Phases in the subsolidus area of the system CuO–V2O5–Fe2O3

The phase equilibria in the solid state in the system FeVO₄?CCu₃V₂O₈ and FeVO₄?CCuO have been determined. Based on the obtained DTA and XRD analysis results and some additional research, a phase diagram in the whole subsolidus area of the system CuO?CV₂O₅?CFe₂O₃ has been worked out. Eighteen subsidiary subsystems can be distinguished in this ternary system. Basic properties of the obtained phases with howardevansite- and lyonsite-type structure have been investigated by DTA, IR, and SEM methods.     

Reinvestigation of Phase Equilibria in the V2O5–ZnO System

A diagram of phase equilibria established in a two-component oxide system V_{2 5}–ZnO has been worked out applying differential thermal analysis and X-ray phase analysis as well as depending on investigations carried out with the aid of high-temperature X-ray attachment and scanning electron microscope linked to an X-ray microanalyser. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of decomposition of the liquid phase of the ternary system LiOH-H2O2-H2O in the presence of the solid phase of Li2O2 · H2O

The kinetics of decomposition of hydrogen peroxide in the liquid phase of the ternary system LiOH-H₂O₂-H₂O was studied in the presence the solid phase of Li₂O₂·H₂O and without it. The main kinetic parameters of the processes studied were determined.     

Phase Equilibria in the System Fe2O3–V2O5 –WO3 in the Solid State

DTA and X-ray phase diffraction methods were used to construct a solidus area projection onto the component concentration triangle plane of the system Fe₂ O₃-V₂ O₅-WO₃. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of (VO)2P2O7 catalystsvia exfoliation-reduction of VOPO4·2H2O in butanol in the presence of ethanol

The exfoliation-reduction of VOPO₄·2H₂O in l-butanol oriso-butanol alone, and in a l-butanol/ethanol oriso-butanol/ethanol mixture, were conducted. Although all precursors were composed of a lamellar compound with intercalated alcohol molecules, VOHPO₄·0.5H₂O was formed when the exfoliation-reduction process was carried out in the mixed alcohol. All precursors transformed to a single phase of (VO)₂P₂O₇ under the reaction conditions forn-butane oxidation, but the crystallinity of (VO)₂P₂O₇ was different. The catalyst synthesized iniso-butanol/ethanol was well crystalline (VO)₂P₂O₇, and exhibited higher selectivity to maleic anhydride than that synthesized iniso-butanol alone for then-butane oxidation.     

Adsorption of benzene on the V2O5/γ-Al2O3 catalyst

Adsorption of benzene on the V₂O₅/-Al₂O₃ catalysts was studied in the temperature interval from 443 to 493 K and at partial pressures of the adsorbate ranging from 1 to 400 Pa. The adsorption isotherms were plotted. The isosteric heats and various entropy characteristics of adsorption were determined. Mobility of benzene in the adsorption layer is restricted compared to the model of ideal dimeric gas. The adsorbed amounts of benzene and chlorobenzene are compared.     

Phase Equilibria in the System V2O5–Fe8V10W16O85 and Some Properties of the Fe8V10W16O85 Phase

A phase diagram of the V₂O₅–Fe₈V₁₀W₁₆O₈₅ system were carried out using XRD and DTA methods. In addition, an indexing of Fe₈V₁₀W₁₆O₈₅ powder diffraction pattern was made and its basic crystallographic parameters were determined. Finally, the phase was studied using IR spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct Synthesis of Acetic Acid from CH4 and CO2 in the Presence of O2 over a V2O5-PdCl2／Al2O3 Catalyst

The possibility of synthesizing acetic acid from CH4 and CO2 in the presence of O2 over a V2O5-PdCl2/Al2O3 catalyst has been explored. The result shows that it is feasible in catalyzing a direct conversion of CH4, CO2 and O2 to acetic acid. It is concluded that both CO2 and O2 are involved in the formation of acetic acid.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.     

