The oxidation of toluene on transition metal oxides

The oxidation of toluene on pure vanadium and molybdenum oxides was found to follow independent paths; it was benzene ring oxidation on V₂O₅ and side chain oxidation on MoO₃. On mixed xV₂O₅ · yMoO₃ oxides, the main reaction was the addition at the double bond preferably positioned meta rather than one-electron oxidation.     

Selective oxidation of methanol on V2O5 and V2O5?MoO3 supported on montrmorillonite

Methanol oxidation on V₂O₅ and V₂O₅–MoO₃ catalysts supported on montmorillonite has been studied in the temperature range of 250–500°C. The V₂O₅–MoO₃ containing sample shows higher selectivity towards formaldehyde formation than the V₂O₅ catalyst.     

Untersuchungen zum ternären System V/Mo/O

Investigation on the Ternary System V/Mo/O During chemical transport reactions mixtures of pseudo-binary line of intersection V₂O₅/MoO₃ are separated into two phases, the V₂O₅-(α) phase, which MoO₃-content depends on the oxygen partial pressure during the deposition and the MoO₃ phase which contains no more than 1% (n/n) V₂O₅. Ternary compounds do not exist on the pseudo-binary line. V₉Mo₆O₄₀ is formed by the reaction of V₂O₅ and MoO₃ (3:2) under exclusion of oxygen. The compound may be chemically transported under the own oxygen coexistence pressure. It was shown by total pressure measurements of V₂O₅/MoO₃ starting mixtures that the insertion of MoO₃ in the α-phase and the formation of the V₉Mo₆O₄₀ phase respectively is connected with elimination of oxygen and the reduction of V^V to V^IV in equivalence of the quantity of incorporated MoO₃.     

Plasma-Catalytic Oxidation of Toluene on MnxOy at Atmospheric Pressure and Room Temperature

Mn_xO_y/SBA-15 catalysts were prepared via the impregnation method and utilized for toluene removal in dielectric barrier discharge plasma at atmospheric pressure and room temperature. The catalysts were characterized by X-ray diffraction, N₂ adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction, and O₂ temperature-programmed desorption methods. The characterization results indicated that manganese loading did not influence the 2D-hexagonal mesoporous structure of SBA-15. The catalyst had various oxidation states of manganese (Mn²⁺, Mn³⁺, and Mn⁴⁺), with Mn³⁺ being the dominant oxidation state. Toluene removal was investigated in the environment of pure N₂ and 80 % N₂ + 20 % O₂ plasma, showing that the toluene removal efficiency and CO₂ selectivity were noticeably increased by Mn_xO_y/SBA-15, especially in the presence of 5 % Mn/SBA-15. This activity was closely related to the high dispersion of 5 % Mn on SBA-15 and the lowest reduction temperature exhibited by this catalyst. Mn loading increased the yield of CO₂ in the N₂ plasma and promoted the deep oxidation of toluene. During toluene oxidation, oxygen exchange might follow a pathway, wherein bulk oxygen was released from the Mn_xO_y/SBA-15 surface; gas-phase O₂ subsequently filled up the vacancies created on the oxide. Each of the manganese oxidation states played an important role; Mn₂O₃ was considered as a bridge for oxygen exchange between the gas phase and the catalyst, and Mn₃O₄ mediated transfer of oxygen between the catalyst and toluene.     

Oxidative ammonolysis of 3-picoline on mixed oxide catalysts

The oxidative ammonolysis of 3-picoline has been studied on the following catalysts: V₂O₅ on corundum, V₂O₅ with the addition of 1% of H₂WO₄ on corundum, V₂O₅ + MoO₃ + P₂O₅ (1∶0.35∶0.35) on silica gel, V₂O₅ + Al₂O₃, and a melt of V₂O₅ + TiO₂ (1∶0.22). Mixed catalysts of vanadium and titanium oxides exhibited the highest activity and selectivity. With the passage of 25–45 moles of oxygen (in the form of air), 5–10 moles of ammonia, and 50–70 moles of water per mole of 3-picoline at a temperature of 390–410° C, the amount of nicotinonitrile formed on these catalysts amounted to 85–90% of the theoretically possible amount.     

