The promotional role of Ce in Cu/ZSM-5 and in situ surface reaction for selective catalytic reduction of NOx with NH3

Cu/ZSM-5 and Ce doped Cu/ZSM-5 catalysts were prepared by the incipient-wetness-impregnation method, and the effect of Ce doping on the structure and the catalytic performance of the Cu/ZSM-5 catalyst was investigated in detail for the selective catalytic reduction (SCR) of NO with NH3. The results showed that the addition of Ce can markedly broaden the operation temperature window of the Cu/ZSM-5 catalyst for NH3-SCR and enhance its H2O and SO2 resistance. The presence of Ce promoted an enrichment of copper species (isolated Cu2+ ions and CuO nanoparticles) on the catalyst surface and the increase in the Lewis acid sites on the surface of the Cu/ZSM-5 catalyst, and strengthened the redox property of the Cu/ZSM-5 catalyst. As a result, Ce-doped Cu/ZSM-5 catalyst possessed the high adsorption ability of NH3 and nitrite/nitrate, which is propitious to the increase in the reactivity of the Ce-doped Cu/ZSM-5 catalyst. In situ DRIFTS results indicated that the NH3-SCR reaction on the Cu/ZSM-5 catalyst and Ce-1-Cu-4/ZSM-5 catalysts definitely followed Langmuir-Hinshelwood mechanisms, and bridged nitrates and bidentate nitrates were the active intermediate. However, Eley-Rideal mechanism can't be confirmed over the Cu/ZSM-5 and Ce-1-Cu-4/ZSM-5 catalysts.