Activated adsorption of ethylene on atomic-oxygen-covered Ag(100) and Ag(210): Formation of an oxametallacycle

The activated adsorption of ethylene on atomic-oxygen-covered Ag(100) surface and on an open-type step edge thereon was studied using density-functional-theory. On perfect Ag(100), such adsorption results in the formation of an oxametallacycle (OMC), with an activation energy slightly larger than 0.3 eV. We find that this activation energy is only weakly dependent on the coverage of on-surface oxygen (for Theta <= 1/2 ML), whereas the OMC-surface interaction is substantially reduced at high oxygen coverage. Three types of OMCs have been identified on the (100) surface, which display similar. stability, and the transformation between them is facile with activation energies below 0.1 eV. We find that the presence of subsurface oxygen reduces the activation energy for ONIC formation and substantially increases the OMC-surface interaction. The reactivity of the step edge toward the OMC formation strongly depends on the local coverage of oxygen. Our calculations indicate that the relative stability of the OMC intermediate in ethylene epoxidation reaction is strongly affected by the coverage and configuration of chemisorbed oxygen.