Aerobic Oxidation of Hydroxymethylfurfural and Furfural by Using Heterogeneous CoxOy-N@C Catalysts

2,5-Furandicarboxylic acid (FDCA) is considered to be a promising replacement for terephthalic acid since they share similar structures and properties. In contrast to FDCA, 2,5-furandicarboxylic acid methyl (FDCAM) has properties that allow it to be easily purified. In this work, we reported an oxidative esterification of 5-hydroxymethylfurfural (HMF) and furfural to prepare corresponding esters over CoxOy-N@C catalysts using O-2 as benign oxidant. High yield and selectivity of FDCAM and methyl 2-furoate were obtained under optimized conditions. Factors which influenced the product distribution were examined thoroughly. The CoxOy-N@C catalysts were recycled five times and no significant loss of activity was detected. Characterization of the catalysts could explain such phenomena. Using XPS and TGA, we made a thorough investigation of the effects of ligand and pyrolysis temperature on catalyst activity.