Mechanistic study of selective catalytic reduction of NO with NH3 over highly dispersed Fe2O3 loaded on Fe-ZSM-5

ZSM-5 supported highly dispersed FexOy clusters were prepared by a sol–gel method for selective catalytic reduction (SCR) of NO with NH3. XRD, SEM, UV-vis, H2-temperature-programmed reduction (H2-TPR), NH3-temperature-programmed desorption (NH3-TPD), and BET analyses all indicated that Fe species mainly existed as highly dispersed surface FexOy clusters with a Fe3+ concentration of 22 wt%. NO-temperature-programmed oxidation (NO-TPO) revealed that the FexOy clusters promoted the oxidation of NO to NO2, which promoted the low temperature NOX removal. NH3 was activated above 250 °C and over-oxidation of NH3 to NOX was not observed, as a result, a NOX removal efficiency of 91% was achieved at 400 °C. Moreover, the SCR reaction route was found to be temperature dependent, below 200 °C, the NOX reduction followed the reaction between NO2 and non-activated NH3. Fast SCR reaction dominated the NOX removal in the temperature window of 200–325 °C. At temperatures above 250 °C, the normal reaction between activated NH3 and NO compensated the thermodynamic limitation induced suppression of fast SCR.