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Cluster chemistry: size-dependent reactivity induced by reverse spill-over
Martin A Röttgen1, Stephane Abbet, Ken Judai
1Lehrstuhl für Physikalische Chemie I, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
Journal of the American Chemical Society
|July 10, 2007
Summary
The CO oxidation rate on palladium (Pd) clusters depends on CO molecule delivery. Reverse spill-over impacts smaller Pd(8) clusters differently than larger Pd(30) clusters, affecting reaction probability.
Area of Science:
- Heterogeneous catalysis
- Surface science
- Nanomaterials
Background:
- Understanding CO oxidation on supported metal clusters is crucial for catalysis.
- The role of CO diffusion (reverse spill-over) on reaction rates is not fully understood.
- Size-dependent catalytic activity of metal clusters is a key area of research.
Purpose of the Study:
- To investigate the CO oxidation rate on size-selected palladium (Pd) clusters.
- To determine the influence of reverse spill-over on catalytic activity for different Pd cluster sizes.
- To differentiate the reaction probability of CO supplied by direct flux versus diffusion.
Main Methods:
- Pulsed molecular beam experiments were used to study CO oxidation.
- Size-selected Pd clusters (Pd(8) and Pd(30)) supported on MgO films were employed.
- Cluster coverage was varied independently of cluster size to alter CO flux ratios.
- The collection zone model was utilized to simulate CO flux onto the clusters.
Main Results:
- The CO oxidation rate varied differently with cluster coverage for Pd(8) and Pd(30) clusters.
- For small Pd(8) clusters, reaction probability was independent of CO supply method (direct or diffusion).
- For larger Pd(30) clusters, CO supplied via reverse spill-over exhibited reduced reaction probability compared to direct flux.
Conclusions:
- Reverse spill-over significantly influences CO oxidation rates on supported Pd clusters.
- The effect of reverse spill-over on reaction probability is cluster size-dependent.
- Catalyst design should consider the impact of CO diffusion on reaction kinetics for optimal performance.
![Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F51444.jpg&w=3840&q=50)
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