Properties and Catalytic Applications

Clays have both Brpnsted and Lewis acid sites, the amount and strength of which can be substantially modified by acid treatments and/or ion exchange [31-34], The strength of the Brpnsted sites can be determined in different ways Hammett indicators, butylamine titration, IR spectroscopy using probe molecules, microcalorimetric or temperature programmed desorption methods [7,9,34-39], There is a direct correlation between acid strength and composition (Table 2), 

The synthesis of a superacid clay, with Hammett acidity ranging from -13,2 to — 12,7 has also recently been reported [40], The surface acidity decreases as the amount of residual water in the clay increases, with an extension related to the nature of the exchangeable cations (significant for Ca and Mg ions or almost negligible for K and Al ) and activation conditions adopted [9,11,24,38], 

Commercial acid-treated clays (e. g. KIO, KSF, etc., from Aldrich or Siid-Che-mie or F13, F20, F20X, etc., from Engelhard), widely used industrially as acid catalysts or adsorbents in hydrocarbon cracking [10,45] and, thus, well-defined and reliable materials, may be employed as reference materials. On the basis of current literature, KIO is by far the most intensively investigated commercially available acid-treated clay, although small differences resulting from the preparation conditions used have also been reported for the widely used KIO [50]. 

Heterocyclic compounds can also be obtained in the vapor phase, with evident advantages in comparison with conventional liquid-phase reactions. For example, the synthesis of alkylquinolines has been recently reported using either zeolites 

The nature of the acylating agent must also be considered. For example, with mesitylene and different acyl chlorides, the yield in the acylation product depended on both the activity and the stability of the eleetrophilic species RCO previously 

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Inorganic layered oxides have attracted considerable attention due to their unique structural properties and applications, such as in intercalation reactions, ionic exchange processes, photochemical and semiconductor properties, and catalytic applications. In this chapter, titanates, niobates, tungstates, molybdates, and molybdenum oxide will be considered as specific examples. However, it is necessary to say that many other specific lamellar oxides are investigated, such as V2O5. 

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