Noble-Metal-Free Single-Atom Catalysts CuAl₄O_7–9 ⁻ for CO Oxidation by O₂

The single copper atom doped clusters CuAl₄O_7–9 ⁻ can catalyze CO oxidation by O₂. The CuAl₄O_7–9 ⁻ 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 CuAl₄O₉CO⁻ is much more reactive than CuAl₄O₉ ⁻ in the reaction with CO to generate CO₂. One adsorbed CO is crucial to stabilize Cu of CuAl₄O₉ ⁻ 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.