The existence regions of the Y2–xMgxFeTaO7–δ (x = 0–0.15), Y2–xMgxFe1–x/2Ta1+x/2O7–δ (x = 0–0.15), Y2Fe1–xMgxTaO7–δ (x = 0–0.3), and Y2Fe1–3/2xMgxTa1+x/2O7–δ (x = 0–0.3) solid solutions were estimated. It was found that, regardless of the composition, the entry of Mg2+ into the crystal lattice of Y2FeTaO7 causes a similar distortion of the structure (space group R 3̅ → space group P3121). Based on XANES and Mössbauer spectroscopy data, it was suggested that Mg2+ ions occupied the eight-coordinated sites in the crystal lattice of solid solutions, displacing iron ions, while vacant yttrium sites in Y2–xMgxFeTaO7–δ and Y2–xMgxFe1–x/2Ta1+x/2O7–δ are occupied by tantalum ions. The XANES method confirmed the existence of Fe4+ ions in the Y2FeTaO7 solid solutions along with Fe3+. The simultaneous presence of the Ta4+ and Ta5+ ions ensures the electroneutrality of there crystal lattices. Herewith, the entry of Mg2+ does not lead to an increase in the Fe4+ concentration.

Single-phase samples of compounds occurring in La2O3–CoO–Sb2O5 system have been prepared by the thermal decomposition of nitrates, citrate method, and co-precipitation with hydrothermal treatment of precipitate followed by annealing. Their catalytic properties in CO oxidation reaction have been studied. It has been found that LaCo1/3Sb5/3O6 catalyst with rosiaite structure obtained by co-precipitation method with hydrothermal treatment of precipitate followed by annealing showed the highest activity at low temperatures and stability in cyclic testing. This catalyst provides 90

Subsolidus phase equilibria in the La2O3–(Ni/Со)O–Sb2O5 systems have been studied. A previously unknown compound La4Sb2O11 was found to exist in the La2O3–Sb2O5 system. La4Sb2O11 has been shown to decompose at 1060°C to form La3SbO7 and LaSbO4. Two ternary oxides (LaNi2SbO6 and La2NiSb2O9) have been discovered in the La2O3–NiO–Sb2O5 system. These new compounds are stable and do not undergo polymorphic transformations throughout the range of temperatures studied (25–1350°C). The existence of previously known ternary oxides, namely perovskite La3Ni2SbO9 and rosiaite LaNi1/3Sb5/3O6, has been verified. In the La2O3–CoO–Sb2O5 system, two new compounds (LaCo2SbO6 and La2CoSb2O9) have been found along with previously known perovskite La3Co2SbO9, rosiaite LaCo1/3Sb5/3O6, and rhombohedral pyrochlore La3Co2Sb3O14. These new compounds are isostructural to those found in the nickel oxide system. La2CoSb2O9, unlike its nickel analogue, decomposes at 990°C. For LaCo2SbO6, no thermal events associated with polymorphic transitions or melting have been detected on DSC curves up to 1350°C. An inspection of diffuse reflectance spectra of the newly synthesized LaNi2SbO6, La2NiSb2O9, LaCo2SbO6, and La2CoSb2O9 phases showed that the oxidation state of nickel and cobalt in them is 2+. The 1050°C isothermal sections of La2O3–(Ni/Co)O–Sb2O5 systems have been constructed.

Methods for the synthesis of LaNi1/3Sb5/3O6 with a rosiaite structure have been developed using citrate method and coprecipitation followed by annealing. The influence of synthesis conditions on the morphology of the samples has been demonstrated. A comparative analysis of the catalytic properties of LaNi1/3Sb5/3O6 synthesized by various methods, in the reaction of CO oxidation has been carried out. The catalyst synthesized by the citrate method demonstrated the greatest efficiency and stability (the temperature of 90% CO conversion was T90 = 336°C). The LaNi1/3Sb5/3O6 surface was studied before and after catalysis by in situ diffuse reflectance IR spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed O2 desorption. It has been shown that the catalytic oxidation of CO on the LaNi1/3Sb5/3O6 surface proceeds according to the Mars–van Krevelen mechanism and is accompanied by redox Sb3+ ↔ Sb5+ processes. It has been established that no contamination of the sample surface occurs during the catalysis process.

