Low-loaded platinum-group single-atom catalysts on CeO2 (M1/CeO2) were synthesized via high-temperature atom trapping (AT) and tested for the NO + CO reaction under dry and wet condition. The activity of these catalysts for NO+CO reaction follows the order Rh > Pd ≈ Ru > Pt > Ir. For Rh, Ru, and Pd single-atom catalysts, the N2O byproduct is formed but not clearly observed on Ir and Pt cases, which may result from the higher reaction temperature (> 200oC) required for Pt and Ir catalysts. The presence of water can promote the activity of these M1/CeO2 catalysts for NO + CO reaction. Under wet conditions, significant NH3 formation occurred during the reaction, which is due to the co-existence of water-gas-shift reaction on these catalysts. Compared with Pt, Pd and Ir, the Rh and Ru single-atom catalysts show higher selectivity to NH3 species, resulting from the more hydride species on the surface. Among all tested catalysts, Ru1/CeO2 shows the highest production of ammonia and highest CO conversion due to excellent water-gas-shift activity, whereas Pd1/CeO2 shows lowest ammonia production.