CO and hydrocarbon light-off inhibition by pre-adsorbed NOx on Pt/CeO2/Al2O3 and Pd/CeO2/Al2O3 diesel oxidation catalysts

Abstract Diesel oxidation catalysts (DOC) for abatement of CO and hydrocarbon (HC) emissions are commonly based on PtPd/CeO2/Al2O3 formulations. PdPt/CeO2-ZrO2 or Pd/zeolite materials are also used in passive NOx adsorbers (PNA) that capture nitrogen oxides during cold start. The DOC and PNA functions can be integrated into one catalytic device. However, the adsorbed NOx species may inhibit the CO and HC light-off. Aim of this work is to investigate this inhibition effect on model Pt/CeO2/Al2O3 and Pd/CeO2/Al2O3 oxidation catalysts. Isothermal NOx adsorption experiments were performed at 80 °C, 120 °C and 160 °C, followed by temperature programmed desorption. Comparative CO and C3H6 light-off experiments on a catalyst with pre-adsorbed NOx revealed an increase of the light-off temperature by up to 30 °C relative to that of a pre-reduced and pre-oxidized catalyst. The inhibition effect was stronger on Pt/CeO2/Al2O3 than on Pd/CeO2/Al2O3 and its extent depended on the amount of adsorbed NOx.