MnOx/MWCNTs低温氨选择性催化还原NOx硫中毒机理

摘要

以经过浓硝酸和等离子体放电预处理后的多壁碳纳米管(MWCNTs)为载体,锰氧化物(MnOx)为活性组分,采用等体积浸渍法制备MnOx/MWCNTs催化剂.利用热重分析(TGA)、扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、程序升温还原/脱附(TPR/TPD)以及傅里叶变换红外(FTIR)光谱对催化剂进行表征,探讨SO2对催化剂低温氨选择性催化还原(SCR)NOx活性的影响及SO2中毒机理.结果表明,低温下SO2对MnOx/MWCNTs催化剂活性有明显毒化作用.反应温度越高,SO2浓度越大,催化剂SCR活性下降越快.活性中心Mn原子硫酸化是催化剂失活的主要原因.另外,催化剂表面生成硫酸铵盐以及SO2对NO吸附的抑制作用也一定程度上造成了催化剂的失活.%Manganese oxides supported on multi-walled carbon nanotubes (MnOx/MWCNTs) catalysts were prepared by pore volume impregnation using MWCNTs as the catalyst support which was pretreated by concentrated nitric acid and oxygen dielectric barrier discharge plasma. The catalysts were characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction/desorption (TPR/ TPD), and Fourier transform infrared (FTIR) spectroscopy. The effect of SO2 on the activity of the catalysts for low-temperature selective catalytic reduction (SCR) of NOx by ammonia and the SO2 poisoning mechanism were investigated. The results showed that SO2 had an obvious poisoning effect on the SCR activity of MnOx/MWCNTs at low temperature. The activity decreased more rapidly as reaction temperature and SO2 concentration increased. The observed deactivation was attributed to the sulfation of the active center atoms. Formation of ammonium sulfate on the catalyst surface and the inhibiting effect of SO2 on NO adsorption also resulted in the deactivation of the catalysts to some extent.