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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.

Fast diffusion along grain boundaries and slow diffusion within grains’ bulk were revealed for Nd tungstates. A significant decrease in diffusivity was shown for their composites as the reduction + reoxidation led to an increase in oxygen mobility.

In this study, the mechanochemical synthesis of substituted hydroxyapatite (HA) containing zinc and silicon ions having a chemical formula of Ca10−xZnx(PO4)6−x(SiO4)x(OH)2−x, where x = 0.2, 0.6, 1.0, 1.5, and 2.0, was carried out. The synthesized materials were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and inductively coupled plasma spectroscopy. We found that HA co-substituted with zinc and silicate formed up to x = 1.0. At higher concentrations of the substituents, the formation of large amounts of an amorphous phase was observed. The cytotoxicity and biocompatibility of the co-substituted HA was studied in vitro on Hek293 and MG-63 cell lines. The HA co-substituted with zinc and silicate demonstrated high biocompatibility; the lowest cytotoxicity was observed at x = 0.2. For this composition, good proliferation of MG-63 osteoblast-like cells and an increased solubility compared with that of HA were detected. These properties allow us to recommend the synthesized material for medical applications, namely, for the restoration of bone tissue and manufacture of biodegradable implants.

A comparison is made of the thermoanalytical characteristics and the composition and structure of solid products of the thermal decomposition of ortho-phthalates [Cu(H2O)2(C8H4O4)], [CuNi(H2O)4(C8H4O4)2], and [Ni(H2O)2(C8H4O4)](H2O)2. It is found that the thermal decomposition of these compounds upon heating to 500°C in a He atmosphere can be conditionally divided into two stages: dehydration and decarboxylation. Polymer conglomerates containing uncoated Cu nanoparticles as large as 75 nm are embedded into the polymer matrix of the composite obtained via the thermal decomposition of [Cu(H2O)2(C8H4O4)]. Three types of nanoparticles with sizes of 40–85, 15–25, and 10–15 nm are embedded in the polymer matrices of composites. The particles are Cux/Ni1−x solid solutions of different compositions, obtained via the thermolysis of [CuNi(H2O)4(C8H4O4)2]. It is found that the onset temperature of [CuNi(H2O)4(C8H4O4)2] decarboxylation at the third part of the second stage with the formation of a three-phase region correlates with the temperature of decomposition of Cux/Ni1 – x solid solutions in the binary metal system, due apparently to the quantum size effect.

A series of Al2O3 nanoparticles with the sizes ranging from ~ 2 to 21 nm, according to XRD, HRTEM and BET, was obtained by vaporization of α-Al2O3 in flowing helium and argon at different pressures under the action of a cw CO2 laser. The particle size was changed by varying the composition of ambient gas (He, Ar) and its pressure in a vaporization chamber from 0.034 to 0.9 bar. The effect of the synthesis conditions on the properties of Al2O3 nanopowders is presented and discussed. Particles with the size smaller than 6–7 nm have a faceted shape, whereas the shape of larger particles is close to spherical. It was found that the resulting nanopowders consist of a mixture of transition aluminas, among which the γ-polymorph is dominant. Thermal analysis showed that for smaller nanoparticles the phase transition to α-Al2O3 occurs at a lower temperature. In nominally pure Al2O3 nanoparticles with different sizes, photoluminescence at RT and 80 K is determined by trace level concentrations (≤10–3 wt%) of uncontrolled impurities of 3d elements (Cr3+(Oh) and Fe3+(Td)), surface hydroxyl groups, and point defects represented mostly by F-type centers. The acquired experimental data indicate that manifestation of the size effect for Al2O3 nanoparticles has a boundary corresponding to 6–7 nm. Al2O3 nanoparticles with the dominant γ-Al2O3 structure obtained by the laser method can be promising in many chemical reactions, particularly as the supports of catalysts and sorbents, for which the high specific surface area is of special importance.

The doping of hydroxyapatite with various substituent ions can give this material new and useful properties. Nonetheless, local distortions of structure after doping can change the properties of the material. In this work, the thermal stability of copper-substituted hydroxyapatite synthesized by the mechanochemical method was investigated. In situ diffraction analyses showed that copper ion diffusion during the heating of Cu-substituted hydroxyapatite promotes phase transformations in the substituted hydroxyapatite. The behavior of copper ions was studied in samples with ratios (Ca + Cu)/P = 1.75 and 1.67. It was found that in both cases, single-phase Cu-substituted hydroxyapatite with the general formula Ca10−xCux(PO4)6−y(CO3)y(OH)2−yOy is formed by the mechanochemical synthesis. When heated at approximately 600–700 °C, the lattice loses copper cations, but at higher temperatures, CuO diffusion into the hydroxyl channel takes place. Cuprate-substituted hydroxyapatite with the general formula Ca10(PO4)6(OH)2−2x(CuO2)x forms in this context. At 1200 °C, the sample is single-phase at (Ca + Cu)/P = 1.75. Nonetheless, slow cooling of the material leads to the emergence of a CuO phase, as in the case of (Ca + Cu)/P = 1.67, where the material contains not only CuO but also Cu-substituted tricalcium phosphate. In the manufacture of ceramic products from Cu-substituted hydroxyapatite, these structural transformations must be taken into account, as they alter not only thermal but also biological properties of such materials.

