THERMOGRAVIMETRIC AND MICROCALORIMETRIC STUDIES OF ZSM-5 ACIDITY

The combination of thermogravimetry, microcalorimetry and infrared spectroscopy studies of pyridine adsorption has been used to characterize the acidity of a ZSM-5 catalyst. The majority of the acid sites are Bronsted acid centers associated with framework Al species, with heats of pyridine adsorption equal to 140 kJ/mol. Non-framework Al species in the zeolite sample of this study eliminate an approximately equal number of Bronsted acid sites. These non-framework Al species also produce strong Lewis acid sites with pyridine adsorption heats greater than 140 kJ/mol, as well as weak adsorption sites (e.g., weak Bronsted acid sites or hydrogen bonding sites) with heats equal to 90-140 kJ/mol.