NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF CATALYTIC ACTIVITY .8. RH-CATALYZED C2H4 OXIDATION

The catalytic activity of polycrystalline Rh films deposited on 8 mol% Y2O3-stabilized ZrO2, (YSZ), an O2- conductor, can be altered dramatically and reversibly by varying the potential of the Rh catalyst film. The complete oxidation of ethylene was investigated as a model reaction in the temperature range 300 to 400 degrees C and at atmospheric total pressure. The rate of C2H4 oxidation can be reversibly enhanced by up to 100 times by supplying O2- to the catalyst via positive potential application (up to 1.5 V). This is the highest rate enhancement observed so far with in situ electrochemical promotion studies. The steady-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 varying the catalyst potential causes the appearance of the well-known compensation effect with an isokinetic point at 372 degrees C. As in previous studies of the effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) the observed behaviour is due to the promotional action of back-spillover oxide ions which migrate from the YSZ 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 affecting the binding strength of chemisorbed oxygen and ethylene. (C) 1995 Academic Press, Inc.