A facile strategy affording high-quality single-crystalline MFI-type nanozeolites (10–55 nm) with hexagonal prism morphology, good monodispersity, high crystallinity, and high product yield (above 97%) has been developed. This is achieved by synergistically using an l-lysine-assisted approach and a two-step crystallization process in a concentrated gel system (H₂O/Si = 9). The morphological evolution of nanosized silicalite-1 is monitored by high-resolution transmission electron microscopy (HRTEM). In this process, metastable irregular nanoparticles are initially obtained at 80 °C as the first step. Consequently, a rearrangement in morphology toward equilibrium crystal shape and without excessive growth for the metastable nanoparticles occurs at 170 °C as the second step. Throughout the whole process, l-lysine acts as an inhibitor to effectively limit the crystal growth of zeolites. Thanks to the high-quality nanosized crystals, the as-prepared ZSM-5 catalysts exhibit superior performance in methanol-to-propylene (MTP) reactions, which deliver a prolonged lifetime of 54 h with a total light olefin selectivity of 74% and a high propylene selectivity of 49% at 470 °C at a high methanol weight hourly space velocity (WHSV) of 7.2 h^–1. This synthetic route provides a general strategy for preparing other types of zeolites with good monodispersity, nanosize, high yield, and high crystallinity.

中文翻译：

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高质量单晶MFI型纳米沸石：简便的合成策略和MTP催化研究

已经开发了一种可行的策略，该策略可提供具有六方棱柱形形态，良好的单分散性，高结晶度和高产品产率（97％以上）的高质量单晶MFI型纳米沸石（10-55 nm）。这是通过协同使用来实现升赖氨酸辅助方式和在浓凝胶系统的两步结晶方法（H ₂O / Si = 9）。纳米尺寸silicalite-1的形态演变通过高分辨率透射电子显微镜（HRTEM）进行监测。在此过程中，第一步是首先在80°C下获得亚稳态的不规则纳米颗粒。因此，作为第二步骤，在170℃下发生了朝向平衡晶体形状的形态重排，并且对于亚稳态纳米颗粒没有过度生长。纵观整个过程，升-赖氨酸起抑制剂的作用，有效地限制了沸石的晶体生长。得益于高质量的纳米级晶体，所制备的ZSM-5催化剂在甲醇制丙烯（MTP）反应中表现出卓越的性能，可延长54 h的寿命，轻质烯烃的总选择性为74％。在7.2 h ^–1的高甲醇重量时空速（WHSV）下，在470°C时，丙烯的选择性达到49％。这种合成路线为制备具有良好单分散性，纳米级，高收率和高结晶度的其他类型的沸石提供了一般策略。