The effect of electrochemical promotion for the selective catalytic reduction of NO by propene was investigated, for the first time, on a Pt impregnated catalyst film directly deposited onto a Na-beta"-Al2O3 solid electrolyte. The effect of sodium promoters on the activity and N-2 selectivity was evaluated at 240 degrees C under different oxygen concentrations (0.5, 1 and 5%). The presence of promoters still enhanced the selectivity to N-2, even under large excess of oxygen (5%), where the N-2 reaction rate was increased by a factor of 1.8. Nevertheless, the promotional effect of sodium on the overall catalytic activity for NO removal was progressively lowered with increasing oxygen concentrations, as a result of a strong inhibition of propene adsorption and a relative increase of the oxygen coverage. Characterization by cyclic voltammetry supported these results, providing useful information about the chemisorption of reactant species under the different reaction conditions. (c) 2007 Elsevier B.V. All rights reserved.