FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

Solubility isotherm for the Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

Solubility in the Na₂MoO₄-Na₂SO₄-H₂O system was studied using isothermal saturation at 5–100°C. The boundaries of crystallization fields were determined for sodium sulfate and sodium molybdate. Solid solutions were not observed within the range of the temperatures studied. The density, refractive index, and dynamic viscosity of the saturated solutions of the system were determined, and these data were used to calculate the molar volume, kinematic viscosity, and apparent molar volume of the sum of salts in these solutions. All property isotherms of solutions are in a strict correlation with the solubility in the system; this correlation is represented as an isobaric-isothermal diagram.     

Preparation and characterization of LiFePO<Subscript>4</Subscript> from NH<Subscript>4</Subscript>FePO<Subscript>4</Subscript>·H<Subscript>2</Subscript>O under different microwave heating conditions

Olivine-type LiFePO₄ is a very promising polyanion-type cathode material for lithium-ion batteries. In this work, LiFePO₄ with high specificity capacity is obtained from a novel precursor NH₄FePO₄·H₂O via microwave processing. The grains grow up in the duration of sintering until they reach the decomposition temperature. The apparent conductivity of the samples rises rapidly with the irradiation time and influences the electrochemical performance of the material greatly at high current density. As a result, the LiFePO₄ cathode material obtained with a sintering time of 15 min has good electrochemical performance. Between 2.5 and 4.2 V versus Li, a reversible capacity is as high as 156 mAh g⁻¹ at 0.05 C.     

Electrotransport properties of ions in aqueous solutions of H<Subscript>2</Subscript>SeO<Subscript>4</Subscript> and Na<Subscript>2</Subscript>SeO<Subscript>4</Subscript>

Coefficients of self-diffusion, absolute speeds of movement of ions and the activation energy of electrical conductivity are found from the conductance measurements of aqueous solutions of selenic acid and sodium selenate at different concentrations in a temperature range of 288–318 K. Both the Stokes and effective radii of ions and their hydrate numbers at 298 K are calculated. The obtained results are interpreted in the frames of Samoilov theory on positive and negative hydration of ions.     

Study on the non-isothermal kinetics of decomposition of 4Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O<Subscript>2</Subscript>·NaCl

The non-isothermal decomposition kinetics of 4Na₂SO₄·2H₂O₂·NaCl have been investigated by simultaneous TG-DSC in nitrogen atmosphere and in air. The decomposition processes undergo a single step reaction. The multivariate nonlinear regression technique is used to distinguish kinetic model of 4Na₂SO₄·2H₂O₂·NaCl. Results indicate that the reaction type Cn can well describe the decomposition process, the decomposition mechanism is n-dimensional autocatalysis. The kinetic parameters, n, A and E are obtained via multivariate nonlinear regression. The n ^th-order with autocatalysis model is used to simulate the thermal decomposition of 4Na₂SO₄·2H₂O₂·NaCl under isothermal conditions at various temperatures. The flow rate of gas has little effect on the decomposition of 4Na₂SO₄·2H₂O₂·NaCl.     

Li<Subscript>0.99</Subscript>Ti<Subscript>0.01</Subscript>FePO<Subscript>4</Subscript>/C composite as cathode material for lithium ion battery

Three kinds of LiFePO₄ materials, mixed with carbon (as LiFePO₄/C), doped with Ti (as Li_0.99Ti_0.01FePO₄), and treated both ways (as Li_0.99Ti_0.01FePO₄/C composite), were synthesized via ball milling by solid-state reaction method. The crystal structure and electrochemical behavior of the materials were investigated using X-ray diffraction, SEM, TEM, cyclic voltammetry, and charge/discharge cycle measurements. It was found that the electrochemical behavior of LiFePO₄ could be increased by carbon coating and Ti-doping methods. Among the materials, Li_0.99Ti_0.01FePO₄/C composite presents the best electrochemical behavior, with an initial discharge capacity of 154.5 mAh/g at a discharge rate of 0.2 C, and long charge/discharge cycle life. After 120 cycles, its capacity remains at 92% of the initial capacity. The Li_0.99Ti_0.01FePO₄/C composite developed here can be used as the cathode material for lithium ion batteries.     

