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Ce0.5Zr0.5O2 mixed oxides were prepared in a flow reactor in supercritical isopropanol with acetylacetone as a complexing agent. Variation of the nature of the Zr salt and the temperature of synthesis affected the phase composition, morphology and specific surface area of oxides. X-ray diffraction and Raman spectroscopy studies revealed formation of metastable t” and t’ phases. Oxides are comprised of agglomerates with sizes depending on the synthesis parameters. Loading NiO decreases the specific surface area without affecting X-ray particle sizes of supports. Such sintering was the most pronounced for a support with the highest specific surface area, which resulted in the lowest surface content of Ni as estimated by X-ray photoelectron spectroscopy and in the formation of flattened NiO particles partially embedded into the support. The catalytic activity and stability of these samples in the dry reforming of methane were determined by the surface concentration of Ni and the morphology of its particle controlled by the metal-support interaction, which also depends on the type of catalyst pretreatment. Samples based on ceria-zirconia oxides prepared under these conditions provide a higher specific catalytic activity as compared with the traditional Pechini route, which makes them promising for the practical application.

Mixed nanocrystalline Ce-Zr-O oxides (Ce/Zr = 1 or 7/3) were prepared by modified Pechini route using ethylene glycol solutions of metal salts. Detailed characterization of their real structure and surface properties by X-ray diffraction on synchrotron radiation with the full-profile Rietveld analysis, high resolution electron microscopy with elemental analysis, Raman spectroscopy, UV-Vis and X-ray photoelectron spectroscopy revealed a high homogeneity of cations distribution in nanodomains resulting in stabilization of disordered cubic phase. This provides a high dispersion of NiO loaded on these mixed oxides by wet impregnation, a high reactivity and mobility of oxygen in these catalysts and strong interaction of Ni with support in the reduced state. This helps to achieve a high activity and coking stability of developed catalysts in CH4 dry reforming in feeds with CH4 concentration up to 15% and CH4/CO2 ratio =1.

The process of biomineralization of apatite in nature has been studied by scientists from various fields of science for more than a century. Unlike the volcanogenic, hydrothermal, and other types of igneous apatites, the genesis of which is entirely clear, the formation of phosphate ores of marine sedimentary origin is still debatable. Since phosphate concentrations in water bodies are too low for the spontaneous precipitation of solid phosphates, the study of different ways for their concentration is of particular interest. In this work, phase equilibria in the system CaO–P2O5–HF–H2O at 298 K, involving fluorapatite formation, have been studied. Fluorapatite is known to be the most common phosphate mineral and the main source of phosphorus on Earth, playing an important role in the mineralization process of dental tissues in vertebrates. The equilibrium in the system defined above was studied at a low mass fraction of the liquid phase components, i.e., in conditions close to natural. It has been shown that the compounds of variable composition with the fluorapatite structure containing HPO42− ions were formed in the acid region of this system. These compounds are formed at pH ≤ 7.0 and have invariant points with monetite, CaHPO4, and fluorite, CaF2. Stoichiometric fluorapatite was formed at the lowest concentrations of the liquid phase components in a neutral and weakly alkaline medium and had an invariant point with Ca(OH)2. The composition of the resulting equilibrium solid phases was found to be dependent on the Ca/P ratio of the initial components and pH of the equilibrium liquid phase. Fluorite CaF2 was present in each sample obtained in this study. [ABSTRACT FROM AUTHOR]

