Electrochemical promotion of the NOx reduction over Pt, Pd and Rh catalysts

Solid electrolytes can be used as active catalyst supports to promote the performance of conducting metal or metal oxide catalysts deposited on them via electrical potential or current application between the catalyst and a counter electrode. This phenomenon is known as Electrochemical Promotion or Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect). More than sixty catalytic reactions have been studied so far using a variety of catalysts and solid electrolytes and it has been found that Electrochemical Promotion is a general phenomenon not limited to any particular group of catalytic reactions, conductive catalysts or solid electrolytes. In this communication we summarize and discuss Electrochemical Promotion studies of NOx reduction catalyzed by Rh, Pt and Pd deposited on O2- and Na+ conducting solid electrolytes. The reduction of NOx under stoichiometric or lean-bum conditions is extremely important in the treatment of the exhaust gases of internal combustion engines operating under stoichiometric or lean-bum conditions. It was found that both O2- and Na+ conducting solid electrolytes can induce dramatic and, in most cases, reversible cases in the catalytic activity and selectivity of Rh, Pt and Pd for the reduction of NO. The rate of NO reduction can be typically enhanced by a factor of 10 but in the case of NO reduction by C3H6 in presence of O-2 more than hundred-fold enhancement in catalytic rate is observed. The observed pronounced promotional phenomena are discussed in terms of the recently established rules of electrochemical and classical promotion.