Solvation of Palladium Clusters in an Ionic Liquid: A QM/MM Molecular Dynamics Study

The mechanism of solvation and stabilization of palladium nanoparticles in the 1,3-dimethylimidazolium tetrafluoroborate ionic liquid (IL) has been studied using a combination of density functional theory and molecular dynamics (MD) simulations-with hybrid quantum mechanics/molecular mechanical (QM/MM) potentials. It is shown that the IL induces a strong polarization in Pd-6 and Pd-19 clusters, which were taken as computationally tractable models of palladium nanoparticles. The clusters have large induced dipole moments and, as a result, interact strongly with the IL. MD simulations demonstrate an accumulation of the IL layer of high density and a negative charge around the Pd-6 and Pd-19 clusters as a result of interactions with the anions of the IL. A single palladium atom does not show any noticeable preference for the positive or negative ions and interacts only very weakly with the IL, which can, to some extent, protect the palladium atom from the energetically favorable process of aggregation into Pd clusters only sterically.