Shao Yaofeng, Wang Lingzhi, Zhang Jinlong, Anpo Masakazu
Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, People's Republic of China.
J Phys Chem B. 2005 Nov 10;109(44):20835-41. doi: 10.1021/jp054024+.
The hydrothermally stable and long-range ordered Ce-MCM-48 and Fe-MCM-48 were conveniently synthesized at 393 K for 24 h by directly adding fluoride ions to the initial gel without posttreatment and pH adjustment. The Ce-MCM-48 with a Si/Ce of 200 and 100, which were prepared by directly adding fluoride ions, could still maintain their mesoporous structures after refluxing in boiling water for 3 days. The incorporation of Ce into MCM-48 could enhance the hydrothermal stability of MCM-48 in the absence of fluoride ions; however, the incorporation of Fe into MCM-48 materials barely improved the hydrothermal stability of MCM-48 materials. The effect of adding NaF was much more efficient in enhancement of hydrothermal stability than that of the incorporation of Ce. The addition of fluoride ions mainly improves the degree of polymerization of silicates. The Ce(4+) ions in Ce-MCM-48 appear to be present partly in tetrahedral coordination in the framework and partly as CeO(2) particles on the surface of framework. The Ce positioned on the surface of pore walls and in the framework both provide the protection against water attack.
通过在初始凝胶中直接添加氟离子，无需后处理和调节pH值，在393K下方便地合成了水热稳定且具有长程有序结构的Ce-MCM-48和Fe-MCM-48，反应时间为24小时。通过直接添加氟离子制备的Si/Ce比为200和100的Ce-MCM-48，在沸水中回流3天后仍能保持其介孔结构。在不存在氟离子的情况下，将Ce掺入MCM-48中可提高MCM-48的水热稳定性；然而，将Fe掺入MCM-48材料中几乎不能提高MCM-48材料的水热稳定性。添加NaF在提高水热稳定性方面比掺入Ce的效果更显著。氟离子的添加主要提高了硅酸盐的聚合度。Ce-MCM-48中的Ce(4+)离子似乎部分以四面体配位形式存在于骨架中，部分以CeO(2)颗粒形式存在于骨架表面。位于孔壁表面和骨架中的Ce都提供了抵御水侵蚀的保护作用。
