Local Fluxionality of Surface-Deposited Cluster Catalysts: The Case of Pt7 on Al2O3.

Subnano surface-supported catalytic clusters can be generally characterized by many low-energy isomers accessible at elevated temperatures of catalysis. The most stable isomer may not be the most catalytically active. Additionally, isomers may interconvert across barriers, i.e., exhibit fluxionality, during catalysis. To study the big picture of the cluster fluxional behavior, we model such a process as isomerization graph using bipartite matching algorithm, harmonic transition state theory, and paralleled nudged elastic band method. All the minimal energy paths form a minimum spanning tree (MST) of the original graph. Detailed inspection shows that, at temperatures typical for catalysis, the cluster geometry changes frequently within several regions in the MST, while transition across regions is less likely. As a further confirmation, the structural similarity analysis was additionally performed based on molecular dynamics trajectories. This local fluxionality picture provides a new perspective on understanding finite-temperate catalytic processes.