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

Abstract

This study evaluated the NOx adsorption and desorption performance as well as the casual relationship underlying a Mn-incorporated catalyst (Pt/Ba/Ce/xMn/γ-Al2O3). NOx adsorption and desorption are regarded as a prominent index for the NOx removal performance of NOx storage and reduction; we utilized NOx 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 NOx-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 NOx adsorption characteristics. The optimal NOx storage performance was found under 10% O2, deteriorating when the concentration was further increased. Furthermore, elevating NO concentration impaired the NOx adsorption due to the low NO2/NOx ratio. It was also found that shorter adsorption time facilitated NOx 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 NOx-TPD tests. These findings provided invaluable information for the application of Mn-incorporated catalyst for NOx removal in diesel exhaust purification to relieve the aerial pollution.