The condensation approximation (CA) and numerical regularization procedure (RP) methods used to solve a Fredholm integral
equation of the first kind describing the adsorption equilibria on a heterogeneous solid surface under isothermal conditions
have been adopted in the present study to evaluate desorption energy distributions from temperature-programmed desorption
(TPD) spectra. From comparisons of the computational results obtained by means of these methods on the basis of simulated
TPD spectra, it follows that the CA gives stable solutions for wide desorption energy distributions and it can be used successfully
for calculations from wide and clear resolved peaks in the TPD spectra. The use of the RP is more advantageous for acquisition
of the distributions from closely related narrow peaks in the TPD spectra.
Authors:B. Hunger, S. Matysik, M. Heuchel, E. Geidel, and H. Toufar
We have investigated the interaction of water with Na+-ion exchanged zeolites of different structures (LTA, FAU, ERI, MOR and MFI) by means of temperature-programmed desorption
(TPD). The non-isothermal desorption of water shows, depending on the zeolite type, differently structured desorption profiles.
In every case the profiles have, however, two main ranges. Using a regularization method, desorption energy distribution functions
have been calculated. The desorption energy distributions between 42–60 kJ mol−1, which can be attributed to a non-specific interaction of water, show two clearly distinguished energy ranges. The water
desorption behaviour of this range correlates with the electronegativity of the zeolites and the average charge of the lattice
oxygen atoms calculated by means of the electronegativity equalization method (EEM). The part of the desorption energy distributions
in the range of 60–90 kJ mol−1, reflecting interactions of water with Na+ cations, shows two more or less pronounced maxima. In agreement with vibrational spectroscopic studies in the far infrared
region, it may be concluded that all samples under study possess at least two different cation sites.
We have investigated the interaction of a few 5-ring organic compounds (cyclopentane, cyclopentene, furan, 2-methylfuran,
2,5-dihydrofuran and tetrahydrofuran) with alkali-metal cation-exchanged faujasites (LSX, X and Y types) by means of temperature-programmed
desorption (TPD). The desorption behavior at higher temperatures of all probe molecules on the sodium ion containing faujasites
with different Si/Al ratios reflects the higher cation content of zeolites with greater aluminum content. Only the desorption
profiles of tetrahydrofuran and 2,5-dihydrofuran show, depending on the kind of cation, additional desorption features at
higher temperatures. Using a regularization method, desorption energy distribution functions for furan and tetrahydrofuran
were calculated. The calculated desorption energy distributions clearly illustrate the very different adsorption behavior
of furan and tetrahydrofuran which leads to large differences in the binding energies between the corresponding adsorption
Authors:M. Błachnio, P. Staszczuk, G. Grodzicka, L. Lin, and Y. Zhu
Uniformly carbon-covered alumina (CCA) was
prepared via the carbonisation of sucrose highly dispersed on the alumina
surface. Using special thermogravimetry and sorptometry methods physicochemical
properties of carbon-covered alumina surfaces were investigated. A numerical
and analytical procedure for the evaluation of total heterogeneous properties
(desorption energy distribution and pore-size distribution functions) on the
basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium
conditions are presented. The desorption energy distribution was derived from
the mass loss Q-TG and the differential mass loss Q-DTG curves of thermodesorption
of pre-adsorbed polar and apolar liquid films. For the first time, the evaluation
of the fractal dimensions of carbon-covered alumina using the sorptometry,
thermogravimetry and AFM data is presented.
Authors:D. Sternik, M. Błachnio, P. Staszczuk, G. Chądzyński, and E. Kowalska
properties (adsorption capacity, desorption energy distribution and pore-size
distribution functions) of nanomaterial surfaces from selected materials,
based on sorptometric and liquid thermodesorption measurements under quasi-equilibrium
conditions, are presented. The fractal dimensions of nanotubes using sorptometric
and AFM data have been evaluated.
