The Effect of Acid Sites of Zeolite in Some Organic Reaction

Since zeolites are widely used as solid acid catalysts in many industrial processes, characterization of their acid sites is critical for evaluation of zeolite performance. Among the various solid acid catalysts, zeolites have received an increasing attention because of their suitable acidity, thermal stability and low cost.The acidity of zeolite could be due to the Bronsted and Lewis acid sites. Exchange of monovalent cations with polyvalent ion creates strong Bronsted centers by the hydrolysis phenomena, which is useful for some of acid catalyst reactions such as alcohol dehydration, acylation, estrification, and Diels-Alder reaction. We can decrease the number of proton sites and increase the number of Lewis sites by dehydration reaction, which is carried out above 875 K°. The time of the cation exchange process can be reduced under microwave irradiation.The Lewis sites can be increased when the metal / zeolite is prepared in the solid state phase ionexchange under microwave irradiation. Interestingly, in some reactions, including intramolecular acylation, isomerization and conversion of acids to benzimidazoles and Biginelli reaction the Lewis sites are the active centers.