Size-selected, supported clusters: the interaction of carbon monoxide with nickel clusters |
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Authors: | U Heiz |
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Institution: | (1) Université de Lausanne, Institut de Physique Expérimentale, 1015 Lausanne, Switzerland (Fax: +41-21/692-3635, E-mail: Ulrich.Heiz@ipe.unil.ch), CH |
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Abstract: | We report on the size-dependent chemical reactivity of nickel clusters with up to 30 atoms. Monodispersed Ni30 clusters show a higher reactivity for CO dissociation than Ni11 and Ni20. Under our experimental conditions the smallest nickel clusters (Nix, x<4) produce nickelcarbonyl complexes. These results demonstrate that such small clusters are unique for catalytic reactions
not only due to their high surface-to-volume ratio but also essentially because of the distinctive properties of different
cluster sizes. In addition thermal desorption spectroscopy of CO shows that on average four molecules are weakly adsorbed
per Ni11 at saturation coverage. Using an isotopic mixture of 12CO and 13CO, infrared spectroscopy reveals the existence of a vibrational coupling interaction between the four COs. A semi-classical
model of interacting dipoles is applied to correlate the observed vibrational frequency shifts with the arrangement of the
COs on the cluster. This simple analysis favors a three-dimensional structure for the deposited clusters.
Received: 23 March 1998/Accepted: 25 August 1998 |
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Keywords: | PACS: 36 40 Jn 33 20 Ea |
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