Electrochemical activation of catalytic reactions using anionic, cationic and mixed conductors

The effect of non-faradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical promotion has been investigated for the oxidation of ethylene on Pt using several types of solid electrolytes and mixed conductors. It was found that, despite the different nature of the solid electrolyte support and promoting ion, there exist important similarities in the NEMCA behavior of ethylene oxidation. Thus, in general, the rate of oxidation increases with increasing catalyst-electrode potential (electrophobic behavior) at high oxygen to ethylene ratios and increases with decreasing potential (electrophilic behavior) at low oxygen to ethylene ratios. There exist, however, significant differences in the magnitude of the observed rate enhancement, which is up to sixty-fold in the case of ZrO2(Y2O3) and in the apparent Faradaic efficiency, which is up to 3.10(5) for the cases of ZrO2(Y2O3) and CeO2 and even higher for the Na+ conductors. The common features and differences are summarized and discussed together with the underlying electrochemical promotion mechanism on the basis of recent experimental and theoretical studies. (C) 2000 Elsevier Science B.V. All rights reserved.