Selective Glucose-to-Fructose Isomerization over Modified Zirconium UiO-66 in Alcohol Media

Modulated zirconium metal–organic framework UiO-66 is shown to catalyze the isomerization of d-glucose to d-fructose in alcohol media. Fructose selectivity can change depending on solvent choice. We hypothesize that the difference in selectivity is related to a combined effect of adsorption and solvation effects, which may lead to the high formation of alkylglucosides in depletion of fructose if methanol or ethanol are used. A fructose selectivity of 72 % at 82 % glucose conversion in 1-PrOH was achieved. The reaction mechanism was investigated using nuclear magnetic resonance spectroscopy. We demonstrate that UiO-66 isomerizes glucose to fructose through an intramolecular C2–C1 hydride transfer. In addition, we show that modulated UiO-66 is a highly active and stable catalyst at the reaction conditions, showing great potential for other sugar reactions.