Effect of alkali metals on the interaction of O2 and CO with some transition-metal surfaces

The interactions of O2 and CO with alkali covered Ni, Ru, and Pt are reviewed with emphasis on the author's own studies. It is shown that the presence of alkalis changes the coadsorbates adsorption rates, heats of adsorption, and dissociative propensity, the strength of the effect depending on the alkali nature and coverage. The differences for the three substrates are interpreted comparing the properties of the clean surface. A detailed analysis of the coadsorbate--modifier interactions suggests that they depend on the adsorption state of the alkali species and the coadsorbate--substrate bond strength. Evidence of the formation of patches of ''surface complexes'' coexisting with the unperturbed surface is given and discussed in terms of strong direct alkali--coadsorbate interactions