Co-doped praseodymium nickelates PrNi1−xCoxO3−δ and their composites with yttrium doped ceria Ce0.9Y0.1O2−δ are known to be promising materials for intermediate temperature solid oxide fuel cells and membranes for oxygen separation. Powdered samples were obtained via Pechini route and ultrasonic dispersion followed by mechanical activation. Pellets were sintered at 870–1100°C by using microwave radiation. In comparison with conventionally sintered materials, the phase transition leading to Ruddlesden–Popper phase formation was shifted down for about 50°C–100°C. The effect of sintering by microwave radiation consisted of dramatically increased sample density, improved phase purity and enhanced oxygen mobility. When undesirable phase transitions at elevated sintering temperatures hinder gas-tight layers preparation, the microwave sintering technique can be used without any deterioration of transport properties of materials in comparison with conventional calcination.

This work aims at elucidating effects composition and microstructure of materials based upon Pr1-ySmyNi1-xCoxO3-delta per ovskites on their oxygen mobility. Pr1-ySmyNi1-xCoxO3-delta and their omposites with Y-doped ceria are perspective materials for inter mediate temperature solid oxide fuel cells and oxygen separation branes. Doping Pr1-ySmyNi1-xCoxO3-delta by Sm results in suppression o the fast channel of oxygen diffusion along extended defects due o Sm segregation in their vicinity For nanocomposites moderate doping by Sm enhances fast oxygen diffusion in fluorite phase domains and along perovskite-fluorite interface due to a higher disordering caused by incorporation of both Pr arid Sm cations into Y-doped ceria.

A unique combination of methods (TPD of O2, thermogravimetry, isotopic heteroexchange of oxygen in different modes) was used to carry out detailed studies of oxygen mobility and reactivity in mixed praseodymium nickelates-cobaltites (PrNi1 − x Co x O3 + δ) and their composites with doped cerium dioxide (Ce0.9Y0.1O2 − δ) as promising cathodic materials stable towards the effect of CO2 in the intermediate-temperature region. It is shown that in the case of composites of PrNi1 − x Co x O3+δ-Ce0.9Y0.1O2 − δ synthesized using the Pechini method and ultrasonic treatment, stabilization of the disordered cubic perovskite phase due to redistribution of cations between the phases provides high oxygen mobility. Preliminary results on tests of cathodic materials of this type supported on planar NiO/YSZ anodes (H.C. Starck) with a thin layer of YSZ electrolyte and a buffer Ce0.9Y0.1O2 − δ layer showed that power density of up to 0.4 W/cm2 was reached in the region of medium (600–700°C) temperatures, which was close to typical values for fuel cells of this type with cathodes based on strontium-doped perovskites and their composites with electrolytes.

В работе представлены результаты изучения механизма переноса кислорода в слоистых никелатах со структурой Раддлсдена–Поппера и их нанокомпозитов с твердыми электролитами Сe0.9Gd0.1O2 - (GDC) и Y2(Ti0.8Zr0.2)1.6Mn0.4O7 - (YTZM) со структурой флюорита и пирохлора методом изотопного гетерообмена кислорода в проточном и статическом реакторах, термопрограммированной десорбции и полуэмпирического метода взаимодействующих связей. Экспериментальные данные гетерообмена удовлетворительно описываются в предположении равноценности по обмену всех атомов в объеме слоистых никелатов, что согласуется с моделью кооперативного процесса миграции кислорода с быстрым обменом между межузельными и регулярными позициями. Сильное взаимодействие между доменами фаз никелатов и твердых электролитов в нанокомпозитах, сопровождающееся перераспределением катионов между фазами, приводит к нарушению кооперативного процесса миграции кислорода и уменьшению коэффициента диффузии при увеличении скорости обмена.

