Films of certain oxides of rare-earth elements as the activators of platinum electrode on ZrO<Subscript>2</Subscript> + 10 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> electrolyte

The characteristics of porous Pt/YSZ (ZrO₂ + 10 mol % Y₂O₃) electrodes activated with small amounts of either oxides of rare-earth elements (REE) of the cerium subgroup (CeO₂, PrO _x , TbO _x ) or a mixed oxide with the Сe₂Tb₄O₁₁ composition by the procedure of impregnating the electrodes with ethanol solutions of REE nitrates and subsequent heating at 850°С are studied by the impedance method. The studies are carried out for those cases where the REE oxides after thermal treatment form a film on the electrolyte and also where no activator film is formed. The characteristics of films and activated electrodes are compared. Film-activated Pt/YSZ electrodes are discussed within the framework of the model of compact oxide electrodes.     

Mid-temperature solid oxide fuel cells with thin film ZrO<Subscript>2</Subscript>: Y<Subscript>2</Subscript>O<Subscript>3</Subscript> electrolyte

Data on the mid-temperature solid-oxide fuel cells (SOFC) with thin-film ZrO₂-Y₂O₃ (YSZ) electrolyte are shown. Such a fuel cell comprises a carrying Ni-YSZ anode, a YSZ electrolyte 3–5 μm thick formed by vacuum ion-plasma methods, and a LaSrMnO₃ cathode. It is shown that the use of a combined method of YSZ electrolyte deposition, which involves the magnetron deposition of a 0.5–1.5-μm thick sublayer and its pulse electron-beam processing allows a dense nanostructured electrolyte film to be formed and the SOFC working temperature to be lowered down as the result of a decrease in both the solid electrolyte Ohmic resistance and the Faradaic resistance to charge transfer. SOFC are studied by the methods of voltammentry and impedance spectroscopy. The maximum power density of the SOFC under study is 250 and 600 mW/cm⁻² at temperatures of 650 and 800°C, respectively.     

Oxygen redistribution during crystal growth of ZrO<Subscript>2</Subscript>-R<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions

This paper presents the results of our experimental studies of quantitative redistribution and isotope fractionation of oxygen during the crystal growth of cubic solid solutions based on ZrO₂. The single crystals were grown by directional crystallization of a melt in a cold container. As stabilizing oxides, we used Y₂O₃, Gd₂O₃, and Yb₂O₃ in concentrations of 8–40 mol %. The results showed that the oxygen isotopic growth effects changed depending on the type and content of the stabilizer in the crystals of ZrO₂-R₂O₃ solid solutions.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> phase diagram

Phase relations in the Y₂O₃-Ga₂O₃ system were studied by the anneal-and-quench technique in air within 1000–2300°C, and a phase diagram was plotted. Three compounds were found to form: Y₃GaO₆, Y₄Ga₂O₉, and Y₃Ga₅O₁₂; the temperature and concentration bounds of stability were determined for these compounds. Indexing results for Y₃GaO₆ are given.     

Oxygen isotope exchange between the gas-phase and the electrochemical cell O<Subscript>2</Subscript>, Pt | YSZ | Pt,O<Subscript>2</Subscript> under conditions of applied potential difference

The kinetics of oxygen isotope exchange between gas-phase oxygen and the electrochemical cell O₂, Pt | ZrO₂ + 10 mol % Y₂O₃ (YSZ) | Pt, O₂ with applied potential difference (ΔU = ±1.2 V) is studied in the temperature range of 600–800°С and the oxygen pressure interval of 3–13 kPa. An original design of a vacuum electrochemical cell with the separated gas space is put forward for studying how the potential difference on the electrochemical cell influences the kinetics of interaction of gas-phase oxygen with the gas electrode O₂, Pt | YSZ in the electrochemical cell. It is shown that the oxygen interphase exchange rate is the higher the more negative the charge on the electrode studied; moreover, the mechanism of gas-phase oxygen exchange with the gas electrode O₂, Pt | YSZ in the electrochemical cell depends fundamentally on the electrode charge sign. The possible reasons for the revealed differences are discussed; the corresponding models are proposed.     

Synthesis and properties of CaZrO<Subscript>3</Subscript> films on YSZ electrolyte surface

CaZrO₃ films are studied that were obtained on ceramic supports of solid electrolyte of ZrO₂ + 9 mol % Y₂O₃ (YSZ, yttria stabilized zirconia) from alcohol solutions of zirconium oxychloride and calcium nitrate using the method of dipping with the following drying and annealing. The thickness and morphology of films depend on the concentration of the film-forming solution. Vickers microhardness of the CaZrO₃ films was determined. The impedance spectroscopy method was used to study conductivity of films at the temperature of 400–600°C by comparison of impedance spectra of clean supports and supports with a film coating.     

