- Direct synthesis of dimethyl carbonate from carbon dioxide and methanol using supported copper (Ni, V, O) catalyst with photo-assistance
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The photo-catalytic effect of a copper modified (Ni, V, O) semiconductor complex catalyst on the direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3OH was investigated. The synthesized catalysts were fully characterized by temperature programmed reduction (TPR), X-ray diffraction (XRD), Ultraviolet visible drift reflection spectra (UV-vis DRS) and transmission electron microscopy (TEM). The nano-scale catalyst particles were observed with TEM and light absorbance was then predicted by UV-vis DRS spectra. The pressure and temperature dependencies of the photo-catalytic activity were studied. The results demonstrated that the catalytic activity was enhanced with the assistance of ultraviolet (UV) irradiation compared with the pure thermal and surface catalytic reaction under the same reaction conditions.
- Wang,Xiao,Wang,Lu,Meng
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- Lipophilic chloro-oxo-bis(hydroxamato)vanadium(V) complexes: synthesis methods and structure
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New methods for the synthesis of vanadium(V) complexes with hydrophobic alkyl- and aryl-substituted hydroxamic acids as well as hydrophilic ones have been developed. A number of novel coordination compounds of the general formula VOL2Cl (where HL is N-phenylaceto-, N-methylbenzo-, N-methyldecano- or N-methylacetohydroxamic acid) have been synthesized. Complexes of the above formula with alkyl substituents on the ligands have been obtained for the first time. All the compounds obtained have been characterized by UV–Vis, IR, 1H and 51V NMR spectroscopy. Studies using the 51V NMR method showed the presence of two forms of the complexes in solution, which coalesce with increasing temperature. Chloro-oxo-bis(N-methylacetohydroxamato)vanadium(V) has been characterized by X-ray crystallography. The effect of the electron donating properties of the ligand substituents on the structure of the complexes is discussed.
- Dzyuba, Valeriy I.,Koval, Lyudmila I.,Shtokvysh, Olherd O.,Trachevskii, Volodymyr V.,Pekhnyo, Vasyl I.
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- Decomposition of dichlorodifluoromethane with simultaneous halogen fixation by vanadium oxide supported on magnesium oxide
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Dichlorodifluoromethane (CCl2F2, 1% in He) decomposition with simultaneous halogen fixation by vanadium oxide supported on magnesium oxide was studied at 723 K in a flow apparatus. The pretreatment condition and vanadium loading of supported vanadium oxide samples affected the CCl2F2 decomposition efficiency. Through characterization studies (XRD, IR, Raman, and XPS) and reference experiments, Mg 3(VO4)2 was revealed to be the active species to initiate CCl2F2 decomposition, leading to MgF 2, MgCl2, and CO2 formation. The model experiments also suggested a detailed mechanism that VOCl3 was formed from Mg3(VO4)2 by a reaction with CCl 2F2 or the major intermediate compound CCl4, and that VOCl3 reacted with MgO to regenerate Mg3(VO 4)2 and to promote chlorine fixation as MgCl2.
- Tamai, Tsukasa,Inazu, Koji,Aika, Ken-Ichi
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p. 1565 - 1574
(2007/10/03)
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- Electrochemical and spectroscopic studies of the chloro and oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl3 melts
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The equilibrium constant for the chloro complex formation of Nb(V) NbCl6-?NbCl5+Cl- (i) in NaCl-AlCl3 melts at 175°C was found to be pKi = 2.86(5). The oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl 3 melts at 175°C could be explained by the following equilibria: MOCl4-?MOCl3+Cl- (ii) MOCl 3?MOCl2++Cl- (iii) where M = Nb and Ta. The equilibrium constants determined by potentiometric measurements with chlorine-chloride electrodes were, for M = Nb, pKii, = 2.21(4) and pKiii = 3.95(5) and, for M = Ta, pKii = 2.743(15) and pKiii = 4.521(13). NbCl6- has two bands in the UV-vis region, a strong one at 34.7 × 103 cm-1 and a weaker one at 41.6 × 103 cm-1. The MOCl 4- complexes showed in the case of Nb(V) absorption bands at 32.7 and 42.9 × 103 cm-1 and in the case of Ta(V) at 38.6 and 48.1 × 103 cm-1.
