Surface and Subsurface Oxygen on Platinum in a 0.5 M H2SO4 + 0.01 M CuSO4 Solution

The formation of a copper adatom layer on polycrystalline platinum in a copper sulfate solution is studied by cyclic voltammetry in different cycling ranges at 0.1 V s^–1. The copper adatom deposition kinetics is controlled by the following factors. The substrate's top layer structure during the oxygen exit onto the surface may be unstable at anodic limits E _a = 0.90–1.35 V. The concentration of copper oxides (active centers) may be higher at E _a = 0.8–0.95 V. The balance between different adsorption sites differs in different cycling conditions. Of importance is the number of complexes O_ss–Pt _n –SO₄ and O_ss–Pt _n –O_c, where O_ss is subsurface oxygen and O_c is chemisorbed oxygen.     

Preparation and Characteristics of Nb<Superscript>5+</Superscript>, Ta<Superscript>5+</Superscript>/TiO<Subscript>2</Subscript> Nanoscale Powders by Sol–Gel Process Using TiCl<Subscript>3</Subscript>

Nanoscale TiO₂ powders doping with niobium and tantalum were prepared using TiCl₃ as a source matter. Characterization of the materials was performed by Thermoanalys, particle size, XRD, BET, FTIR, Magnetic Susceptibility. The influence of niobium and tantalum ions on the phase transition was studied, the changes in the crystal size and microstain distributions obtained at 400C were analyzed. The results show that the substitutes of Nb^{5 +}, Ta^{5 +} for Ti⁴⁺ in the anatase structure cause distortions and improve to form rutile. When the dopant content is over certain molar percent, biphase reappears. The IR spectra and magnetic susceptibility indicate the Nb–Nb (or Ta–Ta) bonds along c-axis in rutile by two Nb^{5 +} (Ta^{5 +}) ions located in sites adjacent along the c-axis appear with the dopant content. The magnetic characteristics at rutile showed a weak paramagnetism.     

Intermediate steps in YBa2Cu3O7−x synthesis by sol-gel method: YBaCuO oxycarbonate

High T _c -superconducting powders of the Y-Ba-Cu-O system are prepared by a solution-polyacrylamide gel using citric acid as a complexing agent. This method provides an easy way to prepare reactive YBaCuO powders by sol-gel synthesis. However this synthesis involves intermediate phases formation which impedes the obtention of the pure phase at low temperature. An intermediate oxycarbonate phase forms between 800° and 850°C in flowing oxygen. From powder X-ray diffraction, thermal analysis and IR spectroscopy, it is concluded that the intermediate oxycarbonate has an average tetragonal structure—SG P4/mmm—similar to that of the parent oxide with a stoichiometry close to YBa₂Cu_2.95(CO₃)_0.35O_6.6. The carbonate group is located in the center of the basal CuO square. This compound has superconducting properties. A pure 123 phase is obtained when the xerogel precursor is annealed at 925°C in O₂ or at 800°C in Ar, then in O₂. The grain growth and microstructure development of YBaCuO have also been investigated and compared using two different powders, i.e. sol-gel route and commercial powder from Hoechst.     

Analytical-kinetical study on the quinalizarin-hydrogen peroxide indicator reaction for Co2+ determination

Summary By a kinetic study of the indicator reaction of quinalizarin with hydrogen peroxide, catalysed by Co²⁺ ions, the optimum conditions necessary for determining traces of the catalyst have been found. These conditions are: pH=12.0 (sodium tetraborate-sodium hydroxide buffer), wavelength of measurement 565 nm,c (H₂O₂)/c(R)=200, temperature=25° C, Co²⁺ concentration range 1×10^–8-2×10^–7 M. A mechanism similar to that for enzymatic reactions, involving the occurrence of two intermediate complexes, gives a good explanation for the optimal conditions found.

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Analytisch-kinetische Untersuchung der Indikator-Reaktion von Chinalizarin mit Wasserstoffperoxid zur Co(II)-Bestimmung

Zusammenfassung Durch eine kinetische Untersuchung der Indikator-Reaktion von Chinalizarin mit Wasserstoffperoxid, die durch Co(II)ionen katalysiert wird, wurden die optimalen Bedingungen für die Bestimmung von Spuren des Katalysators ermittelt: pH=12,0 (Natriumtetraborat-Natriumhydroxid); Wellenlänge: 565 nm;c (H₂O₂)/c(R)=200; Temperatur=25° C; Konzentrationsbereich von Co(II): l·10^–8 bis 2·10^–8 M. Ein Reaktionsmechanismus ähnlich wie für enzymatische Reaktionen einschließlich zwei Zwischenprodukt-Komplexe bieten eine gute Erklärung für die gefundenen Optimalbedingungen.