Selective catalytic oxidation of ammonia into nitrogen and water vapour over transition metals modified Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript>

Copper or iron supported on commercially available oxides, such as γ-Al₂O₃, TiO₂ (anatase) and monoclinic tetragonal ZrO₂ (mt-ZrO₂) were tested as catalysts for selective catalytic oxidation of ammonia into nitrogen and water vapour (NH₃-SCO) in the low temperature range. Different commercial oxides were used in this study to determine the influence of the specific surface area, acidic nature of the support and crystalline phases as well as of the type of species and aggregation state of transition metals on the catalytic performance in selective ammonia oxidation. Copper modified oxide supports were found to be more active and selective to nitrogen than catalysts impregnated with iron. Activities of both transition metal modified samples decreased in the following order: mt-ZrO₂, TiO₂ (anatase), γ-Al₂O₃. Quantitative total ammonia conversion was achieved with the Cu/ZrO₂ catalytic system at 400°C. Characterisation techniques, e.g. H₂-temperature programmed reduction, UV-VIS-diffuse reflectance spectroscopy, suggest that easily reducible copper oxide species are important in achieving high catalytic performances at low temperatures.     

ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> binary oxides as promising supports for palladium catalysts of hydrodechlorination

Deposited palladium catalysts of the hydrodechlorination of 1,3,5-trichlorobenzene were studied. Pure zirconium and aluminum oxides and ZrO₂-Al₂O₃ mixtures with 1, 5, and 10 mol % Al₂O₃ prepared by coprecipitation were used as supports. Palladium was deposited by the precipitation of its hydroxide on supports. Catalysts on binary supports (ZrO₂ + 1% Al₂O₃ and ZrO₂ + 5% Al₂O₃) exhibited higher activity and stability in hydrodechlorination compared with catalysts on pure supports. The suggestion was made that the high activity and stability of these systems in hydrodechlorination was related to the formation of binary oxide in the interaction of ZrO₂ with palladium oxide at the stage of annealing of the catalyst precursor. Binary oxide, which was a center of the activation of the C-Cl bond, was simultaneously a source of active hydrogen. The presence of various palladium states in catalysts was substantiated by the temperature programmed reduction method.     

The Role of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgO Additives on the Photoluminescence Properties of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Nanoparticles

The current research addressed synthesizing and studying photoluminescence studies of β-Si₃N₄ nanoparticles. The effect of MgO and Y₂O₃ as the typical additives on photoluminescence behaviour was evaluated. The β-Si₃N₄ with MgO and Y₂O₃ additive specimens were fabricated by a solid state technique (ball-milled method). The as-prepared products were characterized by X-ray diffraction technique, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman analysis. The results showed that after ball-milled process, hexagonal β-Si₃N₄ with MgO or Y₂O₃ as the additives with the size distribution of 45–50 nm was obtained. The optical properties of the as-synthesized product were also investigated by photoluminescence and diffuse reflection spectroscopy. The obtained results confirmed that employing MgO as an additive, in comparison to the Y₂O₃, could enhance emission properties in the synthesized silicon nitride nanoparticles. The obtained results also showed that MgO–Si₃N₄ pair acted as FRET system to enhance the emission intensity of β-Si₃N₄ nanoparticles.     

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.     

Effect of crystalline modification of the support on the reduction and catalytic properties of Cu/ZrO<Subscript>2</Subscript> catalysts in the steam reforming of bioethanol

A study was carried out on the steam reforming of bioethanol (15 vol.% ethanol in water) at 250–500 °C on copper catalysts supported on ZrO₂ of the monoclinic (Z) and yttrium-stabilized tetragonal crystalline modifications (YSZ). Copper nanoparticles in such catalysts have similar reactivity regardless of the copper content and crystalline modification of the support. Cu/YSZ is highly selective relative to CO₂, which may be related to enhanced mobility of oxygen in the support in the presence of Y₂O₃ stabilizing additive.     