Synthesis and structural investigation of a unique columnar phase in the Bi2O3–TeO2–V2O5 System

A new columnar phase Bi(11.65)Te(1.35)V(5)O(34-δ) (δ ～ 1.3) containing VO(4) tetrahedra has been identified for the first time in the Bi(2)O(3)-TeO(2)-V(2)O(5) system. The phase formation and the extent of substitution of Te(4+) for Bi(3+) ions in order to stabilize V(5+) in this composition have been confirmed by the single crystal analysis, combined with the powder X-ray diffraction of the solid state synthesized bulk crystalline samples. The oxide crystallizes in a monoclinic crystal system, space group P2/c, with unit cell parameters a = 11.4616(7) ?, b = 5.7131(3) ?, c = 23.5090(18) ?, β = 101.071° (6) (Z = 2). The structure retains the basic features of the columnar oxides with the presence of [Bi(10.65)Te(1.35)O(14)](n)(9.35n+) columns along the (010) direction, surrounded by (VO(4)) tetrahedra placed in the planes parallel to (100) and (001), with an isolated bismuth atom in between the columns. The composition with a limited Te(4+) substitution, Bi(11.65)Te(1.35)V(5)O(34-δ) (δ ～ 1.3), exists with a surprisingly high oxygen deficiency as compared to the stoichiometrically known columnar oxides such as Bi(13)Mo(4)VO(34), Bi(12)Te(1)Mo(3)V(2)O(34), and Bi(11)Te(2)Mo(2)V(3)O(34). The structure of this interesting member of the columnar family of oxides based on the single crystal X-ray diffraction and the Raman spectroscopic studies indicates the possibility of the distribution of the oxygen vacancies among the VO(4) tetrahedral units. Further confirmation for the formation of vanadium stabilized columnar structures has been provided by the successful preparation of Bi(11.65)Te(1.35)V(4)CrO(34-δ) (δ ～ 0.83) and Bi(11.65)Te(1.35)V(4)WO(34-δ) (δ ～ 0.83) phases. Preliminary investigation of the photocatalytic efficiencies of the oxides Bi(11.65)Te(1.35)V(5)O(34-δ), Bi(11.65)Te(1.35)V(4)CrO(34-δ), and Bi(11.65)Te(1.35)V(4)WO(34-δ) revealed moderate photocatalytic activities for the decomposition of the dyes such as Rhodamine B under UV-vis light irradiation.     

Interplay between the structural and magnetic probes in the elucidation of the structure of a novel 2D layered [V4O4(OH)2(O2CC6H4CO2)4]·DMF

The title compound has been synthesized under solvothermal conditions by reacting vanadium(V) oxytriisopropoxide with terephthalic acid in N,N-dimethylformamide. A combination of synchrotron powder diffraction, infrared spectroscopy, scanning and transmission electron microscopy, and thermal and chemical analysis elucidated the chemical, structural and microstructural features of a new 2D layered inorganic-organic framework. Due to the low-crystallinity of the final material, its crystal structure has been solved from synchrotron X-ray powder diffraction data using a direct space global optimization technique and subsequent constraint Rietveld refinement. [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF crystallizes in the monoclinic system (space group P2/m (No. 10)); cell parameters: a = 20.923(4) ?, b = 5.963(4) ?, c = 20.425(1) ?, β = 123.70(6)°, V = 2120.1(9) ?(3), Z = 2. The overall structure can be described as an array of parallel 2D layers running along [-101] direction, consisting of two types of vanadium oxidation states and coordination polyhedra: face-shared trigonal prisms (V(4+)) and distorted corner-shared square pyramids (V(5+)). Both configurations form independent parallel chains oriented along the 2-fold symmetry crystallographic b-axis mutually interlinked with terephthalate ligands in a monodentate mode perpendicular to it. The morphology of the compound exhibits long nanofibers, with the growth direction along the layered [-101] axis. The magnetic susceptibility measurements show that the magnetic properties of [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF can be described by a linear antiferromagnetic chain model, with the isotropic exchange interaction of J = -75 K between the nearest V(4+) neighbours of S = 1/2.     

