Search results for "ZSM-5"
showing 7 items of 37 documents
Effect of Size of Solvent Molecule on the Adsorption of p- and o-Xylene on ZSM-5 Type Zeolites and Mechanism of Adsorption
1994
Summary The adsorption isotherms of p- and o-xylene have been studied on MFI-type zeolites of different alumina to silica ratios from solvents of different molecular sizes. The adsorption is mainly controlled by the shape and size of the pore opening relative to the size and shape of the sorbate and the solvent molecules. Aluminum containing zeolites formed colored π-complexes with p-xylene.
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.
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…
Is the formation of a zeolite from a dry powder via a gas phase transport process possible?
1994
Abstract ZSM-5 was synthesized by four methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in the form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO2·A2O3 gels at 650°C were transformed into zeolites in the presence of dried NH4F and TPABr. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure under the given reaction conditions. To explain the formation of a zeolite, we suggest a vapor phase mass transfer process with SiF4 as the mobile species between the solid phase, which contains the amorphous Si/Al pre…
Thermodynamics and Kinetics of Adsorption of Gaseous Single Cl/Br-VOCs of the Ethane Series onto Siliceous ZSM-5 at 25 °C. Prediction of the Adsorpti…
2001
This work deals with a thermodynamic and kinetic experimental study of adsorption of gaseous single Cl/Br-VOCs (1,2-dichloroethane, 1-bromo-2-chloroethane, and 1,2-dibromoethane) onto siliceous ZSM-5 at 25 °C. The adsorbed amounts, adsorption heats, and diffusivities were simultaneously obtained. The isotherms were of the type I and verified Henry's law in a very large domain of filling. The adsorption heats and the diffusivities of the brominated molecules displayed specific behaviors probably owing to a transport resistance. The comparison of the relative position of isotherms and the adsorption heats allowed us to predict that the competitive adsorption of their mixture would be similar …
Controlling the spatial distribution of aluminum in ZSM-5 crystals
1993
Abstract The spatial distribution of aluminum over ZSM-5 crystals was systematically studied using electron microprobing on polished crystals. Crystals synthesized with TPABr as template exhibit a pronounced enrichment of aluminum in the crystal rim, essentially irrespective of the aluminum source employed, although aluminum sources with organic anions are favoring less inhomogeneous profiles. With 1,6-hexanediol or from totally inorganic reaction gels, crystals with completely homogeneous aluminum profiles are obtained, even if the crystals grow larger than 50 μm. In the 1,6-hexanediol system the homogeneous profiles could be changed to profiles similar to the TPABr system by addition of K…
Butene Isomerization and Double-Bond Migration on the H-ZSM-5 Outer Surface: A Density Functional Theory Study
2011
Isomerization of trans-but-2-ene to cis-but-2-ene and double bond migration of trans-but-2-ene to but-1-ene have been investigated by means of density functional theory calculations on a suitable model of H-ZSM-5 surface. The study has been afforded on outer surface sites by considering the hydroxyl group of either a SiO2(OH)2 or a AlO2H(OH)2 moiety. On these outer surface sites, one alkoxide species occurs as a stable intermediate both along the isomerization and double bond migration pathways. The latter process could also occur via a single-step mechanism, which involves a six-center transition state. The energy barriers of the outer surface processes above do not take any advantage by t…