Mg-containing solid solutions based on Y 2 FeTaO 7 and formed by various mechanisms of heterovalent substitution were synthesized and had the following compositions: Y 2 Fe 0.55 Mg 0.3 Ta 1.15 O 7 , Y 2 Fe 0.625 Mg 0.3 Ta 1.075 O 7 , Y 2 Fe 0.7 Mg 0.3 TaO 7 , Y 2 Fe 0.7 Mg 0.2 Ta 1.1 O 7 , Y 2 Fe 0.85 Mg 0.15 TaO 7 , Y 1.85 Mg 0.15 Fe 0.925 Ta 1.075 O 7 , and Y 1.85 Mg 0.15 FeTaO 7 . It was shown that all synthesized solid solutions have a pyrochlore-like layered structure (space group P 3 1 21), in which Fe 3+ ions are distributed over three structural positions. The magnetic properties of these solid solutions are due to the presence of a small ferromagnetic component in a predominantly antiferromagnetic system and characterize a ferrimagnet or a canted antiferromagnet with the Néel transition at the Néel temperature T N above room temperature. According to the data of magnetic measurements, two magnetic phase transitions to the ordered phase occur in all the studied samples. Along with the T N transition, in weak magnetic fields and below T N , there is a second transition, which is most likely due to a spin reorientation of the Morin type. The existence of magnetic ordering at room temperature in one magnetic sublattice or an internal magnetic field ( H in ) was confirmed by Mössbauer spectroscopy.

Methods for the synthesis of LaNi 1/3 Sb 5/3 O 6 with a rosiaite structure have been developed using citrate method and coprecipitation followed by annealing. The influence of synthesis conditions on the morphology of the samples has been demonstrated. A comparative analysis of the catalytic properties of LaNi 1/3 Sb 5/3 O 6 synthesized by various methods, in the reaction of CO oxidation has been carried out. The catalyst synthesized by the citrate method demonstrated the greatest efficiency and stability (the temperature of 90% CO conversion was T 90 = 336°C). The LaNi 1/3 Sb 5/3 O 6 surface was studied before and after catalysis by in situ diffuse reflectance IR spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed O 2 desorption. It has been shown that the catalytic oxidation of CO on the LaNi 1/3 Sb 5/3 O 6 surface proceeds according to the Mars–van Krevelen mechanism and is accompanied by redox Sb 3+ ↔ Sb 5+ processes. It has been established that no contamination of the sample surface occurs during the catalysis process.

Mg-containing solid solutions based on Y2FeTaO7 and formed by various mechanisms of heterovalent substitution were synthesized and had the following compositions: Y2Fe0.55Mg0.3Ta1.15O7, Y2Fe0.625Mg0.3Ta1.075O7, Y2Fe0.7Mg0.3TaO7, Y2Fe0.7Mg0.2Ta1.1O7, Y2Fe0.85Mg0.15TaO7, Y1.85Mg0.15Fe0.925Ta1.075O7, and Y1.85Mg0.15FeTaO7. It was shown that all synthesized solid solutions have a pyrochlore-like layered structure (space group P3121), in which Fe3+ ions are distributed over three structural positions. The magnetic properties of these solid solutions are due to the presence of a small ferromagnetic component in a predominantly antiferromagnetic system and characterize a ferrimagnet or a canted antiferromagnet with the Néel transition at the Néel temperature TN above room temperature. According to the data of magnetic measurements, two magnetic phase transitions to the ordered phase occur in all the studied samples. Along with the TN transition, in weak magnetic fields and below TN, there is a second transition, which is most likely due to a spin reorientation of the Morin type. The existence of magnetic ordering at room temperature in one magnetic sublattice or an internal magnetic field (Hin) was confirmed by Mössbauer spectroscopy.