The mechanism of oxygen transfer in layered nickelates having a Ruddlesden-Popper structure and their nanocomposites with Ce0.9Gd0.1O2 − δ (GDC) and Y2(Ti0.8Zr0.2)1.6Mn0.4O7 − δ (YTZM) solid electrolytes having fluorite and pyrochlore structures were studied by the oxygen isotope heteroexchange method in a flow and static reactor, thermoprogrammed desorption, and semiempirical interacting bonds method. The experimental heteroexchange data were adequately described by assuming that all atoms were equivalent in exchange in the bulk of layered nickelates, which was consistent with the cooperative oxygen migration model with fast exchange between the interstitial and regular positions. Strong interaction between the domains of the nickelate phases and solid electrolytes in nanocomposites, accompanied by a redistribution of cations between the phases, hindered the cooperative oxygen migration and led to a decrease in the diffusion coefficient as the exchange rate increased.

The work presents the results of studying the mechanism of oxygen transport for a new promising class of oxygen-containing electrolytes based on lanthanum silicate with an apatite structure using impedance spectroscopy and isotopic oxygen heteroexchange. At 1000 K, in the case of samples with an optimum composition including codoped Fe and Al, σ ∼ 3 × 10−3 to 10−2 S/cm and D* reaches ∼10−8 cm2/s, which is close to the values of YSZ and Ce0.9Gd0.1O2 − δ (GDC). Lower energies of conductivity activation and oxygen diffusion for doped apatites (∼0.5–0.8 eV instead of ∼1 eV for GDC) and also equivalence as regards exchange of all oxygen atoms within apatite agree with the model, in which oxygen mobility is determined by a nonlinear cooperative migration process of oxygen atoms with fast exchange between interstitial and regular sites.

Nanocrystalline CeO2-ZrO2 (Ce:Zr 1:1) samples doped with La, Pr or Gd cations (containing up to 30 at.%) were prepared via the Pechini route. Pt (1.4 wt.%) was supported via impregnation with H2PtCl6 solution followed by drying and calcination. The samples’ surface features were studied by SIMS and FTIRS of adsorbed CO. The oxygen mobility was characterized by the dynamic oxygen isotope exchange and H2 TPR. Catalytic activity was studied in the flow installation using diluted feeds (0.7% CH4 +0.5% O2 or 1% C3H6O + 0.5% O2 +0.5% H2O in He). In the selective oxidation of methane (POM), the catalytic activity correlates with Pt dispersion controlled by the oxidized sample’s ability to stabilize Pt2+ cations as precursors of small reactive Pt clusters formed under reaction conditions. This is favoured by a larger doping cation (La) and a developed network of nanodomain boundaries. At comparable Pt dispersion, the highest performance was demonstrated by a La-doped system, which correlates with the highest surface/near-surface oxygen mobility controlled by the strength of Ce-O bonds in the surface layer. In the autothermal reforming of acetone, the activity trends differ from those in POM because of the more prominent role of the oxygen mobility required to prevent surface coking.

Nanocomposites consisting of phases with fluorite (doped CeO2) and perovskite (LaMnO3, GdMnO3) structures are synthesized using the method of ester polymeric precursors (the Pechini method) and two sources of rare-earth elements (Ln), such as pure cerium and gadolinium salts or a commercial mixture of rare-earth carbonates containing La, Ce, Pr, Nd, and Sm cations. The genesis of the nanocomposite structure as a function of the sintering temperature is investigated using X-ray diffraction and electron microscopy. It is revealed that the genesis of the nanocomposite structure is governed, in many respects, by the fact that the decomposition of the ester polymeric precursor leads to the formation of a metastable phase, namely, a fluoritelike solid solution based on ceria with an excess concentration of the cations Ln 3+ (Ln 3+ = La3+, Pr3+, Nd3+, Sm3+) as compared to the equilibrium concentration. As a result, the perovskite phase (identified by X-ray diffraction analysis) is formed only after the subsequent annealing at temperatures higher than 800°C, when Ln 3+ cations escape from particles of the solid solution. It is demonstrated that, at annealing temperatures of up to 1100°C, particles of both phases have nanometer sizes and are characterized by a uniform spatial distribution necessary for percolation. The nanocomposites possess a high total electrical conductivity and a high mobility of lattice oxygen. The reduction rate of the nanocomposites with hydrogen or methane is higher than the reduction rate of the individual phases. The characteristics of the nanocomposites prepared from the commercial mixture of rare-earth carbonates are better than those of the samples synthesized from the pure salts.

