Abstract :
The properties of Cs overlayers on silver supported catalysts for ethylene epoxidation and on Ag(1 11) single crystal have
been studied by surface science techniques (XPS, TPD, TPRS) and by measurement of specific catalytic activity. It has been
shown that depending on the mean size of the supported Ag particles and the treatment by reaction mixture three different
types of surface complexes can be produced on the surface of supported catalysts. A comparison of their spectroscopic
characteristics with those for Cs-0 overlayers on Ag(1 1 1) surface indicates that at least two of them are located on silver
particles and are common both for supported and bulk silver. The properties of the Cs-0 complex characterized by the
Cs3d,, line with BE = 724.2 eV enable us to assign it to surface Cs oxide. It does not take a direct part in the stage of
ethylene oxide formation. Unlike Cs oxide, the Cs-0 complex characterized by the Cs3d,, line with BE = 725.0 eV seems
to be involved in the surface centers active in ethylene epoxidation. However, additional studies are necessary to elucidate its
structure. The influence of both Cs-0 surface complexes on silver catalytic action is discussed in the context of possible
mechanisms for ethylene epoxidation.
