Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

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CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

Coherent interfaces: Efficient boundary conditions in solid state reactivity. Study in V2O5AlNbO4, V2O5GaNbO4, and V2O5TiNb2O7 systems

The thermodynamically unexpected reduction of V₂O₅ in the presence of the mixed oxides AlNbO₄, GaNbO₄, and TiNb₂O₇ under nitrogen at 630°C is reported and gives a supplementary example of the kind of interfacial reaction observed in the V₂O₅TiO₂ system. It is shown that this phenomenon comes from the establishment of coherent interfaces between the cleavage planes of two crystals belonging to the same crystallo-chemical family. The reduction enables the system to diminish the elastic stress created by the slight interfacial misfit. A thermodynamic and kinetic explanation, based on structural factors, is given.     

Die Bestimmung V2O2 und V4O5 nebeneinander in Kontaktkatalysatoren auf Kieselgurgrundlage

Ohne Zusammenfassung     

51V NMR studies of systems V2O5-KHSO4 and V2O5?K2SO4

Systems V₂O₅–KHSO₄ and V₂O₅–K₂SO₄ have been studied by the⁵¹V NMR method. The first system demonstrates the same states of vanadium as the previously studied V₂O₅–K₂S₂O₇, in this system a compound with an equimolar ratio of components has been found. In V₂O₅–K₂SO₄ the state of vanadium differs from the above systems and the formation of a compound with V/K=4 is observed.

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⁵¹V KHSO₄–V₂O₅ K₂SO₄–V₂O₅. , K₂S₂O₇–V₂O₅, . K₂SO₄–V₂O₅ V/K4.

     

Preparation and Electrochemical Performance of V2O3-C Dual-Layer Coated LiFePO4 by Carbothermic Reduction of V2O5

The V₂O₃-C dual-layer coated LiFePO₄ cathode materials with excellent rate capability and cycling stability were prepared by carbothermic reduction of V₂O₅. X-ray powder diffraction, elemental analyzer, high resolution transmission electron microscopy and Raman spectra revealed that the V₂O₃ phase co-existed with carbon in the coating layer of LiFePO₄ particles and the carbon content reduced without graphitization degree changing after the carbothermic reduction of V₂O₅. The electrochemical measurement results indicated that small amounts of V₂O₃ improved rate capability and cycling stability at elevated temperature of LiFePO₄/C cathode materials. The V₂O₃-C dual-layer coated LiFePO₄ composite with 1wt% vanadium oxide delivered an initial specific capacity of 167 mAh/g at 0.2 C and 129 mAh/g at 5 C as well as excellent cycling stability. Even at elevated temperature of 55 oC, the specific capacity of 151 mAh/g was achieved at 1 C without capacity fading after 100 cycles.     

Determination of the exposed surface area of V2O5 on a V2O5/Al2O3 catalyst

NH₃, NO and CO₂ were tested as adsorbates for selective determination of exposed surface area of V₂O₅ on a V₂O₅/Al₂O₃ catalyst. The most promising appears to be CO₂ which interacts with the support Al₂O₃ only.

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NH₃, NO CO₂ V₂O₅ V₂O₅/Al₂O₃. CO₂, Al₂O₃.

     

V2O5/TiO2 oxidation catalysts, IV. Adsorption of acrolein on sodium-containing systems

Adsorption of acrolein on vanadia/titania catalysts fits a polymerization kinetics if Na–V compounds are not present or the vanadium content is lower than that corresponding to formation of a monolayer of vanadia on the titania support.

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, Na–V .

     

Catalytic decomposition of H2O2 on Co3O4 doped with MgO and V2O5

The effects of doping of Co₃O₄with MgO (0.4–6 mol%) and V₂O₅ (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H₂O₂ at 30–50°C. Pure and doped samples were prepared by thermal decomposition in air at 500–900°C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V₂O₅ doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co₃O₄ solid. Treatment of Co₃O₄ with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H₂O₂ decomposition, of Co₃O₄ was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant (k) measured at 40°C on Co₃O₄ due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V₂O₅-doping of Co₃O₄ brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40°C over the 0.75 mol% V₂O₅-doped Co₃O₄ solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO³⁺–CO²⁺ ion pairs and created Mg²⁺–CO³⁺ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H₂O₂. V₂O₅-doping exerted an opposite effect via decreasing the number of CO³⁺–CO²⁺ ion pairs besides the possible formation of cobalt vanadate.     

