Requlation and Cotolysis of Strong Solid Acid Generated on Extra-Framework Aluminum

The relationship between the acidic property and the composition of a zeolite was precisely measured using Y-and mordenite-type samples with high aluminum contents. The number of the desorbed ammonia, showing the acid amount, was approximately same to the number of [Al]-[Na] atoms over the experimental range. This is quite different from the conventionally observed relationship where the secondary-neighboring aluminum species is formed. It is pointed out that the isomorphously substituted aluminum in zeolite generates the acid site according to the stoichiometry even when the aluminum atoms locate the secondary-neighboring sites. Very strong acid site was observed on the zeolite ZSM-5 in measurements of temperature programmed desorption of ammonia. The site was ascribable to the non-framework aluminum, which interacted with the usual framework acid site. By impregnation of aluminum cation, the strong acid site was created at the expense of the acid site in a zeolite framework. Conditions of a step for template molecule removal affected strongly the concentration of very strong acid site in HZSM-5. Treatment with ammonia with water at ca 373 K was also studied as a procedure to affect the solid acidity, and a similarity of acid sites created by both methods was identified. From the quantitative measurements of acid sites, it was found that the very strong acid site consisted of two Al cations. Catalytic activity for octane cracking was enhanced by the presence of very strong acid site. Strong Bronsted acid site with a narrow distribution of acid strength and large amount, which was active for alkane cracking, was formed by Na_2H_2-ethylenediaminetetraacetic acid treatment of ultra stable Y zeolite.