Abstract
Temperature-programmed desorption (TPD) of ammonia with improved techniques was applied to quantitative determination of the strength and number of acid sites of a series of modified Y zeolites. A weak acid site was generated by the isomorphous substitution of aluminum for silicon, and the strength was independent of the aluminum concentration. This type of acid site showed almost no activity for cracking of octane at 573 K. Multiple types of extra-framework aluminum were formed on the ultra stable Y (USY) zeolite by steaming to create the cracking activity. Strong Brønsted acid sites were increased by the treatment of USY with a sodium salt of ethylenediaminetetraacetic acid (EDTA). The catalytic activity for alkane cracking showed a positive relationship with the number of this type of acid site, suggesting that the active site of USY for the catalytic cracking is this strong Brønsted acid site.
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