共查询到20条相似文献,搜索用时 46 毫秒
1.
Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V2O5/SiO2 and V2O5/TiO2, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V2O5/SiO2 and V2O5/TiO2 catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V2O5/SiO2 and V2O5/TiO2 were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified. 相似文献
2.
Xiangzhong Ren Yingkai Jiang Peixin Zhang Jianhong Liu Qianling Zhang 《Journal of Sol-Gel Science and Technology》2009,51(2):133-138
One-dimensional (1D) submicron-belts of V2O5 have been prepared by a sol–gel route using V2O5, H2O2 and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform
infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors
as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement
and cyclic voltammeter. The results showed that the synthesized V2O5 appeared to be submicron-belts and orthorhombic structure. The V2O5 submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge
rate in the potential region 1.8–4.0 V. 相似文献
3.
P. Tabero 《Journal of Thermal Analysis and Calorimetry》2007,88(1):37-41
Solid solution phases of a formula Fe8V10W16–xMoxO85 where 0≤x≤4, have been obtained, possessing a structure
of the compound Fe8V10W16O85.
It was found on the base of XRD and DTA investigations that these solution
phases melted incongruently, with increasing the value of x, in the temperature
range from 1108 (x=0) to 1083 K (x=4) depositing Fe2WO6
and WO3. The increase of the Mo6+
ions content in the crystal lattice of Fe8V10W16O85
causes the lattice parameters a=b contraction with cbeing
almost constant. IR spectra of the Fe8V10W16–xMoxO85 solid solution phases have been recorded. 相似文献
4.
Ca3Co4O9 powder was prepared by a polyacrylamide gel route in this paper. The effect of the processing on microstructure and thermoelectric
properties of Ca3Co4O9 ceramics via spark plasma sintering were investigated. Electrical measurement shows that the Seebeck coefficient and conductivity
are 170 μV/K and 128 S/cm, respectively, at 700 °C, yielding a power factor value of 3.70 × 10−4 W m−1 K−2 at 700 °C, which is larger than that of Ca3Co4O9 ceramics via solid-state reaction processing. The polyacrylamide gel processing is a fast, cheap, reproducible and easily
scaled up chemical route to improve the thermoelectric properties of Ca3Co4O9 ceramics by preparing the homogeneous and pure Ca3Co4O9 phase. 相似文献
5.
Majid M. Heravi Khadijeh Bakhtiari Tina Benmorad Fatemeh F. Bamoharram Hossein A. Oskooie Maryam H. Tehrani 《Monatshefte für Chemie / Chemical Monthly》2007,138(5):449-452
Summary. The nitration of aromatic compounds was carried out in the presence of divanadium-substituted molybdophosphoric acid, H5PMo10V2O40, as catalyst and a mixture of nitric acid and acetic anhydride as nitrating agent. In the presence of this heteropolyacid
the ortho- and para-nitro compounds were obtained in good to excellent yields under mild reaction conditions. 相似文献
6.
Large-scale Li1+x
V3O8 nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method.
The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were
characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission
electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts
is mainly determined by the calcination temperature. Electrochemical properties of the Li1+x
V3O8 nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li1+x
V3O8 nanobelts exhibit a high discharge capacity (278 mAh g−1) and excellent cycling stability. 相似文献
7.
Anna Blonska-Tabero 《Journal of Thermal Analysis and Calorimetry》2007,88(1):201-205
Thermal properties of Co2FeV3O11
have been reinvestigated. It has been proved that this compound does not exhibit
polymorphism. It melts incongruently at the temperature of 770±5°C
and the phase with lyonsite type structure is the solid product of this melting.
Phase relations in the whole subsolidus area of the CoO–V2O5–Fe2O3 system have been determined. The solidus area projection onto
the component concentration triangle plane of this system has been constructed
using the DTA and XRD methods. 15 subsidiary subsystems can be distinguished
in this system. 相似文献
8.
