Insights into the function of silver as an oxidation catalyst by ab initio, atomistic thermodynamics

Abstract

To help understand the high activity of silver as an oxidation catalyst, e.g., for the oxidation of ethylene to epoxide and the dehydrogenation of methanol to formaldehyde, the interaction and stability of oxygen species at the Ag(111) surface has been studied for a wide range of coverages. Through calculation of the free energy, as obtained from density-functional theory and taking into account the temperature and pressure via the oxygen chemical potential, we obtain the phase diagram of O/Ag(111). Our results reveal that a thin surface-oxide structure is most stable for the temperature and pressure range of ethylene epoxidation and we propose it (and possibly other similar structures) contains the species actuating the catalysis. For higher temperatures, low coverages of chemisorbed oxygen are most stable, which could also play a role in oxidation reactions. For temperatures greater than about 775 K there are no stable oxygen species, except for the possibility of O atoms adsorbed at under-coordinated surface sites Our calculations rule out thicker oxide-like structures, as well as bulk dissolved oxygen and molecular ozone-like species, as playing a role in the oxidation reactions.

15 pages including 9 figures, Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.html

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Cited by in corpus (4)

• Ab initio atomistic thermodynamics and statistical mechanics of surface properties and functions
• Experimental and theoretical study of oxygen adsorption structures on Ag(111)
• Oxygen dissociation on the C3N monolayer: A first-principles study
• How orbitals and oxidation states determine apparent topographies in scanning tunneling microscopy: the case of fluorine on silver surfaces