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The real/atomic structure of single phase homogeneous nanocrystalline Ce0.5Zr0.5O2±δoxides prepared by a modified Pechini route and Ni-loaded catalysts of methane dry reforming on their bases was studied by a combination of neutron diffraction, synchrotron X-ray diffraction, total X-ray scattering and X-ray absorption spectroscopy. The effects of sintering temperature and pretreatment in H2were elucidated. The structure of the mixed oxides corresponds to a tetragonal space group indicating a homogeneous distribution of Ce and Zr cations in the lattice. A pronounced disordering of the oxygen sublattice was revealed by neutron diffraction, supposedly due to incorporation of water into the structure when in contact with air promoted by the generation of anion vacancies in the lattice after reduction or calcination at high temperatures. However, such disordering has not resulted in any occupation of the oxygen interstitial positions in the bulk of the nanodomains.

The self-sustained kinetic oscillations in the catalytic oxidation of methane over Ni foil have been studied at atmospheric pressure using an X-ray diffraction technique and mass spectrometry. It has been shown that the regular reaction-rate oscillations appear under oxygen-deficient conditions and the period of oscillations varies between approximately 200 and 4000 s. The operando measurements have revealed a higher activity of metallic Ni in the reaction than NiO oxide and have unambiguously showed that the oscillations arise due to the reversible bulk oxidation of Ni to NiO.

This work presents the results from a study of the structure and transport properties of Ca-doped La2NiO4+δ. La2−xCaxNiO4+δ (x = 0–0.4) materials that were synthesized via combustion of organic-nitrate precursors and characterized by X-ray diffraction (XRD), in situ XRD using synchrotron radiation, thermogravimetric analysis (TGA) and isotope exchange of oxygen with C18O2. The structure was defined as orthorhombic (Fmmm) for x = 0 and tetragonal (I4/mmm) for x = 0.1–0.4. Changes that occurred in the unit cell parameters and volume as the temperature changed during heating were shown to be caused by the excess oxygen loss. Typical for Ruddlesden–Popper phases, oxygen mobility and surface reactivity decreased as the Ca content was increased due to a reduction in the over-stoichiometric oxygen content with the exception of x = 0.1. This composition demonstrated its superior oxygen transport properties compared to La2NiO4+δ due to the enhanced oxygen mobility caused by structural features. Electrochemical data obtained showed relatively low polarization resistance for the electrodes with a low Ca content, which correlates well with oxygen transport properties. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. The materials synthesis as well as electrochemical study were performed in a framework of the budget task of the IHTE UB RAS with using the equipment of the shared access center “Composition of compounds”. The TGA and isotope exchange studies were supported by the Ministry of Science and Higher Education of the Russian Federation within the governmental order for Boreskov Institute of Catalysis (projects АААА‐А21‐121011390007‐7, АААА‐А21‐ 121011390009‐1). The SXRD experiments were performed at the shared research center SSTRC on the basis of the Novosibirsk VEPP‐3 complex at BINP SB RAS, using equipment supported by pro‐ ject RFMEFI62119X0022.

The presence of nitric oxide NO in the gas phase was shown to decrease the decomposition rate of the hydrotalcite-like Co–Al LDH phase in the catalysts prepared by co-precipitation or deposition on Al 2 O 3 under the condition of urea hydrolysis. The decrease in LDH decomposition rate is related to the formation of a more crystallized phase of the spinel-like Co–Al oxide due to the ability of nitric oxide to transfer oxygen in consecutive reactions of the oxidation to NO 2 and reduction to NO. The difference in the coherent scattering domain size of the catalyst samples precalcined in the presence of NO or in a pure inert gas is retained at all consecutive steps of the reductive heat treatment in hydrogen: after the formation of a cubic phase of the (Co, Al)O oxide and its reduction to metallic cobalt. The observed changes in the degree of crystallinity and dispersion of the active metal exert only a slight effect or even no effect on the activity of the catalysts in Fischer–Tropsch synthesis. Noteworthy are a lower selectivity for methane and a greater fraction of olefins in the products obtained on the catalysts precalcined in a flow of inert gas containing 3% NO.

