Clay catalysts heterogeneous composite

Properties of a° (pH) curves are basic elements in the Interpretation of more complicated systems involving oxides. One of these is the adsorption of hydrolyzable ions (Cd, Al, etc.) or anions that themselves can be titrated (HPO, etc.). In sec. 3.14 some of the relevant applications will be discussed. Another application is that of mixed oxides. The systems include mechanically mixed pure oxides and mixed crystals (such as spinels and ferrites). A number of authors have studied such mixed oxides, thereby reporting the variation of the pH° as a function of the mole fraction of the solid. Sometimes linearity was found, sometimes not. No genered rules can be given. The surface composition is not necessarily identical to that of the bulk, molecules of one oxide may leach and adsorb onto the other and lateral interactions of surface groups of the two constituents affect their pK s and pK s. Mixed oxides are important for a number of technical applications (heterogeneous catalysts with special properties, components of batteries) and also occur in clay minerals, the topic of the following subsection. 

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