Effect of H₂, H₂O, and CO₂ on the deNO_x characteristics of a combined passive NO_x adsorber and NO_x reduction catalyst

Abstract

The effect of H2, H2O, and CO2 on the NOx removal characteristics of a non‐PGM material (Ag/MgO/γ‐Al2O3) is investigated, which is shown to be active for both NOx adsorption and reduction. H2O facilitates NOx adsorption at early times but inhibits it at longer times. The inhibiting effect of CO2 is observed at low temperatures and is proposed to be due to bicarbonates. However, the inhibiting effect of both H2O and CO2 decreases at higher temperatures. The formation of NO2 at low temperatures is attributed to NO oxidation, and the contribution of stored NOx to NO2 formation increases with temperature. H2O inhibits NH3 oxidation at high temperatures as well as NOx reduction by NH3‐SCR at low temperatures. However, the NOx reduction activity is not affected by CO2. H2 significantly promotes the NH3‐SCR reactions, which is attributed to the facilitation of NOx spillover from the reduced Ag sites to the support.

Effect of H2O and CO on the NO Operating Cycle in Pd/CHA Passive NOx Adsorbers

“…Passive NO x adsorbers (PNAs) have been proposed to address the cold-start NO x emissions by trapping NO x at low temperatures (<200 °C) and releasing it at a higher temperature (>250 °C) where the downstream NO x reduction catalysts such as LNT or SCR are active . Various materials have been synthesized and evaluated for their NO x adsorption and desorption characteristics. − Among the different materials studied, Pd supported on zeolites, especially Pd/Chabazite (Pd/CHA), has been found to be the most suitable. , …”