提出了一种(NH4)2SiF6处理提高SBA-15介孔材料水热稳定性的改良方法.采用SBA-15介孔材料中预引入Al3+离子,再进行1%SiO2计量的(NH4)2SiF6处理,最后用强酸洗脱预引入的Al3+.结果显示,由此处理的SBA-15材料,其水热稳定性明显优于相同条件下未预引入Al3+时(NH4)2SiF6处理的样品.两者在800°C、100%水蒸气处理12 h后,虽然均能很好保持其介观有序度、形貌及六方孔道结构,但前者的比表面积可高达271 m2/g,而后者仅为224 m2/g.表明Al3+离子介入能大幅度提升(NH4)2SiF6处理对SBA-15介孔材料的稳定化作用.这主要得益于预引入的骨架Al3+在保障(NH4)2SiF6处理修复SBA-15材料表面缺陷和进行表面疏水化、提升其水热稳定性的同时,能减缓(NH4)2SiF6释放的多余F-离子对SBA-15材料骨架的刻蚀破坏作用. Al3+离子介入的这种提升作用与其引入方式和SBA-15材料所经受的温度密切相关.
This work demonstrates an improved (NH4)2SiF6 treatment to enhance the hydrothermal stability of mesoporous SBA-15 zeolite. In this treatment, Al3+ ions are incorporated into SBA-15 zeolite first, then it is treated with 5% (NH4)2SiF6 solution according to 1% SiO2 of SBA-15 and finally washed with HCl (2 mol/L) to remove the pre-incorporated Al3+ions. The obtained SBA-15 exhibits higher hydrothermal stability than that without pre-incorporated Al3+. Compared with the latter, the sam-ple maintains a better ordered mesostructure and a larger surface area (271 m2/g) after hydro-thermal treatment at 800 °C for 12 h in 100% steam. The results show that incorporating Al3+ ions into SBA-15 zeolite before (NH4)2SiF6 treatment obviously promotes the stabilization effect of (NH4)2SiF6treatment. The mechanism suggests that the incorporated Al3+ ions can effectively cap-ture F- ions that have been released from (NH4)2SiF6, and thus reduce their etching into the SBA-15 zeolite framework. This ensures that the positive factors of (NH4)2SiF6 treatment, such as silicon insertion and surface hydrophobization by F- ions, play effective roles in the improvement of the hydrothermal stability of SBA-15 zeolite. This promoting effect of the Al3+ ions is closely related to the method that is used to introduce the Al3+ and the SBA-15 zeolite processing temperature.
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