Understanding the Dynamic Aggregation in Single Atom Catalysis

The dynamic response of single atom catalysts to a reactive environment is an increasingly significant topic for understanding the reaction mechanism at the molecular level. In particular, single atoms may experience dynamic aggregation into clusters or nanoparticles driven by thermodynamic and kinetic factors. Herein, we will uncover the inherent mechanistic nuances that determine the dynamic profile during the reaction, including the intrinsic stability and site-migration barrier of single atoms, external stimuli (temperature, voltage, and adsorbates), and the influence of catalyst support. Such dynamic aggregation can have beneficial or deleterious effects on the catalytic performance depending on the optimal initial state. We will highlight those examples where in situ formed clusters, rather than single atoms, serve as catalytically active sites for improved catalytic performance. This is followed by the introduction of typical operando techniques to understand the structural evolution. Finally, we will briefly discuss the emerging strategies via confinement and defect-engineering to regulate dynamic aggregation.