Green synthesis of aluminum-hydrochar for the selective isomerization of glucose to fructose.

Hydrochar microspheres supported Al catalysts with hierarchically porous structure (Al/HPHMs) for glucose to fructose isomerization were fabricated. Superior catalytic selectivity (93.3%) and fructose yield (32.6%) were achieved in aqueous under 160 °C for 20 min. Hierarchically porous structure was formed after KHCO and KCO activation and the roles of KHCO and KCO in controlling the Al phase and tailoring morphology of hydrochar supported Al were evaluated. The major active sites were characterized as Al hydroxides including β-Al(OH), γ-Al(OH), γ-AlO(OH), Al-C-O linkages. Active sites by KHCO activation with high contents of Al-C-O and Al(OH) have better selectivity. Oxygen-containing functional groups including aluminum‑oxygen groups on the hydrochar microspheres have contributed to the formation of hydrogen bond and π-π interactions between glucose and Al species. Green process synthesized aluminum-hydrochars have potential for their application as a variety of stable, recyclable, and efficient catalysts for lignocellulosic biorefining.