Regulation of oxygen vacancy in Mn-Co oxides to enhance selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

The green oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a crucial step in the development of sustainable and degradable plastics. Here, a series of MnCO3-MnxCo3-xO4-Ov composite oxides are synthesized by a simple solid-state grinding and carbonization method, exhibiting a 100 % HMF conversion rate and 98.7 % FDCA yield directly using air as the oxygen source. Physicochemical characterizations indicate that the introduced carbon promotes the diffusion of Mn species and reduction of Co3 +/Co4+, resulting in more unsaturated coordination of Co-O and the enhanced formation of oxygen vacancies (Ov). The kinetic analysis suggests that the oxidation of HMF to FDCA can be effectively promoted by regulating the Ov content in the catalyst after changing the Mn/Co ratio. Moreover, density functional theory (DFT) calculations demonstrate the crucial role of Ov in reducing the adsorption energy of HMF on the catalyst surface and activation of O2 molecules to replenish lattice oxygens during the completion of the catalytic cycle. This work provides a promising strategy to engineer transition metals as alternatives to noble metal-based catalysts towards catalytic oxidation for the production of biofuels and bioplastics.