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Publications (34)
Outsourcing is often viewed by Information Professionals as a threat, and by some managers as a way to get rid of this expensive search service.
We will discuss outsourcing issues based on requirements and experiences, with viewpoints of user and of outsourcing company. We will show how information professionals’ experience and skills are key param...
Over the last few years, the French Patent Information User Group (CFIB) has re-organized itself and considerably developed its activities. This article is an overview of the association's current activities.
A method for the copolymerization of ethylene and a C3+ olefin copolymer in a loop reactor system and polymers formed therefrom are described herein. The method generally includes introducing an ethylene monomer, a C3+ alpha olefin comonomer and a diluent carrier liquid into a reactor system comprising at least one loop reactor; supplying at least...
Abstract A Phillips Cr/SiO2 polymerisation catalyst was converted into an ethylene trimerisation catalyst after assembling new active sites on the silica surface in the presence of TAC (1,3,5-triphenylhexahydro 1,3,5-triazacyclohexane) as ligand and CH2Cl2 as solvent. The reaction conditions play a role in tuning the catalytic activity of this syst...
The present invention relates to a heterogeneous chromium catalyst system for the polymerisation of ethylene and/or alpha olefins prepared by the steps of: (a) providing a silica-containing support, (b) treating the silica-containing support with a chromium compound to form a chromium-based silica-containing support, (c) activating the chromium-bas...
Chromium acetyl acetonate [Cr(acac)3] complexes have been grafted onto the surface of two mesoporous crystalline materials; pure silica MCM-41 (SiMCM-41) and Al-containing silica MCM-41 with an Si:Al ratio of 27 (AlMCM-41). The materials were characterized with X-ray diffraction, N2 adsorption, thermogravimetrical analysis, diffuse reflectance spec...
Chromium acetyl acetonate [Cr(acac)3] complexes have been grafted onto the surface of two mesoporous crystalline materials; pure silica MCM-41 (SiMCM-41) and Al-containing silica MCM-41 with an Si:Al ratio of 27 (AlMCM-41). The materials were characterized with X-ray diffraction, N2 adsorption, thermogravimetrical analysis, diffuse reflectance spec...
In addition to an examination of the crystallization kinetics of the title zeolites, the intermediate gel and crystalline phases progressively formed during the synthesis are characterized by using XRD, thermal analysis, bulk and surface chemical analyses, SEM, and multi-nuclear NMR (7Li, 13C, 23Na, 27Al, 29Si).
The crystallization kinetics, the composition of the various phases and the physical state of the different components are examined during the crystallization of ZSM-5 zeolite via the combined physico-chemical techniques of PIGE, EDX, atomic absorption, X.p.s., thermal analysis (TG-DTA), 29Si, 27Al, 13C, 7Li and 23Na n.m.r. A nucleation process on...
Zeolite ZSM-48 prepared from a hydrogel containing an alkylamine admixed with TMA+ ions incorporates these organic species, so that the total filling of the porous volume is achieved. However, when zeolite ZSM-39 crystallizes from a similar hydrogel (also containing TMA+ ions, and with or without alkylamine and aluminium ions), part of the TMA+ ion...
Combining PIGE, EDX, AA, and thermal analyses with solid-state 29Si-n.m.r spectroscopy allowed us to determine the amounts of SiOR and (SiOAI)-R+ groups (R {double bond, long} H, M, TPA). The amount of SiOR increases with decreasing aluminium content. At the external surface of the crystallites, an Al-rich phase is deposited, which is revealed to b...
Crystallographically non-equivalent tetrahedral sites were resolved and Si-Al orderings were determined in the framework of various natural and synthetic zeolites belonging to the chabazite group by high resolution magic-angle-spinning solid state 29Si-NMR. In sodalite, each Si atom is surrounded by four Al. In chabazite and gmelinite, Al atoms are...
Zeolite ZSM-39 has been synthesized from an aqueous aluminosilicate gel and the product as well as intermediate phases have been characterized by X-ray diffraction, SEM, EDX, thermal analysis, and multinuclear solid and liquid state NMR techniques (29Si, 27Al, 23Na, 11B, 13C).
The stability of TPA species interacting with various (Al,Si) hydrogel environments in the presence of alkali cations has been evaluated by thermal analysis (combined t.g.-d.t.a.-d.t.g.). Three different TPA—gel associations have been characterized by d.t.a. endotherms : crystalline (TPAX)n clusters (X = OH−,Br−) which are also detected by XRD, mon...
The influence of alkali and tetrapropylammonium (TPA+) cations on the organization of hydrogel precursors to ZSM-5 zeolite is examined by multinuclear high power solid state nuclear magnetic resonance techniques. Emphasis is put on the different states of the TPA+ ions and on the interaction between the alkali cations (M+) and the negative charges...
