OSDA-free hydrothermal conversion of kenyaite into zeolite beta in the presence of seed crystals

Abstract

Zeolite beta with high crystallinity has been successfully synthesized by using kenyaite conversion method with seed crystals under hydrothermal treatment at 125 °C for 36 h. The OSDA-free synthesis of zeolite beta could be obtained from the mixture composition of 0.96 NaOH: SiO2: 0.0167 Al2O3: 180 H2O by adding 25 wt % seeds. To study the crystallization behaviours and the medium-range structure changes during the conversion process, the prepared zeolite beta was characterized by powder X-ray diffraction, field-emission scanning electron microscope, Fourier transform infrared spectroscopy, energy dispersive spectroscopy, solid-state 27Al MAS and 29Si MAS NMR spectroscopy. The growth of zeolite beta happened on the surface of kenyaite. The five-membered rings and six-membered rings in kenyaite were partly preserved and the four-membered rings were formed by the connection of five-membered rings during the crystallization process. Meanwhile, the effects of reaction time, the initial mixture composition, the quantity of beta seed crystals and temperature in the synthesis were investigated. The as-synthesized zeolite beta, with relatively high thermal stability, exhibits good catalytic performance in the cyclohexanol dehydration reaction system.