     

Das erste Erdalkalimetall-Argentato-Mercurat(II): BaAg2Hg2O4

Summary BaAg₂Hg₂O₄ was prepared by an oxygen high-pressure technique. Single crystal X-ray investigations led to tetragonal symmetry, space group D _4h ³ – P4/nbm;a=6.793;c=7.086 Å;Z=2. Hg²⁺ and Ag⁺ show dumb-bell like coordination by oxygen whereas Ba²⁺ ions are surrounded by 8 O^2– forming distorted cubes. The BaO₈-polyhedra distortions are discussed in respect to the incorporation of Hg²⁺ ions into the BaAg₂O ₄ ^2– network.

     

High-temperature transport and electrochemical properties of YBaCo4O7+δ

The total conductivity of oxygen-hyperstoichiometric YBaCo₄O₇₊ is predominantly p-type electronic at oxygen partial pressures from 5×10⁴ Pa down to the phase decomposition limit, 10^–11–10^–4 Pa at 973–1223 K. The ion transference numbers, determined by the oxygen permeation and faradaic efficiency measurements at 1073–1223 K, vary in the range 3×10^–5–2×10^–4 and increase with temperature. The oxygen permeability of YBaCo₄O₇₊ ceramics, with overall level similar to that of K₂NiF₄-type cuprates, is mainly limited by the bulk ionic conduction. Heating above 1050–1100 K and redox processes under oxidizing conditions lead to a first-order transition accompanied with extensive oxygen losses from the lattice, resulting in decreasing total oxygen content from 8.5 down to approximately seven atoms per unit formula. Except for the variations associated with this transition, the electron–hole conductivity and Seebeck coefficient are essentially p(O₂)-independent within the phase stability limits. The use of different synthesis methods, namely the standard ceramic technique and the glycine–nitrate process, has no significant effect on the properties of YBaCo₄O₇₊ ceramics. The thermal expansion coefficients averaged at 600–1100 K in air are (7.3–7.6)×10^–6 K^–1. Porous YBaCo₄O₇-based cathodes show a very high electrochemical activity in contact with LaGaO₃-based solid electrolyte at 873–1073 K.     

A study of Lux-Flood acid-base reactions in KBr melts at 800°C

The dissociation of CO₃²⁻ (pK = 2.4 ± 0.2) and precipitation of MgO (pL _MgO = 10.66 ± 0.1) in a KBr melt at 800°C were studied potentiometrically with the use of a Pt(O₂)|ZrO₂|(Y₂O₃) membrane oxygen electrode. The direct calibration of the electrochemical circuit allowed only the equilibrium concentration of O²⁻ (of strong bases) to be determined in the melt. The total concentration of oxygen-containing impurities, including CO₃²⁻ and CO₄²⁻ weak bases, can be found by the potentiometric titration of a sample of KBr by adding MgCl₂ (Mg²⁺), a strong Lux-Flood acid, which causes the decomposition of these oxygen-containing anions. This reaction can also be used to remove oxo anions from alkali metal halide melts.     

New bifunctional N-thiophosphorylated thiourea and 2,5-dithiobiurea derivatives. Crystal structures of R[C(S)NHP(S)(OiPr)2]2 (R = –N(Ph)CH2CH2N(Ph)– and –NHNH–)

A new bifunctional N-thiophosphorylated thiourea and 2,5-dithiobiurea of the common formula R[C(S)NHP(S)(OiPr)₂]₂ [R = –N(Ph)CH₂CH₂N(Ph)– (H₂L^a); –NHNH– (H₂L^b)] have been synthesized and characterized by IR, ¹H, ³¹P spectroscopy and the single crystal X-ray diffraction method. The structure of the latter compound in CDCl₃ and acetone-d₆ solutions has been discussed in comparison with the monofunctional thiosemicarbazide PhNHNHC(S)NHP(S)(OiPr)₂ (HL^c).     

