含铜有序介孔Cu-KIT-6的合成及其苯乙烯环氧化催化性能:pH值的影响（英文）
发布时间：2018-09-18 18:08
【摘要】：苯乙烯侧链C=C的选择性氧化一直是烯烃环氧化研究领域关注的热点之一.近几十年来,苯乙烯环氧化研究主要集中于多相过渡金属催化剂的开发与应用;以铜为主要活性物种的催化剂因具有较高的环氧苯乙烷选择性而备受瞩目.然而,采用pH调节法将铜离子引入三维六方介孔材料KIT-6阵列尚未见报道,尤其是pH值对合成材料的形貌、结构以及催化活性的影响尚未可知.基于此,本文采用pH调节法合成了铜嵌入KIT-6介孔材料Cu-KIT-6x(x代表初始溶胶的pH值,x=1.43,2.27,3.78,3.97,4.24,6.62),并将其应用于苯乙烯环氧化反应.采用X射线粉末衍射、氮气吸附脱附、透射电子显微镜以及X射线光电子能谱等手段对Cu-KIT-6x的表面结构及形貌进行了细致表征.结果表明,随着pH的变化,Cu-KIT-6x催化剂的物理特性、表面结构尤其是铜物种种类和含量均变化较大.较低的pH导致铜物种主要以Cu~(2+)形式存在,难以引入到KIT-6骨架中,且不利于介孔材料的合成,最终导致产生无序介孔结构.当pH增大到3.78时,约有4.6 wt%的Cu(Ⅱ)以 Cu O Si 形式成功引入KIT-6骨架中,获得了具有较高比表面积且有序的孔结构.此外,由于Cu~(2+)的引入,骨架内部分Si~(4+)被取代,促使Cu-KIT-6_(3.78)拥有可与载体KIT-6相媲美的大孔径.然而,当pH继续增大时,过量的Cu~(2+)从KIT-6骨架中析出,以CuO形式存在于载体表面,从而导致Cu-KIT-6的孔径逐渐增大;同时NaOH对三维立方介孔结构的破坏,使得介孔结构坍塌及比表面积显著降低.以苯乙烯环氧化反应评价了Cu-KIT-6x系列催化剂的催化活性.当以叔丁基过氧化氢为氧化剂,乙腈为溶剂,在70 ℃反应6 h后,Cu-KIT-6_(3.78)表现出最优的苯乙烯转化率(43.5%)及环氧苯乙烷选择性(86.6%).使用4次后,Cu-KIT-6_(3.78)展示了稳定的苯乙烯转化率、环氧苯乙烷选择性及有序的孔结构,充分表明其具有出色的稳定性.各表征结果揭示了在适宜pH下合成的Cu-KIT-6_(3.78)催化剂具有较高的铜含量、有序的立方Ia3d介孔结构及合适的结构参数,因而在苯乙烯环氧化反应中表现优异活性和良好稳定性.
[Abstract]:Selective oxidation of side chain C of styrene has been one of the hot topics in the field of epoxidation of olefin. In recent decades, the epoxidation of styrene has focused on the development and application of polyphase transition metal catalysts, and the catalyst with copper as the main active species has attracted much attention for its high selectivity to epoxy-phenylethane. However, the introduction of copper ions into KIT-6 arrays of three-dimensional hexagonal mesoporous materials by pH adjustment method has not been reported, especially the effect of pH value on the morphology, structure and catalytic activity of the synthesized materials. Based on this, the copper intercalated KIT-6 mesoporous material Cu-KIT-6x (x representing the pH value of the initial sol) was synthesized by pH adjustment method and applied to the epoxidation of styrene. The surface structure and morphology of Cu-KIT-6x were characterized by X-ray powder diffraction, nitrogen adsorption and desorption, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that the physical properties of Cu-KIT-6x catalyst vary with the change of pH, and the surface structure, especially the species and content of copper species change greatly. Due to the low pH, copper species mainly exist in the form of Cu~ (2), which is difficult to be introduced into the framework of KIT-6, and is not conducive to the synthesis of mesoporous materials, resulting in the formation of disordered mesoporous structure. When pH increased to 3.78, about 4.6 wt% Cu (鈪，
本文编号：2248702
[Abstract]:Selective oxidation of side chain C of styrene has been one of the hot topics in the field of epoxidation of olefin. In recent decades, the epoxidation of styrene has focused on the development and application of polyphase transition metal catalysts, and the catalyst with copper as the main active species has attracted much attention for its high selectivity to epoxy-phenylethane. However, the introduction of copper ions into KIT-6 arrays of three-dimensional hexagonal mesoporous materials by pH adjustment method has not been reported, especially the effect of pH value on the morphology, structure and catalytic activity of the synthesized materials. Based on this, the copper intercalated KIT-6 mesoporous material Cu-KIT-6x (x representing the pH value of the initial sol) was synthesized by pH adjustment method and applied to the epoxidation of styrene. The surface structure and morphology of Cu-KIT-6x were characterized by X-ray powder diffraction, nitrogen adsorption and desorption, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that the physical properties of Cu-KIT-6x catalyst vary with the change of pH, and the surface structure, especially the species and content of copper species change greatly. Due to the low pH, copper species mainly exist in the form of Cu~ (2), which is difficult to be introduced into the framework of KIT-6, and is not conducive to the synthesis of mesoporous materials, resulting in the formation of disordered mesoporous structure. When pH increased to 3.78, about 4.6 wt% Cu (鈪，
本文编号：2248702
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