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

摘要

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-/SiO2 ratio (more than 2.0) and low temperature (50 degrees 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 SiO2/Al2O3 molar ratio in original gel for synthesizing EMC-2-SOF was affected by OH-/SiO2 ratio. A best fit between the ratio of SiO2/Al2O3 and OH-/SiO2 has been achieved. At OH-/SiO2 = 2.0, the relative crystallinity of EMC-2-SOF first increased, then got to 100% at SiO2/ Al2O3 = 50, and finally decreased with SiO2/Al2O3 ratio increasing. Meanwhile, by changing H2O/SiO2 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 SiO2/Al2O3 = 25, OH-/SiO2 = 2.0, H2O/SiO2 were crystallized at 55 degrees C for 12-20 h, all the samples had crystallinity above 100% with the yield over 25 wt.%. (C) 2015 Elsevier Inc. All rights reserved.