X-ray ultrasoft spectra of vanadium in vanadium oxides

The Lα-emission spectra of vanadium in oxides V₂O₃, VO₂, V₂O₅, V₃O₅, V₄O₇, V₆O₁₁, V₆O₁₃, and V₃O₇ are investigated. It is discovered that the charge fluctuations in V₃O₅, V₄O₇, and V₆O₁₁ have a period greater than the $\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ hole life-time (～10^?15 sec), while in V₆O₁₃ and V₃O₇ this period is less than 10^?15 sec.     

Mechanism of electrochemical reduction of oxamide analytical applications

Oxamide is electrochemically reduced at mercury electrodes between pH 5.6 and 11.6. The overall mechanism proceeds by an initial 2e reduction of the 1,2-carbonyl groups of oxamide to give a dianion. This then protonates, rearranges, and loses ammonia to glyoxylamide, which is reduced in a further 2e/2H⁺ reaction giving glycolamide as the ultimate product. The reaction thus proceeds by a typical e.c.e. mechanism. The overall homogeneous rate contant for the chemical reaction(s) interposed between the two charge-transfer steps was measured by peak voltammetric, potentiostatic and d.c. polarographic methods. The d.c. polarographic wave of oxamide between pH 5.6 and 11 provides the basis for a very simple analytical method for the determination of oxamide.     

Synthesis and characterization of vanadium oxides nanorods

Vanadium oxides nanorods with high crystallinity and high surface area were synthesized by hydrothermal method using laurylamine hydrochloride, metal alkoxide and acetylacetone. The samples characterized by XRD, nitrogen adsorption isotherm, SEM, TEM, and SAED. Uniformly sized B phase VO₂ nanorods had widths about 40-80 nm and lengths reaching up to 1 μm. V₂O₅ rodlike structured with the widths about 100-500 nm and the lengths of 1-10 μm were obtained by calcination at 400 °C for 4 h. This synthesis method provides a new simple route to fabricate one-dimensional nanostructured metal oxides under mild conditions.     

Reduction of nitrogen oxides with ammonia over complex vanadium and chromium oxides

Catalytic properties of -Al₂O₃ -supported complex vanadium and chromium oxides V_2–x Cr _x O_5– (0 < × s 1.3), amorphous to X-rays, in the reduction of nitrogen oxides with ammonia were studied. Vanadium exists in these catalysts mostly in a pentavalent state and chromium exists as Cr³⁺ and Cr⁶⁺. As the content of chromium in the catalysts increases, the optimal temperature of the process decreases, and the degree of conversion of nitrogen oxides increases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 339–342, February, 1996.     

Thermodynamic considerations of screening halide molten-salt electrolytes for electrochemical reduction of solid oxides/sulfides

Journal of Solid State Electrochemistry - Molten salt is an indispensable electrolyte for electrochemically extracting reactive metals that cannot be obtained by a carbothermic reduction or a...     

Theory assisted design of N-doped tin oxides for enhanced electrochemical CO2 activation and reduction

Clearly understanding the structure-function relationship and rational design of efficient CO_2 electrocatalysts are still the challenges.This article describes the molecular origin of high selectivity of formic acid on N-doped SnO_2 nanoparticles,which obtained via thermal treatment of g-C_3N_4 and SnCl_2·2H_2O precursor.Combined with density functional theory(DFT)calculations,we discover that N-doping effectively introduces oxygen vacancies and increases the charge density of Sn sites,which plays a positive role in CO_2 activation.In addition,N-doping further regulates the adsorption energy of*OCHO,*COOH,*H and promotes HCOOH generation.Benefited from above modulation,the obtained N-doped SnO_2 catalysts with oxygen vacancies(Ov-N-SnO_2)exhibit faradaic efficiency of 93% for C_1 formation,88% for HCOOH production and well-suppression of H_2 evolution over a wide range of potentials.     

Porous metal oxides in the role of electrochemical CO2 reduction reaction

The global energy-related CO₂ emissions have rapidly increased as the world economy heavily relied on fossil fuels. This paper explores the pressing challenge of CO₂ emissions and highlights the role of porous metal oxide materials in the electrocatalytic reduction of CO₂ (CO₂RR). The focus is on the development of robust and selective catalysts, particularly metal and metal-oxide-based materials. Porous metal oxides offer high surface area, enhancing ...     

