Relating Structure and Chemical Composition with Lewis Acidity in Zeolites: A Spectroscopic Study with Probe Molecules
| Autor: | R.A. Schoonheydt, Bert M. Weckhuysen, Gabriela Catana, David Baetens, Tim Mommaerts |
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| Přispěvatelé: | Katalyse en spectroscopie, Universiteit Utrecht, Dep Scheikunde |
| Rok vydání: | 2001 |
| Předmět: |
Chemistry
Inorganic chemistry Infrared spectroscopy Surfaces Coatings and Films law.invention Adsorption law Materials Chemistry Molecule Physical chemistry Lewis acids and bases Physical and Theoretical Chemistry Absorption (chemistry) Fourier transform infrared spectroscopy Electron paramagnetic resonance Zeolite |
| Zdroj: | The Journal of Physical Chemistry B. 105:4904-4911 |
| ISSN: | 1520-5207 1520-6106 |
| DOI: | 10.1021/jp003091v |
| Popis: | FTIR and EPR of adsorbed probe molecules were used to study Lewis acid sites in FAU and MFI zeolites with different nonframework Al content. Infrared spectra of adsorbed CO at low temperatures give information about all types of sites. The absorption bands were assigned to CO fixed on Bronsted sites, cations, and true Lewis acid sites with different strengths. The frequency shifts and the relative intensities of these peaks were correlated with the structure type and the nonframework Al amount. In contrast, EPR of adsorbed NO is probing only the sites strong enough to quench the orbital magnetic moment of NO molecule. However, the method can provide an estimation of the strength of the detected Lewis acid sites, via the gzz parameter. A correlation was established between the amount of nonframework Al and the spin concentrations of adsorbed NO. These absolute concentrations are lower than the expected number of Lewis acid sites. Several methods were proposed for creating Lewis acid sites in a controlled w... |
| Databáze: | OpenAIRE |
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