Au7-: A fluxional catalyst for CO oxidation

Gold nano-clusters are well known to catalyze numerous reactions involving epoxidation, hydrogenation/reduction, CO oxidation, C-C bond formation etc. CO oxidation is particularly important due to its enormous environmental impacts. A full understanding of mechanistic details of the CO oxidation on Au surfaces is still lacking in the cluster literature. However according to some recent studies CO adsorption on gold catalysts is believed to be the key step in the entire process and therefore needs to be explored extensively. The CO adsorbed on the gold surface was shown to prefer corner sites on robust nano-structures. As an example we can illustrate the case of anionic gold hexamer (Au ₆ ^-) where three CO bind at the three well defined corners one at a time. The question is, whether this is a universal fact for small sized Au clusters or we are yet to find a more fluxional gold skeleton which can change its structure upon CO adsorption. To answer this we report a joint photo-electron spectroscopy (PES) and density functional theory (DFT) investigation of CO adsorption onto a small-sized anionic gold cluster, Au ₇ ^-. We found both experimentally and theoretically that upon one CO adsorption, the structures of two well known isomers of Au ₇ ^- were completely changed and generated a unique isomer for COAu ₇ ^-. The two or more CO bound isomers are even more interesting and unprecedented 3 dimensional structures emerged out for (CO) ₂Au ₇ ^- and (CO) ₃Au ₇ ^- along with their 2 dimensional counterparts.