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Adsorption and activation properties of precious metal clusters such as Ir, Pt, and Au toward NO were investigated by means of the density functional calculations. We focused on the geometrical features of model clusters such as the shape and the number of consisting atoms that could determine the ability for the adsorption and the activation of NO. We found that the order of the energetical stability of the adsorption states of NO can be described as Ir > Pt > Au. It depends on neither the shape of the pentaatomic clusters nor the number of atoms in the model clusters considered. The ability of the precious metal clusters for the activation of the N–O bond were also discussed from both vibrational and geometrical points of view. The substantial activation of the N–O bond was found on both the NO/Ir5 and the NO/Pt4 systems, indicating that the specific adsorption geometries enhance the ability for the activation of the N–O bond. These results indicate that the Ir cluster has the best properties for the adsorption and activation of NO.