采用液态离子交换法制备了不同含量的Mn/ZSM-5型分子筛催化剂,并考察了上述催化剂的物理化学特性及其在NH3-SCR反应中的催化性能。理化分析结果表明:所制备催化剂在Mn含量≤9.2%时具有高度的分散性,分子筛表面团聚的氧化锰颗粒粒径小于4nm;锰元素主要富集于分子筛的浅层及表面。催化性能研究结果表明:Mn含量达到1.4%时,低温催化中心即达饱和,继续增加Mn含量对低温反应性能影响不大;反应温度超过300℃时,高温催化中心开始起作用;含量为3.1%的Mn/ZSM-5催化剂具有最宽的高活性反应温度窗口。
Mn/ZSM-5 zeolite catalysts with different manganese content were prepared using liquid ion-exchange method. The effects of manganese loading ratios on physical-chemical characterization and selective catalytic reduction of NOx with ammonia were investigated. The physical-chemical analysis showed that manganese species were finely dispersed on the ZSM-5 support with manganese content 〈9.2%, corresponding to the manganese oxide particle size 〈4 nm. Manganese mainly enriches in the surface of the ZSM-5 support. The study on the catalytic performance represents: at manganese loading 〈1.4%, the low-temperature catalytic center tended to saturate, and further increasing the manganese content had little influence on the low-temperature reaction; when the reaction temperature exceeds 300℃, high temperature catalytic center was activated. Among all of the catalyst tested, Mn/ZSM-5 catalysts loading of 3.1% exhibited the most efficient and widest temperature window.