Hao Wenming, Zhang Lei, Ma Jinghong, Li Ruifeng
College of Chemical Engineering and Technology, Taiyuan University of Technology, Taiyuan, 030024, P.R. China.
Dalton Trans. 2022 Sep 26;51(37):14287-14296. doi: 10.1039/d2dt02110b.
Organic molecules are widely used as structure directing agents, mesopore generating agents or zeolite growth modifiers in the synthesis of various zeolites. However, the organic molecules used in zeolite synthesis are mostly positively charged cationic molecules, since the cationic group can balance the negative charge in the zeolite structure. Here we attempt for the first time to apply an anionic surfactant fatty alcohol polyoxyethylene ether ammonium sulfate (AESA) in the crystallization of zeolite Beta. It is found that both the crystallization process and the characteristics of the product were affected by the addition of AESA into the synthesis. Compared with that without AESA, it shows that the induction period was significantly prolonged for the synthesis of zeolite Beta with AESA, and the crystallinity and the completeness of the crystal were improved. The yield of the product was increased when AESA was used in the synthesis. The framework Si/Al ratio was increased when AESA was added into the synthesis gel, which could be due to the fact that the anionic surfactant AESA facilitated the formation of Si-O-Si bonds and hindered the combination of the negatively charged aluminum species to silicon species to form Si-O-Al bonds, thus increasing the incorporation of Si and reducing the incorporation of Al into the framework. Moreover, we demonstrate an ability to enrich chiral polymorph-A in zeolite Beta by using AESA in the crystallization, with the proportion of polymorph-A in the as synthesized zeolite Beta reaching 77.9%. It is reported that AESA did not remain in the structure of zeolite Beta when the crystallization was completed, which implies that AESA plays a role of zeolite growth modifiers during the crystallization. The results of this study suggest that anionic surfactants can be used in zeolite synthesis to optimize the crystallization process and achieve zeolites with the desired properties.
有机分子在各种沸石的合成中被广泛用作结构导向剂、中孔生成剂或沸石生长改性剂。然而，用于沸石合成的有机分子大多是带正电荷的阳离子分子，因为阳离子基团可以平衡沸石结构中的负电荷。在此，我们首次尝试将阴离子表面活性剂脂肪醇聚氧乙烯醚硫酸铵（AESA）应用于β沸石的结晶过程。研究发现，向合成体系中添加AESA会影响结晶过程和产物特性。与不添加AESA的情况相比，添加AESA合成β沸石时诱导期显著延长，结晶度和晶体完整性得到提高。使用AESA进行合成时产物产率增加。向合成凝胶中添加AESA时，骨架Si/Al比增加，这可能是因为阴离子表面活性剂AESA促进了Si - O - Si键的形成，阻碍了带负电荷的铝物种与硅物种结合形成Si - O - Al键，从而增加了Si的掺入量并减少了Al掺入骨架的量。此外，我们证明了在结晶过程中使用AESA能够在β沸石中富集手性多晶型物 - A，合成的β沸石中多晶型物 - A的比例达到77.9%。据报道，结晶完成后AESA不会残留在β沸石结构中，这意味着AESA在结晶过程中起到沸石生长改性剂的作用。本研究结果表明，阴离子表面活性剂可用于沸石合成，以优化结晶过程并获得具有所需性能的沸石。