Structure and surface properties of ZrO<Subscript>2</Subscript>, CeO<Subscript>2</Subscript>, and Zr<Subscript>0.5</Subscript>Ce<Subscript>0.5</Subscript>O<Subscript>2</Subscript> prepared by a microemulsion method according to X-ray diffraction,TPR, and EPR data

It was established by X-ray diffraction, TPR, and EPR that microemulsion (m.e.) synthesis yields the binary oxides ZrO₂(m.e.) and CeO₂(m.e.) and the mixed oxide Zr_0.5Ce_0.5O₂(m.e.) in the form of a tetragonal, cubic, and pseudocubic phase, respectively, having crystallite sizes of 5–6 nm. The bond energy of surface oxygen in the (m.e.) samples is lower than in their analogues prepared by pyrolysis. Hydrogen oxidation on the oxides under study occurs at higher temperatures than CO oxidation. ZrO₂(m.e.) and CeO₂(m.e.) are active in O₂⁻ formation during NO + O₂ adsorption, while CeO₂ is active during CO + O₂ adsorption, too. However, its amount here is one-half to one-third its amount in the pyrolysis-prepared samples, signifying a reduced number of active sites, which are Zr⁴⁺ and Ce⁴⁺ coordinatively unsaturated cations and Me⁴⁺-O²⁻ pairs. O₂⁻ radical anions are stabilized in the coordination sphere of Zr⁴⁺ coordinatively unsaturated cations via ionic bonding, and in the sphere of Ce⁴⁺ cations, via covalent bonding. Ionic bonds are stronger than ionic-covalent bonds and do not depend on the ZrO₂ phase composition. Zr_0.5Ce_0.5O₂ is inactive in these reactions because of the strong interaction of Zr and Ce cations. It is suggested that Ce^{(4 + β)+} coordinatively unsaturated cations exist on its surface, and their acid strength is lower than that of Zr⁴⁺ and Ce⁴⁺ cations in ZrO₂ and CeO₂, according to the order ZrO₂ > CeO₂ ≥ Zr_0.5Ce_0.5O₂. Neither TPR nor adsorption of probe molecules revealed Zr cations on the surface of the mixed oxide.     

Comparative study of the structural,optical, and electrical properties of CuAlO<Subscript>2</Subscript> thin films on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and YSZ substrates via chemical solution deposition

Single-phase delafossite CuAlO₂ thin films are deposited successfully on Al₂O₃ (001) and YSZ (100) substrates using the chemical solution method. X-ray diffraction data present that the CuAlO₂ film on the Al₂O₃ (001) substrate is epitaxial, whereas that on YSZ (100) is c-axis oriented; the same is also demonstrated by the HRTEM images and SAED patterns. Optical transmittance spectra exhibit that both films have high transparency in the visible region. However, in this region, the optical transmittance of the CuAlO₂ thin film deposited on (001) Al₂O₃ is inferior to that deposited on (100) YSZ. This optical anomaly can be attributed to surface scattering. Electrical transport measurements show that the resistivity of the film on (001) Al₂O₃ is one order lower than that on (100) YSZ, suggesting that in-plane orientation is significant in improving hole mobility.     

Mixed amphoteric oxide ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as catalyst for the conversion of 2-methyl-3-butyn-2-ol

The TPR spectra of the conversion of 2-methyl-3-butyn-2-ol (MBOH) on mixed ZrO₂-Al₂O₃ oxides with different ZrO₂ contents were obtained by desorption mass spectrometry. It was shown that MBOH is dehydrated to 3-methyl-3-buten-1-yne on the acid centers (H₀ ≥ –3.3) and is decomposed to acetylene and acetone at the basic centers (H_– ≤ +6.8) of this oxide. The formation of acid centers in the amorphous structure of ZrO₂-Al₂O₃ at 1.5 < Al/Zr < 3is explained by the Tanabe rule.     

Preparation and characterization of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/ZrO<Subscript>2</Subscript> catalyst for carbonation of methanol into dimethyl carbonate

A H₃PW₁₂O₄₀/ZrO₂ catalyst for effective dimethyl carbonate (DMC) formation via methanol carbonation was prepared using the sol–gel method. X-ray photoelectron spectra showed that reactive and dominant (63%) W(VI) species, in WO₃ or H₂WO₄, enhanced the catalytic performances of the supported ZrO₂. The mesoporous structure of H₃PW₁₂O₄₀/ZrO₂ was identified by nitrogen adsorption–desorption isotherms. In particular, partial sintering of catalyst particles in the duration of methanol carbonation caused a decrease in the Brunauer–Emmett–Teller surface area of the catalyst from 39 to 19 m²/g. The strong acidity of H₃PW₁₂O₄₀/ZrO₂ was confirmed by the desorption peak observed at 415 °C in NH₃ temperature-programmed desorption curve. At various reaction temperatures (T?=?110, 170, and 220 °C) and CO₂/N₂ volumetric flow rate ratios (CO₂/N₂?=?1/4, 1/7, and 1/9), the calculated catalytic performances showed that the optimal methanol conversion, DMC selectivity, and DMC yield were 4.45, 89.93, and 4.00%, respectively, when T?=?170 °C and CO₂/N₂?=?1/7. Furthermore, linear regression of the pseudo-first-order model and Arrhenius equation deduced the optimal rate constant (4.24?×?10^?3 min^?1) and activation energy (E_a?=?15.54 kJ/mol) at 170 °C with CO₂/N₂?=?1/7 which were favorable for DMC formation.     

