Size dependence of the adsorption energy of CO on metal nanoparticles: a DFT search for the minimum value.

With a density functional theory method, we studied computationally the size dependence of adsorption properties of metal nanoparticles for CO as a probe on Pdn clusters with n = 13–116 atoms. For large particles, the values slowly decrease with cluster size from the asymptotic value for an (ideal) infinite surface. For clusters of 13–25 atoms, starting well above the asymptotic value, the adsorption energies drop quite steeply with increasing cluster size. These opposite trends meet in an intermediate size range, for clusters of 30–50 atoms, yielding the lowest adsorption energies. These computational results help to resolve a controversy on the size-dependent behavior of adsorption energies of metal nanoparticles.