Synthesis of UiO–66–NH2(Ti/Zr) and its Catalytic Conversion of Cellulose to 5-HMF

UiO–66–NH₂(Ti/Zr) modified by Ti metal oxide (TiO₂) was used to catalyze the hydrolysis of cellulose to prepare 5-HMF. Under the optimal reaction conditions of H₂O(NaCl)/THF(1/4 mL), 190 °C, 2 h and 50 mg UNT-3(Ti/Zr) (TiO₂ and UiO–66–NH₂ with mass of 1.5 and 0.1 g, respectively), the yield of 5-hydroxymethylfurfural reached 59.88%. UiO–66–NH₂(Ti/Zr) nanocomposites with different mass ratios were successfully prepared by simple solvent evaporation method. SEM and TEM have shown that the modified UiO–66–NH₂(Ti/Zr) are wrapped into sphere by TiO₂ densely attached to the surface of UiO–66–NH₂, which provides favorable conditions for the uniform dispersion of TiO₂ and coordination of the Lewis acidic site of UiO–66–NH₂. NH₃–TPD results confirmed the existence of super-strong, strong, middle and weak acid sites in UiO–66–NH₂(Ti/Zr), and Py-FTIR confirmed the existence of Brønsted and Lewis acids. After four cycles, the yield of 5-HMF and FUR decreased slightly from 59.88 to 51.89% and 9.11 to 7.66%, respectively, and the yield of 5-HMF could still remain above 50%. The results showed that the modified composite treatment of TiO₂ with rich Lewis acid/base and UiO–66–NH₂ could provide a certain idea for the extensive application of biomass research in the future.

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