Carbon nanotubes as a conductive additive in LiFePO<Subscript>4</Subscript> cathode material for lithium-ion batteries

The electrochemical properties and cyclic performances of commercial LiFePO₄ cathode material with different ratio of carbon black (CB) and carbon nanotubes (CNTs) as conductive material were tested in this study. Compared with other samples, the sample with 3 wt % CNTs exhibited the best electro-chemical and cyclic performances at various discharging rate at room temperature; and adhesion strength of electrode was improved by adding CNTs. The enhanced electrode performance may due to the unique natures of CNTs and the contact area of CNTs with active material or current collector.     

Structure and electric properties of Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaPO<Subscript>3</Subscript> glasses

The influence of the SO₄²⁻ ion on the temperature and concentration dependences of electric conductivity and the structure of sodium phosphate oxide glasses was studied. The increased electric conductivity of sulfate-phosphate glasses was explained by the formation of mixed sulfate-phosphate fragments with terminal SO₄²⁻ ions in the structure of glasses in the Na₂SO₄-NaPO₃ system. The dissociation energies of the sodium sulfate fragments are lower than those of pure oxide sodium phosphate structural units. As a result, the number of dissociated sodium ions increases, the activation energy of electric conductivity falls, and the conductivity (at 25°C) increases approximately 270-fold relative to the conductivity of NaPO₃. The arrangement of SO₄²⁻ ions in the structure was evaluated from the IR spectra of the glasses.     

Crystal Structure of New One-Dimensional Triple Molybdate Na<Subscript>2</Subscript>K<Subscript>2</Subscript>Cu(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The title compound (disodium dipotassium copper(II) tris-[molybdate (VI)]) is prepared by form melt and characterized by single crystal X-ray diffraction and UV-vis spectroscopy. It crystallizes in the triclinic space group P-1 with a = 7.4946(8) Å, b = 9.3428(9) Å, c = 9.3619(9) Å, α = 92.591(7)°, β = 105.247(9)°, γ = 105.496(9)°, V = 604.7 ų, and Z = 2. Its structure is isotypic with that of Na₄Mn(MoO₄)₃. It is formed by Cu₂O₁₀ distorted bi-octahedral dimers linked by two bridging bidentate Mo₂O₄ tetrahedra and, additionally, two monodentate Mo₁O₄ tetrahedra to form Cu₂Mo₄O₂₀ units. These units are linked by the insertion of Mo₃O₄ tetrahedra to build infinite ribbons disposed along the c axis. All of these ribbons form a one-dimensional framework. Both K1 and K3 cations are located in the inversion center, and all the other atoms are at general positions. The structure model is supported by the bond valence sum (BVS) and charge distribution CHARDI methods. The Cu²⁺ cations adopt the [4+2] CuO₆ Jahn-Teller distortion giving rise to an intense d–d transition in the UV-vis absorption spectra.     

Solubility in the ternary system CaSO<Subscript>4</Subscript> + Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> + H<Subscript>2</Subscript>O at 298.15 K

The solubility in the ternary system, aqueous mixture of CaSO₄ and Na₂SO₄, at T = 298.15 K comprises five different salts: calcium sulfate dihydrate, mirabilite, thenardite, glauberite and labile salt. Using the Extended Pitzer’s Ion Interaction model for pure and mixed electrolyte solutions and criteria of phase equilibria, predicted solubility behavior of salts was compared with experimental results from literature. The agreement between calculated and experimental solubilities was excellent in the ionic strength range up to 10.9062 mol kg⁻¹.     

A study of phase formation in the subsolidus region of the system Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MnMoO<Subscript>4</Subscript>-Cr<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phase relationships in the subsolidus region of the system Na₂MoO₄-MnMoO₄-Cr₂(MoO₄)₃ were studied by means of X-ray diffraction and differential-thermal analyses. The possibility of obtaining a variablecomposition phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ (0 ≤ x ≤ 0.5) and ternary molybdate NaMn₃Cr(MoO₄)₅ was examined. The temperature dependence of the conductivity of the phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ was analyzed.     

