Understanding Reactivity and Stability of Rhodium Supported on Different Ceria Facets in Catalytic NO Reduction and CO/Hydrocarbon Oxidation Reactions

Synthesis of robust and hydrothermally stable PGM/ceria materials for NO, CO and hydrocarbon abatement remains a formidable challenge as ceria and PGMs are known to sinter severely >800 °C under hydrothermal conditions, leading to irreversible activity loss. Herein, we tackle this challenge by synthesizing well-defined catalysts with atomically dispersed rhodium supported on ceria with varying abundance of (100), (101) and (111) facets. Evaluation of these catalysts for NO reduction by CO, as well as CO and propylene oxidation under model and industrially relevant conditions reveals pronounced reactivity and stability differences. Different modes of interaction of Rh+3 ions with the ceria facets and their facile reducibility were shown to be the crucial parameters controlling reactivity, resulting in pronounced activity and stability variations. Facet-dependent poisoning of surfaces by nitrites was identified as the main reason for deactivation of the catalysts at low temperature, which is mitigated for (111) ceria facets. (111)-enriched ceria nanoparticles survive extremely harsh hydrothermal aging at 950 °C by maintaining and preserving (111) facets, unlike ceria nanoparticles which sinter into irregularly shaped particles. Thus, putting atomically dispersed PGM sites on (111) ceria facets leads to the catalytic material with the highest activity and stability for all studied reactions, providing the pathway to novel catalysts that can endure extreme hydrothermal aging conditions.