摘要
用水热法合成了ＳＡＰＯ－５，－１１和－３４硅磷酸铝类分子筛。并对经不同温度焙烧处理的样品进行表征，结果表明：分子筛中模块剂的热分解过程与其结构和孔大小有较大的关系。在ＳＡＰＯ－５和ＳＡＰＯ－３４分子筛中，外部联接的Ｔ－Ｏ－Ｔ键的反对称伸缩振动峰（１２４０ｃｍ^（－１）－１０３８ｃｍ^（－１））和其对称伸缩振动（７３４ｃｍ^（－１）－６００ｃｍ^（－１））及双环的变形振动（６００－５００ｃｍ^（－１））的吸收峰对样品的结晶度比较敏感。但在ＳＡＰＯ－１１中，分子筛骨架中Ｔ－Ｏ－Ｔ反对称伸缩振动（１２２５ｃｍ^（－１）和１０３８ｃｍ^（－１））随结晶度的下降而基本保持不变，但内四面体（ＴＯ_４）的对称伸缩振动，反对称伸缩振动峰及Ｔ－Ｏ弯曲振动峰随样品焙烧温度的升高而减弱并分裂。红外吸收带向低频方向移动。ＳＥＭ－ＥＤＡＸ结果表明：随样品焙烧温度的升高，结晶度下降，分子筛晶形变得不规则，晶面越来越粗糙，但结晶度的下降并非由于其中ＰＯ_４四面体的热分解所引起，而是由外部联结的Ｔ－Ｏ－Ｔ键的断裂，双环被破坏及骨架元素间的重排所引起。
SAPO-5,-11 and -34 molecular sieves were synthesized by hydrothermal method and have been calcined in air at different temperatures for 3 h respectively.All these samples were characterized by XRD,IRS,TG-DTA and electron microscopy,It is shown that the existing form and the chemical environment of the template differ with the structure of the molecular sieves,so thermal decomposition process of the template is different.The weightloss of the sample is related to the silicon content in the framework.For SAPO- 5 and SAPO-34,the characteristic absorption peaks of asymmetric stretching vibrations of external bonds T-O-T(1204 cm￣(-1)-1034 cm￣(-1)) and the deformation vibration of the double ring(650 cm￣(-1)-550 cm￣(-1))are sensitive to the crystallinity of the molecular sieves,However,for SAPO-11,the intensity of the peak of external bond asymmtric stretching vibration increases inappreciably with the decrease in crystallinity,but its deformation vibration of the double ring is sensitive to the crystallinity. Although the SAPO molecular sieves studied are composed of the same elements,their hydroxyls are quite diffferent.It changes with the type of structure and is considreably influenced by the calcination temperature . The results of electron microscopy show that as the temperature is raised,the crystallinity of the sample is lowered,the crystal shape becomes more and more irregular and the surface becomes rougher.EDAX results suggest that the decreases in crystallinity is not caused by the decomposition of PO4 tetrahedron,but by the rupture of T-O-T bonds and the double ring.On the basis of the above results,a simple way to establish the relative crystallinity of SAPO-5,-11 and -34 molecular sieves is proposed.
出处
《分子催化》
EI
CAS
CSCD
1994年第6期429-436,共8页
Journal of Molecular Catalysis(China)
基金
甘肃省青年科学基金
关键词
SAPO
分子筛
模板剂
热稳定性
结构
热致变化
SAPO-5,-11 and -34,Thermal treatment,Structure change,Infrared spectra,TG-DTA.
