Defective NiO as a Stabilizer for Au Single-Atom Catalysts

Single-atom catalysts show outstanding catalytic activity owing to their different electronic and structural properties from those of nanoparticulate catalysts. For Au single-atom catalysts, however, metal oxides that can stabilize a single atomic state are still limited and the stabilizing effect is not well known. Here, we report Au single-atom catalysts supported on NiO (Au1/NiO), their structural features, and their catalytic properties. Atomic Au was dispersed on the surface of NiO with Ni vacancy sites. The formation of Au single-atom sites was more favorable on an NiO surface with Ni vacancy sites than on a clean NiO surface. The Au single atoms were cationic, and their charge states depended on the crystal facets [Au3+-like on NiO(100); Au+-like on NiO(110)]. The turnover frequency (TOF) of 0.011 wt % Au1/NiO for CO oxidation (0.41 s–1) was higher than the TOFs of nanoparticulate Au catalysts supported on NiO (0.033 s–1) at room temperature. Au1/NiO showed a high catalytic stability (120 °C, 120 h) to CO oxidation reaction.