The interrelation of the structure and catalytic properties of hydrogen-reduced iron-ruthenium systems in the ammonia synthesis reaction is studied by X-ray diffraction (XRD), as well as conversion and absorption Mössbauer spectroscopy (MS). It is found that a sample with a metal content of 50Fe/50Ru (wt

Методами рентгеновской дифракции, конверсионной и абсорбционной мессбауэровской спектроскопии изучена взаимосвязь структуры и каталитических свойств восстановленных водородом железорутениевых систем в реакции синтеза аммиака. Найдено, что образец с содержанием металлов 50Fe/50Ru (мас.%) проявляет максимальную каталитическую активность в синтезе аммиака. Показано, что в бинарной системе формируются наноразмерные кластеры интерметаллида Fe–Ru с размером ОКР ~ 11 нм.

The reaction of Fe(III) and Li(I) pivalates and pyridine (py) in acetonitrile affords a molecular heteronuclear complex [Fe 4 Li 2 (O) 2 (Piv) 10 (py) 2 ]·CH 3 CN ( I ), where Piv is pivalic acid anion, with the structural assembly nontrivial for Fe(III) and alkaline metals. The X-ray diffraction data show that complex I contains the hexanuclear motif {Fe 4 Li 2 O 2 } in which, according to the Mössbauer spectroscopy data, the paramagnetic Fe(III) ions exist in the high-spin state ( S = 5/2) in the symmetric octahedral environment of the O and N atoms.

Методами конверсионной, абсорбционной мессбауэровской спектроскопии и рентгеновской дифракции изучены фазовый состав и структура оксидных и восстановленных водородом железо-рутениевых систем. В образцах с содержанием металлов (mass.%) 50Fe-50Ru после прокалки на воздухе при 773 и 973 K формируются наносистемы, содержащие две фазы различной степени дисперсности: alpha-Fe2O3 с примесью Ru и RuO2 с примесью Fe соответственно. Изучены структурные превращения наносистемы, прокаленной при 973 K, при различных условиях восстановления. Показано, что формирование наноструктур зависит от начальной и конечной температур восстановления. Присутствие рутения существенно изменяет кинетику восстановления оксидных систем. Показано, что при повышении температуры восстановления наблюдаются перестройки исходных стехиометрических оксидов в промежуточные оксидные структуры переменного состава с различным типом кристаллической решетки. Завершающим этапом восстановления служит образование кластеров металла или твердых растворов интерметаллидов. Ключевые слова: оксид железа-рутения, восстановленные водородом железо-рутениевые системы, структурные преобразования наносистем, конверсионная (CEMS) и абсорбционная мессбауэровская спектроскопия (МС), рентгеновская дифракция.

The phase composition and structure of oxide and hydrogen-reduced iron–ruthenium systems are studied using conversion and adsorption Mössbauer spectroscopy, as well as X-ray diffraction methods. In samples with metal concentration (mass %) 50Fe–50Ru after calcination in air at 773 and 973 K, nanosystems containing two phases with different degrees of dispersion are formed (α-Fe 2 O 3 with an admixture of Ru and RuO 2 with an admixture of Fe, respectively). Structural transformations of the nanosystem calcinated at 973 K in different reduction conditions are investigated. It is shown that the formation of nanostructures depends on the initial and final reduction temperatures. The presence of ruthenium substantially changes the reduction kinetics of oxide systems. It is shown that upon an increase in the reduction temperature, the rearrangement of initial stoichiometric oxides to intermediate oxide structures with varying compositions and with different crystal lattice types is observed. The terminating stage of reduction is the formation of metal clusters or solid solutions of intermetallides.

The phase composition and structure of oxide and hydrogen-reduced iron–ruthenium systems are studied using conversion and adsorption Mössbauer spectroscopy, as well as X-ray diffraction methods. In samples with metal concentration (mass %) 50Fe–50Ru after calcination in air at 773 and 973 K, nanosystems containing two phases with different degrees of dispersion are formed (α-Fe2O3 with an admixture of Ru and RuO2 with an admixture of Fe, respectively). Structural transformations of the nanosystem calcinated at 973 K in different reduction conditions are investigated. It is shown that the formation of nanostructures depends on the initial and final reduction temperatures. The presence of ruthenium substantially changes the reduction kinetics of oxide systems. It is shown that upon an increase in the reduction temperature, the rearrangement of initial stoichiometric oxides to intermediate oxide structures with varying compositions and with different crystal lattice types is observed. The terminating stage of reduction is the formation of metal clusters or solid solutions of intermetallides.

Методами мессбауэровской спектроскопии, протонной релаксометрии и просвечивающей электронной микроскопии изучены наночастицы магнетита, предназначенные для создания контрастно-диагностических сред. Суперпарамагнитные наночастицы магнетита с размером 5–7 нм и температурой блокования Тb = 50 К были рассмотрены в качестве контрастного средства с временами релаксации T1 и T2 и способностью длительно циркулировать в кровеносном русле. Более крупные ферримагнитные наночастицы ( 30 40 нм) можно накапливать в очаге заболевания с помощью внешнего магнитного поля, и таким образом они могут служить средством для гипертермии.

