Synthesis of Chainlike ZSM-5 Zeolites: Determination of Synthesis Parameters, Mechanism of Chainlike Morphology Formation, and Their Performance in Selective Adsorption of Xylene Isomers
Synthesis of Chainlike ZSM-5 Zeolites: Determination of Synthesis Parameters, Mechanism of Chainlike Morphology Formation, and Their Performance in Selective Adsorption of Xylene Isomers
复制标题
链状ZSM-5沸石的合成：合成参数的确定、链状形貌形成机制及其对二甲苯异构体的选择性吸附性能
DOI：
10.1021/acsami.7b02738
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发表时间：
2017-05-03
影响因子：
9.5
通讯作者：
Wang, Jianguo
中科院分区：
文献类型：
--
作者：
Quan, Yanhong;Li, Shiying;Wang, Jianguo
链状沸石作为催化剂或吸附剂具有特定的选择性，在各种应用中是有利的;然而，由于沸石合成过程的复杂性，通常很难获得所需的形貌。本工作确定了合成理想链状ZSM-5分子筛的适宜工艺参数，说明合成混合物的组成、合成体系中残留醇的量和晶化时间可以控制分子筛的链长。此外，通过对合成过程中表面物种的分析，结合密度泛函理论（DFT）计算，探讨了链状晶体的生长机理。结果表明，具有合适尺寸和表面平坦且含有丰富羟基的盘状晶体的形成是链状ZSM-5晶体生长的关键;（010）晶面上的Si-OH基团比其他晶面上的Si-OH基团更有利于缩合，导致MFI晶体沿着b-取向生长。通过对各种合成参数的微调，在不使用其它有机添加剂的情况下，除了必要的模板剂如四丙基氢氧化铵（TPAOH）外，得到了b-取向长度可控的链状ZSM-5分子筛。由于链状ZSM-5分子筛孔道弯曲度的增加，使得对二甲苯和邻、间二甲苯在吸附和扩散方面的差异大大增强。这些结果有助于阐明链状沸石分子筛的形成机理，进而为获得具有特殊吸附和催化性能的分子筛材料提供了一条有效途径。
Chainlike zeolites are advantageous to various applications as a catalyst or an adsorbent with specific selectivity; however, it is often very difficult to get desired morphology due to the complexity of zeolite synthesis process. In this work, appropriate parameters for the synthesis of perfect chainlike ZSM-5 zeolites were well determined, which illustrates that the chain length can be controlled by the composition of synthesis mixture, the amount of residual alcohol in the synthesis system, and the crystallization time. Moreover, the mechanism of chainlike crystal growth was investigated by analyzing the surface species during the synthesis process, with the help of density functional theory (DFT) calculation. The results indicate that the formation of disk crystals with proper dimension and flat surface having abundant hydroxyl groups is crucial to the growth of chainlike ZSM-5 crystals; the condensation of Si-OH groups on the (010) facet is energetically more favorable than that on other facets, leading to the growth of MFI crystals along the b-orientation. Through finely tuning the multifarious synthesis parameters, chainlike ZSM-5 zeolites with controllable length in b-orientation are obtained without using any other extra organic additives except the necessary template agent such as tetrapropylammonium hydroxide (TPAOH). Owing to the increased tortuosity of pore channels in the chainlike ZSM-5, the difference between p-xylene and o/m-xylenes in their adsorption behavior and diffusivity is greatly enhanced. These results help to clarify the formation mechanism of zeolites with chainlike morphology and then bring forward an effective approach to get zeolite materials with specific properties in adsorption and catalysis.