For catalysts comprised of Pt supported onto dispersed complex fluorite-like oxides (ceria doped by Pr, Gd, Sm, or CeO2–ZrO2 doped by La, Gd or Pr), the effects of the oxygen mobility in supports and Pt dispersion on the performance in methane selective oxidation into syngas at short contact times were elucidated using combination of kinetic and spectroscopic methods. While in general any simple universal relation between the oxygen mobility, Pt dispersion and the rate of methane transformation into syngas was not found, for some series, a good correlation was observed agreeing with the bifunctional scheme of the methane selective oxidation into syngas.

This review summarizes the main achievements of the Boreskov Institute of Catalysis (Siberian Division, Russian Academy of Sciences) in the development of efficient and stable monolith catalysts for selective oxidation of hydrocarbons into synthesis gas at short contact times. Research in this field has included (1) design of new types of active component based on metal oxides, (2) design of new types of monolith support and development of supporting procedures for active components, and (3) optimization of process parameters for different types of fuel (natural gas, isooctane, and gasoline) and oxidant (air oxygen, including its mixtures with water and carbon dioxide), including the start-up regime. Design of active components (platinum, nickel, or their combination) supported on fluorite-like solid solutions based on cerium dioxide and rare-earth (samarium, gadolinium, and praseodymium) or zirconium cations has been aimed at separating hydrocarbon activation (on metal sites) and oxidation (on the support) and conjugating the separated steps of hydrocarbon oxidation at the metal-oxide interface. Optimization of oxygen mobility in the support lattice by varying the nature and concentration of doping cation along with optimization of hydrocarbon activation on supported metal clusters allow hydrocarbons to be completely converted into synthesis gas by selective oxidation or dry or steam reforming at contact times of a few milliseconds, ruling out undesirable carbon build-up on the catalyst surface. The development of new types of monolith support has targeted the enhancement of thermal shock resistance, including testing of supports based on thermally stable metal foils and composites (cermets). The main steps of the production of these supports have been refined, including unique technologies of blast dusting and hydrothermal treatment. The electric conductivity of these systems allows a quick startup of selective oxidation to be performed by passing electric current, and their thermal conductivity minimizes the temperature gradient arising from heat transfer in the bed. Procedures for loading monolith supports with active components have been developed, including impregnation, washcoating, or encapsulation in cermet matrices. The catalysts produced show a high efficiency and an operational stability adequate to the above tasks in the selective oxidation and steam-air autothermal reforming of natural gas (including processes under pressure), isooctane, and gasoline into synthesis gas.

Mobility and reactivity of the surface and bulk oxygen of perovskite-like mixed oxides including lanthanum manganite (I) and ferrite (II) systems modified by Ca (I,II) and fluorine (I), as well as some Co, Fe-containing complex perovskites were considered. Combination of thermal analysis data, oxygen isotope exchange, O2 TPD, reduction by CO, H2 and CH4 TPR, were applied to characterize the accessible surface/bulk oxygen mobility and reactivity. Comparison of these results with earlier data on the real (defect) structure of these systems by TEM, EXAFS, XRD, FTIRS, SIMS allowed to elucidate factors determining the oxygen mobility and reactivity. A quantitative description of the experimental energetic spectrum of oxygen bound with regular and defect surface sites of perovskites was obtained by using the semiempirical Interacting Bonds method with a due regard for the surface face termination and relaxation. Pronounced effect of cation vacancies on the activation barrier for the oxygen migration in the perovskite lattice has been revealed.

