Boosting the activity of catalytic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran over nitrogen-doped manganese oxide catalysts

Approaches for the catalytic oxidation of biomass-based 5-hydroxymethylfurfural (HMF) into valuable chemicals are in great demand; however, their development is still challenging. Herein, we present nitrogen-doped manganese oxide (N-MnO2) catalysts that possess extraordinary catalytic performance (a >99.9% 2,5-diformylfuran selectivity, a 100% HMF conversion, and decent reusability) at room temperature without any additives. Structural changes, i.e. slight elongation of the Mn-O bonds and reduction of the coordination number of Mn sites, occur after doping of nitrogen into MnO2, as confirmed via characterization by extended X-ray absorption fine structure (EXAFS), H-2-temperature programmed reduction (H-2-TPR) and X-ray photoelectron spectroscopy (XPS). Mechanistic studies indicate that surface defect sites and coordinatively unsaturated Mn sites induced by nitrogen doping play a key role in promoting the oxidative activity.