Mild activation of CeO2-supported gold nanoclusters and insight into the catalytic behavior in CO oxidation

Abstract

We report a new activation method and insight into the catalytic behavior of a CeO₂-supported, atomically precise Au₁₄₄(SR)₆₀ nanocluster catalyst (where thiolate –SR = –SCH₂CH₂Ph) for CO oxidation. An important finding is that the activation of the catalyst is closely related to the production of active oxygen species on CeO₂, rather than ligand removal of the Au₁₄₄(SR)₆₀ clusters. A mild O₂ pretreatment (at 80 °C) can activate the catalyst, and the addition of reductive gases (CO or H₂) can enhance the activation effects of O₂ pretreatment via a redox cycle in which CO could reduce the surface of CeO₂ to produce oxygen vacancies—which then adsorb and activate O₂ to produce more active oxygen species. The CO/O₂ pulse experiments confirm that CO is adsorbed on the cluster catalyst even with ligands on, and active oxygen species present on the surface of the pretreated catalyst reacts with CO pulses to generate CO₂. The Au₁₄₄(SR)₆₀/CeO₂ exhibits high CO oxidation activity at 80 °C without the removal of thiolate ligands. The surface lattice-oxygen of the support CeO₂ possibly participates in the oxidation of CO over the Au₁₄₄(SR)₆₀/CeO₂ catalyst.