Electrochemical promotion of conventional and bipolar reactor configurations for NO reduction

The redn. of NO by CO or C3H6 in the presence of O2, a reaction of great technol. importance, was studied on porous polycryst. Rh catalyst films using a single-chamber and a wireless bipolar cell configuration. In the latter case the Rh catalyst films were deposited on the inner side of a YSZ tube, while 2 Au films deposited on the outer side of the tubes were used to polarize the Rh catalyst surface. The exptl. conditions used in this study were close to those in the exhaust of a lean burn or diesel engine, i.e., high flow rates and space velocities and in some cases, considerable excess of oxygen. Both direct (conventional) and indirect (wireless) polarization of the catalyst causes significant enhancement in the reaction rates (up to a factor of 20) and in the reactant conversion. These rate increases are strongly non-Faradaic with apparent Faradaic efficiencies, L, in the order of 100, manifesting the effect of Electrochem. Promotion or Non-faradaic Electrochem. Modification of Catalytic Activity (NEMCA). The Rh catalyst films were subsequently promoted in a classical way, via dry impregnation with NaOH, followed by drying and calcination. The thus Na-promoted Rh films exhibit higher catalytic activity than the unpromoted films, with a considerable decrease in their light-off temp. The effect of Electrochem. Promotion was then studied on these, already Na-promoted Rh catalysts. The effect of Chem. and Electrochem. Promotion on the catalyst performance can be synergetic and their combination may lead to interesting practical applications. This is further supported by the fact that such bipolar tube configurations: (a) do not need elec. connection to the catalyst and (b) can be adapted easier to com. exhaust units. [on SciFinder (R)]