MFI型硅铁沸石水热合成、介孔改性与结构表征

Hydrothermal Synthesis,Mesoporous Modification and Structural Characterization of Ferrisilicate Zeolites with MFI Structure

采用无机铁、硅原料合成不同组成的MFI型硅铁沸石。通过碱酸处理对质子化硅铁沸石进行介孔改性。用X射线衍射、Fourier变换红外光谱、紫外–可见光谱、N_2吸附、扫描电子显微镜和能量色散X射线谱表征沸石的晶体和孔结构性质,探究骨架Si/Fe摩尔比与晶内介孔率和Si、Fe脱除行为的关系。结果表明:合成的硅铁酸盐是结晶性好的Fe^(3+)同构取代MFI型沸石;系列改性硅铁沸石具有较高的结晶度保留率、脱硅选择性、介孔率及二级介孔分布特征。骨架Si/Fe比是影响沸石选择性脱硅和介孔形成的关键因素。起始Si/Fe比为60~120的改性沸石具有更高的介孔率及Si、Fe脱除效率。

MFI-type ferrisilicates with various Si/Fe molar ratios were hydrothermally synthesized using inorganic ferric and silica sources. The mesoporous modification of the MFI-type ferrisilicates in proton form was performed via a combined alkali-acid treatment. The crystal structure and porous distribution of precursor and modified zeolites were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible light absorption spectroscopy, N2-adsorption, scanning electron microscopy, and energy dispersive X-ray spectroscopy, respectively. The results show that the intra-grain mesoporostity and removal behavior of T-atoms （T= Si ＋ Fe） are correlated to Si/Fe ratio in framework. The ferrisilicates as-prepared are MFI zeolites with a complete crystallinity, in which most Fe^3＋ atoms are incorporated into MFI framework. After being subjected to the alkali-acid treatment, the ferrisilicates preserve an adequate crystallinity, a high desilication selectivity and a mesoporosity, and present a two-level mesopore distribution. Moreover, the initial Si/Fe ratio in framework has a crucial effect on the controlled desilication for mesopore formation. The modified zeolites with initial Si/Fe ratios in the range of 60-120 have both greater mesoporostity and removal efficiency of T-atoms.