Heterostructured manganese catalysts for the selective oxidation of 5‐hydroxymethylfurfural to 2,5‐diformylfuran

Abstract A series of manganese oxide catalysts were synthesised in the presence of various precipitants using hydrothermal approach. The manganese oxide synthesised (MnOx−A−U) using manganese acetate tetrahydrate and urea as precursor and precipitant, respectively, was found to be composed of heterostructures of manganese, that is, MnCO 3 , ϵ‐MnO 2 and Mn 2 O 3 , and their presence were confirmed by XRD, FTIR and XPS analyses. The catalytic activity of MnOx−A−U towards selective oxidation of HMF to DFF in ethanol afforded 92.0 % conversion along with 88.0 % DFF yield at 120 °C, 30 bar O 2 , after 4 h of reaction time. Performing HMF oxidation under N 2 atmosphere with MnOx−A−U yielded only 15.0 % DFF, revealing that lattice oxygen played a crucial role in the oxidation process, which was confirmed by subjecting the spent catalyst to XPS analysis. Based on the results obtained from XPS analysis, it was speculated that ϵ‐MnO 2 and MnCO 3 could be the active species which could selectively catalyse the reaction. The MnOx−A−U catalyst was able to recycle for at least three runs with a small loss of activity due to ϵ‐MnO 2 content decreased.