NH3-SCR activity of H-BEA and Fe-BEA after potassium exposure
Artikel i vetenskaplig tidskrift, 2015
A previous developed multisite microkinetic model for hydrothermally deactivated H-BEA and Fe-BEA catalyst used for NH3-SCR applications has been applied and validated using potassium exposed H-BEA and Fe-BEA samples. The catalysts have been exposed to evaporated aqueous solution of potassium (10 ppm KNO3) in a flow-reactor for 14-48 h. The results for the H-BEA samples show an increase in NH3-SCR activity after 48 h of potassium exposure. This is correlated to an increase in NOX storage capacity, indicating that potassium forms new NOX storage sites participating in the SCR reaction. However, the Fe-BEA samples show different results. The SCR activity for the Fe-BEA catalyst decreases significantly after 14 h of exposure to potassium and after longer exposure time the activity slightly increases again compared to the sample exposed to potassium for 14 h. When applying the kinetic model to the flow-reactor measurements the model is able to predict the changes in SCR activity well when changing the site density of the active sites. In overall, combining the experimental results with the simulation indicates that exposure to potassium initially chemically blocks the active iron species which decrease with exposure time. Longer time of exposure to potassium indicates that the iron species are exchanged and lost due to formation of new potassium sites in the zeolite resulting in an overall lower SCR activity compared to a fresh Fe-BEA sample.