Kinetic model of coherent synchronized ethylene monooxidation by hydrogen peroxide on a biomimetic catalyst,per-FTPhPFe<Superscript>3+</Superscript>OH/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

A kinetic model that fits the experimental data is studied on the basis of the most probable mechanism of ethylene oxidation by hydrogen peroxide over a biomimetic catalyst, perfluorinated iron (III) tetraphenylporphyrin, deposited on aluminum oxide (per-FTPhPFe³⁺OH/Al₂O₃). Effective rate constants for the catalase and oxygenase reactions and their effective activation energies are found.     

Adsorption behavior of <Superscript>99</Superscript>Tc on Fe,Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Summary The adsorption of ⁹⁹Tc on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ was studied by batch experiments under aerobic and anoxic conditions. The effects of pH and CO₃^2- concentration of the simulated ground water on the adsorption ratios were also investigated, and the valences of Tc in solution after the adsorption equilibrium were studied by solvent extraction. The adsorption isotherms of TcO₄- on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ were determined. Experimental results have shown that the adsorption ratio of Tc on Fe decreases with the increase of pH in the range of 5-12 and increases with the decrease of the CO₃^2- concentration in the range of 10^-8M-10^-2M. Under aerobic conditions, the adsorption ratios of ⁹⁹Tc on Fe₂O₃ and Fe₃O₄ were not influenced by pH and CO₃^2-concentration. When Fe was used as adsorbent, Tc existed mainly in the form of Tc(IV) after equilibrium and in the form of Tc(VII) when the adsorbent was Fe₂O₃ or Fe₃O₄ under aerobic conditions. The adsorption ratios of Tc on Fe, Fe₂O₃ and Fe₃O₄ decreased with the increase of pH in the range of 5-12 and increased with the decrease of the CO₃^2- concentration in the range of 10^-8M-10^-2M under anoxic conditions. Tc existed mainly in the form of Tc(IV) after equilibrium when Fe, Fe₂O₃ and Fe₃O₄ was the adsorbent under anoxic conditions. The adsorption isotherms of TcO_4- on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ are fairly in agreement with the Freundlich’s equation under both aerobic and anoxic conditions.     

Direct synthesis of hydrogen peroxide from hydrogen and oxygen over Pd-supported HNb<Subscript>3</Subscript>O<Subscript>8</Subscript> metal oxide nanosheet catalyst

A two-dimensional layered niobium oxide and its exfoliated nanosheet were examined as potential solid acid supports for direct synthesis of hydrogen peroxide from hydrogen and oxygen under intrinsically safe and noncorrosive reaction conditions. The catalytic performance strongly depended on the acid strength of the support material. The Pd-supported protonated niobium oxide nanosheet catalyst (Pd/HNb₃O₈-NS) with remarkably enhanced acidity was superior to layered Pd/KNb₃O₈ or Pd/HNb₃O₈ to promote the reaction. Hydrogen peroxide decomposition testing revealed that, although HNb₃O₈ was comparable to its exfoliated counterpart, HNb₃O₈-NS, in suppressing hydrogen peroxide decomposition without hydrogen, HNb₃O₈ was virtually ineffective in preventing hydrogen peroxide hydrogenation in the presence of hydrogen. However, compared with HNb₃O₈, HNb₃O₈-NS was found to be still effective at suppressing hydrogen peroxide hydrogenation. The different efficiency observed between HNb₃O₈ and HNb₃O₈-NS in the prevention of hydrogen peroxide hydrogenation implies that use of a highly acidic support is advantageous to effectively suppress faster and therefore more unfavorable hydrogen peroxide hydrogenation compared with decomposition. This result clearly demonstrates that the highly acidic HNb₃O₈ nanosheet can serve as an efficient solid acid support for direct synthesis of hydrogen peroxide from hydrogen and oxygen.     

Near-infrared quantum cutting in Tb<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanophosphors

Properties of the quantum-cutting phosphors are dependent on various factors such as dopant concentration, crystallinity, homogeneity, particle size and surface morphology. Effective control of the above parameters can enhance the quantum-cutting ability of the phosphor material. Nano-sized particles of Y₂O₃:Tb³⁺,Yb³⁺ were prepared with a solution-based co-precipitation method and subsequent calcination. Effective control of the reaction parameters and doping concentration helped to produce uniform nanostructures with high quantum-cutting efficiency up to 181.1 %. The energy transfer mechanism between Tb³⁺ and Yb³⁺ was studied by considering their spectroscopic properties and time-resolved spectroscopy. The high efficiency and small particle size of the quantum-cutting phosphor Y₂O₃:Tb³⁺,Yb³⁺ make it a suitable candidate for its application in solar cells.     

