Cu交换度对贫燃条件下 Cu-Al-MCM-41上NO选择性催化还原的影响

利用程序升温反应技术考察了cu交换度对Cu-Al-MCM-41上NO选择性还原反应性能的影响,同时结合XRD,N2吸附等温线,NMR,ICP-AES,TPD和TPR等技术对催化剂的结构特征和化学吸附性能进行了表征．结果表明,经Cu离子交换的Al-MCM-41并未改变载体的结构特征,仍保持长程有序的中孔结构．影响Cu-Al-MCM-41催化剂选择性还原活性的主要因素是Cu交换度,而不是Cu含量,前者决定了活性中心(主要是Cu^2 )的浓度．当Cu交换度低于100％时,随着Cu交换度的增加,NO最大转化率增加．当交换度超过100％后,催化剂的还原活性下降,此时出现的CuO起完全氧化的催化作用而非选择性还原的催化作用．在n(Si)／n(Al)=10,Cu交换度接近100％的Cu-Al-MCM-41上360℃时可获得79％的NO最大转化率．

Effect of Ion-Exchanged Degree of Copper on Selective Catalytic Reduction of NO by Propylene over Cu-Al-MCM-41

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 N 2 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 (Cu 2+) 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%.