关键词: 沸石合成 , ZSM-22 竞争相 , ZSM-5 , 方石英 , 相对结晶度 , 相纯度

Abstract: The effect of hydrothermal synthesis conditions on both relative crystallinity and phase purity of ZSM22 zeolites was investigated in SiO₂Al₂O₃K₂ODAHH₂O 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/Al₂O₃ 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 ZSM22 zeolites markedly varied as a function of crystallization temperature, SiO₂/Al₂O₃ and OH^-/SiO₂ 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/Al₂O₃ ratio less than 80 leads to a gradual increase in the ZSM5 phase fraction while the increase in SiO₂/Al₂O₃ ratio larger than 110 also enhances the phase fraction of cristobalite. Furthermore, Si/Al atomic ratios in ZSM22 framework located the range of 41.8~53.4, and by correlating the Si/Al ratio of ZSM22 framework with the SiO₂/Al₂O₃ ratio of aluminosilicate gels, it is noted that the nominal ratios in ZSM22 framework tended to shift towards the center of the Si/Al ratio interval mentioned above.

Key words: Zeolite synthesis,    , ZSM22,    ,  Competing phase,   ,  ZSM5,    , Cristobalite,    ,  Relative crystallinity,   ,  Phase purity