Synthesis of vanadium-phosphorus oxide catalysts deposited onto silica-carbon supports

Effect of conditions of hydrothermal and microwave synthesis of supported vanadium-phosphorus oxide catalysts in an aqueous medium on the physicochemical properties of the vanadyl hydrophosphate obtained was studied. The transformations occurring in the system were examined using X-ray phase and differential-thermal analyses, adsorption-structural method, and scanning electron microscopy.     

n-Butane oxidation over a vanadium-phosphorus catalyst

The activity of vanadium-phosphorus oxide catalysts with respect to maleic anhydride formation in n-butane oxidation has been found to correlate with the concentration of V⁴⁺ ions in the catalysts. The steady catalytic activitv of the samples examined is achieved more rapidly upon prereduction.

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Deep oxidation of hydrocarbons and gasoline (naphtha) ejections on applied oxide catalysts

The properties of VO_x and Co-Cr-O catalysts on carriers of different nature have been studied, synthesized by impregnation and grafting. It has been demonstrated that grafting of the elements to the functional groups of the carrier produces efficient catalysts for the deep oxidation of hydrocarbons (paraffins) and gasoline ejections with a low starting temperature of the catalytic reaction.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 578–583, September–October, 1991. Original article submitted July 1, 1991.     

Direct catalytic oxidation of n-butane to to tetrahydrofuran

The feasibility of partially oxidizing n-butane to tetrahydrofuran in the presence of promoted V-P-O catalyst was demonstrated. Tetrahydrofuran formation was identified by means of chromatography and mass spectrometry. From the relationship between its concentration and reaction temperature tetrahydrofuran could be proposed as a possible intermediate in the transformation of n-butane into maleic anhydride.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 159–162, March–April, 1992.     

Effect of the conditions of hydro-(organo-thermal treatment on the surface composition of oxide vanadium—Phosphorus catalysts

It was shown that hydrothermal, organothermal (with substitution of water by an organic solvent), and vacuum treatment allows altering the surface composition of V-P-Bi-O catalysts of oxidation of n-butane. The effect of the nature of the solvent, temperature, and duration of modification on the surface properties was examined. It was found that all types of treatment increase the P/V surface ratio (except for treatment in tetrahydrofuran) and decrease the Bi/V ratio (except for treatment in water). Increasing the temperature and sample modification time causes reduction of vanadium and an increase in the concentration of phosphorus on the surface. The effect of a change in the surface composition of the samples on the catalytic properties was examined and it was shown that an increase in the surface concentration of phosphorus increases the selectivity of formation of maleic anhydride. Treatment in 1-butanol, phosphoric acid, and in a vacuum are the most promising with respect to increasing the efficiency of catalysts in oxidation of butane.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 31, No. 4, pp. 250–253, July–August, 1995.     

Preparation of nano-dispersed lithium niobate by mechanochemical route

Interaction in the system of lithium carbonate–niobium pentoxide during mechanochemical treatment in air and water has been studied. Prepared samples have been investigated with the help of DTA–TG, XRD, FTIR, Raman, and UV–Vis spectroscopy, adsorption–desorption of nitrogen and TEM. Activation of reagents and direct mechanochemical synthesis are observed at 600–850 and 1,000 rpm, respectively. Lithium metaniobate samples prepared via milling possess high dispersity, defective structure, and improved photocatalytic activity, including under visible illumination.     

Influence of reaction medium on elemental distribution in depth of V?P?O catalyst grains during n-butane oxidation

Redistribution of V–P–O catalyst elements in depth of its grains during the oxidation of n-butane to maleic anhydride gives rise to changes in its physicochemical properties and activity.

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Synthesis of vanadium-phosphorus oxide catalysts supported on pyrogenic silica and titanium dioxide

Various methods for the preparation of vanadium-phosphorus oxide (VPO) catalysts supported on aerosils A-300 and A-50 and TiO₂ were studied: a traditional method (in an organic solvent under varying the support addition time, the nature of the reducing agent, and the degree of reduction of vanadium oxide) and barothermal and mechanochemical syntheses. With the use of XRD analysis, it was found that the composition of the resulting VPO phase depends on the time of support addition to the synthesis and the temperature of thermal treatment. Conditions for the formation of a supported phase of VOHPO₄·0.5H₂O, the precursor of the active component (VO)₂P₂O₇, were determined. The presence of vanadium in an oxidation state of +4 was demonstrated using EPR and UV-VIS spectroscopy. The specific surface areas and pore structures of the synthesized catalysts were determined. The catalytic properties of samples in the reactions of n-butane oxidation in an excess of the hydrocarbon and oxidative ethane dehydrogenation were studied. It was found that, as compared with traditional bulk VPO catalysts, the use of the synthesized supported VPO catalysts made it possible to improve the process characteristics of n-butane oxidation and did not change these characteristics in the reaction of oxidative ethane dehydrogenation.     

Vanadium- and molybdenum-containing compositions prepared by mechanochemical and following thermal treatments of V2O5/(NH4)2Mo2O7 (V/Mo = 0.7/0.3)

X-ray powder diffraction, DTA, FT-IR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), nitrogen adsorption, and mercury porometry were used to characterize samples prepared as a result of mechanochemical treatment (MCT) of a V₂O₅/(NH₄)₂Mo₂O₇ (V/Mo = 0.7/0.3) composition in water, ethanol, and air, as well as after calcining them at temperatures from the range 300–700°C. The MCT of nonporous powders in water yields porous materials with definite meso- and macropore sizes. Heat treatment in air at 300–450°C enhances the formation of a molybdenum substitutional solid solution in V₂O₅ and conserves rather high values of specific surface areas and pore volumes. An increase in heat treatment temperature is accompanied by the degradation of the solid solution and the formation of a V₂MoO₈ phase.