V2O5/TiO2 oxidation catalysts. II. Texture properties

The texture properties (specific surface area and porosity) of V₂O₅/TiO₂ catalysts obtained from VO(acetylacetonate)₂ have been studied. The presence of sodium leads to a marked decrease in the S_BET values, probably as a consequence of the formation of Na-V bronzes, which lead to a rutilization of the support.

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( ) V₂O₅/TiO₂, - VO()₂. S_BET, , Na-V, .

     

Effect of the extent of reduction of V2O5 on the adsorption of propylene and the oxidative dehydrogenation of propane to give propylene on V2O5 and V2O5/TiO2-SiO2

An increase in the propylene output in the oxidative dehydration of propane on V₂O₅/TiO₂-SiO₂ was observed after prior reduction of V₂O₅ in the reaction mixture to V₂O₄, which reduces the destructive chemisorption of propylene. A low titanium dioxide content in TiO₂-SiO₂ hinders the deep reduction of V₂O₅ to V₂O₃, which reduces the conversion of propane. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 373–378, November–December, 2007.     

Phase diagram and infrared-spectral investigation of the 2TeO2 · V2O5-Na2O · V2O5 · 2TeO2 system

The phase diagram of the 2TeO₂ · V₂O₅-Na₂O · V₂O₅ · 2TeO₂ system is studied by X-ray diffraction, ir spectroscopy, and DTA. A new compound with a composition of Na₂O · 3V₂O₅ · 6TeO₂ is established. The ir spectra of the alkaline trivanadates are interpreted. They are considered as structural analogs of the new phase. As a result of this comparison, the postulate is made that the main structural units in the Na₂O · 3V₂O₅ · 6TeO₂ compound are V₂O₈ groups, while tellurium is present both in the TeO₃ and TeO₄ groups. Contrary to the crystal phases, in glasses the transition from VO₅ toward VO₄ does not proceed through the formation of new structural units of vanadium; but rather a gradual transition of the structure is observed with a change in the composition from 2TeO₂ · V₂O₅ to Na₂O · V₂O₅ · 2TeO₂.     

Kinetics of C2H4 polymerization on reduced V2O5/Al2O3 catalyst

Kinetic study of C₂H₄ polymerization on reduced V₂O₅/Al₂O₃ catalysts revealed that the rate equation can be expressed as V=k exp (-Y) K_aP_E/(1+K_aP_E) in the temperature range of –20 to 70°C. The deactivation constant, , was found to have a close relation with the yield and molecular weight of the polymer. C₂H₄ V₂O₅/Al₂O₃ –20 +70°C : V_p=k·exp(-Y_p)·K_aP_e/(1+K_aP_e). .     

A novel nonaqueous route to V2O3 and Nb2O5 nanocrystals

The reaction between transition metal alkoxides and benzyl alcohol provides a novel soft chemistry route to metal oxide nanoparticles. The method allows the preparation of nanocrystals of two important transition metal oxides, namely V₂O₃ and Nb₂O₅. Although the reaction temperatures of 200–220 °C are comparably low, the obtained particles are highly crystalline. According to TEM investigations, the V₂O₃ crystals exhibit particle sizes between 20 and 50 nm, and the Nb₂O₅ crystals display platelet-like particle shapes with sizes of 50–80 nm, without any indications of amorphous character.     

Interaction of propylene with a V2O5/Al2O3 catalyst

IR-spectroscopic studies indicate that on the oxidized surface of V₂O₅/Al₂O₃ catalysts propylene interacts mainly with Brönsted acid centers to form an alcoholate type complex transforming into acetone. On the reduced surface propylene is stabilized as a -complex of V³⁺ and V⁴⁺ ions.

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- , V₂O₅/Al₂O₃ , . - V³⁺ V⁴⁺.

