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

Abstract

ZSM-5 supported highly dispersed Fe_xO_y 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 Fe_xO_y clusters with a Fe³⁺ concentration of 22 wt%. NO-temperature-programmed oxidation (NO-TPO) revealed that the Fe_xO_y clusters promoted the oxidation of NO to NO₂, which promoted the low temperature NO_X removal. NH₃ was activated above 250 °C and over-oxidation of NH₃ to NO_X was not observed, as a result, a NO_X removal efficiency of 91% was achieved at 400 °C. Moreover, the SCR reaction route was found to be temperature dependent, below 200 °C, the NO_X reduction followed the reaction between NO₂ and non-activated NH₃. Fast SCR reaction dominated the NO_X 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.