The growth mechanisms of carbon nanofibers on Ni catalysts and nitrogen-doped carbon nanofibers on Ni and Ni-Cu catalysts were studied. The growth of both types of nanofibers was found to occur by a mechanism that included the formation of surface non-stoichiometric nickel carbide followed by the dissolution and diffusion of carbon, or carbon and nitrogen into the bulk of the catalyst particles.

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.

This work summarizes results of synchrotron radiation (SR) studies of the real/defect structure of nanocrystalline/nanocomposite oxide materials, which determines their functional properties in hydrogen energy field as catalysts and mixed ionic electronic conductors (cathodes and anodes of solid oxide fuel cells, oxygen separation membranes). For nanocrystalline ceria-zirconia mixed oxide prepared via modified Pechini route using ethanol solution of reagents, a high spatial uniformity of cations distribution between domains along with the oxygen sublattice deficiency revealed by full-profile Rietveld refinement of SR diffraction data provide structure disordering enhancing oxygen mobility. For PrNi 0.5 Co 0.5 O 3–δ – Ce 0.9 Y 0.1 O 2–δ nanocomposite extensive transfer of Pr cations into fluorite domains generates a new path of fast oxygen diffusion along chains of Pr 3+ – Pr 4+ cations as directly proved by analysis of the unit cell relaxation after changing pO 2 in perfect agreement with data obtained by oxygen isotope heteroexchange.

Mesoporous tungsten-silicates, W-MMM-E, have been prepared following evaporation-induced self-assembly methodology and characterized by elemental analysis, XRD, N2 adsorption, STEM-HAADF (high angle annular dark field in scanning-TEM mode), DRS UV-vis, and Raman techniques. DRS UV-vis showed the presence of two types of tungsten oxo-species in W-MMM-E samples: isolated tetrahedrally and oligomeric octahedrally coordinated ones, with the ratio depending on the content of tungsten in the catalyst. Materials with lower W loading have a higher contribution from isolated species, regardless of the preparation method. W-MMM-E catalyzes selectively oxidize of a range of alkenes and organic sulfides, including bulky terpene or thianthrene molecules, using green aqueous H2O2. The selectivity of corresponding epoxides reached 85–99% in up to 80% alkene conversions, while sulfoxides formed with 84–90% selectivity in almost complete sulfide conversions and a 90–100% H2O2 utilization efficiency. The true heterogeneity of catalysis over W-MMM-E was proved by hot filtration tests. Leaching of inactive W species depended on the reaction conditions and initial W loading in the catalyst. After optimization of the catalyst system, it did not exceed 20 ppm and 3 ppm for epoxidation and sulfoxidation reactions, respectively. Elaborated catalysts could be easily retrieved by filtration and reused several times with maintenance of the catalytic behavior.

Iron-containing mesoporous mesophase materials Fe,Al-MMM-2 have been synthesized according to a sol-mesophase route under mild acidic conditions (pH 2.3–4.4) using Keggin type cation [FeAl12O4(OH)24(H2O)12]7+ (FeAl127+) as Al and Fe sources. Effect of pH of the synthetic solution on structural and physicochemical properties of Fe,Al-MMM-2 has been evaluated by means of small- and wide-angle XRD, FTIR, DR-UV–vis, and N2-adsorption/desorption analysis. It has been established that deviation of stability of FeAl127+ cation at various pH determines Al/Fe ratio in the resulting material as 12/1 (material synthesized at pH 4.4), and 6/1 (pH 2.4 and 3.3). Correlation between incorporation of Al and Fe in different forms and resulting materials texture is discussed. Fe,Al-MMM-2 materials have been tested as catalysts for wet phenol oxidation with H2O2. Insertion of Al species into the framework of the silicate matrix increases the activity comparing to a reference Fe,Al-pillared clay due to both higher surface acidity and lower diffusion limitations that correspond to Fe,Al-MMM-2.

