期刊
MICROPOROUS AND MESOPOROUS MATERIALS
卷 147, 期 1, 页码 17-29出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.micromeso.2011.05.016
关键词
Toluene adsorption; TPD; DFT; Hydrocarbon traps
类别
资金
- UNL [PI 55-265, PI 68-344]
- CONICET [PIP 2010-190]
- ANPCyT
In this work, we studied the adsorption capacity and thermal stability of toluene on ZSM5 and mordenite zeolites with different exchange cations (H, Na and Cs). The interaction of the hydrocarbon molecules with the adsorption sites was also addressed with both experimental and theoretical techniques. Flow-adsorption measurements were carried out in order to obtain breakthrough curves as well as TPD experiments. Molecular simulations were performed using the Density Function Theory (DFT). The results show that, in general, mordenite samples have a better adsorption capacity than ZSM5 samples and that the thermal stability of the adsorbed toluene is more influenced by the exchanged cations than by the zeolite structure. The overall basicity of the samples depends on the exchanged cations, following the Cs > Na > H order. The main interaction of toluene takes place between the pi electrons of the aromatic ring and the Lewis sites generated, and another interaction takes place between C-H groups and the zeolite network oxygen. The increase of the Cs loading decreases the surface area and pore volume of the zeolites, thus decreasing the available sites for the overall toluene adsorption at 100 degrees C. Through TPD experiments both the Phi, parameter, which represents the fraction of toluene retained at temperatures higher than 100 degrees C, and the temperature at which the toluene desorbs were measured. It was observed that in the Cs exchanged samples, is Phi higher but the thermal stability (temperature of the maximum desorption rate on TPD) follows the order NaMOR = NaZSM5 > CsNaZSM5 > CsNaMOR > CsHMOR = CsHZSM5 > HMOR > HZSM5. The molecular calculations for the NaMOR structure determined that the interaction energies were higher for NaMOR when compared with the HMOR structure and increased even more when Cs was exchanged. These facts are in line with the experimental results. (C) 2011 Elsevier Inc. All rights reserved.
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