氟离子对无胺法合成高硅丝光沸石的结构导向作用

Structure-Directing Effect of Fluoride Anion on Synthesis of Siliceous Mordenite in Amine-Free System

在含氟无胺体系中合成了高硅丝光沸石 ,研究了合成条件对丝光沸石产物的影响 .结果表明 ,投料n(SiO2 ) /n(Al2 O3 ) =2 0～ 2 0 0时 ,控制晶化条件可得到高硅丝光沸石纯相 .由含氟无胺体系中丝光沸石的热力学稳定相区可见 ,氟离子的引入对方沸石的生成的相区无影响 ,ZSM 5和镁碱沸石生成的相区消失 ,丝光沸石生成的相区扩大 ,石英生成的相区缩小 ,且基本上变为两相共存区 .合成产物丝光沸石的硅铝比随着氟硅比的升高同步增大 ,证明氟离子在无胺合成高硅丝光沸石时具有结构导向作用 .

Synthetic mordenite, especially with high SiO 2/Al 2O 3 ratio, is industrially one of the outstanding catalysts. The siliceous mordenite samples with various SiO 2/Al 2O 3 ratios were synthesized using fluoride as structure-directing agent in amine-free system. The products depend heavily on the synthesis parameters. The siliceous mordenite could be obtained in wide n(SiO 2)/ n(Al 2O 3) range (from 20 to 200) of gel and no other contamination was detected in it. In the system without fluoride, the resulting phases were mordenite with n(SiO 2)/ n(Al 2O 3)=10 and quartz contamination even though the n(SiO 2)/ n(Al 2O 3) of gel was up to 100. In the system with fluoride, the fluoride anion played the determinant role in the synthesis of siliceous mordenite. When n(SiO 2)/ n(Al 2O 3)<10, the analcime was the only crystalline phase, regardless of OH -/SiO 2 ratio. When n(SiO 2)/ n(Al 2O 3)>10, the mordenite could be obtained as pure phase; as the SiO 2/Al 2O 3 ratio increased, the OH -/SiO 2 ratio also had to increase to produce pure mordenite, otherwise a mixture of quartz and mordenite was obtained. When the OH -/SiO 2 ratio was lower, such reactant mixture formed amorphous materials. Compared with the system without fluoride, by introducing fluoride anion into the system, the crystallization field of analcime was much less affected, the area of producing mordenite was broadened,the area of quartz obtained was reduced, and the crystallization region towards ZSM-5 and ferrierite was no longer formed. The fluoride anion favored the crystallization of mordenite and restrained the formation of ZSM-5 and ferrierite, showing the marked action in directing the system towards the formation of siliceous mordenite.