Density Functional Theory Investigation on the Nucleation and Growth of Small Palladium Clusters on a Hyper-Cross-Linked Polystyrene Matrix

Abstract

Density Functional Theory calculations were employed to investigate the nucleation and growth of small palladium clusters, up to Pd 9 , into a microcavity of the porous hypercrosslinked polystyrene (HPS). The geometries and the electronic structures of the palladium clusters inside the HPS cavity, following the one-by-one atom addition, are affected by a counterbalance between the Pd-phenyl (Pd-F) and Pd-Pd interactions. The analysis performed on energetics, cavity distortions and cluster geometries indeed suggest that the cluster growing is dominated by the Pd-F interactions up to the formation of Pd 4 aggregates, while the metal-metal interactions are actually ruling the growth of the larger clusters. The elasticity of the hypercrosslinked polystyrene matrix plays also an important role in the cluster development processes.

α-d-Glucopyranose Adsorption on a Pd30 Cluster Supported on Boron Nitride Nanotube

“…A Pd 30 cluster was chosen to model the metal catalyst whereas a (12,12) armchair single walled nanotube was chosen to mimic the BNNT support. The metallic fragment, cut out from the fcc bulk Pd structure, was purposely shaped so as to expose both the (111) and (100) planes [10,29].…”

“…Molecular mechanics employing the Universal Force Field (UFF) [31] was used as the low level method in the ONIOM prescription, while DFT was selected for the high level. The exchange-correlation functional chosen is the hybrid Coulomb-attenuated CAM-B3LYP [39]; this was joined with the Los Alamos LANL2 effective core potential for the Pd atoms, with the corresponding double-f valence basis set, and the dunning D95V basis set for B, N, C, O and H. Full geometry relaxation was carried out on the systems resulting from the adsorption on the BNNT of the Pd 30 cluster and of a-D-glucopyranose on Pd 30 /BNNT. The adsorption energy of a Pd 30 cluster on the BNNT was obtained through the general formula:…”

“…where E Pd/BN is the total energy of the supported cluster system, E BN the energy of the pristine BNNT support fragment and E Pd the energy of the isolated Pd 30 cluster. The adsorption energy of the a-D-glucopyranose on the supported Pd 30 cluster was conversely obtained through the general formula: BNNT system and E G the energy of the isolated a-Dglucopyranose.…”

“…SMSI, firstly introduced by Tauster [33], thanks to the improvement of usable experimental techniques and to the synergy of experiments and computational simulations, has been widely investigated and discussed during the last 25 years [4,25,36,38]. It seems, out of any doubt, that the electronic effects play a crucial role in determining the activity of supported metal particles [5,26,28,30,37], also when the latter are not so strongly adsorbed on the support. The wide majority of the metal/support interaction studies deals usually with metal oxides, such as titania and alumina, but recently new layered and tubular materials have started to draw more interest.…”

“…In order to deepen the topics above, a computational study addressed to simulate the adsorption of a-D-glucopyranose molecule on a model heterogeneous catalyst formed by a Pd 30 cluster supported on a BNNT surface, is presented. By the use of a properly shaped Pd cluster it was possible to evaluate the influence of different low Millerindex planes upon adsorption.…”