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Non-oxidative propane dehydrogenation (PDH) is becoming an increasingly important approach to propylene production, while cobalt-containing catalysts have recently demonstrated great potential for use in this reaction, providing efficiencies comparable to those of industrially employed Pt- and Cr-based catalytic systems. It is therefore essential to clarify the nature of their active sites, especially since contradictory opinions on this issue are expressed in the literature. In this study, efforts were made to determine the state of Co in cobalt aluminates (CoAl2O4-Al2O3) responsible for PDH under typical operating conditions (600 °C, 1 atm). It is shown that the catalyst with a low cobalt content (Co/Al = 0.1) ensured the highest selectivity to propylene, ca. 95%, while maintaining significant propylene conversion. The structural motifs such as cobalt oxide and metallic cobalt nanoparticles, in addition to tetrahedral Co2+ species in the CoAl2O4 spinel system, were evaluated as potential active-site ensembles based on the obtained catalytic performance data in combination with the XRD, H2-TPR, TEM and XPS characteristics of as-synthesized, spent and spent–regenerated catalysts. It is revealed that the most likely catalytic sites linked to PDH are the Co-oxide forms tightly covering alumina or embedded in the spinel structure. However, additional in situ tuning is certainly needed, probably through the formation of surface oxygen vacancies rather than through a deeper reduction in Co0 as previously thought. [ABSTRACT FROM AUTHOR]

The reduction of Co-based oxides doped with Al3+ ions has been studied using in situ XRD and TPR techniques. Al3+-modified Co3O4 oxides with the Al mole fraction Al/(Co + Al) = 1/6; 1/7.5 were prepared via coprecipitation, with further calcination at 500 and 850 °C. Using XRD and HAADF-STEM combined with EDS element mapping, the Al3+ cations were dissolved in the Co3O4 lattice; however, the cation distribution differed and depended on the calcination temperature. Heating at 500 °C led to the formation of an inhomogeneous (Co,Al)3O4 solid solution; further treatment at 850 °C provoked the partial decomposition of mixed Co-Al oxides and the formation of particles with an Al-depleted interior and Al-enriched surface. It has been shown that the reduction of cobalt oxide by hydrogen occurs via the following transformations: (Co,Al)3O4 → (Co,Al)O → Co. Depending on the Al distribution, the course of reduction changes. In the case of the inhomogeneous (Co,Al)3O4 solid solution, Al stabilizes intermediate Co(II)-Al(III) oxides during reduction. When Al3+ ions are predominantly on the surface of the Co3O4 particles, the intermediate compound consists of Al-depleted and Al-enriched Co(II)-Al(III) oxides, which are reduced independently. Different distributions of elemental Co and Al in mixed oxides simulate different types of the interaction phase in Co3O4/γ-Al2O3-supported catalysts. These changes in the reduction properties can significantly affect the state of an active component of the Co-based catalysts. [ABSTRACT FROM AUTHOR]

In this paper, structural features of the NiO-SiO2 nanocrystalline catalyst synthesized by the sol-gel method were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and differential dissolution (DD). The XRD pattern of NiO-SiO2 significantly differs from the "ideal" NiO pattern: the peaks of the NiO-like phase are asymmetric, especially the 111 diffraction peak. The NiO-SiO2 nanocrystalline catalyst was investigated by means of XRD simulations based on two approaches: conventional Rietveld analysis and statistical models of 1D disordered crystals. Through a direct simulation of XRD profiles, structural information is extracted from both the Bragg and diffuse scattering. XRD simulations showed that the asymmetry of all the diffraction peaks is due to the presence of two NiO-like oxides with different lattice constants and different average sizes: ~90 wt% of mixed Ni-Si oxide (Ni:Si = 0.14:0.86) with average crystallite sizes (D ~ 27.5 Å) and ~10 wt% of pure NiO (D ~ 50 Å). The high asymmetry of the 111 diffraction peak is due to the appearance of diffuse scattering caused by the inclusion of tetrahedral SiO2 layers between octahedral NiO layers. Such methods as TEM and DD were applied as independent criteria to prove the structural model, and the results obtained confirm the formation of mixed Ni-Si oxide. [ABSTRACT FROM AUTHOR]

Structurally different nitrogen doped nanotubes and nanofibers (N-CNTs and N-CNFs) synthesized by a standard method of decomposing ethylene-ammonia mixtures on metal catalysts were studied. In N-CNTs the uniform distribution of nitrogen and the formation of the ordered defects were registered. The ordered defects comprise four carbon vacancies and pyridine-like nitrogen, according to the performed structural simulation. On the contrary, N-CNFs were found to have the non-uniform distribution of nitrogen; their structural defects are disordered and also contain the pyridine-like nitrogen. An increase in the nitrogen content in N-CNTs, and hence in the amount of ordered defects, leads to a monotonic decrease in conductivity. For N-CNFs the dependence of conductivity on the nitrogen content is non-monotonic and is characterized by the extremum due to the competition of electron doping and structure disordering. A similar enhancement of the electrode capacity with raising the nitrogen content both in N-CNTs and N-CNFs was observed and explained by improved hydrophilic properties of the nitrogen doped carbon nanomaterials. [ABSTRACT FROM AUTHOR]

A superstructural peak at ∼12° in X-ray diffraction patterns of nitrogen-doped carbon nanotubes compared to the undoped carbon nanotubes was observed and assigned to the formation of spatially ordered defects. The simulation of the N-CNT structure using the graphitic g-C3N4phase and turbostratic ordering made it possible to propose a new model of the spatially ordered defects in the N-CNT layer, which consist of clusters of carbon vacancies and pyridine-like nitrogen. A correlation between this type of defects and electrical conductivity of the N-CNTs is defined. [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]

The transformations of single-phase Pt/Cd 1− x Zn x S and multiphase Pt/Cd 1− x Zn x S/ZnO/Zn(OH) 2 and Pt/Cd 1− x Zn x S/Zn(OH) 2 during photocatalytic hydrogen evolution from aqueous solutions of ethanol under visible light ( λ = 450 nm) were investigated. Cyclic tests including long-term experiments were conducted for all photocatalysts. The photocatalysts were investigated before and after the photocatalytic reaction by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy techniques. Activation during photocatalytic hydrogen evolution was observed for all multiphase photocatalysts, whereas single phase Pt/Cd 1− x Zn x S was shown to exhibit a strong deactivation. The activation is likely caused by the formation of the ϵ-Zn(OH) 2 phase in a basic medium. The highest exhibited rate of hydrogen evolution on the composite photocatalyst was 3400 μmol g −1 h −1 , and stability during ten 5-hour photocatalytic runs was observed. [ABSTRACT FROM AUTHOR]

