The present study proposed a scheme for the reaction between NOx and C3H6 in the presence of excess O-2 over a proton-conducting Sn0.9In0.1P2O7-supported PtRh catalyst. C3H6 dissociated to protons and electrons at an anodic site of the PtRh catalyst, causing a negative potential. NOx reacted with protons and electrons to form N-2 and H2O at a cathodic site of the PtRh catalyst, resulting in a positive potential. As a result, an electrochemical local cell was formed at the PtRh/Sn0.9In0.1P2O7, followed by self-discharge. This series of reactions could be clearly distinguished from conventional catalytic reduction of NOx by C3H6. (C) 2008 The Electrochemical Society.