Ethanol steam reforming catalyst’s precursors, i.e., nanocomposites of complex oxides with the general formula [Pr0.15Sm0.15Ce0.35Zr0.35O2 + LaMn0.45Ni0.45Ru0.1O3] (1:1 by mass), were synthesized by three different methods. It was shown that two synthesis methods – ultrasonic dispersion and sequential polymeric method, lead to the formation of the nanocomposite perovskite–fluorite system with the specific surface area up to 50 m2/g. Reduction of samples at 400–500°C lead to the formation of Ni–Ru alloy nanoparticles strongly bound with the surface of oxide nanocomposite. Catalytic tests in ethanol steam reforming reaction at 500–600°C showed the highest specific activity of the sample prepared by the sequential polymeric method due to the location of Ni- and Ru-containing perovskite mainly on the surface of the composite providing a high concentration of active metal centers. At higher temperatures for all samples, ethanol conversion approached 100% with hydrogen yield varying in the range of 65–75%. A study of spent catalysts confirmed the absence of carbon deposits after long-term catalytic tests at 650°C.

Composites comprising MoVTeNbO mixed oxide and zirconia-pillared montmorillonite clays (PilCs) were prepared. XRD and TEM with EDX studies confirmed the preservation of M1 MoVTeNbO phase in these composites responsible for high activity and selectivity in ethane oxidative dehydrogenation into ethylene. For composites with PilC content of 10 wt%, the best ethylene yield exceeding that of bulk MoVTeNbO oxide was demonstrated for clays with zirconia pillars doped with Ce and Al possessing the highest specific surface area. This is explained by optimized chemical interaction of these clays with MoVTeNbO mixed oxide improving its bulk oxygen mobility and reactivity by structure disordering while blocking surface sites responsible for combustion due to the stabilization of the reactive terminal oxygen species.

Some results on the mechanochemical synthesis of apatites with simultaneous substitutions of calcium by lanthanum and of phosphate by silicate are presented. The reagents of reaction mixtures are taken such that to synthesize the compounds containing equal concentrations of lanthanum and silicon. The synthesis is performed in an AGO-2 planetary mill. The complete conversion of initial reagents in the synthesis of substituted apatite takes a longer period as compared to the time required for the synthesis of unsubstituted apatite. The mechanochemical synthesis time must be 40 min to synthesize lanthanum-and-silicate substituted apatite with a degree of substitution of

Formic acid is well-recognized as safe and convenient hydrogen carrier. Development of active and cost-effective catalysts for formic acid to hydrogen conversion is important problem of hydrogen energy field. Herein, we report on new Co catalysts supported on oxidized multi-walled carbon nanotubes (MWCNTs), which demonstrate high efficiency in the gas-phase formic acid decomposition affording molecular hydrogen. Various parameters of the catalysts, Co loading, MWCNTs structure, and nanotubes treatment conditions, have been investigated in terms of their influence on the catalytic properties. The catalysts morphology has been characterized with a set of physicochemical methods. It is found that the catalytic activity of Co particles depends on their electronic state and location on the support. Co species located inside the MWCNTs channels are less active than Co species stabilized on the outer surface. An increase in the content of Co nanoparticles on the MWCNT outer surface leads to a higher catalytic activity.

Novel methods were applied in this work to elucidate the structure evolution of Ln2-xCaxNiO4+δ oxides (Ln = La, Pr, Nd; x = 0, 0.3) and study their oxygen mobility. Relationship between cations state, structural, electrical, electrochemical and kinetic properties was revealed. In all doped materials the overall oxygen mobility characterized by Do declined by more than an order of magnitude due to decreasing the interstitial oxygen content and hampering cooperative mechanism of oxygen migration. For La nikelate additional slow diffusion channel appears with DO 5.4·10−14 cm2/s at 700 K. Correlation of electrochemical and oxygen transport properties was demonstrated. A high electrical conductivity (up to 120 S/cm at 700 K) in Ln1.7Ca0.3NiO4+δ (Ln = Pr, Nd) along with satisfactory oxygen mobility and electrochemical properties makes these materials promising for a wide row of electrochemical applications.

