Acidity-activity correlation over bimetallic iron-based ZSM-5 catalysts during selective catalytic reduction of NO by NH3

Abstract

The effect of acidic properties over a series of Lanthanide metal incorporated Fe-based H-ZSM-5 (Si/Al=15) catalysts on catalytic activity during selective catalytic reduction (SCR) of NO by NH3 was investigated. Various mono- (M1-ZSM-5; M1=Fe, Ce, Pr, Nd, and Sm) and bimetallic (M2Fe-ZSM-5; M2=Ce, Pr, Nd, and Sm) catalysts were prepared and their physicochemical properties were characterized by a variety of analytical and spectroscopic techniques. In particular, their acidic properties were studied by different molecular probe techniques, including the conventional ammonia-TPD and pyridine-IR methods, as well as solid-state 31P MAS NMR of adsorbed trimethylphosphine oxide (TMPO). Among various catalysts examined, the CeFe-ZSM-5 catalyst was found to exhibit an optimal NO conversion exceeding 95% over a temperature range of 300–500°C (WHSV=68,000cm3g−1h−1). The superior SCR activity observed for the bimetallic Fe-based catalysts is attributed to the synergistic effect from the Brønsted acidity of the MFI zeolite and strong Lewis acidity induced by the incorporated active metal ion species, particularly when incorporated with a secondary Lanthanide metal ion.