Abstract
Pd is often used in diesel oxidation catalysts (DOC) together with Pt to ensure thermal stability and durability. Besides CO and hydrocarbon oxidation, NO oxidation is important for the function of subsequent converters in the exhaust line, such as SCR and DPF. Though Pt sites exhibit a significantly higher NO oxidation rate, Pd also provide some catalytic activity for this reaction and therefore affect the overall NO2 yield in DOC. Palladium oxides (PdOx) formation decreases the NO oxidation activity like PtOx.We present a global kinetic model for Pd/γ-Al2O3 catalyst considering standard DOC reactions extended with the PdOx formation and its influence on the NO2 yield. The dynamics of transition between the metallic Pd and oxidized PdOx state is studied in repeated temperature ramps and isothermal deactivation experiments, revealing the individual impact of O2 and NO2. The model describes well a dual NO oxidation light-off behavior observed in the experiments.
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