Oxygen Adsorption on Hydrated Gold Cluster Anions:  Experiment and Theory

• Published in: Journal of the American Chemical Society Vol. 125; no. 27; pp. 8408 - 8414
• Main Authors: Wallace, William T, Wyrwas, Richard B, Whetten, Robert L, Mitrić, Roland, Bonačić-Koutecký, Vlasta
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 09-07-2003
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solid-gas interface; Surface physical chemistry; Inorganic adsorbate; Gold; Oxygen; Collisional activation; Ionic cluster; Adsorption energy; Coadsorption; Theoretical study; Transition metal; Experimental study; Time of flight mass spectroscopy; Gas solid adsorption; Metal cluster; Gas solid interface; Metallic adsorbent; Density functional method; Adsorption structure
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja034905z

The discovery that supported gold clusters act as highly efficient catalysts for low-temperature oxidation reactions has led to a great deal of work aimed at understanding the origins of the catalytic activity. Several studies have shown that the presence of trace moisture is required for the catalysts to function. Using near-atmospheric pressure flow reactor techniques, we have studied humidity and temperature effects on the reactivity of gas-phase gold cluster anions with O2. Near room temperature, the humid source produces abundant gold-hydroxy cluster anions, Au N OH-, and these have a reversed O2 adsorption activity:  Nonreactive bare gold clusters become active when in the form Au N OH-, while active bare clusters are inactive when −OH is bound. The binding energies for the stable structures obtained from density functional calculations confirm fully these findings. Moreover, the theory provides evidence that electron-transfer induced by the binding of a OH group enhances the reactivity toward molecular oxygen for odd anionic gold clusters and suppresses the reactivity for the even ones. The temperature dependence of O2 addition to Au3OH- and Au4 - indicates deviations from equilibrium control at temperatures below room temperature. The effects of humidity on gold cluster adsorption activity support the conclusion drawn for the mechanism of O2 adsorption on “dry” gold cluster anions and provides insight into the possible role of water in the enhanced activity of supported gold cluster catalysts.