Search results for "ZEOLITE"
showing 10 items of 203 documents
Chromatographic Air Analyzer Microsystem for the Selective and Sensitive Detection of Explosive-related Compounds
2014
Abstract The detection of explosives and explosive-related compounds is of major importance for the monitoring of explosive- contaminated sites. Current methods need to become cheaper and portable while maintaining a high sensitivity and selectivity level. In that sense, a silicon micro-analytical platform consisting of a three-dimensional micro-preconcentrator based on a hydrophobic zeolite, coupled to a silicon spiral micro-column was built. A chemical gas sensor acted as a miniaturized gas detector. This system allowed selective detection of orthonitrotoluene (ONT), an explosive-related compound at the sub-ppm level in the presence of toluene and moisture.
Stabilization of ZSM-5 zeolite catalysts for steam catalytic cracking of naphtha for production of propene and ethene
2012
In order to increase ethene and propene, naphtha steam catalytic cracking has been considered. The cracking of C 5-C 12 n-alkanes with ZSM-5 has been studied in absence and in presence of steam and the influence of the operation variables was studied. Irreversible catalyst deactivation by dealumination also occurs in the reactor when the cracking is carried out in the presence of steam. To diminish steam deactivation, the influence of zeolite Si/Al framework and a postsynthesis treatment by phosphorous have been studied and optimized. Much more stable catalyst can be achieved that result in an increase in activity without penalty for production of ethene and propene.
TCE adsorption on hydrophobic Y and MFI zeolites. Possibilities of using such materials for solvent recovery
1996
Des isothermes d'adsorption de la vapeur d'eau et du tetrachloroethene (TCE) ont ete tracees a 25°C pour etudier le caractere hydrophobe et organophile et la porosite de faujasites Y et d'une zeolithe ZSM-5 desaluminees. Les quantites de solvant adsorbe en phase vapeur pure ou en atmosphere ambiante sont peu differentes du fait du caractere hydrophobe des echantillons. Ces derniers presentent une grande capacite d'adsorption vis-a-vis du TCE. Contrairement au charbon actif, une zeolithe Y desaluminee saturee avec du TCE peut etre totalement regeneree a basse temperature (T<100°C) et de ce fait son utilisation potentielle pour une recuperation propre des solvants est digne d'interet.
ChemInform Abstract: Catalytic Activity of Large-Pore High Si/Al Zeolites: Cracking of Heptane on H-Beta and Dealuminated HY Zeolites
1988
Abstract The catalytic activity, selectivity, catalyst decay, thermal and hydrothermal stability, and acidity of H-Beta and HY zeolites with Si Al ratios of 7.5 and 10, respectively, have been studied during cracking of n-heptane at 450 °C and atmospheric pressure. It has been found that the H-Beta zeolite is more active and decays more slowly than HY. H-Beta presents a higher steric hindrance for dibranched molecules and therefore its open structure should be smaller than that of HY. A lower hydrogen transfer activity and hydrothermal stability is observed for H-Beta in comparison with the corresponding HY.
Azoxybenzene rearrangement catalyzed by solid acids
2008
Abstract For the first time, the potential of acidic cation-exchange resin (sulfonated polystyrene) to catalyze the Wallach rearrangement of azoxybenzene into 4-hydroxyazobenzene has been proved. This finding reveals an alternative reaction path possible in a heterogeneous process using solid acids and may help to clear some doubts concerning the rearrangement mechanism postulated so far. The resin-induced reaction was found to proceed exclusively in a non-polar medium. Reasonable yield was obtained particularly in isooctane due to favorable distribution of azoxybenzene throughout the resin's matrix. On the contrary, the HY type zeolite did not activate the rearrangement, most probably beca…
Influence of preparation conditions on the catalytic performance of mo/h-zsm-5 for methane dehydroaromatization
2021
[EN] Methane, the main component of natural gas, is an interesting source of chemicals and clean liquid fuels, and a promising alternative raw material to oil. Among the possible direct routes for methane conversion, its aromatization under non-oxidative conditions has received increasing attention, despite the low conversions obtained due to thermodynamic limitations, because of its high selectivity to benzene. Mo/H-ZSM-5, the first bifunctional zeolite-catalyst proposed for this reaction, is still considered as one of the most adequate and has been widely studied. Although the mono- or bifunctional nature of the MDA mechanism is still under debate, it is generally accepted that the Mo spe…
Cu-Exchanged CHA-Type Zeolite from Organic Template-Free Synthesis: An Effective Catalyst for NH3-SCR
2020
A Cu-containing CHA-type zeolite was prepared via aqueous ion exchange of the CHA zeolite from organic template-free synthesis. The thus-obtained template-free Cu-CHA showed the best catalytic perf...
Ship-in-a-Bottle Synthesis of a Large Guest Occupying Two Y Zeolite Neighbour Supercages: Characterisation and Photocatalytic Activity of the Encapsu…
2003
In a series of papers we reported the ship-in-a-bottle synthesis, photochemical properties and photocatalytic applications of 2,4,6-triphenylpyrylium cation (TP ) encapsulated inside the cavities of large pore zeolites Y and Beta. 2] The identity of encapsulated TP was then confirmed spectroscopically, particularly by the match of the IR spectra of the encapsulated organic material and that of the tetrafluoroborate solid of TP (TPBF4). In addition, the electrochemical response of zeolite Y encapsulated TP (TP@Y) consisted of a reversible single reduction process taking place at the same redox potential as that measured for TPBF4 solutions. Encapsulation of TP has a dramatic influence on its…
Adsorption of m-Xylene on Prehydrated Zeolite BaX: Correlation between Temperature-Programmed Desorption and Low-Temperature Neutron Powder Diffract…
1999
Adsorption of m-xylene on partially hydrated zeolite BaX is studied by thermogravimetry, mass spectrometry, temperature-programmed desorption and neutron diffraction for different m-xylene loadings of the zeolite. Macroscopic and microscopic measurements, for both molecules, were correlated and relationships were found between the crystallographic positions of the adsorbed molecules on the zeolite and macroscopic properties such as the number and the area of the peaks in the desorption spectra for m-xylene or water. The influence of water molecules on the adsorption phenomenon of m-xylene on BaX zeolite was characterized. In particular, it was shown that the increase of the filling of the p…
Hydrogen Adsorption in Zeolite Studied with Sievert and Thermogravimetric Methods
2012
Natural clinoptilolite (mixture from clinoptilolite, quartz and muscovite) is activated with palladium and tested for hydrogen adsorption capability at temperatures RT - 200 o C. Thermogravimetric and volumetric methods showed that zeolite activated with palladium (1.25%wt) shows markedly high hydrogen adsorption capacity - up to 3 wt%. Lower amount of adsorbed hydrogen (~1.5 wt%) was found for raw zeolite and activated with higher amount of palladium sample. Hypothesis is proposed that the heating of zeolite in argon atmosphere forms and activates the pore structure in zeolite material, where hydrogen encapsulation (trapping) is believed to occur when cooling down to room temperature. An e…