MetalCenter‐Dependent Selectivity Divergence in MN ₄ Single‐Atom Catalysts for Aerobic HMF Oxidation

ABSTRACT Selective oxidation of carbohydrate‐derived 5‐hydroxymethylfurfural (HMF) to high‐value chemicals is a critical pathway for sustainable development. However, the primary challenge is controlling selectivity, as the narrow energy gaps between intermediates make discriminating between specific functional groups difficult. Herein, two single‐atom catalysts (SACs) with M‐N ₄ configurations were synthesized by varying the metal active center. The FeN ₄ catalyst achieved 99.9% HMF conversion with 93.9% selectivity toward 2‐formyl‐5‐furancarboxylic acid (FFCA) at 333.15 K. Conversely, the CoN ₄ catalyst yielded 2,5‐furandicarboxylic acid (FDCA) as the predominant product with comparable HMF conversion. Despite divergent product selectivities, the two catalysts displayed nearly identical TOFs for HMF consumption (∼18.2 h ⁻¹ ). DFT calculations revealed that the metal center governs the adsorption/activation of the FFCA intermediate. Specifically, lower FFCA adsorption energy on FeN ₄ inhibits dehydrogenation at the α ‐C position, while stronger adsorption on CoN ₄ facilitates its subsequent oxidation to FDCA. Moreover, the catalysts showed distinct O ₂ activation mechanisms. FeN ₄ preferentially generates superoxide anions (O ₂ ^•− ) for HMF oxidation, while CoN ₄ utilizes hydroxyl radicals (•OH) for FFCA oxidation to FDCA. This study demonstrates an effective strategy for controlled HMF oxidation, providing a theoretical basis for tailoring reaction selectivity through a mechanistic divergence driven by the intrinsic electronic structure of the metal center.