Mössbauer spectroscopy, proton relaxometry, and transmission electron microscopy are used to study magnetite nanoparticles designed for creating diagnostic contrast media. Superparamagnetic magnetite nanoparticles with a size of 5–7 nm and blocking temperature of T b = 50 K are examined as a component of diagnostic contrast media with relaxation times T 1 and T 2 capable of circulating in the bloodstream for a long time. Larger ferrimagnetic nanoparticles (30–40 nm) can be concentrated in pathological tissues by applying an external magnetic field, thereby providing a means for hyperthermia.

The electronic and magnetic properties of copolymers on the basis of methyl methacrylate-methacrylic acid and butyl acrylate, (MMA)-(IAA)-(BA), and magnetite Fe3O4 nanoclusters at concentrations of 25, 45 and 67 wt % have been studied. A sharp decrease in the superparamagnetic relaxation time of the magnetic moment of the magnetite clusters was observed at their concentration of 45 wt %. This decrease in the relaxation time is associated with the emergence of the percolation threshold, when the copolymer was doped with magnetite clusters, and with the appearance of the exchange interactions via conduction electrons. The magnetic anisotropy along the sample surface and perpendicular to the surface in strong magnetic fields observed for this concentration is associated with the exchange interaction as well. The magnetic anisotropy of samples in weak magnetic fields corresponds to the dipole-dipole interaction between magnetite nanoclusters.

The evolution of a nickel-containing catalyst based on a mixed oxide substrate obtained from vermiculite etching solutions has been investigated using the methods of Moessbauer and EXAFS spectroscopy, XRD, and transmission electron microscopy. The catalyst manifests high activity in the process of methane vapor reforming (MVR) and is resistant to low sulfur hydride content. Upon the deposition of active components (Ni-La) and thermal treatment at 900°C, the phases of nickel oxide and superparamagnetic particles of γ-Fe 2 O 3 distributed in the structure of the mixed spinel of a composition Mg(FeAl)O 4 ± δ are formed on the catalyst surface. In the course of the preliminary reduction activation by hydrogen, the surface phases interact with the formation of hybrid systems of a core-shell type with a size of 15–17 nm. The core comprises particles of the reduced α-Fe, invar alloy: γ-FeNi and α-FeNi surrounded by a shell of superparamagnetic clusters of γ-Fe 2 O 3 1–4 nm in size with a strong interaction with the nucleus and isostructural mixed oxide with the structure of spinel. After catalysis in the MVR process, at T = 790–820°C the particles of the catalyst containing 30 ppm of H2S become enlarged up to 40–45 nm without a change in shape. The particle enlargement occurs as a result of the increase in the core size, whereas the shell size remains unchanged. It is assumed that the shell decomposes sulfur hydride until elementary sulfur, whereas the system core manifests high activity in the MVR process.

X-ray photoelectron and Mössbauer spectroscopy were used to study the composition and structure of 57Fe-Pd bimetallic black and 57Fe-Pd/SiO2 nanocomposites prepared by metal-vapor synthesis. The main parameters of the core level photoelectron spectra of 57Fe-Pd systems were determined. The bimetallic system was shown to be a disordered amorphous structure consisting of Pd particles, superparamagnetic γ-Fe2O3 nanoparticles with size 8–10 nm, and a Fe-O-Pd solid solution. Considerable broadening of Pd 3d peaks in 57Fe-Pd/SiO2 and an increase in the O 1s-Si 2p energy interval by 0.4 eV with respect to the spectrum of initial SiO2 were observed; this was evidence of the interaction of Pd with the support. The binding energy of Fe 2p 3/2 peak in the nanocomposite spectrum was close to that of Fe2O3, but had a smaller width of the satellite peak and a larger spin-orbit splitting, which was indicative of a considerable amount of FeOOH on the surface compared with the other iron oxides.

The magnetic properties of monodisperse magnetite in a docosane matrix are investigated. A cluster-organized nanostructure based on nanomagnetite loses its magnetization by means of the first-order phase transition (jumplike) upon increasing the temperature to over 16 K. The thermodynamic model of such a transition is studied by taking into account magnetostriction and the compressibility of nanoclusters in the nanostructure. A value of 10−2 T for the critical field strength of the transition from a paramagnetic to a magnetically ordered (supermaramagnetic) state of the magnetite cluster matching the experimental value is obtained when the thermodynamic model of the magnetic phase transition of a nanocluster in an external magnetic field is analyzed. A model of the oxidized magnetite which differs from γ-Fe2O3 is examined.

