Alkali‐promoted gas adsorption and surface reactions on metals

Alkali metals adsorbed on transition metal surfaces do not only change the electronic properties of these metals but alter also their chemical reactivity. This effect is well known in heterogeneous catalysis as the promotion of metallic catalysts by alkali additives. The more fundamental physics of this effect is being studied by applying surface spectroscopies to coadsorbed layers of alkali and gas molecules (e.g., O2, N2, CO, NO) on well defined transition metal surfaces. These studies show that the adsorbed alkali causes the transfer of additional electronic charge into certain molecular orbitals of the adsorbed molecules. This electron transfer may weaken or strengthen the metal–adsorbate or intramolecular bonds. In some cases the dissociation of the adsorbed molecule occurs. Heterogeneous surface reactions on these alkali promoted samples show significant changes in both the surface composition of the catalyst and the gaseous product spectrum. Examples for this effect are given in connection with a s...