Kinetics of oxidation of acrolein on a vanadium-molybdenum oxide catalyst

A kinetic study has shown that, in the range of low conversions, the reaction rate depends only on the partial pressure of oxygen. Comparison of the oxidation of acrolein and I-deuteroacrolein suggests that the splitting of the H–CO bond is not rate-limiting.

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, , , . 1- , H–CO .

     

Formation of the active component of a vanadium-molybdenum oxide catalyst in acrolein oxidation

An acrolein-containing reaction mixture reduces V⁵⁺ to V⁴⁺, accompanied by decomposition of the ammonium salt of vanadium-molybdenum-silicon heteropolyacid (HPA) to form a compound with the tentative composition of VMo₃O_11+x, which is the active component of the catalyst.

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V⁵⁺ V⁴⁺, VMo₃O_II+X, .

     

Study of the steps of acrolein oxidation over a vanadium-molybdenum catalyst

Acrolein is oxidized to acrylic acid over a V–Mo catalyst by lattice oxygen, while the formation of CO₂ also involves gas phase oxygen. The steady state of catalyst reduction is about 5% monolayer and is characterized by an oxygen binding energy of 61 kcal/mol.

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V–Mo- , CO₂ . 5% 61 /.

     

Catalytic oxidation of propylene to acrolein on a multicomponent oxide catalyst

Rate equations have been found and reaction schemes for oxidation of propylene to acrolein and acrylic acid have been suggested.

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.

     

Surface component distribution in a vanadium-molybdenum oxide catalyst for making acrylic acid from acrolein

A scanning electron microscope and microprobe analyzer have been used to examine the surfaces of vanadium-molybdenum catalysts on aerosil. It is found that the phase VMo₃O₁₁ is formed, which is dispersed on the SiO₂. MoO₃ crystals of various shapes occur at the surface of the dispersed phase. It is suggested that this catalyst is highly active in oxidizing acrolein to acrylic acid because of the presence of VMo₃O₁₁.Translated from Teoreticheskaya i Éksperinental'naya Khimiya, No. 3, pp. 374–378, May–June, 1986.     

Catalytic properties of V?Sb?O systems in acrolein oxidation

Catalytic properties of V-Sb-O systems in acrolein oxidation have been studied. It has been established that the changes in the activity and selectivity of the catalysts are due to the phase and chemical properties of the system.

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-- . , .

     

Catalytic properties of V?Mo?O systems in acrolein oxidation

Catalytic properties of V–Mo–O systems have been studied in acrolein oxidation. When catalysts are activated in reaction mixtures at 673 K, then a solid solution of molybdenum oxides in reduced vanadium oxides is formed, which is responsible for deep oxidation. Also, several compounds are produced, which by their activity and selectivity to acrylic acid formation are arranged in the sequences VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, and VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅, respectively.

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V–Mo–O . 673 K , , , : VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, : VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅.

     

Catalytic properties of phosphorus and sodium promoted VMo catalysts in acrolein oxidation

The change in the ratio of stepwise and concerted routes of acrolein conversion to complete oxidation products upon promotion of a V-Mo catalyst by phosphorus and sodium dopants is ascribed to modification of surface acid-base properties.

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V-Mo - .

     

Catalytic oxidation of acrolein to acrylic acid over a molybdenum-vanadium catalyst

By the method of gas chromatography it has been found that the adsorption of acrolein takes place without dissociation whereas acrylic acid is adsorbed dissociatively. The adsorption of water vapor proceeds also dissociatively and results in increasing the number of the Brönsted acid centers. The presence of water vapor has a positive effect on the desorption rate of acrylic acid and a negative effect on the reoxidation rate of the catalyst.

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, , . , . , — .

     

Catalytic properties of Ti?Mo oxide catalysts in propylene oxidation

Catalytic properties of Ti–Mo oxide catalysts are shown to be determined to a great extent by the Ti–Mo heteropoly acid anchored to the TiO₂ surface which is formed during the catalyst preparation.

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, - - , .

     

ESR investigation of vanadium-molybdenum oxide catalysts

Upon calcination of vanadium-molybdenum catalysts in air at 500°C two ESR signals are observed. They are attributed to a solid solution of MoO₃ in V₂O₅ (a) and to the incorporation of VO²⁺ into the compound V₂MoO₈ (b).

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500°C - - , MoO₃ V₂O₅, - VO⁺² V₂ MoO₅.

     

Catalytic properties of nickel oxide and its solid solutions in magnesium oxide in hydrogen oxidation

Temperature dependence of the reaction rate of H₂ oxidation on nickel oxide and solid solutions of nickel ions in MgO prepared at 573–1373 K, has been studied. The variation of the catalytic properties with temperature is attributed to the presence of nickel ions in different oxidation states simultaneously, i. e. Ni(II) and Ni(III).

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H₂ MgO, 573–1373 K. — Ni(II) Ni(III).

