Concurrent processes of N2O/NO2 formation and NH3 oxidation competing with the main course of NH3-SCR over Cu/SSZ-13 and Fe-Cu/SSZ-13 catalysts

Abstract The catalytic activity and selectivity of Fe-Cu-SSZ-13 samples prepared by a two-step method, i.e., one-pot synthesis and impregnation or ion exchange were evaluated for NH 3 -SCR with or without H 2 O in the TPSR mode. The catalysts were characterized by XRD, TEM/EDX/EELS, XRF, N 2 -sorption, UV–Vis, EPR and operando IR techniques. Speciation of copper and iron sites in various pretreatment and reaction ( p $${\text{O}}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>O</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , p $${\text{H}}_{2}\text{O}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> <mml:mtext>O</mml:mtext> </mml:mrow> </mml:math> ), and their interaction with NH 3 was examined by DFT and first-principles thermodynamic (FPT) modeling. The SCR versus AMO (ammonia oxidation) competition was examined in the steady-state conditions using 14 NH 3 / 15 NH 3 reactants. The NH 3 -SCR activity, SCR versus AMO trade-off, and N 2 , NO 2 /N 2 O selectivity of the investigated catalysts depend significantly on the method of introducing iron into the zeolite and the dry and wet reaction conditions. The beneficial effect of water was associated with controlling the oxo/hydroxo nature of the dual active sites. The catalysts obtained by impregnation were active in a wider temperature window and exhibited higher selectivity to N 2 , compared to their counterparts obtained by ion exchange. Additionally, the introduction of iron by impregnation to parent Cu-SSZ-13 prepared by the one-pot method allows for attenuation of the concomitant NH 3 oxidation (AMO), and a fivefold reduction in N 2 O production.