Abstract
The silver-catalyzed epoxidation of ethylene is a reaction of great technological importance and also represents one of the most challenging and thoroughly studied catalytic systems.
It was found that the catalytic activity and selectivity of polycrystalline Ag for the epoxidation and complete oxidation of ethylene can be affected in a pronounced and reversible manner by electrochemically supplying or removing oxygen ions O2- or Na+ to or from the silver catalyst surface in ZrO2 (8 mol%Y2O3) or β″-Al2O3 solid electrolyte cell reactors and in the presence or absence of traces of chlorinated hydrocarbons in the gas phase.
The steady-state changes in catalytic rates of formation of C2H4O and CO2 are typically 10 to 100 times larger than the corresponding rate of ion transport to or from the catalyst surface, i.e., the reaction exhibits the effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) or “Electrochemical Promotion”. The selectivity to C2H4O can be very significantly altered, relative to open circuit conditions.
Under fuel rich conditions, temperatures near 250°C and in the presence of traces of 1,2-C2H4Cl2 in the gas phase selectivity values as high as 88% can be obtained, well above the ones reported in the open literature.
The observed phenomena are discussed and interpreted within the framework of previous NEMCA studies and the currently prevailing ideas regarding the mechanism of ethylene epoxidation.
Similar content being viewed by others
7. References
R.A. van Santen and H.P.C.E. Kuipers, Adv. Catal.35, 265 (1987)
W.M.H. Sachtler, C. Backx and R.A. van Santen, Catal. Rev.-Sci. Eng.23, 127 (1981).
G. Rovida, F. Pratesi, and E. Ferroni, J. Catal.41, 140 (1976).
N.D. Spencer and R.M. Lambert, Chem. Phys. Lett.83, 388 (1981).
M. Kitson and R.M. Lambert, Surf. Sci.109, 60 (1981).
M. Kitson and R.M. Lambert, Surf. Sci.110, 205 (1981).
M. Peuckert, Surf. Sci.146, 329 (1984).
S.A. Tan, R.B. Grant and R.M. Lambert, J. Catal.106, 54 (1987).
C.T. Campbell, J. Catal.99, 28 (1986).
M. Dean and M. Bowker, J. Catal.115, 138 (1989).
R.B. Grant and R.M. Lambert, J. Catal.92, 364 (1985).
S.A. Tan, R.B. Grant and R.M. Lambert, J. Catal.104, 156 (1987).
J.T. Gleaves, A.G. Sault, R.J. Madix and J.R. Ebner, J. Catal.121, 202 (1990).
P.J. van den Hoek, E.J. Baerends and R.A. van Santen, J. Phys. Chem.93, 6469 (1989).
C.G. Vayenas, Solid State Ionics28–30, 1521 (1988).
M. Stoukides, Ind. Eng. Chem. Res.27, 1745 (1988).
C.G. Vayenas, S. Bebelis, I.V. Yentekakis and H.-G. Lintz, Catalysis Today11(3), 303, (1992).
C.G. Vayenas, S. Bebelis and S. Ladas, Nature (London)343, 625 (1990)
J. Pritchard, Nature343, 592 (1990)
I.V. Yentekakis and C.G. Vayenas, J. Catal.111, 170 (1988).
C.G. Vayenas, S. Bebelis and S. Neophytides, J. Phys. Chem.92, 5083 (1988).
S. Bebelis and C.G. Vayenas, J. Catal.118, 125 (1989).
S. Neophytides and C.G. Vayenas, J. Catal.118, 147 (1989).
C.G. Vayenas, S. Bebelis, S. Neophytides and I.V. Yentekakis, Appl. Phys.A49, 95 (1989).
C.G. Vayenas and S. Neophytides, J. Catal.127, 645 (1991).
C.G. Vayenas, S. Bebelis and M. Despotopoulou, J. Catal.128, 415 (1991).
C.G. Vayenas, S. Bebelis, I.V. Yentekakis, P. Tsiakaras and H. Karasali, Platinum Met. Rev.34, 122 (1990).
P. Tsiakaras and C.G. Vayenas, J. Catal.140, 53 (1993).
I.V. Yentekakis, G. Moggridge, C.G. Vayenas and R.M. Lambert, J. Catal.146, 292 (1994)
T.I. Politova, V.A. Sobyanin and V.D. Belyaev, React. Kinet. Catal. Lett.41(2), 321 (1990)
C.A. Cavalca, L. Larsen, C.G. Vayenas and G.L. Haller, J. Phys. Chem.97, 6115 (1993)
S. Bebelis and C.G. Vayenas, J. Catal.138, 588 (1992)
S. Ladas, S. Bebelis and C.G. Vayenas, Surf. Sci.251/252, 1062 (1991).
S. Ladas, S. Kennou, S. Bebelis and C.G. Vayenas, J. Phys. Chem.97, 8845 (1993)
M. Stoukides and C.G. Vayenas, J. Catal.70, 137 (1981)
M. Stoukides and C.G. Vayenas, J. Catal.69, 18 (1981)
I.V. Yentekakis and S. Bebelis, J. Catal.137, 278 (1992)
S. Bebelis and C.G. Vayenas, J. Catal.138, 570 (1992)
J. Hölzl and F.K. Schulte in “Solid Surface Physics”, Springer Verlag, Berlin 1979, pp. 1–150.
B. Krüger and C. Benndorf, Surf. Sci.178, 704 (1986)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Karavasilis, C., Bebelis, S. & Vayenas, C.G. Selectivity maximization of ethylene epoxidation via NEMCA with zirconia and β″-Al2O3 solid electrolytes. Ionics 1, 85–91 (1995). https://doi.org/10.1007/BF02426013
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF02426013