Physicochemical properties and mixed electronic and ionic conduction of composite ceramics in the system ZrO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

Composites ZrO₂-(Bi₂CuO₄+ 20 wt % Bi₂O₃) (50–80 vol % ZrO₂) are synthesized and their physicochemical properties are studied. It is demonstrated that the composites comprise triple-phase mixtures of ZrO₂ of a monoclinic modification, Bi₂CuO₄, and solid solution Bi_2?x Zr _x O_{3 + x/2} and retain their mechanical strength up to 800°C. Impedance spectroscopy is used to examine their electroconductivity at 700–800°C in the interval of partial oxygen pressures extending from 37 to 2.1 × 10⁴ Pa. Contributions made by electronic and ionic constituents to their overall conductivity are evaluated. The best specimens’ conductivity is ～0.01 S cm^?1, with the electronic and ionic transport numbers nearly equal. The composite consisting of 50 vol % ZrO₂ and 50 vol % (Bi₂CuO₄ + 20 wt % Bi₂CuO₄) is tested in the role of an oxygen-separating membrane. The selective flux of oxygen in the temperature interval 750–800°C amounts to (2.2–6.3) × 10^?8 mol cm^?2 s^?1, testifying that these materials may be used as gas-separating membranes.     

Synthesis and High-Temperature Heat Capacity of Y<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>

Yttrium germanate Y₂Ge₂O₇ was prepared by solid-phase synthesis from a stoichiometric Y₂O₃–GeO₂ mixture under multistage calcination in air within a temperature range of 1273–1473 K. The molar heat capacity of polycrystalline samples was measured by differential scanning calorimetry (DSC), and the C _P = f(T) dependence was used to calculate the thermodynamic properties of yttrium digermanates, such as the enthalpy and entropy changes and the reduced Gibbs energy.     

A comparative study of Ir/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, Pt/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Ru/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in selective hydrogenation of crotonaldehyde

Catalytic performance of gallia-supported iridium catalysts in the reaction of selective hydrogenation of crotonaldehyde in the gas phase was studied and compared to that of platinum and ruthenium catalysts. The best catalytic properties in terms of the selectivity to crotyl alcohol are shown by 5 wt % Pt/α-Ga₂O₃ and 5 wt % Ir/α-Ga₂O₃ catalysts prepared from nonchlorine precursors: Pt(acac)₂ and Ir(acac)₃, but for the 5 wt % Pt/α-Ga₂O₃ a very high selectivity of 75% at the high conversion (ca. 60%) is observed. A high selectivity of galia-supported iridium and platinum catalysts was explained by the surface reducibility of gallium oxide leading to covering (decoration) of platinum and iridium by gallium suboxides and the promoting effect of gallium.     

Thermal stability and catalytic properties of the composite amorphous Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-nanocrystals ZrO<Subscript>2</Subscript>

Catalytic properties in relation to the hydrogen oxidation reaction and thermal stability of materials based on the nanocomposite amorphous Al₂O₃-nanocrystalline ZrO₂ were studied.     

Effect of the alkoxides addition order on the properties of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> catalysts used for methane combustion

A series of Pd/Al₂O₃–ZrO₂ catalysts were prepared to be used in methane oxidation. The effect of the addition order of metal alkoxides on the texture, structure and catalytic properties of the solids is studied. The control of the preparation parameters is achieved via sol gel way as an attractive route of the preparation of these catalysts. N₂ physisorption, XRD, Scanning Electronic Microscopy (SEM) and H₂ chemisorption are the main techniques used to characterize the prepared Pd/Al₂O₃–ZrO₂ catalysts. Textural analysis reveals the mesoporosity of all the catalysts independently of the addition order of alkoxides while surface area is more pronounced when the aluminium alkoxide is added before or with the zirconium precursor. XRD patterns show the development of the zirconia tetragonal phase for all the catalysts. Better metallic dispersion is obtained when aluminium alkoxide is added first which can be justified by the high homogeneity observed on the corresponding catalyst as revealed by SEM technique.