Multiple CO Oxidation Promoted by Au₂Dimers in Au₂TiO₄⁻Cluster Anions

Time-of-flight mass spectrometry experiments demonstrated that laser ablation generated and mass selected Au₂TiO₄⁻cluster anions can unexpectedly oxidize three CO molecules in an ion trap reactor. This is an improvement on the more commonly observed oxidation of at most two CO molecules by a doped cluster. Quantum chemistry calculations were performed to rationalize the reactions. The lowest energy isomer of Au₂TiO₄⁻contains a superoxide unit, the participation of which in CO oxidation can be promoted by the Au₂dimer. The Au₂dimer functions as a rather flexible electron reservoir in each CO oxidation step in terms of the release and storage of electrons to drive the dissociation of superoxide to peroxide and then to lattice oxygen atoms, which can be removed by reaction with CO molecules. This gas-phase study enriches our understanding toward the nature of reactive oxygen species involved in gold-catalyzed oxidation reactions.