Standard and Fast Selective Catalytic Reduction of NO with NH₃ on Zeolites Fe-BEA

Abstract

Two Fe-containing BEA zeolites were prepared by ion-exchange (IE; Fe-BEA) and postsynthesis (PS; Fe-BEA/DeAl) procedures. Similar Fe content (0.8 to 0.9 Fe wt %) was evidenced for studied samples. Fe-BEA, prepared by ion exchange, contained essentially iron cations at the exchange sites of the zeolite. These iron cations are either isolated or bridged through an oxygen atom (Fe-oxo cations). In Fe-BEA/DeAl, a high portion of iron was introduced in the T-positions of zeolite lattice. The other part was either at an exchange positions or deposited as oxide clusters on the outer surface of zeolite grains. For Fe-BEA, significantly higher acidity than for Fe-BEA/DeAl was evidenced by FT-IR studies with adsorption of NH 3 and CO. The catalytic performance of Fe-BEA and Fe-BEA/DeAl was investigated in standard selective catalytic reduction (SCR) (NO 2 /NO = 0) and fast SCR (NO 2 /NO = 0.85). Fe-BEA revealed high catalytic activity in both SCR NO x reactions; however, production of N 2 O was much more apparent over this catalyst than over Fe-BEA/DeAl. In line with EPR and IR studies, the isolated or bridged-through-an-oxygen-atom extraframework iron oxo-sites in Fe-BEA were found to deliver higher catalytic activity than the iron oxo-sites in tetrahedral framework positions in Fe-BEA/DeAl.