Coadsorption of CO and O2 on small free gold cluster anions at cryogenic temperatures: Model complexes for catalytic CO oxidation

Abstract

The cluster ions Au_n(CO)_m(O₂)_u⁻ (n = 2,3; m = 1, u = 1,2) are successfully synthesized via coadsorption of oxygen and carbon monoxide onto mass-selected gold clusters inside a temperature controlled ion trap at 100 K. The investigated gold clusters Au_1–3⁻ show a significant size dependence in the reactivity toward oxygen and carbon monoxide. Whereas no reaction products are detected for the monomer ion, simultaneous adsorption of CO and O₂ onto the dimer leads to the formation of Au₂(CO)(O₂)⁻ which is regarded as a model complex to study the mechanism of catalytic CO oxidation on gold clusters. In the case of Au₃⁻ the conditioning of the cluster by CO preadsorption is found essential to enable O₂ coadsorption.