石墨烯负载MnOx催化剂的制备及其低温NH3-SCR活性

通过改进的Hummers法合成氧化石墨烯(GO), 随后采用水热法制备石墨烯负载锰氧化物(MnO_x/GR)催化剂. 考察了催化剂的低温NH₃选择性催化还原(NH₃-SCR)去除NO_x的性能, 并通过傅里叶变换红外(FTIR)光谱, 拉曼(Raman)光谱, X射线衍射(XRD), 透射电镜(TEM), N₂吸附-脱附, X射线光电子能谱(XPS)及H₂程序升温还原(H₂-TPR)等多种表征手段对催化剂的结构及NH₃-SCR性能进行分析. 结果显示, 不同MnO_x负载量的MnO_x/GR催化剂均展现了较好的低温SCR催化活性, 且在负载量为20%(w)时活性最优. 表征分析结果表明, 制备的GO表面含有丰富的含氧基团, 锰可以通过与含氧基团结合而负载到GO上; MnO_x/GR催化剂中MnO_x以纳米颗粒分散于石墨烯载体表面, 且以多种氧化物(MnO、Mn₃O₄和MnO₂)共同存在; 负载量为20%(w)的催化剂中高价锰和表面吸附氧含量增加, 低温区氧化还原能力增强及活性位点数量增加是其SCR活性提高的原因.

Preparation of Manganese Oxides Supported on Graphene Catalysts and Their Activity in Low-Temperature NH3-SCR

Graphene oxide (GO) was synthesized using an improved Hummers method. Subsequently, catalysts of manganese oxides (at varying loadings) supported on graphene (MnO_x/GR) were prepared by hydrothermal reaction for application in the selective catalytic reduction (SCR) of NO_x with NH₃ at low temperatures. The structural properties and catalytic performance were evaluated by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption, X-ray photoelectron spectroscopy (XPS), and H₂ temperature-programmed reduction (H₂-TPR). The characterization results indicated that abundant functional groups existed on the surface of the prepared GO that could combine with manganese during preparation of the catalysts. Manganese oxide entities, with different crystallinities (MnO, Mn₃O₄, or MnO₂), were dispersed on the surface of graphene. The results of the catalytic studies showed that the MnO_x/GR catalysts prepared with different MnO_x loadings all exhibited excellent low-temperature SCR activities. The catalyst with 20%(w) MnO_x displayed the best activity, which was attributed to the high content of high-valent manganese and oxygen adsorbed onto the catalyst surface, as well as to the enhancement in redox abilities and the addition of active sites at low temperatures.