A procedure for the synthesis of the LaCo1/3Sb5/3O6 layered oxide with a rosiaite structure has been developed. The method is based on the hydrothermal treatment of coprecipitated sediments with their subsequent annealing. The resulting material has proven to be an efficient catalyst in the CO oxidation reaction. This result confirms the prospects of using compounds with the rosiaite structure in oxidative catalysis reactions.

n isothermal section of the Sm 2 O 3 –Fe 2 O 3 –Ta 2 O 5 system was constructed in the subsolidus region at 1200°C. A region of the Sm 2 – x Fe 1 + x TaO 7 solid solution with the cubic pyrochlore structure (space group Fd 3̅ m ) was found. A study of the polythermal section of the system along the Sm 2 – x Fe 1 + x TaO 7 section showed that the previously known compound Sm 2 FeTaO 7 (R) with the structure of rhombohedrally distorted pyrochlore (space group R 3̅ ) is stable in the temperature range <1200°C. With increasing temperature, Sm 2 FeTaO 7 (R) becomes an intermediate phase, and a reversible transition to the cubic pyrochlore (C) phase is observed. The kinetic hindrances of the transition R 3̅ → Fd 3̅ m determine the short-term stability of the R phase at temperatures exceeding the phase transition temperature by 200°C. It was established that cubic pyrochlore exists as the Sm 2 – x Fe 1 + x TaO 7 solid solution in the ranges x = 0–0.4 at t ≥ 1200°C and x = 0.15–0.4 at lower temperatures. Two independent methods—Mössbauer spectroscopy and XANES—detected that the rhombohedral phase contains not only Fe 3+ ions but also Fe 4+ ions. The magnetic properties were studied, and it was shown that both the R phase and the C phase at T < 10 K undergo two magnetic transitions of different types: an antiferromagnetic transition observed in a strong magnetic field at 7.2 and 5.5 K, respectively, and a transition to the spin glass state in a field of 100 Oe at 8.4 and 4.8 K, respectively. It was determined that the spin glass state coexists with short-range antiferromagnetic interactions until 2.3 K. Despite the fact that the R and C phases formally have geometrically frustrated magnetic sublattices, the experimental data showed that frustration manifests itself only in the R phase.

An isothermal section of the Sm2O3–Fe2O3–Ta2O5 system was constructed in the subsolidus region at 1200°C. A region of the Sm2 – xFe1 + xTaO7 solid solution with the cubic pyrochlore structure (space group Fd 3̅ m) was found. A study of the polythermal section of the system along the Sm2 – xFe1 + xTaO7 section showed that the previously known compound Sm2FeTaO7 (R) with the structure of rhombohedrally distorted pyrochlore (space group R 3̅ ) is stable in the temperature range <1200°C. With increasing temperature, Sm2FeTaO7 (R) becomes an intermediate phase, and a reversible transition to the cubic pyrochlore (C) phase is observed. The kinetic hindrances of the transition R 3̅ → Fd 3̅ m determine the short-term stability of the R phase at temperatures exceeding the phase transition temperature by 200°C. It was established that cubic pyrochlore exists as the Sm2 – xFe1 + xTaO7 solid solution in the ranges x = 0–0.4 at t ≥ 1200°C and x = 0.15–0.4 at lower temperatures. Two independent methods—Mössbauer spectroscopy and XANES—detected that the rhombohedral phase contains not only Fe3+ ions but also Fe4+ ions. The magnetic properties were studied, and it was shown that both the R phase and the C phase at T < 10 K undergo two magnetic transitions of different types: an antiferromagnetic transition observed in a strong magnetic field at 7.2 and 5.5 K, respectively, and a transition to the spin glass state in a field of 100 Oe at 8.4 and 4.8 K, respectively. It was determined that the spin glass state coexists with short-range antiferromagnetic interactions until 2.3 K. Despite the fact that the R and C phases formally have geometrically frustrated magnetic sublattices, the experimental data showed that frustration manifests itself only in the R phase.

