The Sr2TiO4 samples were synthesized by mechanical activation (MA) from a mixture of SrCO3 and TiO2 precursors followed by calcination at 900 and 1100 degrees C. The accumulation of internal energy stresses in the mechanical mixture of precursors was controlled by varying the mechanical activation time (10, 20 and 25 min) through the use of mills of different power. Powder mixtures of precursors as-blend, after MA, and after calcinations were studied using XRD, FTIR, thermal analysis, and SBET methods. The energy impact in Sr2TiO4 synthesis is more pronounced at calcination temperature of 900 degrees C, the increase in the energy load at a temperature of 1100 degrees C is levelled out, due to the formation of practically single-phase Sr2TiO4.

We propose a procedure for estimating the content of layer alternation defects in A 2 B O 4 structures of the homologous Ruddlesden–Popper series by analysing the ratio of certain interplanar distances. The calibration plots are constructed from the calculated diffraction patterns using a probabilistic model of one-dimensionally disordered crystals with different concentrations of defects. The procedure is tested on Sr 2 TiO 4 samples using the synchrotron experiment data.

Разработана методика оценки содержания дефектов чередования слоев в структурах типа А2BO4 гомологического ряда Раддлесдена-Поппера, основанная на анализе соотношения определенных межплоскостных расстояний. Калибровочные графики построены по результатам расчета дифракционных картин на основе вероятностной модели одномерно разупорядоченных кристаллов при различной концентрации дефектов. Тестирование методики выполнено на образцах Sr2TiO4 с использованием данных синхротронного эксперимента.

Methane oxidative coupling (OCM) is considered a potential direct route to produce C2 hydrocarbons. Layered perovskite-like Sr2TiO4 is a promising OCM catalyst. Mechanochemical activation (MA) is known to be an environmentally friendly method for perovskite synthesis. Sr2TiO4 were synthesized using MA of the mixtures containing SrCO3 or SrO and TiO2 or TiO(OH)2 and annealing at 900 and 1100 °C. XRD and FT-IRS showed that MA leads to the starting component disordering and formation of SrTiO3 only for SrO being pronounced when using TiO(OH)2. After annealing at 900 °C, Sr2TiO4 was mainly produced from the mixtures of SrCO3 or SrO and TiO(OH)2. The single-phase Sr2TiO4 was only obtained from MA products containing SrCO3 after calcination at 1100 °C. The surface enrichment with Sr was observed by XPS for all samples annealed at 1100 °C depending on the MA product composition. The OCM activity of the samples correlated with the surface Sr concentration and the ratio of the surface oxygen amount in SrO and perovskite (Oo/Op). The maximal CH4 conversion and C2 yield (25.6 and 15.5% at 900 °C, respectively), and the high long-term stability were observed for the sample obtained from (SrCO3 + TiO2), showing the specific surface morphology and optimal values of the surface Sr concentration and Oo/Op ratio.

Double oxides with the structure of the Ruddlesden–Popper (R-P) layered perovskite An+1BnO3n+1 attract attention as materials for various electrochemical devices, selective oxygen-permeable ceramic membranes, and catalytic oxidative reactions. In particular, Sr2TiO4 layered perovskite is considered a promising catalyst in the oxidative coupling of methane. Our high-resolution transmission electron microscopy (HRTEM) studies of Sr2TiO4 samples synthesized using various methods have shown that their structure often contains planar defects disturbing the periodicity of layer alternation. This is due to the crystal-chemical features of the R-P layered perovskite-like oxides whose structure is formed by n consecutive layers of perovskite (ABO3)n in alternating with layers of rock-salt type (AO) in various ways along the c crystallographic direction. Planar defects can arise due to a periodicity violation of the layers alternation that also leads to a violation of the synthesized phase stoichiometry. In the present work, a crystallochemical analysis of the possible structure of planar defects is carried out, structures containing defects are modeled, and the effect of such defects on the X-ray diffraction patterns of oxides of the A2BO4 type using Sr2TiO4 is established as an example. For the calculations, we used the method of constructing probabilistic models of one-dimensionally disordered structures. For the first time, the features of diffraction were established, and an approach was demonstrated for determining the concentration of layer alternation defects applicable to layered perovskite-like oxides of the A2BO4 type of any chemical composition. A relation has been established between the concentration of planar defects and the real chemical composition (nonstoichiometry) of the Sr2TiO4 phase. The presence of defects leads to the Ti enrichment of particle volume and, consequently, to the enrichment of the surface with Sr. The latter, in turn, according to the data of a number of authors, can serve as an explanation for the catalytic activity of Sr2TiO4 in the oxidative coupling of methane.