     

Studies of copper-modified V?Mo oxide catalyst for acrolein oxidation to acrylic acid

Modification of a V–Mo oxide catalyst by copper improves its catalytic properties due to the formation of a variable composition V–Cu–Mo–O phase with varying the ratio Mo/Me (Me=V+Cu).

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T–Cu–Mo–O, Mo/Me, Me=V+Cu.

     

Bond energy of surface oxygen in multicomponent oxide catalysts for propylene oxidation to acrolein

Bond energy of surface oxygen for the multicomponent oxide catalyst Mo₁₂Bi₁Ni_2.5Fe₃Co_4.5K_0.07P₁/SiO₂ has been measured in conditions of propylene oxidation and found to be 272 kJ/mol.

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Mo₁₂Bi₁Ni_2,5Fe₃Co_4,5K_0.07P₁/SiO₂, , 272 /.

     

Vapor-phase oxidation of 2,6-dimethylpyridine on vanadium-molybdenum catalysts

The catalytic activity of vanadium-molybdenum catalysts in oxidation of 2,6-dimethylpyridine is compared with their adsorption properties and phase composition. The increase of molybdenum content results in the decrease of irreversible adsorption and total conversion of 2,6-dimethylpyridine. The reversible adsorption depends on the phase composition and character of crystalline modifications of MoO₃ in the catalysts.

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2,6- . 2,6-. MoO₃ .

     

TPD studies of benzene adsorption over vanadium-molybdenum oxide catalysts

Benzene is shown to be adsorbed on the surface of a V₂O₅-MoO₃ catalyst in two forms. The activation energies of benzene desorption for its first and second forms are 50 and 134 kJ/mol, respectively, in the latter case the adsorption proceeding with dissociation.

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, - . 50 / –134 /, .

     

氮掺杂氧化石墨催化苄胺氧化

酰胺类化合物是重要的化工原料和生物医药合成的中间体,但其制备大部分需要使用贵金属催化剂,因此,发展廉价金属乃至非金属催化剂具有重大意义.本文使用化学气相沉积法合成了氮掺杂的层状氧化石墨材料,并将其应用于苄胺氧化反应中,实现了液相中酰胺合成的非金属催化过程.在水相中可以活化氧气较高产率地生成亚胺化合物N-苄亚甲基苄胺,并且成功实现了在氨水反应介质中高转化率和选择性地生成苯甲酰胺.此外,对反应中的影响因素进行了逐一研究,并从多方面探究了该反应中氨水的作用以及反应最可能的历程,提出了一条经过包括亚胺在内的多个中间产物的反应路径.本工作对于研究碳氢键的活化过程以及拓宽碳催化领域进行了有益的尝试.     

BiMo基复合氧化物催化剂晶格氧性质与丙烷选择氧化性能

研究了不同组成、结构的BiMo基复合氧化物催化剂的丙烷选择氧化至丙烯醛的性能.X射线衍射(XRD)、X光电子能谱(XPS)、原位傅里叶变换激光拉曼光谱(FT-LRS)、电子顺磁共振(ESR)等多种表征结果表明,BiMo基复合氧化物催化剂上丙烷经由中间物丙烯选择氧化至丙烯醛,催化剂的晶格氧为选择性活性氧物种.丙烷直接氧化下丙烷至丙烯醛的选择性和收率与催化剂的Mo=O物种的氧化-还原性质密切关联,而Mo=O物种的性质又取决于Mo离子的配位环境,Mo=O物种的选择性转化丙烷经由丙烯至丙烯醛活性随畸变MoO6八面体、共顶点八面体、共边八面体、MoO4四面体配位环境递增.组成、结构优化调变的催化剂上丙烷选择氧化至丙烯醛选择性和收率可达45%和13.5%,催化剂中具有选择氧化活性的晶格氧物种数可达258 μmol/g.     

Study of the mobility of lattice oxygen in complex oxide catalysts for partial oxidation of propylene to acrolein

The amount of oxygen in the lattice of solids that participates in the elementary stages of partial propylene oxidation is determined for two types of Co-Mo-Bi-Fe-Sb-K-O catalysts (I, II) differing in the method of introduction of antimony and potassium. Two independent methods are used: (1) on the basis of the yield of the oxygen-containing products of propylene oxidation by oxygen of the catalyst in a pulse regime and (2) with the use of Möessbauer spectroscopy. Coincidence of the results obtained by both methods indicates that the active oxygen of the catalyst lattice is formed during redox transformations of iron(III) molybdate entering the composition of the catalysts. Data on the reduction of the catalysts in a pulse regime at various temperatures, which were processed in the framework of the diffusion model, allowed the estimation of the rate constants for diffusion of the lattice oxygen. An increase in the mobility of the lattice oxygen in catalyst I, which is modified with a small amount of antimony as compared to catalyst II, results in an increase in the overall productivity of the sample and in a decrease in the selectivity of propylene oxidation to acrolein. This correlates with the increase in the total amount of the lattice oxygen participating in the process.