Hydroxy and surface oxygen effects on 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid on β-MnO2: DFT, microkinetic and experiment studies

Abstract

Manganese dioxide, β-MnO₂, has shown potential in catalyzing the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), a monomer of bioplastic polyethylene furanoate (PEF). Herein, the insight into the hydroxy (OH) and surface oxygen effects on the HMF-to-FDCA reaction over β-MnO₂ is clarified through a comprehensive investigation using density functional theory (DFT) calculations, microkinetic modeling, and experiment. Theoretical analyses revealed that both active surface oxygen and OH species (from either base or solvent) facilitate C–H bond breaking and OH insertion, promoting the catalytic activity of β-MnO₂. Microkinetic modeling demonstrated that the FFCA-to-FDCA and DFF-to-FFCA steps are the rate-limiting steps of the hydroxylated and non-hydroxylated surfaces, respectively. These theoretical results agree well with the experiment when water and dimethyl sulfoxide (DMSO) were used as solvents. In addition, the synthesized β-MnO₂ catalyst showed high stability and activity, maintaining stable HMF conversion (≥99 mol%) and high FDCA yield (85–92 mol%) during continuous flow oxidation for 72 hours at pO₂ of 1 MPa, 393 K and LHSV of 1 h⁻¹. Thus, considering both hydroxy and surface oxygen species is a new strategy for enhancing the catalytic activity of Mn oxides and other metal oxide catalysts for the HMF-to-FDCA reaction.