Ordered mesoporous MgAl2O4 support was synthesized by one-pot evaporation-induced self-assembly method with block copolymers. Nanocomposite catalysts were prepared by loading this support with PrNi0.9Ru0.1O3 perovskite or Ni + Ru-doped Ce0.35Zr0.35Pr0.3O2 fluorite oxides. Their texture, structure, surface properties and reactivity have been studied by combination of modern structural, spectroscopic and kinetic methods. Suppression of MgAl2O4 support acidity, strong interaction of small Ru-Ni alloy nanoparticles with the surface layers of this support modified by perovskite and fluorite oxides with a high oxygen mobility and reactivity provide a high activity and stability to coking and sintering of these catalysts in all studied reactions of methane and ethanol transformation into syngas. Ni + Ru/Ce0.35Zr0.35Pr0.3O2/MgAl2O4 active component loaded on honeycomb Fechraloy foil substrate demonstrated a high performance and stability to coking in autothermal natural gas oxi-dry reforming, ethanol steam reforming and autothermal reforming of ethyl acetate in concentrated feeds promising for the practical application.

Mechanism of ethanol partial oxidation into syngas over catalysts based on mesoporous MgAl2O4 spinel loaded with fluorite PrCeZrO or spinel MnCr2O4 oxides and promoted by Ru + Ni was studied by in situ FTIRS and 18O SSITKA. Surface species (ethoxy, adsorbed ethanol, acetaldehyde, acetate, etc.) were identified and their thermal stability and reactivity were estimated. Analysis of kinetics of the 18O transfer into reaction products (CO, CO2, CH3CHO) allowed to estimate the rates of steps and present a scheme of the reaction mechanism including (1) fast CH3CHO formation on mixed metal oxide sites; (2) rate-limiting stage of surface oxygen species incorporation into acetaldehyde or ethoxy species with C–C bond rupture yielding CO and CO2 along with H2 and H2O; (3) water gas shift reaction by redox mechanism affecting CO/CO2 ratio and their oxygen isotope fraction. Strong interaction of PrCeZrO or MnCr2O4 oxides with MgAl2O4 support results in decreasing constants of main reaction steps in comparison with those for catalysts based on bulk fluorite and spinel oxides, correlating with a higher surface oxygen bonding strength and its low coverage revealed by pulse microcalorimetry. DFT analysis confirmed a low energy barrier of the step of Ru–O oxygen incorporation into C–C bond of ethoxy species with its rupture explaining a higher syngas selectivity for Ru-doped catalysts.

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.

This review considers the problems associated with the development and operation of highly active and stable structured catalysts for biogas/biofuel conversion into syngas and hydrogen based on nanocrystalline oxides with fluorite, perovskite, and spinel structures and their nanocomposites promoted by nanoparticles of platinum group metals and alloys based on nickel. The design of these catalysts is based on finding the relationships between the methods of their synthesis, composition, real structure/microstructure, surface properties, and oxygen mobility and reactivity largely determined by the metal–support interaction. This requires the use of modern structural, spectroscopic, kinetic methods, and mathematical modeling. Thin layers of optimized catalysts deposited on structured heat-conducting supports demonstrated high activity and resistance to carbonization in the processes of biogas and biofuels conversion into syngas, and catalysts deposited on asymmetric ceramic membranes with mixed ionic–electronic conductivity allowed oxygen or hydrogen to be separated from complex mixtures with 100% selectivity.

Oxygen transport (including oxygen mobility and surface reactivity) is one of the important factors governing electrochemical activity of solid oxide fuel cells electrodes as well as oxygen and hydrogen separation membranes based on materials with mixed oxide-ionic and electronic conductivity. In this work, oxygen mobility data obtained for a series of materials destined for such devices using modern techniques of oxygen isotope heteroexchange are summarized. Series of solid oxide fuel cells’ and membranes’ materials were studied by isotope exchange of their oxygen with 18O2 and C18O2 in isothermal and temperature-programmed modes using closed and flow reactors and data analysis based on developed model of oxygen diffusion and exchange. For solid electrolytes’ materials (Sc- and Ce-doped zirconia) as well as for proton-conducting materials [Ln5.5(Mo,W)O11.25], the effect of composition heterogeneity on the oxygen mobility was demonstrated. For Ln6 – xWO12 – δ, a strong effect of structure on the oxygen mobility was demonstrated. For oxides with asymmetric structure, where oxygen migration proceeds via cooperative mechanisms [La2(Mo,W)2O9, (Ln,Ca)2NiO4], the doping hampers the cooperative migration, resulting in oxygen mobility deterioration and sometimes forming additional slow diffusion channels. In the PrNi0.5Co0.5O3–Ce0.9Y0.1O2 nanocomposites that are materials of the solid oxide fuel cells’ cathode and functional layer of the oxygen separation membranes, two diffusion channels were observed, where more mobile oxygen corresponds to the fluorite phase and interfaces; less mobile, to the perovskite phase. This is due to special features of cations redistribution between the phases.

