Seed-directed synthesis of EMT-type zeolite from an organic-template-free system

Abstract EMT-type zeolite has been prepared by usage of seed directed method from an organic-template-free system (named as EMC-2-SOF). Powder X-ray diffraction (XRD) patterns verified that the diffraction patterns of EMC-2-SOF matched very well with EMC-2 synthesized using 18-crown-6 ether as template. EMT-type zeolite with complete diffraction patterns was prepared at high OH − /SiO 2 ratio (more than 2.0) and low temperature (50 °C) for 3 days. It has been found that, without organic template, calcined EMC-2 (denoted as EMC-2-C) showed better directing effect than as-synthesized one for the synthesis of EMC-2-SOF. Besides, the variation of SiO 2 /Al 2 O 3 molar ratio in original gel for synthesizing EMC-2-SOF was affected by OH − /SiO 2 ratio. A best fit between the ratio of SiO 2 /Al 2 O 3 and OH − /SiO 2 has been achieved. At OH − /SiO 2  = 2.0, the relative crystallinity of EMC-2-SOF first increased, then got to 100% at SiO 2 /Al 2 O 3  = 50, and finally decreased with SiO 2 /Al 2 O 3 ratio increasing. Meanwhile, by changing H 2 O/SiO 2 ratio from 46.6 to 30, yield of EMC-2-SOF increased from 15.8 to 33.4 wt.%. A relationship of mutual compensation among three intensive parameters in preparing zeolites (alkaline, temperature and crystallization time) has been used to improve the crystallinity of EMC-2-SOF. When gels with SiO 2 /Al 2 O 3  = 25, OH − /SiO 2  = 2.0, H 2 O/SiO 2 were crystallized at 55 °C for 12–20 h, all the samples had crystallinity above 100% with the yield over 25 wt.%.