Seed-assisted template-free synthesis of nano-sized ZSM-5 via two-stage crystallization with related investigation of mechanism

• Published in: Microporous and mesoporous materials Vol. 312; p. 110754
• Main Authors: Zhang, Ruizhen, Zhao, Piaorou, Han, Lina, Wang, Jiancheng, Zhao, Liangfu
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.01.2021
• Subjects: Dispersion and crystallinity; Nano-sized ZSM-5; Template-free; Two-stage crystallization; Template-free; Two-stage crystallization; Dispersion and crystallinity; Nano-sized ZSM-5
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2020.110754

High crystalline and well dispersed nano-ZSM-5 was rapidly synthesized in template-free system using high-low temperature two-stage process with as-synthesized silicalite-1 as the seed, and characterized via XRD, SEM, N2 adsorption, FT-IR, Py-IR, TG and so on. Firstly, seed-assisted one-stage crystallization was examined and the results showed that high crystalline nano-ZSM-5 (>90%) could be obtained at 180 °C and 220 °C when the duration time was more than 12 h and 2 h, respectively, but the products tended to be agglomerated with the increase of crystallinity. Based on this, two-stage crystallization was comparatively studied between 220 °C/1 h-180 °C/1–6 h and 220 °C/4 h-180 °C/1–4 h, and high crystalline ZSM-5 (Z-1-6) (97%) with the size of 70–90 nm and good dispersion was synthesized at 220 °C/1 h-180 °C/6 h, while submicron aggregates consisted of 60–120 nm irregular cuboids with high crystallinity (>90%) were obtained at 220 °C/4 h-180 °C/1–4 h. Structural and acidic characterization indicated that Z-1-6 had excellent surface adsorption properties and moderate acidity compared with the commercial micron-ZSM-5. Finally, seed-assisted two-stage crystallization mechanism was proposed about accelerating the depolymerization of silicalite-1 into more smaller nucleation sites and avoiding the aggregation of crystal nuclei by controlling a shorter duration time at a higher temperature and ensuring the stable growth of nano-crystals at a lower temperature. [Display omitted] •Nano-sized ZSM-5 with well-dispersion, high crystallinity, large surface and moderate acidity was synthesized.•As-synthesized silicalite-1 seed assisted two-stage template-free process was applied.•Rapid depolymerization of seeds at high temperature provided more smaller nucleation sites.•Strict control of the time duration at high temperature was the key of assuring well dispersion.•Stable growth of nano-crystals at low temperature was the guarantee of high crystallinity.