MnOx/P25 with tuned surface structures of anatase-rutile phase for aerobic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran

A series of MnO_x/P25 (TiO₂) catalysts were prepared by a simple impregnation method and evaluated for the selective oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-diformyfuran (DFF). The as-prepared catalysts were characterized by N₂ adsorption/desorption isotherms, transmission electron microscope (TEM), X-ray powder diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), Raman, and thermogravimetric analysis. The surface anatase-rutile structure of P25 can be tuned via calcination at different temperature for different time and has significant effects on the catalytic activity of MnO_x/P25 for HMF oxidation. The results reveal that MnOx supported on P25 pretreated at 600 °C for 5 h (MnO_x/P25-600-5 h) shows the best catalytic performance achieving 33.2% HMF conversion along with 97.0% selectivity to DFF in a two-hour reaction time. The catalytic activity of MnO_x/P25-600-5 h is almost twice higher than untreated MnO_x/P25 catalyst, attributing to the optimized surface structures of anatase/rutile ratio (1.83). In addition, the effects of MnO_x loadings, reaction time and temperature of the catalysts for HMF oxidation were also investigation. Furthermore, the MnO_x/P25-600-5 h catalyst can be used for five consecutive runs without significant loss of its catalytic activity.