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Abstract  

Temperature-programmed desorption coupled with mass spectrometer as a detector (TPD), IR and 13C NMR measurements are used to study the adsorption of n-hexane on hydrated HZSM-5 and NH4ZSM-5 zeolites. The 13C NMR measurements show that n-hexane can access the pore structure of ZSM-5 zeolites previously saturated with water. TPD spectra of n-hexane are monitored in the temperature region 50–300C, in the case of fully or partially hydrated samples; two-stage desorption of n-hexane is found. Simultaneous desorption of water and n-hexane in the same temperature region are found, in all investigated samples.

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Journal of Thermal Analysis and Calorimetry
Authors: B. Hunger, M. v. Szombathely, J. Hoffmann, and P. Bräuer

Abstract  

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 the zeolites.

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Abstract  

Sol-gel-derived titania films were analyzed by temperature programmed desorption (TPD) and X-ray diffraction (XRD) techniques. The relationship between the TPD curves measured for two types of titania gel films and their crystal structures was investigated. On the basis of the analyses, a preparation process for a titania sol solution containing anatase nanocrystals was designed and developed. Using this process, a colloidal anatase titania sol solution was prepared by heating aqueous titanium hydroxide containing HCl at 60�C for 2 h. The nanocrystal structure of the titania films obtained by coating the sol on glass substrates was confirmed by TPD and XRD measurements.

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The temperature-programmed desorption (tpd) of the amount of ammonia which is preadsorbed at about 373 K at HZSM-5 zeolites yields a complex desorption curve consisting of two overlapped peaks (Β andγ peak). Parts of the ammonia desorbed can be attributed to SiOHAl groups considering also1H-MAS NMR measurements.

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Temperature programmed desorption is a typical non-isothermal method and therefore it needs a careful experimentation and a careful evaluation of the experimental data, in order to obtain meaningful kinetic parameters.

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The interactions of propylene with zinc oxide have been studied by temperature-programmed desorption (TPD) under experimental conditions free of inter- or intraparticle limitations or readsorption phenomena.

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A graphic method is proposed to determine all of the kinetic parameters in Wigner-Polanyi equation of desorption. A desorption rate curve from a single temperature-programmed desorption experiment is required by this method to determine the order of reaction (n), the activation energy (E d) and the pre-exponential factor (v) of the equation. The proposed method has been applied to the oxygen desorption from PdO/Al2O3 samples prepared by impregnating γ-Al2O3 with H2PdCl4 solution used as examples. From the graphic method, the values ofn=2, andv=1.37±0.80×109 s−1 were successfully determined for the desorption. The value ofE d depended on the dispersion of palladium (D) on PdO/Al2O3 samples, and was expressed by the equation:E d=175+174D kJ·mol−1. This graphic method is a direct and time-saving technique, on comparing with other methods suggested in the literature, for analysis of data from temperature-programmed desorption of simple desorption processes.

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Abstract  

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.

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Abstract  

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 complexes.

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