Understanding Heterogeneously Catalyzed Hydrogenation of Carbonyl Compounds Through Keto‐Enol Tautomerization

The possibility of low-barrier hydrogenation of carbonyl compounds via keto-enol tautomerization as the initial step is a highly debated question in catalysis research. Here, a comprehensive description is provided, supported by theoretical and experimental techniques, of surface-assisted keto-enol tautomerization and subsequent hydrogenation of carbonyl compounds to alcohols. The crucial role of the ketone-ketone dimers as key reaction intermediates is elucidated, in which one ketone species undergoes a low-barrier tautomerization to form a stable ketone-enol dimer. This phenomenon arises from the strong intermolecular interactions within the dimers and the substantial charge-transfer between the adsorbates and the surface. Remarkably, the reduction of the barrier is primarily attributed to the charge-transfer from the inner HOMO-1 orbital. This work explores the atomic details underlying the tautomerization reaction, contributing to the rational design of high-performance metal catalysts for low-barrier hydrogenation of carbonyl compounds.