Structural engineering of metal-organic framework catalysts for efficient conversion of glucose into 5-HydroxyMethylFurfural

The research on sustainable and efficient routes to produce valuable chemicals from renewable biomass has garnered considerable attention in recent years. Among these chemicals, 5-hydroxymethylfurfural (5-HMF) holds significant promise as a versatile platform molecule for various applications in the chemical industry. This study investigates the production of 5-HMF from glucose using zirconium-based metal-organic frameworks (Zr-MOFs) as environmentally friendly catalysts, an alternative to the traditional homogeneous catalysts. UiO-66 and its functionalized derivatives (e.g. UiO-66(NH2), UiO-66(COOH)2, and UiO-66(OH)2) were synthesized to study the effect of the functional groups on the dehydration reaction. The synthesized MOFs were fully characterized using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), N2 adsorption-desorption, Infrared spectroscopy (IR), Pyridine-Fourier Transform Infrared spectroscopy (Py-FTIR), and scanning electron microscopy (SEM). The catalytic performance of the synthesized MOFs was evaluated for the dehydration of glucose to 5HMF in DMSO and further optimized in other monophasic and biphasic systems. Results indicated that UiO66(COOH)2 exhibited exceptional catalytic activity for the conversion of glucose to HMF, with a significantly higher HMF yield of 44 % compared to other reported MOF catalysts and to that of H2SO4, which yielded 35 % at a temperature of 140 degrees C and a 6 h reaction time. This is mainly attributed to the effect of the bifunctional active acid sites of the metal nodes and the functional group of the organic linker (free carboxylic groups), which acted as the main source of Lewis and Br & Oslash;nsted acid sites respectively, compared to UiO-66. Additionally, the results suggested that the catalyst with higher acid density, higher relative mesopority, and a moderate B/L ratio could enhance glucose dehydration regardless of the surface area. Furthermore, the catalyst demonstrated excellent reusability and stability, with a decrease of only 10% after four reaction cycles. The recycled catalyst revealed no structural alterations in its framework. This study contributes to the growing body of research on Zr-based MOF as a stable and efficient catalyst for glucose valorization to produce 5-HMF under mild reaction conditions.