Phase diagram of the NaF–CaF<Subscript>2</Subscript> system and the electrical conductivity of a CaF<Subscript>2</Subscript>-based solid solution

The phase diagram of the NaF–CaF₂ system was studied by thermal analysis and X-ray powder diffraction analysis with the determination of the chemical composition. The system was found to be of the eutectic type. A narrow range of the existence of solid solution Ca_1–xNa_xF_2–x was established. The NaF solubility reaches a maximal value of x = 0.035 at 1200 ± 50°C (the temperature at which there is a diffuse phase transition in fluorite). At 920 ± 25°C, the NaF solubility reaches a minimum (<0.4 mol %) and increases again to 2.2 ± 0.2 mol % at a eutectic temperature (818°C). The ionic conductivity increases by three orders of magnitude after adding NaF to CaF₂.     

Highly Efficient Mesoporous V<Subscript>2</Subscript>O<Subscript>5</Subscript>/WO<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> Catalyst for Selective Catalytic Reduction of NO<Subscript>x</Subscript>: Effect of the Valence of V on the Catalytic Performance

Mesoporous WO₃–TiO₂ support was synthesized by hydrothermal method, mesoporous V₂O₅/WO₃–TiO₂ catalyst was synthesized by impregnation method and used for selective catalytic reduction (SCR) of NO_x with a excellent NO_x conversion at a wider operating temperature ranging from 200 to 460?°C. In the range of 260–440?°C, NO_x conversion reached to 98.6%, and nearly a complete conversion. Even with the existence of 300 ppm SO₂, NO_x conversion was only a little decline. The catalyst was characterized by a series of techniques, such as XRD, BET, XPS, TEM, Raman and H₂-TPR. It was concluded that V₂O₅/WO₃–TiO₂ catalyst was ascribe to antase TiO₂, and also the high crystallinity of anatase TiO₂ could improve the SCR performance. More interested, V₂O₅/WO₃–TiO₂ catalyst exhibited the typical mesoporous structure according to the BET results. In addition, the TEM results indicated that the active components of V and W were well-dispersed on the surface of TiO₂, while the enhancement of dispersion could improve the activity of catalysts. More importantly, the concentration ratio of V⁴⁺/(V⁵⁺?+?V⁴⁺?+?V³⁺) performed the key role in improving the activity of V₂O₅/WO₃–TiO₂ catalyst.     

Diagram of the PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript> system

A phase diagram of the PbF₂–SnF₂ system has been studied by differential thermal analysis and X-ray powder diffraction. The system forms Pb_1–хSn_хF₂ (х ≤ 0.33) solid solution and three compounds. Pb₂SnF₆ decomposes in solid state by a peritectoid reaction at 350°С; Pb₃Sn₂F₁₀ and PbSnF₄ melt by peritectic reactions at 565 and 380°С, respectively. The eutectic coordinates are 180°С, 90 mol % SnF₂.     

Formation of the center of ignition in a CH<Subscript>3</Subscript>Cl–Cl<Subscript>2</Subscript> mixture under the action of UV light

The dependence of temperature on time is investigated using a microthermocouple at different distances from a UV light source in a mixture of chlorine and chloromethane. These relationships give an idea of the size and location of a center of photoignition. It is found that if the size of the reaction vessel in the direction of the luminous flux is much greater than the dimensions of the ignition center, the thermal expansion of a reacting gas mixture has a huge impact on such photoignition parameters as the critical concentration limits and the critical intensity of UV radiation. It is found that by increasing the length of the vessel, some chlorinated combustible mixtures lose the ability to ignite when exposed to UV light.     

Effect of ZrO<Subscript>2</Subscript> on Catalyst Structure and Catalytic Sulfur-Resistant Methanation Performance of MoO<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts

