Influence of mechanochemical activation on structure and some properties of mixed vanadium–molybdenum oxides (original) (raw)
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Effect of mechanochemical modification on the catalytic properties of the V2O5−TiO2 system
Theoretical and Experimental Chemistry, 2000
The mechanochemical modification of a V-Ti-O composition in ethanol and water was carried out in a planetary mill X-ray phase analysis was used to show that the X-ray diffraction patterns of the modified samples result.from overlapping of the patterns of the individual oxides, while the modification conditions affect the relative intensity of the reflections. The micro-Raman spectra indicated that homogeneity of this composition is achieved after only 30 min treatment in water and 20 min treatment in ethanol X-ray photoelectron spectroscopy showed that the medium and duration of the treatment do not affect the valence state of the elements but do significantly alter the ratio of the elements in the surface layer. Mechanochemical treatment of mixtures of vanadium and titanium oxides permits enhancement of the activity and selectivity of the V-Ti-O compositions in the oxidation of n-pentane and o-.~lene.
Physicochemical and textural characterization of vanadium–magnesium mixed oxides
Materials Letters, 2004
A series of vanadium -magnesium mixed oxides (V -Mg -O) with a mesoporous structure used for the propane oxidative dehydrogenation was synthesized by combining the impregnation and precipitation methods. Several techniques such as N 2 physisorption, X-ray diffraction (XRD), FTIR and temperature-programmed reduction (TPR) were applied to characterize the textural properties, phase composition and surface oxygen reduction features of the oxides. Textural properties of the calcined V -Mg -O oxides were found very sensitive to chemical composition: bimodal or multimodal pore size distributions was developed, which progressively varied with vanadium content. XRD analysis and infrared (IR) characterization confirm that the V -Mg -O oxides consist of a Mg 3 V 2 O 8 structure with VO 4 tetrahedral units together with periclase phase. Magnesium incorporation with vanadium completely inhibits the formation of V 2 O 5 containing exposed VMO bonds. TPR results showed two peaks located between 500 and 750 jC, corresponding to the reduction of V 5 + species in distorted VO 4 units and to V 5 + species belonging to bulk Mg orthovanadate, respectively. D 2004 Elsevier B.V. All rights reserved.
Preparation and Characterization of Vanadium Oxide Deposited on Thermally Stable Mesoporous Titania
The Journal of Physical Chemistry B, 2006
The homogeneous liquid-phase direct catalytic oxidation of benzene to phenol was performed at 60°C in acetonitrile solvent using various catalysts of VO x supported on aluminum-substituted mesoporous silica (Al-MPS) and hydrogen peroxide as the oxidant. We employed the molecular designed dispersion method to prepare the VO x catalyst supported on Al-MPS. The deposit of monolayer VO(acac) 2 complexes (acac: acetylacetonate) could be achieved by hydrogen bonding or a ligand-exchange mechanism and subsequently decomposition of organic acac ligands in an oxygen atmosphere at elevated temperature, yielding the six coordination of V V center. The octahedral vanadium oxide samples possess much mobile ligands (i.e., H 2 O or solvent) around the catalytic center that could be easily substituted by hydrogen peroxide and yielded the active peroxo intermediate for the hydroxylation of benzene. From the studies of powder X-ray diffraction, N 2 adsorption and desorption isotherms, diffuse reflectance UV-vis, and electron paramagnetic resonance, we show that highly dispersed isolated vanadium oxide catalyst centers could be formed. For comparison, we also prepared the tetrahedral vanadium oxide catalyst by the coordination of V V center with mono-, di-, and triamine-modified SiO 2 . The tetrahedral coordination of vanadium oxide catalysts lack mobile ligands with good leaving groups in the catalytic medium and yield a lower activity toward the hydroxylation of benzene.
Preparation and characterization of vanadium oxide (V2O5) sheet like nanostructure
AIP Conference Proceedings, 2022
Vanadium oxide was deposited on mesoporous titania by the molecular designed dispersion method to investigate the potential properties of these catalysts. Mesoporous titania was synthesized following the evaporation-induced self-assembly (EISA) method with a subsequent treatment with ammonia to increase the thermal stability. As a result, the mesoporous titania obtained shows a high surface area (∼350 m 2 /g) and high stability. Vanadium oxide was deposited by the MDD method using a vanadyl acetylacetonate complex that was transformed into VO x after a controlled calcination in air flow at 300°C. The mesostructure and porosity characteristics of titania remain even until the maximum V-loading was reached (0.4 mmol/g), as it was shown by N 2 sorption measurements at-196°C. The catalysts were characterized by chemical analysis, Fourier transform infrared-photoacoustic spectroscopy (FTIR-PAS), UV-vis diffuse reflectance (DR), and Fourier transform Raman spectroscopy. Raman spectra showed isolated V species for the different V-containing catalysts. Furthermore, UV-vis-DR revealed a higher contribution of polymeric species as the V loading increases. The VO x /mesoporous titania catalysts were highly active in the selective catalytic reduction of NO x. A high activity in the NO conversion was observed, which increases with increasing metal loading.