Vapor-phase oxidation of β-picoline to nicotinic acid on V2O5 and modified vanadium oxide catalysts

Modification of V₂O₅ with Ti, Sn, Zr, Nb, and Al oxides improves the activity and selectivity of the vanadium oxide catalyst in vapor-phase oxidation of β-picoline to give nicotinic acid. It is shown that the conversion of β-picoline and the yield of nicotinic acid on two-component V₂O₅-TiO₂, V₂O₅-SnO₂, V₂O₅-ZtrO₂, V₂O₅-Nb₂O₅, and V₂O₅-Al₂O₃ catalysts may be several times those on the V₂O₅ catalyst. It was found that, on passing from V₂O₅ to double-component vanadium-containing catalysts, the proton affinity of active oxygen bonded to vanadium, calculated by the quantum-chemical method, grows simultaneously with the increase in the activity of the catalysts in the oxidation reaction.     

Oxidative desulfurization of benzene fraction on transition metal oxides

It is established that molecular oxygen is able to oxidize thiophene selectively in a mixture with benzene on V₂O₅ · MoO₃. The introduction of thiophene inhibits the oxidation of benzene. It is shown that the conversion of thiophene during operation of the catalyst is reduced at first and then increases until it reaches its initial value.     

Effect of γ-irradiation and doping with MoO3 and V2O5 on surface and catalytic properties of manganese oxides

The effects of γ-irradiation (0.2–1.6 MGy), thermal treatment and doping with MoO₃ and V₂O₅ (0.25–4 mol%) on the surface and catalytic properties of manganese oxides prepared by thermal decomposition of manganese carbonate at 400°C and 600°C have been investigated. The techniques employed were X-ray diffraction, nitrogen adsorption at −196°C, oxidation of CO by O₂ at 120–220°C and decomposition of H₂O₂ at 20–50°C. The results revealed that γ-irradiation decreased the particle size of manganese oxides, increased their specific surface areas, decreased the amount of surface excess oxygen and decreased their catalytic activities. The doping with MoO₃ and V₂O₅ conducted at 600°C brought about a measurable decrease in the BET-surface area and catalytic activities of the treated solids. These results were discussed in terms of splitting of manganese oxide particles and removal of chemisorbed oxygen by treating with γ-irradiation and formation of manganese molybdate and vanadates by treating with the used dopant oxides.     

Keggin型钼钒磷杂多酸催化剂上丙烷选择氧化性能的研究

系统研究了不同数目V⁵⁺取代的钼钒磷杂多酸H_3+nPMo_12－nV_nO₄₀ (n＝0～4)催化剂上丙烷选择氧化反应性能. 通过BET, IR, TPR, 紫外-可见光谱等表征手段对催化剂的理化性质进行了考察, 并对催化剂的结构-性能关系进行了初步关联. 在杂多酸的一级结构中, V⁵⁺对Mo⁶⁺的取代不仅改变了杂多阴离子金属-氧桥的键强以及晶格氧的插入能力, 而且也相应地调变了样品的酸量. 催化剂活性随V⁵⁺取代数量的递增而增强; 适宜数量的V⁵⁺取代提高了含氧酸产物的选择性, 而过量的V⁵⁺取代则导致部分氧化产物的深度氧化. 考察了在Keggin型杂多酸二级结构上引入钒物种的影响, 也即将钒物种(VO)²⁺作为抗衡离子取代部分质子以调变催化剂的结构与性质. 实验表明, 处于一级结构和二级结构[(VO)²⁺抗衡离子]中的V在反应中均可离析出少量V₂O₅物种. 适宜量的(VO)²⁺物种以及离析出来的少量V₂O₅物种可能均对催化剂的性能有贡献. 显然, 钒在不同位置的价态变化以及形态的不同, 会导致催化性能的相应改变.     

Vapour phase synthesis of quinoline from aniline and glycerol over mixed oxide catalysts

The vapour phase synthesis of quinoline from aniline and glycerol (1:2 mole ratio) in a single step was investigated over ZnO–Cr₂O₃, CuO–ZnO/Al₂O₃, MoO₃–V₂O₅/Al₂O₃ and NiO–MoO₃/Al₂O₃ catalysts in the presence of air at 623–723 K under normal atmospheric pressure. Among these catalysts investigated, the CuO–ZnO/Al₂O₃ combination effectively performed this reaction with high activity and selectivity.     

