First-principles study of the origin of alkali promotion of reactivity of metal surfaces

Alkali metals are known as efficient promoters in heterogeneous catalysis but the nature of this phenomenon is as yet not understood. Our first principles calculations reveal a huge increase and delocalization of the isoelectronic reactivity index of Cu and Pd surfaces on alkali adsorption. We trace this phenomenon to an unusual feature in the surface potential formed by the adsorbate and propose it as a driving force for the "promotion effect". Our results also provide clues to some of the unusual optical properties of quantum wells formed when alkali adsorb on Cu surfaces.