Redox features of β-VOPO4 catalyst using tracer and laser Raman spectroscopy

The oxygen ions of the β-VOPO₄ catalyst were exchanged with an tracer by a reduction–oxidation method and by a catalytic oxidation of but-1-ene using ₂. The bands at 992 and 900 cm⁻¹ were more shifted to lower frequencies than those at 1076 and 1002 cm⁻¹. Applying the correlation between the Raman bands and stretching vibrations in the literature, the exchanged oxygen species were estimated. The results suggest that the P–O–V vacancies corresponding to 992 and 900 cm⁻¹ were responsible for reoxidation and the V=O oxygen corresponding to the 1002 cm⁻¹ band of β-VOPO₄ was not. The (VO)₂P₂O₇ was oxidized to β-VOPO₄ by O₂ above 823 K. The insertion position of oxygen was determined at the bands at 992 and 900 cm⁻¹ of β-VOPO₄ using ₂, which is the same as the exchanged position.     

Surface and Subsurface Oxygen on Platinum in a 0.5 M H2SO4 Solution

The oxidation of polycrystalline platinum in 0.5 M H₂SO₄ is studied by cyclic voltammetry at potential scan rates of 5–500 mV s^–1 while varying the potential cycling range. The scheme, which is proposed for explaining the observed acceleration and deceleration of oxygen sorption at 0.75–1.0 V, accounts for the presence of oxygen in the subsurface layers of platinum (O_ss) and the formation of a barrier layer comprising complexes O_ss–Pt _n –SO₄. Cycling platinum secures certain steady-state contents of O_ss at 0.01–1.35 V. In an anodic scan, O_ss accumulates at E > 0.85 V (slow post-electrochemical stage) due to exchange of platinum and oxygen atom sites. In a cathodic scan, the desorption of most oxygen gives way to the adsorption of anions, which prevent residual O_ss from appearing on the surface. The residual O_ss disappears at E < 0.1 V after a sufficiently complete desorption of anions and the destruction of stable complexes O_ss–Pt _n –SO₄. Varying the potential cyclic limit leads, after a delay, to other steady-state O_ss contents.     

Methylpyrazine Ammoxidation over Binary Oxide Systems: V. Effect of Phosphorus Additives on the Physicochemical and Catalytic Properties of a Vanadium–Titanium Catalyst in Methylpyrazine Ammoxidation

Oxide vanadium–titanium catalysts modified by phosphorus additives (20V₂O₅–(80 –n)TiO₂–nP₂O₅, n = 1, 3, 5, 10, and 15 wt %) are studied in methylpyrazine ammoxidation. Two regions of compositions are found corresponding to radically different catalytic properties, namely, catalysts with a low (5 wt % P₂O₅) and high (10 wt % P₂O₅) concentration of the additive. In the first case, the introduction of phosphorus is accompanied by a gradual increase in the activity. In the second case, an increase in the additive concentration results in a decrease in the activity and selectivity to the target product, pyrazineamide, and a simultaneous increase in the selectivities to by-products, pyrazine and carbon oxides. The catalysts are characterized by X-ray diffraction analysis, differential dissolution, IR, and NMR spectroscopic data. As in the binary system, the active sites of the samples with a low concentration of phosphorus contain V⁵⁺ cations in a strongly distorted octahedral oxygen environment, which are strongly bound to a support due to the formation of V–O–Ti bonds. The catalytic properties of the samples containing 10 wt % P₂O₅ are due to the presence of the phase of a triple V–P–Ti compound with an atomic ratio V : P : Ti approximately equal to 1 : 1 : 1. The V⁵⁺ cations in this compound occur in a weakly distorted tetrahedral oxygen environment and are bound to the tetrahedral P⁵⁺ cations.     

Transport and electrocatalytic properties of La0.3Sr0.7Co0.8Ga0.2O3−δ membranes

Incorporation of gallium into the perovskite lattice of La_0.3Sr_0.7CoO_3– leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973–1223 K, the oxygen permeation fluxes through La_0.3Sr_0.7Co_0.8Ga_0.2O_3– ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La_0.3Sr_0.7Co_0.8Ga_0.2O_3–, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the p(O₂) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9×10^–6 K^–1 at 360–710 K and 27.9×10^–6 K^–1 at 710–1030 K. On decreasing oxygen pressure down to 4–30 Pa at 973–1223 K, perovskite-type La_0.3Sr_0.7Co_0.8Ga_0.2O_3– transforms into a brownmillerite-like modification, whose electrical properties are essentially p(O₂) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at p(O₂)=8×10^–10–3×10^–4 Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La_0.3Sr_0.7Co_0.8Ga_0.2O_3– membranes are, however, kinetically stable under an air/CH₄ gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO₂ concentrations (>90%), indicating a dominant role of complete CH₄ oxidation on the membrane surface.     