- Von Barner,Bjerrum
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p. 9847 - 9851
(2008/10/09)
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- Decomposition of CCl3F over vanadium oxides and [MgV xOy]MgO shell/core-like particles
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Decomposition of gaseous CCl3F over in-house-prepared V 2O3 (HP-V2O3), commercial V 2O3, VO2, V2O5, a mechanical mixture of the HP-V2O3/Aerogel-prepared MgO (AP-MgO), and [MgVxOy]MgO shell/core-like particles at 280°C has been investigated with FTIR spectroscopy. The reaction of CCl 3F with the HP-V2O3 proceeds vigorously. Intermediate compounds including CCl4, CCl2F2, CCl2O, and final gaseous products CClF3, CO2 were detected. No chloride/fluoride was found on the sample surface, suggesting the formation of volatile vanadium-halogen products as well. Vanadium-chloride product was found to react with the surface of the bare AP-MgO leading to deposition of vanadium-chloride species. Activities of VO2 and V 2O3 were found to be qualitatively similar to the HP-V2O3. The reaction of CCl3F with V 2O5 proceeds much slower, with only CCl2O and CO2 gaseous products observed. Activation of the AP-MgO with vanadium-containing species leads to formation of [MgVxO y]MgO shell/core-like particles. The MgO crystalline phase was the only one detected in the [MgVxOy]MgO samples. In the reaction with CCl3F, the [MgVxOy]MgO samples retain some properties characteristic for the bare AP-MgO (presence of an induction period for V/Mg=1 mol%, lower activity toward CCl4 than toward CCl2F2 for V/Mg=1, 10 mol%), and some properties characteristic for the HP-V2O3/AP-MgO mechanical mixture (accumulation of chlorine but no fluorine on the [MgVxO y]MgO, V/Mg=10 mol% sample surface).
- Martyanov, Igor N.,Klabunde, Kenneth J.
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p. 340 - 346
(2008/10/09)
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- Vanadium oxide complexes in room-temperature chloroaluminate molten salts
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The dissolution of vanadium(V) oxide (V2O5) in various ionic liquids has been studied to determine the complexes formed with respect to melt composition and V2O5 concentration. Vanadium oxide did not dissolve in either 1-n-butyl-3-methylimidazolium tetrafluoroborate or 1-n-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquids. V2O5 was found to dissolve at temperatures greater than 70 °C in 1-ethyl- and 1-n-butyl-3-methylimidazolium tetrachloroaluminate ionic liquids. Analyses of vanadium-containing melts by 51V, 1H, and 13C NMR and infrared spectroscopy indicate the emergence of different species as a function of melt acidity. In basic and neutral melts, VO2Cl2- and a metavanadate species of the form [(VO3)n]n- are observed. The species VO2Cl2- is the prominent product in basic melts, but as the melt becomes neutral or as the concentration of V2O5 is increased, the concentration of the metavanadate species is found to increase. However, V2O5 has been found to react in acidic melts to form volatile VOCl3.
- Bell,Castleman Jr.,Thorn
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p. 5709 - 5715
(2008/10/08)
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- Proof of existence and thermochemical characterization of the gaseous molecule VOCl2
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By use of the Knudsen-cell mass spectrometry the existence of VOCl2(g) is proven. Lines of fragmentation are set up for VOCl3(g). The vapor above V2O3(s) with Cl2(g) is examined. The sublimation of VOCl2 is measured at a temperature of 550-620 K. By 2nd law calculations the heat of sublimation is defined. The calculation for the gaseous VOCl2 leads to ΔBH°(VOCl2(g), 298 K) = -(130,4 ± 1,5) kcal · mol-1. The influence of VOCl2(g) for chemical vapor transport reactions of vanadium oxides with Cl2 is discussed by equilibrium calculations. Johann Ambrosius Barth 1996.
