Aerobic oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-diformylfuran with cesium-doped manganese dioxide
The selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) has attracted much attention in recent years. Cesium-doped manganese dioxide (Cs/MnOx) was prepared by a soft template method, and was found to be active for the selective oxidation of HMF to DFF with molecular oxygen. Various reaction conditions have been investigated, and DFF was attained with a high yield of 94.7% at a HMF conversion of 98.4% at 100 °C and 10 bar O2 in N,N-dimethylformamide. Cs/MnOx demonstrated much higher catalytic activity than un-doped MnOx, suggesting that the introduction of Cs into MnOx plays a crucial role in the oxidation of HMF to DFF. Kinetic studies demonstrated that the oxidation of HMF to DFF depends on both the HMF and oxygen concentration, with the reaction order being 0.44 and 0.53, respectively. Compared with other heterogeneous non-noble metal catalysts, Cs/MnOx demonstrated a much lower activation energy for the oxidation of HMF to DFF. The catalyst can be reused without much loss of catalytic activity, suggesting that the catalyst is highly stable. Furthermore, the direct production of HMF from fructose was also successfully realized by a one-pot reaction strategy via two consecutive steps.