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 MnCO 3 -Mn x Co 3-x O 4 -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 Co 3 + /Co 4+ , resulting in more unsaturated coordination of Co–O and the enhanced formation of oxygen vacancies (O v ). The kinetic analysis suggests that the oxidation of HMF to FDCA can be effectively promoted by regulating the O v content in the catalyst after changing the Mn/Co ratio. Moreover, density functional theory (DFT) calculations demonstrate the crucial role of O v in reducing the adsorption energy of HMF on the catalyst surface and activation of O 2 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.