Abstracts Thermal decomposition of Mg–Al and Ni–Al layered double hydroxides LDH at temperatures lower than 800 °C leads to the formation of oxides with different structures. Mg–Al oxide has a very defective structure and consists of octahedral layers as in periclase MgO and mixed octahedral–tetrahedral layers as in spinel MgAl 2 O 4 . Mixed Ni–Al oxide has a sandwich-like structure, consisting of a core with Al-doped NiO-like structure and some surface layers with spinel NiAl 2 O 4 structure epitaxial connected with the core. Suggested models were verified by simulation of X-ray diffraction patterns using DIFFaX code, as well as HRTEM, IR-, UV-spectroscopies, and XPS. [ABSTRACT FROM AUTHOR]

Series of the oxygen-deficient strontium ferrites SrFe 1− y M y O 2.5+ x ( M =V, Mo, y <0.1; x <0.2) substituted with high-charged cations have been investigated by HRTEM and synchrotron radiation XRD. For artificial lowering of x , all the compounds were treated and quenched in vacuum from 950 °C, which led to the formation of the vacancy-ordered brownmillerite phase at local order. Depending on y , the substituted strontium ferrites have three differently disordered nano-domain states. At y ≤0.03 there are twinned lamellar 1D nano-domain structures. At 0.04≤ y ≤0.05 and 0.06≤ y ≤0.08 the intergrown 3D nano-domain structures with two different types of disorder are formed. The higher the y , the lower the domain size. Disordering phenomena of the 3D nano-domain states were examined with local structure simulations followed by the Debye calculation of XRD patterns. [ABSTRACT FROM AUTHOR]

Noble-metal-free photocatalysts CuS/Cd 0.3 Zn 0.7 S and Ni z Cd 0.3 Zn 0.7 S 1 + z were prepared by a two-step technique. The photocatalysts were characterized by a wide range of experimental techniques: X-ray diffraction, high-resolution transmission electron microscopy, low-temperature N 2 adsorption/desorption, X-ray photoelectron spectroscopy, and UV–vis spectroscopy. The photocatalytic activity was tested in a batch reactor in the hydrogen evolution from aqueous solutions of Na 2 S/Na 2 SO 3 under visible light irradiation ( λ > 420 nm). The activity of CuS/Cd 0.3 Zn 0.7 S photocatalysts was shown to exceed that of Ni z Cd 0.3 Zn 0.7 S 1+ z photocatalysts likely because of the hetero-junctions between CuS and Cd 0.3 Zn 0.7 S nanoparticles. The highest photocatalytic activity (3520 μmol g −1 h −1 ) was possessed by 1 mol% CuS/Cd 0.3 Zn 0.7 S. A model of the photocatalytic hydrogen production from aqueous solutions of Na 2 S/Na 2 SO 3 was proposed on the basis of the Langmuir–Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

In this work, new photocatalysts based on Cd1−xMnxS sulfide solid solutions were synthesized by varying the fraction of MnS (x = 0.4, 0.6, and 0.8) and the hydrothermal treatment temperature (T = 100, 120, 140, and 160 °C). The active samples were modified with Pt and NiS co-catalysts. Characterization was performed using various methods, including XRD, XPS, HR TEM, and UV-vis spectroscopy. The photocatalytic activity was tested in hydrogen evolution from aqueous solutions of Na2S/Na2SO3 and glucose under visible light (425 nm). When studying the process of hydrogen evolution using an equimolar mixture of Na2S/Na2SO3 as a sacrificial agent, the photocatalysts Cd0.5Mn0.5S/Mn(OH)2 (T = 120 °C) and Cd0.4Mn0.6S (T = 160 °C) demonstrated the highest activity among the non-modified solid solutions. The deposition of NiS co-catalyst led to a significant increase in activity. The best activity in the case of the modified samples was shown by 0.5 wt.% NiS/Cd0.5Mn0.5S (T = 120 °C) at the extraordinary level of 34.2 mmol g−1 h−1 (AQE 14.4%) for the Na2S/Na2SO3 solution and 4.6 mmol g−1 h−1 (AQE 2.9%) for the glucose solution. The nickel-containing samples possessed a high stability in solutions of both sodium sulfide/sulfite and glucose. Thus, nickel sulfide is considered an alternative to depositing precious metals, which is attractive from an economic point of view. It worth noting that the process of photocatalytic hydrogen evolution from sugar solutions by adding samples based on Cd1−xMnxS has not been studied before. [ABSTRACT FROM AUTHOR]

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]

Abstract: Genesis of the structure of zirconia particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO3)2 solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000°C has been studied by X-ray diffraction (XRD), Raman and FTIRS. As revealed by FTIRS of lattice modes, the local structure of amorphous zirconia subjected to HTT is close to that in m-ZrO2. This helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5–15nm) already after a mild calcination at 500°C. Stability of this phase with nanoparticles sizes below the critical value determined by thermodynamic constraints is due to its excessive hydroxylation demonstrated by FTIRS. Dehydroxilation and sintering of these nanoparticles at higher (600–650°C) temperatures of calcination leads to reappearance of the (111) “cubic” reflection in XRD patterns. Modeling of XRD patterns revealed that this phenomenon could be explained by polysynthetic (001) twinning earlier observed by HRTEM. [Copyright &y& Elsevier]

The title radical R⋅, synthesized by reduction of the corresponding cation R+, is thermally stable up to ~380 K in the crystalline state under anaerobic conditions. With SQUID magnetometry, single‐crystal and powder XRD, solid‐state EPR and TG‐DSC, reversible spin‐Peierls transition between diamagnetic and paramagnetic states featuring ~10 K hysteretic loop is observed for R⋅ in the temperature range ~310–325 K; ΔH=~2.03 kJ mol−1 and ΔS=~6.23 J mol−1 K−1. The transition is accompanied by mechanical movement of the crystals, i. e. by thermosalient behavior. The low‐temperature diamagnetic P‐1 polymorph of R⋅ consists of R⋅2 π‐dimers arranged in (...R⋅2...)n π‐stacks; whereas the high‐temperature paramagnetic P21/c polymorph, of uniform (...R⋅...)n π‐stacks. With the XRD geometries, CASSCF and broken‐symmetry DFT jointly suggest strong antiferromagnetic (AF) interactions within R⋅2 and weak between R⋅2 for the (...R⋅2...)n stacks; and moderate AF interactions between R⋅ for the (...R⋅...)n stacks. The fully hydrocarbon archetype of R⋅ does not reveal the aforementioned properties. Thus, the fluorinated 1,3,2‐benzodithiazolyls pave a new pathway in the design and synthesis of metal‐less magnetically‐bistable materials. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4) modified with bromine and iodine was synthesized by a novel two-stage technique that included hydrothermal pre-treatment of melamine and its calcination in a mixture with ammonium halide. Prepared photocatalysts were tested by a set of methods including X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermal gravimetric analysis (TGA), low temperature nitrogen adsorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CVA), impedance spectroscopy, and the Mott – Schottky method. All the photocatalysts were studied in the photocatalytic hydrogen production from triethanolamine (TEOA) under visible light irradiation (λ = 428 nm). The most active photocatalyst was prepared from a mixture of 50% NH 4 I and 50% melamine. Its catalytic activity (2120 μmol g−1 h−1) was 35 times higher than that of the catalyst synthesized by the simple calcination of melamine. The highest short-circuit current density of 2.7 mA/cm2 was obtained with a sample synthesized from the mixture of 80% NH 4 Br and 20% melamine. [Display omitted] • Halide-modified g-C 3 N 4 was prepared by a novel two-stage technique. • High catalytic activity was assigned to changes in S BET and electronic structure. • I-doped samples were more active in H 2 production than Br-doped ones. • The highest catalytic activity was 2120 μmol Н 2 g−1 h−1. • Br-doped samples demonstrated higher J sc than I-doped samples. [ABSTRACT FROM AUTHOR]