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al₂O₃–TiO₂–MgO and Al₂O₃–TiO₂–SiO₂ systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al₂TiO₅. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.     

Thermal decomposition of lanthanide(III) and Y(III) 3,4,5-trihydroxybenzoates: Preparation, properties

Complexes of lanthanides(III) (La-Lu) and Y(III) with 3,4,5-trihydroxybenzoic acid (gallic acid) were obtained and their thermal decomposition, IR spectra and solubility in water have been investigated. When heated, the complexes with a general formula Ln(C₇H₅O₅)(C₇H₄O₅)·nH₂O (n=2 for La-Ho and Y: n=0 for Er-Lu) lose their crystallization water and decompose to the oxides Ln₂O₃, CeO₂, Pr₆O₁₁, and Tb₄O₇, except of lanthanum and neodymium complexes, which additionally form stable oxocarbonates such as Ln₂O₂CO₃. The complexes are sparingly soluble in water (0.3·10^–5–8.3·10^–4 mol dm^–3).This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis and Study of Complexes of Some Trivalent Lanthanides and Americium with N,N-Dimethylacetamide and PW12O403–Anions

The synthesis of crystalline complexes of trivalent lanthanides and americium with N,N-dimethylacetamide (DMAA) and PW₁₂O₄₀ ^3–anions was described. Their IR and electronic absorption spectra were studied. The structure of the neodymium complex [Nd(DMAA)₆PW₁₂O₄₀] was determined using X-ray diffraction analysis. The thermal behavior of the lanthanide complexes was studied. In the 300–400°C temperature interval, even in air, intramolecular partial reduction of the anion occurs to form products which can be characterized as tungsten bronzes.     

Synthesis and Characterization of Nanocrystalline Zinc Aluminum Spinel by a New Sol-Gel Method

Using Al(OⁱPr)₃ (aluminium-iso-propoxide) and Zn(NO₃)₂⋅ 6H₂O as starting materials, HNO₃ as catalyst, ZnAl₂O₄ spinel nanometer powders were prepared at lower sintering temperatures. The gels and sintered samples of ZnAl₂O₄ were characterized by means of thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra and transmission electron microscope (TEM). Pure ZnAl₂O₄ spinel nanometer powders were produced by calcining the gel above 450^∘C, with the crystallite size of 7–20 nm in the temperature range of 500–900^∘C.     

Solubility of europium oxides in NaI melts at 700°C

The solubility product of EuO (pP _EuO = 8.65 ± 0.5) and its dissociation constant (pK _EuO = 5.67 ± 0.5) in NaI melts at 700°C have been determined by potentiometric titration with the use of a Pt(O₂)|ZrO₂(Y₂O₃) membrane oxygen electrode. Estimated on the basis of these parameters, the total solubility of EuO in NaI melts (1.12 × 10⁻³ mol/kg, logs _EuO = −2.95) is close to the value obtained by the consecutive additions method (2.8 × 10⁻³ mol/kg, logs _EuO = −2.55). The values obtained show that Eu²⁺ (EuI₂) is a stable cationic activator in NaI melt, but it yet cannot be recommended as an agent for the removal of oxygen-containing admixtures from this melt.     

Syntheses and pharmacological characterization of achiral and chiral enantiopure C/Si/Ge-analogous derivatives of the muscarinic antagonist cycrimine: a study on C/Si/Ge bioisosterism