A series of MoO₃/ZrO₂–Al₂O₃ catalysts was prepared and investigated in the sulfur-resistant methanation aimed at production of synthetic natural gas. Different methods including impregnation, deposition precipitation, and co-precipitation were used for preparing ZrO₂–Al₂O₃ composite supports. These composite supports and their corresponding Mo-based catalysts were investigated in the sulfur-resistant methanation, and characterized by N₂ adsorption–desorption, XRD and H₂-TPR. The results indicated that adding ZrO₂ promoted MoO3dispersion and decreased the interaction between Mo species and support in the MoO₃/ZrO₂–Al₂O₃ catalysts. The co-precipitation method was favorable for obtaining smaller ZrO₂ particle size and improving textural properties of support, such as better MoO₃ dispersion and increased concentration of Mo⁶⁺ species in octahedral coordination to oxygen. It was found that the MoO₃/ZrO₂–Al₂O₃ catalyst with ZrO₂Al₂O₃ composite support prepared by co-precipitation method exhibited the best catalytic activity. The ZrO₂ content in the ZrO₂Al₂O₃ composite support was further optimized. The MoO₃/ZrO₂–Al₂O₃ with 15 wt % ZrO₂ loading exhibited the highest sulfur-resistant CO methanation activity, and excess ZrO₂ reduced the specific surface area and enhanced the interaction between Mo species and support. The N₂ adsorption-desorption results indicated that the presence of ZrO₂ in excessive amounts decreased the specific surface area since some amounts of ZrO₂ form aggregates on the surface of the support. The XRD and H₂-TPR results showed that with the increasing ZrO₂ content, ZrO₂ particle size increased. These led to the formation of coordinated tetrahedrally Mo⁶⁺(T) species and crystalline MoO₃, and this development was unfavorable for improving the sulfur-resistant methanation performance of MoO₃/ZrO₂–Al₂O₃ catalyst.     

State of active components on the surface of the PdCl<Subscript>2</Subscript>-CuCl<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for the low-temperature oxidation of carbon monoxide

The state of the active constituents of the freshly prepared PdCl₂-CuCl₂/γ-Al₂O₃ catalyst for the low-temperature oxidation of the carbon monoxide by molecular oxygen was studied by X-ray absorption spectroscopy (XAS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and diffuse reflectance IR Fourier transform spectroscopy (DRIFTS). It was shown that copper in the form of a crystalline phase of Cu₂Cl(OH)₃ with the structure of the mineral paratacamite and palladium chloride in an amorphous state occurred on the surface of γ-Al₂O₃. According to XAS data, the local environment of palladium consisted of four chlorine atoms, which formed a flat square with an increased distance between palladium and one of the chlorine atoms. The evolution of the local environments of copper and palladium upon a transition from the initial salts to the impregnating solutions and chlorides on the surface of γ-Al₂O₃ was considered. The role of γ-Al₂O₃ in the formation of the Cu₂Cl(OH)₃ phase was discussed. It was found by the DRIFTS method that linear (2114 cm⁻¹) and bridging (1990 and 1928 cm⁻¹) forms of coordinated carbon monoxide were formed upon the adsorption of CO on the catalyst surface. The formation of CO₂ upon the interaction of coordinated CO with atmospheric oxygen was detected. Active sites including copper and palladium were absent from the surface of the freshly prepared catalyst.     

Fourier Transform Infrared Spectroscopy and Atomic Force Microscopy Studies of a SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>-Zeolite Matrix for a CuO-CoO Catalyst Prepared by a Sol–Gel Method

Combinations of SiO₂–TiO₂ mixed with zeolites may open new opportunities as base supports for acid-base and oxidation reactions. These solids would endow the catalysts with specific acid sites, which may not necessarily be found in those supports with only Si-Al oxides as basic materials. Using a standard sol–gel methodology, SiO₂–TiO₂ mixtures are prepared and mixed with β, Y and ZSM-5 zeolites. By partially hydrolyzing the SiO₂ precursor at the beginning of the sol–gel procedure it is possible to maximize the number of Si–O–Ti bridges formed. FTIR and AFM analyses show that the size of sols formed depend upon the type of zeolite. Metal loading helps surface dehydroxylation of the materials, possibly indicating a good insertion of the metal into the network.     

Mechanochemical Activation of Cu–CeO<Subscript>2</Subscript> Mixture as a Promising Technique for the Solid-State Synthesis of Catalysts for the Selective Oxidation of CO in the Presence of H<Subscript>2</Subscript>

A new ecologically clean method for the solid-phase synthesis of oxide copper–ceria catalysts with the use of the mechanochemical activation of a mixture of Cu powder (8 wt %) with CeO₂ was developed. It was established that metallic copper was oxidized by oxygen from CeO₂ in the course of mechanochemical activation. The intensity of a signal due to metallic Cu in the X-ray diffraction analysis spectra decreased with the duration of mechanochemical activation. The Cu¹⁺, Cu²⁺, and Ce³⁺ ions were detected on the sample surface by X-ray photoelectron spectroscopy. The application of temperature-programmed reduction (TPR) made it possible to detect two active oxygen species in the reaction of CO oxidation in the regions of 190 and 210–220°C by a TPR-H₂ method and in the regions of 150 and 180–190°C by a TPR-CO method. It is likely that the former species occurred in the catalytically active nanocomposite surface structures containing Cu–O–Ce bonds, whereas the latter occurred in the finely dispersed particles of CuO on the surface of CeO₂. The maximum conversion of CO (98%, 165°C) reached by the mechanochemical activation of the sample for 60 min was almost the same as conversion on a supported CuO/CeO₂ catalyst.     