In the present article we report on the laser synthesis of Eu3+ doped nanophosphor with improved red color based on single-phase monoclinic Y 2 O 3 and an experimentally measured quantum yield as high as 60% at λ = 395 nm excitation. HRTEM and SEM studies evidence the formation of nanoparticles with a spherical morphology, the average diameter of ca. 20 nm, and high crystallinity. We demonstrate that such a high quantum yield can be achieved by adding oxygen during laser synthesis in a combination with post-synthesis treatments in air at T = 750 °C. The thermal annealing effects in air and vacuum in the range of 250–750 °C on the morphology, structure, optical and photoluminescence properties of as-synthesized m -Y 2 O 3 :Eu3+ have been discussed. The obtained chromaticity coordinates (0.659, 0.332), high color purity (96%) and high absolute quantum yield indicate the possibility of using red nanophosphor based on monoclinic Y 2 O 3 :Eu3+ in numerous luminescence applications. [ABSTRACT FROM AUTHOR]

In the recent decade, various potential applications of the luminescence of nanosized ZrO 2 :Eu3+ have been demonstrated. However, the particle size effect on the luminescence properties of ZrO 2 :Eu3+ still requires intensive investigation. To this end, a series of tetragonal ZrO 2 :Eu3+ nanopowders with the europium concentration of 4 wt% and particle size of 3.0 ± 0.7 to 12.0 ± 4.8 nm was synthesized by laser vaporization. It was shown that the dominant role in the optical properties of ZrO 2 :Eu3+ nanoparticles belongs to OH groups, oxygen vacancies, and Eu3+ ions. It was found that a decrease in the particle size is accompanied by a significant increase in the emission intensity in the region of ∼440 nm. Based on the results of thermal analysis, IR and UV–vis DR spectroscopies, it was concluded that this luminescence is due to the emission of adsorbed OH groups. At the same time, a decrease in the number of vacancies with a decrease in the particle size leads to a change in the absolute quantum yield QY from ∼7 to 3.5%. In addition, despite the overall decrease in the intensity of the red luminescence of Eu3+, a decrease in the particle size leads to the appearance and increase in the emission intensity of the surface Eu3+. Thus, changing the particle size from 12.0 to 3.0 nm leads to a twofold decrease in the luminescence efficiency of ZrO 2 :Eu3+ and a shift in the color of its emission from pink-red (0.36, 0.26) to blue (0.19, 0.10). The results obtained are expected to be useful for further optimization of the luminescence properties of nanosized ZrO 2 :Eu3+ in numerous applications. [ABSTRACT FROM AUTHOR]

The nanoscale Co–Mg–O oxide sample (15 wt% in terms of Co 3 O 4) was prepared from the corresponding xerogel synthesized by the modified sol-gel method. The hydrolysis of as-prepared Mg(OCH 3) 2 was carried out using the aqueous solution of Co(NO 3) 2 precursor. The CoO x nanocrystallites of about 10–20 nm in size were shown to be uniformly distributed within the MgO matrix. The reduction of Co–Mg–O in H 2 flow was found to proceed in two separate stages within the temperature ranges of 200–350 °C and 350–600 °C. The prepared binary Co–Mg–O system was demonstrated to possess completely reproducible reduction behavior in the consecutive reduction/reoxidation cycles. The phase composition of the sample exposed to both the reducing and oxidative environment was followed by an in situ X-ray diffraction analysis performed at temperatures of 25, 300, 500 and 700 °C. The determined lattice parameters for MgO (a = 4.219 Å) and Co 3 O 4 (a = 8.110 Å) were found to be slightly increased as compared with the values from Powder Diffraction File, so that the formation of joint non-stoichiometric (Mg 1-x Co x)O and (Co 3-x Mg x)O 4 phases was suggested. The strong chemical interaction of cobalt oxide with MgO matrix was also evidenced by the data of a diffuse reflectance UV–vis spectroscopy. Image 1 • The nanoscale Co–Mg–O oxide system was prepared by the modified sol-gel method. • CoO x species of 10–20 nm in size are uniformly distributed within the MgO matrix. • The prepared Co–Mg–O system possesses completely reproducible reduction behavior. • Strong interaction between Co and Mg oxides was proved by DR UV–vis spectroscopy. [ABSTRACT FROM AUTHOR]

In this study, we proposed photocatalysts based on graphite-like carbon nitride with a low content (0.01–0.5 wt.%) of noble metals (Pd, Rh) for hydrogen evolution under visible light irradiation. As precursors of rhodium and palladium, labile aqua and nitrato complexes [Rh2(H2O)8(μ-OH)2](NO3)4∙4H2O and (Et4N)2[Pd(NO3)4], respectively, were proposed. To obtain metallic particles, reduction was carried out in H2 at 400 °C. The synthesized photocatalysts were studied using X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy and high-resolution transmission electron microscopy. The activity of the photocatalysts was tested in the hydrogen evolution from aqueous and aqueous alkaline solutions of TEOA under visible light with a wavelength of 428 nm. It was shown that the activity for the 0.01–0.5% Rh/g-C3N4 series is higher than in the case of the 0.01–0.5% Pd/g-C3N4 photocatalysts. The 0.5% Rh/g-C3N4 sample showed the highest activity per gram of catalyst, equal to 3.9 mmol gcat–1 h–1, whereas the most efficient use of the metal particles was found over the 0.1% Rh/g-C3N4 photocatalyst, with the activity of 2.4 mol per gram of Rh per hour. The data obtained are of interest and can serve for further research in the field of photocatalytic hydrogen evolution using noble metals as cocatalysts. [ABSTRACT FROM AUTHOR]

Influence of composition and heterogenization to titania matrix of Pd-Zn nanoparticles has been studied in selective hydrogenation of the triple bond of 2-methyl-3-butyn-2-ol (MBY). Pd-Zn bimetallic nanoparticles with the various molar ratios Pd/Zn have been obtained by chemical reduction method. Composition- controlled sol-gel technique was employed to synthesize Pd-Zn/TiO 2 catalysts. The structure properties of the bimetallic catalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Computer modeling for XRD patterns was first used to identify the composition of Pd-Zn alloy and to determine the particle size. For the colloidal and embedded nanoparticles dependences of physicochemical and catalytic properties on composition are different being determined respectively by geometric and electronic effects. The addition of zinc with Pd/Zn ratio of 1 increased selectivity to alkene at 99% conversion from 92.9% for the Pd catalyst to 96.9% for bimetallic catalysts, which is mainly caused by alloy formation. [ABSTRACT FROM AUTHOR]

