New heteroleptic oxovanadium(V) chloro oximato complexes of the type [VO{Cl}3-n{ON=C(CH3)(Ar)}n] (where Ar = C4H3O-2, C4H3S-2, C5H4N-2 and n = 1 or 2) have been synthesized in excellent yields by the reaction of VOCl3 with the sodium salts of corresponding internally functionallized oximes in refluxing anhydrous benzene. The complexes are
characterized by elemental analyses and spectroscopic techniques (FT-IR, 1H-, 13C{1H}- and 51V-NMR). FAB mass spectral analysis of one of the derivatives, [VOCl{ON=C(CH3)C4H3S}2] indicates the monomeric nature of the complex. 51V-NMR spectral studies of these complexes suggest tetra-coordination around the vanadium atom in solution. However, the single
crystal X-ray diffraction study of a redistribution product [VOCl{ON=C(CH3)(C4H3S-2)}2] · CH3OH obtained on recrystallization of [VOCl2{ON=C(CH3)(C4H3S-2)}] from a methanol-hexane mixture shows the vanadium(V) atom is hepta-coordinated with distorted pentagonal bipyramidal
geometry. The oxo-atom occupies the axial position while the weakly coordinated CH3OH group is trans to the V=O atom. The two oximato ligands in the approximate pentagonal plane are bonded to the central vanadium atom in dihapto
(η2-N, O) manner with the formation of three-membered rings. The V–Cl bond occupies the fifth position in the approximate plane. 相似文献
Proof of Existence and Thermochemical Characterization of the Gaseous Molecule VOCl2 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°(VCl2(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. 相似文献
Reaction of VOCl3 with 2‐phenoxyethanol in n‐hexane in a 1:1 fashion gives dichlorooxo(2‐phenoxyethanolato)vanadium(V). HCl elimination yields the orange vanadium(V) complex, which is the first structurally characterized dichlorooxovanadium(V) alkoxide. The structure analysis reveals an unexpected tetrahedral coordination around the vanadium atom in the monomeric compound. Alcoholysis and hydrolysis reactions of [VOCl2(OCH2CH2OPh)] are monitored by 51V NMR spectroscopy. Activated with Me3SiCH2MgCl or nBu2Mg the complex catalyses the polymerisation of styrene. 相似文献
Kinetics of the polymerization of methyl methacrylate with the VOCl3? AlEt3 catalyst system at 40°C in n-hexane have been studied. A linear dependence of rate of polymerization on the monomer and catalyst concentrations as well as an overall activation energy of 5.87 kcal/mole were found. Characterization of the structure of the polymer by NMR spectra revealed the presence of stereoblock units. The mechanism of polymerization is discussed in relation to the kinetic data obtained. 相似文献
Methyl methacrylate was polymerized at 40°C with VOCl3–AlEt2Cl catalyst system in n-hexane. The rate of polymerization was proportional to catalyst and monomer concentration at Al/V ratio of 2 and overall activation energy of 9.25 kcal/mole support a coordinate anionic mechanism of polymerization. The catalytic activity and stereospecificity of this catalyst system is discussed in comparison with that of VOCl3–AlEt3 catalyst system. 相似文献
The polymerization of styrene with VOCl3 in combination with AlEt3 and with Al(i-Bu)3 in n-hexane at 40°C. has been investigated. The rate of polymerization was found to be second order with respect to monomer in both systems. With respect to catalyst the rate of polymerization was first order for VOCl3–AlEt3 and second order for VOCl3-Al(i-Bu)3 systems. The activation energies for VOCl3–AlEt3 and VOCl3–Al(i-Bu)3 systems were 7.37 and 11.25 kcal./mole, respectively. The molecular weight of polystyrene in the AlEt3 system was considerably higher than that in the Al(i-Bu)3 system. The valence of vanadium obtained by a potentiometric method showed that the catalyst sites in the AlEt3 system are different in nature from those in the Al(i-Bu)3 system. The effect of diethylzinc as a chain-transfer agent in the AlEt3 system was also studied. 相似文献
Diffusion coefficients of Cu2+ in the form of its carboxylate have been measured in isotactic polypropylene as a function of temperature (90–128°C) and extent of preoxidation. Diffusion take place from the metal catalyst/polymer interface into the bulk polymer. The diffusion is dependent on the extent of preoxidation and temperature but not on the type of catalyst (Cu, CuO, CuO0.67). Analysis of polymer sections for Cu2+ ions was carried out with a selective Cu2+ electrode. Diffusion in isotactic polypropylene is about 1000 times faster than in lowdensity polyethylene. The carboxylate anion appears to have about 7 C-atoms for diffusion in isotactic polypropylene compared with 29 C-atoms for low-density polyethylene. 相似文献