Study of the kinetic aspects of formation of calcium monosilicate in the model system CaSO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>O·SiO<Subscript>2</Subscript>

The possibility and kinetic aspects of formation of X-ray amorphous calcium monosilicate in the model system CaSO₄·2H₂O-Na₂O·SiO₂ at room temperature were studied.     

The effect of the synthesis method on the morphological and luminescence characteristics of α-Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

A promising yellow phosphor, α-Zn₂V₂O₇, was synthesized at temperatures below the phase transition temperature (610 ± 5°C) by three different methods: solid-phase and microwave processes and thermolysis of a water–salt composition. According to powder X-ray diffraction, the structures of all samples belonged to space group C/2c. Depending on the method of synthesis, the particle size varied from 500 nm (thermolysis of a water–salt composition) to 5–8 μm (ceramic and microwave methods). The excitation spectra of all samples are in the UV region (220–400 nm) and the emission spectra are in the 400–750 nm wavelength range. The photoluminescence spectra of the samples are non-elementary, which is caused by specific features of the electronic charge transfer in the structural VO₄ tetrahedra.     

Effect of ionic conductivity of a PAN–PC–LiClO<Subscript>4</Subscript> solid polymeric electrolyte on the performance of a TiO<Subscript>2</Subscript> photoelectrochemical cell

A nanoparticle TiO₂ solid-state photoelectrochemical cell has been fabricated. The effect of ionic conductivity of a solid electrolyte of polyacrylonitrile (PAN)–propylene carbonate (PC)–lithium perchlorate (LiClO₄) on the performance of a photoelectrochemical cell of indium tin oxide (ITO)/TiO₂/PAN–PC–LiClO₄/graphite has been investigated. A nanoparticle TiO₂ film was deposited onto ITO-covered glass substrate by controlled hydrolysis technique. A solid electrolyte of PAN–LiClO₄ with PC plasticizer prepared by solution casting technique was used as a redox couple medium. The room temperature conductivity of the electrolyte was determined by AC impedance spectroscopy technique. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows a photovoltaic effect under illumination. The short-circuit current density, J _sc, and open-circuit voltage, V _oc, vary with the conductivity of the electrolyte. The highest J _sc of 2.82 μA cm⁻² and V _oc of 0.56 V were obtained at the conductivity of 4.2 × 10⁻⁴ Scm⁻¹ and at the intensity of 100 mW cm⁻².     

Regularities of formation of complex oxides with the fluorite structure in the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The crystal and local structures of the complex oxides (1–x)ZrO₂ ? xY₂O₃ (YSZ) (x = 0.08–0.40) prepared by precipitation from solutions of metal salts followed by heat treatment in air were comprehensively studied by X-ray diffraction and Raman spectroscopy. Despite the same crystal structure type of the YSZ powders (cubic system, space group \(Fm\overline 3 m\) (225)), there are differences in the local structure of the samples. Comparison of the Raman spectra recorded at different laser excitation wavelengths provided the conclusion that the peaks observed in the Raman spectra of the YSZ samples with high yttrium content (x = 0.18–0.40) are likely to be due to luminescence of the powders.     

Kinetics and mechanism of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl<Subscript>2</Subscript>–CuCl<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A systematic study of the kinetics of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl₂–CuCl₂/γ-Al₂O₃ supported catalyst was carried out over a wide range of the partial pressures of oxygen, water, and CO in order to test hypotheses on the reaction mechanism. It was shown that, as the temperature was increased from 20 to 38°C, rate of formation of CO₂ decreased and the apparent activation energy was about–40 kJ/mol. The hypotheses of different degrees of complexity concerning the reaction mechanism were formulated based on physicochemical data and a Langmuir–Hinshelwood model. Mechanisms in which carbon dioxide is formed on the interaction of the surface Pd(I) and Pd(II) complexes that include carbon monoxide and water with the surface complex of Cu(I) that coordinates oxygen were recognized as the most probable.     

Regime of superhigh reactivity of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + δ</Subscript> superconductor toward the components of air

Physicochemical features of the YBa₂Cu₃O_{6 + δ} superconductor synthesized via ceramic route and subjected to a kind of modification by long-term exposure to an atmosphere with low pH₂O have been studied by X-ray diffraction, thermal analysis, and magnetometry. The resulting material had a high degree of saturation with air components at room temperature and 30% humidity, up to 1.5 wt % in 30 days, which is not inherent in YBa₂Cu₃O_{6 + δ}.     