Two-component Fe Mg O oxide system was prepared via sol-gel technique. An aqueous solution of iron nitrate was used to hydrolyze the magnesium methoxide instead of distilled water. The iron loading in a final sample was 15 wt% with respect to Fe 2 O 3 . The method was shown to provide a uniform distribution of iron oxide within MgO matrix. The sample was characterized by means of a low-temperature nitrogen adsorption and scanning electron microscopy. Reduction behavior of the sample was studied in a temperature-programmed regime using hydrogen as a reducing agent. In order to follow the possible phase transformations, the sample was examined by an in situ X-ray diffraction analysis in both reductive and oxidative atmospheres within the temperature range of 25–700 °C. It was found that after the first cycle of reduction/re-oxidation, the sample stabilizes in a novel state, and hydrogen uptake profiles of further cycles of reductive/oxidative treatment become completely reproducible. According to X-ray diffraction data, the sample consists of small particles (9 nm) of Fe 3 O 4 phase well-dispersed within the structure of nanocrystalline MgO. [ABSTRACT FROM AUTHOR]

Abstract: The photocatalytic properties of a Cd0.3Zn0.7S photocatalyst modified either by NiS doping or by supporting NiS on the catalyst surface were studied. The obtained samples were investigated by different characterization techniques, including X‐ray diffraction (XRD), UV/Vis diffuse reflectance spectroscopy (DRS), high‐resolution transmission electron microscopy (HRTEM), and X‐ray photoelectron spectroscopy (XPS). The photocatalytic activity was measured in hydrogen evolution from aqueous solutions of Na2S/Na2SO3 under visible‐light irradiation (λ=450 nm). Nickel modifications on the surface and in bulk led to improvements in the photocatalytic activity compared to the pristine sample. The samples modified in bulk underwent changes in composition and an increase of the catalytic activity during illumination was measured. In contrast, the rate of hydrogen photoproduction for the photocatalysts modified by NiS on the surface did not change appreciably. The highest photocatalytic activity values were 11.2 mmol h−1 g−1 and 12.8 mmol h−1 g−1 for the 0.3 % NiS/Cd0.3Zn0.7S and Ni0.001Cd0.3Zn0.7S1.001 photocatalysts, respectively. [ABSTRACT FROM AUTHOR]

Nanosized zirconia doped with europium (ZrO 2 :xEu3+, x = 0.07–9.95 wt%) and represented by weakly agglomerated spherical particles with the size of 9.7 ± 4.3 nm was synthesized by laser vaporization in an argon atmosphere using a cw CO 2 laser. The specific surface area of the obtained nanoparticles is 92 ± 4 m2/g. The XRD study with Rietveld refinement revealed that the phase composition of the samples is represented predominantly by the tetragonal phase with a small content of monoclinic phase. At the concentrations above 4.57 wt%, stabilization of the cubic phase also occurs. The dependence of the PL intensity, PL lifetime, absolute quantum yield, and color coordinates of ZrO 2 :Eu3+ on the Eu concentration was studied. It was shown that the maximum PL intensity is observed at the concentration of 8.39 wt%. The Eu3+ lifetime decreases from 5.60 to 3.21 ms with a growth of the Eu content. Aging of the samples due to the adsorption of OH groups was revealed. The absolute quantum yield QY was measured for the 575–725 nm region corresponding to the luminescence of europium, and for the 410–725 nm region, which also includes the emission of oxygen vacancies. The QY was found to increase with the growth of Eu concentration, reaching the highest values for ZrO 2 :8.39Eu3+; it is equal to 1.6 and 17.6% for 575–725 and 410–725 nm regions, respectively. It was shown that variation of the Eu3+ concentration and excitation wavelength makes it possible to obtain color coordinates with red and close to white light. Along with the high QY for the region of 410–725 nm, this indicates that it is more promising to use ZrO 2 :Eu3+ as the white phosphor rather than the red one. [ABSTRACT FROM AUTHOR]

The paper presents the low-temperature nitrogen adsorption, TG, XRD, IR spectroscopy, XPS, TEM and SEM data for ruthenium promoted (0.2–1 wt.%) Сo-δAl 2 O 3 catalysts and characteristics of the catalysts in Fischer-Tropsch synthesis after their activation under the conditions ensuring the reduction of comparable fractions of metallic cobalt. It was shown that cobalt in oxide precursors is a component of the spinel-like Со 3-x Al x O 4 phase containing the impurity anions СО 3 2− , NO 3 − , ОН − , and NO in promoted samples, which belong to the thermolysis product of the Ru precursor. Average sizes of Со 3-x Al x O 4 crystallites are in a range of 5–10 nm. As ruthenium content in the catalyst increases upon reduction, the temperature of metallic phase formation decreases substantially (by more than 150 °C). After the reduction, selectivity of promoted catalysts for α-olefins and high-molecular hydrocarbons was higher in comparison with unpromoted catalysts, without a noticeable decrease in catalytic activity. Therewith, in 0.5–1.0 wt.% catalysts, a part of ruthenium forms individual ultradispersed metallic particles ca. 1 nm in size that are located on the surface of oxide support and are not active in Fischer-Tropsch synthesis. The oxide layer decorating the surface of metallic cobalt particles is also strongly enriched with ruthenium. In the 0.2 wt.% catalyst, the major part of ruthenium resides in metallic cobalt particles. Although the ruthenium-cobalt alloy segregates with enrichment of the surface with cobalt, the presence of ruthenium in the metallic particles and probably in the decorating oxide layer exerts a considerable effect on selectivity of the catalysts. [ABSTRACT FROM AUTHOR]

ABSTRACT Data on new modifications of supported titanium-magnesium catalysts (TMCs) with improved performance in ethylene polymerization are reported. These catalysts possess a high and stable activity, an enhanced ability to regulate molecular weight of the polymer by hydrogen, a controllable particle size at a narrow particle size distribution, and the ability to produce the polymer with an increased bulk density. Various physicochemical methods were used to obtain data on the chemical composition of novel supports and catalysts, their phase composition and crystal structure as well as the pore structure. The results obtained were used to discuss possible correlations between composition and structure of TMCs and their catalytic properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2545-2558 [ABSTRACT FROM AUTHOR]