New investigations on acute toxicities of vanadium oxides

Summary The in-vivo-toxicity of the Vanadium-oxides V₂O₅ and V₂O₃ (administered orally, dermally and by inhalation) has been reinvestigated with particular emphasis on the safety and handleability of vanadium-oxides in the vanadium processing industry. Chemical-thermodynamic properties of vanadium-oxides make it likely that some earlier results on vanadium-toxicities have introduced artefacts as a consequence of the administration-techniques used. Special precautions have therefore been taken to avoid any chemical changes or artificial interactions during sample-preparation to ensure that the results significantly reflect the toxicities of the vanadium-compounds as exposure to them might occur. The LD₅₀(14d)-values indicate, that V₂O₅ should be classified as hamful (V₂O₅ techn. grade fused oral LD₅₀(14d): 716 mg/kg b.w. (rats m.) resp. 658 mg/kg b.w. (rats f.); inhal. LC₅₀ 16.2 mg/l (rats m.) resp. 4.0 mg/l (rats f.) for a 4-hour exposure), while V₂O₃ should be classified as relatively non toxic (V₂O₃ tech. grade powder oral: LD₅₀(14d): 5639 mg/kg b.w. (rats f.) resp. 8713 mg/kg b.w. (rats m.)) according to the EEC-commission directive of July 29, 1983 (83/467/EEC). Based on interaction-studies and considering new results reported in literature, a 3-level-model of the mechanism of vanadium-toxicity via oxygen-radicals is suggested.

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Neue Untersuchungen zur akuten Toxizität von Vanadiumoxiden

Zusammenfassung Die in-vivo-Toxizität der Vanadium-Oxide V₂O₅ und V₂O₃ bei oraler, dermaler und inhalativer Applikation wurde neu untersucht. Aufgrund einer Analyse der chemisch-thermodynamischen Eigenschaften dieser V-Oxide wird nahegelegt, daß die Resultate einiger früherer Toxizitätsuntersuchungen durch chemische Veränderungen der zu untersuchenden Stoffe bei der Probenvorbereitung verfälscht wurden. Nach den in-vivo-LD₅₀(14d)-Werten ist V₂O₅ als mindergiftig (V₂O₅ techn. fused oral LD₅₀(14d): 716 mg/kg b.w. (Ratten m.) bzw. 658 mg/kg b.w. (Ratten w.); inhalotiv LC₅₀ 16.2 mg/l (Ratten m.) bzw. 4.0 mg/l (Ratten w.) for a 4-hour exposure) bzw. V₂O₃ (techn. pulv. peroral LD₅₀(14d): 5639 mg/kg KG (Ratten w.) bzw. 8713 mg/kg KG (Ratten m.) als relativ nicht toxisch-nicht klassifiziert gemäß EEC-Commission-Directive vom 29. Juli 1983 (83/467/EEC) einzustufen. Basierend auf Studien der Interaktionswirkung bestimmter Substanzen und unter Eibeziehung der Resultate jüngst mitgeteilter Befunde zur Vanadium-Toxizität an Zellkulturen, wird ein Modell zum Vanadium-Toxizitäts-Wirkungsmechanismus vorgeschlagen, das 3 Hauptmechanismen — abhängig von der Konfrontations-Intensität (Konzentration und Expositionsdauer) — nahelegt.

     

Mechanism of carbothermal reduction of iron, cobalt, nickel and copper oxides

A new scheme of thermal dissociation which is based on the dissociative evaporation of the reactant with simultaneous condensation of the low-volatile product has been invoked to interpret the kinetics of reduction of FeO, CoO, NiO and Cu₂O by carbon. A critical analysis of literature data and their comparison with theoretical calculations has shown that the main kinetic characteristics of carbothermal reduction, including the initial decomposition temperature and activation energy are in full agreement with the proposed mechanism of decomposition. Condensation of the low-volatile product (metal vapour) in the reaction zone and partial transport of condensation energy to the oxide account for the features which are typical of solid state reactions and manifest themselves in the appearance of periods of induction and acceleration in the course of the process. Carbon fulfils the role of buffer in this process. This is supported by an appearance of metals in the condensed phase and a higher than equilibrium partial pressure of oxygen in high-vacuum experiments with Knudsen cells.     

Mechanism of the electrochemical reduction of 2-halo-5-nitrothiophenes in dimethylformamide

The reduction of 2-bromo-5-nitrothiophene and 2-iodo-5-nitrothiophene in dimethylformamide (DMF) was studied by means of classical and commutated polarography, EPR spectroscopy, a rotating platinum disk electrode with a ring, and preparative electrolysis. It was established that, depending on the nature of the halogen, their anion radicals may undergo further reduction to 2-nitrothiophene anion radicals or decomposition with splitting out of a halide anion and conversion to nitrothienyl radicals, which were identified on the ring electrode. The latter are capable of undergoing dimerization to 2,2-dinitro-5,5-dithienyl. The spectra of the anion radicals of 2-nitrothiophene and 2,2-dinitro-5,5-dithienyl were recorded by means of EPR. A mechanism for the reduction of halonitrothiophenes is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 195–198, February, 1981.     

