Abstract
Large octahedral and cuboctahedral palladium clusters, ranging from
Pd55 to Pd146, have been investigated by means of all-electron relativistic
density functional calculations. Adsorption of CO molecules on the
(111) facets of these clusters was also studied. In particular, we
focused on the interaction of CO (a single molecule per facet) with
threefold hollow sites to inspect the variation of the calculated
adsorption parameters with cluster size. We considered how observables
calculated for that adsorption position on cluster facets relate
to adsorption properties of the corresponding site at the single
crystal surface Pd(111). We demonstrated for the first time that,
with three-dimensional cluster models proposed here, one can reach
cluster size convergence even for such a sensitive observable as
the adsorption energy on a metal surface. We also addressed size
effects on interatomic distances and the cohesive energy of bare
Pd nanoclusters whose structure was fully optimized under the imposed
Oh symmetry constraint. These quantities were found to correlate
linearly with the average coordination number and the inverse of
the cluster radius, respectively, allowing a rather accurate extrapolation
to the corresponding values of Pd bulk. Finally, we considered the
size convergence of adsorption properties of the optimized Pd clusters,
as probed by CO adsorption. We also outlined implications of using
these symmetric clusters for investigating adsorption and reactions
on oxide-supported nanoparticles of model Pd catalysts.
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