Polymerized precursor route [M.P. Pechini, US Patent 3, 330 (1967) 697] was applied for synthesis of dispersed ceria-based solid solutions Ce1−xMex3+O3−y (Me3+= Sm3+ or Bi3+, x up to 0.5). The surface properties of those samples were modified by supporting Pt. Their bulk and surface structural features were characterized by using XRD, TEM, EXAFS, X-ray wide angle scattering (RED), UV–vis, Raman, FTIRS of lattice modes and adsorbed CO. To elucidate factors controlling the surface/bulk oxygen mobility and reactivity, these results were compared with the data of‘ the oxygen isotope exchange and/or H2/CH4 temperature-programmed reduction (TPR). Single-phase fluorite-like solid solutions with a nanodomain microstructure are characterized by distortion of the coordination polyhedra caused by dopants followed by the lattice local rearrangement into that of a lower symmetry at a high dopant content. The highest performance in methane selective oxidation into syngas by the lattice oxygen is found for samples where isolated oxygen vacancies dominate. Earlier studied Pt/Ce–Zr–La–O system [Stud. Surf. Sci. Catal. 143 (2002) 659; T.G. Kuznetsova, V.A. Sadykov, S.A. Veniaminov, G.M. Alikina, E.A. Paukshtis, Ya.N. Kulikova, E.M. Moroz, E.B. Burgina, V.A. Rogov, V.N. Kolomiichuk, V.V. Kriventsov, D.I. Kochubei, O.N. Martyanov, V.F. Yudanov, I.S. Abornev, S. Neophytides, ISO22, Europacat VI, September 2003, Innsbruck, Austria] has a lower oxygen mobility, is less stable in redox cycles and less selective for syngas. Bi–Ce–O system mainly combusts methane and is irreversibly decomposed by deep reduction due to metallic Bi evaporation.

As a result of transformation of isotope-exchange rate equations (isotope-kinetic equations), a relationship was derived that does not contain time and universally relates the variables of isotope composition (an isotope-mechanistic equation). With the use of this relationship, mechanistic parameters that characterize atomic rearrangements can be determined from experimental data even in cases when the rate of exchange varied in the course of a process, for example, under nonisothermal conditions. The use of the proposed approach for the treatment of the results of dynamic thermal isotope exchange in the O 2 –YBa 2 Cu 3 O y and O 2 –Pt/CeZrO systems demonstrated that the experimental data were excellently described by the theoretical equation derived in this work

The work reported here concerns the investigation of several different complex mechanisms of activation of molecules containing two atoms of a labelled element in open systems (Plug Flow Reactors, Continuously Stirred Tank Reactors) and the relationship between kinetic exchange parameters and the parameters of elementary steps. General sets of kinetic equations are used to simulate the responses of different types of reactor and to illustrate the special characteristics of these systems.

Strict kinetic equations of isotope exchange of diatomic molecules were used for the first time far studying the mechanism of the catalytic activation of dihydrogen in homogeneous metal-complex systems. Theoretical bases and formal apparatus of the exchange kinetics are presented; types of exchange are classified, and approaches to the determination of their contributions from experimental data are analyzed. The kinetics of exchange of deuterium-labeled dihydrogen in homogeneous palladium phosphine complex-CF3COOH/H2O-H-2 systems was studied. It is shown that in these systems, the homoexchange of dihydrogen is absent, and two types of heteroexchange are observed, whose relative contributions vary within wide limits depending on the composition of the systems. Possible mechanisms of the catalytic activation of dihydrogen in the studied systems were analyzed on the basis of the isotope-kinetic data obtained. Taking into account the spectroscopic information on the state of the palladium complexes, we concluded that the observed regularities of exchange can be interpreted in terms of a mechanism including consecutive stages of heterolysis of dihydrogen on the Pd(II) phosphine complex and acid-type dissociation of the Pd-H bond in the palladium monohydride complex formed. It is shown that the rates of these two stages are unambiguously related to the isotope-kinetic parameters of the dihydrogen exchange.

Activation of CnH4 (n = 1,2) and H-2 on MgO, elucidated by new isotopic method, proceeds as a results of reversible adsorption with extraction of one atom H.

The evolution of microstructural, morphological and surface chemical properties of Sm2O3–MgO nanocomposites are determined during and after isothermal heat treatments in the range of 500–1000 °C. The samples are investigated using (high temperature) X-ray diffraction, energy-filtered transmission electron microscopy including electron energy loss spectroscopy, nitrogen adsorption, and temperature programmed desorption of CO2. With small amounts of MgO the initial micropore fractions are low and mainly coarsening of Sm2O3 is observed. Large amounts of MgO result in high initial micropore fractions giving rise to enhanced densification. The different thermal degradation behaviors are explained by means of the respective characteristic diffusion distances which are determined by the volume phase fractions. The surface chemical properties of Sm2O3 and MgO remain qualitatively unchanged, however, the specific CO2 chemisorption capacities are increased through the nanocomposite formation.