NO_x adsorption and desorption of a Mn-incorporated NSR catalyst Pt/Ba/Ce/xMn/γ-Al₂O₃

This study evaluated the NO_x adsorption and desorption performance as well as the casual relationship underlying a Mn-incorporated catalyst (Pt/Ba/Ce/xMn/γ-Al₂O₃). NO_x adsorption and desorption are regarded as a prominent index for the NO_x removal performance of NO_x storage and reduction; we utilized NO_x storage experiments with various inlet NO and O₂ concentrations and cycling adsorption/desorption experiments with a couple of adsorption time protocols for performance evaluation. In-suit DRIFT and NO_x-TPD tests were implemented to reveal the instant stored species and their thermal stability. Eight percent of Mn catalyst at 350 °C was adopted in the described experiments for its desirable NO_x adsorption characteristics. The optimal NO_x storage performance was found under 10% O₂, deteriorating when the concentration was further increased. Furthermore, elevating NO concentration impaired the NO_x adsorption due to the low NO₂/NO_x ratio. It was also found that shorter adsorption time facilitated NO_x removal via maintaining an unsaturated state for active storage components in terms of a fixed desorption time. The stored species existed as nitrites and nitrates with a good low-temperature thermal stability which however decayed at higher temperatures as exhibited in the DRIFT and NO_x-TPD tests. These findings provided invaluable information for the application of Mn-incorporated catalyst for NO_x removal in diesel exhaust purification to relieve the aerial pollution.