SAPO-5分子筛结晶过程的SEM、EDAX研究

SEM and EDAX Study on the Crystallization of SAPO-5 Molecular Sieve

采用不同的硅源和晶化时间合成的了一系列SAPO-5分子筛。用扫描电镜(SEM)观察不同晶化阶段分子筛的晶体及晶粒大小,用EDAX分析不同样品及同一样品中不同晶粒的元素组成.所得结果表明:当以SiO_2为硅源时,优先生成低硅含量的SAPO-5分子筛晶粒。随晶化时间加长,硅逐渐取代磷进入分子筛骨架并使分子筛晶形改变,晶粒变小。当晶化时间达72h时,产物中伴生有SAPO-34,而以Si(OEt)_4为硅源时,硅对磷的取代速度较慢、随晶化时间的增长,硅进入分子筛骨架并使其晶形变得更加规则。实验结果还暗示,SEM结合微区EDAX是分辨结晶物中无定形硅的有效手段。

A Series of SAPO-5 molecular sieves have been synthesized by changing the aging time and with different silicon sources.SEM was employed to analyze the shape and size of the crystal at different stage.EDAX was used to analyze the element composition of different samples and different particles of the some sample.The ex- perimental results indicate that the SAPO-5 with dumbbell-like crystal and low silicon content was firstly yield- ed when SiO_2 was used as a silicon source.With the increase of aging time,silicon atoms tend to occupy the framework by substitution of themself for phosphrus atoms and thus to alter the crystal shape and reduce its size.When the crystallization time was upto 72h,SAPO-34 grew into the product.While Si(OEt)_4 was used as a silicon source,the replacement rate of P by Si was relatively slow and the occupation of Si in the framework made a relative regular shape of SAPO-5 crystal.The results demonstrate that SEM combined with EDAX is an effective method to investigate the amorphous silicon in the SAPO-5 molecular sieve.