Mn/Fe-Mn改性HZSM-5在NH_3-SCR中的催化性能

Catalytic performance of HZSM-5 modified by Mn/Fe-Mn in the NH_3-SCR

采用离子交换法制备了不同Mn含量及不同Fe/Mn物质的量比的HZSM-5改性分子筛,并以NH3为还原剂,在体积空速为12000h-1条件下,考察了上述催化剂选择性催化还原NO性能.同时,运用环境扫描电镜(ESEM)、比表面积(BET)和X-射线衍射(XRD)等方法对催化剂进行了表征.结果表明,改性催化剂中活性组分在载体表面呈高度分散形式,催化活性较高,复合改性较单独改性性能更为优越,适量Fe的加入提高了催化剂催化活性和稳定性;(0.25)Fe-Mn/HZSM-5(Fe/Mn物质的量比为0.25)的NO转化率于300℃时最高达到98%,在300～500℃范围内NO转化率均保持在90%以上.实验还研究了不同焙烧温度下制备的(0.25)Fe-Mn/HZSM-5对NO转化率的影响.结果表明,焙烧温度对催化剂的活性影响较大,550℃为最佳焙烧温度.

A series of catalysts of manganese and iron-manganese supported on HZSM-5 zeolites with different amounts of manganese and different molar ratios of iron/manganese were prepared by ion-exchange. The activities of these catalysts for selective catalytic reduction （SCR） of NO by NH3 were tested, with a gas hourly space velocity （GHSV） of 12000 h^-1. A combination of techniques such as SEM, BET surface area and X-ray diffraction （XRD） were used to characterize the catalysts. The experimental results showed that the active components of the modified catalysts were highly scattered. The catalytic activities of these catalysts were better than that of HZSM-5, and the Fe-Mn/HZSM-5 catalyst showed the best catalytic activity. Furthermore, the addition of a certain amount Fe increased the catalytic activity and stability of the catalyst. The activity of （0.25） Fe-Mn/HZSM-5 （iron/manganese molar ratio of 0. 25 ） reached 98% at 300℃ , and remained above 90% when the temperature was 300 - 500℃. The effect of calcination temperature on the activity of （0.25）Fe-Mn/HZSM-5 in the SCR was also investigated. The activity of the catalyst was greatly influenced by calcination temperature and 550℃ was the best calcination temperature.