From Transient Fluctuations to Programmable Dynamics: Operando-Reversible Reconstruction of Single-Atom Sites

The dynamic nature of single-atom catalysts, manifested as transient coordination fluctuations during individual molecular turnovers, has provided crucial mechanistic insights. However, the practical exploitation of such molecular-level dynamics remains fundamentally challenging due to their experimental elusiveness and poor controllability. Here, we report a paradigm shift from these stochastic fluctuations to programmable coordination switching, enabled by the operando-reversible reconstruction of single-atom Cu sites in a Pt/bpy-UiO-CuX₂ model catalyst. Triggered by a reductive environment during hydrogenation, a metastable N₂-Cu-H configuration is generated under reducing conditions and remains the dominant Cu state during catalysis, before reversibly converting to an oxidized Cu-(OH)₂ form after depletion of reducing species and air exposure. Meanwhile, the coordination anions can be reprogrammed through external acid/anion environments, enabling interconversion among Cl^-, OH^-, and sulfate-containing Cu coordination states. Multimodal operando spectroscopy combined with theoretical calculations demonstrates that the N₂-Cu-H intermediate modulates the electronic state of the active Pt center, thereby boosting phenylacetylene-to-styrene selectivity by simultaneously lowering styrene desorption energy by 0.68 eV while raising the barrier for styrene hydrogenation by 0.66 eV. This work elevates dynamic single-atom sites from stochastic structural fluctuations to programmable coordination switching, establishing a new paradigm for enzyme-mimetic catalysts with adaptive responsiveness to redox and acid-base environments.