Nanosized cerium oxide (CeO2) has been extensively used as the oxygen storage component in automotive emission control systems. However, the possible influence of atomically dispersed Ce in these catalysts has not been recognized. Here, we demonstrate the controllable transformation of ceria nanoparticles into isolated cerium cations on γ-Al2O3 via reductive atom trapping in 10% H2 at 800 °C, achieving over half-monolayer coverage. Dispersed Ce1</