CO oxidation catalyzed by single gold atoms supported on aluminum oxide clusters

The single gold atom doped aluminum oxide clusters AuAl3O3(+), AuAl3O4(+), and AuAl3O5(+) have been prepared and mass-selected to react with CO, O2, and mixtures of CO and O2 in an ion trap reactor under thermal collision conditions. The reactions have been characterized by mass spectrometry with isotopic substitution ((16)O2 → (18)O2) and density functional theory calculations. The AuAl3O5(+) cluster can oxidize two CO molecules consecutively to form AuAl3O4(+) and then AuAl3O3(+), the latter of which can react with one O2 molecule to regenerate AuAl3O5(+). The AuAl3(16)O3(+) ions interact with a mixture of C(16)O and (18)O2 to produce the fully substituted (18)O species AuAl3(18)O3-5(+), which firmly identifies a catalytic cycle for CO oxidation by O2. The oxidation catalysis is driven by electron cycling primarily through making and breaking a gold-aluminum chemical bond. To the best of our knowledge, this is the first identification of catalytic CO oxidation by O2 mediated with gas-phase cluster catalysts with single-noble-metal atoms, which serves as an important step to understand single-atom catalysis at strictly a molecular level.