In this paper, room-temperature chemiresistive gas sensors for NO2 detection based on CVD-grown carbon nanofibers (CNFs) were investigated. Transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction were used to investigate the carbon nanomaterials. CNFs were synthesized in a wide range of pressure (1–5 bar) by COx-free decomposition of methane over the Ni/Al2O3 catalyst. It was found that the increase in pressure during the synthesis of CNFs induced the later deactivation of the catalyst, and the yield of CNFs decreased when increasing pressure. Sensing properties were determined in a dynamic flow-through installation at NO2 concentrations ranging from 1 to 400 ppm. Ammonia detection was tested for comparison in a range of 100–500 ppm. The obtained sensors based on CNFs synthesized at 1 bar showed high responses of 1.7%, 5.0%, and 10.0% to 1 ppm, 5 ppm, and 10 ppm NO2 at 25 ± 2 °C, respectively. It was shown that the obtained non-modified carbon nanomaterials can be used successfully used for room temperature detection of nitrogen dioxide. It was found that the increase in relative humidity (RH) of air induced growth of response, and this effect was facilitated after reaching RH ~35% for CNFs synthesized at elevated pressures. [ABSTRACT FROM AUTHOR]

Nd tungstates and molybdates are promising materials for hydrogen separation membranes due to their high protonic conductivity. This work aims at elucidating the structural, textural and oxygen transport features of Nd5.5WO11.25−δ, Nd5.5W0.5Mo0.5O11.25−δ and (Nd5/6La1/6)5.5WO11.25−δ and their composites with Ni0.5Cu0.5O synthesized by mechanical activation. The oxide materials obtained were distorted double fluorites but their composites with Ni0.5Cu0.5O possess a complex phase composition. Extended defects such as grain boundaries, stacking faults and surface steps/terraces were observed in TEM images, which allow fast diffusion transport along grain boundaries (D* ∼ 10−6 cm2 s−1 at 700 °C) and slower diffusion within grains' bulk (D* ∼ 10−11, 10−12 and 10−13 cm2 s−1 at 700 °C for the rather fast, "middle" and slow channels of bulk diffusion) (2D diffusion). The model gives the best description of experimental data obtained by the isotope exchange of oxygen with C18O2 in a flow reactor. For composites with Ni0.5Cu0.5O, a significant decrease in oxygen diffusivity was shown. The reduction and subsequent reoxidation of composites resulted in an increase in oxygen mobility probably due to the partial unblocking of oxygen diffusion corresponding to the Ln tungstates/molybdates. Fine oxygen transport features allow us to increase the hydrogen yield of hydrogen separation membranes due to the proton transport mechanisms involving oxide anions and the water splitting reaction. Hence, the features of Nd tungstates and their composites with nickel(II)–copper(II) oxide studied demonstrated their high potential for use in catalytic reactors based on hydrogen separation membranes. [ABSTRACT FROM AUTHOR]

In our study, we have obtained a multicomponent MoVSbNbCeOx/SiO2 catalyst with high catalytic activity for oxidative dehydrogenation of ethane (ODE) to ethylene. To date, multicomponent MoVTe(Sb)NbOx catalysts, which have been intensively studied during the last years, were found as very promising for the ODE to produce ethylene. It was generally agreed that the MoVTeNbOx catalyst was more efficient than MoVSbNbOx. The major drawback of using Te‐containing catalysts is the presence of environmentally harmful, toxic tellurium, and its volatility during the catalyst preparation and catalytic reaction conditions. In our work, the Mo1V0.24Sb0.23Nb0.08Ce0.01Ox/50 wt. % SiO2 catalyst was prepared via the spray‐dry method of aqueous solutions of the starting components, followed by heat‐treatment in He at 350 and 600 °C. For comparative purpose, one of the best Te‐containing catalysts Mo1V0.3Te0.23Nb0.12Ox was also tested in this reaction under the similar reaction conditions. A comparison of the catalytic properties of Sb− and Te− containing catalysts at the reaction temperature of 400–450 °C illustrates for both catalysts relatively high catalytic properties for ODE. The yield of ethylene of ca. 74 % was obtained for these catalysts, which exceeds the best yield reported in literature for Sb‐containing catalysts. The two main phases – M1 and M2 were revealed by XRD in the Sb‐containing catalyst. Intergrowth between the crystals of M1 and M2 phases with the formation of the interphase boundary in the highly active and selective Sb‐containing catalyst can be proposed from HRTEM results. The nature of the active state in this catalyst is discussed. [ABSTRACT FROM AUTHOR]