Hydrogen adsorption on Pd-containing Au(111) bimetallic surfaces.

Configurations of different Pd-containing Au(111) bimetallic surfaces with Pd substituents varying from one to three atoms have been studied using density functional theory. The stability of the so-formed Pd monomers, dimers or trimers in the surface and subsurface layers of a Au(111)-(3 x 3) unit cell and their influence on the adsorption of hydrogen have been investigated. We find that before hydrogen adsorption the surface prefers to form Pd monomers over dimers or trimers located in subsurface positions, which is in agreement with experimental observations. However, adsorption of atomic hydrogen reverses this trend, leading to a stabilization of Pd trimers over dimers or monomers all located in the surface layer. Also, the binding energies of two or three hydrogen atoms on clean Au(111) and selected PdAu(111) ensembles have been determined. While pure Au(111) is not able to promote hydrogen splitting, after substitution of surface atoms with Pd the adsorption energy becomes sufficiently high for this activation.