II International Symposium on Carbon for Catalysis ABSTRACTS

CHARACTERIZATION OF POROUS STRUCTURE OF CARBONACEOUS
MATERIALS BY MEANS OF DENSITY FUNCTIONAL THEORY
PL-3
Ustinov E.
Scientific and Production Company “Provita”, St Petersburg, Russia
e-mail: eustinov@mail.wplus.net
It has long been recognized that adsorption isotherms provide quite reliable information on
structure of different porous materials and complements the data obtained with other tools of
the pore structure analysis such as high resolution transmission electron microscopy
(HRTEM), X-ray diffraction (XRD) and small angle X-ray scattering. The topology of
activated carbons is known to be highly complex and is far from being completely
understood. Nevertheless, simulation technique and molecular theories developed for the
latest decades allow determination basic structural properties of porous solids like the pore
size distribution (PSD), surface area and energetic heterogeneity. One of the most effective
tools for the PSD analysis is the nonlocal density functional theory (NLDFT), which is widely
used in the software for the pore structure analysis with nitrogen and argon low temperature
adsorption isotherms. Results of the PSD analysis are strongly dependent on a reference
nonporous solid. In the case of carbonaceous materials the graphitized carbon black is mainly
used as the reference system to adjust solid–fluid interaction parameters in the framework of
the Lennard–Jones (LJ) potential. Given those parameters, the NLDFT is used for generating
the set of local nitrogen or argon adsorption isotherms for slit pore model over the wide range
of pore width accounting for the enhancement of the potential due to the overlapping
potentials exerted by the opposite pore walls. The final stage of the technique is the inverse
task to determine the pore size distribution function with the Tikhonov regularization
procedure.
Despite the technique described above is commonly used, there are still unresolved
problems mainly associated with poor correlation of adsorption isotherms. A source of such
discrepancies could arise from inadequate model of the pore wall surface and the pore shape.
To overcome this shortcoming we developed a refined NLDFT version as applied to
amorphous solids assuming that the nongraphitized carbon black is a better choice for the
reference system. To this end, a series of different samples of nongraphitized carbon black
having specific surface area from 30 to 1500 m 2 /g was thoroughly investigated using the
13