Role of α-sites in the selective catalytic reduction of nox with ammonia over Fe-ZSM-5 catalysts

摘要

The catalytic properties of Fe-ZSM-5 zeolites with different iron contents have been investigated in the selective catalytic reduction (SCR) of NOx with ammonia. The observed catalytic properties the zeo-lites are correlated with the concentration of the iron-containing sites that are stabilized in the zeolite and effect N_2O decomposition (α-sites). The catalysts activated at a high temperature to increase the α-site con-centration (by a factor of 5-10) are more active in NOx SCR with ammonia than the unactivated samples. However, the difference between the activities of the activated and unactivated catalysts is well below the dif-ference between the α-site concentrations in these catalysts. The nonlinear relationship between these parameters is evidence that the α-sites in Fe-ZSM-5 is not the only factor determining the activity of Fe-ZSM-5 in NO_xSCR with ammonia. The activated catalysts show a low activity in nonselective ammonia oxi-dation and, accordingly, a high selectivity in the target process at high temperatures.