SAPO-11分子筛晶化过程研究

Study of crystallization process of SAPO-11 molecular sieve

采用X射线衍射、X射线荧光光谱、扫描电镜和固体核磁等方法研究了SAPO-11分子筛的水热晶化过程.结果表明,晶化初期,SAPO-11和一种具有磷硅铝组成的未知晶相同时生成;随着晶化的进行,中间相溶解,SAPO-11的生成速率大大增加,呈现快速晶化的特征;至2.33h后,SAPO-11的结晶度接近100%,并保持至晶化结束.硅从晶化初期即参与了SAPO-11的形成,它在晶体中的含量随晶化时间的延长而逐渐增加.硅原子主要以硅岛的形式分布于SAPO-11分子筛骨架中,从而导致多种硅配位环境的存在.分析显示,SAPO-11分子筛呈现外表面富硅的特点,结合晶化过程的分析可推测,硅在SAPO-11分子筛晶体中的分布不均匀,其含量从内向外递增.

The crystallization process of SAPO-11 was studied using a combination of X-ray diffraction,scanning electron microscopy,X-ray fluorescence,nuclear magnetic resonance,and X-ray photoelectron spectroscopy.In the initial stage of crystallization,SAPO-11 was formed along with an unknown crystalline material composed of Si-P-Al.As crystallization evolved,the crystalline material dissolved.The SAPO-11 formation rate increased greatly,which is characteristic of fast crystallization.After 2.33 h,the relative crystallinity of SAPO-11 reached ~100% and remained at a high level until crystallization was complete.Si was incorporated into the SAPO-11 framework from the initial stage of crystallization.The Si content of the solid samples increased with crystallization time.Most of the Si atoms existed as Si islands in the SAPO-11 framework,resulting in the presence of multiple coordination environments,i.e.,Si(nAl,(4 - n)Si),n = 0-4.X-ray photoelectron spectroscopy analysis revealed Si enrichment on the external surfaces of the SAPO-11 crystals.Based on the experimental results,the distribution of Si in the crystals is not uniform,showing an increasing trend from the core to the surface.