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Ceria is one of the world’s most prominent material for applications in heterogeneous catalysis, as catalyst support or catalyst itself. Despite an exhaustive literature on the structure of reactive facets of CeO₂ in line with its catalytic mechanisms, the temporal evolution of the atomic surface structure exposed to realistic redox conditions remains elusive. Here, we provide a direct visualization of the atomic mobility of cerium atoms on {100} surfaces of CeO₂ nanocubes at room temperature in high vacuum, O₂, and CO₂ atmospheres in an environmental transmission electron microscope. Through quantification of the cationic mobility, we demonstrate the control of the surface dynamics under exposure to O₂ and CO₂ atmospheres, providing opportunities for a better understanding of the intimate catalytic mechanisms.