Redox-inactive ions control the redox-activity of molecular vanadium oxides

Polyoxometalates are key materials for energy conversion and storage due to their unique chemical tunability and electrochemical reactivity. Herein, we report that functionalization of molecular vanadium oxides, polyoxovanadates, with redox-inert Ca²⁺ cations leads to a significant increase in their electron storage capabilities. The electrochemical performance of the Ca²⁺-functionalized dodecavanadate [Ca₂V₁₂O₃₂Cl(DMF)₃]²⁻ (={Ca₂V₁₂}) was thus compared with that of the precursor compound (H₂NMe₂)₂[V₁₂O₃₂Cl]³⁻ (={V₁₂}). {Ca₂V₁₂} can store up to five electrons per cluster, while {V₁₂} only shows one reversible redox transition. In initial studies, we demonstrated that {Ca₂V₁₂} can be used as an active material in lithium-ion cathodes. Our results show how redox-inert cations can be used as structural and electrostatic stabilizers, leading to major changes in the redox-chemistry of polyoxovanadates.

The enhanced redox-activity of a molecular vanadium oxide cluster upon functionalization with redox-inert Ca²⁺ ions is reported together with initial insights into its performance as a lithium ion battery cathode.     

Mechanism of halogen substitution in the electrochemical reduction of halonitrofurans in dimet hylformamide

The polarographic reduction of 2-halo-5-nitrofurans in dimethylformamide, which leads ultimately to replacement of the halogen by hydrogen to give a nitrofuran, was studied. The ESR spectra of halonitrofuran anion radicals (Hal=Cl, Br) were recorded. Only the spectrum of the nitrofuran anion radical can be observed in the reduction of 2-I-5-nitrofuran. It is shown that the stabilities of the anion radicals of the halonitrofurans and the mechanism of their subsequent transformations depend to a considerable degree on the nature of the halogen.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 23–26, January, 1977.     

Mechanism of electrochemical reduction of hydrogen peroxide on copper in acidic sulfate solutions

Hydrogen peroxide is a commonly used oxidizer component in chemical mechanical planarization slurries, used in the processing of Cu metallization in microelectronics applications. We studied the electrochemical reduction of hydrogen peroxide on Cu in 0.1 M H2SO4 solutions using methods including cyclic voltammetry, rotating disk electrode experiments, surface-enhanced Raman spectroscopy, and density functional theory (DFT) calculations. The spectroscopy reveals that the hydrogen peroxide molecule is reduced at negative potentials to form a Cu-OH surface species in acidic solutions, a result consistent with the insight from Tafel slope measurements. DFT calculations support the instability of peroxide relative to the surface-coordinated hydroxide on both Cu(111) and Cu(100) surfaces.     

Kinetics and mechanism of electrochemical reduction of multilayer oxides on a smooth platinum electrode surface in acidic electrolyte

The electrochemical reduction of multilayer oxides which were formed on a smooth Pt electrode surface under severe anodic conditions was investigated using a galvanostatic transient, a linear potential sweep and a potential step technique. Four regions of the surface oxide reduction were distinguished in the galvanostatic E?t curve and four corresponding cathodic current peaks were observed in the potentiodynamic i?E profile. These four regions or peaks are attributed to the reduction of four O-containing layers: an oxygen monolayer adsorbed on the oxide surface, two oxide layers in a first and a second lattice and a multilayer oxide in the deeper lattices having a phase property. The reduction rate of the first lattice oxide layer is determined by a second electron transfer. Under a rapid stripping condition, the reduction of the second oxide layer is considered to be controlled by the place exchange reaction. The extremely large reduction rate of the multilayer oxide compared with the formation rate is explained in terms of the proton-electron model.     

Mechanism of reduction of nitrogen oxides with propene in excess oxygen catalyzed by bifunctional catalysts

HC-SCR (selective reduction of nitrogen oxide by hydrocarbon) and our view on its reaction mechanism are briefly described, and then our attempts in the last few years to design catalysts based on the concept of bifunctional catalysis for HC-SCR are reviewed. The example chosen is the NO-C₃H₆-O₂-H₂O reaction catalyzed by mechanical mixtures of transition metal oxides (e.g., Mn₂O₃) and metal-loaded ZSM-5 zeolites. The synergistic effect of two components was explained based on a reaction mechanism comprising NO oxidation, oxidative decomposition of the products of NO₂-C₃H₆ reactions and polymerization of (or carbon deposition from) C₃H₆.