Preparation of hydrophobic acidic metal−organic frameworks and their application for 5-hydroxymethylfurfural synthesis

The production of 5-hydroxymethylfurfural (HMF) by the acid-catalyzed dehydration of fructose is of great significance for the comprehensive utilization of biomass resources. However, the water generated in situ not only leads to the deactivation of the active sites but also triggers the rehydration side reaction of HMF, resulting in an unsatisfactory catalytic activity and selectivity. Herein, for the first time, metal−organic frameworks (MOFs) with strong Brønsted acidity and hydrophobicity were prepared by grafting arenesulfonic acid by a diazo method. These functionalized MOFs have a large specific surface area of 1700−2600 m²/g, a high acid density of over 1.2 mmol/g, and a strong hydrophobicity with an H₂O contact angle of greater than 125°. Compared with the MOF directly functionalized with sulfonic acid, the arenesulfonic acid-functionalized MOFs, which have a stronger hydrophobicity, exhibit higher activity and selectivity (up to 98.3% yield) in the transformation of fructose to HMF. Meanwhile, these arenesulfonic acid-functionalized MOFs also exhibit an excellent HMF yield for glucose and inulin reactions via the cooperative catalysis of Lewis and Brønsted acids. Furthermore, the good activity and stability of the functionalized MOFs can be maintained after recycling for five runs. The successful preparation of hydrophobic acidic MOFs provides not only an efficient catalytic system for the synthesis of HMF but also a novel, efficient route for MOF functionalization.