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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. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes (SWCNTs) are promising materials for use in multifunctional polymer composites. A special feature of SWCNTs is their tendency to aggregate into bundles with 2D close packing. The coherence of such packing leads to the appearance of diffraction maxima at small-angle X-ray scattering. Using the Debye equation for X-ray scattering, this work presents the results of a theoretical analysis of the influence exerted by various parameters of SWCNT bundles (length and diameter of SWCNTs, transverse dimensions of SWCNT bundles, distribution of diameters and the number of SWCNTs in bundles) on the position, width, and shape of these diffraction peaks. To this end, atomic models of both the individual tubes and their bundles were constructed taking into account the diameter distribution of nanotubes, which has a significant effect. The results obtained can be used to correctly interpret the experimental diffraction data. [ABSTRACT FROM AUTHOR]

Mixed Ni-Al oxide catalytic precursors with different elemental ratios (20, 50, and 80 wt.% Ni0) were synthesized using green supercritical antisolvent co-precipitation (SAS). The obtained oxide precursors and metal catalysts were characterized in detail by X-ray diffraction (XRD) analysis, atomic pair distribution function (PDF) analysis, CO adsorption, and high-resolution transmission electron microscopy (HRTEM). It was found that the composition and structure of the Ni-Al precursors are related to the Ni content. The mixed Ni1−xAlxO oxide with NiO-based crystal structure was formed in the Ni-enriched sample, whereas the highly dispersed NiAl2O4 spinel was observed in the Al-enriched sample. The obtained metal catalysts were tested in the process of anisole H2-free hydrogenation. 2-PrOH was used as a hydrogen donor. The catalyst with 50 wt.% Ni0 demonstrated the highest activity in the hydrogenation process. [ABSTRACT FROM AUTHOR]

In our study, we have obtained a multicomponent MoVSbNbCeOx/SiO2 catalyst with high catalytic activity for oxidative dehydrogenation of ethane (ODE) to ethylene. To date, multicomponent MoVTe(Sb)NbOx catalysts, which have been intensively studied during the last years, were found as very promising for the ODE to produce ethylene. It was generally agreed that the MoVTeNbOx catalyst was more efficient than MoVSbNbOx. The major drawback of using Te‐containing catalysts is the presence of environmentally harmful, toxic tellurium, and its volatility during the catalyst preparation and catalytic reaction conditions. In our work, the Mo1V0.24Sb0.23Nb0.08Ce0.01Ox/50 wt. % SiO2 catalyst was prepared via the spray‐dry method of aqueous solutions of the starting components, followed by heat‐treatment in He at 350 and 600 °C. For comparative purpose, one of the best Te‐containing catalysts Mo1V0.3Te0.23Nb0.12Ox was also tested in this reaction under the similar reaction conditions. A comparison of the catalytic properties of Sb− and Te− containing catalysts at the reaction temperature of 400–450 °C illustrates for both catalysts relatively high catalytic properties for ODE. The yield of ethylene of ca. 74 % was obtained for these catalysts, which exceeds the best yield reported in literature for Sb‐containing catalysts. The two main phases – M1 and M2 were revealed by XRD in the Sb‐containing catalyst. Intergrowth between the crystals of M1 and M2 phases with the formation of the interphase boundary in the highly active and selective Sb‐containing catalyst can be proposed from HRTEM results. The nature of the active state in this catalyst is discussed. [ABSTRACT FROM AUTHOR]

The study revealed peculiarities in the formation of mixed oxides with the Mn 3-x Al x O 4 spinel structure that were obtained from initial simple oxides β-Mn 3 O 4 and γ-Al 2 O 3 by calcination in various media at 600–1200 °C. The phase composition of the samples treated in air, argon or hydrogen was investigated using ex situ and in situ X-ray diffraction. It was shown that the occurrence of phase transformations depends on the treatment conditions and is related to the charge state of manganese cations. A scheme of the structural transformations induced by temperature and medium was proposed. The formation temperature of spinel was found to decreases from 950 to 600 °C when the oxidizing medium is replaced by the reducing one. Mn 3-x Al x O 4 spinel (x ∼ 1.5) was produced in air at temperatures above 1050 °C or in an inert medium at 800–1200 °C. [ABSTRACT FROM AUTHOR]