     

Formation of aromatic carbonium ions on V2O5/Al2O3

A comparison of IR spectra of individual toluene, mesitylene, hexamethylbenzene, triene and their carbonium ions with IR spectra of the same molecules adsorbed on V₂O₅/Al₂O₃ has indicated the formation of carbonium ions on catalyst surface.

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- , , , , - , V₂O₅/Al₂O₃ Al₂O₃, t, V₂O₅/Al₂O₃ .

     

V2O5电致变色薄膜的Raman光谱

The amorphous V 2O 5 films prepared by vacuum evaporation are unstable and easily dissolved by electrolyte during the electrochromic process, so unfit to make electrochromic materials. We found that the annealed films have enhanced stability and electrochromic properties. We studied the microstructural changes during the electrochromic process by Raman spectra and discussed the mechanism for the enhancement. The results indicated that the amorphous films annealed by 400-500℃became polycrystalline and the films contained (V 2O 5)n ordered chains which prevented the films from solution effectively and enhanced the electrochromic characteristics. When colored and decolored, the microstructure of the polycrystalline V 2O 5 films changed inversely. During the cathodic polarization process, Li+ inserted into the V 2O 5 crystal cell , formed V-O-Li band, disordered the films and UV absorption of the films blue shifted. On the contrary , during the anodic polarization process, Li +escaped from the crystal cell. The films largely restored .     

超级电容器用无定形V2O5电容性能研究

本文采用淬冷法制备了V₂O₅样品。采用FTIR、XRD对其进行了表征。结果表明所制样品为无定形V₂O₅。通过循环伏安法和恒电流充放电测试研究其电容特性，并探讨了电化学反应机理。电化学性能测试结果表明，水基电解液种类及浓度、电压范围、扫描速度、电流密度均对无定形V₂O₅ 电容性能产生影响。在1 mol·L^-1 NaNO₃溶液中，电位窗口为-0.2～0.8 V(vs SCE)范围内，5 mV·s^-1的扫描速度下，无定形V₂O₅具有良好的电容性能；在250 mA·g^-1的电流密度下，比电容为185.1 F·g^-1，循环性能良好。     

V2O5/TiO2 oxidation catalysts. I. Preparation and characterization by XRD and IR spectroscopy

V₂O₅/TiO₂ systems have been prepared by reacting VO-(acetylacetonate)₂ with differently hydroxylated TiO₂ supports. When the OH population is increased, a larger vanadia content, but well dispersed, is achieved. The presence of sodium ions leads to the formation of Na–V bronze crystallites, decreasing the dispersity of the supported phase.

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V₂O₅/TiO₂ VO()₂ TiO₂, . OH V₂O₅, , , . Na–V, .

     

V2.38Nb10.7O32.7: A V2O5-Nb2O5 mixed oxide tunnel structure related to the tetragonal tungsten bronzes

A crystal structural model for the orthorhombic compound V_2.38Nb_10.7O_32.7, which is known as “V₂Nb₉O_27.5”, was developed by means of selected area electron diffraction (SAED), Rietveld refinement and high resolution electron microscopy (HREM). The metastable compound is obtained by thermal decomposition of freeze-dried precursors as chain-like agglomerated nanoparticles or by reaction of V₂O₅ with fresh-precipitated Nb₂O₅ as more compact micro-scaled crystals. With the latter, it was possible to identify its structure for the first time (space group Cmmm). The tetragonal tungsten bronze (TTB)-type structure shows high potential for ionic intercalation, since easily reducible [V⁵⁺₂O²⁻] units are implemented in the tunnels of a rigid niobium oxide framework.     

Role of the V=O double bond in the selective oxidation of benzene on V2O5 and V2O5?MoO3 catalysts

Infrared spectra of both fresh and reductively activated V₂O₅ and V₂O₅–MoO₃ catalysts were recorded and compared with the results of catalytic measurements. The results indicate that the presence of V=O double bonds in the catalytically active mass is not essential for the selective oxidation of benzene to maleic anhydride.

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, V₂O₅ V₂O₅–MoO₃. . , V=O .