Vanadium incorporated molybdophosphoric acid (MPAV) was used as a precursor to prepare Mo V P oxide supported on alumina catalysts. The catalysts were prepared by impregnation of MPAV on alumina and subjecting them to calcination at 450 • C. The catalysts were characterized by X-ray diffraction, Fourier transform infrared, temperature programmed reduction and X-ray photo electron spectroscopy to study the nature of interaction of MPAV with Al 2 O 3 . The characterization results revealed the decomposition of MPAV Keggin ion on alumina and the formation of its constituent oxides during calcination. The nature of metal oxide species formed on the surface of alumina depended on MPAV loading and the V content. The crystalline nature of metal oxides derived from the decomposition of MPAV x increased with increase in vanadium content. The activity of the catalysts during the ammoxidation of m-xylene also depended on MPAV loading and the content of V, as they were responsible for the dispersion of the constituent metal oxides on alumina.
Materials
This study deals with the behavior of molybdenum–vanadium (Mo/V) mixed oxides catalysts in both disproportionation and selective oxidation of toluene. Samples containing different Mo/V ratios were prepared by a modified method using tetradecyltrimethylammonium bromide and acetic acid. The catalysts were characterized using several techniques: nitrogen adsorption–desorption isotherms, X-Ray diffraction (XRD), ammonia temperature-programmed desorption (TPD-NH3), temperature-programmed reduction by hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier-transform infrared-spectroscopy (FTIR) and ultraviolet-visible spectroscopies (UV–VIS). The XRD results evidenced the presence of orthorhombic α-MoO3 and V2O5 phases, as well as monoclinic β-MoO3 and V2MoO8 phases, their abundance depending on the Mo to V ratio, while the TPD-NH3 emphasized that, the total amount of the acid sites diminished with the increase of the Mo loading. The TPR investigations indic...
Structure, properties, and MEMS and microelectronic applications of vanadium oxides
Sadhana, 2009
Vanadium oxides have for many decades attracted much attention for their rich and unique physical properties which pose intriguing questions as to their fundamental origins as well as offering numerous potential applications for microelectronics, sensors, and microelectromechanical systems (MEMS). This paper reviews the unique structure and properties of the two most common vanadium oxides which have entered into microfabricated devices, VO 2 and V 2 O 5 , and some of the past and future device applications which can be realized using these materials. Two emerging new materials, sodium vanadium bronzes and vanadium oxide nanotubes are also discussed for their potential use in new microelectronic devices.
2009
Abstract. V-Mg-Al mixed-oxide catalysts for oxidative dehydro-genation of propane were prepared by thermal decomposition of Mg-Al-layered double hydroxides with vanadium interlayer doping. The obtained catalysts were tested for the oxidative dehydrogenation of propane, obtaining good results in catalytic activity (conversion 16.55 % and selectivity 99.97 %). Results indicated that catalytic per-formance of these materials depends on how vanadium is integrated in the layered structure, which is determined by the Mg/Al ratio. Vanadium interlayer doping modifies the oxidation state of vanadium and consequently catalytic properties. Surface properties were studied by X-ray photoelectron spectroscopic and diffuse reflectance, UV-vis-ible spectroscopy, and temperature programmed reduction (TPR). The analyses provided information about the oxidation state, before and after the reaction. From these results, it is suggested that selectivity to propylene and catalytic activity depend mainly o...
Mechanochemical Modification of V-Mo-Zr Oxide Compositions
Acta Physica Polonica A, 2014
The inuence of mechanochemical treatment by high-energy ball milling in two media (water and ethanol) of dierent V2O5/MoO3/ZrO2 compositions on its structure modication and photocatalytic properties is considered. Milling process in both media leads to nal products Zr(V2O7) and Mo4V6O25. Their subsequent thermal treatment provides to formation of Zr(MoO4)2 and V2MoO8 composition. They show the photocatalytic activity in the dyes degradation process in aqueous solution.