Amphiphilic organosilane and seed assisted hierarchical ZSM-5 synthesis: Crystallization process and structure

• High quality meso-ZSM-5 was synthesized by amphiphilic organosilane and seed.
• Meso-ZSM-5 is core/shell structure of ZSM-5 nanoparticle aggregates.
• Different degree of connection in different part of nanoparticle aggregate.
• Meso-ZSM-5 formed by nanoparticle oriented-aggregation mechanism.
• Meso-ZSM-5 is a kinetically controlled product in ZSM-5 crystallization process.

The synthesis, characterization, and catalytic applications of hierarchical zeolite has drawn a lot of research interest. During hierarchical zeolite synthesis, different products can be formed due to the difference in crystallization mechanism. Here we detail the crystallization process and structure of the hierarchical ZSM-5 synthesized with amphiphilic organosilane and seed. First, the effects of synthesis parameters on zeolite products were studied in detail to optimize the hierarchical zeolite synthesis process. Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC), seed and rotation are the required conditions for the synthesis of high quality hierarchical ZSM-5 with both high micropore and mesopore volume. The obtained hierarchical zeolite samples were then subjected to detailed structural analysis including XRD, SEM, TEM, nitrogen sorption and a sonication fragmentation method. Hierarchical ZSM-5 synthesized herein was a mesoporous aggregate of ZSM-5 nanoparticles with a core/shell structure based on the characterization results. The core part is hierarchical ZSM-5 with a higher degree of connectivity between zeolite nanoparticles or even the so-called mesoporous zeolite single crystal. The shell component is the hierarchical ZSM-5 aggregate with loosely packed ZSM-5 nanoparticles. The formation process and structure change was finally investigated by monitoring the morphology, crystallinity, and porosity of samples obtained with different crystallization times. The results indicated that hierarchical ZSM-5 is a kinetically controlled product in ZSM-5 crystallization process through a nanoparticle-oriented aggregation mechanism. The TPOAC, seed, and crystallization time are the conditions kinetically controlling the crystallization process.

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