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⁺.

     

Lattice oxygen removal from nearly stoichiometric V2O5

The activation energy of the removal of lattice oxygen connected with slight thermal dissociation of V₂O₅ was measured by the TPD method. The small value (24.7 kcal/mol O₂) of this energy is discussed as the result of bivariant equilibria V₂O_5–x–O₂ within the range x<0.01.

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, V₂O₅, . V₂O_5–x–O₂ x<0,01.

     

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.

     

Die Bestimmung V2O2 und V4O5 nebeneinander in Kontaktkatalysatoren auf Kieselgurgrundlage

Ohne Zusammenfassung     

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.     

Products of V2O5?MoO3 catalyst reduction with benzene in the absence of oxygen

In the products of V₂O₅–MoO₃ catalyst reduction with benzene in the absence of oxygen, carbon monoxide and carbon dioxide were detected in all the reduction region of the catalyst. Maleic anhydride is formed at the beginning of the reduction (first several pulses), and p-benzoquinone was detected in some experiments at the very beginning (in the first few pulses). The remaining products, which were detected in catalytic oxidation of benzene, such as phenol, hydroquinone, biphenyl and acrylic acid, were absent in all the reduction region.

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V₂O₅–MoO₃ - . ( ) , , - , -. , , , , , .

     

Lattice oxygen removal from the V2O5?x oxide system

Lattice oxygen removal from the V₂O_5–x oxide system has been studied by the TPD method in relation to the catalytic activity of this system. The differences between the removal of oxygen from the oxidized and reduced V₂O₅ phase are discussed.

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V₂O_5–x . V₂O₅.

     

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.     

The effect of the gas atmosphere on the phase transformation in the solid solution of MoO3 in V2O5

The nature of the structure transformation occurring under the influence of oxidizing or reducing gas atmosphere in powdered oxide (V₂O₅)_0.93 (MoO₃)_0.07 has been investigated. The formation of an intermediate compound in the inner parts of the catalyst grains during the oxidation and in the subsurface layers during the reduction has been observed.     

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.     

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 .     

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.     

浆态反应器中铁／活性炭催化剂上还原研究

众所周知，费托合成（Fischer-Tropsch synthesis,FTS)反应是一个有理论与应用价值的研究课题。数十年来，学者们已发现了铁系，钴系和钌系等具有优良FTS反应性能的催化剂体系，铁／活性炭（Fe/Activated Carbon,AC)催化剂是中国科学院大连化学物理研究所八十年代末开发的一类费托合成催化剂，由于活性炭载体发达的孔结构使得该催化剂上FTS反应产物中汽油，柴油选择性高（烃类碳数小于20）和油收率大（C5^ ,112g/m^3 sysgaa)^[1,2]，具有工业放大前景。本文采用1L浆态床反应器，应用不同的还原方法（原位高压还原和反应器外还原）和XRD物相表征手段，了铁／活性炭催化剂在浆态床中的还原与反应问题，得到了一些有用的信息。     

Vapor phase oxidation of 2-methylpyridine on V2O5/TiO2 (anatase) catalysts

The influence of catalyst composition and reaction parameters on the yield of pyridine-2-carboxaldehyde has been studied for the title process. It has been established that monolayer vanadia on TiO₂ (anatase) is a highly selective catalyst for the partial oxidaton of 2-methylpyridine to pyridine-2-carboxaldehyde.

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-2-. , TiO₂ () 2- -2-.

     

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.

     

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 .

     

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 .

     

Comparative study of the catalytic properties of V2O5, Nb2O5 and Ta2O5 in the oxidation of methanol to formaldehyde

The selectivity of the oxides under consideration to the oxidation of methanol to formaldehyde is shown to increase in the sequence V₂O₅–Nb₂O₅–Ta₂O₅. The same sequence corresponds to the decrease in specific activity. The activation energy of the reaction is 12 kcal/mol for V₂O₅, 14 kcal/mol for Nb₂O₅ and 22 kcal/mol for Ta₂O₅.

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, V₂O₅–Nb₂O₅–Ta₂O₅. . : V₂O₅ 12 /, Nb₂O₅ 14 / Ta₂O₅ 22 /.

     

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.     

A cataluminescence gas sensor based on nanosized V2O5 for tert-butyl mercaptan

This work proposed a gas sensor for the determination of tert-butyl mercaptan, one of the highly toxic volatile sulfur compounds, which was based on cataluminescence emission during its catalytic oxidation on the surface of nanosized V₂O₅. The cataluminescence characteristics and the optimum conditions, including the morphology of sensing material, the wavelength of cataluminescence emission, the oxygen flow rate and working temperature were investigated in detail. Under the optimized conditions, the calibration curve of the relative cataluminescence intensity versus the concentration of tert-butyl mercaptan vapor was made, with the linear range of 5.6-196 μg mL⁻¹ and the detection limit of 0.5 μg mL⁻¹ (S/N = 3). The relative standard deviation (R.S.D.) (n = 5) of relative cataluminescence intensity for 84 μg mL⁻¹ tert-butyl mercaptan was 3.6%. There is no or weak response to some common substances, such as formic acid, alcohol (methanol, ethanol, propanol, isopropanol, n-butanol, isoamyl alcohol), o-dichlorobenzene, acetonitrile, ethyl acetate, aldehyde (formaldehyde, acetaldehyde and propanal), 1,2-dichloroethane and ammonia. Furthermore, the proposed sensor was successfully used for determining tert-butyl mercaptan in four artificial samples, with a good recovery. The results demonstrated that the proposed gas sensor had a promising capability for the tert-butyl mercaptan in routine monitoring.