Enhancement of thermoelectric performance of Na<Subscript>x</Subscript>Co<Subscript>2</Subscript>O<Subscript>4</Subscript> with Ag dispersion by precipitation from Ag<Superscript>+</Superscript> aqueous solution

Thermoelectric Na_xCo₂O₄/Ag composites were synthesized by citric acid complex (CAC) method and Ag precipitation from CH₃COOAg aqueous solution on the Na_xCo₂O₄ powders. Effects of the synthesis process on microstructure and thermoelectric performance of Na_xCo₂O₄/Ag composites were investigated. When the Na_xCo₂O₄ CAC powders were dipped in CH₃COOAg aqueous solution and dried, fine Ag particles less than around 300 nm in size were precipitated on the surface of Na_xCo₂O₄ powders. After the subsequent sintering process, the flaky Ag phase, the length and thickness of which were up to 5 and 1 μm, respectively, existed along interfaces between Na_xCo₂O₄ grains. The sizes of Ag particles obtained in this study were found to be smaller than those of the conventionally prepared Na_xCo₂O₄/Ag composites. The fine dispersion of Ag grains was effective for suppressing the increase in thermal conductivity due to the addition of metallic phase, Ag, and for improving the thermoelectric performance of Na_xCo₂O₄/Ag composites, suggesting that the synthesis technique composed of the CAC method and Ag precipitation from CH₃COOAg aqueous solution is significantly important process for thermoelectric Na_xCo₂O₄/Ag composites.     

Non-isothermal kinetics of the thermal decomposition of sodium oxalate Na<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The thermal transformation of Na₂C₂O₄ was studied in N₂ atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na₂C₂O₄ and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS) methods. The activation energies (E _α) of Na₂C₂O₄ decomposition were found to be consistent. Decreasing E _α at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated through the Liqing–Donghua method was ‘cylindrical symmetry (R₂ or F_1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy pathway and revealed a very hard mechanism.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>/carbon nanotubes nanocomposites as improved anode materials for lithium-ion batteries

Mn₃O₄ and Mn₃O₄ (140)/CNTs have been investigated as high-capacity anode materials for lithium-ion batteries (LIBs) applications. Nanoparticle Mn₃O₄ samples were synthesized by hydrothermal method using Mn(Ac)₂ and NH₃·H₂O as the raw materials and characterized by XRD, TG, EA, TEM, and SEM. Its electrochemical performances, as anode materials, were evaluated by galvanostatic discharge-charge tests. The Mn₃O₄ (140)/CNTs displays outstanding electrochemical performances, such as high initial capacity (1942 mAh g^?1), stable cycling performance (1088 mAh g^?1 and coulombic efficiency remain at 97% after 60 cycles) and great rate performance (recover 823 mAh g^?1 when return to initial current density after 44 cycles). Compared to pure Mn₃O₄ (140), the improving electrochemical performances can be attributed to the existence of very conductive CNTs. The Mn₃O₄ (140)/CNTs with excellent electrochemical properties might find applications as highly effective materials in electromagnetism, catalysis, microelectronic devices, etc. The process should also offer an effective and facile method to fabricate many other nanosized metallic oxide/CNTs nanocomposites for low-cost, high-capacity, and environmentally benign materials for LIBs.     

Thermal behavior of cellulose fibers with enzymatic or Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> treatment

Summary New regenerated cellulose fibers were developed during the last decades as environmentally friendly systems. In this work, three fibers: lyocell, modal and viscose were subjected to an enzymatic treatment. Likewise, different lyocell fibers were washed in a Na₂CO₃ solution under severe conditions. Analysis was performed by means of differential scanning calorimetry, thermogravimetry and scanning electron microscopy. In all samples, at low temperature, water desorption was detected. Furthermore, thermal analysis shows wide exothermic processes that began between 250 and 300°C corresponding to the main thermal degradation and it is associated to a depolymerization and decomposition of the regenerated cellulose. It is accompanied with mass more than 60% mass loss. Kinetic analysis was performed and activation energy values 152-202 kJ mol^-1 of the main degradation process are in agreement with literature values of cellulose samples.     

