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Ab initio multireference configuration-interaction study of hydrogen molecule activation by Cs-promoted Pt clusters
J I Benitez1, S Castillo, E Poulain
1Area de Fisica Atómica y Molecular Aplicada, CBI, UAM-Azcapotzalco, Avonida San Pablo No. 180, Colonia Reynosa-Tamaulipas, Azcapotzalco, Mexico Distrito Federal, 02200 Mexico.
The Journal of Chemical Physics
|January 21, 2006
Summary
This study investigates hydrogen (H2) adsorption on cesium-platinum (Cs/Pt) clusters. Lower Cs/Pt ratios activate H2 similarly to platinum (Pt4), while higher ratios introduce activation barriers, altering H2 adsorption behavior.
Area of Science:
- Computational chemistry
- Materials science
- Surface science
Background:
- Understanding hydrogen adsorption on metal clusters is crucial for catalysis.
- Cesium-platinum (Cs/Pt) alloys offer tunable electronic properties for potential catalytic applications.
- Investigating the role of composition in H2 interaction with bcc (111) clusters.
Purpose of the Study:
- To explore the adsorption of H2 molecules on Cs_nPt_(5-n) bcc (111) clusters with varying Cs/Pt ratios (20%, 40%, 80%).
- To compare the H2 adsorption behavior of these clusters with pure Pt4 clusters.
- To elucidate the influence of cesium on the electronic structure and H2 activation of Pt clusters.
Main Methods:
- Ab initio multiconfigurational self-consistent field (MCSCF) calculations.
- Multireference configuration-interaction (MRCI) variational and perturbative methods.
- Geometry optimization for ground and excited states of H2 interaction with clusters.
Main Results:
- Cs/Pt clusters with 20% and 40% Cs/Pt ratios (CsPt4 and Cs2Pt3) capture and activate H2, similar to Pt4, with no activation barriers.
- H2 capture distances were comparable or smaller, and H-H bond dissociation distances were larger than for Pt4.
- The Cs4Pt cluster (80% Cs/Pt) also captures and activates H2 but exhibits different behavior, featuring a smaller capture distance after overcoming an activation barrier.
- No hydrogen absorption into the clusters was observed, only H2 adsorption.
Conclusions:
- The electronic properties and H2 adsorption behavior of Pt clusters are significantly modified by cesium doping.
- Lower Cs concentrations (20-40%) enhance H2 activation without barriers, suggesting potential catalytic activity.
- Higher Cs concentrations (80%) alter the adsorption mechanism, introducing an activation barrier, which may impact catalytic efficiency.
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