II International Symposium on Carbon for Catalysis ABSTRACTS

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developed NLDFT model, which allowed us to determine the solid–fluid potential as a
function of the distance from the surface. It turned out that the adsorption in the first
molecular layer is localized and controlled by short-range forces, with the surface being
highly heterogeneous. Beyond the first molecular layer the solid–fluid potential obeys the
power law and decays inversely the third power of the distance. Interestingly enough that the
absolute value of the potential outside the first molecular layer is several times smaller than it
is predicted by the LJ pair potential. This means that the individuality of a nonporous material
is mainly restricted by the first molecular layer (more exact estimation is 1.3 of monolayer
capacity) and partly explains the universality of adsorption isotherms at relative pressures
above approximately 0.1, which is reflected in so-called t-curve. Some additional information
we have obtained by the comparison of the behavior of nitrogen adsorbed on nongraphitized
carbon black and nonporous silica. In the latter case the solid–fluid potential decays inversely
the fourth power of the distance, meaning that, as opposed to carbon blacks, the potential is
exerted by surface (oxygen) atoms. Analysis of N 2 adsorption in highly ordered MCM-41
silica samples has shown a startling result that the effect of the surface curvature on the solid–
fluid potential is nearly absent, which indirectly confirms the conclusion that the adsorption
potential of amorphous solids in contact layer is short-range.
Application of the developed NLDFT to activated carbons has convincingly shown that
the use of nongraphitized carbon black as a reference system leads to much more reliable PSD
functions and excellent fitting of experimental adsorption isotherms. For example, the PSD
functions have become smoother and do not show any artificial peaks and gaps. Thus, the
pore structure of carbonaceous materials, the surface area and its distribution over the pore
size can now be reliably disclosed with the developed approach. Additionally, this technique
provides the prediction of differential heat of adsorption and adsorption deformation
(adsorption-induced contraction and swelling). The latter is important for the problem of
methane and hydrogen storage. At present we carry out further investigations to develop a
NLDFT-based tool to determine the surface chemistry of nonporous and porous carbonaceous
materials. In particular, it will allow us to identify different functional surface groups,
crystalline defects, relation of basal, prismatic, and defect surfaces, which is important for the
application of those materials in catalysis. To summarize, one can state that the analysis of
adsorption isotherms with NLDFT is a promising tool for determination of porous materials
structure and further efforts are needed.
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