水热合成过程中Silicalite-1晶体形貌和尺寸的调控

Manipulation of Morphology and Size of Silicalite-1 Crystals in Hydrothermal Synthesis

以气相SiO2为硅源、四丙基铵(TPA)为模板剂,水热合成了Silicalite-1分子筛,考察了合成液的水量、碱度(Na2O含量)、四丙基铵(TPA)含量和晶化条件(合成时间和搅拌方式)对Silicalite-1分子筛晶体形貌和尺寸的影响,采用X射线衍射(XRD)、扫描电镜(SEM)、激光粒度仪(LLS)等技术对合成的Silicalite-1分子筛晶体进行表征。结果表明,减少水量和增大碱度可以使Silicalite-1晶体由棺形转变为球形,但碱度过高或过低时,分子筛晶体的产率很低;增加TPA浓度和缩短晶化时间可以减小Silicalite-1分子筛晶体的粒径,且均能获得较高的收率;不同的搅拌方式会影响晶体的粒径大小和分布,转动式合成能够得到粒径较为均一的晶体,而搅拌式合成能得到粒径分布较广的晶体,粒径相对较小。因此,通过调节合成液组成和合成条件,可以控制Silicalite-1晶体的形貌和尺寸。

Silicalite-1 crystals were synthesized with the fumed silica as silica source and TPA+as template.The influences of the synthesis conditions,including the contents of water,alkaline(Na_2O)and tetrapropyl ammonium(TPA^+),the crystallization conditions of time and stirring mode,on the size and morphology of Silicalite-1 crystals were investigated.The physicochemical properties of the products were characterized by X-ray diffraction(XRD),scanning electronic microscopy(SEM)and laser light scattering(LLS).It is found that the shape of Silicalite-1crystals changed from coffin to sphere with the decrease of water content or the increase of alkalinity of the synthesis solution.However,the yield of crystals was low when the alkalinity was too high or too low.The crystal size of Silicalite-1decreased with the increase of TPA content or the decrease of crystallization time,keeping the yield of crystals relatively high.The stirring methods also affect the crystals size and size distribution.Silicalite-1crystals synthesized in a magnetically stirred reactor got smaller size and wider size distribution than those synthesized in a rotation reactor.That is,Silicalite-1crystals with different morphology and size can be successfully synthesized by adjusting the synthesis solution composition and synthesis conditions.