Atomic engineering of platinum alloy surfaces.

Area of Science:

• Materials Science
• Catalysis
• Surface Chemistry

Background:

• Minimizing expensive platinum group metal (PGM) loading in heterogeneous catalysis is crucial without compromising efficiency.
• Atomic-scale understanding of catalyst changes during manufacture and operation can lead to optimized nano-engineered catalysts.

Purpose of the Study:

• Investigate the oxidation behavior of a platinum-31 at% palladium (Pt-Pd) alloy.
• Determine how oxidation temperature influences the surface structure and composition of Pt-Pd alloys.
• Compare the oxidation trends of Pt-Pd alloys with other binary alloys like Pt-Rh and Pd-Rh.

Main Methods:

• Atom probe tomography (APT) was used to analyze the oxidation behavior of a Pt-31 at% Pd alloy.
• Oxidation experiments were conducted across a temperature range of 673-1073 K.
• Comparative analysis with Pt-Rh and Pd-Rh alloys under identical conditions.

Main Results:

• Three distinct surface chemical structures were observed upon oxidation between 673-1073 K.
• At lower temperatures (673-773 K), the surface becomes enriched with palladium (Pd).
• At 873 K, a palladium oxide (PdO) layer forms, leaving a platinum-rich (Pt-rich) sublayer. Above 873 K, the surface switches to platinum enrichment, increasing with temperature.
• Pt-Pd alloys exhibit different oxidation trends compared to Pt-Rh and Pd-Rh alloys.

Conclusions:

• Oxidation temperature is a key parameter for tuning the surface composition of Pt-Pd nanoparticles.
• Controlled oxidation can create core-shell structures with either Pd-rich or Pt-rich surfaces.
• This provides a strategy for designing cost-effective and high-performance catalysts.