Chemical vapor deposition (CVD) along with thermal decomposition of monosilane (SiH4) in a fluidized bed of multiwalled carbon nanotubes (MWCNTs) is used to prepare MWCNT-Si composites containing silicon nanoparticles deposited on the nanotube surfaces. The structure of obtained Si nanoparticles in composites based on MWCNTs with different average diameters is studied by TEM, SEM, XRD, Raman spectroscopy, and FTIR spectroscopy of diffuse reflection. The size of Si particles varies from 3 nm to 45 nm and increases together with the MWCNT diameter. The major part of precipitated silica in the nanoparticles occurs in the amorphous state with small (below 3 nm in size) inclusions of nanocrystalline silicon. Specific discharge capacity of prepared composites used as the anode material for lithium-ion batteries is estimated.

The conductivity of three types of composites prepared by mechanical melt mixing from polyethylene (PE) and multi-walled carbon nanotubes (MWCNTs) with an average diameter of 9.8 nm and an aspect ratio of ∼3000, 112, 36 is studied. The structure of these composites is investigated by optical and scanning electron microscopies and powder X-ray analysis. Cyclic measurements of current-voltage (I–V) characteristics and the use of a 3-point measurement scheme showed that the current density through the composite is nonlinearly increasing with increasing voltage or upon sequential measurements of I–V characteristics with the same voltage. The results of I–V measurements were used to determine concentration dependences of conductivity and their changes for each type of MWCNTs. It is shown that the percolation threshold determined from the third I–V measurement for MWCNTs in composites prepared by mechanical melt mixing decreases with decreasing aspect ratio of nanotubes from 3000 to 36.

Formation features of mono- (Fe, Co, Ni), bi- (Fe-Co, Fe-Ni, Co-Ni), and trimetallic (Fe-Co-Ni) catalysts for the synthesis of multiwalled carbon nanotubes (MWCNTs) prepared by the method of polymerized complex precursors are revealed. It is shown that initial bimetallic and trimetallic catalysts occur in a wide range of phases with spinel structure consisting of different mixed metal oxides (Me(II)Me(III)2O4). The influence of the active component composition and the catalyst activation conditions on their activity in the reaction of MWCNT synthesis is determined. MWCNTs with specific structural characteristics, a narrow diameter distribution and a relatively low degree of defectiveness, can be obtained by varying the composition of the catalyst active component.

The effect of the residual catalyst for the synthesis of multi-walled carbon nanotubes (MWCNTs) on the electrophysical properties of MWCNT–polyethylene composites produced by melt mechanical mixing was studied. The residual catalyst content was varied by changing the MWCNTs synthesis time. The nanotubes used in the work were characterized using transmission and scanning electron microscopy, atomic emission analysis, X-ray phase analysis, and magnetic permeability measurements. The structure of the synthesized composites was studied using optical and scanning electron microscopy. The dependences of the specific magnetization on the applied magnetic field, bulk electrical conductivity on the volumetric content of the filler in the composite, and the frequency dependences of the reflection, transmission, and absorption of electromagnetic radiation in the range 0.01–18 GHz were obtained. It was established that the obtained composites are characterized by a uniform distribution of nanotubes in the polymer matrix, and the dependence of the bulk electrical conductivity on the content of MWCNTs in the composite has a percolation character. Variation in the synthesis time of nanotubes allows producing MWCNTs with a high content of ferromagnetic particles, which are an alloy close in stoichiometry to the composition of the active component of the catalyst. It was shown that the use of composites modified with MWCNTs with a high content of residual catalyst is more effective for absorbing electromagnetic radiation due to an increase in their magnetic losses.

Zinc-substituted hydroxyapatite samples with a preset degree of substitution (Са10 –хZnx(PO4)6(OH)2, x = 0.1–2.0) have been synthesized by a mechanochemical method. The composition of starting components ((Zn(H2PO4)2 ⋅ 2Н2О and ZnO) and water of crystallization have been shown to influence the apatite structure formation process and the degree of zinc substitution for calcium in the mechanochemical synthesis and annealing processes. When ZnO was used as a dopant, beta-tricalcium phosphate was observed to form as a reaction intermediate directly in the mill after 5–10 min of the reaction mixture milling and disappear after 20 min of milling. The final synthesis product—zinc-substituted hydroxyapatite—remains single-phase for x ≤ 0.8 in the case of Zn(H2PO4)2 ⋅ 2Н2О and x ≤ 0.25 in the case of ZnO. After annealing, the zinc-substituted hydroxyapatite is single-phase only in the case of zinc phosphate using at x ≤ 0.1.

