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:B. Hunger, S. Matysik, M. Heuchel, and W.-D. Einicke
Using temperature-programmed desorption (TPD), we have investigated the desorption behavior after subsequent co-adsorption
of methanol and water and after adsorption of their mixtures on a NaZSM-5 zeolite. The course of desorption indicates that
a strong mutual displacement of both components occurs. However, on the strongest adsorption sites methanol is preferentially
adsorbed, and already the addition of small amounts of methanol leads to a displacement of water. Our results support the
idea of a subdivision of the pore space for adsorption of water/methanol mixtures. Above all, the experiments show that in
the part of the pore space where both components are adsorbed, different sites are of importance which vary significantly
in their interaction strength.
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. Turco, G. Bagnasco, G Russo, P. Ciambelli, P. Patrono, M. A. Massucci, and S. Vecchio
The ion exchange technique was employed for the preparation of VO2+ modified titanium phosphates as catalysts for the selective reduction of NO with NH3. The samples were prepared by contacting with a vanadyl sulphate solution different precursor materials, amorphous, crystalline or sodium half exchanged titanium phosphate. The vanadium contents of modified phosphates were in the range 0.08–2.3 wt%. XRD and thermal analysis TG/DTA showed that vanadium loading does not cause structural modification in hydrogen titanium phosphate. A vanadyl containing phase was obtained when half sodium titanium phosphate was employed. The NH3 TPD measurements indicated the presence of a wide distribution of NH3 adsorbing sites with medium-high strength. Catalytic activity measurements were performed under dilute conditions. It was found that the presence of vanadium even in low amounts strongly promote the catalytic activity.
Authors:L. Chmielarz, M. Zbroja, P. Kuśtrowski, B. Dudek, A. Rafalska-Łasocha, and R. Dziembaj
Alumina, zirconia and titania pillared montmorillonites additionally modified with silver were tested as catalysts of NO reduction
with NH3 or C2H4. Ammonia was much more effective reducer of NO than ethylene. The silver containing TiO2-pillared clay has been found to be the most active catalyst for NO reduction both with NH3 or C2H4. Oxidation of the reducing agents by oxygen limited the NO conversion in the high temperature region. The ammonia and nitric
oxide adsorption sites were studied by the temperature programmed desorption methods (TPD).
Authors:M. Wang, S. Tokiwa, T. Nishide, Y. Kasahara, S. Seki, T. Uchida, M. Ohtsuka, T. Kondo, and Y. Sawada
Amorphous indium-tin-oxide (ITO) transparent conducting film (15 at% Sn; thickness, 150–190 nm) was deposited on silicon wafer
at room temperature by RF magnetron sputtering for temperature programmed desorption (TPD) in vacuum. The thermal crystallization
was accompanied by evolution of water vapor (the main gas), argon and carbon dioxide. The total amount of evolved water vapor
(H2O [mol]/(In [mol]+Sn [mol])>0.2) was one or two orders of magnitude more than that from the nanocrystalline ITO films reported
in our previous papers. The thermal change of amorphous ITO film was remarkably affected by the position of the substrate.
An abrupt gas evolution was characteristic of the amorphous ITO films deposited on the position near the target center. The
evolution temperature (548–563 K) was higher than the gas evolution temperature from the crystalline films. The far from center
positioned films crystallized at higher temperature with relatively slower evolution of the gases.
Authors:Y. Sawada, S. Seki, M. Sano, N. Miyabayashi, K. Ninomiya, A. Iwasawa, T. Tsugoshi, R. Ozao, and Y. Nishimoto
Tin-doped indium oxide In2O3 (indium-tin-oxide) transparent conducting films were fabricated on silicon substrates by a dip coating process. The thermal
analysis of the ITO films was executed by temperature-programmed desorption (TPD) or thermal desorption spectroscopy (TDS)
in high vacuum. Gas evolution from the ITO film mainly consisted of water vapor. The total amount of evolved water vapor increased
on increasing the film thickness from approx. 25 to 250 nm and decreased by increasing the preparation temperature from 365
to 600C and by annealing at the same temperature for extra 10 h. The evolution occurred via two steps; the peak temperatures
for 250 nm thick films were approx. 100-120 and 205-215C. The 25 nm thick films evolved water vapor at much higher temperatures;
a shoulder at approx. 150-165C and a peak at approx. 242C were observed. The evolution temperatures increased by increasing
the preparation and the annealing temperatures except in case of the second peak of the 25 nm thick films. The evolution of
water vapor at high temperature was tentatively attributed to thermal decomposition of indium hydroxide, In(OH)3, formed on the surface of the nm-sized ITO particles.
TPD studies on the kinetics of deammoniation of an NH4NaY zeolite showed that the use of a hyperbolic temperature programme led to kinetic parameters agreeing with those resulting from a linear heating process. Because of the progressive increase of the heating rate in the case of hyperbolic heating schedules, the parameters can be considered as independent of the heating rate within certain limits. The better resolution of complex desorption spectra with hyperbolic programmes is an additional reason for their use.
Authors:N. He, D. Li, M. Tu, J. Shen, S. Bao, and Q. Xu
The acidity of mesoporous materials FeSiMCM-41, LaSiMCM-41, SiMCM-41, AlSiMCM-41 and HAlSiMCM-41 has been investigated by microcalorimetric studies of the adsorption of ammonia and temperature programmed ammonia desorption method. In the initial stage, the acid strength sequence is SiMCM-41>HAlSiMCM-41>AlSiMCM-41>FeSiMCM-41>LaSiMCM-41, in agreement with that found for microporous molecular sieves materials. A small number of strong acid sites of SiMCM-41 may result from the aluminum impurity contained in the silica source material. The acid density sequence is HAlSiMCM-41>AlSiMCM-41>FeSiMCM-41>LaSiMCM-41SiMCM-41 and can be explained by the studies of existing states of trivalent atoms in these samples reported in previous work. Since some NH3-TPD plots of these samples show the profiles that could not be back to baseline at elevated temperature, the technique of microcalorimetric adsorption is preferable in studying these samples.
Through simulation of TPD model curves for desorption from adsorption sites of different strength could be shown that the use of non-linear temperature programmes influences the complex desorption process in such a manner that the appearing desorption maxima are better visible.