低温NH_3-SCR催化剂MnO_x-CeO_x/ACF的SO_2中毒机理(英文)

Deactivation of MnO_x-CeO_x/ACF Catalysts for Low-Temperature NH_3-SCR in the Presence of SO_2

在二氧化硫(SO2)气氛下,对Fe、Cu和V改性的催化剂MnOx-CeOx/ACF(活性碳纤维)的氨选择性催化还原(NH3-SCR)一氧化氮的低温活性进行研究.实验结果表明:以Cu和V改性催化剂未提高MnOx-CeOx/ACF的低温抗SO2性能;Fe改性MnOx-CeOx/ACF在初始6h内提高了催化剂的抗SO2性能,但较长时间仍然失活.以N2吸附、X射线光电子能谱(XPS)、傅里叶变换红外(FT-IR)光谱以及热重分析(TGA)等手段对中毒催化剂进行分析.在SO2存在下,催化剂中毒归因于两个方面:一是覆盖于催化剂表面的铵盐类物质,二是SO2与催化剂中的金属氧化物反应生成的金属硫酸盐及亚硫酸盐.在中毒催化剂中硫元素主要以金属硫酸盐及亚硫酸盐的形式存在,其在中毒的MnOx-CeOx/ACF、Fe-MnOx-CeOx/ACF、Cu-MnOx-CeOx/ACF和V-MnOx-CeOx/ACF催化剂中所占比例分别为70.4%、68.9%、86.3%和71.4%(w).进一步揭示了MnOx-CeOx/ACF催化剂在低温SCR条件下的SO2中毒机理.

The low-temperature selective catalytic reduction of NO with NH3 （NH3-SCR） over MnOx-CeOx/ACF （activated carbon fiber） modified by Fe, Cu, or V was investigated in the presence of SO2. The results revealed that the SO2 tolerance of MnOx-CeOx/ACF was not enhanced after Cu and V modification. The addition of Fe to MnOx-CeOx/ ACF enhanced its resistance to SO2 poisoning over the first 6 h in the presence of SO2, but then deactivated quickly. The samples were analyzed by N2 adsorption, X-ray photoelectron spectroscopy （XPS）, Fourier transform infrared （FT- IR） spectroscopy, and thermogravimetric analysis （TGA）. We found that catalyst surface coverage by ammonium salts as well as metallic sulfates and sulfites formed by the reaction between SO2 and metal oxides in the catalysts was responsible for catalyst deactivation in the presence of SO2. Sulfur on the surface of the deactivated catalysts was mainly in the form of metallic sulfates and sulfites with 70.4%, 68.9%, 86.3%, and 71.4%（w） on deactivated MnOx-CeOx/ACF, Fe- MnOx-CeOx/ACF, Cu-MnOx-CeOx/ACF, and V-MnOx-CeOx/ACF, respectively. A valuable contribution towards understanding the deactivation of catalysts based on MnOx-CeOx/ACF for the SCR in the presence of SO2 was made.