The morphological and structural properties of Pd–CeO2/Al2O3 catalytic compositions annealed at 100, 500, and 1000°С are studied, along with thereof coatings deposited on metallic foil via cold gas dynamic spraying. The influence of the preparation technique of the initial catalytic composition and introducing active component into a coating on their phase states, particle sizes, and activitites is elucidated. It is shown that introducing active components via impregnation into preliminarily sprayed alumina layer ensures the uniform distribution of Pd and Ce in the support profile, the formation of nanosized PdO particles, and the phase of interaction between the components of the catalyst and support. The impregnated catalyst shows the highest activity in the reaction of methane oxidation. The technique for preparing coatings has no limitations when scaled up and can find application in manufacturing full-size catalysts on metallic foil for different types of power engineering devices.

A relationship is established between the structural and thermoanalytical characteristics of the decomposition of hydrogen maleates and phthalates of Fe(II), Co(II), Ni(II), Cu(II). The temperatures of the onset of the first and second stages of decomposition grow in the series of both hydrogen maleates Cu ≤ Fe < Co < Ni and phthalates Fe ≤ Co < Ni < Cu, while the lengths of M– $${{{\text{O}}}_{{{{{\text{H}}}_{2}}{\text{O}}}}}$$ and M–Oanion bonds shrink in these structures. At the third stage, the temperature of the onset of the decarboxylation of hydrogen maleates and phthalates falls in the order Fe > Co > Ni > Cu. The size of metal nanoparticles additionally contained in a polymer or graphene shell grows from 3.5 to 5 nm (Co) and from 4.5 to 7 nm (Ni) upon moving from composites obtained through the decomposition of hydrogen maleates to hydrogen phthalates. Polymeric conglomerates containing shell-less copper nanoparticles, the average size of which ranges from 7.5 to 50 nm, are incorporated into a polymer matrix of composites obtained via the thermolysis of Cu(II) hydrogen maleate and phthalate.

Morphologies and structures of catalytic compositions and coats based thereon were studied using Pd-CeO2/Al2O3 calcined at 100, 500, 1000 °C and the coats prepared by gas dynamic cold spraying onto a metal foil. It was established that the methods for preparation of the initial catalytic composition and for introduction of the active components to the coat influenced the phase composition, particle size and activity to oxidation of methane. The introduction of the active components by impregnation of the pre-deposited alumina layer was shown to provide the uniform distribution of Pd and Ce through the support profile, formation of nanosize PdO particles and of the interacting phases between the catalyst and support components. The impregnated catalyst was most active to oxidation of methane. The method for preparation of the coats has no limitations in scaling-up and, therefore, can be widely used for production of full-size catalysts on metal foils to be used for various energy devices.

We have studied interaction between the microwave activation product of gibbsite and an aqueous cobalt nitrate solution at room temperature, atmospheric pressure, and pH 8.0 ± 0.3. The results demonstrate that, under such conditions, the reaction in the near-surface region of the microwave-activated gibbsite particles leads to the formation of an aluminum cobalt oxyhydroxide with fragments of spinel structure and the composition Со2.3Al0.7O4, and a Со6 –xAl2 –x(OH)1.5 · 3.5H2O (0 ≤ x ≤ 1) nonstoichiometric hydrotalcite. The morphology of such compounds is determined by 2D nanoparticles in the form of bent sheets 2–5 nm in thickness and 500 nm or more in length. After calcination at 500°C, the composition of the reaction products corresponds to the aluminum cobalt oxide Со2.3Al0.7O4 with the spinel structure.

Reactivity of nanosized objects is a hot topic in modern solid-state chemistry and materials science. The present work is focused on the interaction between multi-walled carbon nanotubes (MWCNTs) and metallic titanium during high-energy ball milling and thermal explosion, a rapid temperature rise in a mixture caused by an exothermic reaction ignited by external heating and occurring throughout the sample volume. A fundamental property of the nanocomposite mixture—the ability of its components to react in the combustion mode—is explained; an analysis of the dependence of the combustion characteristics of the nanocomposites on the milling duration of powder mixtures is provided. The phase and structural transformations of the Ti-MWCNT mixtures have been analyzed using X-ray diffraction and transmission electron microscopy. It was found that the ball-milled powders contain nanostructured titanium, nanotube fragments, amorphous carbon and nanosized carbon-deficient titanium carbide TiCx. Within the nanocomposite powder particles, TiCx nanoparticles are covered with layers of amorphous carbon. Thermal explosion was observed in Ti-4mass%MWCNT mixtures milled for 1.5–7 min. Shorter milling times were apparently not sufficient for establishing a proper interfacial contact, while longer milling times led to the extensive formation of titanium carbide TiCx, which acted as a barrier lowering the heat release by the mixture upon ignition. Both the ignition temperature of Ti-4mass%MWCNT and the maximum temperature developed during thermal explosion decrease with the milling time. A comparison of the behavior of MWCNT with that of carbon black under conditions of thermal explosion in the mixtures with titanium is also presented.

