In-situ observation of structural evolution of single-atom catalysts: From synthesis to catalysis

Atomically dispersed single-atom catalysts (SACs) have been extensively studied over the past decade because of their high atom utilization efficiencies and specific selectivities. Although numerous strategies have been proposed to obtain SACs with high densities and stabilities, the transformation mechanism that occurs during the reaction is still unclear. This review summarizes the structural evolution of SACs in the preparation process and reaction with various electron microscopy techniques at atomic scale under environmental conditions. Current state-of-the-art environmental electron microscopy studies on SACs mainly focus on porous carbons, metals or metal oxides, and some specific composite materials. The dynamic evolution of SACs under various reaction conditions is also investigated in this study. Finally, we highlight the challenges and drawbacks of the current studies and the prospects for the future exploration of SACs with environmental strategies.