Nanostructured powders xFe/nano-Al2O3 with the Fe loading of x = 0.0 – 5.0 wt% were obtained using laser vaporization by CO2 laser. XRF, XRD, HRTEM, PL and UV–Vis DRS techniques were employed to investigate physicochemical, structural and optical properties of the synthesized nanopowders with the average particle size of 9 nm. Nanopowders xFe/nano-Al2O3 as model catalysts were tested in isobutane dehydrogenation reaction. The results obtained were compared with similar data for the xFe/γPb-Al2O3 systems synthesized by the conventional sol–gel method. According to XRD and UV–Vis DRS data, in the series of xFe/nano-Al2O3 samples a great part of Fe3+ ions is in the disordered environment of subsurface layers of Al2O3 nanocrystallites, predominantly in the tetrahedral coordination. In distinction to samples of the xFe/γPb-Al2O3 series, in the case of nanostructured xFe/nano-Al2O3 powders the formation of Fe2O3 phase does not occur at any concentrations of iron or conditions of testing. The analysis of the PL spectra of xFe/nano-Al2O3 powders also showed the presence of surface sites of Fe3+ ions, which were not detected for xFe/γPb-Al2O3. Catalytic testing of the xFe/nano-Al2O3 series samples in isobutane dehydrogenation revealed the formation of the iron active sites that ensure catalytic activity of the samples. Differences in the catalytic properties of FeOx/Al2O3 samples obtained by the sol–gel method and laser vaporization are related to different states of Fe3+ ions. Thus, the xFe/nano-Al2O3 nanopowders, in contrast to xFe/γPb-Al2O3, contain a large amount of active Fe3+ sites. These sites, being involved in the dehydrogenation reaction, are present predominantly on the surface of the nanopowders. [ABSTRACT FROM AUTHOR]

Multiphase photocatalysts Pt/Cd 1− x Zn x S/ZnO/Zn(OH) 2 , Pt/Cd 1− x Zn x S/ZnO, and Pt/Cd 1− x Zn x S/Zn(OH) 2 were synthesized by a new two-step technique. The photocatalysts were characterized by a wide range of experimental techniques: X-ray diffraction, high-resolution transmission electron microscopy combined with energy-dispersive X-ray spectroscopy, low-temperature N 2 adsorption/desorption, and UV/VIS spectroscopy. The photocatalytic activity was tested in a batch reactor in the reaction of H 2 evolution from aqueous solutions of ethanol under visible light irradiation ( λ > 420 nm). The highest achieved photocatalytic activity was 2256 μmol H 2 per gram of photocatalyst per hour; the highest quantum efficiency was 10.4%. The activity of Pt/Cd 1− x Zn x S/Zn(OH) 2 was higher than that of Pt/Cd 1− x Zn x S/ZnO/Zn(OH) 2 and Pt/Cd 1− x Zn x S/ZnO. The explanation of enhanced activity of zinc–cadmium sulfide/ε-zinc hydroxide based on quantum calculations was suggested. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • Al 2 O 3 NPs with the particle size from 2 to 21 nm were synthesized by CO 2 laser vaporization. • The structure, morphology, thermal, and optical properties of Al 2 O 3 NPs were studied. • Photoluminescence is determined by 3d elements, surface hydroxyl groups, and F-type centers. • The size effect for Al 2 O 3 NPs has a boundary corresponding to 6–7 nm. A series of Al 2 O 3 nanoparticles with the sizes ranging from ~ 2 to 21 nm, according to XRD, HRTEM and BET, was obtained by vaporization of α-Al 2 O 3 in flowing helium and argon at different pressures under the action of a cw CO 2 laser. The particle size was changed by varying the composition of ambient gas (He, Ar) and its pressure in a vaporization chamber from 0.034 to 0.9 bar. The effect of the synthesis conditions on the properties of Al 2 O 3 nanopowders is presented and discussed. Particles with the size smaller than 6–7 nm have a faceted shape, whereas the shape of larger particles is close to spherical. It was found that the resulting nanopowders consist of a mixture of transition aluminas, among which the γ -polymorph is dominant. Thermal analysis showed that for smaller nanoparticles the phase transition to α-Al 2 O 3 occurs at a lower temperature. In nominally pure Al 2 O 3 nanoparticles with different sizes, photoluminescence at RT and 80 K is determined by trace level concentrations (≤10–3 wt%) of uncontrolled impurities of 3d elements (Cr3+(O h) and Fe3+(T d)), surface hydroxyl groups, and point defects represented mostly by F-type centers. The acquired experimental data indicate that manifestation of the size effect for Al 2 O 3 nanoparticles has a boundary corresponding to 6–7 nm. Al 2 O 3 nanoparticles with the dominant γ-Al 2 O 3 structure obtained by the laser method can be promising in many chemical reactions, particularly as the supports of catalysts and sorbents, for which the high specific surface area is of special importance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcium aluminate aerogels with mayenite stoichiometry were prepared. • The surface area of amorphous aerogel obtained was as high as 330 m2/g. • Aerogel calcined at 500 °C mostly consisted of 10–20 nm amorphous platelets. • Mayenite phase was observed after drying if excess water was used for hydrolysis. • Diphenyloxyl nitroxide radicals were formed on the aerogels calcined at 500 °C. Calcium aluminate aerogels with mayenite stoichiometry C12A7 were prepared for the first time. The surface area of amorphous aerogel obtained after hydrolysis with stoichiometric amount of water was about 330 m2/g after the supercritical drying and 170 m2/g after calcination at 500 °C. The latter sample mostly consisted of 10–20 nm amorphous platelets. The mayenite phase was observed after the supercritical drying only if overstoichiometric amount of water was used for hydrolysis. Diphenyloxyl nitroxyl radicals were observed on the surface of calcined C12A7 aerogels after diphenylamine adsorption. Their formation on the surface of the samples calcined at 500 °C suggests that mayenite cages capable of stabilizing active forms of oxygen are present on the surface of the amorphous aerogels. [ABSTRACT FROM AUTHOR]

Surface SiO 2 coating strategy was used to enhance the photoluminescent properties of Eu3+ doped nanophosphor based on monoclinic Y 2 O 3. Laser-synthesized m -Y 2 O 3 :Eu3+ spherical nanoparticles with high crystallinity and diameter of ca. 18 nm were used as a core for the preparation of m -Y 2 O 3 :Eu3+@SiO 2 core-shell structures. According to HRTEM and HAADF-STEM data, a thin SiO 2 shell uniformly encapsulated the crystal core with a thickness of about 1.5 nm. The SiO 2 shell increases the absolute photoluminescence quantum yield of Eu3+ at λ = 395 nm excitation from 14 % to 68 %. To the best of our knowledge, the obtained quantum yield exceeds the known values for Eu3+ doped oxide-based nanophosphors and is comparable to those of some other commercial red microphosphors. The SiO 2 coating was shown to reduce the luminescence quenching effect associated with the annealing-induced migration of Eu3+ from the bulk to the surface of nanoparticles. The obtained results demonstrate that m -Y 2 O 3 :Eu3+@SiO 2 core-shell nanoparticles with intense red luminescence have significant potential for use in LEDs, high resolution displays, bioimaging technologies and in other solid-state lighting applications. [Display omitted] • SiO 2 coating strategy has been used to enhance the PLQY of m -Y 2 O 3 :Eu3+ nanophosphor. • The m -Y 2 O 3 :Eu3+ core with diameter of ca. 18 nm was prepared by laser synthesis. • The SiO 2 shell increases the PLQY of m -Y 2 O 3 :Eu3+ at λ ex = 395 nm from 14 % to 68 %. • Coating reduced the PL quenching associated with annealing-induced migration of Eu3+. [ABSTRACT FROM AUTHOR]