—Onedimensional nanostructures based on singlelayer carbon nanotubes (CNTs) with FeBr 2 chains and twodimensional nanostructures with Fe–O–Fe layers deposited on the surface of silica gel bymolecular layering have been synthesized. An Mossbauer spectroscopy examination has shown that a magnetic structure with T C = 21 K and B in = 29.8 ± 0.5 T is formed in nanotubes with FeBr 2 · 2H 2 O at T = 15 K.In the case of the Fe–O–Fe layers, the surface of silica gel has a nonmagnetic monolayer along with αFe 2 O 3 nanoclusters with B in (1) = 48.5 ± 0.5 T and B in (2) = 46.4 ± 0.5 T at T = 15 K and the temperature T C = 210 K.The variation in magnetization with temperature is calculated using three models of phase transitions,namely, the model of critical indices, the twodimensi onal Ising model (the Onsager formula), and the threedimensional Heisenberg model. The experimental data are fitted best by the model of critical indices with thecritical parameters α = 0.22 and 0.18 for 1D and 2D structures, respectively, demonstrating that these nanosystems approach twodimensional structures ( α = 0.15).

Using magnetization and Mössbauer spectroscopy, investigations of the magnetic properties of α-Fe2O3-SiO2 and γ-Fe2O3-SiO2 nanostructures, including α-Fe2O3 nanoclusters 2 nm in size and γ-Fe2O3 nanoclusters 3–4 nm in size in silica gel pores, have been conducted. For α-Fe2O3-SiO2 nanostructures, magnetic phase transitions of the first order are detected and examined with the transition temperature dependent on the nanocluster size and intercluster interactions. α-Fe2O3 nanoclusters up to 16 K remain in the noncompensated antiferromagnetic state (upper Morin point temperature). At low temperatures, α-Fe2O3 nanoclusters reveal quantum-size effects. For γ-Fe2O3-SiO2 nanostructures, supermagnetic behavior with a blocking point dependent on intercluster interactions is typical. At low temperatures, intercluster interactions lead to the appearance of a coercive force of 0.03 T.

One-dimensional nanostructures based on single-layer carbon nanotubes (CNTs) with FeBr2 chains and two-dimensional nanostructures with Fe-O-Fe layers deposited on the surface of silica gel by molecular layering have been synthesized. An Mössbauer spectroscopy examination has shown that a magnetic structure with T C = 21 K and B in = 29.8 ± 0.5 T is formed in nanotubes with FeBr2 · 2H2O at T = 15 K. In the case of the Fe-O-Fe layers, the surface of silica gel has a nonmagnetic monolayer along with α-Fe2O3 nanoclusters with B in(1) = 48.5 ± 0.5 T and B in(2) = 46.4 ± 0.5 T at T = 15 K and the temperature T C = 210 K. The variation in magnetization with temperature is calculated using three models of phase transitions, namely, the model of critical indices, the two-dimensional Ising model (the Onsager formula), and the three-dimensional Heisenberg model. The experimental data are fitted best by the model of critical indices with the critical parameters α = 0.22 and 0.18 for 1D and 2D structures, respectively, demonstrating that these nanosystems approach two-dimensional structures (α = 0.15).

Nanostructures have been synthesized by (i) the micellar template method with the subsequent organization of Fe2O3 nanoclusters about 10 nm in size to a cluster crystal and (ii) by the aerosol method with the fixation of Fe2O3 nanoclusters about 10 nm in size in the NaCl matrix. The magnetic properties of the synthesized nanostructures have been studied. The Mössbauer spectroscopic examination of the cluster crystal revealed a magnetic phase transition of the first order, with the transition temperature being near the room temperature. This nanostructure is characterized by a steep magnetization curve, which is typical of an ordered structure with a weak intercluster interaction like a molecular crystal and a low energy of the magnetic anisotropy K = 3.5 × 104 J/m3. The disordered Fe2O3 nanostructure in the NaCl matrix is characterized by superparamagnetic behavior and smooth magnetization curves without saturation at 1 T and the magnetic anisotropy energy K = 2.5 × 104 J/m3, which is close to the corresponding value in bulk α- and γ-Fe2O3.

FeCl2@OCHT, FeBr2@OCHT, and FeI2@OCHT nanocomposites were obtained by capillary filling of the channels of carbon single-walled nanotubes (SWNTs) with melts of iron halogenides. The composites were studied by high resolution transmission electron microscopy (HRTEM), the capillary condensation of nitrogen at 77K, Raman spectroscopy, optical absorption spectroscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and Moessbauer spectroscopy. Substantial distinctions in the combination scattering spectra of SWNTs and nanocomposites in the region of radial modes and in the region of longitudinal and tangential oscillations were revealed. The presence of electron transfer between the nanocrystal and the SWNT wall was established in the nanocomposites. For the FeCl2@OCHT nanocomposite, two states of Fe+2 were found: the first is characterized by electron transfer from the nanotube to the nanocrystal, which leads to the electron structure of the SWNT and FeCl2 changing; the second corresponds to the strained intercalated state resulting from the mechanical effect of the small SWNT diameter on the FeCl2 nanocrystal.