PNNL

Abstract

We report the various characteristics of Pt-K/MgAl2O4 lean NOx trap (LNT) catalysts including the effect of K loading on nitrate formation/decomposition, NOx storage activity and durability. Upon the adsorption of NO2 on K/MgAl2O4 samples, potassium nitrates formed on Mg-related sites in MgAl2O4 support are observed, in addition to the typical two potassium nitrates (ionic and bidentate) formed also on Al2O3 supported sample. Based on NO2 TPD and FTIR results, the Mg-bound KNO3 thermally decompose at higher temperature than Al-bound KNO3, implying its superior thermal stability. At a potassium loading of 5wt%, the temperature of maximum NOx uptake (Tmax) is 300 ºC. Increasing the potassium loading from 5wt% to 10 wt%, the Tmax gradually shifted from 300 ºC to 450 ºC, indicating the dependence of Tmax on the potassium loading. However, increase in potassium loading above 10 wt% only gives rise to the reduction in the overall NOx storage capacity. This work also underlines the obstacles these materials have prior to their practical application (e.g., durability and sulfur poisoning/ removal). This work provides fundamental understanding of Pt-K/MgAl2O4-based lean NOx trap catalysts, which could be good candidates for high temperature LNT applications.