Impact of surface arrangement and composition on ethylene adsorption over Pd–Ag surface alloys: a computational study

Abstract

The adsorption of ethylene on three low-index Pd–Ag bimetallic surfaces, which are the (111), (100), and (110) facets, is investigated using gradient-corrected periodic density functional calculations with dispersion correction. The surfaces have been modeled by 5 layers of Pd atoms and different Ag atomic concentrations, allowing us to study ethylene adsorption from 100% Pd to 25% Pd on the surfaces. The adsorption energy and the geometry have been computed for different adsorption sites (on top of a Pd or bridging two Pd atoms) for different facets and Ag atomic concentrations. For bare Pd surfaces and their surface alloys, the bridge site is always found to be more stable than any other site. For the surface alloys, the local density of states, charges of ethylene and Pd atom, and differential electron density have been investigated to illustrate the importance of ligand and ensemble effects of the guest metal Ag atoms. The adsorption is weakened because of the ensemble effect when the surface Ag atomic concentration increases. The amount of electrons transferred to the ethylene molecules from the surface increases slightly when the concentration of the surface atomic Ag increases. The ligand effect becomes more significant when the surface is closer, and its effect is not the same for different surface facets.