Crystal growth,structure, and properties of manganese orthovanadate Mn3(VO4)2

Manganese orthovanadate Mn₃(VO₄)₂ single crystals were grown for the first time from a flux of MnO/V₂O₅/MoO₃. The flux and oxygen partial pressure used are the key factors for the crystal growth and prevention of the oxidation of Mn²⁺ and the reduction of V⁵⁺ during the crystallization process. The reduction and oxidation chemistry of Mn₃(VO₄)₂ was studied. Mn₃(VO₄)₂ is isostructural with magnesium orthovanadate Mg₃(VO₄)₂, orthorhombic, space group Cmca, a=6.247(1) Å, b=11.728(2) Å, c=8.491(2) Å and Z=4, as determined by single crystal X-ray diffraction. Because it is a Mn²⁺ deficient spinel structure there are two-dimensional sheets of Mn²⁺O₆ octahedra within the structure which show unusual ferrimagnetic properties.     

Effect of the mechanochemical treatment of a V<Subscript>2</Subscript>O<Subscript>5</Subscript>/MoO<Subscript>3</Subscript> oxide mixture on its properties

The mechanochemical treatment of a V₂O₅/MoO₃ oxide mixture (V/Mo = 70/30 at %) was performed in planetary and vibratory mills under varying treatment times and media. The resulting samples were characterized using XRD analysis, micro-Raman spectroscopy, and XPS; their specific surface areas and catalytic activities in n-butane and benzene oxidation reactions were determined. It was found that the treatment of the oxide mixture in water resulted in chaotic degradation of the parent oxides, a decrease in crystallite sizes, and an increase in the specific surface area at a sufficiently uniform oxide distribution over the sample. The treatment in ethanol was accompanied by an anisotropic deformation of the V₂O₅ crystal by layer sliding in parallel to the vanadyl plane (010) and a chaotic degradation of MoO₃ crystals. This process was accompanied by the partial nonuniform supporting of vanadium oxide crystals onto the surface of molybdenum oxide to increase the V/Mo ratio on the sample surface. In this case, the particle size of oxides decreased and the specific surface areas of samples increased. It was found that the treatment of the oxide mixture in air (dry treatment) resulted in the most significant decrease in the sizes of V₂O₅ and MoO₃ crystals and a growth in the specific surface area. The amorphization of the parent oxides and the formation of MoV₂O₈ were observed as the treatment time was increased; in this case, an excess of amorphous vanadium oxide was supported onto the surface of this compound. It was found that, in all types of mechanochemical treatment, the binding energies of the core electrons of vanadium and molybdenum remained almost unchanged to indicate the constancy of the oxidation states of these elements. Mechanochemical treatment resulted in an increase in the activity of the samples in n-butane and benzene oxidation reactions and in an increase in the selectivity of maleic anhydride formation. In this case, an increase in the specific catalytic activity of the samples correlated with a decrease in the crystallite size of vanadium oxide, whereas selectivity correlated with an increase in the relative concentration of the V₂O₅ plane (010). In these reactions, samples after dry treatment exhibited a maximum activity, which can be related to the formation of MoV₂O₈.     

Phase Relations in The V2O5–MoO3–α-Sb2O4 System in The Solid State in Air Atmosphere

The phase equilibria established in the V₂O₅–MoO₃–α-Sb₂O₄ system in the solid state in an air atmosphere were examined by using XRD and DTA methods. The obtained results allowed us to find that in this system a novel compound is formed involving three oxides. Its formula can be written as Sb₃V₂Mo₃O₂₁. The synthesis of this compound requires picking up the atmospheric oxygen. X-ray characteristics of this compound were determined and it was found that it melted incongruently at 740°C. The results obtained until now allow us to divide the investigated V₂O₅–MoO₃–α-Sb₂O₄ system into five partial subsystems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxidation of sulfites on vanadium-molybdenum oxides

The low temperature emission of ¹O₂ singlet oxygen from xV₂O₅ · yMoO₃ binary oxides is investigated by means of flash desorption. Conditions for the generation of ¹O₂ on their surfaces are determined, along with the correlation between the amount of ¹O₂ and the degree of NaHSO₃ conversion in the oxidation reaction. It is shown that on the surface of oxides there are oxygen species that upon decomposition produce ¹O₂ involved in the oxidation of HSO ₃ ^? .     

