NOx Storage and Reduction over Pt Based Catalysts with Hydrogen as Reducing Agent – NH3 Formation and Influence of CO2 and H2O

Louise  Olsson, Chalmers University of Technology

The storage and reduction have been investigated by means of transient flow reactor experiments for three different catalysts: Pt/BaO/Al2O3, Pt/Al2O3 and Pt/SiO2. The influence of temperature, hydrogen concentration, cycle time and the effect of H2O and CO2 on the behavior of the catalysts have been investigated. The influence of H2O and CO2 for the Pt/BaO/Al2O3 catalyst at a temperature of 300 ºC is shown in figure 1. From the figure it is clear that the storage is much better in the absence of water and CO2. It is also apparent that the presence of water decreases the storage efficiency more than the presence of CO2.

The high reduction efficiency of hydrogen is also shown in figure 1. The NOx concentration reaches zero at the end of the rich period, which means that the catalyst is completely regenerated. From the figure it can also be seen that a large amount of ammonia is formed during regeneration. However, ammonia is only formed when there is enough hydrogen present (> 2000 ppm for 300 ppm NOx). The presence of water and CO2 also affects the ammonia formation. Furthermore, the results indicate that water and CO2 has a promoting effect on the NOx release at 100 ºC and 200 ºC.