C. Pliangos et al., NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF CATALYTIC ACTIVITY .8. RH-CATALYZED C2H4 OXIDATION, Journal of catalysis, 154(1), 1995, pp. 124-136
The catalytic activity of polycrystalline Rh films deposited on 8 mol%
Y2O3-stabilized ZrO2, (YSZ), an O2- conductor, can be altered dramati
cally and reversibly by varying the potential of the Rh catalyst film.
The complete oxidation of ethylene was investigated as a model reacti
on in the temperature range 300 to 400 degrees C and at atmospheric to
tal pressure. The rate of C2H4 oxidation can be reversibly enhanced by
up to 100 times by supplying O2- to the catalyst via positive potenti
al application (up to 1.5 V). This is the highest rate enhancement obs
erved so far with in situ electrochemical promotion studies. The stead
y-state rate increase is typically 10(4) times larger than the steady-
state rate of O2- supply to the catalyst. It was also found that varyi
ng the catalyst potential causes the appearance of the well-known comp
ensation effect with an isokinetic point at 372 degrees C. As in previ
ous studies of the effect of non-Faradaic electrochemical modification
of catalytic activity (NEMCA) the observed behaviour is due to the pr
omotional action of back-spillover oxide ions which migrate from the Y
SZ solid electrolyte onto the catalyst surface under the influence of
the applied potential. The back-spillover oxide ions are less reactive
with C2H4 than normally chemisorbed oxygen and act as promoters by af
fecting the binding strength of chemisorbed oxygen and ethylene. (C) 1
995 Academic Press, Inc.