Spurred by the recent demonstrations of the size- and support-dependent reactivity of supported gold clusters, here we present results on the coadsorption of CO and O2 on selected anionic gold clusters, AuN-, in the gas phase. O2 adsorbs in a binary (0,1) fashion as a one-electron acceptor on the AuN- clusters, with even-N clusters showing varying reactivity toward O2 adsorption, while odd-N clusters show no evidence of reactivity. CO shows a highly size-dependent reactivity for AuN- sizes from N = 4 to 19, but no adsorption on the gold dimer or trimer. When the gold clusters are exposed to both reactants, either simultaneously or sequentially, interesting effects have been observed. While the same rules pertaining to individual O2 or CO adsorption continue to apply, the preadsorption of one reactant on a cluster may lead to the increased reactivity of the cluster to the other reactant. Thus, the adsorbates are not competing for bonding sites (competitive coadsorption), but, instead, aid in the adsorption of one another (cooperative coadsorption). New peaks also arise in the mass spectrum of Au6- under CO and O2 coadsorption conditions, which can be attributed to the loss of a CO2 molecule (or molecules). By studying the relative amount of reaction, and relating it to the reaction time, it is found that the gas-phase Au6 anion is capable of oxidizing CO at a rate 100 times that reported for commercial or model gold catalysts.
ASJC Scopus subject areas
- Colloid and Surface Chemistry