NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF CATALYTIC ACTIVITY .10. ETHYLENE EPOXIDATION ON AG DEPOSITED ON STABILIZED ZRO2 IN THE PRESENCE OF CHLORINE MODERATORS
C. Karavasilis et al., NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF CATALYTIC ACTIVITY .10. ETHYLENE EPOXIDATION ON AG DEPOSITED ON STABILIZED ZRO2 IN THE PRESENCE OF CHLORINE MODERATORS, Journal of catalysis, 160(2), 1996, pp. 190-204
The effect of non-Faradaic electrochemical modification of catalytic a
ctivity (NEMCA), or in situ controlled promotion was investigated duri
ng ethylene epoxidation on Ag films deposited on yttria-stabilized zir
conia at temperatures from 240 to 300 degrees C and 500 kPa total pres
sure in the presence of chlorinated hydrocarbon moderators. It was fou
nd that the rates of epoxidation and complex oxidation change by a fac
tor of 230 as the catalyst potential and work function are varied by 0
.6 V and 0.6 eV, respectively. The change in the total reaction rate i
s typically a factor of 100 higher than the rate I/2F of electrochemic
al supply or removal of promoting oxide ions. The selectivity to ethyl
ene oxide can be varied between 0 and 78% by varying the catalyst pote
ntial and dichloroethane partial pressure. At low catalyst potentials
acetaldehyde becomes the main product with a selectivity up to 55%. Th
e observed behavior is discussed on the basis of previous NEMCA studie
s and of the prevailing ideas about the mechanism of ethylene epoxidat
ion. (C) 1996 Academic Press, Inc.