RESUMEN
The single copper atom doped clusters CuAl4 O7-9 - can catalyze CO oxidation by O2 . The CuAl4 O7-9 - clusters are the first group of experimentally identified noble-metal free single atom catalysts for such a prototypical reaction. The reactions were characterized by mass spectrometry and density functional theory calculations. The CuAl4 O9 CO- is much more reactive than CuAl4 O9 - in the reaction with CO to generate CO2 . One adsorbed CO is crucial to stabilize Cu of CuAl4 O9 - around +I oxidation state and promote the oxidation of another CO. The widely emphasized correlation between the catalytic reactivity of CO oxidation and Cu oxidation state can be understood at the strictly molecular level. The remarkable difference between Cu catalysis and noble-metal catalysis was discussed.