Electrochemical promotion of a classically promoted Rh catalyst for the reduction of NO

The reduction of NO by CO in presence of O-2, a reaction of great technolog ical importance, was investigated on porous polycrystalline Rh catalyst-ele ctrodes deposited on YSZ (Y2O3-stabilized-ZrO2) an O2- conductor. It was fo und that application of current or potential between the Rh catalyst electr ode and a Au counter-electrode enhances the rate of NO reduction and CO2 fo rmation by up to a factor of 20. These rate increases are strongly non-Fara daic with apparent Faradaic efficiencies, Lambda, up to 20, manifesting the effect of Electrochemical Promotion or Non-faradaic Electrochemical Modifi cation of Catalytic Activity (NEMCA). The Rh catalyst electrodes were subse quently promoted in a classical way, via dry impregnation with NaOH, follow ed by drying and calcination. The thus Na-promoted Ph films were found, as expected, to exhibit much higher catalytic activity than the unpromoted fil ms, with a pronounced decrease in their light-off temperature from 440 to 3 20 degreesC. The effect of Electrochemical Promotion was then studied on th ese, already Na-promoted Ph catalyst. Positive (+1 V) 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 temper ature down to 260 degreesC. This is the first demonstration of electrochemi cal promotion on an already promoted catalyst surface. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.