A two-step ionothermal synthesis of MFI zeolite framework and its potential applications in adsorption and catalysis

초록

This study explores the ionothermal synthesis of MFI-type zeolites using the ionic liquid (IL) [BMIM]Br, with a focus on framework development and functional performance. By tuning synthesis parameters of temperature, Si/Al ratio, and employing a two-step heating strategy, well-crystallized ZSM-5 materials with enhanced porosity were obtained. Structural characterization by XRD, SEM, and N2 physisorption confirmed that the two-step synthesis improved crystallinity and microporosity, while also promoting uniform mesopore formation and better pore accessibility. Functional assessments, including room-temperature N2 adsorption, methylene blue adsorption, and catalytic toluene methylation, were conducted. Using the two-step heating treatment, the N2 adsorption capacity of ionothermally synthesized zeolites increased from 2.57 cm3 g-1 to 3.86 cm3 g-1, and methylene blue adsorption (within 6 h) improved from 61.18 mg/kg to 74.54 mg/kg. Furthermore, toluene conversion rose by 11 %, and xylene selectivity increased by 10 %, confirming the enhanced structural properties achieved through the 2-step heating treatment. Kinetic modeling indicated a shift from diffusion-limited physisorption in single-step samples to chemisorption-driven processes in two-step products. The recyclability of [BMIM]Br was demonstrated after single-step use, but structural degradation occurred following reuse from high-temperature treatments. Comparisons with TPAOH-templated hydrothermal syntheses further highlighted the superior structural direction offered by ILs. These findings advance the understanding of crystal growth in ionothermal systems and emphasize the potential of ILs in tailoring high-performance zeolite materials for catalytic and adsorption applications.

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