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.

Pt-rich clusters can reversibly precipitate from, and dissolve into, a Pt-doped CaTiO3 perovskite support under reducing and oxidizing conditions, respectively. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging confirms that these clusters remain largely within the perovskite bulk.Figure optionsDownload high-quality image (184 K)Download as PowerPoint slideHighlights
► Powders and thin films of Pt-doped CaTiO3 were examined by HAADF-STEM.
► Reduction induces the precipitation of Pt-rich clusters from the CaTiO3 support.
► Oxidation induces re-dissolution of Pt-rich clusters into the CaTiO3 support.
► The formation of Pt-rich clusters is more facile than their re-dissolution.
► Re-dispersion in this system occurs mostly in the bulk rather than on the surface.