Influence of NO on the Reduction of NO2 with CO over Pt/SiO2 in the Presence of O2

Reduction of NO2 with CO in the presence of NO and excess oxygen, a model mixture for flue gas, over a 0.1% Pt/SiO2 catalyst was studied. The related reaction mechanisms, such as oxidation of CO and NO, were discussed. It was found that there was a narrow temperature window （180-190 ℃） for the reduction of NO2 by CO. When the temperature was lower than the lower limit of the window, the reduction hardly occurred, while when the temperature was higher than the upper limit of the window, the direct oxidation of CO by O2 occurred and thereby NO2 could not be effectively reduced by CO. The presence of NO shifted the window to higher temperatures owing to the inhibition effect of NO on the activation of O2 on Pt, which made it possible to reduce NO2 by CO in flue gas.     

Comparative studies in subsolidus areas of ternary oxide systems PbO–V2O5–In2O3 and PbO–V2O5–Fe2O3

Thermal stability of PbO was studied. Reactivity of oxides in the systems PbO–M₂O₃ (M = In, Fe) was investigated up to 650 °C. Using the DTA and XRD methods, parts of investigated ternary oxide systems, labelled by compounds: V₂O₅, Pb₈V₂O₁₃ and M₂O₃ (M = In, Fe), have been divided into partial ternary systems. IR spectra of compounds Pb₂MV₃O₁₁ (M = In, Fe) have been compared.     

The nature of the O—O bond in hydroperoxides

Quantum-chemical calculations of the H₂O₂ and F₂ molecules using different computational schemes, basis sets, and procedures for the inclusion of electron correlation were performed. High-resolution X-ray diffraction study of the electron density distribution in the crystals of 2,5-dimethyl-2,5-dihydroperoxyhexane and 2,5-dimethyl-2,5-dihydroperoxyhex-3-yne was carried out. Joint analysis of the results obtained showed that the formally covalent O—O and F—F bonds correspond to a specific type of interatomic interaction. This type is intermediate between the shared and closed-shell interactions (the latter are typical of the ionic systems and van der Waals molecules).     

Oxo Peroxo Glycolato Complexesof Vanadium (V). Crystal Structureof (NBu4)2[V2O2(O2)2(C2H2O3)2]ċH2O

Summary.  Oxo peroxo glycolato complexes of vanadium(V) (M ₂[V₂O₂(O₂)₂(C₂H₂O₃)₂]ċnH₂O (n=0, 1; M=NBu₄ ⁺ (1), K⁺ (2), NH₄ ⁺ (3), Cs⁺ (4), NPr₄ ⁺ (5)) as well as (NBu₄)₂[V₂O₄(C₂H₂O₃)₂]ċ H₂O (6) have been prepared and characterized by spectroscopic methods. X-Ray structure analysis of 1 revealed the presence of dinuclear [V₂O₂(O₂)₂(C₂H₂O₃)₂]²⁻ anions with a (chemical structure) bridging core and six coordinated vanadium(V) atoms in a distorted pentagonal pyramidal array. Received July 12, 1999. Accepted (revised) October 28, 1999     

Unexpected phase transformation from VO2(R) to VO2(A) during hydrothermal treatment in the V2O5�CH2C2O4�CH2O system

Vanadium dioxide (VO₂) was directly synthesized via the reduction of V₂O₅ with oxalic acid adopting two different types of hydrothermal processes in the temperature ranging from 180 to 260 °C. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In all these processes, the VO₂(B) phase was first formed at a relative lower temperature or the initial stage at higher temperature and then it transformed to the VO₂(R) phase with the increase of temperature. The building-block-stacking mechanism was proposed to elucidate the transformation from VO₂(B) nano-plates to snowflake-like VO₂(R) powders. During this transformation, no trace of the VO₂(A) phase was observed when one-step hydrothermal treatment method was used, whereas some part of the branches of the snowflake-like VO₂(R) particles transformed to metastable VO₂(A) nanofibers in the autoclave during cooling process when the two-step hydrothermal treatment method was conducted. The reason for this transformation can be contributed to the defects formed during the stacking process.     

