Reduction of NO2 stored in a commercial lean NOx trap at low temperatures

Isothermal storage of NO2 and subsequent reduction with different reducing agents (H-2, CO or H-2 + CO) in a lean NO (x) trap catalyst was tested by Temperature Programmed Desorption (TPD) and Temperature Programmed Reduction (TPR) experiments at temperatures representative of automotive "cold-start" conditions (< 200 degrees C) using a commercial NO (x) trap catalyst. Results from the TPR experiments revealed that no reduction of stored NO2 to N-2 was observed at 100-180 degrees C, and at 200 degrees C 10% reduction only of NO2 to N-2 was measured. A special affinity of H-2 to form NH3 was observed during the reduction of stored NO2. The formation of NH3 increases with increasing amount of stored NO2 and decreases with increasing storage temperature. Direct relation exists between the amount of adsorbed and/or stored NO2 and the formation of H2O and NH3.