A new multiphase photocatalyst – 1%Pt/Cd 0.6 Zn 0.4 S/Cd 0.1 Zn 0.9 S – was synthesized by a simple hydrothermal treatment of as-prepared Cd 0.3 Zn 0.7 S solid solution and thoroughly characterized by different methods. The activity was tested in a sustainable process of hydrogen evolution from aqueous solutions of two saccharides (glucose and xylose) under visible light. The mechanism of the photocatalytic hydrogen evolution from complex organic substrates is still controversial. In this research it was shown that optimizing the experimental conditions (pH, substrate concentration) leads to a significant increase in the photocatalytic activity for both saccharides. A kinetic equation based on a Langmuir model and including the degree of dissociation of the substrate was proposed and verified for the first time. The highest activities during hydrogen evolution for glucose and xylose were achieved in strongly alkaline media. The photocatalyst 1%Pt/CdZnS120 possessed an activity equal to 3.4 mmol H 2 h−1 g−1 (glucose, apparent quantum efficiency 8.4%), that exceeds recently reported values. Image 1 • New photocatalyst 1%Pt/Cd 0.6 Zn 0.4 S/Cd 0.1 Zn 0.9 S was synthesized and characterized. • Activity was tested in H 2 evolution from solutions of glucose and xylose (450 nm). • The highest activity for glucose solution was 3.4 mmol H 2 h-1 g-1 with AQE = 8.4%. • High stability of the proposed photocatalyst at a high pH (5 M NaOH) was confirmed. • Kinetic equation based on a Langmuir model was proposed for both saccharides. [ABSTRACT FROM AUTHOR]

Two types of nickel-modified Cd1−xZnxS-based photocatalysts, CdxZn1−xNiySy+1 (mol% Ni = 0.05–0.5; x = 0.8) and yNiS/CdxZn1−xS (mol% Ni = 0.1–1.0; x = 0.8), were prepared via a simple two-stage technique. The samples were characterized by XRD, UV–vis spectroscopy, and XPS techniques. The activity of the synthesized photocatalysts were tested in the gas-phase photocatalytic reduction of CO2 under visible light (λ = 450 nm). It has been shown that both CdxZn1−xNiySy+1 and yNiS/CdxZn1−xS samples with ultra-low content of nickel sulfide have improved activity in the carbon dioxide reduction in comparison to bare CdxZn1−xS solid solutions. Also, it has been demonstrated that the addition of the reducing agent—hydrogen—into the system does not lead to a positive effect: the rate of CO2 reduction either remains unchanged or decreases. [ABSTRACT FROM AUTHOR]

Novel composite photocatalysts consisting of a cadmium and zinc sulfide solid solution (Cd 0.6 Zn 0.4 S) and zinc sulfide (ZnS) nanoparticles were successfully prepared by a simple hydrothermal treatment of suspended Cd 0.3 Zn 0.7 S at 120 °C. The as-obtained materials were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and UV-VIS diffuse reflection spectroscopy. The obtained photocatalysts were tested in the photocatalytic evolution of hydrogen from a Na 2 S/Na 2 SO 3 aqueous solution under visible light irradiation (λ = 450 nm). It is shown that the hydrothermal treatment of Cd 0.3 Zn 0.7 S at 120 °C increases the activity by a factor of 7.5 due to the phase transformations of the solid solution with the formation of the multiphase Cd 0.6 Zn 0.4 S/ZnS sample. The deposition of gold on the surface of Cd 0.6 Zn 0.4 S/ZnS leads to a further increase in activity: the achieved photocatalytic activity and quantum efficiency (450 nm) for 1%Au/Cd 0.6 Zn 0.4 S/ZnS are 17.4 mmol g−1 h−1 and 42.6%, respectively. This excellent performance is found to be attributable to the transformation of Cd 1-x Zn x S from the cubic to the hexagonal phase during the hydrothermal treatment. Additionally, photoelectrodes based on Cd 0.6 Zn 0.4 S/ZnS and FTO were synthesized and tested in a two-electrode cell. A high value of the photocurrent equal to 0.5 mA/cm2 is achieved for the Cd 0.6 Zn 0.4 S/ZnS/FTO electrode. An investigation by means of impedance spectroscopy reveals the longer lifetime of photogenerated charge carriers in the Cd 0.6 Zn 0.4 S/ZnS/FTO photoelectrode if to compare with Cd 0.3 Zn 0.7 S/FTO system. Image 1 • Au/Cd 0.6 Zn 0.4 S/ZnS photocatalysts were prepared via simple hydrothermal synthesis. • The highest value of the photocatalytic activity was 17.4 mmol H 2 per hour per gram. • The highest apparent quantum efficiency was 42.6% (450 nm). • Photocurrent 0.5 mA/cm2 was achieved for the Cd 0.6 Zn 0.4 S/ZnS/FTO electrode. [ABSTRACT FROM AUTHOR]

[Display omitted] The optimal conditions for the synthesis of platinized graphitic carbon nitride (Pt/g-C 3 N 4) have been found. It was investigated as a catalyst for the production of hydrogen from aqueous solutions of triethanolamine (TEOA) under irradiation with visible light. The highest photocatalytic activity of 450 μmol h−1 g−1 and an apparent quantum efficiency of 1.1% were demonstrated by the 1% Pt/g-C 3 N 4 sample prepared from melamine by calcining at 600 °C for 2 h. [ABSTRACT FROM AUTHOR]

Novel photocatalysts for CO2 reduction, which consist of a cadmium and zinc sulfide solid solution (Cd1−xZnxS), were successfully prepared by a simple two-step technique. The photocatalysts were characterized by X-ray diffraction, UV-VIS diffuse reflectance spectroscopy, and low-temperature N2 adsorption techniques and were tested in the gas-phase photocatalytic reduction of CO2 under visible light (λ = 450 nm). All the synthesized Cd1−xZnxS solid solutions were capable of enabling the chemical transformations of CO2 under the conditions considered. Carbon monoxide was the major product during the CO2 reduction over Cd1−xZnxS (x = 0–0.87). Methane and hydrogen were also detected in the gas phase in low amounts. The activity of the prepared samples and the distribution of the reduction products strongly depended on the actual cadmium to zinc ratio. The Cd0.94Zn0.06S photocatalyst showed the highest activity, 2.9 μmol CO per gram per hour, and selectivity, 95%, during CO2 reduction under visible light in the presence of water vapor. The achieved values are very high for the sulfide-based photocatalysts. [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]

