Island Formation on Pt/Pd(557) Surface Alloys in the Presence of Adsorbed CO: A Molecular Dynamics Study

Abstract

Stepped surfaces of bimetallic Pt/Pd alloys were exposed to a range of coverages of adsorbed carbon monoxide (CO) using molecular dynamics (MD) simulations. Metal–CO interactions for both metals were parametrized from experimental data and density functional theory (DFT) calculations, providing classical potentials that capture the atop binding preference on Pt and the hollow/bridge preference on Pd. The MD simulations indicate significant restructuring in the surface alloy, with Pt-rich islands forming on the Pd substrate within 60 ns. The time dependence of the surface domain sizes and the dynamics of nearest-neighbor metal populations suggest that multilayer Pt islands form more rapidly in the presence of adsorbed CO. We find that the different binding preference of CO adsorbed to the two metals can help explain the observed stabilization of the Pd surface structures as well as the roughening of the Pt step edges. Because the CO acts to lower the surface energy of the Pt, we conclude that the mechanism for accelerating Pt-island formation is kinetic in nature.