We studied on the function of Pd species located in mesopores and inside zeolite channels (micropores) of the montmorillonite-modified zeolite catalyst for the hydrodesulfurization of diesel fraction with 350 ppm of sulfur as DBT, 4-MDBT, and 4,6-DMDBT. It was shown that the ex-dihydrogentetrachloropalladate impregnated catalyst as well as the ex-tetraamminepalladium(II) chloride ion-exchanged catalyst have high efficiency of sulfur removal from the diesel fuel in temperature range 280–300 оC. The sulfur tolerance of catalyst depended on the method of Pd adding. The catalyst prepared by ion-exchange with tetraamminepalladium chloride solution exhibited the highest sulfur tolerance. According to FTIR of adsorbed CO, this catalyst contains a small Pd metal atoms or cluster in electron-deficient state inside zeolite channels. They probably ensure sulfur tolerance due to hydrogen spillover. The montmorillonite addivite significantly modifies performance of the Pd-Zeolite catalyst in hydrotreating of diesel fraction. It leads to a decrease of cracking function, while those of hydrogenolysis of sulfurorganic molecules and hydrogenation of aromatic molecules are strengthened in comparison with the unmodified catalyst. This effect is explained by the change of acidic properties of the catalyst, limitations of diffusion of various molecules into the zeolite channels, and diffusion of Pd from the zeolite channels.

The Ni-containing catalysts based on ceria–zirconia doped with Ti and Ti+Nb were prepared by the solvothermal method in supercritical fluids. Ni deposition was carried out by incipient wetness impregnation and the one-pot technique. All materials were investigated by a complex of physicochemical methods (XRD, BET, TEM, H2-TPR). Samples catalytic properties were studied in methane dry reforming in the plug-flow reactor. Conversions of CH4 and CO2, H2/CO ratio, and CO and H2 yields were measured, and detailed kinetics analysis was carried out. The influence of Ni loading method and support modification on the catalytic behavior in the methane dry reforming process was studied. The preparation method of catalysts affects the textural characteristics. For one-pot samples, pore volume and surface area are lower than for impregnated samples. For catalysts on modified supports, strong metal–support interaction was shown to increase catalytic activity. A reduction pretreatment of samples was shown to have significant influence on their catalytic properties. The kinetic parameters such as reaction rate constant at 700 °C, effective activation energy, and TOF were estimated and analyzed.

Investigating the size distributions of Co nanoparticle ensembles is an important problem, which has no straightforward solution. In this work, we use the combination of 59Co internal field nuclear magnetic resonance (59Co IF NMR) and ferromagnetic resonance (FMR) spectroscopies on a metallic Co nanoparticle sample with a narrow Co nanoparticle size distribution due to encapsulation within the inner channels of carbon nanotubes. High-resolution transmission electron microscopy (TEM) images showed that the nanoparticles can be represented as prolate spheroids, with the majority of particles having an aspect ratio between 1 and 2. This observation has increased the accuracy of superparamagnetic blocking size calculations from Neel relaxation model by introducing the actual volume of the ellipsoids taken from the image processing. 59Co IF NMR and FMR experiments conducted under different temperatures allowed us to observe the thermal blocking of superparamagnetic particles in full accordance with the TEM particle volume distribution. This proved that these magnetic resonance techniques can be used jointly for characterization of Co nanoparticles in the bulk of the sample.

The effect of different regimes of combustion of glycine&ndash, nitrate precursors on the formation of perovskite phases (LaMnO3 and LaCrO3) without additional heat treatment was studied. The following three combustion regimes were compared: the traditional solution combustion synthesis (SCS), volume combustion synthesis (VCS) using a powdered precursor, and self-propagating high-temperature synthesis (SHS) using a precursor pellet. The products of combustion were studied using a series of physicochemical methods (attenuated total reflection infrared spectroscopy (ATR FTIR), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and thermal analysis). SHS was found to be the most productive regime for the formation of perovskite because of its ability to develop high temperatures in the reaction zone, which led to a reduced content of the thermally stable lanthanum carbonate impurities and to an increased yield and crystallite size of the perovskite phase. The reasons for the better crystallinity and purity of LaCrO3 as compared with LaMnO3 is also discussed, namely the low temperatures of the onset of the thermolysis, the fast rate of combustion, and the favorable thermodynamics for the achievement of high temperatures in the reaction zone.