Kinetics of oxidation of methane to formaldehyde on Na<Subscript>4</Subscript>[PFeMo<Subscript>11</Subscript>O<Subscript>40</Subscript>]/SiO<Subscript>2</Subscript>

The kinetics of oxidation of CH₄ to formaldehyde on the catalytic system Na₄[PFeMo₁₁O₄₀]/SiO₂ were studied, and a significant role of the redox potential of the CH₄-O₂ system with respect to the catalyst was shown. The density of centers participating in the reaction was determined, and dissociative competitive adsorption of methane and oxygen was established. The equation was deduced in the framework of the Langmuir-Hinshelwood theory taking into account the side conversion of formaldehyde. Possible participation of lattice oxygen in the reaction was suggested.     

Low-temperature heat capacity of sodium erbium molybdophosphate Na<Subscript>2</Subscript>Er(MoO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)

Adiabatic calorimetry is used to measure the low-temperature heat capacity of Na₂Er(MoO₄)(PO₄)from 6.41 to 347.87 K. Experimental data are used to calculate the thermodynamic functions of Na₂Er(MoO₄)(PO₄), which at 298.15 K are as follows: C _p ⁰ (298.15 K) = 243,3 ± 0.4 J/(K mol), S ⁰(298.15 K) = 312.8 ± 0.8 J/(K mol), H ⁰(298.15 K) ? H ⁰(0 K) = 45280 ± 90 J/mol, and Φ⁰(298.15 K) = 136.1 ± 0.3 J/(K mol). A diffuse heat-capacity anomaly associated with splitting of the Stark levels (Schottky anomaly) is discovered in the low-temperature region.     

Synthesis of sodium tungstate from the system Na<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaNO<Subscript>3</Subscript>-WO<Subscript>3</Subscript>

The physicochemical basis of the heterogeneous reaction between the components of the system (sodium oxalate)-(sodium nitrate)-(tungsten(VI) oxide) has been studied. The reaction of WO₃ with sodium oxalate-nitrate mixtures occurs at a lower temperature and at a higher rate than the reaction with pure sodium carbonate. A high-yield process for the synthesis of high-purity sodium tungstate has been developed on the basis of this study.     

Thermal stability of layered perovskite-like oxides NaNdTiO<Subscript>4</Subscript> and Na<Subscript>2</Subscript>Nd<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript>

Thermal stabilities of layered perovskite-like oxides NaNdTiO₄ and Na₂Nd₂Ti₃O₁₀ were studied in the temperature ranges from 780 to 1100°C and from 1100 to 1400°C, respectively. Chemical mechanism of their thermal decomposition was proposed. Higher thermal stability of Na₂Nd₂Ti₃O₁₀ was rationalized on the basis of crystallochemical data.     

Electrochemical performance of LiFePO<Subscript>4</Subscript>/C doped with F synthesized by carbothermal reduction method using NH<Subscript>4</Subscript>F as dopant

The effect of fluorine doping on the electrochemical performance of LiFePO₄/C cathode material is investigated. The stoichiometric proportion of LiFe(PO₄)_1−x F_3x /C (x = 0.01, 0.05, 0.1, 0.2) materials was synthesized by a solid-state carbothermal reduction route at 650 °C using NH₄F as dopant. X-ray diffraction, scanning electron microscope, energy-dispersive X-ray, and X-ray photoelectron spectroscopy analyses demonstrate that fluorine can be incorporated into LiFePO₄/C without altering the olivine structure, but slightly changing the lattice parameters and having little effect on the particle sizes. However, heavy fluorine doping can bring in impurities. Fluorine doping in LiFePO₄/C results in good reversible capacity and rate capability. LiFe(PO₄)_0.95 F_0.15/C exhibits highest initial capacity and best rate performance. Its discharge capacities at 0.1 and 5 C rates are 156.1 and 119.1 mAh g⁻¹, respectively. LiFe(PO₄)_0.95 F_0.15/C also presents an obviously better cycle life than the other samples. We attribute the improvement of the electrochemical performance to the smaller charge transfer resistance (R _ct) and influence of fluorine on the PO₄³⁻ polyanion in LiFePO₄/C.