Oxidation of 5-hydroxylmethylfurfural to 2,5-furandicarboxylic acid catalyzed by magnetic MnO2-Fe3O4composite oxides

MnO2with different crystal structures was used to catalyze the oxidation reaction of 5-hydroxylmethylfurfural (HMF), and α-MnO2exhibited the highest catalytic activity. Magnetic MnO2-Fe3O4oxides were prepared by α-MnO2and Fe3O4and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of NH3/CO2(NH3/CO2-TPD) and Fourier transform infrared reflection spectra of pyridine adsorption (Py-FTIR). The results showed that the composite catalyst still maintained the basic structure of α-MnO2and Fe3O4, whereas the number of active center Mn4+·O2−ion pair increased compared with α-MnO2and Fe3O4, which significantly improved the catalytic activity on HMF oxidation reaction. The reaction conditions of HMF oxidation to 2,5-furandicarboxylic acid (FDCA) were optimized. The composite oxide Mn8Fe3Oxshowed the best catalytic performance for HMF oxidation. HMF could be completely converted, with 76.9% of FDCA yield under the optimal conditions.