ELECTROCHEMICAL PROMOTION OF THE CATALYTIC REDUCTION OF NO BY CO ON PALLADIUM

It was found that the catalytic activity and selectivity of Pd for the reduction of NO by CO at temperatures of 600 to 750 K can be markedly and reversibly affected by depositing a polycrystalline Pd film on 8 mol% Y2O3-stabilized-ZrO2 (YSZ), an O2- conductor, and applying extern al negative currents or potentials between the catalyst and a Au count er electrode. The increase in the rate of reduction of NO is typically more than 700 times larger than the rate of removal of O2- from the c atalyst via negative current application, while the CO2 and N-2 format ion rates can be respectively doubled and tripled. The promotional eff ect is explained by an enhanced dissociation of NO on the Pd surface w hich is moderated by a stronger adsorption of CO relative to NO. The N 2O + CO reaction was also studied and exhibited a twofold enhancement of the rate, in the most favorable cases, as negative or positive pote ntials or currents were applied. It was concluded that this reaction i s not an important route to the formation of N-2 during the NO + CO re action under these conditions. (C) 1997 Academic Press.