Collisional Activation of N2O Decomposition and CO Oxidation Reactions on Isolated Rhodium Clusters

The reactions of nitrous oxide decorated rhodium clusters, RhnN2O+ (n = 5, 6), have been studied by Fourier transform ion cyclotron resonance mass spectrometry. Collision induced dissociation with Ar is shown to lead to one of two processes; desorption of the intact N2O moiety (indicating molecular adsorption in the parent cluster) or N2O decomposition liberating molecular nitrogen with the latter becoming increasingly dominant at higher collision energies. Consistent with the results of earlier studies, which employed infrared excitation [Hermes, A. C.; et al. J. Phys. Chem. Lett. 2011, 2, 3053], Rh5ON2O+ is observed to behave qualitatively differently to Rh5N2O+ with decomposition of the nitrous oxide dominating the chemistry of the former. In other experiments, the reactivity of RhnN2O+ clusters with CO has been studied. Chemisorption of (CO)-C-13 is calculated to deposit ca. 2 eV into the parent cluster, initiating a range of chemical processes on the cluster surface, which are fit to a simple reaction mechanism. Clear differences are again observed in the reaction branching ratios for Rh5N2O+ and Rh6N2O+ parent cluster ions. For the n = 5 cluster, the combined N2O reduction/CO oxidation is the most significant reaction channel, while the n = 6 cluster preferentially is oxidized to Rh6O+ with loss of N-2 and CO. Even larger differences are observed in the reactions of the N2O decorated cluster oxides, RhnON2O+, for which more reaction possibilities arise. The results of all studies are discussed in relation to infrared driven processes on the same parent cluster species [Hamilton, S. M.; et al. J. Am. Chem. Soc. 2010, 132, 1448; J. Phys. Chem. A, 2011, 115, 2489].