LAUSR

Abstract Dual CO light-off may occur during simultaneous oxidation of CO and hydrocarbon on three-way catalysts (TWC) and diesel oxidation catalysts (DOC). A plateau, shoulder or secondary peak may occur on the CO light-off curve after a cold start. In this paper we present a comparative experimental study of this effect on Pt/CeO2/ γ -Al2O3, Pd/CeO2/ γ -Al2O3, Pt/ γ -Al2O3 and Pd/ γ -Al2O3 catalysts, focusing particularly on the role of CeO2 in the catalyst formulation. Two mechanisms for dual CO light-off are identified: (i) blocking of active sites by the hydrocarbon oxidation intermediates, and (ii) CO by-production during the hydrocarbon oxidation. The presence of CeO2 does not suppress the accumulation of C3H6 oxidation intermediates on the catalyst surface. Longer transients and more complex patterns are observed on Pt/CeO2/ γ -Al2O3, Pd/CeO2/ γ -Al2O3 when compared to the corresponding ceria-free catalyst formulations. On the other hand, the presence of CeO2 decreases the light-off temperature and minimizes CO formation during C3H6 oxidation.