Orchestrating structure and chemistry dynamics for cluster catalysis

Supported metal clusters maximize atom efficiency and expose diverse low-coordination metal motifs, but under reaction conditions, they are inherently fluxional-adsorbed reactants can constantly reform and even break the underlying metal-metal and metal-support bonds, generating an ensemble of metastable structures for catalysis. Identification of the interplay between supported clusters and surface chemistries is vital but a challenge for their complex dynamic evolutions. Here, we uncover three characteristic and universal regimes: (i) a fluxional regime, where fast restructuring erases site individuality; (ii) a kinetically trapped regime, where slow restructuring freezes the catalyst into a single geometry; and (iii) a unique coupled regime, where structural dynamics and chemistry occur on comparable timescales and where multiple metastable motifs actively participate in turnover. Moreover, we identify a single, dimensionless metric, N _c = τ _struct /τ _chem, the ratio between the structural rearrangement timescale (τ _struct) and the chemical residence time of the reactant (τ _chem), to differentiate these three regimes with distinct activity and stability. It is found that N _c should be neither too small (fluxional regime) nor too large (kinetically trapped regime). When the optimal value N _c ∼ 1 is approached (coupled regime), structural and chemical 'clocks' match, enabling the multiple active metastable isomers to persist long enough to participate in turnover and maximize reaction rates. Using CO adsorption-desorption on size-selected Cu _n /TiO₂(110) clusters as a model system, we demonstrate a master kinetic curve versus N _c and reveal tunable levers that drive clusters into the optimal coupled regime. Trends generalize across metals: coinage clusters (Ag, Au) prefer fluxionality, Rh/Pd favor trapping, and Cu and Pt/Ru often lie near the coupled boundary. Time-scale matching thus emerges as a design rule for adaptive, fluxional catalysts with high activity and stability at the same time.