Abstract
The acidic properties and 2-methylpentane cracking turnover frequencies (TOFs) were compared for HY and two dealuminated HY zeolites with similar levels of framework Al: HDY that was dealuminated by ammonium hexafluorosilicate, and a (H,NH 4)-USY zeolite that was dealuminated by steam. The acid strength distributions were determined by microcalorimetry of NH 3 adsorption, and the types of acid sites by FTIR spectroscopy. All zeolites possessed Brønsted acid sites with very few Lewis acid sites. The differential heat of adsorption of NH 3 on these zeolites was nearly constant: about 120 kJ/mol for HY and HDY and approximately 7 kJ/mol higher for the (H,NH 4)-USY. The cracking TOF for HDY was five times larger than HY, while the TOF of (H,NH 4)-USY was 80 times higher. These results suggest that the cracking activity may be affected by other factors in addition to acid strength.
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