The synthesis of solketal from acetone and glycerol (I) was investigated in the presence of the isostructural MOFs of the families MIL-100(M) and MIL-53(M) (M = V, Al, Fe and Cr) and mixed MIL-53(Al,V) (Al/V – 100/0, 75/25, 50/50, 25/75 and 0/100 atom/atom). The main products were a five-membered solketal (2,2-dimethyl-1,3-dioxane-4-methanol, (II)) and a six-membered acetal (2,2-dimethyl-dioxane-5-ol, (III)). It was demonstrated that the reaction rate and isomer selectivity depend on different parameters such as the type of metal ion, the length of the M-O bond, the rate constant for the exchange of the water molecules from the first coordination sphere of a metal ion and the value of the zero point of the surface charge (pH PZC ). Investigation of mixed MIL-53(Al,V) shows that the reaction rate and selectivity towards (II) increase with increasing V 3+ content in MIL-53(Al,V). V-containing MOFs possess a high activity and selectivity at 25 °C. The efficiencies of MIL-100(V) and MIL-47(V) were higher than those of H 2 SO 4 , SnCl 2 and p -toluenesulfonic acid at 25 °C. The MIL-100(V) catalyst showed good reusability for 4 catalyst recycles. [ABSTRACT FROM AUTHOR]

Spinel-like Mn1.5Al1.5O4 is an unstable compound whose decomposition is induced by partial oxidation of Mn2+ ions in the temperature range of 300–800 °C in air. According to XRD, two spinel-like phases, Mn0.4Al2.4O4 and Mn2.8Al0.2O4, are formed during both cooling and heating of Mn1.5Al1.5O4. In this paper, we have studied microstructural changes of Mn1.5Al1.5O4 to understand its decomposition mechanism. During heating, low-temperature oxidation takes place and decomposition proceeds via a nucleation and growth mechanism. As a result slightly Al-doped β-Mn3O4 nanoparticles are formed on the surface of the parent spinel particles. On the contrary, cooling leads to high-temperature oxidation that results preferably in spinodal decomposition and formation of alternating Mn- and Al-rich lamellas of nanosized thickness. The present study provides a fundamental reference for the nanostructure design of a Mn–Al–O system and probably some other ones subjected to oxidative decomposition. [ABSTRACT FROM AUTHOR]

Two calcium-rich natural layered aluminosilicates containing 90–95 wt.% montmorillonite were chemically activated using 0.125–3.0 M HCl solutions. Structural and textural properties were characterized by X-ray diffraction, elemental analysis and N 2 -adsorption/desorption analyses. According to infrared spectroscopy using pyridine as probe molecule, the amount of Brønsted acid sites increased when increasing HCl concentration. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2 H -chromen-4-ol, carried out in toluene at 35 °C. It was found that the amount of Brønsted acid sites and the microporosity of the catalysts are key factors for the control of the reaction rate and the selectivity towards octahydro-2 H -chromen-4-ol. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalytic properties of MnO x /Al2O3 catalysts were studied in the CO oxidation. [•] Activity of the Ar-calcined catalysts was related to the Mn3−x Al x O4 formation. [•] Active component in the air-catalysts contains Mn3O4 and amorphous Mn–Al–O phase. [Copyright &y& Elsevier]

Abstract: The preparation of multiphase CdS/TiO2 photocatalysts by the deposition of cadmium sulfide nanoparticles on the surface of commercial titania Hombifine N and Degussa P25 in the presence of a chelating agent (ammonia) was carried out. The photocatalysts were characterized by a wide range of experimental techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) combined with energy-dispersive X-ray (EDX) spectroscopy, X-ray fluorescence (XRF) spectroscopy, and UV/VIS spectroscopy. The photocatalytic activity was tested in the reaction of ethanol gas-phase oxidation under visible light irradiation (λ >420nm) in a batch reactor. The deposition of cadmium sulfide on the surface of anantase/rutile titania Degussa P25 was found to produce higher activity in comparison to the deposition on anatase Hombifine N. The good stability and activity of the multiphase system seem to be caused by the formation of hetero-junctions between CdS and TiO2 nanoparticles resulting in the efficient charge separation and decreased electron–hole recombination. [Copyright &y& Elsevier]