An infrared study of the stretching modes of the water molecules in ZnF2·4H2O

The IR spectra of ZnF₂·4H₂O and its deuterated analogues are reported at ambient and liquid-nitrogen temperatures. The OH and OD stretching and bending vibrations of the water molecules are analysed in detail. The two types of water molecules give rise to different absorption peaks in the OH and OD stretching regions in samples that contain isotopically dilute HDO groups. The strongly hydrogen-bonded water molecules H₂O(1) and H₂O(4) show four broad OH and OD stretching modes at lower frequencies, while the weaker hydrogen-bonded ones H₂O(2) and H₂O(3) give rise to four narrow bands at higher frequencies. The ν_OD frequencies of isotopically dilute HDO groups correlate very well with the known R(H---F) and R(H---O) distances in the crystals and the assignment of these modes was done on this basis. It was also found that the ratio ν_OH/ν_OD decreases with decreasing values of R(H---O) or R(H---F) in ZnF₂·4H₂O.     

Synthesis and characterization of sodium vanadium oxide gels: the effects of water (n) and sodium (x) content on the electrochemistry of Na(x)V2O5·nH2O

Sodium vanadium oxide gels, Na(x)V(2)O(5)·nH(2)O, of varying sodium content (0.12 < x < 0.32) were prepared by careful control of an ion exchange process. The water content (0.23 > n > 0.01) and interlayer spacing were found to be inversely proportional to the sodium level (x), thus control of sodium (x) content provided a direct, chimie douce approach for control of hydration level (n) and interlayer spacing, without the need for high temperature treatment to affect dehydration. Notably, the use of high temperatures to modify hydration levels can result in crystallization and collapse of the interlayer structure, highlighting the distinct advantage of our novel chimie douce synthesis strategy. Subsequent to synthesis and characterization, results from an electrochemical study of a series of Na(x)V(2)O(5)·nH(2)O samples highlight the significant impact of interlayer water on delivered capacity of the layered materials. Specifically, the sodium vanadium oxide gels with higher sodium content and lower water content provided higher capacities in lithium based cells, where capacity delivered to 2.0 V under C/20 discharge ranged from 170 mAh/g for Na(0.12)V(2)O(5)·0.23H(2)O to 300 mAh/g for Na(0.32)V(2)O(5)·0.01H(2)O. The capacity differences were maintained as the cells were cycled.     

What are the Implications of Nonequilibrium in the O+OH and O+HO2 Reactions?

Vibrationally excited O2, OH, and HO2 species have been suggested (J. Phys. Chem. A 2004, 108, 758) to provide clues for explaining the "ozone deficit problem" and "HOx dilemma" in the middle atmosphere under conditions of local thermodynamic disequilibrium (LTD), but the question arises of how much LTD will affect the title ozone sink reactions. Besides providing novel kinetic results, it is shown that LTD tends to disfavor ozone depletion relative to traditional atmospheric modeling under Boltzmann equilibration, which is partly due to competition between the various reactive channels. The calculations also suggest that the title LTD processes can be important sources of highly vibrationally excited O2 in the middle atmosphere. Moreover, LTD is shown to offer an explanation for the fact that some down revision of the O + HO2 rate constant, or the ratio of the O + HO2 to O + OH rate constants, is required to improve agreement between the predictions of traditional modeling and observation. This, in turn, provides significant evidence supporting LTD at such altitudes.     

Synthesis and Properties of The Solid Solutions Formed in The Fe2V4O13–Cr2V4O13 System

DTA and XRD studies of the Fe₂V₄O₁₃–Cr₂V₄ O₁₃ system have shown that continuous solid solutions of a Fe_2–xCr_xV₄O₁₃ type, bearing a Fe₂ V₄ O₁₃ structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe₂ V₄ O₁₃ structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe_2–x Cr_x V₄ O₁₃ type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr³⁺ ion incorporation. The solid product of melting Fe_2–x Cr_x V₄ O₁₃ solid solutions for 0.2<x >1.2 is the Fe_1–x Cr_x VO₄ solution phase, and for x ≤0.2 and x ≥1.4 – the Fe_1–x Cr_x VO₄ phase as well as FeVO₄ or CrVO₄ , respectively. This revised version was published online in July 2006 with corrections to the Cover Date.