The dealumination of mordenite, Na8Al8Si40O96 · n H2O, by acidification (HCl, HNO3) and by SiCl4 and steaming treatments has been investigated by high-resolution solid state 29Si and 27Al MAS NMR.
The dealumination of mordenite by acidification (HCl, HNOâ) and by SiClâ and steaming treatments is followed by high-resolution magic-angle-spinning solid-state ²â¹Si and ²â·Al NMR spectroscopy. The combined use of these techniques leads to the determination of the silicon-aluminum ordering. It is demonstrated that aluminum atoms preferentially...
On presente une etude systematique de la synthese des zeolithes Y, mordenite et ZSM-5. Les processus de cristallisation peuvent etre expliques par la transformation directe de l'hydrogel (nucleation de surface) (ZSM-5 type B), par transport d'ions en phase aqueuse (mordenite, ZMS-5 type A), ou par la combinaison de ces deux mecanismes (zeolithe Y)....
Various aluminosilicate hydrogels having the composition 106 SiO//2 multiplied by (times) 26 Na//2O, Al//2O//3 multiplied by (times) 17. 3 H//2SO//4 multiplied by (times) 47 NaCl multiplied by (times) 2400 H//2O multiplied by (times) 9 R, where R is a mono- di- or trialkylamine, a diaminoalkane or a tetraalkylammonium (Alk//4N** plus ) cation, have...
Aqueous aluminosilicate hydrogels having the composition 20 Na//2O. Al//2O//3. 20 SiO//2. 700 H//2O, heated at 100 degree C in polypropylene autoclaves, usually yield pure zeolite Y. The influence of various alkali and ammonium cations, added in varying amounts as chlorides to this initial hydrogel, was systematically examined. Increasing amounts o...
The effect of acidity and channel sizes of K- and Cs-exchanged ZSM-5 and mordenite on the reactivity of isopropanol is thoroughly investigated by **1**3C-NMR in the adsorbed phase. The catalysts are characterized by X-ray diffraction technique, and by magic-angle-spinning high resolution solid state **2**9Si-, **2**7Al- and **1**3C-NMR, as well as...
Mordenite was obtained in high yield from an aqueous hydrogel of composition 2.4 Na2O . A12O3 . 11 SiO2 . 219 H20, left to crystallize in static Pyrex auto-claves at 165°C for 3 days. The progressive variation of pH and density of the liquid phase with synthesis time suggest that mordenite crystallites are grown at the expense of the solid hydrogel...
Mordenite is synthesized from different aluminosilicate gels in sealed pyrex tubes at 165 degree C. Its crystallization domain is established for these conditions and the coexisting phases are identified. Differences with published data are explained assuming partial dissolution of the silica-rich pyrex glass. Morphologies and composition of the mo...
ZSM-5 was crystallized at 165 degree C in Teflon autoclaves from synthesis mixtures having the molar composition 60 SiO//2 - 1. 2 Al//2O//3 - 700 H//2O and containing variable amounts of TPABr, TPAOH and MOH (M equals Li, Na, K, Rb, Cs). The nature and the composition of the intermediate solid and liquid phases, as determined by combining a variety...
High resolution solid state MAS 11B-NMR was used to detect quantitatively variously coordinated BOx structural units in zeolites. Boron stemming from Pyrex autoclaves is progressively incorporated into the tetrahedral sites of ZSM-5 and mordenite frameworks during synthesis. The final crystalline zeolite phases may contain up to 0.8 B atoms in thei...
Solid intermediate phases obtained from amorphous aluminosilicate gels during mordenite crystallization have been characterized by multinuclear solid-state NMR spectroscopy. The progressive reorganization of the amorphous gel into the crystalline ordered zeolitic phase has been detected by high resolution magic-angle-spinning (HRMAS) solid state 29...
The structure of various natural and synthetic zeolites was investigated by high resolution magic-angle-spinning (HRMAS) solid state 29Si-NMR spectroscopy. The NMR analysis is based on the great sensitivity of the 29Si-chemical shifts either on the chemical environment (i.e. the number of aluminium atoms in the second coordination shell of silicon)...
High-resolution magic-angle-spinning (HRMAS) solid-state 29Si NMR has been applied to characterize the structure of various natural and synthetic zeolites belonging to different families, i.e. the pentasil group (ZSM-5, ZSM-11, ZSM-8, ZSM-48), the mordenite group (mordenite, ferrierite, ZSM-35), the chabazite group (erionite, offretite, zeolite T,...
A series of chemically dealuminated mordenites were investigated by 29Si and 27Al NMR spectroscopy. High-resolution magic-angle-spinning (HRMAS) solid state 29Si NMR lines with varying intensity were observed at δ=−95, −105 and −110 ppm. When it is assumed that the Al atoms are located exclusively in the 4-membered rings of the structure, these var...
