Cluster Chemistry: Size-Dependent Reactivity Induced by Reverse Spill-Over

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• 作者：Martin A. Rö ; ttgen ; Stephane Abbet ; Ken Judai ; Jean-Marie Antonietti ; Anke S. Wö ; rz ; Matthias Arenz ; Claude R. Henry ; Ulrich Heiz
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：August 8, 2007
• 年：2007
• 卷：129
• 期：31
• 页码：9635 - 9639
• 全文大小：137K
• 年卷期：v.129,no.31(August 8, 2007)
• ISSN：1520-5126

文摘

In the present work, the CO oxidation rate on size-selected Pd clusters supported on thin MgOfilms is investigated in pulsed molecular beam experiments. By varying the cluster coverage independentof the cluster size, we were able to change the ratio of direct and diffusion flux (reverse spill-over) of COonto the cluster catalyst and thus probe the influence of reverse spill-over on the reaction rate for differentcluster sizes (Pd₈ and Pd₃₀). The experimental results show that the change in reaction rate as a functionof cluster coverage is different for Pd₈ and Pd₃₀. In order to explain these findings, the CO flux onto theclusters is modeled utilizing the collection zone model for the given experimental conditions. The resultsindicate that, for small clusters (Pd₈), the reaction probability of an impinging CO molecule is independentof whether it is supplied by diffusion or direct flux. By contrast, for larger clusters (Pd₃₀) a reduced reactionprobability is found for CO supplied by reverse spill-over compared to CO supplied by direct flux.