Dawei He,Danhua Yuan,Zhijia Song,Yunpeng Xu,Zhongmin Liu
Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure-directing agents (OSDAs), which are chronically hazardous to humans and the environment. It is a growing trend to develop an eco-friendly and nuisanceless OSDA for zeolite synthesis. Herein, choline is employed as a non-toxic and green OSDA to synthesize high silica Y zeolite with SiO 2 /Al 2 O 3 ratios of 6.5–6.8. The prepared Y zeolite samples exhibited outstanding (hydro)thermal stability at ultrahigh temperature owing to the higher SiO 2 /Al 2 O 3 ratio. The XRF, SEM, 29 Si-NMR and 13 Na+ results suggested that choline plays a structure-directing role in the synthesis of Y zeolite, while the feed molar fraction of Na + is a crucial determinant for the framework SiO 2 /Al 2 O 3 ratio and the crystal morphology.
Y Zeolite plays an irreplaceable role in many important applications due to its unique physicochemical properties, which has attracted extensive attention from researchers. Response surface methodology (RSM) was used to optimize the process parameters for the hydrothermal synthesis of Y zeolite using kaolin activated by microwave heating. The best relative crystallinity was 108.17% could be achieved at the condition: the aging temperature of guiding agent was 65 ℃, the crystallization temperature was 100 ℃, the crystallization time was 24 h. In addition, the aging temperature of guiding agent was the most important influence factor. Under the optimal condition, the SiO 2 /Al 2 O 3 ratio of synthesized Y zeolite was 4.54, 90% of the particle size was less than 60 μm, and the specific surface area of Y zeolite was 479 m 2 /g. The successful preparation of Y zeolite with high crystallinity is expected to provide reference for the application of wastewater treatment, CO 2 sequestration and fluid catalytic cracking for petroleum.
ZSM-48 zeolite is characteristic of 10-member ring (10-MR) one-dimensional tubular channel structure and finds extensive applications in catalytic hydroisomerization reactions. Here we developed an efficient synthetic strategy for low-silica ZSM-48 zeolite with a SiO 2 /Al 2 O 3 ratio at 30–176 via a seed-assisted hydrothermal synthesis method, overcoming the limit that 1,6-hexanediamine (HDA) template can only be used to synthesize high-silica (i.e., SiO 2 /Al 2 O 3 ratio >200) zeolites. A two-step crystallization procedure coupled with zeolite seed-assisted synthesis strategy was enrolled to realize well crystallized ZSM-48 zeolites, in which the zeolite nuclei are sufficiently produced at the nucleation temperature at 100 °C for 24 h with the aid of zeolite seeds, and the zeolite growth is proceeded at the crystallization temperature at 160 °C for 48 h. The morphology and particle size of low-silica ZSM-48 zeolite have been manipulated by adjusting the synthetic parameters, such as the alkalinity and silicon source of aluminosilicate gel for zeolite, the crystallization manner (static or dynamic crystallization), as well as the presence of additive (i.e., sodium chloride). The as-synthesized ZSM-48 zeolite possesses a high acid content of 0.194 mmol/g, highlighting its potential as an excellent acidic support for hydroisomerization catalysts. The cost-effective and environmentally friendly synthesis strategy, which is anticipated to expand the application of alkylamine organic templates in the synthesis of low-silica ZSM-48 zeolite.
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