| Worldwide interest was raised by the discovery that gold could engage in catalytic activities. Previously viewed as essentially inert, it was found that small gold clusters highly dispersed on metal oxide substrates were active for reactions such as low-temperature oxidation of carbon monoxide, hydrogenation, and reduction of nitrogen oxides, among others. This discovery led to many studies on different forms of these systems, a common finding of which was that the catalytic activity was closely tied to the size of the gold clusters. However, a definitive understanding of the active species of the supported gold catalysts has remained a mystery. Therefore, studies on the gas-phase gold cluster species in the absence of the support material were necessary in order to indisputably determine whether the gold clusters or the support material, or a combination of the two, produce the catalytic activity.; This thesis concentrates on the study of gas-phase gold cluster anions with reactants that have been studied on the supported cluster catalysts. Molecular oxygen (important for oxygen-atom transfer reactions) is found to adsorb as a superoxo species, resulting from electron transfer from the gold cluster anions. Combined with CO adsorption, in which highly size-dependent adsorption and saturation characteristics are observed, this O2 adsorption activity provides insight into the CO oxidation processes seen on the supported gold catalysts. Surprisingly, the presence of moisture was found to allow adsorption of CO and O2 on previously inactive clusters. When introduced together, the coadsorption properties of these two reactants are seen to be, in many cases, cooperative, and, for some of the clusters, lead to the loss of carbon dioxide, the result of CO oxidation. |
