Low-Temperature Cluster Catalysis

Ken Judai, Stéphane Abbet, Anke S. Wörz, Ulrich Heiz, Claude R. Henry

Research output: Contribution to journalArticlepeer-review

156 Scopus citations

Abstract

Free and supported metal clusters reveal unique chemical and physical properties, which vary as a function of size as each cluster possesses a characteristic electron confinement. Several previous experimental results showed that the outcome of a given chemical reaction can be controlled by tuning the cluster size. However, none of the examples indicate that clusters prepared in the gas phase and then deposited on a support material are indeed catalytically active over several reaction cycles nor that their catalytic properties remain constant during such a catalytic process. In this work we report turn-over frequencies (TOF) for Pdn (n = 4, 8, 30) clusters using pulsed molecular beam experiments. The obtained results illustrate that the catalytic reactivity for the NO reduction by CO (CO + NO → 1/2N 2 + CO2) is indeed a function of cluster size and that the measured TOF remain constant at a given temperature. More interestingly, the temperature of maximal reactivity is at least 100 K lower than observed for palladium nanoparticles or single crystals. One reason for this surprising observation is the character of the binding sites of these small clusters: N2 forms already at relatively low temperatures (400 and 450 K) and therefore poisoning by adsorbed nitrogen adatoms is prevented. Thus, small clusters not only open the possibility of tuning a catalytic process by changing cluster size, but also of catalyzing chemical reactions at low temperatures.

Original languageEnglish
Pages (from-to)2732-2737
Number of pages6
JournalJournal of the American Chemical Society
Volume126
Issue number9
DOIs
StatePublished - 10 Mar 2004
Externally publishedYes

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