Support-Mediated Reversible Redox Dynamics of Pt and Au on CeO₂ at Room Temperature

Noble metals such as platinum and gold are widely regarded as resistant to oxidation under ambient conditions. We show that interfacing these metals with a reducible oxide alters their redox behavior through dynamic metal-support interactions. Using in situ environmental transmission electron microscopy, we visualize reversible room-temperature redox cycling of Pt and Au nanoparticles on CeO₂ under alternating O₂ and vacuum. Oxygen vacancies in the partially reduced support dissociate O₂ into reactive atomic oxygen, which spills over to oxidize the supported metal, driving complete conversion of Pt to crystalline Pt₃O₄, and the formation of ordered oxide species on Au. For Pt/CeO₂, redox cycling also induces a reversible wetting-dewetting restructuring in which oxidation promotes dewetting into three-dimensional oxide islands, whereas reduction drives wetting of metallic Pt into atomically thin rafts, progressively increasing metal dispersion. In contrast, Au/CeO₂ exhibits self-limiting surface oxidation, highlighting the role of metal identity in governing restructuring pathways. Density functional theory modeling shows that this process is sustained by a Cabrera-Mott-type field-assisted oxidation mechanism enabled by the CeO₂ support. These results establish reducible oxides as active redox partners rather than passive supports, providing a mechanistic framework for designing low-temperature oxidation catalysts through support-driven dynamic chemistry.