Metody badań niejednorodności energetycznej powierzchni katalizatorów i adsorbentów Methods of investigation energetical heterogeneity on the surface of catalysts and adsorbents
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.
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