The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
The preferred location of platinum clusters in the {111}-twin planes (TP) of zeolite NaY (FAU) has been observed by high-resolution transmission electron microscopy (HRTEM). The platinum was incorporated in the zeolite by ion exchange followed by oxidation and reduction. Samples from each of the three different synthesis stages were examined by HRTEM. Ion exchange provides a homogeneous platinum...
By using an original synthesis procedure in which the OH - ions are replaced by the F - anions as the mineralizing agent, the preparation of a LEV-type zeolite was possible from near-neutral nonalkaline reaction mixtures containing 1-azabicyclo[2.2.2]octane (quinuclidine) and optionally methylamine. The LEV-type zeolite could be synthesized only with a very narrow range of SiAl molar...
The nickel-deposited USY (ultrastable Y) zeolite samples were simulated by a method of impregnation with nickel naphthenate benzene solution followed by drying and calcination. Characterization of the Ni-impregnated USY zeolites was carried out by f.m.r. The reducibility, distribution, and dispersion of nickel deposited on USY zeolites were investigated after calcination in air, hydrogen reduction,...
The activity, stability, and selectivity of a series of bifunctional Pt/SAPO-5 and Pt/SAPO-11 catalysts containing 0.5 wt% platinum, were compared for n-hexane transformation at 300-425°C and atmospheric, 3- and 5-bar hydrogen pressures. Hydrogen pressure had a strong influence on the activity, isohexane selectivity, and time-on-stream deactivation. Isomerization to isohexanes was the major reaction...
The hydrothermal crystallization of SAPO-5 in a biphasic water-hexanol system in the presence of surfactants has been studied. Large crystallite aggregates with a high organic content are obtained by using a high concentration of cationic surfactants in the synthesis. The Si content of crystals is much less affected. 29 Si MASn.m.r. also shows deep modifications of the mechanism of...
Monocationic Ca, Na, and K gmelinite crystals were obtained by cation exchange from three natural samples. Their crystal structures were refined from single crystal XRD data in the P6 3 /mmc space group down to R values <8%. The structures of the isocationic forms derived from the different natural samples agree within the experimental error, whereas marked differences were found in the...
A new and accurate method of predicting enthalpy of formation based on known crystal structures has been proposed by Vieillard (Geochim. Cosmochim. Acta, 1994, 58(19), 4049-4063). This method has been tested on 180 different minerals and has given an excellent precision (residual average lower than 0.3%) within the zeolite family (nine different compounds). Calculating the enthalpy of formation...
Titanium-containing silicoaluminophosphates with the AFI structure type (TAPSO-5) have been synthesized hydrothermally. Titanum could be incorporated into the SAPO-5 structure without formation of TiO 2 up to Ti = 0.05 in the precursor gel. Under the synthesis conditions, Ti 4+ ions were most likely isolated and tetrahedrally coordinated in the siliceous domains of the crystals,...
Synthesis in fluoride-containing medium leads to large silicalite crystals without SiOX defect groups. The four occluded tetrapropylammonium (TPA + ) ions/unit cell are ion pairs with 2 F - and 2 OH - . Grinding the samples in the presence of water leads to SiOH groups that are eliminated during calcination. The two endothermic peaks at 420 and 560°C of the TPA + ...
The adsorption isotherms of xylenes are described by Henry's law and Langmuir's model on NaY and KY and the Dubinin-Radushkevich model on BaY. The isoteric enthalpies of adsorption show on each zeolite that the adsorbate-adsorbent interactions are nearly the same with both isomers. They are stronger on BaY than on NaY and KY. The adsorbate-adsorbate interactions are stronger with m-xylene than with...
Iron was incorporated into H-[Al]-MFI by synthesis. The state of iron was characterized by e.s.r. and Mossbauer spectroscopies. Because of the location of iron species inside the channel system this zeolite showed a higher activity in the aromatization of ethane at 823 K than an iron-impregnated H-[Al]-MFI.
In this paper, the results of the first high-field (B 0 = 17.6 T) 27 Al MAS n.m.r. measurement on zeolite MCM-22 are reported. The 29 Si and 27 Al MAS n.m.r. spectra of as-synthesized and dealuminated zeolite MCM-22 were interpreted by signals of framework silicon and aluminum atoms located on at least five crystallographically nonequivalent T sites...
Potassium ferrate, as a primary source of iron, has been investigated in the hydrothermal synthesis of zeolite LTL. Crystalline material with Fe(III) incorporated into lattice sites was isolated from starting gels containing up to 0.825 mole fraction Fe 2 O 32 O 3 . The use of basic, tetrahedral iron species has extended previous maximum substitution levels. X-ray diffraction,...
The influence of tribochemical activation of seeds on the crystallization of zeolite Y was studied. Two conditions are discussed: pretreatment of the seeds alone and pretreating them simultaneously with the gel. It is shown that the later procedure is much more effective than the former. The results obtained indicate that the duration of the tribochemical treatment is the dominant parameter in...
The clathrasil dodecasil 3C (MTN) with the guest molecules pyrrolidine and t-butylamine was studied by powder diffraction as a function of temperature and time. The symmetry of the room-and low-temperature structures of MTN depends on the symmetry of the enclathrated guest molecule in the [5 12 6 4 ] cage. Whereas the common high-temperature form (above 180°C) is cubic (Fd3),...
The interaction of benzene with the framework of the Na + -exchanged form of Y-type zeolite is studied using a combination of ab initio molecular orbital calculations and molecular graphics. Using this combination a visual rationalization of the forces governing the adsorption process is developed. The observed adsorption sites, i.e., over the SII Na + and the center of the twelve...
The transformation of the solid obtained by calcination of sodium carbonate-kaolinite mixtures into LSX zeolite, in hydrothermal systems, was studied by using either pure Na or mixtures of Na and K, at a constant total cation concentration. The role of the alkali cations in the zeolite phases obtained, the size and the morphology of the crystals, as well as the influence of these cations on the processes...
A novel titanium-containing zeolite TS-12 with the MTW-type structure has been synthesized under hydrothermal conditions in the presence of hexamethylene bis(diethylmethylammonium) cation (Et 2 MeN + C 3 H 6 ) 2 as templating agent. Physicochemical characterization of the samples showed that Ti atoms were part of the framework, probably in a tetrahedral coordination...
Change of particulate and morphological properties of the samples obtained during the high-energy ball milling of zeolites A and X were studied by scanning-electron microscopy, X-ray diffraction, and determination of particle size distribution. It was found that decrease of crystallinity is followed by considerable change of particulate properties during the milling, but that the change of particulate...
The mechanism of milling ZSM-5 ferrisilicate analog in the centrifugal planetary mill was studied by means of adsorption, electron microscopy, and X-ray diffraction. The process of zeolite lattice destruction obeyed a first-order kinetic equation. The 40-min milling resulted in a practically complete amorphization of the material and disappearence of its catalytic activity in oxidation of benzene...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.