Abstract
The interaction of Pd atoms and Pd-n (n = 4 and 6) clusters with the regular three-dimensional (3D) and layered 2D Silicalite-1 was investigated computationally. The interaction of Pd clusters with Silicalite-1 is driven by dispersion interactions, and has only a small electrostatic contribution, therefore, Pd clusters are preferably located inside the channel system of bulk Silicalite-1.
The Pd-6 cluster fits inside the main channel, where the density of framework atoms around the metal cluster is larger. The interaction of a single Pd atom with Silicalite-1 is stronger with dominant contributions coming from induction and electrostatic effects; isolated Pd atoms preferably bind in the vicinity of surface silanol on the external surface.
These conclusions are based on the calculations employing the periodic models of Silicalite-1 and DFT/CC correction scheme that accounts for the dispersion interactions. The DFT/CC approach provides a reliable description of the system based on CCSD(T) calculations for cluster models.
The comparison of different exchange-correlation functionals with and without dispersion correction is also shown. It can be concluded that commonly employed functionals underestimate the interaction between Pd-silica and adding the dispersion correction either empirical or non-local causes significant overestimation of the Pd-silica interaction energy.