Observing the oxidation of platinum.

Area of Science:

• Surface science
• Heterogeneous catalysis
• Materials science

Background:

• The active phase of platinum (Pt) in oxidation catalysis is not well understood, even on well-defined surfaces like Pt(111).
• Previous studies have not identified the precise surface structures responsible for catalytic activity under reaction conditions.

Purpose of the Study:

• To identify the catalytically relevant surface structures of platinum under oxidation conditions.
• To characterize the structure and stability of these surface oxides.

Main Methods:

• Utilized a Reactor Scanning Tunneling Microscope (ReactorSTM) to observe platinum surfaces under controlled gas environments.
• Investigated platinum surfaces under varying oxygen pressures and temperatures (400-500 K).

Main Results:

• Identified two distinct surface oxide structures, different from bulk α-PtO₂, formed from expanded oxide rows.
• Observed these oxides assemble into 'spoked wheels' at 1-5 bar O₂ and 'parallel lines' above 2.2 bar O₂.
• Demonstrated that these oxide structures are only stable under O₂ atmosphere and at elevated temperatures, indicating the presence of active oxygen species.

Conclusions:

• The catalytically active phase of platinum involves specific surface oxides, not bulk platinum dioxide.
• These active structures require high oxygen pressure and elevated temperatures to form and remain stable.
• Future catalyst design and studies should consider these high-pressure, high-temperature surface phenomena for improved oxidation catalysis.