铁改性的Mo/ZSM-5催化剂上NO的选择性催化还原反应

采用浸渍法制备了Mo/ZSM-5, Fe/ZSM-5和不同Fe和Mo摩尔比的Fe-Mo/ZSM-5样品, 并以氨为还原剂对其NO选择性催化还原活性以及反应条件对催化性能的影响进行了研究. 结果表明, Fe-Mo/ZSM-5样品的NOx转化率明显比单独的Mo/ZSM-5和Fe/ZSM-5的高. 当n(Fe):n(Mo)为1.5时, Fe-Mo/ZSM-5样品具有最佳催化性能, 其NOx转化率在430 ℃时达到了96%, 并且能在高空速和不同O2气浓度的条件下保持高的催化活性. 同时采用XRD和XPS技术分别对催化剂的体相结构和表面性质进行了研究, 结果表明, 当n(Fe):n(Mo)=1.5时, Fe和Mo元素之间以及与载体HZSM-5之间存在较强的相互作用, 并且其表面的Mo3d的含量最高. 这可能与其高的催化活性有关. 另外还发现, 在反应过程中Fe-Mo/ZSM-5催化剂表面的氮氧物种主要是吸附态NO, 因此可以推测NO的催化还原反应机理是, 在催化剂表面上, 吸附态NO与吸附NH3物种直接反应生成氮气, 而非经过氧化为NO2的途径.

Selective Catalytic Reduction of NO with Ammonia over Fe Promoted Mo/ZSM-5 Catalysts

The Fe-Mo/ZSM-5 catalysts with different Fe/Mo molar ratios were prepared by using impregnation method. The activity of Fe-Mo/ZSM-5 catalysts for selective catalytic reduction of NO with ammonia and the effects of reaction conditions were also studied. It was found that Fe-Mo/ZSM-5 is more active than both of Mo/ZSM-5 and Fe/ZSM-5 separately, and it exhibits the best performance for SCR reaction when n(Fe)/n(Mo) ratio is 1.5, for which the highest NOx conversion reached 96% at the temperature of 430 ℃. The experiment results also show that Fe-Mo/ZSM-5 catalyst has a good stability of SCR reaction, for higher catalytic activity was gained under the condition of high space velocity and varied O2 concentrations. The bulk phase and surface structures were determined by XRD, XPS techniques respectively. The results show that there is a strong interaction among Fe, Mo and HZSM-5, and the surface Mo3d percentage is the largest when n(Fe)/n(Mo) ratio is 1.5, which may be related to its better catalytic performance for catalytic reduction of NO. It is also important to notice that NO2 was not detected during the XPS measurement, and NO was the main species during SCR reaction on the surface of Fe-Mo/ZSM-5 catalyst. From this it can be deduced that NO is directly reacted with ammonia to form nitrogen and water on the surface of the catalyst.