TiO2 (rutile) samples with a hierarchical 3D nanostructure of the particles were synthesized by two methods: liquid hydrolysis of TiCl4 at 90 °С and atmospheric pressure; hydrothermal synthesis from TiCl4 at 160 °С and different [H2O]/[Ti] ratios. The effect exerted by conditions of the synthesis and post-treatments on the crystallite size, morphology, electronic properties and pore structure of the rutile samples was investigated. It was shown that severe hydrothermal conditions with the ratio [H2O]/[Ti] = 20 provide the formation of a more perfect crystal structure of rutile with a smaller band gap energy (3.00 eV against 3.06 eV for the rutile obtained by liquid hydrolysis at atmospheric pressure). The study revealed the stabilizing effect of cerium cations on the pore structure of rutile, which changes upon thermal treatment.

A series of 5%Ni-CexZr1−xO2 (x = 0.3, 0.5, 0.7) catalysts has been prepared via one-pot solvothermal continuous synthesis in supercritical isopropanol and incipient wetness impregnation of CexZr1−xO2 obtained by the same route. The textural, structural, red-ox, and catalytic properties in methane dry reforming (MDR) of Ni-modified Ce-Zr oxides synthesized by two routes have been compared. It was shown by XRD, TEM, and Raman spectroscopy that the method of Ni introduction does not affect the phase composition of the catalysts, but determines the dispersion of NiO. Despite a high dispersion of NiO and near-uniform distribution of Ni within Ce-Zr particles observed for the one-pot catalysts, they have shown a lower activity and stability in MDR as compared with impregnated ones. This is a result of a low Ni concentration in the surface layer due to segregation of Ce and decoration of nickel nanoparticles with support species.

To achieve a high activity and coking stability of nickel catalysts in dry reforming of methane, materials comprised of ceria–zirconia doped by Ti were investigated as supports. Ceria–zirconia supports doped with titanium were prepared either via the Pechini method or by synthesis in supercritical alcohol media. Ni-containing catalysts were prepared by two techniques: standard incipient wetness impregnation and one-pot synthesis. The catalytic reaction of DRM to synthesis gas was carried out in the 600–750 °C range over 5% wt. Ni/Ce(Ti)ZrO2. Dried and calcined supports and catalysts were characterized by physicochemical methods including N2 adsorption, XRD, Raman, H2-TPR, and HRTEM. Both preparation methods led to formation of solid solution with cubic fluorite-like structure, as well as after addition of Ti. Introduction of Ti should provide improved oxygen storage capacity and mobility of support oxygen. The highest activity was observed with the catalyst of 5% wt. Ni/Ce0.75Ti0.2Zr0.05O2−δ composition due to optimized oxide support structure and support oxygen mobility.

Three noble metal catalysts (Rh-, Pt-, Ru/Ce0.75Zr0.25O2–δ) for reforming of hydrocarbons were studied in steam and autothermal process conditions. Each catalyst was prepared by sorption-hydrolytic deposition with a metal loading of 0.1 mmol/g. The main idea of this technical approach was to form a solution of “metal complex + alkaline agent” that was metastable at given conditions (temperature, concentrations) with respect to homogeneous metal hydroxide precipitation, due to the kinetic inertness of the metal complexes for ligand exchange. As the support surface accelerated heterogeneous nucleation and growth of metal hydroxide particles, addition of the support to the reagent mixture initiated the hydrolysis which led to uniform depositing of 1–2 nm metal particles over the support surface. The Rh-based catalyst synthesized surpassed the Ru- and Pt-based catalysts in activity and stability in that under the experimental conditions, complete n-hexadecane conversion and equilibrium reformate product distribution were observed for 1-wt. % Rh/Ce0.75Zr0.25O2–δ for 17 h. This catalyst also showed competitive performance in autothermal reforming of diesel fuel providing stable operation for 9 h.

Conditions of synthesis are optimized and XRD and thermoanalytical studies are performed for normal maleate [Zn(H2O)2(C4H2O4)] and acid maleate [Zn(H2O)4(C4H3O4)2], along with acid Co(II)–Zn(II), Ni(II)–Zn(II) maleates. It is shown that when solid solutions thermally decompose in acidic maleate systems, the kinetically less stable component causes the temperature of decomposition of the more stable component to fall. It is established that the solid residue of Zn(II) maleate after heating to 500°C in a He atmosphere is a composite containing Zn oxide whose reduction to metal begins at 675°C. The decomposition of [(Co0.1Zn0.9)(H2O)4(С4H3O4)2] leads to the oozing of metallic cobalt atoms embedded in the channels of the ZnO structure that act as a catalyst for the spontaneous growth of uniform carbon nanotubes on the surface of the composite. After thermal decomposition of the samples in a system of acid Ni(II) maleate–acid Zn(II) maleate, only the bimetallic phase is observed in the composites, and there is no zinc oxide.

