Abstract. The selective catalytic reduction of NO by propylene or CO in the presence of excess oxygen is a system of great technological importance. The effect of Electrochemical Promotion (or Non-faradaic Electrochemical Modification of Catalytic Activity -NEMCA) was used to promote this reaction (C3H 6 or CO]NO/O2) on Rh/YSZ catalyst-electrodes.It was found that both the catalytic activity and the selectivity of the Rh catalyst-electrode is affected dramatically upon varying its potential with respect to a Au pseudoreference electrode. Catalytic rate enhancements up to 15000% and 6000% were observed in the case of NO reduction by propylene, while the product selectivity to N2 production is affected significantly (up to 200%) upon positive potential application. Remarkable promotion of the catalytic activity was also observed in the case of NO reduction by CO, since up to 20-fold increases both in catalytic rates and in NO conversion were obtained under NEMCA conditions.

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The electrochemical promotion of Rh/YSZ catalysts for C 2 H 4 oxidation was investigated together with the mechanism of electrochemical promotion via the use of AC impedance spectroscopy. The impedance response consists of two distinct semicircles and provides strong support for the sacrificial promoter mechanism of electrochemical promotion. The impedance analysis of the low frequency part of all spectra show the existence of a finite length Gerischer impedance which corresponds to the effective double layer formed by the spillover of promoting anionic oxygen from the YSZ support to the rhodium/gas interface and its slow consumption there by adsorbed hydrocarbon fragments. AC impedance analysis provides values both for the rate of consumption of the promoting spillover oxygen species as well as for the stability and capacitance the catalyst/gas double layer in various gaseous environments and temperatures.

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