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451.
Thermal dehydration and decomposition characteristics of Fe(III) chloride hydrate have been studied by both isothermal and non-isothermal methods. After the initial melting at 35–40°C both dehydration and decomposition of the salt proceed simultaneously at temperature above 100°C. At 250–300°C a stable hydrated Fe(OH)2Cl is formed representing the first plateau region in the TG curve. Around 400°C, a second plateau is observed corresponding to the formation of mostly Fe2O3 which however retains some OH groups and Cl– ions. However, these temperature ranges vary with the TA equipments used. Chemical analysis of the products of decomposition at temperatures above 140°C also gives evidence for the formation of FeOCl which on hydrolysis in water gives FeCl3 in solution. The FT-IR spectra suggest the presence of structural OH groups even for samples calcined at 300–400°C. The XRD patterns of the products of decomposition in the temperature range 160–400°C indicate the presence of -FeOOH, some unidentified basic chlorides and -Fe2O3.The authors wish to thank the Director, R. R. L. Bhubaneswar for his kind permission to publish this paper. One of the authors (SKM) is grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi for the award of a fellowship. 相似文献
452.
含亚砜基功能高分子可用作高分子药物载体,高分子螯合剂,高分子催化剂及气体分离膜材料等,近年来已引起各国学者的兴 相似文献
453.
Igor?P.?Stolarov Zhanna?V.?Dobrokhotova Galina?N.?Kryukova Alexander?E.?Gekhman Michael?N.?VargaftikEmail author 《Journal of Cluster Science》2005,16(3):367-378
α−Alkyl- and α,α′-dialkyl-substituted benzylic alcohols PhCR′R′′OH (R′=H, Me, Et, Bu; R′′=H, Me) are transformed to the corresponding
dilbenzylic ethers and water in acid-free neat substrate media shortly after the addition of the palladium(I) cluster [Pd4(CO)4(OAc)4] (1). During the catalytic reaction occurring under anaerobic conditions, cluster 1 is gradually decomposed to form Pd black, whereas neither original cluster 1 nor Pd black is responsible for the observed reaction. The true reaction catalyst is generated from cluster 1 after a short induction period. On the basis of the reaction kinetics and the HREM, X-ray diffraction, DTA-TG, and elemental
analysis data, the catalytic dehydration is suggested to occur through a nonradical chain mechanism involving an unstable
intermediate Pd cluster as the chain carrier.
相似文献
Michael N. VargaftikEmail: |
454.
Some of the mechanistic studies on dehydrogenation, dehydration and decarboxylation over metal oxide catalysts are reviewed.
The type of activity of a catalyst is determined by the nature of the surface-substrate interaction, the same catalyst giving
rise to different relative activities depending on the substrate. In addition to dehydrogenation and dehydration reactions
many oxide catalysts promote hydrogen transfer reactions too. In the mixed oxide systems the interfaces between the pure oxides
as well as interfaces arising from new phases formed by the interaction of component oxides are active regions. In the ketonization
of acids the same active sites as those effective for the decomposition of alcohols are involved. The type of the intermediate
depends on the conditions of reaction, the most important being the temperature. The technique of competitive reactions has
been used to establish that the catalytic ketonization is a bimolecular process on the surface of the catalyst. 相似文献
455.
Tatiana S. Glazneva Vera P. Shmachkova Ludmila G. Simonova Evgeny A. Paukshtis 《Reaction Kinetics and Catalysis Letters》2007,92(2):303-309
Acidic properties of fiberglass materials were investigated using the adsorption of NH3 and the rate of isopropanol dehydration. It is shown that the specific catalytic activity of such materials and amount of
the Br?nsted acid sites per their surface unit (100 ?2) exceed considerably those in zeolite HZSM-5. 相似文献
456.
