Transformation of CeO ₂ Nanoparticles into Atomically Dispersed Ce Cations Leads to Enhanced Reactivity for Automotive Emissions Control

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 ions anchored by surface penta- and octa-coordinated Al sites exhibit outstanding thermal stability in air up to 500 °C, enabling further loading of active metals with well-defined catalyst structures. With this strategy, supported single-atom Rh₁ surrounded by dispersed Ce₁ is confirmed to exhibit much superior performance to Rh₁ on bare Al₂O₃ or nanocrystalline CeO₂ in catalyzing NO reduction by CO, exhibiting a striking one-order-of-magnitude increase in activity. Dispersed Ce₁ exhibits greatly enhanced oxygen transfer capability compared to ceria nanoparticles and introduces a modified reaction mechanism that involves an adjacent Rh₁-Ce₁ motif, resulting in a greatly decreased activation barrier (from 192 to 96 kJ/mol). The reactivity enhancements are also seen with Ce₁-promoted Pt nanoparticles for oxidation of CO and hydrocarbons.