Synthesis of AEI/CHA intergrowth zeolites by dual templates and their catalytic performance for dimethyl ether to olefins

A series of SAPO molecular sieves were hydrothermally synthesized by employing mixture template of diethylamine (DEA) and N, N′-diisopropylethylamine (DIEA). The influences of template composition and crystallization time were investigated systematically. The results revealed that the crystalline products switched from SAPO-34/5 to SAPO-18/34 and finally to SAPO-18, the crystal size and acidity decreased with the increasing of DIEA ratio in the mixed template. Furthermore, crystallization time was also found to play a significant role in the particulate properties of the zeolites, the metastable AEI phase converted into more stable CHA phase, the Si content and acidity increased with the prolonged crystallization time. Dimethyl ether (DME) to olefins (DTO) reactions showed that the extending of the crystallization time was against the formation of light olefins, but favorable for the formation of light alkanes, due to the increase in CHA/AEI ratio, particle size and acidity may increase the probability of unfavorable hydrogenation of the target light olefins.