Photocatalysis enhancement of CaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, Nd<Superscript>3+</Superscript>@TiO<Subscript>2</Subscript> composite powders

CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were synthesized by a sol–gel method under mild conditions (i.e. low temperature and ambient pressure). The as-prepared powders were characterized by transmission electron microscopy (TEM) and analyzed by X-ray diffraction (XRD). The photocatalytic behavior of the TiO₂-base surfaces was evaluated by the degradation of nitrogen monoxide gas. It suggested that CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were composed of anatase titania and that CaAl₂O₄:Eu²⁺, Nd³⁺. TiO₂ particles were deposited on the surface of CaAl₂O₄:Eu²⁺, Nd³⁺ to form uniform film. CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders exhibited higher photocatalytic activity compared with pure TiO₂ under visible light. And the result also clearly indicated that the long afterglow phosphor absorbed and stored lights for the TiO₂ to remain photocatalytic activity in the dark.     

Improvement of the cycle life of composite xerogel V<Subscript>2</Subscript>O<Subscript>5</Subscript>/C in aqueous LiNO<Subscript>3</Subscript> solution by addition of vinylene carbonate

The xerogel V₂O₅/C composite was synthesized by a sol-gel method, using the suspension of carbon black in the solution of crystalline V₂O₅ in hydrogen peroxide as the precursor solution. The Li⁺ intercalation/deintercalation reactions of the xerogel V₂O₅/C composite, used as an anode material of a two-electrode cell with an aqueous LiNO₃ solution as the electrolyte, was studied before and after the addition of vinylene carbonate (VC). Upon addition of vinylene carbonate in an amount of only l wt %, the coulombic capacity during galvanostatic cycling, instead of commonly observed permanent fade, displayed an initial increase and then a stable plateau.     

Synthesis and characterization of Eu<Superscript>3+</Superscript> doped Lu<Subscript>2</Subscript>O<Subscript>3</Subscript> nanophosphor using a solution-combustion method

Fine Eu³⁺-doped lutetium oxide (Lu₂O₃:Eu³⁺) nanophosphor were synthesized using a low-temperature solution-combustion method in a methyl-alcohol solution. The characteristics of the nanophosphors synthesized at various sintering temperatures with different Eu³⁺ concentrations were analyzed to determine the optimum synthesis conditions. Thermogravimetry/differential thermal analysis showed that Lu₂O₃:Eu³⁺ crystallizes completely when the dry powder is sintered at 500 °C. The Lu₂O₃:Eu³⁺ crystals had a cubic structure and monoclinic phase. The peak position of the luminescence spectrum did not differ with the concentration of Eu or the sintering temperature or atmosphere, whereas the luminescence intensity was strongly dependent on the concentration and sintering conditions.     

Chemical composition optimization and characterization of the NiO/B<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system as a catalyst for ethylene oligomerization

The samples of the NiO/B₂O₃-Al₂O₃ system with NiO contents from 0.48 to 38.30 wt % were synthesized by the impregnation of borate-containing alumina (20 wt % B₂O₃). It was found that nickel oxide occurred in an X-ray amorphous state in the samples containing to 23.20 wt % NiO. At a NiO content of 4.86 wt % or higher, the support was blocked by the modifier to cause a decrease in the specific surface area from 234 to 176 m²/g and in the amount of acid sites from 409–424 to 333 μmol/g. An extremal character of the dependence of catalyst activity in ethylene oligomerization on NiO content was found with a maximum in the range of 4.86–9.31 wt %. Based on spectroscopic data, it was found that ethylene activation on the NiO/B₂O₃-Al₂O₃ catalyst can be associated with the presence of Ni²⁺ cations, which chemically interact with the support. The catalyst containing 4.86 wt % NiO at 200°C, a pressure of 4 MPa, and an ethylene supply rate of 1.1 h⁻¹ provided almost complete ethylene conversion at the yield of liquid oligomerization products to 90.0 wt %; the total concentration of C⁸⁺ alkenes in these products was 89.0 wt %.     

Oxidation of Diethyl Sulfide in Aqueous Solutions by Peroxynitrite and the H<Subscript>2</Subscript>O<Subscript>2</Subscript>-NO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> System

It was found that nitrite anions are effective activators of hydrogen peroxide in the reaction with diethyl sulfide. The observed kinetics are consistent with the proposed intermediate formation of peroxynitrous acid (ONOOH). The rate constants for the reaction of diethyl sulfide Et₂S with the acid ONOOH (k₀ = 1.8⋅10³ L/mol⋅s) and with the anion ONOO⁻ (k₋ = 6⋅10⁻² L/mol⋅s) are respectively 10⁵ and three times higher than with hydrogen peroxide. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 290–295, September–October, 2005.     

