GENERAL HYPOTHESIS ON ZEOLITES PHYSICOCHEMICAL PROPERTIES - APPLICATIONS TO ADSORPTION, ACIDITY, CATALYSIS, AND ELECTROCHEMISTRY

Based on a large number of zeolite properties a sharp comparison of zeolites with solutions is suggested. For example, it is proposed first that the increase in zeolite acid strength as the aluminum content is decreased may be explained on the basis of an analogy with inorganic acids in solution. Secondly the importance of interactions in zeolites imply the definition of activity coefficients for the ions or atoms of the framework, not only in ion exchange as postulated for a long time but also for other properties. The values of these activity coefficients will decrease as the interactions, i.e., the Al/Al + Si ratio, is increased. Such activity coefficients will have to be considered in studies on kinetics, adsorption, ion migration, etc. The properties of the adsorbed phase are also changed by activity coefficients as for a solute in a solvent. The behavior of transition metal cations in zeolites strongly suggests that electrode phenomena occur and that many of the reactions described are relevant to electrochemistry. In conclusion it is suggested that the zeolites' properties are governed by the changes in the chemical potential of their framework ions and atoms. Their strong analogy with solutions suggests considering these solids as crystalline liquids" where nearly all of the framework atoms belong to the surface. © 1979 American Chemical Society."