xylose oxidation. The highly active and cost-effective Ni-NCNT developed in this study provided a promising route to generate valuable chemicals from biomass.