surface*

Single-atom catalysis of CO oxidation on metal-oxide surfaces is of paramount importance for greenhouse recycling, automotive catalysis, and beyond, but the atomic-scale mechanism is still sparse. Here, using scanning probe microscopy techniques, we show that charging single Au atoms on oxidized rutile TiO₂ surface, both positively and negatively, considerably promotes adsorption of CO. No CO adsorption is observed on neutral Au atoms. Two different CO adsorption geometries on Au atoms are identified. We demonstrate a full control over the redox state of adsorbed Au single atoms, the CO adsorption geometry and CO adsorption/desorption by the AFM tip. On charged Au atoms we activate Eley–Rideal oxidation reaction between CO and a neighboring oxygen adatom by the tip. Perhaps surprisingly, DFT methods fail to describe the adsorption system correctly. Our experimental results provide unprecedented control over and insights into the CO adsorption and suggest that the Au dual activity for CO oxidation after electron or hole attachment is the key ingredient also in photocatalysis under realistic conditions.