The reduction of NO by propylene in the presence of excess oxygen is a very important reaction from the environmental point of view. In recent years an intense research effort has been focused on this catalytic system due to the need to design effective catalysts for lean burn and diesel engines. The effect of electrochemical promotion (or non-faradaic electrochemical modification of catalytic activity - NEMCA) was used to promote this reaction by employing Rh polycrystalline films interfaced with yttria-stabilized-zirconia (YSZ) in galvanic cells of the type: C3H6, NO, O-2, products, Rh/YSZ/Au, C3H6, NO, O-2, products 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 the Au pseudoreference electrode. Catalytic rate enhancements up to 15 000% and 6000% were observed for direct propylene oxidation and NO reduction, respectively, while the product selectivity to N-2 production is affected significantly (up to 200%) upon positive potential application.