Kinetics of the oxidation of diethyl sulfide in the B(OH)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O system

Data obtained for the kinetics of oxidation of diethyl sulfide (Et₂S) by hydrogen peroxide in aqueous solution catalyzed by boric acid indicate that monoperoxoborates B(O₂H)(OH) ₃ ⁻ and diperoxoborates B(O₂H)₂(OH) ₂ ⁻ are the active species. The rates of the reactions of Et₂S with B(O₂H)(OH) ₃ ⁻ and B(O₂H)₂(OH) ₂ ⁻ are 2.5 and 100 times greater than with H₂O₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 38–42, January–February, 2007.     

Eu<Superscript>3+</Superscript>-fluorescence properties in nano-crystallized SnO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

Fluorescence and spectral hole burning properties of Eu³⁺ ions were studied in nanocrystals-precipitated SnO₂-SiO₂ glasses. The glasses were prepared to contain various amount of Eu₂O₃ using the sol-gel method, in which SnO₂ nanocrystals were precipitated by heating in air. In the glasses containing Eu₂O₃ less than 1%, the Eu³⁺ ions were preferentially doped in the SnO₂ nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons and holes excited in SnO₂ crystals. The SnO₂ nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence intensities of the Eu³⁺ ions. With the increasing Eu₂O₃ concentration, the amount of SnO₂ nanocrystals decreased and the Sn⁴⁺ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities and the hole depth to decrease.     

WO<Subscript>3</Subscript> thin film coating from H<Subscript>2</Subscript>O-controlled peroxotungstic acid and its electrochromic properties

We prepared PTA coating solution by hot plate evaporation, N₂ bubbling evaporation, and rotary evaporation. N₂ bubbling and rotary evaporation are very efficient way to synthesize PTA which reduces the synthesis process time to 1/5, compared to hot plate evaporation method. Another strong point is that N₂ bubbling and rotary evaporation make it possible to control excess hydrogen peroxide and water contents in PTA. The PTA formula were WO₃·0.13H₂O₂·10.0H₂O for hot plate method, WO₃·0.16H₂O₂·7.1H₂O for N₂ bubbling method, and WO₃·0.15H₂O₂·3.00H₂O for rotary evaporation method. Thermal analysis and mass spectroscopy analysis show that water is evaporated at around 100 °C and hydrogen peroxide is dissociated at the range of 150 and 250 °C. Amorphous phase of WO₃ thin film prepared from rotary evaporated PTA solution has the best electrochromic property, light transmission difference from 91% at its bleached state and 5.5% colored state, and charge density of 22 mC/cm². It is thought that the control of excess hydrogen peroxide and water contents in PTA is very important to enhance the electrochromic properties of WO₃ thin film.     

Effect of the Support on the Nature of Metal-Promoter Interactions in Ru-Cs<Superscript>+</Superscript>/MgO and Ru-Cs<Superscript>+</Superscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Ammonia Synthesis

The Ru-Cs⁺/MgO and Ru-Cs⁺/γ-Al₂O₃ catalysts, which were prepared by an impregnation method using RuOHCl₃ and Cs₂CO₃ as precursor compounds and reduced with H₂ at 450°C, are characterized by X-ray diffraction, high-resolution transmission electron microscopy (with X-ray microanalysis), and X-ray photoelectron spectroscopy (XPS). The Cs⁺/MgO(Al₂O₃) systems, Ru-Cs⁺ black, and model systems prepared by cesium sputtering onto polycrystalline ruthenium foil are studied as reference samples. It is found that, in the Ru-Cs⁺/MgO sample, cesium is present as a Cs_{2 + x}O cesium suboxide, which weakly interacts with the support, localized on the surface of Ru particles or near them. In the case of Ru-Cs⁺/γ-Al₂O₃, cesium occurs as a species that is tightly bound to the support; this is likely surface cesium aluminate, which prevents promoter migration to Ru particles. The Ru-Cs⁺/MgO sample exhibits a considerable shift of the Ru3d line in the XPS spectra toward lower binding energies, as compared to the bulk metal. It is hypothesized that this shift is due to a decrease in the electron work function from the surface of ruthenium because of the polarizing effect of Cs⁺ ions in contact with Ru particles. Based on the experimental results, the great difference between the catalytic activities of the Ru-Cs⁺/MgO and Ru-Cs⁺/γ-Al₂O₃ systems in ammonia synthesis at 250–400°C and atmospheric pressure is explained.     

Oxidative desulfurization of thiophene derivatives with H<Subscript>2</Subscript>O<Subscript>2</Subscript> in the presence of catalysts based on MoO<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> under mild conditions

The catalysts based on MoO₃/Al₂O₃ were synthesized and tested using aqueous hydrogen peroxide as the oxidant in the oxidative desulfurization of thiophene, benzothiophene (BT) and dibenzothiophene (DBT) into the corresponding sulfones. Among catalysts tested, 15%(MoO₃–WO₃)/Al₂O₃ prepared by a conventional impregnation method was considerably active for the oxidation of thiophene, BT and DBT, which could achieve higher than 99.2% conversions at lower reaction temperature (≤338 K). The use of hexadecyltrimethyl ammonium bromide as the phase-transfer reagent in small amounts could promote the reaction efficiently.     