Elidia M. Guerra Herenilton P. Oliveira 《Journal of Sol-Gel Science and Technology》2009,50(1):103-110
New hybrid composites based on mesostructured V2O5 containing intercalated poly(ethylene oxide), poly-o-methoxyaniline and poly(ethylene oxide)/poly-o-methoxyaniline were prepared. The results suggest that the polymers were intercalated into the layers of the mesostructured
V2O5. Electrochemical studies showed that the presence of both polymers in the mesostructured V2O5 (ternary hybrid) leads to an increase in total charge and stability after several cycles compared with binary hybrid composites.
This fact makes this material a potential component as cathode for lithium ion intercalation and further, a promising candidate
for applications in batteries. 相似文献
9.
Lei Ge 《Journal of Sol-Gel Science and Technology》2007,44(3):263-268
Novel visible-light-activated In2O3–CaIn2O4 photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In2O3–CaIn2O4 composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm).
The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive
spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed
that the In2O3–CaIn2O4 composite samples with different In2O3 and CaIn2O4 content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption
spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light
activity for decomposition of methyl orange. The significant enhancement in the In2O3–CaIn2O4 photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in
the In2O3 and CaIn2O4 coupling semiconductors. 相似文献
10.
Areas of fusion and crystallization peaks of K3TaO2F4 and KTaF6 were measured using the DSC mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering
the temperature dependence of the calorimeter sensitivity, values of the fusion enthalpy of K3TaO2F4 at the fusion temperature of 1181 K of (43 ± 4) kJ mol−1 and of KTaF6 at the fusion temperature of 760 K of (8 ± 1) kJ mol−1 were determined. 相似文献
11.
Ji-min Yang Yan Yao Run-zhi Zhang Ai-de Sun Bao-hui Li Hong-zhi Lu Qi-ying Xia 《Journal of solution chemistry》2009,38(4):429-439
Osmotic coefficients and water activities for the Li2B4O7+LiCl+H2O system have been measured at T=273.15 K by the isopiestic method, using an improved apparatus. Two types of osmotic coefficients, φ
S and φ
E, were determined. φ
S is based on the stoichiometric molalities of the solute Li2B4O7(aq), and φ
E is based on equilibrium molalities from consideration of the equilibrium speciation into H3BO3,B(OH)4− and B3O3(OH)4−. The stoichiometric equilibrium constants K
m
for the aqueous speciation reactions were estimated. Two types of representations of the osmotic coefficients for the Li2B4O7+LiCl+H2O system are presented with ion-interaction models based on Pitzer’s equations with minor modifications: model (I) represents
the φ
S data with six parameters based on considering the ion-interactions between three ionic species of Li+, Cl−, and B4O72−, and model (II) for represents the φ
E data based on considering the equilibrium speciation. The parameters of models (I) and (II) are presented. The standard deviations
for the two models are 0.0152 and 0.0298, respectively. Model (I) was more satisfactory than model (II) for representing the
isopiestic data. 相似文献
12.
Fe3O4 nanorods and Fe2O3 nanowires have been synthesized through a simple thermal oxide reaction of Fe with C2H2O4 solution at 200–600°C for 1 h in the air. The morphology and structure of Fe3O4 nanorods and Fe2O3 nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals
Fe3O4 nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air.
When the temperature was 600°C, the samples completely became Fe2O3 nanowires with hexagonal structure. It was found that C2H2O4 molecules had a significant effect on the formation of Fe3O4 nanorods. A possible mechanism was also proposed to account for the growth of these Fe3O4 nanorods.
Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China
(Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010) 相似文献
13.
Chiwei Wang Xiaoling Ma Jinguo Cheng Jutang Sun Yunhong Zhou 《Journal of Solid State Electrochemistry》2007,11(3):361-364
LiNi0.8Co0.2O2 and Ca-doped LiNi0.8Co0.2O2 cathode materials have been synthesized via a rheological phase reaction method. X-ray diffraction studies show that the
Ca-doped material, and also the discharged electrode, maintains a hexagonal structure even when cycled in the range of 3.0–4.35 V
(vs Li+/Li) after 100 cycles. Electrochemical tests show that Ca doping significantly improves the reversible capacity and cyclability.
