凝胶制备对气相合成MCM-22沸石的影响

以硅酸钠为硅源、硫酸铝为铝源制备硅铝干凝胶，六亚甲基亚胺（HMI）为模板剂，采用气相法合成MCM-22沸石。对硅铝干凝胶进行了29 Si MAS NMR、27 Al MAS NMR、红外以及透射电镜表征，讨论了pH值对硅铝干凝胶及合成MCM 22沸石的影响。结果表明，pH值的改变影响硅铝聚集态、干凝胶的结构及其粒径等物理性质，合成时硅铝干凝胶解聚、气固间传质及固相溶解速度不一致，影响产物MCM-22的结晶度。当制备干凝胶的pH值为8.7～10.7时，得到结晶度高的MCM-22沸石；当pH值增大到11.1时，产物出现杂晶丝光沸石；pH为11.6时只能得到丝光沸石。

Synthesis of zeolite MCM-22 by the vapor-phase method with xerogels prepared in different pH conditions

Zeolite MCM-22 was synthesized by vapor phase transport method (VPT) with sodium silicate as silicon source, aluminium sulfate as aluminum source and HMI as the template. The characterization of xerogels was carried out using29Si MAS NMR,27 Al MAS NMR, FTIR and TEM. The effect of pH value on the structure of xerogels and synthesis of MCM-22 was investigated. It was indicated that the structure and the proportion of different composing aluminium silicates of xerogels were changed with pH value. The periods for the hydrosol turning into hydrogel increased with the increase of the pH. The xerogels had different particle sizes and properties in the different pH conditions. The alkalinity of the xerogel had very important impact on the crystallization of MCM-22. The pure MCM-22 was obtained when the pH of preparation hydrogels was between 8.7 and 10.7. MOR appeared partially when the pH value reached 11.1 and pure MOR was obtained when the pH was 11.6.