Acidity and basicity of zeolites: A fundamental approach

- Spectroscopic features of cationic and protonic zeolites are discussed critically.
- Orthosilicate species in high Al zeolites have relevant basicity.
- Cationic zeolites have strong ionicity and moderate Lewis acido-basicity.
- Stabilization of anionic charge by Si-O-Si bridges is crucial for H-zeolites acidity.
- Stabilization of protonated species by cavities is also key for H-zeolites acidity.

The main data concerning acidity and basicity characterization of protonic and cationic zeolites are described and discussed. In particular, experimental data concerning IR studies of the adsorption of pyridine, CO and CO2 on Na-zeolites (Na-X, Na-A, Na-MOR) and on protonic zeolites (with emphasis on H-Y and USY) are described and discussed. The nature of the Lewis acid and basic sites as well as of the Brønsted acid sites is discussed with a fundamental chemical approach.

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