Study of the effect of methods for liquid-phase synthesis of nanopowders on the structure and physicochemical properties of ceramics in the CeO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Two alternative chemical synthesis methods—cryotechnological coprecipitation of hydroxides and cocrystallization of salts—were used for preparing (CeO₂)_1–x (Y₂O₃) _x nanopowders (x = 0.10, 0.15, 0.20) with a mean coherent scattering domain size of ~7–11 nm and S _sp = 2.1–97.5 m²/g. From these nanopowders, ceramic nanomaterials with mean coherent scattering domain sizes of ~61–85 nm were synthesized. It was studied how the phase composition, microstructure, and electrical transport properties of the produced samples depend on the Y₂O₃ content of a CeO₂-based solid solution and on the synthesis method. It was shown that, in the series (CeO₂)_1–x (Y₂O₃) _x (x = 0.10, 0.15, 0.20), the solid solution (CeO₂)_0.90(Y₂O₃)_0.10 has the highest ionic conductivity with the ion transport number t _i = 0.73 (600°C). In its physicochemical characteristics, this ceramic can be used as a solid electrolyte of intermediate-temperature fuel cells.     

The influence of the organolithium reagent nature on the possibility of the O→C<Subscript>sp</Subscript> migration of the R<Subscript>3</Subscript>Si group in propynes HC≡CCH<Subscript>2</Subscript>OSiR<Subscript>3</Subscript>

A possibility of the O→C_sp 1,4-migration of the R₃Si group in silyl ethers of terminal acetylenic alcohols upon treatment with organolithium reagents (RLi) was studied. In the case of 3-trimethylsilyloxypropyne, depending on the nature of RLi, the heterolysis of the Si—O bond occurs either by the action of acetylide formed as a result of deprotonation with the formation of 3-trimethylsilylprop-2-yn-1-ol trimethylsilyl ether, or by the action of the metalation agent with the formation of propargyl alcohol. The realization of the O→C_sp 1,4-migration of the Me₃Si group requires the use of mild organolithium reagents (lithium hexamethyldisilazanide and diisopropylamide). Silyl ethers having steric hindrance at the carbon atom bonded to the reaction center or around the silicon atom do not react with the studied organolithium reagents.     

Formation of nanocrystals in the ZrO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO₂ in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperature up to 800°C and higher activates mass transfer processes and, as a result, activates the nanoparticle growth and increases the fraction of the phase based on monoclinic modification of ZrO₂ due to mass transfer from the nanoparticles with the non-equilibrium tetragonal structure. Herewith, formed ZrO₂ nanocrystals with monoclinic structure have a broad size distribution of crystallites, and the average crystallite size after thermal treatment at 1200°C for 20 min is about 42 nm.     

Phase complex of a NaCl—KCl—SrCl<Subscript>2</Subscript>—Sr(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> four-component system and the physicochemical properties of a eutectic mixture

Tree of phases and crystallization were plotted via a priori prediction, and the coordinates (composition) of a nonvariant point of a NaCl-KCl-SrCl₂-Sr(NO₃)₂ four-component system were determined according to calculations and experimental data. The promise of the method for determining the coordinates of nonvariant points in multicomponent systems was confirmed experimentally. The dependence of density and electroconductivity vs. temperature was studied. The volume dilation of a melt was calculated up to the maximum operating temperature.     

Synthesis and investigation of the heat capacity of Sm<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> in the 346–1050 K range

Optimal conditions for the synthesis of Sm₂Sn₂O₇ with pyrochlore crystal structure by solid-phase reactions were determined. The effect of temperature (346–1050 K) on the molar heat capacity of samarium stannate was studied by differential scanning calorimetry. Thermodynamic properties of Sm₂Sn₂O₇ in the temperature range under study were determined using the experimental data.     

Specific features of the crystal and local structures of compounds formed in the Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>–HfO<Subscript>2</Subscript> system

The crystal and local structures of compounds formed in the Dy₂O₃–HfO₂ system (at molar ratios from 1: 3 to 3: 1) in the course of isothermal annealing of X-ray amorphous mixed hydroxides at temperatures up to 1600°C have been studied. At the molar ratio Dy₂O₃: HfO₂ from 1: 3 to 1: 1, crystallization leads to formation of single-phase defect fluorite solid solutions nDy₂O₃ ? mHfO₂ with clearly pronounced nonequivalence of parameters of local environment of Dy³⁺ and Hf⁴⁺ cations. It has been found that Dy₂H₂O₇ (Dy₂O₃: HfO₂ = 1: 2) samples have a tendency to pyrochlore-type ordering in both the cationic and anionic sublattices.