William H. Ojala Rajendra K. Khankari David J. W. Grant William B. Gleason 《Journal of chemical crystallography》1996,26(3):167-178
The crystal structure of one of the hydrated forms of nedocromil zinc, the heptahydrate, and that of one of the hydrated forms of nedocromil magnesium, the pentahydrate, have been determined. Crystal data: zinc salt,a=11.769(3),b=7.000(2),c=14.022(4); Å; =105.35(2)°; monoclinic, space groupP21,Z=2;magnesium salt,a=7.460(1),b=10.233(2),c=13.934(2) Å, =86.54(1)°, =79.74(1)°, =77.25(1)°; triclinic, space groupP,Z=2. The major differences between the crystal structures are the environment and bonding of the cations. The zinc cation is linked directly to the carbonyl oxygen of the pyridone ring and to five water molecules in an octahedral coordination. The magnesium cation is linked directly to two different carboxyl oxygens, one in asyn orientation and the other in ananti orientation in different asymmetric units and to four water molecules in an octahedral coordination. Thermal analytical methods show that the zinc salt hydrate undergoes thermal dehydration at lower temperatures than the magnesium salt hydrate. This behavior may be related to the presence of continuous water channels in the zinc salt hydrate and to their absence in the magnesium salt hydrate. For each salt hydrate 1 mole of water is lost at a higher temperature than the other waters. 相似文献
457.
Frost R. L. Martens W. Ding Z. Kloprogge J. T. 《Journal of Thermal Analysis and Calorimetry》2003,71(2):429-438
A combination of DSC and high resolution DTG coupled to a gas evolution mass spectrometer has been used to study the thermal
properties of a series of Mg/Zn hydrotalcites of formulae MgxZn6-xAl2(OH)16(CO3) ·4H2O where x varied from 6 to 0. The effect of increased Zn composition results in the decrease of the endotherms and mass loss steps
to lower temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps. The interlayer carbonate
anion is lost simultaneously with hydroxyl units.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
458.
M. E. Manríquez T. Lpez R. Gmez J. Navarrete 《Journal of molecular catalysis. A, Chemical》2004,220(2):229-237
Titania–zirconia mixed oxides with various ZrO2 content in TiO2 (10, 50 and 90 wt.%) were prepared by the sol–gel method. High specific surface areas (77–244 m2/g) were obtained. Acidity determined by NH3-TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 μmol NH3/g for TiO2 to 1226–1456 μmol NH3/g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO2 adsorption, suggesting the formation of mixed oxides with acid–basic properties. XRD spectra identified anatase in the TiO2 rich region, amorphous material in the mixed oxide 50–50 TiO2–ZrO2 and tetragonal and monoclinic crystalline phases in the ZrO2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid–basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density. 相似文献
459.
Guangming Liu Dan Wu Chengcheng Ma Guangzhao Zhang Hongfei Wang Shihe Yang 《Chemphyschem》2007,8(15):2254-2259
We investigate the effects of pH and temperature on the conformational changes of poly[2-(dimethylamino)ethyl methacrylate] (PDEM) chains at the air/water interface by using Langmuir balance and sum frequency generation vibrational spectroscopy. At pH 4, the tertiary amine groups are fully charged and the PDEM chains are so hydrophilic that they completely enter into the water phase and do not exhibit thermosensitivity. At pH 7, these groups are only partially charged, and the accompanying hydration/dehydration--followed by repartitioning into the water and air phases--gives rise to a marked thermosensitivty. Finally, at pH 10, the tertiary amine groups become uncharged and thus preferentially stay in the hydrophobic air phase, devoid of associated water molecules, which results in the surface-pressure change (DeltaPi) being nearly independent of the temperature. Our Langmuir-balance experiments, coupled with surface-sensitive spectroscopy, demonstrate that: 1) the thermosensitivity of the PDEM chains relates to the hydration/dehydration of the tertiary amine groups, 2) the phase transition of thermosensitive polymers is most likely initiated by the dehydration of the chains, and 3) the phase transition of thermosensitive polymers at the air/water interface is markedly different from that in aqueous solution because of the redistribution of the macromolecular segments induced by the asymmetric forces at the air/water interface. 相似文献
460.
Dense membranes made by crosslinking of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) were prepared and tested in pervaporation and differential permeation of water–alcohol mixtures. Instead of a decrease of permeation flux as generally observed with most crosslinking agents, an increase in the permeability was observed with PAA crosslinked membranes at low PAA contents. The permeation flux increases with PAA contents in the polymer with no selectivity reduction for membranes containing less than 15 wt. % PAA. The membranes show good performances to water–2-propanol and water–ethanol mixtures, i.e. high fluxes and high selectivities to pure water. The membranes were stable and highly permeable to water. The enhancement of the permeability of PVA can be explained by a reduced crystallinity and an improved diffusivity due to the presence of PAA. 相似文献