Abstract
An Ag/MgO/γ-Al2O3 catalyst is developed, which can perform the dual role of a passive NOx adsorber (PNA) at low temperatures and a NOx reduction catalyst at higher temperatures. The effect of H2O and CO2, as well as various reductants such as H2, NH3, and C3H6 on its deNOx performance is investigated. The NOx storage is comparable to that obtained by Pd-based PNAs, and occurs through a spillover mechanism. The presence of H2 remarkably increases the low-temperature NOx adsorption and binding strength, and is attributed to the significant formation of nitrates as opposed to the predominant formation of nitrites in the absence of H2. Moreover, the positive effect of H2 is not related to the H2-SCR activity of the catalyst or an enhancement in the NO oxidation activity. C3H6 inhibits NOx storage, but the presence of H2 promotes it considerably. A significantly high NH3-SCR activity with negligible N2O formation is measured at 150 °C, while C3H6-SCR activity is exhibited at higher temperatures. However, the presence of NH3 does not affect the binding of NOx on the various adsorption sites, which is primarily governed by the presence of H2.
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