Synthesis and characterization of microporous EU-1/ZSM-5 composite zeolite containing iron
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摘要: 采用预置晶种法合成了含铁的微孔EU-1/ZSM-5复合分子筛,并采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、热重-微分热重(TG-DTG)、N2吸附-脱附、紫外-可见吸收光谱(UV-vis DRS)、X射线吸收精细结构(XAFS)等手段进行了表征。结果表明,复合分子筛具有EU-1和ZSM-5的特征衍射峰,是两种晶相相互作用的分子分散晶相材料,微孔孔径较Fe-EU-1分子筛有所增大。随原始溶胶中铁的质量分数增加,复合分子筛具有的23.09°和23.94°处的特征衍射峰逐渐向低角度方向偏移;紫外-可见漫反射谱图中在220~245 nm出现了宽的吸收谱带;XAFS表征表明,1s→3d电子跃迁的弱吸收峰逐渐增强,同时在吸收边顶部出现的1s→4p吸收峰逐渐由宽变窄。合成工艺的最佳条件为,原始溶胶中铁的质量分数为0.075%~0.15%,晶种添加比例为15.0%~21.0%,晶种SiO2/Al2O3物质的量比为50~60。
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关键词:
- 预置晶种 /
- Fe-EU-1/ZSM-5 /
- 复合分子筛 /
- 合成
Abstract: Microporous EU-1/ZSM-5 composite zeolites containing iron were synthesized using preset crystal seed method. The as-synthesized Fe-EU-1/ZSM-5 samples were characterized by a serious of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric-derivative thermogravimetric (TG-DTG), N2 adsorption/desorption, UV-visible diffuse reflectance spectroscopy (UV-Vis DRS) and X-ray absorption fine structure (XAFS). The results show that the composite zeolite is found consisting characteristic diffraction peaks for two kinds of zeolite structure: EU-1 and ZSM-5. The composite zeolite is a kind of molecular dispersion material with two crystal phases interaction and its micropore size is larger than Fe-EU-1 zeolite. With increasing the mass fraction of Fe in the original sol-gel, the characteristic diffraction peaks of composite zeolites in the 23.09° and 23.94° gradually migrate to lower angle direction. UV-vis spectrum shows that there is a broad absorption band at about 220~245 nm. The XAFS results show that the week pre-edge absorption peak for 1s→3d gradually strengthen, at the same time the absorption peak for 1s→4p in the top of absorption edge has tapper. The optimized synthesis conditions for the microporous EU-1/ZSM-5 composite zeolites containing iron are as follows: 0.075%~0.15% of the mass fraction of Fe in the original sol-gel, 15.0%~21.0% of the mass fraction of ZSM-5 zeolite in the original sol-gel and 50~60 of SiO2/Al2O3 mol ratio of ZSM-5 zeolite.-
Key words:
- preset crystal seed /
- Fe-EU-1/ZSM-5 zeolite /
- composite molecular sieves /
- synthesize
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