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 Pd(n) 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.