How Adsorbed Oxygen Atoms Inhibit Hydrogen Dissociation on Tungsten Surfaces.

Area of Science:

• Surface Science
• Physical Chemistry
• Computational Materials Science

Background:

• Hydrogen molecule (H2) dissociation on metal surfaces is crucial for many chemical processes.
• Tungsten (W) is a known catalyst for H2 dissociation, but surface contaminants can alter its reactivity.
• The effect of oxygen (O) adsorbates on H2 dissociation on W(110) requires atomic-scale understanding.

Purpose of the Study:

• To investigate the influence of adsorbed oxygen atoms on the dissociation of hydrogen molecules on a W(110) surface.
• To rationalize the observed inhibition of H2 dissociation at the atomic level using theoretical methods.
• To determine the role of oxygen coverage in modulating the H2 dissociation reaction dynamics.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Ab initio molecular dynamics (AIMD) simulations.
• Calculation of reaction probabilities for H2 with kinetic energies below 300 meV at varying O coverages.

Main Results:

• Adsorbed oxygen atoms act as repulsive centers, significantly inhibiting H2 dissociation.
• Oxygen atoms modulate the dynamics of impinging H2 molecules by closing accessible dissociation pathways.
• H2 dissociation is completely absent at an oxygen coverage of half a monolayer, consistent with experimental data.

Conclusions:

• The inhibitory effect of oxygen on W(110) goes beyond simple site blocking.
• Adsorbed oxygen forms a 'chemical shield' that prevents H2 molecules from approaching and dissociating.
• This study provides atomic-scale insights into adsorbate-mediated reactivity on catalytic surfaces.