ZSM-22沸石合成与共生竞争相控制

Synthesis of Pure ZSM-22 Zeolites via Suppressing Intergrowths of Competing Phases

在SiO2-Al2O3-K2O-DAH-H2O(1,6-己二胺,DAH)体系中,研究水热合成条件对ZSM-22沸石相对结晶度和相纯度的影响。采用X射线衍射(XRD)和电感耦合等离子体(ICP)技术表征合成产物的结构、物相及化学组成。结果表明,合成胶n(SiO2)/n(Al2O3)在80～110,n(OH-)/n(SiO2)在0.33～0.35和433～438K条件下,合成出系列相纯度较高的ZSM-22沸石。产物相对结晶度和相纯度依赖于合成胶硅铝物质的量比、碱度和晶化温度。适当升高晶化温度有利于提高产物的相纯度和相对结晶度;n(SiO2)/n(Al2O3)在80～110之外,合成胶硅铝物质的量比的降低或提高分别导致ZSM-5或方石英相分率的逐渐增加。此外,纯ZSM-22骨架n(Si)/n(Al)分布于41.8～53.4;与n(SiO2)/n(Al2O3)关联可知,n(Si)/n(Al)比值向该区间中心呈收敛趋势。

The effect of hydrothermal synthesis conditions on both relative crystallinity and phase purity of ZSM-22 zeolites was investigated in SiO2-A12Oa-K20-DAH-H20 system, hereby DAH referring to 1, 6-diaminohexane as template. The resulting samples were characterized by powder X-ray diffraction （XRD） and inductively coupled plasma （ICP） analyses in order to examine the structure, XRD phase, and chemical composition. As a result, several ZSM-22 zeolites with the higher phase purity were synthesized at respective temperatures from 433 K up to 438 K by use of the different gels which involved SiO2/A12 Oa molar ratios of 80~100 and OH-/SiO2 molar ratios of 0.33~0.35. It is found that the relative crystallinity and phase purity of ZSM-22 zeolites markedly varied as a function of crystallization temperature, SiO2/A12Oa and OH-/SiOz molar ratios. In fact, an adequate increase in crystallization temperature improves on ZSM-22 phase purity, followed a significant enhancement of relative crystallinity. Although the ZSM-5 crystal growth takes place predominantly in the solid phase, the decrease in the range of SiO2/A12 03 ratio less than 80 leads to a gradual increase in the ZSM-5 phase fraction while the increase in SiO2/A12 Oa ratio larger than 110 also enhances the phase fraction of cristobalite. Furthermore, Si/A1 atomic ratios in ZSM-22 framework located the range of 41.8~53.4, and by correlating the Si/A1 ratio of ZSM-22 framework with the SiO2/A12 Oa ratio of alumino-silicate gels, it is noted that the nominal ratios in ZSM-22 framework tended to shift towards the center of the Si/A1 ratio interval mentioned above.