Orchestrating structure and chemistry dynamics for cluster catalysis

Abstract 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, Nc = τstruct/τchem, the ratio between the structural rearrangement timescale (τstruct) and the chemical residence time of the reactant (τchem), to differentiate these three regimes with distinct activity and stability. It is found that Nc should be neither too small (fluxional regime) nor too large (kinetically trapped regime). When the optimal value Nc ≈ 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 Cun​/TiO2(110) clusters as a model system, we demonstrate a master kinetic curve versus Nc and reveal tunable levers that drive clusters into the optimal coupled regime. Trends generalize across metals: coinage clusters (Ag, Au) bias 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.