MnO_x/WO₃/TiO₂低温NH₃选择性催化还原NO_x的性能

丁中海¹，张亚平²，汪小蕾²，左玉辉¹，徐海涛²

(1. 南京大学 环境学院 污染控制与资源化研究国家重点实验室，江苏 南京，210093；2．东南大学 能源与环境学院，能源热转换及其过程测控教育部重点实验室，江苏 南京，210096)

摘 要：采用一步浸渍法制备不同WO₃含量的MnO_x/WO₃/TiO₂催化剂，在模拟氨气选择性催化还原NO_x的反应条件下(NH₃-SCR)对催化剂的低温反应活性进行考察，同时设计3种工况的宏观暂态实验考察烟气各组分影响因子在催化反应过程中的作用，研究NO_x的催化还原过程。研究结果表明：适度添加WO₃可以显著提高锰系催化剂的反应活性，15%MnO_x/5%WO₃/TiO₂表现出较好的低温活性，80~240 ℃的温度窗口内NO转化率超过85%；添加过量和过少均导致催化剂的活性呈现不同程度的下降趋势，尽管添加7.5% WO₃提高催化剂的高温活性(＞240 ℃)。在NH₃-SCR反应中，NH₃的吸附活化作为控制步骤对整个反应至关重要，气质有氧状态下NH₃可较小程度的还原NO_x。O₂的存在促进NO的氧化，保护催化剂表面的氧化活性中心，促进NH₃的吸附与活化。

关键词：MnO _x/WO₃/TiO₂；低温选择性催化还原；催化性能；宏观暂态实验

Catalytic performance of MnO_x/WO₃/TiO₂ catalyst for low-temperature selective catalytic reduction of NO_x by NH₃

DING Zhonghai¹, ZHANG Yaping², WANG Xiaolei², ZUO Yuhui¹, XU Haitao²

(1. State Key Laboratory of Pollution Control and Resource Reuse, School of Environment,Nanjing University, Nanjing 210093, China;2. Educational Key Laboratory of Energy Thermal Conversion and Process Control,School of Energy and Environment, Southeast University, Nanjing 210096, China)

Abstract:Series of MnO_x/WO₃/TiO₂ with different WO₃ contents were prepared by a one-step impregnation method and their catalytic performance for the low-temperature selective catalytic reduction of NO_x with NH₃(NH₃-SCR) was investigated under the condition of simulated composition of flue gas. Three conditions for macro-transient experiments were designed to study the role of components in the smog on the process of catalytic reaction in order to figure out the process of the catalytic reduction of NO_x. It is found that the addition of appropriate amount of WO₃ can improve remarkably the catalytic activity of Mn-based catalysts. Particularly, the 15%MnO_x/5%WO₃/TiO₂ exhibited better low-temperature catalytic performance with above 85% NO conversion in the wide temperature range of 80-240 ℃. However, higher and lower WO₃ contents can reduce the catalytic activities of the tertiary oxides, though the catalyst with 7.5% WO₃ content has better high-temperature activity (＞240 ℃). Macro-transient experiments reveal that the absorption and activation of NH₃ is of the utmost importance in the NH₃-SCR reaction. Gaseous NH₃ in the presence of O₂ can reduce NO_x slightly and O₂ can stimulate the oxidization of NO_x and protect the active center on the surface of catalysts so as to promote the absorption and activation of NH₃.

Key words:MnO_x/WO₃/TiO₂; low-temperature SCR; catalytic performance; macro-transient experiment