Eur. Phys. J. D (2013) 67: 19
https://doi.org/10.1140/epjd/e2012-30623-1

Regular Article

Is gold actor or spectator in the reaction of small Au_nPd_m⁺ clusters with O₂?^*

Institute of Surface Chemistry and Catalysis, University of Ulm, Albert-Einstein-Allee 47, 89069 Ulm, Germany

^a e-mail: thorsten.bernhardt@uni-ulm.de

Received: 10 October 2012
Received in final form: 14 November 2012
Published online: 5 February 2013

Abstract

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 Au_n⁺ and Pd_m⁺ (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, Au_nPd_mO₄⁺. 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 Pd_n⁺ 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.