The existence of dual Cu site involved in the selective catalytic reduction of NO with propene on Cu/ZSM-5

Abstract

In order to establish the role of surface species in the selective catalytic reduction (SCR), in situ IR studies were carried out using a DRIFT (diffuse reflectance infrared Fourier transform) cell in gas mixtures of various C₃H₆/NO ratios containing excess oxygen. The location and mobility of Cu ions were investigated by recording the relevant bands of CO adsorbed on Cu/ZSM-5. The nitro species coordinated on Cu²⁺ and the -NCO surface complex as possible intermediates were observed in the reduction of NO with propene on Cu/ZSM-5 between 350 and 400°C. The reactivities of these species toward NO, O₂ and propene were examined. The nitro species can react with propene very rapidly to form N₂ without the formation of NCO species. NCO also reacts with NO₂ and/ or NO at 350°C. IR spectra of CO adsorbed on cuprous ions show that two kinds of Cu ions, which are responsible for the activation of NO and propene respectively, exist on Cu/ZSM-5. From these results, a dual site mechanism involving nitro species and -NCO species as intermediates is suggested.