Gold Atoms Supported on Gas-Phase Cerium Oxide Cluster Ions: Stable Stoichiometry and Reactivity with CO

The stability and reactivity of cationic gold-cerium oxide clusters, Au_mCe_nO_2n+x⁺ (m ≤ 4, n ≤ 7, -1 ≤ x ≤ 2), were examined experimentally and computationally. These clusters were generated by simultaneous laser ablation of gold and cerium oxide targets and analyzed by time-of-flight mass spectrometry combined with gas-phase temperature-programmed desorption. Stable compositions of gold-cerium oxide clusters were identified as Au_mCe_nO_2n⁺ and Au_mCe_nO_2n+1⁺ for m ≥ 1, containing one oxygen atom more than the stable gold-free cerium oxide clusters Ce_nO_2n-1⁺ and Ce_nO_2n⁺. In either case, the stable clusters mainly consisted of Ce⁴⁺ and O^2-, and the gold atoms had an oxidation state of +1. The reactivity of cerium oxide clusters toward CO was modified by gold atoms, which hindered CO oxidation while efficiently promoting its adsorption. According to density functional theory calculations, the oxygen-centered radical of cerium oxide clusters, considered to be the reactive site, was geometrically and electronically inactivated by gold atoms, which functioned as a CO adsorption site.