Niobium phosphates as bifunctional catalysts for the conversion of biomass-derived monosaccharides

The direct conversion of glucose and xylose into HMF and furfural is more efficient using a combination of Lewis and Brønsted acids. Herein, niobium phosphates were prepared with different compositions, which affect its surface acidity and, consequently, the catalytic activity. The catalysts with a high P/Nb molar ratio presented a low molar ratio between Lewis and Brønsted acid sites (L/B ratio), while those with low P/Nb molar ratio displayed a high L/B ratio. NbP-2, the sample with the highest L/B ratio, showed the highest reaction rate for both HMF and furfural formation. It was found, indeed, that the reaction rate for monosaccharides conversion and furans formation correlate linearly with the L/B ratio. The results presented not only introduce niobium phosphates with a high L/B molar ratio as promising catalysts for HMF and furfural production but also provide fundamental knowledge that will guide the design of other bifunctional heterogeneous catalysts.