Abstract
Abstract Zeolite beta has been successfully synthesized by magadiite conversion method in the absence of organic structure-directing agents. By using powder X-ray diffraction, fourier transform infrared spectroscopy and Raman spectroscopy, solid-state 27Al and 29Si MAS nuclear magnetic resonance spectroscopy and electron microscope, the crystallization behavior and changes of medium-range structure were investigated in detail. It was found that part of medium-range structure of magadiite remained during the crystallization process and part of seed crystals were dissolved, providing active surface for the formation of zeolite beta. Meanwhile, with the growth of zeolite beta, five-membered rings existing in magadiite were retained and their connection probably resulted in the formation of four-membered rings. An increasing number of Al atoms favourably entered the T1 and T2 positions which were mainly located in four-membered rings, while Si atoms resided in T3-T9 sites. The influence of reaction time, temperature, alkalinity in starting gel and the amount of seed crystals were also examined. With the reactive gel composition: 0.96 NaOH: SiO2: 0.0125 Al2O3: 240 H2O by adding 25 wt % seeds into the synthesis system, pure and highly crystalline zeolite beta could be obtained at 125 °C after 48 h.
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