Department of Chemistry and Applied Bioscience, Institute for Chemical and Bioengineering, ETH Zurich, Vladimir-Prelog-Weg 1, 8093, Zurich, Switzerland.
Paul Scherrer Institute, 5232, Villigen, Switzerland.
Chemistry. 2019 Dec 10;25(69):15879-15886. doi: 10.1002/chem.201903852. Epub 2019 Nov 12.
Hollow ZSM-5 zeolites of size below one micrometer can be produced by desilication of crystals with aluminium zoning. The parent crystals have a core-shell structure: the core part has nearly no aluminium, whereas the aluminium content in the shell increases when extending to exterior surface. Transmission electron microscopy confirmed the preservation of the crystalline shell after base leaching, but could not identify its subtle change. An increase of the Si/Al ratio of the surface was detected upon leaching the parent material to form the hollow zeolite by using ambient pressure X-ray photoelectron spectroscopy and infrared spectroscopy of substituted alkylpyridines. Al MAS NMR showed that base leaching results in a reduced percentage of distorted tetrahedrally coordinated aluminium. The reprecipitation of dissolved species occurs and tetrahedrally coordinated tin atoms can thus be introduced to the shell framework. Overall, the formation of hollow ZSM-5 zeolites by desilication involves not only the removal of silicon-rich core, but also a reduced percentage of exterior aluminium-related acid sites, which should be considered while using hollow zeolites in acid-catalyzed reactions.
可以通过脱硅作用来制备小于 1 微米的中空 ZSM-5 沸石，脱硅作用针对的是具有铝分区的晶体。母体晶体具有核壳结构：核心部分几乎不含铝，而当延伸到外表面时，壳层中的铝含量增加。透射电子显微镜证实了在碱浸后晶体壳的保留，但无法识别其细微变化。通过使用环境压力 X 射线光电子能谱和取代的烷基吡啶的红外光谱，在母体材料中浸出以形成中空沸石时，检测到表面的 Si/Al 比增加。Al MAS NMR 表明，碱浸导致变形的四配位铝的百分比降低。溶解物种的再沉淀发生，因此四配位的锡原子可以引入到壳层骨架中。总体而言，通过脱硅作用形成中空 ZSM-5 沸石不仅涉及去除富硅的核心，还涉及减少外部与铝相关的酸位的百分比，在酸催化反应中使用中空沸石时应考虑到这一点。
