MnCo改性的MCM-41催化剂用于氯苯催化燃烧的研究

doi:10.1016/S1872-2067(17)62950-4

摘要/Abstract

摘要：

含氯挥发性有机化合物（CVOCs）是对人体健康和环境危害极大的有机化合物.常见的有二氯乙烷、三氯乙烯、三氯甲烷、四氯化碳和氯苯等.有些CVOCs是"三致"（致畸、致癌、致突变）物质，有些少量进入大气就能破坏臭氧层，亦或与臭氧等形成光化学烟雾，引起全球变暖.因此，对于其消除迫在眉睫.CVOCs通常采用高温直接燃烧、吸附、光催化氧化和催化燃烧等方法降解.其中，催化燃烧是非常有效的.我们选择氯苯作为CVOCs探针分子是因其不仅存在于农药和化工产品中，在室内环境中也大量存在，而负载贵金属和非贵金属型催化剂可用于其催化降解.贵金属催化剂价格高而且易氯中毒，但过渡金属催化剂价格低且抗失活，因而是不错的选择.通常过渡金属催化剂使用V₂O₅，Cr₂O₃，MnO₂，Co₃O₄及NiO等活性组分，而Mn和Co氧化物有较好活性且没有环境污染，常用作活性组分.另外，MCM-41是有序介孔硅酸盐和硅铝酸盐家族中M41S的一员，具有高的比表面积和较窄的孔径分布，常用作催化剂的载体.我们利用具有大比表面积、大孔径的MCM-41作为载体，采用浸渍法负载MnO_x，CoO_x，MnO_x-CoO_x等活性组分，制备系列的催化剂用于低浓度氯苯的催化燃烧，研究催化剂的催化活性、选择性及稳定性.并利用XRD、N₂吸脱附、高分辨电镜-能谱分析、H₂-TPR和CB-TPD等手段对MCM-41及催化剂的织构-结构、表面形貌、活性组分分散状态、氧化还原性能及吸附性能等做了系统的研究.
采用表面活性剂软模板技术合成了具有大比表面积、大孔径、耐热稳定性高的MCM-41介孔分子筛，负载不同比例的Mn/Co（摩尔比是3：1、6：1及9：1，其中总负载量为10%），以氯苯催化燃烧为探针反应，筛选出活性最佳时的Mn/Co比例.活性评价实验结果表明，各催化剂的活性以下列顺序依次降低：MnCo（6：1）/MCM-41 > MnCo（9：1）/MCM-41 > MnCo（3：1）/MCM-41 > Mn/MCM-41 > Co/MCM-41，其中MnCo（6：1）/MCM-41活性最佳，在270℃即可完全催化燃烧氯苯.耐久性实验结果显示，MnCo（6：1）/MCM-41在连续反应1000h后，其活性没有降低，表明其具有非常良好的稳定性.XRD实验结果表明，在Mn/MCM-41及Co/MCM-41催化剂上分别检测到MnO₂及Co₃O₄的特征衍射峰.在MnCo（6：1）/MCM-41催化剂上，MnO₂及Co₃O₄的特征衍射峰消失，同时出现了MnCoO_x的特征衍射峰，这是由于MnO₂及Co₃O₄的强相互作用经过焙烧后形成的，且MnCoO_x的特征衍射峰较小，表明双金属活性组分的分散比单金属催化剂好.N₂吸脱附结果显示，MCM-41的比表面积达到805.9m²/g，孔体积达到0.795cm³/g.负载活性组分后其比表面积及孔体积均有不同程度的减小，这是由于活性组分进入了MCM-41的孔隙.高分辨电镜结果表明，MCM-41具有均匀的介孔孔道结构，MnCoO_x在MCM-41表面的颗粒小，分散好.能谱扫描出Mn，Co，O等元素，表明活性组分成功地负载在MCM-41载体上.H₂-TPR表明，双金属催化剂的还原峰温较单金属催化剂低，表明其具有更好的氧化性能.CB-TPD结果表明，MnCo双金属催化剂脱附氯苯的温度高于单金属催化剂，说明氯苯与催化剂之间的相互作用更强，即双金属催化剂对氯苯的吸附能力更强，使得氯苯催化燃烧更加充分，因此其催化性能更好.同时，深入探讨了MnO_x，CoO_x，MnCoO_x和MCM-41之间的相互作用及对催化燃烧性能的影响.

关键词: MCM-41分子筛, Mn/Co, 催化燃烧, 氯苯, 表征

Abstract:

MCM-41 was synthesized by a soft template technique. The specific surface area and pore volume of the MCM-41 were 805.9 m²/g and 0.795 cm³/g, respectively. MCM-41-supported manganese and cobalt oxide catalysts were prepared by an impregnation method. The energy dispersive X-ray spectroscopy clearly confirmed the existence of Mn, Co, and O, which indicated the successful loading of the active components on the surface of MCM-41. The structure and function of the catalysts were changed by modulating the molar ratio of manganese to cobalt. The 10%MnCo(6:1)/MCM-41 (Mn/Co molar ratio is 6:1) catalyst displayed the best catalytic activity according to the activity evaluation experiments, and chlorobenzene (1000 ppm) was totally decomposed at 270℃. The high activity correlated with a high dispersion of the oxides and was attributed to the exposure of more active sites, which was demonstrated by X-ray diffraction and high-resolution transmission electron microscopy. The strong interactions between MnO₂, Co₃O₄, MnCoO_x, and MCM-41 indicated that cobalt promoted the redox cycles of the manganese system. The bimetal-oxide-based catalyst showed better catalytic activity than that of the single metal oxide catalysts, which was further confirmed by H₂ temperature-programmed reduction. Chlorobenzene temperature-programmed desorption results showed that 10%MnCo(6:1)/MCM-41 had higher adsorption strength for chlorobenzene than that of single metal catalysts. And stronger adsorption was beneficial for combustion of chlorobenzene. Furthermore, 10%MnCo(6:1)/MCM-41 was not deactivated during a continuous reaction for 1000 h at 260℃ and displayed good resistance to water and benzene, which indicated that the catalyst could be used in a wide range of applications.

Key words: MCM-41, Mn/Co, Catalytic combustion, Chlorobenzene, Characterization

成珍, 李敬荣, 杨鹏, 左树锋. MnCo改性的MCM-41催化剂用于氯苯催化燃烧的研究[J]. 催化学报, 2018, 39(4): 849-856.

Zhen Cheng, Jingrong Li, Peng Yang, Shufeng Zuo. Preparation of MnCo/MCM-41 catalysts with high performance for chlorobenzene combustion[J]. Chinese Journal of Catalysis, 2018, 39(4): 849-856.

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