The results obtained in this study show that Sb-containing catalysts MoVSbNbGdO x /SiO 2 are highly active in ethane oxidative dehydrogenation to produce ethylene. The ethylene yield of 72% (79.3% ethylene selectivity and 91.1% ethane conversion) was obtained at 400 °C on one of the best catalyst. The effect of Gd additives on the catalytic properties of MoVSbNbGdO x /SiO 2 catalysts was investigated. The catalysts with Gd/Mo = 0.010 – 0.015 demonstrated relatively high catalytic activity coupled with high selectivity to ethylene and excellent stability in ODE reaction, but further growth of the gadolinium content (Gd/Mo = 0.02) was accompanied by the decrease in the activity and ethylene selectivity. XRD, HRTEM, SEM, XPS and adsorption methods were used to reveal the phase composition, morphology and the structure of the obtained catalysts. [Display omitted] • The catalysts MoVSbNbGdO x /SiO 2 with different gadolinium content were synthesized. • The effect of Gd on the catalytic and physicochemical properties were investigated. • The ethylene yield of 72% was obtained at 4000 C on one of the best catalyst. • The active mass of catalyst contains two main phases, M1 (80%) and M2 (20%). • Phase M1is stabilized as needle-like morphology particles inside the SiO 2 particles. [ABSTRACT FROM AUTHOR]

In this work, we investigate commercially available γ-Al 2 O 3 oxides with regard to their nanostructure. A deep analysis of high-resolution transmission electron microscopy data as well as total X-ray scattering data, including both Bragg peaks and defect-related diffuse scattering, is performed. The atomistic models of 3D nanostructured γ-Al 2 O 3 nanoparticles are constructed and validated by the Debye function analysis and atomic pair distribution function analysis. It is revealed that the specific defects lying on {100} and {111} planes fragment the γ-Al 2 O 3 nanoparticles into nanosized crystalline blocks. The interblock interfaces are partially coherent because the planar defects locally disturb the cation sublattice and keep anion sublattice intact. The observed shape and mutual arrangement of the primary crystalline blocks are specified by the revealed planar defects. The work shows that the γ-Al 2 O 3 oxides can differ in the density of the defects causing the particle nanostructuring. The proposed models of 3D nanostructure complement the recent crystallographic models of γ-Al 2 O 3 structure by providing further insights into the nature of non-spinel cations. The non-spinel cations are concentrated near the interblock interfaces formed by the planar defects. [Display omitted] • Nanocrystalline γ-Al 2 O 3 oxides are studied with regard to nanostructure. • Atomic models of 3D nanostructure of γ-Al 2 O 3 oxides were constructed. • Nanostructure models fully comply with total XRD and HRTEM data. • Nanostructure models were verified by PDF analysis at the atomic level. • Non-spinel cations are concentrated at interblock interfaces in nanostructured particles. [ABSTRACT FROM AUTHOR]

The Mn-Ce oxide catalysts active in the oxidation of CO were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transition electron microscopy (TEM), energy dispersive X-Ray (EDX), and a differential dissolution technique. The Mn-Ce catalysts were prepared by thermal decomposition of oxalates by varying the Mn:Ce ratio. The nanocrystalline oxides with a fluorite structure and particle sizes of 4–6 nm were formed. The introduction of manganese led to a reduction of the oxide particle size, a decrease in the surface area, and the formation of a MnyCe1−yO2−δ solid solution. An increase in the manganese content resulted in the formation of manganese oxides such as Mn2O3, Mn3O4, and Mn5O8. The catalytic activity as a function of the manganese content had a volcano-like shape. The best catalytic performance was exhibited by the catalyst containing ca. 50 at.% Mn due to the high specific surface area, the formation of the solid solution, and the maximum content of the solid solution. [ABSTRACT FROM AUTHOR]

This article attempts to study changes in the microstructure of solid solutions with the perovskite structure La0.5Ca0.5Mn0.5Fe0.5O3 under the action of the methane oxidation reaction medium. By the methods of XRD, XPS and HRTEM the initial condition of the structure and the surface of the perovskite were both investigated. A feature of the structure of this solid solution is the presence of planar defects in the direction of the planes (101). After the methane oxidation reaction, a similar study of perovskite structure was conducted to obtain the changes. It was shown that under the action of the reaction medium, Ca1−xMnxO particles form on the surface of the perovskite phase, while planar defects in La0.5Ca0.5Mn0.5Fe0.5O3 structure remain. In situ XRD experiments on perovskite calcination in helium current up to 750 °C showed the formation of a similar Ca1−xMnxO phase on the perovskite surface. [ABSTRACT FROM AUTHOR]