Spontaneous Dispersion of Oxides and Salts to Zeolites and Its Applications

Abstract:

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, Sb₂O₃, B₂O₃ and P₂O₅ etc.to HZSM-5 zeolite. Solid electrolytes with high conductivity can be made by dispersing salts such as NaCL, LiCL to zeolites.

Key words:

zeolites; monolayer dispersion; zeolites modification

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