Acid-base surface sites, adsorption organic molecules

Acid-base surface sites, adsorption of organic molecules, 23... 

An additional difficulty in the determination of actual TOF values for zeolite catalysed reactions deals with the accessibility by reactant molecules to the narrow micropores in which most of the potential active sites are located. The didactic presentation in Khabtou et al.[37] of the characterization of the protonic sites of FAU zeolites by pyridine adsorption followed by IR spectroscopy shows that the concentration of protonic sites located in the hexagonal prisms (not accessible to organic molecules) and in the supercages (accessible) can be estimated by this method. Base probe molecules with different sizes can also be used for estimating the concentrations of protonic sites located within the different types of micropores, which are presented by many zeolites (e.g. large channels and side pockets of mordenite1381). The concentration of acid sites located on the external surface of the... 

Adsorption of molecules such as ammonium and organic bases is used in the study of chemical surface properties of oxide catalysts. The acidity of an oxide can be evaluated based on the classic Brbnsted and Lewis concepts, i.e., according to their capacity to donate a proton and accept electrons, respectively. Thus, spectroscopic evidence of the presence of these sites on the surface of oxides is obtained from the adsorption of molecules capable of adsorbing at the acidic sites on the surface of the oxide. 

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