The improvement is attributed to the formation of defects caused by the partial occupancy of Ca2+ ions in lithium lattice sites, which reduce the resistance and thus improve the electrochemical properties. 相似文献
14.
V. N. Krasil’nikov A. P. Tyutyunnik V. G. Zubkov I. F. Berger L. A. Perelyaeva I. V. Baklanova 《Russian Journal of Inorganic Chemistry》2011,56(1):18-25
Potassium oxosulfatovanadate(V) K3VO2(SO4)2 has been obtained by solid-phase synthesis from K2SO4, K2S2O7, and V2O5 (2: 1: 1), and its formation conditions, crystal structure, and physiochemical properties have been studied. The conversions of K3VO2(SO4)2 in contact with potassium vanadates and other potassium oxosulfatovanadates(V) are considered in terms of phase relations in the K2O-V2O5-SO3 system, which models the active component of vanadium catalysts for sulfur dioxide oxidation into sulfur trioxide. The X-ray diffraction pattern of K3VO2(SO4)2 is indexed in the monoclinic system (space group P21) with unit cell parameters of a = 10.0408(1) Å, b = 7.2312(1) Å, c = 7.3821(1) Å, β = 104.457(1)°, Z = 2, and V = 519.02 Å3. The crystal structure of K3VO2(SO4)2 is built from [VO2(SO4)2]3? complex anions, in which the vanadium atom is in an octahedral oxygen environment formed by two terminal oxygen atoms (V-O(6) = 1.605(7) Å, V-O(10) = 1.619(7) Å and four oxygen atoms of the two chelating sulfate anions. The vibrational spectra of K3VO2(SO4)2 are analyzed using these structural data. 相似文献
15.
Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC),
TiO2, Al2O3, MgO, CaO, SiO2 and various zeolites. The CO2 capture capacity and regeneration property of various sorbents were measured in the presence of H2O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO2 absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such
as KAl(CO3)2(OH)2, K2Ca(CO3)2, K2Mg(CO3)2, and K2Mg(CO3)2·4(H2O), which did not completely convert to the original K2CO3 phase at temperatures below 200 °C, during the CO2 absorption process in the presence of 9 vol.% H2O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO3 crystal structure was formed during CO2 absorption. The formation of active species, K2CO3·1.5H2O, by the pretreatment with water vapor and the formation of the KHCO3 crystal structure after CO2 absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In
particular, the KTiI30 sorbent showed excellent characteristics with respect to CO2 absorption and regeneration in that it satisfies the requirements of a large amount of CO2 absorption (87 mg CO2/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature
condition (1 atm, 150 °C). In addition, the higher total CO2 capture capacity of KMgI30 (178.6 mg CO2/g sorbent) than that of the theoretical value (95 mg CO2/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce
the CO2 capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties
of the sorbents before/after CO2 absorption, and the role of water vapor and its effects on CO2 absorption. 相似文献
16.
As a result of solid-state reactions three cadmium vanadates(V) have been obtained, i.e. CdV2O6, Cd2V2O7 and Cd4V2O9. Melting temperature and the product of melting has been determined for Cd4V2O9. Thermal properties of the obtained cadmium
vanadates(V) have been reinvestigated. The phase equilibria being established in the CdO-V2O5 system over the whole components concentration range up to the solidus line were described. 相似文献
17.