The phase stability of SrCo0.8Fe0.2O3−d perovskite doped with niobium was studied by in situ high-temperature X-ray diffraction in the temperature range of 30–1000 °C and oxygen partial pressure 0.2–10−5 atm. The stability of the cubic perovskite structure in a wide range of oxygen partial pressures is the main advantage of SrCo0.8−xFe0.2NbxO3−d (x = 0.1–0.3) system in comparison with SrCo0.8Fe0.2O3−d. It is suggested that equilibrium of the thermal expansion with changes of the oxygen non-stoichiometry leading to the same lattice parameters in the oxidizing and reducing environments at the catalytic temperatures is a necessary requirement for stable operation of perovskite as an oxygen-conducting membrane. In the case of SrCo0.8−xFe0.2NbxO3−d perovskite this condition is met at x = 0.2. This makes the SrCo0.6Fe0.2Nb0.2O3−d composition promising for application as oxygen-conducting membrane.

International audience; A combined high-resolution Co K-edge extended x-ray absorption fine structure (EXAFS) and high-resolution X-ray powder diffraction (XRD) study has been performed to clarify the detail of anomalous behavior of temperature-dependent magnetic susceptibility curve on the LaCoO3 across the spin-state (similar to 120 K) transition. According to XRD analysis, the Debye-Waller factor of Co-O bond exhibit rapid growth below 20 K whereas the temperature dependence of the average Co-O bond length shows linear behavior from 10 K to 400 K. The EXAFS data show an anomalous decrease of the Co-O bond lengths with respect to those obtained by XRD. No local distortion of CoO6 octahedral as temperature increases up to 400 K has been detected

Physical and chemical properties of TSEFLAR™-treated gibbsite/hydrargillite (centrifugal thermal activation) CTA HG were studied with X-ray analysis, TA, EM, BET and IRS. CTA HG product obtained at the temperature range of 330–580 °C and contact time ∼1 s is the one with a transitional non-equilibrated layered hydroxide structure with partly lost hydroxide groups. The CTA HG structure does not correspond to the produced chemical composition Al 2 O 3 ·(0.4–2)H 2 O and, therefore, the products reveal a higher reactivity. Such products are already readily hydrated at room temperature in water and aqueous ammonia to form eventually the stable bayerite-like hydroxide structure.

Coprecipitated Fe-Al 2 O 3 , Fe-Co-Al 2 O 3 and Fe-Ni-Al 2 O 3 catalysts is shown to be very efficient in carbon deposition during methane decomposition at moderate temperatures (600–650 °C). The carbon capacity of the most efficient bimetallic catalysts containing 50–65 wt.% Fe, 5–10 wt.% Co (or Ni) and 25–40 wt.% Al 2 O 3 is found to reach 145 g/g cat . Most likely, their high efficiency is due to specific crystal structures of the metal particles and formation of optimum particle size distribution. According to the TEM data, catalytic filamentous carbon (CFC) is formed on them as multiwall carbon nanotubes (MWNTs). The phase composition of the catalysts during methane decomposition is studied using a complex of physicochemical methods (XRD, REDD, Mossbauer spectroscopy and EXAFS). Possible mechanisms of the catalyst deactivation are discussed.

Genesis of the composition and structure of the active component of coprecipitated iron containing catalysts (Fe-Al 2 O 3 , Fe-Co-Al 2 O 3 , Fe-Ni-Al 2 O 3 ) with high metal loadings (>50 wt.%) for methane decomposition at moderate temperatures (600–650 °C) has been investigated by XRD, EXAFS, radial electron density distribution (REDD), TEM, FTIR and Mossbauer spectroscopy. The main stages of the catalyst genesis during drying, thermal decomposition and reduction have been studied. For bimetallic systems (Fe-Co-Al 2 O 3 , Fe-Ni-Al 2 O 3 ) intermediate spinel phases with a composition (M II , Fe) 3 O 4 (M=Co, Ni) have been shown to form during heat treatment and reduction. This leads to a decrease of the reduction temperature for iron oxides. Reduced bimetallic catalysts (Fe-Co-Al 2 O 3 , Fe-Ni-Al 2 O 3 ) are composed of alloys. The structure and parameters of their crystal lattices depend on the type and concentration of the added metal. Alumina has been shown to behave as a structural promoter. A model of the reduced catalysts consisting of highly dispersed (20–50 nm) metal and alumina particles with a spinel phase at their interface has been suggested.

