Journal
CHEMISTRY OF MATERIALS
Volume 30, Issue 8, Pages 2750-2758Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.chemmater.8b00527
Keywords
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Funding
- National Key Research and Development Program of China [2016YFB0701100]
- State Basic Research Project of China [2014CB931802]
- National Natural Science Foundation of China [21320102001, 21621001]
- 111 Project [B17020]
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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 degrees 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 degrees 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 degrees 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.
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