煅烧温度影响MnO_x/ZSM-5催化NO氧化性能研究

Study of the Influence of the Calcination Temperature on the Performance of NO Oxidation Catalyzed by MnO_x/ZSM-5

采用浸渍法制备了一系列不同煅烧温度（350～650℃）的MnO_x/ZSM-5催化剂,使用X射线衍射（XRD）、X射线光电子能谱分析（XPS）、H_2程序升温还原（H_2-TPR）和N_2吸附/脱附等技术对催化剂特征进行了测试。结果表明,煅烧温度对于MnO_x/ZSM-5催化剂催化NO氧化的活性有显著影响,与350℃下煅烧样品相比,550℃煅烧后样品最大NO转化率提高7%。较高的煅烧温度有利于Mn_2O_3的生成,在煅烧温度高于550℃后,Mn_2O_3成为催化剂表面的主要晶相。但提高煅烧温度,会导致催化剂表面分散度和比表面积降低,还原性能和晶格氧含量下降,不利于催化反应的进行。在反应器入口NO体积分数0.1%,体积空速约17 000 h^（-1）的实验条件下,550℃煅烧后的催化剂样品表现出最佳的催化NO氧化效率,350℃时NO转化率达到46.8%。但MnO_x/ZSM-5抗硫性能较差,还需进一步优化制备方式以提高其含SO_2氛围下的适用性。

A series of MnOx/ZSM -5 catalysts were prepared at different calcination temperatures（from 350℃ to 650℃） by using the immersion method and the XRD （ X-ray diffraction）, XPS （ X-ray photo- electronic spectrum）, H2 -TPR （H2 temperature program reduction） and N2adsorption/desorption tech- nology etc. were employed to test the characteristics of the catalysts. It has been found that the calcination temperature will have a notable influence on the activity of NO oxidation catalyzed by MnOx/ZSM -5. Compared with the sample caleinated at 350 ~C ,the maximum NO conversion rate of the sample calcinat- ed at 550℃ will increase by 7%. A relatively high calcination temperature will be favorable to the forma- tion of Mn203. When the calcination temperature is higher than 550℃ , Mn203 will become the main crys- tal phase on the surface of the catalysts. However, to enhance the calcination temperature will result in a decline of the surface dissipation degree on the surface of the catalysts and specific surface area and a drop of the reduction performance and oxygen content in the crystal lattice, thus unfavorable to catalytic reactions. Under the test condition of the volumetric fraction of NO at the inlet of the reactor being 0.1% and the volumetric space velocity being around 17 000 h-1 , the catalyst sample after calcinated at 550 ℃ will exhibit the optimum No catalytic oxidation efficiency. The NO conversion rate of the sample after cal- cinated at 350 ℃ will reach 46.8%. However, MnOx/ZSM -5 will have a relatively poor performance to resist sulfurization and it will be necessary to further optimize the preparation method to improve the a- daptability in the atmosphere containing S02.