Comparison of thermogravimetric
and other data provide new information about the adsorption and pore structure
of the studied materials. The fractal dimensions of nanomaterial surfaces
using sorptometry are in good agreement with those from AFM.
Authors:B. Hunger, M. v. Szombathely, J. Hoffmann, and P. Bräuer
Desorption energy distributions were calculated for temperature-programmed desorption (TPD) of ammonia from H zeolites of
different type by means of regularization. This method does not require any limiting assumptions about the distribution function.
It could be shown that the desorption energy distributions obtained are nearly independent of the experimental conditions
and therefore they should represent a suitable measure for the distribution of the strength of acidic sites. The calculated
desorption energy distributions for the ammonia desorption from the isolated bridging SiOHAl groups of H zeolites of different
type significantly differ from each other in shape. The increase of the desorption energy of the main range of the distribution
functions correlates well with the increase of the average acid strength of the SiOHAl groups with decreasing Al content of
Authors:D. Sternik, P. Staszczuk, M. Majdan, A. Gładysz-Płaska, E. Dąbrowska, and K. Bigda
The paper presents physico-chemical properties
of mixed adsorbents in the clinoptylolite (mordenite)/SiO2
system containing 30, 50, 80 mass% zeolite. Adsorption capacity towards polar
(water, butanol) and non-polar (n-octane)
substances as well as total surface heterogeneity (energetic and geometrical)
were determined. Desorption energy distribution functions as well as fractal
dimensions were also determined and compared with the low-temperature nitrogen
adsorption data. Irregular shapes of the curves q=f(Ed)
as well as large values of volumetric fractal dimensions (Df~2.6)
revealed heterogeneous properties of the zeolite/SiO2 system surfaces. Addition
of zeolite increases total heterogeneity of the material.
Authors:P. Staszczuk, D. Sternik, and G. Chądzyński
Using thermo-analytical and sorptometric methods physicochemical properties and especially surface heterogeneity of HgBa2Ca2Cu3O8+, (Hg-1223) was investigated. The desorption energy distribution was derived from mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption in quasi-isothermal conditions of pre-adsorbed n-octane and water vapour. It is shown that the superconducting Hg-1223 phase is highly sensitive to water vapours. The mechanism of water adsorption depends largely on the activation time. By water vapour saturation in a period of 90 min, physisorption takes place. Prolonged periods result in a chemical decomposition. From nitrogen ad- and desorption isotherms the fractal dimension of superconductors were calculated. A new approach is proposed to calculate fractal dimension from Q-TG curves.
A simple method has been adopted to obtain an important information on the heterogeneous properties of materials studied,
adsorbed liquid films and liquid-solid interactions. The method utilizes Q-TG mass loss and the first derivative Q-DTG mass
loss curves with respect to temperature and time obtained during programmed liquid thermodesorption in quasi-isothermal conditions.
The values of the adsorption capacity, total porosity of material, the value of active centers, desorption energy distribution
and mesopore-size distribution functions obtained by this method are in good agreement with those estimated on the basis of
independent methods. The theoretical and experimental results provided novel and unique data on the heterogeneity of solid
surfaces, properties of liquid adsorbed films and thermal stability of the liquid/solid interfaces.
This paper presents the more important results obtained so far in the studies the liquid/solid systems by means of the Paulik's
classical and quasi-isothermal techniques.
Summary Using temperature-programmed desorption (TPD), we have investigated the interaction of carbon dioxide with alkali-metal cation-exchanged faujasite type zeolites (LSX, X and Y). TPD in the temperature range between 300 and 500 K results in desorption profiles of different intensities depending on the kind of cation and the aluminium content of zeolites. For NaX the desorbed amount corresponds to about one percent of the saturation capacity at 298 K. In case of NaX and X type zeolites exchanged with Cs+ ions an additional desorption peak above 500 K could be observed. Taking into account desorption curves of different heating rates, desorption energy distribution functions were calculated by using an extended integral equation. Initial adsorbed CO2 could be assigned to carbonate species in different environments by DRIFT spectroscopy.