The C/Si/Ge-analogous compounds rac-Ph(c-C₅H₉)El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, rac-3a; El=Si, rac-3b; El=Ge, rac-3c) and (c-C₅H₉)₂El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, 5a; El=Si, 5b; El=Ge, 5c) were prepared in multi-step syntheses. The (R)- and (S)-enantiomers of 3a–c were obtained by resolution of the respective racemates using the antipodes of O,O′-dibenzoyltartaric acid (resolution of rac-3a), O,O′-di-p-toluoyltartaric acid (resolution of rac-3b), or 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (resolution of rac-3c). The enantiomeric purities of (R)-3a–c and (S)-3a–c were ≥98% ee (determined by ¹H-NMR spectroscopy using a chiral solvating agent). Reaction of rac-3a–c, (R)-3a–c, (S)-3a–c, and 5a–c with methyl iodide gave the corresponding methylammonium iodides rac-4a–c, (R)-4a–c, (S)-4a–c, and 6a–c (3a–c→4a–c; 5a–c→6a–c). The absolute configuration of (S)-3a was determined by a single-crystal X-ray diffraction analysis of its (R,R)-O,O′-dibenzoyltartrate. The absolute configurations of the silicon analog (R)-4b and germanium analog (R)-4c were also determined by single-crystal X-ray diffraction. The chiroptical properties of the (R)- and (S)-enantiomers of 3a–c, 3a–c·HCl, and 4a–c were studied by ORD measurements. In addition, the C/Si/Ge analogs (R)-3a–c, (S)-3a–c, (R)-4a–c, (S)-4a–c, 5a–c, and 6a–c were studied for their affinities at recombinant human muscarinic M₁, M₂, M₃, M₄, and M₅ receptors stably expressed in CHO-K1 cells (radioligand binding experiments with [³H]N-methylscopolamine as the radioligand). For reasons of comparison, the known C/Si/Ge analogs Ph₂El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, 7a; El=Si, 7b; El=Ge, 7c) and the corresponding methylammonium iodides 8a–c were included in these studies. According to these experiments, all the C/Si/Ge analogs behaved as simple competitive antagonists at M₁–M₅ receptors. The receptor subtype affinities of the individual carbon, silicon, and germanium analogs 3a–8a, 3b–8b, and 3c–8c were similar, indicating a strongly pronounced C/Si/Ge bioisosterism. The (R)-enantiomers (eutomers) of 3a–c and 4a–c exhibited higher affinities (up to 22.4 fold) for M₁–M₅ receptors than their corresponding (S)-antipodes (distomers), the stereoselectivity ratios being higher at M₁, M₃, M₄, and M₅ than at M₂ receptors, and higher for the methylammonium compounds (4a–c) than for the amines (3a–c). With a few exceptions, compounds 5a–c, 6a–c, 7a–c, and 8a–c displayed lower affinities for M₁–M₅ receptors than the related (R)-enantiomers of 3a–c and 4a–c. The stereoselective interaction of the enantiomers of 3a–c and 4a–c with M₁–M₅ receptors is best explained in terms of opposite binding of the phenyl and cyclopentyl ring of the (R)- and (S)-enantiomers. The highest receptor subtype selectivity was observed for the germanium compound (R)-4c at M₁/M₂ receptors (12.9-fold).     

Comparison of the specific adsorption of sulfate (HSO<Subscript>4</Subscript><Superscript>−</Superscript>) ions on Cr and Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>

The specific adsorption of sulfate ions on powdered Cr was studied by a radiotracer technique using ³⁵S-labeled sulfuric acid in low concentration (c<10^–3 mol dm^–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined. On the basis of a comparison of the results obtained for Cr₂O₃ and Cr, it can be assumed that, similar to other metals, the overall sorption behavior of Cr is determined by the protective oxide film present on the surface.     

Synthesis,Structure and Property of Oxo-Bridged Binuclear Iron(III) Complex [Fe(phen)(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]<Subscript>2</Subscript>O⋅2SO<Subscript>4</Subscript>

An oxo-bridged binuclear iron(III) complex, [Fe(phen)(H₂O)₃]₂O2SO₄, has been synthesized and structurally characterized by elemental analysis (EA), IR, TG-DSC and X-ray. Its crystal structure has been determined by X-ray crystallography. It crystallizes in the orthorhombic system, space group P2₁2₁2, with lattice parameters a = 17.650(4), b = 8.5133(17), c = 9.971(2) Å; V = 1498.2(5) ų, _calcd = 1.763 g/cm³ and Z = 4 for R₁ = 0.0601. The crystal structure indicated that two octahedrally coordinated iron(III) ions bridged with oxygen atoms formed a non-linear complex. The bond angle of Fe–O–Fe is 163.9(4). The data of EA and IR are in good agreement with the crystal structure. The thermal gravity (TG) data indicate that there are four decomposition steps with three endothermic peaks. The final product of the thermal decomposition may be Fe(C₂H₈N₂)SO₄.