Is gold actor or spectator in the reaction of small AunPdm+ clusters with O2?*
Institute of Surface Chemistry and Catalysis, University of Ulm, Albert-Einstein-Allee 47, 89069 Ulm, Germany
Received: 10 October 2012
Received in final form: 14 November 2012
Published online: 5 February 2013
The reactivity of free binary gold-palladium clusters (AuPd2+, Au2Pd+, Au2Pd2+, and Au2Pd3+) toward molecular oxygen was investigated in an ion trap experiment under multi-collision conditions and compared to the reactivities of bare Aun+ and Pdm+ (n, m = 2 − 5) clusters. Reaction kinetics measurements revealed that the reaction rate is mainly determined by the number of palladium atoms in the clusters and only weakly influenced by additional gold atoms. The same holds true for the observed reaction product distributions. Most interestingly, the most reactive cluster ions Pd3+, Au2Pd3+, and Pd5+ exhibit a strong preference to form tetroxide products, AunPdmO4+. In addition, employing temperature dependent mass spectrometry, a second adsorption species consisting of several weakly bound oxygen molecules was identified for all investigated palladium containing clusters which is, however, only formed at cryogenic temperatures. All these observations suggest that the gold atoms largely act upon a spectator role in the reaction of the binary clusters. Nevertheless, a rough estimation of the relative O2 binding energies via statistical rate theory indicates that the addition of gold to the Pdn+ clusters decreases the O2-cluster interaction strength, although the reaction rate stays constant. This effect in the binary clusters may be of importance to a potential activation and dissociation of the adsorbed O2 molecules.
Key words: Topical issue: ISSPIC 16 - 16th International Symposium on Small Particles and Inorganic Clusters. Guest editors: Kristiaan Temst, Margriet J. Van Bael, Ewald Janssens, H.-G. Boyen and Françoise Remacle
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag 2013