Lifen Xiao Yanqiang Zhao Yanyan Yang Xinping Ai Hanxi Yang Yuliang Cao 《Journal of Solid State Electrochemistry》2008,12(6):687-691
LiNi0.5Mn1.5O4 powders were prepared through polymer-pyrolysis method. XRD and TEM analysis indicated that the pure spinel structure was
formed at around 450 °C due to the very homogeneous intermixing of cations at the atomic scale in the starting precursor in
this method, while the well-defined octahedral crystals appeared at a relatively high calcination temperature of 900 °C with
a uniform particle size of about 100 nm. When cycled between 3.5 and 4.9 V at a current density of 50 mA/g, the as prepared
LiNi0.5Mn1.5O4 delivered an initial discharge capacity of 112.9 mAh/g and demonstrated an excellent cyclability with 97.3% capacity retentive
after 50 cycles. 相似文献
18.
The surface of the spinel LiMn2O4 was coated with AlF3 by a chemical process to improve its electrochemical performance at high temperatures. The morphology and structure of the
original and AlF3-coated LiMn2O4 samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). All the samples exhibited
a pure cubic spinel structure without any impurities in the XRD patterns. It was found that the surfaces of the original LiMn2O4 samples were covered with a nanolayer AlF3 after the treatment. The charge/discharge of the materials were carried at 220 mA/g in the range of 3.0 and 4.4 V at 55°C.
While the original LiMn2O4 showed 17.8% capacity loss in 50 cycles at 55°C, the AlF3-coated LiMn2O4 (118.1 mA h/g) showed only 3.4% loss of the initial capacity (122.3 mA h/g) at 55°C. It is obvious that the improvement in
cycling performance of the coated-LiMn2O4 electrode at 55°C is attributed to the presence of AlF3 on the surface of LiMn2O4.
Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 817–819.
The article is published in the original 相似文献
19.
Sagrario M. Montemayor L. A. García-Cerda J. R. Torres-Lubián O. S. Rodríguez-Fernández 《Journal of Sol-Gel Science and Technology》2007,42(2):181-186
In this work the synthesis of CoFe2O4-SiO2 and NiFe2O4-SiO2 nanocomposites was studied via the sol–gel method, using the polymerized complex route. The polymerized precursors obtained
by the reaction of citric acid, ethylene glycol, tetraethylorthosilicate, ferric nitrate, and cobalt nitrate or nickel chloride
were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. NMR and IR spectra of the precursors,
without and with metallic ions, show the formation of polymeric chains with ester and ether groups and complexes of metal-polymeric
precursor. The nanocomposites were obtained by the thermal decomposition of the organic fraction and characterized by X-ray
diffraction (XRD) and vibrating sample magnetometry (VSM). XRD patterns show the formation of CoFe2O4 and NiFe2O4 in an amorphous silica matrix above 400 °C in both cases. When the calcination temperature was 800 °C the particle size of
the crystalline phases, calculated using the Scherrer equation, reached ∼35 nm for the two oxides. VSM plots show the ferrimagnetic
behavior that is expected for this type of magnetic material; the magnetization at 12.5 KOe of the CoFe2O4-SiO2 and NiFe2O4-SiO2 compounds was 29.5 and 17.4 emu/g, respectively, for samples treated at 800 °C. 相似文献
20.
N. N. Gedam P. R. Padole S. K. Rithe G. N. Chaudhari 《Journal of Sol-Gel Science and Technology》2009,50(3):296-300
Thick film of nanocrystalline Co0.8Ni0.2Fe2O4 was obtained by sol–gel citrate method for gas sensing application. The synthesized powder was characterized by X-ray diffraction
(XRD) and transmission electron microscopy. The XRD pattern shows spinel type structure of Co0.8Ni0.2Fe2O4. XRD of Co0.8Ni0.2Fe2O4 revels formation of solid solution with average grain size of about 30 nm. From gas sensing properties it observed that nickel
doping improves the sensor response and selectivity towards ammonia gas and very low response to LPG, CO, and H2S at 280 °C. Furthermore, incorporation of Pd improves the sensor response and stability of ammonia gas and reduced the operating
temperature upto 210 °C. The sensor is a promising candidate for practical detector of ammonia. 相似文献