Novel high-temperature, high-vacuum, all-metal sample cells for microcalorimetric measurements of solids

The design of a novel microcalorimetric sample cell which allows rapid transfer of heat from the sample to the cell wall is described. The solid sample is dispersed around the internal walls of the cell. Since the thermopiles of the microcalorimeter are in contact with the outer surface of the cell, the new design of the cell allows rapid recording of the heat generated by the sample. The robust all-metal cell allows in situ sample activation under conditions of high vacuum and at temperatures up to 500 °C. The dispersion of the sample avoids any “deep bed” effects where gas may not be able to diffuse freely to the surface of all of the sample, which may be the case when a thick layer or plug of the sample is used. The cell enables faster acquisition of heat data and minimizes effects of self-heating of the sample. A simple tool, which assists the introduction of the solid sample into the cell and a compact resistor-element, which fits inside the cell for calibration, are described

Solid-state Reactions of Zeolites

The principle of preparation of modified zeolites by solid-state reaction is illustracted using simple systems such as mixtures of alkaline, alkaline earth or lanthanum chlorides and ammonium or hydrogen forms of zeolites. The avantages of this approach are discusse solid-state reaction is an attractive route to preparation of acidic or bifunctional catalysts. Finally, it is shown that solid-state modification is also possible using the as-synthesized sodium forms, for instance for an ion exchange with mono-, bi-and trivalent cations, which is investigates by IR, 23Na MAS NMR, TPE and, in the case of FeCI2, additionally with Mössbauer spectroscopy

Comparative Measurements on Acidity of Zeolites

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