Size-Dependence of Adsorption Properties of Metal Nanoparticles:A Density Functional Study on Palladium Nanoclusters

摘要

Interatomic distances in metal nanoparticles are reduced from their values in the bulk.We studied computationally how this size-dependent geometry change(from the bulk)relates to the size-dependence of other properties of large metal clusters,including their reactivity.For this purpose,using an all-electron scalar-relativistic densitgamma-functional approach,we calculated structures and binding energies for the example of CO adsorption on 3-fold hollow sites at the center of(111)facets of cuboctahedral nanoscale clusters Pd_n(n=55-260).The average nearest-neighbor Pd-Pd distance of optimized structures is 4-7 pm(2-3%)shorter than the extrapolated limit of the lateral distance within an infinite(111)surface.In consequence,the energy of CO adsorption on a cluster of ~100 atoms is ~15 kJ mol~(-1)smaller than the extrapolated limit.On the basis of these results,we suggest a strategy for modeling particles of larger size,e.g.of 1000 atoms and more,with the help of smaller model particles of up to ~300 atoms where one keeps the core of a model cluster fixed at the bulk structure and restricts the structure optimization to the outermost shell of cluster atoms.