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Abstract  

The aim of the present work was to combine different physicochemical techniques, namely X ray diffraction, IR spectroscopy, and multinuclear (29Si and 27Al) solid-state NMR spectroscopy, to study the aluminum distribution and to determine the silicon–aluminum ordering in the Y-zeolite framework when the latter was submitted to acid leaching (HCl, HNO3, H2SiF6). It was shown that all acids were effective in removing Al from the framework. Moreover, the extra-framework Al extraction from the lattice was dependent on the nature and the concentration of the acid. After the dealumination treatment, different species (silanol nest, six-coordinated non-framework Al) were detected. The investigation showed that the breakdown of the parent Y-zeolite mainly depends on the degree of dealumination.

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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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dioxide molecule and extra-framework cation of zeolites. Since concentration of cations in the MFI zeolite with Si/Al = 30 is 0.44 mmol per gram of zeolite (see Table 1 ), the amount of adsorbed CO 2 molecules is considerably higher. It implies that so

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Abstract  

TPR method was used to elucidate the status of nickel ions in chrysoprase. Temperature profiles of chrysoprase samples were interpreted by comparing them with TPR curves of references. Two kinds of nickel species were identified in the studied samples. The first one is nickel in 2:1 layer silicates while the other is nickel in the extra-framework positions. Apparent activation energies (853 and 205 kJ mol−1) which were obtained from TPR data support the above attribution.

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Abstract  

Pure HEU-type zeolite (heulandite) crystals were allowed to interact with Sr2+ cations in aqueous solution. The powdered solid experimental products obtained from batch-type sorption experiments, using solutions of Sr2+-concentrations between 10 and 1000 mg/l, were investigated using INAA, RI-XRF and SEM-EDS. The Sr uptake by the mineral which can adequately be described with a Freundlich-type isotherm, varies from 3.14 to 6.22 mg/g. The distribution coefficients increase progressively by decreasing the solutions concentration reaching a value of 1800 ml/g. The investigated zeolite interacts with Sr2+ cations through ion exchange reactions and initial exchangeable Ca2+ cations are replaced into the structural micropores. However, in the best case, only ca. 43% of the theoretical CEC can be covered because of the limited availability of the extra framework Ca2+ cations that can be removed from the lattice under ambient treatment conditions. The XPS investigation of Sr-loaded single crystals indicated that adsorption of Sr2+ cations on the outer surface also occurs while surface precipitation phenomena must be excluded. Similar surface analyses by means of12C-RBS showed that the Sr depth-distribution at near-surface layers is quite homogenous in contrast to a previous relevant study revealing an intense surface Sr-accumulation on a natural Ca-zeolite of different structural characteristics (scolecite).

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slightly compared with series BC i samples, which indicates that the removal of extra-framework aluminum produced by acid leaching enhances the crystallinity of ZSM-5 zeolite. Kumar [ 22 ] also obtained the similar results. Fig. 1

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it was formed of extra framework anatase TiO 2 in sample 8. It means that the formation of extra framework anatase TiO 2 has a great influence on the pore diameter. TiO 2 on the silica matrix drastically decreases the surface area of the samples

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solution with two different concentrations 0.1 and 1.0 mol dm −3 . It was found [ 26 ] that extra framework cations in zeolites have influence on the adsorption of organic compounds, affecting both the initial adsorption in the micropores as well as

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should be white, since the isolated Fe 3+ ions in octahedral coordination sites in LDHs do not give rise to any coloration, as reported in literature [ 24 ]. The coloration of Fe containing LDHs suggests the presence of extra framework iron and can be

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materials are employed instead of them [ 1 – 7 ]. The carbon monoxide is frequently used as a probe molecule for zeolite characterization due to its high sensitivity of adsorption interaction to nature of zeolite extra framework cations and their environment

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