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Why silver is the unique catalyst for ethylene epoxidation
Article in Journal of Catalysis · December 2011
DOI: 10.1016/j.jcat.2011.08.004
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M. Oluş Özbek
Isik Onal
Gebze Technical University
Middle East Technical University
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Rutger van Santen
Eindhoven University of Technology
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Why silver is the unique catalyst for ethylene
epoxidation
M.O. Ozbek, I. Onal, R.A. van Santen
Journal of Catalysis
Volume 284, Issue 2, 1 December 2011, Pages 230-235
https://doi.org/10.1016/j.jcat.2011.08.004
https://www.sciencedirect.com/science/article/pii/S0021951711002466
The activities of Cu2O(0 0 1), Ag2O(0 0 1), and Au2O(0 0 1) surfaces for direct ethylene epoxidation and alternative paths
for EO isomerization are studied. Among these three oxide surfaces, only Ag2O(0 0 1) surface enables direct path
without a barrier. Au2O cannot regenerate surface oxygen, and overall reaction on Cu2O is endothermic. Furthermore,
ring opening of ethylene oxide (EO) and subsequent acetaldehyde (AA) formation on Cu2O is more favorable than EO
desorption. Ethylene adsorption on an oxygen vacancy results in the oxametallacycle (OMC) formation, which causes AA
formation and reduces EO selectivity. Cl adsorption removes these surface vacant sites and hence prevents the
formation of the OMC intermediate.
The difference in selectivity of ethylene epoxidation of Ag, Cu, and Au relates to the different reactivity of their oxidized
surfaces. Au2O is predicted to have the highest selectivity for ethylene oxide (EO) formation; however, catalytically it
cannot be applied because O2 will not regenerate the oxide. Cu2O is found to activate ring opening EO with subsequent
acetaldehyde formation. The latter barrier is higher than the desorption energy of EO on Ag2O.
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