H2 saturation on palladium clusters.

Area of Science:

• Surface Science
• Computational Chemistry
• Materials Science

Background:

• Understanding hydrogen-metal interactions is crucial for catalysis and hydrogen storage.
• Palladium clusters are model systems for studying hydrogen adsorption and dissociation on metal surfaces.

Purpose of the Study:

• To investigate the interaction of palladium clusters (PdN, N=2-13) with hydrogen molecules (H2).
• To determine the maximum number of H2 molecules that can stably bind to PdN clusters at 0 K and 300 K.
• To explore the effect of molecular H2 coverage on dissociated hydrogen atom migration.

Main Methods:

• Density Functional Theory (DFT) using the hybrid PBE0 functional.
• Systematic sequential addition of H2 units to PdN clusters.
• Calculation of adsorption energies and Gibbs free energies to determine stable binding and saturation coverage.

Main Results:

• For small clusters (N=2-4), H2 dissociation occurs, with varying numbers of additional molecular H2 binding depending on temperature.
• For larger clusters (N=7, 13), increased H2 dissociation is observed, especially at 300 K, suggesting molecular H2 binding is less favorable.
• Molecular H2 coverage influences the migration barriers and stability of dissociated H atoms on Pd4 clusters.

Conclusions:

• At room temperature, larger palladium particles favor H2 dissociation over molecular adsorption.
• The degree of molecular H2 coverage significantly affects the behavior of dissociated hydrogen atoms on palladium surfaces.
• These findings have implications for catalytic processes and hydrogen storage applications involving palladium.