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Study on the selective oxidation of methane over highly dispersed molybdenum-incorporated KIT-6 catalysts

机译：甲烷的选择性氧化研究高度分散molybdenum-incorporated KIT-6催化剂

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摘要

A series of molybdenum-incorporated mesoporous silica (Mo-KIT-6) catalysts were successfully synthesized by a one-pot hydrothermal synthesis method, and were applied in the selective oxidation of methane to formaldehyde using oxygen as an oxidizing agent under atmospheric pressure. Comparatively, the corresponding supported catalysts (Mo/KIT-6) were prepared by incipient-wetness-impregnation method. The results of the small angle XRD, nitrogen adsorption/desorption isotherms, UV-vis, H-2-TPR and UV-Raman spectroscopy characterization combined with the catalytic activity tests demonstrated that molybdenum atoms were inserted into the framework of the mesoporous materials for the Mo-KIT-6 catalysts and the highly dispersed Mo = O bonds dominantly existed, which were responsible for the efficient selective formation of formaldehyde. However, for Mo/KIT-6 catalysts, the molybdenum oxide species were mainly loaded on the surface or inside the outer pore channels of the support and abundant emergence of the Mo-O-Mo bond played a major role in the activation of methane to COx. Furthermore, with equivalent molybdenum content, the methane selective oxidation performance of 8Mo-KIT-6 was obviously better than that of 4.6Mo/KIT-6, and the formaldehyde yield (2.1%) of 8Mo-KIT-6 was 2.3 times as much as that (0.9%) of 4.6Mo/KIT-6. In situ and operando UV-Raman results demonstrated that the structures of the MoOx active sites have a strong effect on the formation and elimination of carbon deposition during the separated redox reaction with methane and O-2, respectively. The polymerized MoOx active sites are favorable for the formation of graphitic carbon (G), which is called ordered carbon, while the isolated MoOx active sites are favorable for the formation of disordered carbon (D). The reduced highly dispersed MoOx active sites incorporated in the framework of silica are more easily reoxidized than those on the supported catalysts.
机译：一系列molybdenum-incorporated介孔硅(Mo-KIT-6)催化剂成功合成了一锅法水热合成方法,并应用于选择性使用氧气氧化甲烷的甲醛作为氧化剂在大气压力下。相比之下,相应的支持催化剂(Mo / KIT-6)准备的incipient-wetness-impregnation方法。小角x射线衍射结果,氮吸附/解吸等温线,紫外- H-2-TPR和UV-Raman光谱表征结合催化活性测试表明,钼原子被插入框架的介孔材料Mo-KIT-6催化剂和高度分散莫= O债券存在居多,这负责有效选择性甲醛的形成。催化剂,氧化钼物种主要是加载到外表面或内部孔隙通道的支持和丰富出现的Mo-O-Mo债券起到了重要作用甲烷活化的考克斯。随着钼当量,甲烷8 mo-kit-6的选择性氧化性能明显优于4.6 mo / KIT-6,和8 mo-kit-6的甲醛收率(2.1%)2.3倍(0.9%)的4.6 mo / KIT-6。原位和operando UV-Raman结果证明MoOx的结构活跃的站点有强烈的影响形成和消除碳沉积在分离与甲烷氧化还原反应分别和0 2。活跃的网站有利于形成的石墨碳(G),这被称为命令碳,而孤立MoOx活跃的网站有利于无序碳的形成(D)。减少高度分散MoOx活跃网站的框架纳入二氧化硅比那些更容易reoxidized支持的催化剂。

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