Persistent Mn 3+ Sites on Reduced MnO Enable Efficient Syngas Conversion

Mn‐based materials are widely used for syngas conversion, where MnO is generally regarded as the catalytically active phase under reducing conditions. Yet catalysts derived from different Mn oxide precursors often exhibit markedly different performances despite evolving into the same MnO bulk structure during reaction. Here we show that trace Mn 3+ sites stabilized on oxygen‐deficient MnO surfaces serve as the decisive active sites. Time‐resolved energy‐dispersive x‐ray absorption spectroscopy combined with iterative target transformation factor analysis and depth‐resolved synchrotron photoemission spectroscopy reveals a persistent minor Mn 3 O 4 ‐like spectral contribution and its enrichment near the surface of Mn 2 O 3 ‐derived MnO. These stabilized sites strongly enhance CO adsorption and activation, thereby promoting C─O bond cleavage and markedly improving activity and selectivity for syngas‐to‐light‐olefin conversion. More broadly, this work reveals how minority surface sites can govern catalytic function despite identical bulk phases and establishes an operando strategy for quantitatively resolving low‐coverage active sites in reducible oxide catalysts.