The model of structure and structural transformation of the mesostructured carbon material CMK-1 was established by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) investigations. The investigations showed that the enantiomeric carbon subframeworks formed within the pores of the MCM-48 mesoporous template used for the material synthesis displaced with respect to one another without significant distortions after the dissolution of the silica wall of the template. The model proposed agrees well with TEM images observed. The XRD structural modeling of CMK-1 done using the continuous density function technique allowed perfect fit of the calculated to the experimental powder diffraction pattern and provided geometric characteristics of the material texture. The structural characteristics obtained agreed fairly well with TEM analysis and with previously reported adsorption data.

Structural and textural characteristics as well as coordination states of aluminium and some catalytic properties are studied for highly-ordered (with very narrow XRD reflections) aluminosilicate mesoporous mesophase materials ((Si,Al)-MMM) prepared with different aluminium concentrations by hydrothermal synthesis in the presence of C 16 H 33 N(CH 3 ) 3 Br. As shown, all physico-chemical parameters measured for these systems including their structural hydrostability are strongly influenced by the aluminium content. Based on analysis of the results obtained, a description of probable transformations during formation of mesoporosity in the C16-(Si,Al)-MMM is considered.

The real structure of silver supported catalysts for ethylene epoxidation (Ag/α-Al2O3) was investigated using precision X-ray diffraction on synchrotron radiation, in situ high-temperature X-ray diffraction, and transmission electron microscopy. Stacking faults and intergrain boundaries were found to be main types of defects in the structure of silver microcrystals. In situ study revealed that under reaction conditions the intergrain boundaries remain unchanged, whereas stacking faults are annealed. We found a correlation between the reaction rate of ethylene epoxidation and parameters responsible for the relationship among the regular and defect regions in the bulk structure of silver particles.

The structure of MCM-48 mesoporous silicate materials has been fully characterized from X-ray diffraction data by applying recently developed methods of mesostructure analysis and full-profile refinement. The pore wall thickness of both as-made and calcined MCM-48 was determined with high precision to be 8.0(1) Angstrom. No regular variations of the wall thickness were detected, but its density was found to be ca. 10% higher in the low-curvature regions. The surfactant density in the pores was assessed around 0.6-0.7 g/cm(3) and was found to have a distinct minimum in the pore center similar to that detected previously in MCM-41. A new extended model function of the density distribution in MCM-48 is proposed on the basis of the structural features that were revealed.

Rietveld profiles, Moessbauer spectra and x-ray absorption fine structure (XAFS) were analyzed through the structural phase transition at Ts = 355 K in HoBaCo4O7. Excess of the oxygen content over O7 was avoided via annealing the samples in argon flow at 600 degree C. Space groups (S.G.) Pbn21c and P63mc were used to refine the structure parameters in the low- and high-temperature phases, respectively. Additionally, the Cmc21 symmetry was considered as a concurrent model of structure of the low-temperature phase. In the high-temperature phase, severe anisotropy of thermal motion of the major part of the oxygen atoms was observed. This anisotropic motion turns to be quenched as the sample is cooled below Ts. The variation of quadrupole splitting near Ts is not similar to a steplike anomaly frequently seen at the charge-ordering transition. We observe instead a dip-like anomaly of the average quadrupole splitting near Ts. Narrow distribution of the electric field gradient (EFG) over different cobalt sites is observed and explained on the basis of point-charge model. XAFS spectra show no evidence of significant difference between YBaCo4O7 (T > Ts) and HoBaCo4O7 (T < Ts). The origin of the transition at Ts is ascribed to the condensation of the libration phonon mode associated with the rigid-body rotational movements of the starlike tetrahedral units, the building blocks of kagome network. It is shown that the condensation of the libration mode is not compatible with translation symmetry for the hexagonal S.G., but compatible for the orthorhombic S.G. The orthorhombic lattice parameters and EFG components (Vxx, Vyy, Vzz) vary smoothly with temperature at approaching Ts and closely follow each other., 13 figures