One Pot Cascade Conversion of Bio-Based Furfural to Levulinic Acid with Cu-Doped Niobium Phosphate Catalysts

Liquid-phase catalytic hydrogenation of furfural, followed by hydration to levulinic acid has been considered as one of efficient approaches for upgrading pentose sugars. However, a two-step process is generally employed, which involves the separation and purification of the key intermediate furfuryl alcohol from the reaction mixture. To simplify this catalytic process with improved efficiency, Cu-doped niobium phosphate (xCu/NbP; x = 0.1–5.0 wt%, denoted as Cu loading) catalysts with different Cu loadings were prepared by impregnation and reduction, which could catalyze furfural conversion to levulinic acid through a one pot single-step process. The as-prepared xCu/NbP catalysts were characterized by H2-TPR, XRD, NH3-TPD, XPS, the pore size and pore volume and pyridine-adsorption FT-IR. In this study, the effect of Cu loading, formic acid amount, support type, reaction temperature/time and catalyst reusability on the reaction were investigated. It was found that 1.5 wt% Cu/NbP loading exhibited predominant catalytic activity in the cascade conversion of furfural, producing levulinic acid with a high yield of up to 67.0 mmol% using ten equivalent of formic acid at 160 °C for 3 h. Moreover, the possible mechanism was further elucidated. Also, the catalyst could be easily separated from the mixture, and reused with no remarkable loss of reactivity.