The results of Density Functional Theory (DFT) calculations on optical properties of vanadium complexes VOCl3, VOCl4-, VOCl52-, as well as the VO43- ion, are presented. The spectra of excited states in the range 25000-60000 cm-1 have been analyzed using the time-dependent DFT method (TDDFT). Spectroscopic features of structural defects (low-coordinated (LC) oxygen ions), as well as surface point defects (F+ and F sites) in MgO, have been studied within the cluster approach. The charge-transfer spectra and frequencies of normal vibrations for a number of active site models of finely dispersed oxides MgO and V2O5 on silica have been calculated. Comparison of the obtained results with experimental electronic diffuse reflectance spectra and fundamental frequencies confirms a hypothesis about the structure of active centers of finely dispersed oxide V2O5 on silica as monomeric forms, (O=V-On). 相似文献
New solid polymer electrolytes are developed for a lithium power source used at the temperatures up to 100°C. Polyester diacrylate (PEDA) based on oligohydroxyethylacrylate and its block copolymers with polyethylene glycol were offered for polymer matrix formation. The salt used was LiClO4. The ionic conductivity of electrolytes was measured in the range of 20 to 100°C using the electrochemical impedance method. It is shown that the maximum conductivity in the whole temperature range is characteristic of the electrolyte based on the PEDA copolymer and polyethylene glycol condensation product (2.8 × 10?6 S cm?1 at 20°C, 1.8 × 10?4 S cm?1 at 95°C). 相似文献
A supported magnesium-vanadium-aluminium catalyst was prepared by depositing –with the use of a milling technique–VOCl3 on the MgCl2(THF)2 support and subsequent activation with diethylaluminium chloride. Catalytic activity of the obtained system for ethylene polymerization was evaluated as a function of Mg/V and Al/V ratios as well as catalyst ageing time and polymerization temperature. High concentrations of THF in the catalytic system and considerable excess of an organoaluminium co-catalyst were found to have no deactivating action on vanadium active sites. The catalyst obtained is stable and its activity for ethylene polymerization is high. It yields polyethylene with higher molecular weight and higher melting point than offered by the materials produced with the use of a corresponding unsupported vanadium catalyst or a titanium-based system on the same magnesium support. Kinetic investigations confirmed stability of this catalyst irrespective of its concentration in the polymerization medium or of monomer concentration. Moreover, analysis of the kinetic findings revealed that over 80% of vanadium employed forms active polymerization sites. 相似文献
A continuous flow reactor was operated at 420 °C and feed rate of 0–1.5 kg h−1 for catalytic degradation of polyethylene (PE) over SA-1 silica–alumina in order to investigate the effect of catalyst on the reaction rate and the quantity and quality of degradation products. SA-1 was either mixed with the PE inside reactor or placed in a catalyst cage, the efficiency being slightly higher in the first case. The catalyst did not have a significant effect on the reaction rates but the volatile products clearly had lower molecular weights. More gases were produced on SA-1 compared to thermal degradation, containing higher amounts of C4 and less amounts of C2 compounds. 相似文献
The effect of temperature, water content, and the type of reagent on the silylation of fused silica capillaries was studied by 29Si and 13C CP-MAS NMR. Fumed silica (Cab-O-Sil M5), which is essentially a highly dispersed vitreous quartz with a surface comparable to that of fused silica capillary columns, was selected as a model material. Hexamethyldisilazane (HMDS) and 1,2-diphenyl-1,1,3,3-tetraphenyldisilazane (DPTMDS), which were used as silylation reagents, yielded trimethyl- and dimethylphenylsilyl surface groups respectively at lower temperatures (< 350°C and <250°C respectively). At higher temperatures, increasingly more dimethylsilyl groups are formed, with the silicon bound to two oxygen atoms. This process occurs for DPTMDS at a considerably lower temperature than for HMDS. The formation of silyl groups on the surface and the disappearance of hydroxyl groups are followed independently. The 13C NMR and GC-MS of the reaction products showed that with DPTMDS, the formation of two Si-O-Si links is accompanied by a loss of phenyl groups rather than of methyl groups. After the Cab-O-Sil had been dried over P2O5, the formation of these double links occurred for HMDS only at temperatures above 460°C and for DPTMDS at 400°C. Thus we concluded that water supplies oxygen atoms for double Si-O-Si links (possibly crosslinks) necessary for efficient deactivation. This may explain the less successful silanization of fused silica capillaries because their water content is lower than that of glass capillaries. 相似文献