Catalytic properties of Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al₂O₃ catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H₂PtCl₆. The highest rate of hydrogen production (452 μmol min⁻¹ g⁻¹) obtained with the Pt/α-Al₂O₃ catalyst can be related to the highest extent of dispersion of Pt on α-Al₂O₃. XPS, TEM-EDX and TPR-H₂ measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al₂O₃ catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al₂O₃ and Pr/δ-Al₂O₃ catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.     

Effects of boric acid on structural and luminescent properties of BaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:(Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript>) phosphors

Eu²⁺/Dy³⁺-codoped BaAl₂O₄ phosphors were prepared by conventional solid-state reaction with boric acid flux. The effects of boric acid on structural and luminescent properties of BaAl₂O₄:(Eu²⁺, Dy³⁺) were investigated. The crystallinity of BaAl₂O₄ improved with increasing amount of H₃BO₃. Incorporation of Eu²⁺ and Dy³⁺ ions into effective lattice sites was promoted by H₃BO₃ addition. As a result, Eu²⁺ emission in BaAl₂O₄ was greatly enhanced by H₃BO₃, and the duration of persistent luminescence increased with the amount of H₃BO₃. However, the decay lifetime of persistent luminescence was not strongly influenced by the amount of H₃BO₃.     

Optical energy storage properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript>,R<Superscript>3+</Superscript> persistent luminescence materials

The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr₂MgSi₂O₇:Eu²⁺,R³⁺ material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 °C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R³⁺ co-dopants.     

A New Molybdophosphate Constructed From {Mo<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>O<Subscript>4</Subscript>(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>}<Superscript>2+</Superscript> and 1-Hydroxyethylidenediphosphonate

A new molybdophosphate (NH₄)₈{Mo₂^VO₄[(Mo₂^VIO₆)CH₃C(O)(PO₃)₂]₂}·14H₂O (1), has been synthesized by the reaction of {Mo₂^VO₄(H₂O)₆}²⁺ fragments with 1-hydroxyethylidenediphosphonate (hedp HOC(CH₃)(PO₃H₂)₂), and it is characterized by ³¹P NMR, IR, UV, element analysis, TG and single-crystal X-ray analysis. The structure analysis reveals that the polyoxoanion can be described as two {(Mo₂^VIO₆)(CH₃C(O)(PO₃)₂} units connected by a {Mo₂^VO₄}²⁺ moiety. In the structure, the six Mo atoms are arranged into a new “W-shaped” structure, which represents a new kind of molybdophosphate.     

Two color up-conversion emissions of Er<Superscript>3+</Superscript>-doped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowders prepared by non-aqueous sol-gel method

Er³⁺-doped Al₂O₃ nanopowders have been prepared by the non-aqueous sol-gel method using the aluminum isopropoxide as precursor, acetylacetone as a chelating agent, nitric acid as a catalyzer, and hydrated erbium nitrate as a dopant under isopropanol environment. The different phase structure, including three crystalline types of (Al, Er)₂O₃ phases, α, γ, θ, and an Er–Al–O stoichiometric compound phase, Al₁₀Er₆O₂₄, was observed for the 0.01–0.5 mol% Er³⁺-doped Al₂O₃ nanopowders at the sintering temperature of 1,000 °C. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the ²H_11/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978 nm semiconductor laser diodes excitation. With increasing Er³⁺ doping concentration from 0.01 to 0.1 mol%, the intensity of the green and red emissions increased with a decrease of the intensity ratio of the green to red emission. When the Er³⁺ doping concentration rose to 5 mol%, the intensity of the green and red emissions decreased with an increase of their intensity ratio. The maximum intensity of both the green and red emissions with the minimum of intensity ratio was obtained, respectively, for the 0.1 mol% Er³⁺-doped Al₂O₃ nanopowders composed of a single α-(Al,Er)₂O₃ phase. The intensity ratio of the green emission at 523 and 545 nm increased monotonously for all Er³⁺ doping concentrations. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er³⁺-doped Al₂O₃ nanopowders.     

The synthesis and thermochemical study of (Mg,Fe)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Nanotubular (Mg,Fe²⁺,Fe³⁺)₃Si₂O₅(OH)₄ hydrosilicates with a chrysotile structure were synthesized under hydrothermal conditions. The phases prepared were studied thermochemically on a high-temperature Tian-Calvet microcalorimeter by solution calorimetry. The standard enthalpies of formation of magnesium-iron nanotubular hydrosilicates were determined. The formation of iron-containing nanotubes was shown to be lass favorable energetically than the formation of magnesium nanotubes.