Novel eco-friendly method for preparation of mesoporous alumina from the product of rapid thermal treatment of gibbsite (CTA product) without “reprecipitation” stage is described. Compared with the nitrate-ammonia technology of “reprecipitation” of gibbsite to boehmite and its further calcination to γ-Al 2 O 3 , the new method consumed less amount of HNO 3 per 1 kg of Al 2 O 3 (by 30 times), while the amount of effluents is twice lower. Effluents do not contain ammonium nitrate, since the preparation of boehmite does not include ammonia. It is shown that the method makes it possible to obtain boehmite with needle-shaped particle morphology. The particle size of boehmite and the textural characteristics of alumina are easily adjusted over a wide range by changing the temperature, aging time or peptizing agent. Thus, the pore volume of alumina may be 0.45–0.95 cm 3 /g with an average pore diameter of 81–256 Å and S BET  = 140–240 m 2 /g. [ABSTRACT FROM AUTHOR]

The process of mechanical alloying in the 33Al-45Cu-22Fe (at.%) powder mixture subjected to high-energy ball milling was studied. Due to complexity of the alloy formation in this system, several methods – X-ray diffraction phase analysis, Differential Dissolution, thermal analysis and Transmission and Scanning Electron Microscopy – were combined to obtain the detailed information on the structure and composition of the mechanical alloying products. Possible formation mechanisms of these phases during mechanical alloying are discussed. No crystalline phase containing Fe and Cu, Al has been found in the products of mechanical alloying of the 33Al-45Cu-22Fe mixture. The formation of Cu-Al phases followed the sequence of Al 2 Cu → Al 4 Cu 9 → Cu(Al) solid solution. When only those phases that were detected by the XRD analysis were taken into account, the mass balance of Al and Fe in the products of mechanical alloying was not satisfied. The Differential Dissolution and high-resolution Transmission Electron Microscopy data suggest the formation of non-stoichiometric X-ray amorphous phases containing all three elements. Reasons for the retardation of the solid-state interaction between aluminum and copper in the ternary powder mixture are discussed. [ABSTRACT FROM AUTHOR]

The promotion of the photocatalytic activity of the Cd 0.3 Zn 0.7 S nanoparticles via deposition of some copper species, such as Cu x S and Cu 0 , as a co-catalyst, in the hydrogen production under visible light irradiation from aqueous solutions of a sacrificial Na 2 S/Na 2 SO 3 system was studied. The state of the samples was characterized with a wide range of physical methods both in the initial state as well as after their photocatalytic operation. An evolution of both photocatalytic activity and the state of the photocatalyst particles was registered by a set of the physical methods. The highest apparent quantum efficiency and photocatalytic activity which were achieved at illumination by light with λ = 450 nm over the 0.1 wt% Cu x S/Cd 0.3 Zn 0.7 S sample for the photocatalytic hydrogen evolution from Na 2 S/Na 2 SO 3 aqueous solutions were 23.1% and 6.4 mmol g −1 h −1 , respectively. It was shown that the deposited Cu species undergo the transformation to Cu x S during the photocatalytic production of hydrogen, and these are the copper sulfide nanoparticles that increase the activity of the Cd 1-x Zn x S solid solutions. This statement agrees well with the principle of a constancy of the state of heterogeneous catalysts under their operation in the same reaction media established by G.K. Boreskov in the 1950s. [ABSTRACT FROM AUTHOR]

A set of novel CoMoNi hydrotreating catalysts supported on sepiolite-like mineral and modified by H3PO4 have been prepared and studied in hydrodesulfurization (HDS) and hydrodemetallization (HDM) of heavy Tatar oil with extremely high viscosity and sulfur content. Catalysts had a multiphase composition, represented by calcium/magnesium oxides, silicates, or phosphates, and were found to be of great interest for studying the role of support surface properties in heavy oil hydrotreating. For monitoring the catalyst properties, all the samples have been investigated by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XFS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), CO- and CDCl3-Fourier transform infrared (FTIR), mercury porosimetry, and N2 adsorption methods. The catalyst with a small phosphate content showed higher initial HDS conversion due to the more developed specific surface area, increased Lewis acidity, and better active component distribution; however, the sulfur removal substantially reduced during 240 h on stream. The sample with a high amount of phosphates demonstrated better stability, higher HDM, and hydrocracking/hydroisomerization activity despite lower acidity and poor active phase dispersion that may be accounted for by the higher fraction of macropores. [ABSTRACT FROM AUTHOR]

A pair of mesoporous and hierarchical macro/mesoporous alumina-supported catalysts having distinct textural parameters have been chosen to elucidate the effect of texture on activity in hydrodesulfurization (HDS) and hydrodemetallization (HDM) of heavy tatar oil possessing extremely high viscosity and sulfur content. For monitoring catalyst properties, the samples have been investigated by XRD, XFS, XPS, EXAFS, SEM, TEM, FTIR, TPD-NH3, mercury porosimetry, and N2 adsorption methods. Among different factors such as support acidity, active component dispersion, and texture, the last one has been found to play the most significant role in this process. The hierarchical macro/mesoporous catalyst shows lower coking rate of the hydrotreated products, as well as higher HDS and HDM conversions despite its lower active component dispersion and decreased support acidity. [ABSTRACT FROM AUTHOR]

The presence of nitric oxide NO in the gas phase was shown to decrease the decomposition rate of the hydrotalcite-like Co–Al LDH phase in the catalysts prepared by co-precipitation or deposition on Al 2 O 3 under the condition of urea hydrolysis. The decrease in LDH decomposition rate is related to the formation of a more crystallized phase of the spinel-like Co–Al oxide due to the ability of nitric oxide to transfer oxygen in consecutive reactions of the oxidation to NO 2 and reduction to NO. The difference in the coherent scattering domain size of the catalyst samples precalcined in the presence of NO or in a pure inert gas is retained at all consecutive steps of the reductive heat treatment in hydrogen: after the formation of a cubic phase of the (Co, Al)O oxide and its reduction to metallic cobalt. The observed changes in the degree of crystallinity and dispersion of the active metal exert only a slight effect or even no effect on the activity of the catalysts in Fischer–Tropsch synthesis. Noteworthy are a lower selectivity for methane and a greater fraction of olefins in the products obtained on the catalysts precalcined in a flow of inert gas containing 3% NO. [ABSTRACT FROM AUTHOR]

Multiphase photocatalysts Cd1-xZnxS/TiO2 were synthesized through the deposition of solid solutions of cadmium and zinc sulfides on the surface of titania samples with different porous structures, including a 3D-ordered meso/macroporous structure. The photocatalysts were characterized by a wide range of experimental techniques: X-ray diffraction, high-resolution transmission electron microscopy combined with energy-dispersive X-ray spectroscopy, N2 adsorption at 77 K, X-ray photoelectron spectroscopy, and UV/VIS spectroscopy. The photocatalytic activity was tested in a batch reactor for the H2 evolution reaction from aqueous solutions of Na2S/Na2SO3 under visible-light irradiation (λ=450 nm). The highest achieved photocatalytic activity was 1.8 mmol H2 per gram of photocatalyst per hour. The regular porous structure of titania was demonstrated to enhance the photocatalytic activity and stability of Cd0.4Zn0.6S/TiO2 samples. [ABSTRACT FROM AUTHOR]

