Zeolite crystallization occurs in the presence of inorganic and/or organic structure-directing agents (SDAs) that facilitate the formation of microporous crystals with various pore geometries. One of the most common zeolites is ZSM-5 (MFI type), which is used as a catalyst and sorbent in a wide range of industrial applications. One of the challenges with ZSM-5 synthesis is to identify new and inexpensive organic SDAs that can tailor the physicochemical properties of the final product. The most frequently used SDA in ZSM-5 synthesis is tetrapropylammonium (TPA); however, recent studies have shown that the surfactant cetyltrimethylammonium (CTA) can be used as an alternative SDA. Here, we examine the effects of dual structure-directing agents using CTA and TPA as organic SDAs in combination with a variety of alkali metals as inorganic SDAs. Our findings reveal that the selection of SDA combinations has a significant impact on the kinetics of ZSM-5 crystallization, as well as the properties of the resulting crystals. Notably, we show that TPA/Na and CTA/K are optimal combinations of SDAs that can markedly alter the size, morphology, and aluminum distribution in ZSM-5. Using a combination of experiments and molecular modeling, we explore the use of CTA as an alternative organic SDA for zeolite MFI and show that we can achieve smaller crystals (ca. 600 nm) in similar time (<24 h) as syntheses employing TPA. Given the relatively low cost of CTA and its high market availability compared to other organic SDAs, these findings have the potential to impact commercial production of ZSM-5 for a variety of applications.

中文翻译：

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无机和有机结构导向剂在ZSM-5结晶中的协同作用

沸石的结晶是在无机和/或有机结构导向剂（SDA）的存在下发生的，该试剂有助于形成具有各种孔几何形状的微孔晶体。ZSM-5（MFI型）是最常见的沸石之一，在许多工业应用中用作催化剂和吸附剂。ZSM-5合成面临的挑战之一是确定可以调整最终产品的理化性质的新型廉价有机SDA。ZSM-5合成中最常用的SDA是四丙基铵（TPA）；但是，最近的研究表明，表面活性剂十六烷基三甲基铵（CTA）可以用作替代的SDA。在这里，我们研究了使用CTA和TPA作为有机SDA结合多种碱金属作为无机SDA的双重结构导向剂的效果。我们的发现表明，SDA组合的选择对ZSM-5结晶动力学以及所得晶体的性能有重大影响。值得注意的是，我们显示TPA / Na和CTA / K是SDA的最佳组合，可以显着改变ZSM-5中的尺寸，形态和铝分布​​。通过结合实验和分子建模，我们探索了将CTA用作沸石MFI的替代有机SDA的方法，并表明我们可以实现较小的晶体（约。与使用TPA进行合成的时间（<24小时）相似的时间（<600 nm）。与其他有机SDA相比，由于CTA的成本相对较低且其市场可用性较高，因此这些发现可能会影响ZSM-5的商业化生产，以用于各种应用。