A facile and green method for the synthesis of hierarchical ZSM-5 zeolite aggregates from rice husk ash
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Hierarchical ZSM-5 zeolite has been successfully synthesized from rice husk ash by a facile and solvent-free method. The obtained samples were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscopy, magic angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, ultraviolet raman spectroscopy, thermogravimetric analysis–differential scanning calorimetry, Brunauer–Emmett–Teller (BET) analysis and temperature-programmed desorption of ammonia. The influences of synthesis time on ZSM-5 crystal growth and ZSM-5 zeolite properties were evaluated. The results suggested that the ZSM-5 synthesis process was solid-phase conversion and the crystallization was accomplished within 72 h at 150 °C. The Si, Al and Fe are tetrahedral coordinated and minute quantities of non-framework octahedral coordinated aluminium exist in synthetic ZSM-5, and it has weak and strong acid sites. The resultant ZSM-5 aggregates exhibited well-defined crystallinity and porosity, and possessed micro-/mesoporous structures. The BET surface area of the synthetic ZSM-5 zeolite was 308.41 m2/g, slightly less than that synthesized from a hydrothermal approach (320.69 m2/g). Moreover, this hierarchically porous ZSM-5 zeolite show a high-hierarchy factor up to 0.18. The proposed synthetic route in this work provides novel green alternative for the synthesis of hierarchical ZSM-5 zeolite from rice husk ash.