Dynamic structural changes in the reactive environment often lead to catalyst deactivation in the thermal-catalysis field. Taking advantage of the dynamic changes in bulk phases, interfaces, and surface structures to design highly active catalysts is a unique but important strategy. Herein, we report a supersaturated ceria solid solution catalyst enabling a styrene yield of 91.8% over extended redox cycles at 430 °C in the redox oxidative dehydrogenation (ODH) of ethylbenzene. In-situ characterizations reveal that the oxygen anions (O2–) and transition-metal cations (Fe and Mn) reversibly shuttle through a ceria solid solution (bulk ↔ surface) in a K–Ce0.47Fe0.2Mn0.33O2−δ catalyst during the redox ODH process. The ceria solid solution acts as a dynamic transition-metal cations/oxygen reservoir, creating atomic interfaces of K–Fe–O/K–Mn–O and an oxygen gateway for efficient ethylbenzene ODH. The findings concerning the formation of a supersaturated ceria solid solution and cations, lattice oxygen migration, and the coupling between oxygen donation and catalytic reactions offer new strategies for designing high-performance dynamic catalysts.