S. V. Khalameida

Effect of the mechanochemical treatment of a V2O5/MoO3 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.

Mechanochemical synthesis of BaTiO3 from barium titanyl oxalate

The effect of mechanochemical processing in air and water on the physicochemical transformations of barium titanyl oxalate has been studied using X-ray diffraction, thermal analysis, FTIR spectroscopy, temperature-programmed argon desorption, and particle size measurements. The results demonstrate that mechanochemical processing of barium titanyl oxalate in air leads to the formation of structurally imperfect barium titanate. During subsequent air calcination at 550°C, this material transforms into well-crystallized cubic BaTiO3, whereas thermal decomposition of barium titanyl oxalate only yields cubic BaTiO3 starting at 800°C. Mechanochemical processing in water leads to partial amorphization of barium titanyl oxalate, and conversion of the product to BaTiO3 requires heat treatment at 700°C. All of the BaTiO3 samples obtained via mechanochemical processing have a larger specific surface in comparison with samples prepared by conventional calcination of barium titanyl oxalate or other known processes.

Synthesis, physical–chemical, and catalytic properties of mixed compositions Ag/H3PMo12O40/SiO2

Deposited catalysts composition H3PMo12O40/SiO2 and Ag/H3PMo12O40/SiO2 have been synthesized on the basis of fumed silica, including milling technique. Physical–chemical characteristics of prepared catalysts have been studied by means of XRD, DTA-TG, FTIR, UV–Vis spectroscopy, and adsorption of nitrogen. Catalysts possess meso- or meso-macroporous structure and contain deposited Keggin heteropolycompounds. Deposition of heteropolycompounds on support with high specific surface area results in increase of selectivity to epoxide in epoxidation reactions. The use of milling during catalyst synthesis leads to further growth of selectivity of epoxides formation.

Sol-gel synthesis and properties of compositions containing heteropoly compounds in porous silica matrix

Compositions containing heteropoly compounds (ammonium phosphoromolybdate (APM) and phosphoromolybdenum acic (PMA)) are synthesized in a porous silica matrix using the sol-gel method. The obtained compositions containing 5–20 w/w % of APM and PMA are studied with the help of the X-ray-phase and differential-thermal analyses, IR and electron spectroscopy, and nitrogen adsorption. The APM and PMA maintain the Keggin structure after being introduced into an oxide matrix. The samples prepared by the sol-gel method have mesoporous and meso-macroporous structures and enhanced photocatalytic activity in comparison to the initial heteropoly compounds.

Mechanochemical degradation of Safranin T catalyzed by oxides

Mechanochemical treatment of aqueous solutions of Safranin T in the presence of oxides as catalysts was studied.

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.

Physical-chemical transformations in the system V2O5/(NH4)2Mo2O7 under hydrothermal conditions

AbstractModified compositions in the system V2O5/(NH4)2Mo2O7 have been prepared by means of mechanochemical, hydrothermal, microwave and ultrasonic treatments in aqueous medium. Chemical and phase transformations occurring on the stages of modification and following calcinations have been studied with the help of XRD, DTA-TG, FTIR and UV-Vis spectroscopy, nitrogen adsorption, and SEM. It has been established that precursors of catalytically active phases possessing meso-macroporous structure have been formed during modification. The comparison of the properties of compositions prepared via different methods has been carried out. Particularly, precursors modified via various procedures possess different morphology.

Mechanochemical preparation of vanadium- and molybdenum-containing catalysts: I. Mechanochemical activation of vanadium oxide and ammonium dimolybdate

V2O5 and ammonium dimolybdate (ADM) were mechanochemically activated in various media. Physicochemical transformations were studied using X-ray powder diffraction, differential thermal analysis, and IR spectroscopy. During mechanochemical treatment in water, water molecules are intercalated into the interlayer spaces of V2O5 and hydrate ADM to yield ammonium paramolybdate (APM) tetrahydrate.

Formation of Porous Vanadium- and Molybdenum-Containing Oxides during Mechanochemical Activation of Pore-Free Powders

Porous V- and Mo-containing oxides have been produced by mechanochemical processing of pore-free coarse powders in different environments: air, water, and ethanol. The materials have been characterized by nitrogen adsorption-desorption measurements, mercury porosimetry, scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The results demonstrate that the only effect of air milling is to reduce the particle size of the powders, whereas wet milling leads to the formation of meso- and macropores with several maxima in the pore volume-size distribution.

Photocatalytic Properties of Tin Dioxide Doped with Chromium(III), Silver and Zinc Compounds in the Oxidation of Organic Substrates by the Action of Visible Light

Sonochemical preactivation of moist gels of tin dioxide in the presence of additives of chromium(III) oxide, silver nitrate, and zinc acetate with subsequent heat thermal treatment leads to change in the porous and crystal structure of the resulted SnO2 samples obtained via doped with compounds of these metals. The doped samples have a narrower band gap and stronger absorption of visible light. Among the materials studied, Ag/SnO2 displays the highest photocatalytic activity in the oxidation of rhodamine B, safranin T, methyl orange, and phenol upon irradiation with visible light.