Search results for "ZEOLITE"
showing 10 items of 203 documents
Mild Hydrocracking of Vacuum Gasoil over NiMo-Beta Zeolite Catalysts: The Role of the Location of the NiMo Phases and the Crystallite Size of the Zeo…
1998
Abstract Mild hydrocracking composite catalysts based on NiMo/γ-Al2O3-Beta zeolite have been prepared and the influence of the location of the NiMo phases has been studied. A good hydrocracking activity and the highest HDS conversion was found during the hydrocracking of a vacuum gasoil with the composite catalyst where the NiMo is located on the alumina component and then mixed with the zeolite in a proportion of 1 : 1 by weight. The crystal size of the beta zeolite had a significative influence on the catalytic behaviour, being better the smaller the crystallite size is. The small crystallite beta-based catalyst displayed a higher hydrocracking activity than conventional USY and silica-al…
Static and Dynamic Properties of the Nonframework Cations in Na-Mordenites Zeolite
2004
This work consists of exploring the effect of Si/Al ratio and water content on both the static and dynamic properties of the extra-framework cations in a typical zeolite system Na+-Mordenites. Atomistic simulations based on interatomic potentials and minimisation techniques have been used to determine the location of the cations as a function of the Si/Al ratio and the hydration level. Our calculations showed two different cation behaviours depending on the type of channels that they occupy, the positions of the cations in the main channels being substantially perturbed upon the sorption of water molecules whereas those of the cations located in the small side channels being only slightly s…
Synthesis of micro-mesoporous aluminosilicates on the basis of ZSM-5 zeolite using dual-functional templates at presence of micellar and molecular te…
2017
Abstract Micro-mesoporous aluminosilicates consisting of agglomerates of the ZSM-5 nanoparticles were obtained using dual-functional templates [C6H13–N+(CH3)2–C6H12–N+(CH3)2–C6H13](Br−)2 (C6–6–6Br2), [C8H17–N+(CH3)2–C6H12–N+(CH3)2–C8H17](Br−)2 (C8–6–8Br2). Aluminosilicates with randomly oriented flake-like particles built from ZSM-5 layers were obtained using [C16H33–N+(CH3)2–C6H12–N+(CH3)2–C6H13](Br−)2 (C16–6–6Br2). Use of С8–6–8Br2 and additive of cetyltrimethylammonium bromide CTAB (CTAB concentration is lower than the first critical micelle concentration, CMC1) leads to an increase of the total specific surface area, mesopore surface area and the mesopore size uniformity in the product,…
Influence of layer structure preservation on the catalytic properties of the pillared zeolite MCM-36
2010
MCM-36 is a catalytically active material made by swelling and subsequent pillaring of a layered zeolite precursor, MCM-22(P). However, the swelling procedures lead to significant destruction of layer structure and alteration of framework silicon/aluminum (Si/Al) ratio, which are likely to influence the acidity and catalytic activity of the final materials. We report a milder swelling and pillaring process to prevent such structural destruction. The resulting pillared materials show higher crystallinity and improved retention of the zeolitic layer structure when compared to the ones prepared by the previously reported methods involving more aggressive treatments. Implications of such struct…
Cu-exchanged Al-rich SSZ-13 zeolite from organotemplate-free synthesis as NH3-SCR catalyst: Effects of Na+ ions on the activity and hydrothermal stab…
2017
Abstract The relatively low activity at lower temperatures and high cost of SSZ-13 zeolite from organotemplate synthesis are two of major problems of presently commercialized Cu-SSZ-13 catalysts for NH3-SCR reaction. Cu-exchanged Al-rich SSZ-13 catalysts with Si/Al = 4 from organotemplate-free synthesis have been prepared, and show superior NH3-SCR performance with NO conversions above 85% at wide-temperature window ranging from 150 to 650 °C. Cu-Na-SSZ-13 catalysts with varied amount of residual Na+ were prepared by partial ion-exchange of as-prepared Al-rich Na-SSZ-13, and it’s found that Cu-Na-SSZ-13 catalyst with moderate Na+ content can improve both the low-temperature activity and its…
Isomerization of α-pinene oxide over ZSM-5 based micro-mesoporous materials
2018
Abstract Few types of ZSM-5 based micro-mesoporous materials obtained via a dual template method, steam-assisted conversion and dual-functional templating were evaluated in α-pinene oxide isomerization. Complete conversion and the highest selectivity towards trans-carveol (ca. 40–43%) were achieved over X-ray amorphous micro-mesoporous aluminosilicates as well as mesoporous molecular sieves AlSi-SBA-15. In addition, X-ray amorphous samples containing the secondary building units of ZSM-5 zeolite demonstrated the highest rate of α-pinene oxide isomerization. The yield of the most desired product trans-carveol to a large extent depends on the accessibility of acid sites to the reagents molecu…
Novel synthesis of spherical MCM-48
1999
Abstract A novel synthesis route was developed for the cubic member of the M41S family, MCM-48, with a three-dimensional pore system allowing the formation of submicrometre- to micrometre-sized beads with a narrow pore-size distribution. The synthesis is based on the modified Stober method applying tetraethoxysilane, ethanol, water, ammonia and n -hexadecyltrimethylammonium bromide as template. The specific surface area, the specific pore volume and the average pore diameter were varied in the following ranges: 900–1600 m 2 g −1 , 0.5–0.9 cm 3 g −1 and 2–3 nm. Aluminium-, chromium-, gallium-, niobium- and vanadium-MCM-48 were also synthesized following this procedure.
Confinement of Water in Hydrophobic Nanopores: Effect of the Geometry on the Energy of Intrusion
2013
International audience; Water confinement in the hydrophobic nanopores of highly siliceous zeolite having MFI and CHA topology is investigated by high pressure manometry coupled to differential calorimetry. Surprisingly, the intrusion of water is endothermic for MFI but exothermic for CHA. This phase transition depends on the geometry of the environment in which water is confined: channels (MFI) or cavities (CHA). The energy of intrusion is mainly governed by the change in the coordination of water molecules when they are forced to enter the nanopores and to adopt a weaker, hydrogen-bonded structure. At such a nanoscale, the properties of the molecules are governed strongly by geometrical r…
Identification of off-flavor compounds in high-density polyethylene (HDPE) with different amounts of abscents
1998
The use of synthetic pipes for drinking water distribution has increased. High desnity polyethylene (HPDE) is preferred because of its favorable mechanical properties, ease of handling during manufacturing, and low permeability to external contaminants. Off-flavor drinking water is a problem with plastic pipes. The compounds causing off-flavors are mainly carbonyl compounds. A combined zeolite called Abscents is used to eliminate odors and to remove odor-causing compounds. In this study, four different amounts of Abscents were added to raw HDPE pellets, and the influence on the off-flavor properties were analyzed. When the maximum amount of Abscents was added, almost all the carbonyl compou…
Studies of Reversible Hydrogen Binding in Nano- Sized Materials
2015
Experimental review of materials suitable for reversible hydrogen binding in nanoporous and nanosized structures of materials, based on natural zeolite (clinoptilolite) and graphene (exfoliated electrochemically from raw graphite), were analyzed. Characterization of materials with SEM, XRD, EDS and Raman spectroscopy methods and aspects of synthesis of a nanostructured zeolite and a few-layer graphite material was done in this work. It was established from gas analyzer results that hydrogen mass fraction in natural zeolite ranged from 1.1 % to 1.4 %, but in the few-layer graphite material − from 0.39 % to 0.46 %.