Characterization and reaction studies of acid zeolites

The acidity characteristics of H-ZSM-5, H-mordenite and H-Y zeolite were studied using microcalorimetry, infrared spectroscopy and gravimetry. H-mordenite and H-ZSM-5 have Bronsted acid sites that are homogeneous in strength, with H-mordenite having the higher strength, while H-Y zeolite shows Bronsted sites of varying acid strength. The acid strength distribution of the aluminum rich H-Y zeolite is interpreted using aluminum coordination concepts. Entropies of adsorption were calculated; stronger adsorption is related to greater entropy loss on adsorption for a variety of solid acid catalysts.; Characterization studies were performed on a series of modified zeolites. Steam treatment of H-Y zeolite based fluid catalytic cracking catalysts reduces total acidity, the ratio of Bronsted to Lewis site population and the Bronsted acid strength. Exchange of cations by protons in NaHY and KHZSM-5 results in a larger number of Bronsted sites. For NaHY the strength of these sites depends on the exchange level, while for KHZSM-5, the added sites are constant in strength.; Reaction studies of acid catalyzed methylamine synthesis from ammonia and methanol were performed. The reaction is first order in ammonia for all catalysts studied. The reaction is first order in methanol, but it decreases to zero order at higher methanol pressures and negative methanol order is observed over H-ZSM-5. Apparent activation energies for methylamine formation are in the range 14-27 kcal mol{dollar}sp{lcub}-1{rcub}{dollar}. Higher Bronsted acid strength is related to a lower apparent activation energy except for the zeolite with the highest acid strength studied (H-mordenite), which shows a reversal in the trend.; Coadsorption and infrared spectroscopy experiments were carried out to determine the nature of adsorbed species on the acid zeolites during reaction. The results indicate the presence of methoxyl groups which can only be removed via reaction. A reaction mechanism based on methoxyl groups as the active species for methylamine synthesis is forwarded and discussed.