On the Role of Subsurface Oxygen and Ethylenedioxy in Ethylene Epoxidation on Silver

The thermochemical stability of various three-component phases containing oxygen, ethylene, and Ag(111) was determined as a function of oxygen and ethylene chemical potential using periodic, self-consistent density functional theory calculations. Ethylenedioxy is stable over a wide range of conditions, although its formation may be kinetically hindered in some cases. Ethylene and ethylene-containing oxametallacycles are also found to be stable over a reasonably large range of chemical potentials, particularly if ethylenedioxy formation is neglected. Furthermore, subsurface oxygen (O sb ) is seen to be present in the three-component systems at a variety of conditions; minimum energy path calculations performed at a coverage of 1/2 ML O sb suggest that this species may actually increase the reaction barrier for ring closure leading to ethylene oxide elimination from Ag(111).