Behavior and Local Structure of Surface Sites in Zeolites

Investigations of Chemical Behavior and Local Structure of Surface Sites in Zeolites and Microporous Silicoaluminophosphates 

The incorporation of Al atoms into the framework of zeolites occurs in a tetrahedral oxygen coordination and leads to negative framework charges. These framework charges are compensated by protons in acidic hydroxyl groups or by extra-framework cations such as Li , Na, Cs , Mg , etc. Accordingly, these surface sites are responsible for the chemical behavior of zeolites in separation processes and in catalysis (199,200). 

Loaded zeolites (with added material designated following slash)  

The conversion of methanol to hydrocarbons (MTHC) on acidic zeolites is of industrial interest for the production of gasoline or light olefins (see also Section X). Upon adsorption and conversion of methanol on calcined zeolites in the H-form, various adsorbate complexes are formed on the catalyst surface. Identification of these surface complexes significantly improves the understanding of the reaction mechanism. As demonstrated in Table 3, methanol, dimethyl ether (DME), and methoxy groups influence in a characteristic manner the quadrupole parameters of the framework Al atoms in the local structure of bridging OH groups. NMR spectroscopy of these framework atoms under reaction conditions, therefore, helps to identify the nature of surface complexes formed. 

Quadrupole Coupling Constant, Cqcc, and Asymmetry Parameter, g, of Framework Al Atoms in Dehydrated Zeolites Y (faujasite), MOR (mordenite), and ZSM-5 

Loaded zeolites (with added material designated following slash) HZSM-5/1 CHsOH/SiOHAl 8.0 0.9 (206) 

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