Liquid Coordination Environment-Induced Liquid-Like Metal Behavior: Mobile Single-Atom Copper Catalytic Centers

Heterogeneous single-atom catalysts are typically stabilized by rigid anchoring to solid supports, which limits their dynamic response under the reaction conditions. Here, we demonstrate that liquid-metal-like catalytic behavior can be realized in heterogeneous systems through a liquid coordination environment rather than a liquid-metal phase. An ionic liquid membrane is introduced onto Al₂O₃ to construct a high-loading single-ion Cu catalyst, in which reversible coordination exchange between N-heterocyclic carbene and Cu generates dynamically reconfigurable active centers. Spectroscopic analyses reveal the coexistence of NHC-Cu and Bis-NHC-Cu species with an average Cu coordination number of 2.5 ± 0.8 and a continuously tunable valence state between Cu⁺ and Cu^δ+. In acetylene-selective hydrogenation, the catalyst achieves 98% C₂H₂ conversion and 92% ethylene selectivity at 200 °C with only 0.25 wt % Cu, exhibiting a 35 °C lower half-conversion temperature than CuCl/Al₂O₃ and stable performance over 200 h. Kinetic and operando spectroscopic studies demonstrate that the liquid coordination environment strengthens acetylene adsorption while weakening ethylene binding; density functional theory calculations further reveal a reduced H₂ dissociation barrier, enhanced C₂H₂ adsorption, suppressed C₂H₄ binding, and an inhibited further hydrogenation of *C₂H₅, collectively directing the reaction toward selective semihydrogenation. This work establishes coordination dynamics as a general route to dynamic, self-adaptive, single-atom catalysis beyond static anchoring strategies.