Dynamics of low temperature N2O formation under SCR reaction conditions over a Cu-SSZ-13 catalyst

Abstract

Small pore Cu-SSZ-13 zeolite can effectively catalyze selective catalytic reduction (SCR) for NOx (NO and NO2) using NH3 as a reductant. However, side reactions leading to the formation of N2O, a greenhouse gas, occur in parallel under SCR reaction conditions. This work investigates the fundamental characteristics of N2O formation during SCR reactions over a Cu-SSZ-13 catalyst under both steady-state and transient conditions during reactant transitions at 200 °C. The absence of nitrate bands from in situ DRIFTS experiments and the inconsistencies between high stability of NH4NO3 and N2O formation at low temperature exclude the formation of surface nitrate or NH4NO3 as a precursor of N2O formation as the major path under standard SCR reaction conditions at 200 °C. The analysis from the transient N2O formation behavior during reactant transitions and NO + NH3 titration experiments indicates that more oxidized Cu-SSZ-13 catalyst, containing higher amount of Cu-oxy species, produces higher amount of N2O.