Zr-Based Metal Organic Framework for Efficient Conversion of Glucose into 5-HydroxyMethylFurfural: Effect of Functionalized Linker on Brønsted-to-Lewis Acid Sites Ratio

Abstract

The research on sustainable and efficient routes to produce valuable platform chemicals from renewable biomass has garnered considerable attention in recent years. Among these chemicals, 5-hydroxymethylfurfural (HMF) holds significant promise as a versatile platform molecule for various applications in the chemical industry. A significant approach to the synthesis of different heterogeneous catalysts was recognized due to the lower cost, ease of separation, reusability, and regeneration compared to homogeneous ones. This study investigates the production of HMF from glucose using Zirconium-based Metal Organic Frameworks (Zr-MOFs) as environmentally friendly catalysts, an alternative to traditional homogeneous catalysts. UiO-66, UiO-66-NH_2, UiO-66-〖(COOH)〗_2, and UiO-66-〖(OH)〗_2 were synthesized using different Linkers to study the effect of the linkers’ functional groups and the introduced defects in the framework. The synthesized MOFs are fully characterized using Powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), Attenuated Total Reflectance (ATR), and scanning electron microscopy (SEM). The catalytic performance of each of the synthesized MOFs was evaluated in the dehydration of glucose to HMF in DMSO as a polar aprotic solvent. Reaction parameters, including temperature, time, catalyst loading, and agitation speed, were systematically optimized to achieve an enhanced HMF yield. Results showed that UiO-66-〖(COOH)〗_2 exhibited exceptional catalytic activity for the conversion of glucose to HMF, with a significantly high HMF yield of 40% compared to that of H2SO4, which yielded 35%, at a temperature of 140 °C, 1% (w/v) catalyst loading, and 6 h reaction run. This is mainly attributed to the effect of both the defected sites and the additional active acid functional group (carboxylic group) of UiO-66-〖(COOH)〗_2, which acted as the main source of Brønsted acid sites, compared to the unfunctionalized UiO-66. In addition to that, UiO-66-〖(COOH)〗_2 was in accordance with literature having a high relative mesopority and low relative microporosity. Furthermore, the catalyst demonstrated a decent reusability and stability over 3 reaction cycles with only 9% decrease in the final 5-HMF yield. This study contributes to the growing body of research on Zr-based MOF as a catalyst for biomass conversion and provides valuable insights for the future design and optimization of efficient catalytic systems for the valorization of renewable feedstocks.