以MnOx/TiO2作为催化剂的低温SCR反应过程中还原剂NH3的作用

研究了在以MnOx/TiO2作为催化剂的低温SCR反应过程中,还原剂NH3所起的作用.当系统中NH3浓度较低时,增加气相中NH3的浓度可以大幅度提高NO的去除率.但当系统中NH3浓度较高时,NO去除率基本不随NH3浓度变化而变化.并且瞬态研究中,NH3对NO去除率的影响较为复杂.为了探明NH3在SCR反应中的作用,用原位傅立叶红外检测了各个反应历程中NH3在催化剂表面形成的基团变化及其活性特征.结果表明,在SCR反应过程中,在催化剂表面形成的配位态的NH3是参与反应的主要物质.并且在催化剂表面,此种NH3会与NO生成的硝酸盐形成竞争吸附,当催化剂活性点首先被硝酸盐占领时,将会影响配位态NH3的生成,从而在一定程度上降低了NO的转化率.

The role of NH3 in the low-temperature selective catalytic reduction of NO over MnOx/TiO2

In this study, a catalyst based on MnOx/TiO2 was prepared by a sol-gel method for low-temperature selective catalytic reduction (SCR) of NO, and the effect of NH3 on the SCR reaction was studied. It was found that NO conversion increased with the increase of NH3 concentration when the concentration of NH3 was low. However, when NH3 concentration was relatively high, the change of NH3 concentration had a negligible effect on the NO removal efficiency. In situ diffuse reflectance infrared transform spectroscopy (DRIFT) was used to study the reactivity of the NH3 species formed on the surface of the catalyst. The results showed that the coordinated NH3 was the activated form in the reaction, and it was in competition with nitrate formed from NO for adsorption on the catalyst. When the active sites are occupied by nitrate, the coordination of NH3 is inhibited and the NO conversion is reduced.