Μελέτη του φαινομένου της ηλεκτροχημικής ενίσχυσης για την αναγωγή του NO από το C3H6 ή το CO παρουσία οξυγόνου σε Rh/YSZ και μελέτη της αρχής του φαινομένου της ηλεκτροχημικής ενίσχυσης με την τεχνική της φασματοσκοπίας σύνθετης αντίστασης

Abstract

Electrochemical promotion of ΝΟ reduction by C3H6 on Rh/YSZ catalystelectrodes, in presence of excess oxygen: The reduction of ΝΟ by propylene in the presence of excess oxygen is a very important reaction from the environmental point of view. The effect of electrochemical promotion (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, O2, products, Rh/YSZ/Au, C3H6, NO, O2, 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 reference electrode. Catalytic rate enhancements up to 15000% and 6000% were observed for direct propylene oxidation and NO reduction, respectively, while the product selectivity to N2 production is affected significantly (up to 200%) upon positive potential application. Electrochemical promotion of a classically promoted Rh catalyst with NaOH for the reduction of NO by CO in the presence of Ο2: The reduction of NO by CO in presence of Ο2, a reaction of great technological importance, was investigated on porous polycrystalline Rh catalyst-electrodes on YSZ (Y2O3-stabilized-ZrO2)-an O2- conductor. It was found that application of current or potential between the Rh catalyst and a Au counter-electrode enhances the rate of NO reduction and CO2 formation by up to a factor 20. These rates increases are strongly non- Faradaic with apparent Faradaic efficiencies, Λ, up to 20, manifesting the effect of Electrochemical Promotion or Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA). The Rh catalyst electrodes were subsequently promoted in a classical way, via dry impregnation with NaOH, followed by drying and calcination. The thus Na-promoted Rh films were found to exhibit much higher catalytic activity than the unpromoted films, with a pronounced decrease in their light-off temperature 440ο to 320oC. The effect of Electrochemical Promotion was then studied on these, already Na-promoted Rh catalyst. Positive (+1V) potentials were found to further increase the rate of NO reduction by up to a factor of 4 with a Faradaic efficiency up to 20 and concomitant reduction in light-off temperature down to 260oC.