Studies on the acidity of mordenite and ZSM 5. 1. Determination of Broensted acid site concentrations in mordenite and ZSM 5 by conductometric titration
| Autor: | J. N. Van der Moolen, C. A. Emeis, Ruud H. M. Herold, M. H. W. Sonnemans, Mark Crocker, A. E. Wilson |
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| Rok vydání: | 1993 |
| Předmět: | |
| Zdroj: | The Journal of Physical Chemistry. 97:432-439 |
| ISSN: | 1541-5740 0022-3654 |
| DOI: | 10.1021/j100104a027 |
| Popis: | The Broensted acidity of H-mordenite and H-ZSM-5 samples of varying proton concentration has been studied using aqueous conductometric titration, IR spectroscopy, and aqueous potentiometric titration. Good agreement is observed between Broensted acid site concentrations determined by conductometric titration and IR measurements, while indirect potentiometric titration affords acid site concentrations consistently lower than those measured using the conductometric technique. This finding is rationalized on the basis that, in a conductometric titration, all the accessible Broensted acid sites are direct;y titrated, whereas in the potentiometric procedure utilized, only those protons which can be ion-exchanged out of the zeolite are titrated. After allowing for the presence of extraframework aluminum in the zeolites (determined by [sup 27]Al NMR), the measured acidity for H-mordenite is found to increase linearly with increasing Al content within the range 0-1.5 mmol Al/g but appears to reach a limiting value at higher Al concentrations. For H-ZSM-5, the experimentally determined number of Broensted acid sites is also found to be linearly dependent on the Al molar fraction within the range measured (0-1.20 mmol Al/g). For both series of zeolite samples, the measured acidity is generally found to be less than the theoretical maximum calculated on the basis of an H[supmore » +]/Al ratio of 1. 43 refs., 10 figs., 4 tabs.« less |
| Databáze: | OpenAIRE |
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