Reversible precipitation/dissolution of precious-metal clusters in perovskite-based catalyst materials: Bulk versus surface re-dispersion

High-angle annular dark-field imaging with aberration-corrected scanning transmission electron microscopy unambiguously establishes that nanometer-size Pt-rich clusters reversibly precipitate and dissolve under reducing and oxidizing conditions, respectively, within the oxide matrix of Pt-doped CaTiO3, previously proposed as a novel self-regenerating perovskite-based three-way catalyst. In fact, most of the Pt-rich clusters formed upon reduction are within the oxide matrix and thus unavailable for gas-phase catalysis. Those clusters of Pt that do form on the surface tend to coarsen rather than dissolve upon oxidation.