A dynamic assessment of MFI acidity using microcalorimetric techniques

✍ Scribed by M. Muscas; J.F. Dutel; V. Solinas; A. Auroux; Y. Ben Taarit

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 727 KB
• Volume: 106
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/1381-1169(95)00266-9

✦ Synopsis

The number and strength of the acid sites of a variety of NaHZSM-5 zeolites were measured as a function of the exchange level using NH, adsorption monitored by microcalorimetry.

While the number of acid sites increased quasi linearly with the exchange level, the acid strength remained almost constant over a wide range of exchange levels then dramatically increased when 80% of the original Na + ions were removed. The removal of the residual Na+ ions not only generated much stronger sites but resulted also in a general increase of the acid site population already present. This phenomenon, which is fairly similar to those encountered with faujasites and other acids, was interpreted in terms of remote perturbation of the acid centers structure by the very few residual Na + ions modifying significantly the TOT bond angles. In addition possible general cation redistribution induced by NH, adsorption may also affect the evolved heats of adsorption.