Redox-Switchable Single-Atom Iron Dimer Catalysts for Controlled Oxidation of Biomass-Derived Hydroxymethylfurfural in Water

The development of highly active and selective oxidation catalysts is essential for a broad range of reactions. Here, we introduce a robust catalyst comprising single-atom iron dimers anchored on nitrogen-doped graphene acid (Fe-NGA). The lattice stabilizes the pair in a redox-flexible Fe ²⁺ /Fe ³⁺ manifold that evolves into an oxo-bridged Fe ³⁺ –Fe ⁴⁺ ferryl species. X-ray absorption spectroscopy and in-situ electron paramagnetic resonance reveal the Fe dimers, whose synergy enables controlled two-electron oxidation. As a proof of concept, Fe-NGA catalyzes the oxidation of 5-hydroxymethylfurfural –one of the top sustainable platform chemicals– to 2,5-diformylfuran with 97% conversion, 95% selectivity and a mean turnover frequency of 17.3 h⁻ ¹ , which is among the highest observed so far. Unlike previous catalysts that operate in organic solvents, Fe-NGA works in pure water. By merging such functionalities within a stable and reusable heterogeneous framework, Fe-NGA provides a blueprint for the green oxidation of renewable feedstocks.