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Schlagwörter:
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Zusammenfassung:
Methods of identification of various acidic sites in zeolites (Brønsted sites, different types of Lewis sites, cations) are briefly reviewed. Similarly, techniques for determination of the density of acid sites are discussed and illustrated with selected examples. In particular, a good agreement between the results obtained by IR (using pyridine as a probe molecule) and ESR (employing NO) in determining Lewis site densities of, for instance, progressively dehydroxylated H-Y is demonstrated. Emphasis is laid on the discussion of techniques, such as titration, in aprotic solvents, IR with and without probe molecules, 1H MAS NMR, temperature-programmed desorption and microcalorimetric measurements of heats of adsorption of basic probe molecules, which are suitable for characterising the strength of acidic sites. Quantitative evaluation of TPD spectra using a kinetics model as well as the combination of different methods is described in more detail, and results obtained by various techniques on selected examples of acidic zeolites are compared.
