Observing the oxidation of platinum

Despite its importance in oxidation catalysis, the active phase of Pt remains uncertain, even for the Pt(111) single-crystal surface. Here, using a ReactorSTM, the catalytically relevant structures are identified as two surface oxides, different from bulk α-PtO₂, previously observed. They are constructed from expanded oxide rows with a lattice constant close to that of α-PtO₂, either assembling into spoked wheels, 1-5 bar O₂, or closely packed in parallel lines, above 2.2 bar. Both are only ordered at elevated temperatures (400-500 K). The triangular oxide can also form on the square lattice of Pt(100). Under NO and CO oxidation conditions, similar features are observed. Furthermore, both oxides are unstable outside the O₂ atmosphere, indicating the presence of active O atoms, crucial for oxidation catalysts.