Polyethylene based composites modified with multi-walled carbon nanotubes (MWCNTs) were produced via in situ polymerization of ethylene with the Ti-Ziegler–Natta catalyst preliminarily immobilized on MWCNTs. The composite structure was characterized with transmission and scanning electron microscopy, differential scanning calorimetry (DSC) and in situ synchrotron X-ray Diffraction (in situ XRD). For the first time the Ti-containing catalyst species of the size 2–3 nm were observed on the MWСNTs surface stabilized in the polymer matrix. A comparative study of the melting-crystallization cycles of neat polyethylene (PE) and MWCNT-PE composites with in situ XRD and DSC provide information on the nucleation of PE crystals. For the first time, the in situ XRD technique was used for estimation of the coherent scattering region of PE blocks during the melting-crystallization cycles. These experiments and molecular dynamic modeling showed that MWCNTs act as the template for the PE chain orientation and as the nucleating agent for PE crystallization. However, the nucleation of PE crystals in composites occurs on the nanotube surface and also within the space between nanotubes. Thus, the relative volume of PE nucleated on nanotubes depends on their content in the composite and can be significant only for the composites with high nanotube loading.

Decoration of one-dimensional multi-walled carbon nanotubes (MWCNTs) with zero-dimensional Co nanoparticles leads to hybrid structures with chemical and electromagnetic features that are not available to the individual components. This work addresses the influence of the nature and structure of MWCNTs on the localization of Co nanoparticles. Depending on synthesis conditions, Co can be deposited on the external or in inner surfaces of the nanotubes. Co/MWCNTs hybrids have been characterized by in situ X-ray powder diffraction, high-resolution transmission electron microscopy and 59Co internal field nuclear magnetic resonance. It has been shown that the average diameter (7.2, 9.4 and 18.6 nm), number of walls (5–7, 12–15, 15–20), and functional composition of the MWCNTs have a remarkable effect on the size of Co nanoparticles and their distribution in the structure of MWCNTs. The observed phenomenon has been rationalized in terms of nanotubes surface properties. Parent MWCNTs being hydrophobic and having limited porosity do not stabilize Co nanoparticles and, therefore, they are localized on the outside surface with relatively large average size and broad size distribution. On the other hand, the oxidation of the MWCNTs resulted in the penetration of Co nanoparticles inside of the nanotubes, presumably because of pore opening as well as increased hydrophilicity of the nanotubes.

New results of an investigation of NH3BH3 dehydrogenation with supplying a limited quantity of aqueous solution of a catalyst precursor to a solid-state bed of the hydride particles with subsequent external heating at 40–90 °C are presented. Measurements of the reaction layer temperature and the amount of the evolved hydrogen have shown that at external heating temperature higher than 85°С there was acceleration of the first stage of the process, the highly exothermic catalytic hydrolysis of a portion of ammonia borane, which resulted in a stronger heating of the reaction layer and the start of NH3BH3 thermolysis. This type of process is referred to as hydrothermolysis. A TEM, ATR FTIR, and XRD investigation has shown that in the reaction medium the metal chlorides become reduced to an amorphous catalytically active phase. During this process, ammonia reacts with chlorides to form NH4Cl. All of this leads to increased rate of hydrogen generation and hydrogen yield. Gravimetric hydrogen capacity of 7.6 wt% and the average rate of H2 evolution of 39 ml·gcomp.−1min−1 have been achieved at molar ratios of NH3BH3/MCl2 = 50 (M = Co, Ni) and H2O/NH3BH3 = 2 and at external heating of 85°С.

The cobalt-boron composition by reduction of cobalt chloride in an aqueous solution of sodium borohydride is an amorphous ferromagnetic black powder consisting of spherical particles covered with a shell. Transformations of cobalt-boron composition upon its heat treatment from 20 to 1000 °С in an inert atmosphere have been studied by thermal analysis, magnetic susceptibility and HR TEM. On the basis of the obtained results the heating process was divided into five temperature intervals characterized by considerable changes in the structure of cobalt-boron composition. The end products of chemical and structural transformations are cobalt metal and cobalt borates – Co 2 B 2 O 5 , Co 3 BO 5 , Co 3 (BO 3 ) 2 . In our study it was shown for the first time that the metallic phase with a face-centered cubic lattice forms from the amorphous core while the cobalt borates form as a result of transformation of an oxygen-containing shell under an inert atmosphere. The study of the effect of physicochemical properties of the calcined cobalt-boron composition on the rate of NaBH 4 hydrolysis has shown that it decreases with decline specific surface area of the sample and its phase composition determines the rate of formation of the catalytic active component in the reaction medium.

