Steps on Pt stereodynamically filter sticking of O₂

Area of Science:

• Surface science
• Heterogeneous catalysis
• Chemical dynamics

Background:

• Low coordinated sites on catalytic surfaces are known to enhance reactivity.
• The dynamical processes governing this enhanced reactivity are not well understood.
• Understanding these processes is crucial for designing more efficient catalysts.

Purpose of the Study:

• To investigate the reactivity of oxygen molecules (O2) impinging on platinum surfaces.
• To elucidate the role of step edges on (111) terraces in enhancing O2 sticking.
• To resolve the dynamical processes and stereodynamics involved in O2 chemisorption and dissociation.

Main Methods:

• Utilized two independent experimental approaches to study O2-Pt interactions.
• Analyzed the dependence of sticking probability on step density and step type.
• Investigated the influence of O2 molecular alignment on sticking and dissociation at different incident energies.

Main Results:

• At low incident energies, O2 trapping into a physisorbed state precedes chemisorption and dissociation, linearly dependent on step density.
• At higher impact energies, direct molecular chemisorption occurs on both terraces and step edges.
• Step edges exhibit a preference for O2 molecules impacting with their internuclear axis parallel to the edge, unlike terraces.

Conclusions:

• Step edges play a crucial, twofold role in controlling O2 sticking and dissociation on platinum.
• Stereodynamical filtering at step edges dictates the efficiency of O2 chemisorption and dissociation.
• The findings provide fundamental insights into the dynamics of gas-surface interactions at catalytically active sites.