V2O5/C catalyst for liquid phase oxidation of glyoxal to glyoxylic acid

A study of the catalytic activity of V₂O₅/C catalyst for the oxygen oxidation of glyoxal has been made, showing that glyoxylic acid can be formed without control of pH value and there is little oxalic acid from the excessive oxidation of glyoxylic acid. The studies of XRD and TEM have shown that V₂O₅ diffraction peaks gradually strengthen with the increase of the content of V₂O₅. With the content of 3% V₂O₅ and the calcination temperature of 573 K, V₂O₅/C catalyst displayed the best activity and selectivity. The conversion of glyoxal and the selectivity of glyoxylic acid reached 18.76% and 77.70% after 5 h, respectively. Moreover, V₂O₅/C catalyst showed small deactivation after recycling three times, which indicates that V₂O₅/C has a higher stability than noble metal catalysts in the reaction medium. Supported by the Technology Research and Development Project for University of Shanxi Province of China (Grant No. 20051272)     

Catalytic properties of oxides in vapor phase oxidation of acetone

The temperature dependences of the rate of oxidation of acetone vapors by oxygen on oxide surface catalysts: V₂O₅, Co₃O₄., MoO₃ and TiO₂ (rutile), and the industrial catalyst VKSh were determined. A series of the catalytic activity of the above surface catalysts was established. The relationship between the catalytic properties of the oxides in the oxidation of acetone and their redox and acid-base characteristics was analyzed. The catalytic activity of the oxides in the oxidation reaction of acetone and methanol were compared.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 114–117, January–February, 1988.     

Selective oxidation using catalyst electrodes supported on solid electrolyte

The major oxygenated products of the selective oxidation of 1-butene by using a catalyst electrode were maleic anhydride on V₂O₅/YSZ/Ag and butadiene on MoO₃–Bi₂O₃–Ag/YSZ/Ag. Their selectivities were enhanced as compared with the non-electrochemical system.     

Investigation on the TeO2–MoO3–V2O5 System. II. Properties of the obtained glasses

Some of the properties of glasses obtained in the systems TeO₂–MoO₃ and TeO₂–MoO₃–V₂O₅ had been studied. A good correlation between the properties and the phase diagram of the TeO₂–MoO₃ system was established. The glass resistance-composition function varied between 6.85 · 10⁹ ohm · cm and 2.93 · 10¹⁰ ohm · cm. The isolines of the properties (softening temperature, density, resistance at room and higher temperatures and activation energy) of the glasses obtained from the TeO₂–MoO₃–V₂O₅ system were ploted. The electrical resistance is influenced by the concentration of V₂O₅ and MoO₃ and by temperature. The glass absorption characteristics of thin layers were determined in the visible range.     

Formation of rutile-type Ta(IV)O2 by shock reduction and cation-deficient Ta0.8O2 by subsequent oxidation

Ta₂O₅ is reduced to Ta(IV)O₂ with the rutile structure by shock-loading to 50–60 GPa. Tetragonal unit cell parameters at room conditions are measured to be a = 4.7518(5)Å, c = 3.0878(4) Å, $\text{c}\text{a}\text{= 0.6498(1)}$, and V = 69.72(1) ų. The chemical composition is thermogravimetrically determined to be Ta_0.97±0.04O₂ by heating shock-reduced products in an oxygen gas flow to 1200°C. In the oxidation process a cation-deficient rutile-type compound Ta_0.8O₂ is found to be metastably formed.     

On the nature of oxygen particles in the low-temperature desorption from vanadium oxides

The nature of oxygen particles produced in low-temperature desorption from V₂O₅ and V₂O₅ · MoO₃ was studied. It was found that there was no low-temperature desorption from samples in the presence of a quartz trap cooled to −195°C, which was evidence of the absence of possible desorption of O₃ and the presence of ¹Δ_g O₂. Under these conditions, the latter was frozen completely, and ozone was not.