Synergy between Pd and Au in a Pd-Au(100) bimetallic surface for the water gas shift reaction: a DFT study

Density functional theory calculations were performed to model a reaction relevant bimetallic surface and study the water gas shift reaction. It was found that under vacuum, Pd prefers to stay in the bulk due to more negative formation energies. However, the strong CO-phillic nature of Pd makes the surface segregation of Pd a relevant process, with segregation energy increasing linearly with the number of Pd atoms segregated. Therefore, it is expected that under CO rich environments, Pd covered Au could be the relevant structure of a Pd-Au bimetallic surface. The surface is highly active for water dissociation and subsequent reactions leading to CO oxidation. Based on our results, it is predictable that the adsorbed carboxyl pathway will dominate the kinetics. Our results show that H-2 adsorbs dissociatively on this surface, which opens new channels for research regarding the candidature of such model surfaces as hydrogen storage materials. An important consequence of our results is that they may be useful in the selective development of alloy surfaces keeping adsorbate induced surface segregations in view.