Effective Decomposition of Nitric Oxide Using Pd/YSZ/Au Electrochemical Membrane Reactor

The direct decomposition of NO (2NO → N 2 +0 2 ) has been carried out using an electrochemical membrane reactor composed of an yttria-stabilized zirconia (YSZ) disc deposited with Pd and Au metal films at reaction temperature of 773∼1023 K and applying voltage of 0∼1.8 V. N 2 and O 2 were continuously produced in the cathode and anode chambers, respectively. NO decomposition activity increased by applying electrical potential. It was clearly shown that the enhancement of the catalytic activity was due to electrochemical pumping, by which the surface oxygen species formed by the dissociation of NO were transported from cathode to anode through YSZ. By comparing the catalytic activity between Pd/YSZ/Au and Au/YSZ/Au systems, it is suggested that the NO decomposition occurs mainly on the Pd surface, and YSZ itself did not catalyze the reaction at lower temperature. The rate-determining step for the reaction was the adsorption of NO at 973 K, while at 773 K, the step was either a diffusion of O 2- in YSZ or a migration of surface oxygen species on the Pd surface. The surface observation of Pd films by SEM showed that many microvoids were created throughout the Pd surface after the reaction. The creation of the microvoids results in an increase in the number of three-phase boundary sites, which will play an important role for the enhancement of the NO decomposition. Moreover, it was found that Pd/YSZ/Au resisted a serious degradation of the activity in the presence of O 2 in the feed stream.