Cu-Al-MCM-41 catalysts with different copper ion-exchanged degree were investigated for the reduction of NO by propylene under lean-burn conditions. The characterization using XRD, NMR and N₂ adsorption isotherms revealed that the structure of Al-MCM-41 remained unchanged after the complete exchange of protons for copper ions. Experimental results based on the temperature programmed reduction/desorption and reaction techniques showed that Cu-Al-MCM-41 is an effective catalyst for the selective reduction of NO_x. It was revealed that the major influence factor on the catalytic activity was the ion exchange degree which had an effect on the concentration of the active center (Cu²⁺) for NO reduction. For the underexchanged catalyst, it was found that the NO reduction activity increased with increasing copper exchange. A further increase in the ion-exchanged degree would result in a decrease of NO maximum conversion. The reason could be the formation of CuO phase in the catalyst that mainly catalyzed the deep oxidation of propylene. Over 79% of NO conversion was obtained on the catalyst with Si/Al ratio of 10 and copper exchanged degree of 93%.

Key words: copper ion-exchanged degree, Al-MCM-41, selective catalytic reduction, ,NO_x