The paper presents a comparative study of the activity of magnetite (Fe3O4) and copper and cobalt ferrites with the structure of a cubic spinel synthesized by combustion of glycine-nitrate precursors in the reactions of ammonia borane (NH3BH3) hydrolysis and hydrothermolysis. It was shown that the use of copper ferrite in the studied reactions of NH3BH3 dehydrogenation has the advantages of a high catalytic activity and the absence of an induction period in the H2 generation curve due to the activating action of copper on the reduction of iron. Two methods have been proposed to improve catalytic activity of Fe3O4-based systems: (1) replacement of a portion of Fe2+ cations in the spinel by active cations including Cu2+ and (2) preparation of highly dispersed multiphase oxide systems, involving oxide of copper.

Europium doped Gd2O3 sphere-like nanoparticles with dm = 9.3 ± 3.5 nm were synthesized by cw CO2 laser vaporization technique in a flowing mixture of argon and oxygen. According to XRD data, the Eu:Gd2O3 nanoparticles crystallize in the monoclinic symmetry class (C2/m space group). High-resolution luminescence spectroscopy study showed that the ultra-narrow 5D0 → 7F0 transition of Eu3+ demonstrates only two peaks corresponding to two inequivalent Cs positions of Eu3+ ion in monoclinic Gd2O3 lattice that is explained by the peculiarities of local environment of Eu3+ ion at these sites. The hypersensitive transition 5D0 → 7F2 dominates in the spectrum and is expanded to the red part of the spectrum in comparison with cubic Eu:Gd2O3 due to intense transitions terminating at higher-lying components of the crystal-field-split 7F2 state. In the luminescence spectrum, an additional weak band with the maximum at 407 nm corresponding to the electronic transitions 4f65 d1(7FJ) → 4f7(8S7/2) of Eu2+ was detected. The obtained values of chromaticity coordinates and absolute quantum yield are (0.644; 0.325) and ca. 1%, respectively. The phase transformations have been investigated using differential scanning calorimetry and thermogravimetry (50–1400 °C). After annealing in air at 700 °C, the monoclinic symmetry class of the Eu:Gd2O3 nanoparticles is preserved and the particle size increases to dm = 17.8 ± 6.1 nm. After annealing, the chromaticity coordinates (0.659; 0.334) and absolute quantum yield (ca. 4%) can be obtained using red phosphor based on monoclinic Gd2O3:Eu3+. The lifetime of the excited 5D0 state of Eu3+ in the annealed nanoparticles is longer than that in the as-synthesized nanoparticles, due to the suppression of nonradiative decay after annealing.

Ce0.5Zr0.5O2mixed 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.

The structure of a cobalt-boron catalyst obtained by reduction of cobalt chloride in an aqueous solution of sodium borohydride at ambient temperature has been investigated by TEM HR, XPS, EXAFS and X-ray diffraction method. It was found that nanoparticles of the forming catalyst consisted of a core and a shell. The oxygen-containing compounds (cobalt hydroxide and cobalt borates) mainly reside in the shell. In spite of the amorphous state of the catalyst the EXAFS and X-ray diffraction analysis indicated the presence of ferromagnetic clusters with the shortest Co Co distance of about 2.5 A and coordination number of 2.7 which are regularly distributed within the core with average separations of 5.8 A. The presence in the catalyst of the Co B bonds, a short Co Co distance and the absence of long Co Co distances (4.3 and 4.8 A) as well as the presence of boron bound to hydrogen allows suggestion to be made that stabilization of the cobalt tetramers occurs due to the presence of a boron-hydrogen structure formed by BH 4 − ions upon the reduction of cobalt chloride. To substantiate the above model of the active phase of the cobalt-boron catalyst the DFT method with a PBE functional in the plane-wave basis has been employed which showed that the ferromagnetic tetramers may exist within a boron-hydrogen matrix isolated from the surrounding medium by an oxygen-containing shell.

Regularities of the thermolysis of acidic salts of unsaturated (maleic) [M(H2O)4(C4H3O4)2] and aromatic (ortho-phthalic) [M(H2O)6](C8H5O4)2 (M = Fe(II), Co(II), and Ni(II)) acids are established. The thermolysis of both maleates and phthalates can conventionally be divided into three stages. The onset decomposition temperature of the maleates is insignificantly higher than that of the phthalates for the salts of similar metals. The onset dehydration temperature increases in the series of the acidic transition metal maleates and phthalates Fe Co > Ni. Composites consisting of a metal, an organic polymer, and amorphous carbon are the thermolysis products of both maleates and phthalates in a helium flow. The composites with iron and cobalt in the polymer contain nanosized metal particles and oxide nanoparticles, whose content increases in the composites obtained by the decomposition of phthalates, whereas only metal nanoparticles are observed in the composite with nickel. The compositions and structures of the carbon/polymer matrix differ in these composites.