MnOx/WO3/TiO2低温NH3选择性催化还原NOx的性能

摘要

Series of MnO/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 NOx 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 NOx It is found that the addition of appropriate amount of WO3 can improve remarkably the catalytic activity of Mn-based catalysts. Particularly, the 15%MnOx/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 NOx slightly and O2 can stimulate the oxidization of NOx and protect the active center on the surface of catalysts so as to promote the absorption and activation of NH3.%采用一步浸渍法制备不同WO3含量的MnOx/WO3/TiO2催化剂,在模拟氨气选择性催化还原NOx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NOx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％MnOx/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NOx.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.