Strongly Electron-Interacting Ru–Ce Pair Sites in RuOx/CeO2–HAP for Efficient Oxidation of MMF to FDCA

As a potential alternative to petroleum-derived terephthalic acid (TPA), the general production of 2,5-furandicarboxylic acid (FDCA) through 5-hydroxymethylfurfural (HMF) oxidation has fallen short of industrial expectations due to HMF's storage instability and cost. Here, we propose a strategy involving Ru cation coordination manipulation to achieve efficient oxidation of 5-methoxymethylfurfural (MMF) to FDCA by constructing a Ru–Ce paired site on a CeO2-doped hydroxyapatite precursor (CeO2–HAP). By optimizing reaction conditions, the RuOx/CeO2–HAP catalyst demonstrated a complete MMF conversion of 100% and a high FDCA yield of 83.7% under base-free conditions (130 °C, 5 bar O2 pressure, 15 h). Hydrogen temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) revealed a strong interaction between Ru and Ce with electron transfer from Ce to Ru. Density functional theory (DFT) computations indicated that the strong d–d π and σ orbital interactions between Ru and Ce provided sufficient electrons for the vacant orbitals of Ru, dispersing the density of states (DOS) of orbitals around the low energy level to facilitate MMF and FDCA adsorption with appropriate strength, thereby enhancing the MMF oxidation process. This study not only provides an MMF oxidation catalyst with high activity but also conducts a comprehensive investigation into the impact of the Ru–Ce interaction on MMF oxidation, offering insights into the subsequent production of high-value-added products such as FDCA.