Highly efficient and stable catalysts PdO/LnFe0.5Sb1.5O6, Ln – La, Ce, Pr, Nd, Sm, promising in the reaction of complete methane oxidation have been obtained using the deposition–precipitation method. The catalysts contain complex oxides, which crystallize in a rosiaite-type structure (sp.gr. P31m). These oxides have been used for the first time as support. The catalysts samples are characterized by a uniform distribution of PdOx particles the average size of which is 13 nm. The 90

A new compound SmFe0.5Ta1.5O6 has been synthesized and its structure has been calculated from synchrotron powder diffraction data by the Rietveld method. It has been demonstrated that SmFe0.5Ta1.5O6 has an aeschynite structure (space group Pnma). A study of its magnetic properties has shown that the SmFe0.5Ta1.5O6 compound is paramagnetic.

New compounds with the rosiaite type structure LaM1/3Sb5/3O6, M = Co, Ni, and Cu, were synthesized. The compounds belong to quasi-two-dimensional magnets, in which magnetic interactions occur in the layers with a honeycomb structure. It is shown that there is no long-range magnetic order in these compounds. The temperature and field dependences of the magnetization in the compounds with M = Co, Ni indicate the presence of short-range anti-ferromagnetic and ferromagnetic exchange interactions. In the LaM1/3Sb5/3O6, M = Co, Ni, compounds, the interactions occur between Co2+ or Ni2+ ions of isolated magnetic clusters randomly distributed in the paramagnetic matrix in the chains of (M/Sb)O6 octahedrons. These clusters have sizes comparable with the crystal cell size. The LaCu1/3Sb5/3O6 compound is paramagnetic.

A procedure for the synthesis of the LaCo 1/3 Sb 5/3 O 6 layered oxide with a rosiaite structure has been developed. The method is based on the hydrothermal treatment of coprecipitated sediments with their subsequent annealing. The resulting material has proven to be an efficient catalyst in the CO oxidation reaction. This result confirms the prospects of using compounds with the rosiaite structure in oxidative catalysis reactions.

The isobaric heat capacity of pyrochlore-related compounds RE2FeTaO7 (RE = Sm and Gd) was measured using an adiabatic and a differential scanning calorimetry over a wide temperature range using adiabatic and differential scanning calorimetry. An anomaly on the curves of all the compounds is clearly observed within the low-temperature range, T < 25 K, while at the high temperatures the peculiarities were not detected. The standard thermodynamic functions: heat capacity, entropy, enthalpy change and reduced Gibbs energy of studied RE2FeTaO7 were calculated. The entropy of the anomalous contribution was equal to (14.8 and 19.6) J.K-1.mol(-1) for Sm2FeTaO7 and Gd2FeTaO7, respectively. A comparative study of Y2FeTaO7 and Sm2FeTaO7 confirmed the relationship of low temperature magnetic properties with a heat capacity anomaly. The DC and AC magnetization measurements within the (300-2.3) K temperature range and in magnetic fields up to 5 kOe revealed spin glass (SG) transitions for Y2FeTaO7 and Sm2FeTaO7 at 4 K and 9 K, respectively. Against the background of developing SG in the frustrated Kagome sublattice, an antiferromagnetic transition at T similar to 8 K was detected for Sm2FeTaO7 in a large magnetic field. This transition occurs in Sm-sublattice and is responsible for the large magnetic contribution to the anomalous low temperature heat capacity in Sm2FeTaO7. (C) 2021 Elsevier Ltd.

X-ray photoelectron spectroscopy has been applied to examine the surface electronic structure of layered oxides CeFe 0.5 Sb 1.5 O 6 and PrFe 0.5 Sb 1.5 O 6 with PbSb 2 O 6 structure (sp. g. P‑ 31 m ). The analysis of the XP-spectra for both compounds revealed only Ce 3+ and Pr 3+ oxidation state before and after catalytic tests. The observed variation of the Sb 5+ /Sb 3+ and Fe 3+ /Fe 2+ ratios after catalysis can point to that CO oxidation on these catalysts proceeds by virtue of redox transformations Sb 3+ ↔ Sb 5+ and Fe 3+ ↔ Fe 2+ with direct involvement of lattice oxygen and anionic vacancies.

