Dynamic Activation of Single-Atom Catalysts by Reaction Intermediates: Conversion of Formic Acid on Rh/Fe ₃ O ₄ (001)

The stability and activity of supported single-atom catalysts (SACs) represent critical yet opposing factors limiting our ability to explore and exploit their catalytic properties. This study demonstrates the operation of a catalyst that is dynamically activated in the presence of surface intermediates and reverts to a stable but inactive form when the reaction is completed. We employ atomically defined Rh/Fe3O4(001) catalysts to demonstrate how structurally stable Rh, bound in surface octahedral Fe sites, gets destabilized to form highly active Rh adatoms and small clusters. Conversion of formic acid, leading initially to surface formate and hydroxyl species, is employed as a model reaction to probe the dynamics of such processes. We find that surface hydroxyl recombination to water through the Mars–van Krevelen mechanism reduces Rh coordination, triggering its conversion to active Rh adatoms. Upon completion of the reaction (surface-intermediate free catalyst), Rh adatoms return back to the stable octahedral Rh sites, limiting Rh sintering. Since lattice oxygen exchange is observed in many acid–base and redox chemistries, the process can be broadly applicable to controlling the activation and stability of the range of SACs.