- Hackert,Plies,Gruehn
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p. 1651 - 1657
(2008/10/09)
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- Multidentate lewis acids. Adducts of monodentate and bidentate vanadyl dichloride alkoxides with ketones
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Combined use of 1H, 13C, and 51V NMR spectroscopy shows that the interaction of VOCl3 with 2 equiv of a ketone in solution at low temperatures produces complex mixtures of neutral and ionic adducts. In contrast, vanadium dichloride isopropoxide (4) forms neutral 1:2 adducts under similar conditions. These adducts are presumably octahedral, with ketones trans to the oxo and alkoxy oxygens. Bound and free ketones exchange by dissociation with free energies of activation near 7 kcal/mol. Analysis of the temperature dependence of the 51V chemical shift of mixtures of compound 4 and excess pinacolone gives ΔH = -10.9 kcal/mol and ΔS = -51 eu for the formation of the 1:2 adduct. At low temperatures, solutions of compound 4 containing 1 equiv of a ketone consist primarily of a 1:1 mixture of free compound 4 and the neutral 1:2 adduct. Vanadyl dichloride alkoxide 6, a bidentate Lewis acid, behaves similarly, and solutions containing 1 equiv of a ketone consist largely of free compound 6 and its unsymmetric 1:2 adduct 8. Significant amounts of symmetric 1:1 adduct 9 with a cooperatively bound carbonyl ligand are not formed, and no other unusual chemical effects can be attributed to the special juxtaposition of electrophilic sites in bidentate Lewis acid 6.
- Viet, Minh Tan Phan,Sharma, Vijay,Wuest, James D.
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p. 3026 - 3032
(2008/10/08)
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- Comparative kinetic and thermodynamic study on the chlorination of V2O5 with CCl4, COCl2 and Cl2
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The chlorination kinetics of pure vanadia was studied via isothermal thermogravimetric measurements, with CCl4, COCl2 and Cl2 as chlorinating agents. At temperatures where chemical control was predominant, apparent activat
- Pap,Mink,Bertoti,Szekely,Babievskaya,Karmazsin
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p. 163 - 173
(2008/10/08)
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- The Preparation of Vanadium Tetrachloride from Vanadium Dichloride Oxide and Vanadium Trichloride and the Hydrogen Reduction Process of Vanadium Tetrachloride
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The reactions of VCl2O and VCl3 with chlorine, and the reaction of VCl3O, formed by the chlorination of VCL2O, with chlorine in the presence of carbon were examined.The products formed by the reaction between gaseous VCl4 and hydrogen at various temperatures, and the behavior of VCl3 and VCl2 on heating in a hydrogen stream were examined.The reaction between VCl2O and chlorine occurs above ca. 120 deg C and proceeds markedly above ca. 170 deg C to form VCl3O.VCl4 can be obtained by passing the gaseous VCl3O together with chlorine through a carbon bed held at ca. 700 deg C.The reaction between VCl3 and chlorine occurs above ca. 80 deg C and proceeds markedly above ca. 170 deg C to form VCl4.The hydrogen reduction process of VCl4 in the vapor phase may be represented as follows: The reaction between VCl4 and hydrogen, 2VCl4(g) + H2(g) -> 2VCl3(s) + 2HCl(g), proceeds above ca. 500 deg C to form VCl3.Subsequently, the hydrogen reduction of the VCl3, 2VCl3(s) + H2(g) -> 2VCl2(s) + 2HCl(g), and the disproportionation of the VCl3, 2VCl3(s) -> VCl4(g), proceed to form VCl2.Above ca. 620 deg C, the reaction between the VCl2 and hydrogen, VCl2(s) + H2(g) -> V(s) + 2HCl(g), proceeds to form vanadium.
- Yajima, Akimasa,Matsuzaki, Ryoko,Saeki, Yuzo
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p. 2843 - 2846
(2007/10/02)
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