Au@h-Al2O3 analogic yolk-shell nanocatalyst for highly selective synthesis of biomass-derived d-xylonic acid via regulation of structure effects

Selective oxidation of biomass-based monosaccharides into value-added sugar acids is highly desired, but limited success of producing d-xylonic acid has been achieved. Herein, we report an efficient catalyst system, viz., Au nanoparticles anchored on the inner walls of hollow Al2O3 nanospheres (Au@h-Al2O3), which could catalyze the selective oxidation of d-xylose into d-xylonic acid under base-free conditions. The mesoporous Al2O3 shell as the adsorbent first adsorbed d-xylose. Then, the interface of Au nanoparticles and Al2O3 as active sites spontaneously dissociated O-2, and the exposed Au nanoparticle surface as the catalytic site drove the transformation. With this catalyst system, the valuable d-xylonic acid was produced with excellent yields in the aerobic oxidation of d-xylose. Extensive investigation showed that Au@h-Al2O3 is an efficient catalyst with high stability and recyclability.