The impact of the synthesis method and morphology of the LaFe0.5Sb1.5O6 samples on their catalytic activity in CO oxidation was studied in detail. The samples obtained by solid-phase reaction and co-precipitation showed higher catalytic activity. The features of the morphology, which cause the lowering of catalytic activity, were revealed for the samples synthesized in molten salts with and without preliminary microwave-hydrothermal treatment. A comparative study of all synthesized rosiaites LnFe(0.5)Sb(1.5)O(6), Ln = La-Pr, LaFe0.5-xGaxSb1.5O6 and also pyrochlore Pr-2(Fe,Sb)O-7 using an in situ diffuse reflection IR spectroscopy method was undertaken to clarify the mechanism of CO oxidation. It was revealed that in the course of the reaction the intermediate complexes of metal carbonyls are formed on the surface. At the same time, inactive carbonyls, which exist on the of Ce- and Pr-containing samples surface before the reaction mixture is fed, were found. This feature gives rise to a decrease in their catalytic activity. A reaction mechanism occurring via intermediate carbonyl complexes on the active centers - [Sb3+ - V-O(-) - Fe3+] - is proposed. The CO oxidation on completely gallium-substituted samples indicates the existing of an additional channel for proceeding of redox process, which is not associated with Fe3+. It is suggested that the nature of this channel is possibly associated with a rosiaite layered structure, which creates a unique environment conducive to complex adsorption phenomena.

New complex Cr-containing pyrochlores Ln(2)CrTaO(7), Ln = Y, Sm, Gd, were synthesized. The Rietveld refinement of the Ln(2)CrTaO(7) composition confirmed the pyrochlore type of the structure. The Cr3+ oxidation state is corroborated by XANES spectra. The detailed study of DC and AC magnetization of Ln(2)CrTaO(7), Ln = Y, Sm, Gd, was carried out in the temperature range 2-300 K and magnetic field up to 5 T. FM phase transitions at 143, 192, and 163 K were observed in pyrochlores with Y, Sm, and Gd, respectively. It is shown that these transitions are due to canted antiferromagnetism or weak-ferromagnetism in the Ln(2)CrTaO(7) pyrochlores. AFM interactions between Ln- and Cr-sublattices in Sm2CrTaO7 and Gd2CrTaO7 causes AFM transition at T = 42 K, after which magnetization continues increasing. Unusual magnetic properties were observed for Gd2CrTaO7 at low temperatures. Competitive FM and AFM interactions in Cr-and Gd-sublattice give rise to the occurrence of reentrant spin glass at T < 20 K. FM transition at 11 K is also detected. Spin glass state exists along with strong FM interactions. The effect of the magnetic properties on thermal expansion is also investigated for these compounds.

Results of the catalytic hydrogenation of lignin in a hydrogen-donor solvent medium are described. Nickel-containing systems are deposited directly on the lignin surface in an amount of 1.5–3.4 wt %. Nickel systems are deposited by two methods: from a Ni(OAc) 2 × 4Н 2 О aqueous solution and from a colloidal solution in toluene of nickel particles prepared by metal vapor synthesis (MVS). The hydrogen donor solvent is tetralin taken in a tetralin/lignin ratio of 1 : 1. Hydrogenation was carried out in a rotating autoclave at a temperature of 400°C and a pressure of 100 atm. It is shown that the preactivation of nickel-containing lignin by ultrasonication at 39 kHz for 20 min leads to an almost exhaustive conversion of the organic matter: the hydrogenation products comprise 13.1 wt % gas and 86.3 wt % liquid hydrocarbons. The liquid hydrogenation products contain aromatic hydrocarbons and nonvolatile condensed compounds with an average molecular weight of 300 Da. The effect of sonication on nickel-containing lignin and the evolution of nickel-containing components during lignin hydrodepolymerization are studied by electron microscopy and magnetic susceptibility methods.