On the Mechanism of the Reaction between Thiolate-Protected Gold Clusters and Molecular Oxygen: What is Activated?

Abstract

The various energy pathways of Au20(SCH3)16 oxidation were simulated in the gas phase and on a CeO2 surface at the density functional theory/Perdew–Burke–Ernzerhof (DFT/PBE) level. Due to the high stability and strong Au–S bonds of the protected cluster, there was no stable complex with oxygen. Alternative processes were considered: oxidation of staple (AuSCH3)x fragments and the cluster, in which one, two, and three thiolate ligands were removed (Au20(SCH3)16–x, x = 1–3). It was shown that peroxide and superoxide complexes formed only if the cluster fragments reacted with singlet oxygen. Oxygen was sufficiently absorbed on Au20(SCH3)16–x. The structures of Au20(SCH3)16 and Au20(SCH3)16–x on the CeOx surface were studied in detail. After deposition of the cluster on ceria, the thiolate ligands were lost. Oxygen was activated on Au20(SCH3)13/CeOx near the particle–support interface (the adsorption energy was −112 kJ/mol).