OSDA-free chabazite (CHA) zeolite synthesized in the presence of fluoride for selective methanol-to-olefins

A series of cost-effective aluminum-rich chabazite (Al-rich CHA) zeolites with improved textural properties has been synthesized without using templates. Herein, we report a detailed synthesis of CHA zeolite without using organic structure directing agent (OSDA-free). Pure CHA zeolites were successfully synthesized under different gel compositions. The prepared CHA samples were characterized using different characterization techniques. The crystallinity, the textural properties, the morphology and the acidity were characterized using X-ray diffraction (XRD), nitrogen physisorption, field-emission scanning electron microscopy (SEM) and ammonium temperature programing desorption (NH₃-TPD), accordingly. The ion-exchange enhanced the surface area from around 1 m²/g to around 485 m²/g. Aging time had a significant influence on the crystallization rate and morphology. The H-form of the synthesized CHA zeolite was evaluated in the conversion of methanol-to-olefin (MTO) at different reaction temperatures. Conversion was maintained 100% for 4 h at 350 °C and then life-time was decreased with the increase of temperature. The selectivity to lower olefins was correlated to the reaction temperature and time on stream (TOS). The highest olefins selectivity was ca. 93.8 at TOS and reaction temperature of 180 min and 350 °C, respectively.