ALKALI-METAL PROMOTERS AND CATALYSIS - A SINGLE-CRYSTAL INVESTIGATION OF ETHYLENE EPOXIDATION ON CS-DOPED AG(111)

Cs adsorbs on Ag(111) to form layers of relatively low atomic density, unlike the other alkalis, it does not significantly penetrate the Ag lattice. Multilayer growth proceeds by the Frank-van der Merwe mechanism, but oxygen chemisorption followed by heating drastically perturbs the structure of the alkali film; bare Ag sites are created, and there is evidence for the formation of a 'surface alloy'. The behavior of such cesiated surfaces in the selective and total oxidation of ethylene was investigated by two different approaches. Detailed molecular mechanisms are suggested.