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Metody badań niejednorodności energetycznej powierzchni katalizatorów i adsorbentów

Woszczyński P.

Wiadomości Chemiczne

2013

[Z] 67, 7-8

635--664

The knowledge of the properties and a surface structure of catalysts and adsorbents is of great importance in the selection of these materials to the relevant objectives. Interesting structural information can be obtained in many ways, for example: with the use of spectroscopic or microscopic techniques or in direct examination of the adsorption isotherms. This article focuses on these last-mentioned methods, which can be a source of information on energy heterogeneity of the catalyst or adsorbent surface. Heterogeneity is usually determined by measuring adsorption isotherms of a selected adsorbate on the examined adsorbent, which is dependent of adsorbate coverage on the adsorbent relative to the equilibrium pressure under isothermal conditions. Among the many mathematical models describing this relationship particularly interesting is the adsorption isotherm model described by generalized integral Fredholm equation. The solution of this equation is density function with the assumed local isotherm model. There are different ways to solve the Fredholm equation, depending on measurement methods of obtained adsorption isotherms. For example, an application of static techniques (gravimetric or volumetric) needs to use advanced, sophisticated numerical methods for directly solving integral equations, other techniques (e.g. such as calorimetric or chromatographic) provide specific values that simplify these calculations. The resulting energy density function allows to observe active centers as peaks or inflections of the curve on the energy spectrum graph.