Fe–N–C single‑atom catalysts unlock efficient and selective oxidation of 5‑hydroxymethylfurfural to value‑added 5‑formyl‑2‑furancarboxylic acid

A ZIF-8-derived Fe–N–C single-atom catalyst is developed for HMF-to-FFCA oxidation. • The catalyst obtained 99.4% HMF conversion and 94.2% FFCA yield under mild conditions. • O 2 • and 1 O 2 are identified as the key reactive species governing selective oxidation. • Fe–N x moieties are confirmed as the active centers for O₂ activation and selectivity. The catalytic valorization of 5-hydroxymethylfurfural (HMF) to high-value chemicals is critical for sustainable chemistry. However, 5-formyl-2-furancarboxylic acid (FFCA), a key oxidation intermediate, remains a significant challenge. Herein, a Fe N C single-atom catalyst derived from zeolitic imidazolate framework-8 (ZIF-8) is developed for efficient HMF-to-FFCA conversion under mild conditions (90 °C, 0.1   MPa O 2 ). It has been revealed that the isolated Fe–N x sites are dispersed on a nitrogen-doped carbon matrix. The optimized catalyst delivers 99.4% HMF conversion with 94.2% FFCA yield within one hour, and exhibits excellent catalytic and structural stability over consecutive reaction cycles. Mechanistic studies combining Electron paramagnetic resonance (EPR) spectroscopy and radical trapping experiments demonstrate that superoxide radicals (O 2 • ) and singlet oxygen ( 1 O 2 ) govern the selective oxidation pathway. Active-site poisoning with thiocyanate confirms the essential role of Fe–N x moieties in oxygen activation. This work presents a robust non-noble metal catalyst platform for HMF valorization and advances the fundamental understanding of single-atom catalyst design for biomass oxidation reactions. Download: Download high-res image (189KB) Download: Download full-size image