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decrease cracking [ 14 ], but also the global activity since the acidic step is rate-limiting. Zhang and Smirniotis [ 15 ] observed in beta zeolites an increase in the selectivity of branched octanes with the Si/Al ratio; the opposite effect being observed

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The thermal analysis of crystalline zeolite ZSM-5 precurcors with different Si/Al ratios was carried out in a nitrogen atmosphere. Different interactions between tetrapropylammonium species and the zeolitic environment were evidenced, depending on the Al content of the crystalline precursors. The results support the mechanism of ZSM-5 formation through a condensation process from the liquid phase.

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volume (>0.7 cm 3 g −1 ) and large surface area (>1,000 m 2 g −1 ) [ 4 – 7 ]. In this work, the catalytic properties in n -C7 conversion in the presence of hydrogen of Pt/Al-HMS catalysts with different Si/Al ratios have been evaluated in order to

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Abstract  

In this work was studied the acid properties of a series of HZSM-12 zeolites with different Si/Al molar ratio. The samples of ZSM-12 were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na2O:xAl2O3:100SiO2:200H2O, where: x=2, 1, 0.67 and 0.50, respectively. After the synthesis, the samples of ZSM-12 were ion-exchanged NH4Cl solution to obtain zeolite in the acid form (HZSM-12). The acid properties were evaluated by n-butylamine thermodesorption in a TG equipment at three different heating rates. The model-free kinetic model was applied in the TG integral curves to estimate the apparent activation energy (E a) of the n-butylamine desorption process. The results obtained showed that the HZSM-12 zeolite presents two kinds main of acid sites: one with E a in the range of 115-125 kJ mol-1 classified as weak and other kind with E a varying of 230-250 kJ mol-1 classified as strong.

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The elemental composition of various synthetic crystalline sodium-boroaluminosilicates, especially the Al content and the silicon to aluminium bulk ratio, were determined by means of the combination of PIGE (Proton-Induced Gamma-Ray Emission Spectrometry) and PIXE (Proton-Induced X-Ray Emission Spectrometry). Light elements (B, O, Na, Al) were determined by means of gamma-ray emission. Proton-induced X-ray emission provided information on heavy elements present down to impurities. The Si/Al ratios, which mainly determine the catalytic and adsorptive properties of the zeolites, are compared with those obtained with other methods (EPMA, H2O sorption capacity) and show good agreement.

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Abstract  

Alkylation of benzene with 1-alkenes (C6–C18) was performed in liquid phase at 160–200 °C over beta zeolites with Si/A molar ratio 12.5–75.0. With increasing alkyl chain length, the conversion of 1-alkene decreased. The alkylation activity decreased with increasing Si/Al ratio of beta-zeolite. The increase of Si/Al molar ratio was connected with the enhancement of the portion of Lewis acid sites in total acidity of beta zeolites, resulting in greater dimerization/oligomerization activity and consequently in more rapid deactivation of beta-zeolites.

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Abstract  

Et(Ind)2ZrCl2 and MAO co-catalyst, which polymerize ethylene and propylene, were heterogenized on partially dehydroxylated Davison silica 955, following the method of equilibrium adsorption. The dispersion of these catalyst components on the silica support was investigated by measuring the spatial concentration profiles of Si, Al, and Zr using a micro-PIXE technique. These components were found to be uniformly distributed over the support irrespective of the variation in the heterogenization procedures and the experimental conditions used. The Si∶Al ratios determined by the micro-PIXE technique were similar to those measured by the spectrophotometric method. However, the Al∶Zr ratios measured by the former were somewhat lower than those determined by the latter. Micro-PIXE measurements confirmed the presence of several trace impurities such as K, Ca, Ti, Fe, Ni, Cu, and Zn which may potentially poison the resulting catalyst.

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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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