An active-phase monolayer has been deposited on SiO2 using replacement of the surface OH groups by VOCl3 vapour. The amount of vanadium fixed on the SiO2 surface depends on the initial concentration of the silanol groups and ranges from 3.36 to 1.43%. In combination with diethyl aluminium chloride, the products are active catalysts for ethylene polymerization. The effects of the reaction conditions (the time of catalyst-complex formation, the catalyst life time and the temperature of polymerization) as well as the effect of the vanadium content, the A1:V ratio and the presence of diphenyl magnesium on the activity of the catalyst system have been investigated. The catalyst activity was found to depend strongly on the amount of vanadium fixed on the support surface. The maximum productivity obtained is about 22,000 gPE/g vanadium. Some basic characteristics of the synthesized polymer such as tensile strength, elongation at break, density and crystallization degree are given. 相似文献
Phillips catalyst is one of the most significant industrial ethylene polymerization catalysts. Chemical modifications have been carried out to tune the Phillips catalyst performance and improve the polyethylene properties. After the modification of the catalyst by fluorine, the polyethylene product with higher molecular weight (MW) and narrower molecular weight distribution (MWD) is suitable for producing automobile fuel tanks. Vanadium containing Phillips catalyst enhances α‐olefin incorporation and MW regulation. In present work, fluorine modified and unmodified chromium–vanadium (Cr–V) bimetallic catalysts are prepared and explored. Compared with the fluorine‐free catalyst, the activities of F‐modified bimetallic catalysts slightly decrease with the increasing MW of the product and the hydrogen response increases slightly. Due to the synergistic effect of the chromium, vanadium and fluorine on the silica gel support, the short‐chain branch distribution (SCBD) of copolymers from F‐modified Cr–V bimetallic catalyst (Cr–V–F)600 is more beneficial than that of Cr–V bimetallic catalyst (Cr–V)600 and F‐modified Cr–V bimetallic catalyst (Cr–V–F)500. The fluorination of Cr–V bimetallic catalysts has not only preserved the high polyethylene activity of bimetallic active sites but also produced the advantage of the high MW ability from fluorine.
NiO/SiO2 catalysts were prepared with Ni contents ranging from 2–15% using a microporous silica support at pH ~11.5. The role of the method of preparation on the resulting catalyst is also investigated. Structural and textural changes were followed using X-ray diffraction, TG and DTA techniques—the surface area measurements were carried out on the parent catalysts and those produced in the temperature range 250–1000°C.Impregnation of the silica gel in the nickel ammine complex solution (catalyst series 1N–4N) with subsequent drying at 80°C overnight produced crystalline catalysts with two distinct peaks at d-spacings of 2.035 and 2.349 Å resulting from a surface silicate. This is easily destroyed by thermal treatment at 250°C for Ni contents ? 10% but is stable to this temperature for the higher Ni content. Drying the catalyst at room temperature (3Nb) gives rise to an amorphous product. A non-crystalline catalyst is also obtained when concentrated ammonia solution is added to the adsorbed nickel salt (3Nc). At high Ni content, the hydroxo ligand becomes significant and results in a surface compound in which one silanol group is attacked. This gives rise to a crystalline product at 500°C with characteristic d-spacings at 2.201 and 2.049 Å which, subsequently, produces a poorly crystalline NiO product at 1000°C. The presence of this hydroxo ligand is manifested by a small endotherm at 260°C.At Ni contents below 15% but greater than 2% a small exotherm is observed at ~ 500°C resulting from a reduction process. Entrained SO42? ions present as an impurity are evolved at temperatures & > 750°C and can be estimated by TG analysis.The specific surface area decreases with Ni contents ? 5% but increases for higher Ni contents. Catalyst samples containing 15% Ni possess the highest specific area at all temperatures.Pore structure analysis showed that microporosity increased with increase in Ni content for the catalyst series 1N–4N. Samples from preparations 3Nb and 3Nc showed more mesoporosity than that of 3N. Thermal treatment causes widening of the pores for catalysts 1N–3N becoming predominantly mesoporous, co-existing with some micropores. Catalyst samples with 15% Ni remained predominantly microporous-mesoporosity increasing only at 1000°C. 相似文献
The phase and chemical compositions of precipitates formed in the system Zn(VO3)2–HCl–VOCl2–H2O at pH 1?3, molar ratio V4+: V5+ = 0.1?9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V4+: V5+ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula ZnxV4+yV5+2-yO5 ? nH2O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5?1.2). Vanadate ZnxV2O5 ? nH2O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V4+: V5+ = 1.5?9.0. Investigation of the kinetics of the formation of ZnxV2O5 ? nH2O at pH 3 determined that tetravalent vanadium ions VO2+ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl2 can be used as a precursor for producing V3O7 ? H2O nanorods 50–100 nm in diameter. 相似文献