Effects of cerium on the selective catalytic reduction activity and structural properties of manganese oxides supported on multi-walled carbon nanotubes catalysts

Abstract

A series of manganese and cerium oxides supported on multi-walled carbon nanotubes (MWCNTs) catalysts for low-temperature NH 3 selective catalytic reduction (SCR) of NO x were prepared by the pore volume impregnation method. The SCR activity of Mn-Ce/MWCNTs catalysts was compared with that of Mn/MWCNTs catalyst. The effects of Ce were characterized by transmission electron microscopy, N 2 adsorption-desorption, H 2 temperature-programmed reduction, X-ray photoelectron spectroscopy and X-ray powder diffraction. The results show that the addition of cerium oxides could improve the SCR activity of Mn/MWCNTs catalysts. Mn-Ce/MWCNTs catalyst with a Ce/Mn ratio of 0.6 was found to have the highest activity. The addition of cerium oxides enhanced the dispersion of metal oxides on the MWCNTs. It could also increase the specific surface area and total pore volume, and decrease the average pore size of the catalysts. Ce would improve the concentration of oxygen and the valence of manganese. Furthermore, from the XRD results, it was obvious that the crystalline MnO x disappeared because of the introduction of Ce to the catalyst. MnO x mainly existed in an amorphous state or microcrystal structure in the Mn-Ce/MWCNTs catalysts. CeO 2 was found to be the main phase for CeO x . 采用等体积浸渍法制备多壁碳纳米管(MWCNTs)负载Ce-Mn的催化剂, 考察了Ce掺杂对Mn/MWCNTs催化剂上NH 3 选择性催化还原(SCR)NO x 反应活性的影响. 并运用透射电镜扫描/N 2 吸附-脱附/程序升温还原/X射线光电子能谱/X射线衍射等手段, 重点考察了Ce掺杂对Mn/MWCNTs催化剂结构性质的影响. 结果表明, Ce掺杂能显著提高催化剂的SCR活性, 其活性增量随着Ce含量的增加先增大后减小; 当Ce/Mn为0.6时, 催化剂活性最佳. 表征结果显示, Mn/MWCNTs中添加Ce后, 金属氧化物在MWCNTs上的分散程度提高; 催化剂的比表面积和孔体积增大, 平均孔径减小; 氧化能力提高; 表面氧含量增加, Mn化合价升高; 结晶度降低, Mn主要以无定形或微晶形式存在, Ce主要以CeO 2 物相存在. This study examines the effects of cerium on the selective catalytic reduction (SCR) activity and the structure of Mn/MWCNTs by comparing SCR activity, specific surface area, crystallization, oxidizability, and superficial species and elements.