Effect of gas composition on the NOx adsorption and reduction activity of a dual-function Ag/MgO/γ-Al2O3 catalyst

An Ag/MgO gamma-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 H-2, NH3, and C3H6 on its deNO(x) performance is investigated. The NOx storage is comparable to that obtained by Pd-based PNAs, and occurs through a spillover mechanism. The presence of H-2 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 H-2. Moreover, the positive effect of H-2 is not related to the H-2-SCR activity of the catalyst or an enhancement in the NO oxidation activity. C3H6 inhibits NOx storage, but the presence of H-2 promotes it considerably. A significantly high NH3-SCR activity with negligible N2O formation is measured at 150 degrees 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 H-2.