Effect of the NH_4NO_3 Addition on the Low-T NH_3-SCR Performances of Individual and Combined Fe- and Cu-Zeolite Catalysts

摘要

We have measured NOx conversions and N_2O productions over Fe-BEA and Cu-SAPO catalysts and over their sequential arrangements under Enhanced SCR conditions, resulting from the addition of an aqueous solution of ammonium nitrate (AN) to the typical Standard SCR feed stream, and we have compared them to those observed under Standard and Fast SCR conditions. The expected strong enhancement of the poor low temperature activity of the Fe-BEA catalyst was confirmed: both NH_3 and NOx conversions and N_2O formations similar to those of the Fast SCR reaction were achieved when cofeeding ammonium nitrate. On the other hand, the Cu-SAPO efficiency was drastically decreased by the addition of AN at low temperatures, possibly due to trapping of the ammonium nitrate salt within the SAPO zeolite, characterized by smaller pores than those of the BEA zeolite. The Cu-SAPO performances were recovered only at T > 250 ℃ with a huge release of N_2O due to the thermal decomposition of AN. The combined system with the Fe-zeolite sample placed upstream of the Cu-zeolite also exhibited outstanding low temperature deNOx performances, with even lower N_2O production than over the Fe-zeolite only at the same Enhanced SCR (E-SCR) conditions.