A consecutive model of surface reaction, consisting of two steps (desorption and diffusion) was applied. It was concluded that diffusion modifies the temperature programmed desorption spectra, although the single peak curves appear. The differential method for calculation of kinetic parameters based on thesTM shift give values close to predicted ones only in the cases when particular steps are rate limiting. Generally, the desorption process have to be considered as a complex reaction, with the overall kinetic parameters. As a consequence of diffusion influence, the overall kinetic parameters are smaller than those for desorption step was obtained.
Authors:V. Rakić, V. Dondur, R. Hercigonja, and V. Andrić
The active sites of hydrogen-exchanged Y zeolite (HY) and dealuminated (HDY) zeolites are investigated by TPD of carbon monoxide.
Only the high temperature TPD spectra of CO (TM620-690C) were observed, meaning that CO molecules interact with very strong
acid sites. The amounts of CO bonded on these sites are small (less than 1 molecule per unit cell). The strong influence of
dealumination on the coverage degree is found. The calculated values for kinetic parameters indicate chemisorption of CO in
the investigated systems (Edes240 kJ mol-1, A1011 s-1).
Authors:B. Dragoi, V. Rakic, E. Dumitriu, and A. Auroux
This work is focused on the gas and liquid-phase adsorption of pollutants: propanol, 2-butanone, phenol and nicotine onto
zeolites (H-BETA, H-ZSM-5, H-MCM-22, and clinoptilolite). Textural properties and origin of zeolites were taken into account
as criteria of adsorbents selection. The aldehyde and the ketone were adsorbed in the gas phase using microcalorimetry linked
to a volumetric line to evaluate adsorption. Adsorptions in water were carried out for phenol and nicotine and the evolved
heats during adsorption were measured by a differential heat flow reaction calorimeter with stirring. Results are discussed
in relation with the pore sizes and various interactions which could occur between the adsorbent and the adsorbate.
Authors:V. Rac, Vesna Rakić, S Gajinov, Vera Dondur, and Aline Auroux
In this work, room temperature interaction of n-hexane with HZSM-5 (Si/Al=20) and ion-exchanged
samples containing one (CuZSM-5, FeZSM-5 and MnZSM-5) or two transition-metal
cations (Fe,CuZSM-5; Cu,MnZSM-5 and Fe,MnZSM-5) was studied by microcalorimetry
and TPD methods. Both differential heats and the amounts of n-hexane
adsorbed per one unit cell were quantitatively determined. Higher heats of
adsorption and higher amounts of adsorbed gas were found for ion-exchanged
samples than for HZSM-5. The experiments of n-hexane
adsorption on hydrated samples were also performed. The amounts of n-hexane
adsorbed on hydrated ZSM-5 were lower in comparison with dehydrated samples,
while the energies of interaction were similar.