In this review problems related to design and performance of stable and efficient catalysts of biogas/biofuels transformation into syngas and hydrogen based on nanocrystalline oxides with fluorite, perovskite and spinel oxides and their nanocomposites promoted by nanoparticles of Pt group metals and Ni-based alloys are considered. Tailor-made design of these catalysts is based upon elucidation of the relationships between their synthesis procedure, composition, real structure/microstructure, surface properties, oxygen mobility and reactivity determined in a great extent by the metal-support interaction, which requires application of modern sophisticated structural, spectroscopic, kinetic (including in situ FTIRS and isotope transients) methods and mathematical modeling. Thin layers of these optimized catalysts supported on structured heat-conducting substrates, asymmetric supported oxygen or hydrogen separation membranes demonstrated high and stable performance in transformation of biogas and biofuels into syngas and hydrogen.

Abstract The ordered mesoporous Mg- and Ni-Mg-alumina samples of general formula xwt%Mg-Al2O3 and ywt%Nixwt% Mg-Al2O3(x, y = 5, 10 % wt) have been prepared by the one-pot evaporation induced self-assembly (EISA) method using Pluronic P123 as a template. The textural and structural properties of the prepared samples have been characterized by N2adsorption-desorption analysis, BET, XRD, TEM with EDX, HAADF-STEM, and H2-TPR. The samples calcined at 700°C had an ordered mesoporous structure with a SSA of 170-250 m2/g, a pore volume of 0.5-0.64 cm3/g and a narrow distribution of the pore size (mean 12-16 nm). For the catalysts prepared by the one-pot EISA method, the size of the metal Ni particles was in the range of 3-12 nm and was conditioned by their confinement in the mesopores and the interaction with MgO and Al2O3. Testing in methane dry reforming in the 15v.% CH4+ 15v.%CO2feed, with He balance, at 650-750°C and the contact time of 0.015 s has shown the higher activity and stability of the ordered mesoporous 10w%Ni- 10w%Mg-Al2O3catalysts prepared by the one-pot method as compared with the catalyst of the same composition obtained by impregnation.

For structured catalysts of biofuels reforming new types of inexpensive functionally graded substrates with a high thermal conductivity and thermochemical stability comprised of amorphous carbon foams with protective Ni, Ni-Al and NiAl2O4/corundum layers were designed. Procedures for supporting nanocomposite active components (Ni+Ru)/CaTiO3/10%Mg-Al2O3 and PrNi0.95Ru0.05O3 /10%Mg-Al2O3 on these substrates providing uniform spatial distribution were elaborated. These structured catalysts have a high and stable performance in reactions of steam and autothermal reforming of biofuels (ethanol, ethyl acetate, etc) in real feeds without coking and thermochemical degradation.

For structured catalysts of biofuels transformation into syngas inexpensive and stable to sintering active components based upon Mg-doped gamma-alumina with supported LaNi0.9Ru0.1O3 perovskite or MnCr2O4 spinel promoted by Ru + Ni were developed. Characterization of the surface features, reactivity, catalytic activity and routes of ethanol transformation on these catalysts demonstrated that suppression of support acidity, strong interaction of Ru-Ni alloy nanoparticles with manganese chromite layers on support and a high redox ability provide a high yield of syngas and stability to coking. The most promising active component (2 wt% Ni + 2 wt% Ru)/MnCr2O4/10 wt% MgO gamma-Al2O3 supported on microchannel heat-conducting CrAlO cermet plates demonstrated a high performance and stability to coking in the autothermal reforming of such reactive fuels as glycerol, anisol and turpentine, oil.

The effect of the features of starting zirconium compounds on the solvothermal synthesis of mixed Ce–Zr oxides in a flow reactor using ethanol and isopropanol as a supercritical medium was studied. The phase composition and structural properties of the synthesized samples were investigated using X-ray diffraction analysis (XRD) and Raman spectroscopy. The morphology and textural properties were studied by transmission electron microscopy (TEM) and thermal desorption of nitrogen. It was found that the use of zirconium oxychloride or acetate as the starting substances results in the formation of a mixture of phases enriched with cerium or zirconium, whereas the use of zirconium butoxide with acetylacetone as a complexing agent allows obtaining a homogeneous solid solution. The catalytic properties of the synthesized oxides with supported Ni were tested in methane dry reforming (MDR). The catalyst containing a single-phase oxide synthesized in the presence of acetylacetone exhibited much higher activity, selectivity and coking stability.

This work aims at studying protonic transport of mixed proton–electron-conducting Nd5.5WO11.25-δ oxide synthesized by a citrate method as material for hydrogen separation membranes. Structure of samples was characterized by X-ray diffraction (XRD), and protonic mobility was studied using temperature-programmed desorption of H2O and isotope heteroexchange of the bulk protons with D2O as well as mass relaxation after an abrupt change of H2O partial pressure. The temperature range of Nd5.5WO11.25-δ efficient operation is 300–400 °C, where H+ tracer diffusion and chemical diffusion coefficients are ∼1 × 10−11 and ∼2 × 10−5 cm2/s, respectively, being comparable to or even better than those for similar systems. Hence, Nd5.5WO11.25-δ is a promising material for the design of hydrogen separation membranes.