Hydrothermal Stability of Fe–BEA as an NH₃-SCR Catalyst

Abstract

The hydrothermal stability of Fe–BEA as a selective catalytic reduction (SCR) catalyst was experimentally studied. Cordierite supported Fe–BEA samples were hydrothermally treated at 600 and 700 °C for 3–100 h to capture the effect of aging time and temperature. Before and after aging the samples were characterized with BET, XPS, XRD, and NH 3 -TPD. The catalytic performance of the samples with respect to NO oxidation, NH 3 oxidation, and NO reduction (NH 3 -SCR) was studied by flow reactor experiments to correlate changes of the catalytic performance with structural changes of the zeolite and the iron phases. The NH 3 -SCR experiments did not show any significant decrease in activity after a short time of aging (3 h at 700 °C) even though the ammonia storage capacity decreased by 40% and the oxidation state of iron slightly increased. A longer time of aging resulted in decreased activity for NO reduction during low temperatures (150–300 °C), while at higher temperatures (400–500 °C) the activity remained high. The results indicate that the NO reduction is more sensitive at low temperatures to changes in the oxidation state of iron caused by hydrothermal aging than at higher temperatures. Furthermore, a maximum in activity for NO oxidation and increased oxidation state of iron (Fe 3+ ) indicate Fe 2 O 3 particle growth.