Improving the glucose to fructose isomerization via epitaxial-grafting of niobium in UIO-66 framework

Abstract

Glucose to fructose transformation is an essential transformation for the success of biorefinery. Herein, the epitaxial-grafting of Nb in UIO-66 significantly improved the fructose yield. Post-synthesis incorporating Nb in the UIO-66 phenomenally improved the glucose conversion from 31.1 % to 71.8 % and fructose selectivity from 38.2 % to 71.2 %. The incorporation of Nb was confirmed from the FTIR, HR-TEM investigation, EDX analysis, and elemental mapping. The XPS analysis distinctly stated the successful incorporation of Nb and generation of Zr−O−Nb oxo clusters in the UIO-66 framework. The NH3-TPD provided distinguishable information about the chemical interaction of Nb with the UIO-66 framework that resulted in the increase of the acid strength after the Nb incorporation in the UIO-66 catalyst. The content of Nb and reaction parameters, especially temperature and duration, control the glucose to fructose isomerization over glucose to mannose epimerization. The structure-activity relationship was established, and a reaction mechanism was proposed. The catalyst was recycled five times with only a lower decrease in the fructose yield (47.3 % to 42.2 %) than several reported MOFs catalysts. The activity of the developed catalyst was higher or similar to the reported catalysts. The successful grafting of Nb demonstrates that by swiftly modifying the acidity of the catalyst, a superior activity can be achieved.