A carbon nanoreactor concept was applied to study the stabilization effect of carbon shell on phase composition and morphology of dodecacalcium hepta-aluminate Ca 12 Al 14 O 33 . The starting C12A7 powder was obtained using aluminum and calcium hydroxides as precursors. Carbon shell was formed by a chemical vapor deposition of divinyl at 550 °C. After the calcination at 1400 °C, the product was characterized by X-ray diffraction analysis (XRD) and high resolution transmission electron microscopy (HRTEM). It was observed for a first time that spontaneous formation of calcium aluminate whiskers take place under the conditions described. Each whisker consists of a ‘head’ (globular particle of 0.5 microns in diameter) and a ‘tail’ (prolonged whisker of few microns in length and 0.1–0.2 microns in diameter). According to HRTEM, the ‘head’ is characterized with microcrystal lattice of Ca 12 Al 14 O 33 compound. XRD data show the presence of CaAl 2 O 4 phase traces. The ‘head’ and ‘tail’ of the whisker are covered with structured graphene layers of 10 nm and 3 nm, correspondingly. [ABSTRACT FROM AUTHOR]

Basic stages of porous cermets preparation from MeAl (Me = Cr, Cu, Co, Fe) powders are elaborated including mechanical activation of Me–Al blends, soft hydrothermal treatment of mechanically alloyed blends followed by thermal treatment thus allowing to control their mechanical, thermophysical and textural properties. Ceramometal monoliths with metallic particles (up to 80 wt.%) randomly distributed in the oxide matrix are characterized by the hierarchical pore structure with developed ultramacropores which provides their high permeability. Mesoporosity of ceramometal monoliths was developed by incorporation of mesoporous components into their structure. Monolithic catalysts based on these cermet substrates were shown to be promising for different fields of application in catalysis. [ABSTRACT FROM AUTHOR]

We report the phase and microstructure evolution of the Cu–13 wt.% Al mixture during treatment in a high-energy planetary ball mill with a particular focus on the early stages of mechanical alloying. Several characterization techniques, including X-ray diffraction phase analysis, nuclear magnetic resonance spectroscopy, differential dissolution, thermal analysis, and electron microscopy/elemental analysis, have been combined to study the evolution of the phase composition of the mechanically alloyed powders and describe the microstructure of the multi-phase products of mechanical alloying at different length scales. The following reaction sequence has been confirmed: Cu + Al → CuAl 2 (+Сu) → Cu 9 Al 4 + (Cu) → Cu(Al). The phase evolution was accompanied by the microstructure changes, the layered structure of the powder agglomerates disappearing with milling time. This scheme is further complicated by the processes of copper oxidation, reduction of copper oxides by metallic aluminum, and by variation of the stoichiometry of Cu(Al) solid solutions with milling time. Substantial amounts of X-ray amorphous phases were detected as well. Differential dissolution technique has revealed that a high content of aluminum in the Cu(Al) solid solution-based powders is due to the presence of Al-rich phases distributed between the Cu(Al) crystallites. [ABSTRACT FROM AUTHOR]

Two types of photocatalysts, 1%Pt/Cd1−xZnxS/g-C3N4 (x = 0.2–0.3) and Cd1−xZnxS/1%Pt/g-C3N4 (x = 0.2–0.3), were synthesized by varying the deposition order of platinum, and a solid solution of cadmium and zinc sulfides onto the surface of g-C3N4. The characterization of photocatalysts showed that, for 1%Pt/Cd1−xZnxS/g-C3N4, small platinum particles were deposited onto a solid solution of cadmium and zinc sulfides; in the case of Cd1−xZnxS/1%Pt/g-C3N4, enlarged platinum clusters were located on the surface of graphitic carbon nitride. Based on the structure of the photocatalysts, we assumed that, in the first case, type II heterojunctions and, in the latter case, S-scheme heterojunctions were realized. The activity of the synthesized samples was tested in hydrogen evolution from triethanolamine (TEOA) basic solution under visible light (λ = 450 nm). A remarkable increase in hydrogen evolution rate compared to single-phase platinized 1%Pt/Cd1−xZnxS photocatalysts was observed only in the case of ternary photocatalysts with platinum located on the g-C3N4 surface, Cd1−xZnxS/1%Pt/g-C3N4. Thus, we proved using kinetic experiments and characterization techniques that, for composite photocatalysts based on Cd1−xZnxS and g-C3N4, the formation of the S-scheme mechanism is more favorable than that for type II heterojunction. The highest activity, 2.5 mmol H2 g−1 h−1, with an apparent quantum efficiency equal to 6.0% at a wavelength of 450 nm was achieved by sample 20% Cd0.8Zn0.2S/1% Pt/g-C3N4. [ABSTRACT FROM AUTHOR]

A series of Eu doped ZrO 2 micropowders with different concentration of Eu (0.04–6.85 wt%) was obtained by incipient wetness impregnation followed by annealing at 1200 °C. X-ray diffraction analysis revealed that the phase composition of samples with the minimum Eu concentrations in the series is represented predominantly by the monoclinic phase. An increase in the Eu content leads to proportional stabilization of the tetragonal phase, and at concentrations above 2.00 wt% the cubic ZrO 2 phase is also stabilized. It was shown that red luminescence of the samples is responsible for the radiation transitions 5D 0 → 7F J (J = 0–4) in Eu3+ ions. It was shown that shaping the photoluminescence spectrum of monoclinic ZrO 2 :Eu3+ phosphor depending on Eu concentration is related to the stabilization of ZrO 2 tetragonal and cubic structure by Eu3+. The local symmetry of Eu3+ in each of the detected phases was identified. The lifetime of Eu3+ in the monoclinic phase of ZrO 2 does not depend on the dopant concentration and is in the range of 0.73–0.81 ms, whereas in the tetragonal phase it first increases from 1.7 to 1.85 ms and then reaches a maximum at a concentration of 2.00 wt%. The absolute quantum yield increases from 1.6 to 4.8% over the entire range of Eu concentration. • ZrO 2 :Eu3+ (0.04–6.85 wt%) powders with red emission was achieved. • The local symmetry of Eu3+ in ZrO 2 polymorphs was identified. • Eu content leads to stabilization of the tetragonal and cubic ZrO 2 phase. • Shaping the PL spectrum of ZrO 2 :Eu3+ via polymorphism of the lattice was observed. • QY increases from 1.6 to 4.8% over the entire range of Eu content. [ABSTRACT FROM AUTHOR]