氧化物和盐类在分子筛内外表面及孔穴中的自发分散及其应用

Spontaneous Dispersion of Oxides and Salts to Zeolites and Its Applications

氧化物和盐类可在分子筛内外表面及孔穴中自发形成原子水平的分散，原因是分散后体系的熵可大大增加，同时在表面生成的新键，其强度和未分散时化合物内部的键强度不相上下，结果导致体系的总自由能下降。熔点较低的化合物的分散可通过它们与分子筛混合在适当温度下加热来实现；熔点较高的化合物的分散，则需要通过用其溶液浸渍分子筛后烘干和热分解来实现。这种自发分散现象已为ＸＲＤ，ＸＰＳ和ＥＸＡＦＳ等多种谱学实验所证实。用ＸＲＤ和ＸＰＳ等技术可测各种化合物在各种分子筛中的最大分散容量。氧化物和盐类在分子筛中分散的作用包括：正负离子在分子筛内外表面上的分散，也包括正负离子同时进入分子筛中的小笼生成“包合物”，同时也可发生固体离子交换。氧化物和盐类在分子筛上自发分散是分子筛改性的一个重要原理和方法，有广泛的用途。例如将ＣｕＣｌ分散在分子筛中制得高效ＣＯ和乙烯吸附剂。将ＭｇＯ，Ｂ２Ｏ３，Ｓｂ２Ｏ３和Ｐ２Ｏ５等氧化物分散到ＨＥＳＭ－５分子筛孔道中，使分子筛孔道变窄，可获得甲苯甲基化择形催化剂，生成对二甲苯的选择性可达９０％以上。利用ＬｉＣｌ和ＮａＣｌ等在分子筛中的分散还可得到导电率高的固体电解质。

It has been shown that metal oxides and salts can disperse spontaneously to the surface and pores of zeolites as atomically dispersion.The reason for the spontaneous dispersion is the decrease of free enthalpy of the whole systems,owing to that the dispersion results in significant increase in entropy and formation of surface bonds comparable to the original bonds of the compounds.For a compound with not too high melting point,its dispersion to a zeolite can be done by heating it with the zeolite at a suitable temperature well below its melting point.For a compound with high melting point,its dispersion to a zeolite can be done by using its solution or its precursor solution to impregnate zeolites then drying or thermolysis.The dispersion has been verified by XRD,XPS,EXAFS etc.Dispersion capacities of compounds on zeolites measured by XRD and XPS are listed(table 2).The dispersion of a salt or an oxide to a zeolite includes that both cations and anions disperse on the external surface and ,on the internal surface (wall of larger cages and channels) of the zeolite,inclusion in small cages of the zeolite,in addition,solid ion exchange might occur at the same time.Spontaneous dispersion of oxides and salts to zeolites as a principle and method for modification of zeolites might have extensive applications.For example,highly efficient adsorbents for CO and ethylene adsorption has been made by dispersing CuCl to zeolites.Highly selective catalyst for making para xylene can be obtained by dispersing oxides such as MgO,Sb 2O 3,B 2O 3 and P 2O 5 etc.to HZSM 5 zeolite.Solid electrolytes with high conductivity can be made by dispersing salts such as NaCL,LiCL to zeolites.