Anionic composition of precursors of the Co/Al2O3 catalysts for the Fischer-Tropsch synthesis

Cobalt and aluminum hydroxo compounds with the hydrotalcite-type structure containing nitrate, carbonate, and hydroxyl groups are formed due to the deposition by precipitation of cobalt cations from a nitrate solution on ??- and ??-Al₂O₃ under the conditions of urea hydrolysis. The influence of the method of preparation on the anionic composition of the hydroxo compounds (precursors of the Co-Al catalyst) was studied. A correlation between the anionic composition of the precursor compound and the catalytic properties of the catalysts in the Fischer-Tropsch synthesis was established.     

Iridium–nickel composite oxide catalysts for oxygen evolution reaction in acidic water electrolysis

A series of Ir_1–xNi_xO_2–y (0 ≤ x ≤ 0.5) composite oxides have been prepared by a simple pyrolysis method in ethanol system and used as the electrocatalysts for OER in acidic medium. The materials have been characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). The electrochemical performances of these Ir_1–xNi_xO_2–y composite catalysts are evaluated by cyclic voltammetry (CV) and steady-state measurements. The resulting oxides with the Ni content (x) less than 0.3 have a complex nature of metal Ir and rutile structure IrO₂ which is similar to the Ir oxide prepared by the same approach and possess the contracted lattice resulted from the Ni-doping. Although the addition of Ni reduces the electroactive surface areas due to the coalescence of particles, the catalytic activity of the Ir_1–xNi_xO_2–y (0 < x ≤ 0.3) catalysts is slightly higher than that of the pyrolyzed Ir oxide. Regardless of the surface area difference, the intrinsic activity first increases and then decreases with the Ni content in Ir_1–xNi_xO_2–y catalysts, and the intrinsic activity of Ir_0.7Ni_0.3O_2–y catalyst is about 1.4 times of the Ni-free Ir oxide mainly attributed to the enhancement of conductivity and a change of the binding energy as increasing amount of the incorporated Ni with respect to the pure IrO₂. The Ir_0.7Ni_0.3O_2–y catalyst shows a prospect of iridium-nickel oxide materials in reducing the demand of the expensive Ir oxide catalyst for OER in acidic water electrolysis.     

New catalysts of dry reforming of methane into synthesis gas

New catalysts have been developed for the production of synthesis gas via a resource-saving and environmentally friendly process—dry reforming of methane. The catalysts are fabricated from NdCaCo_1–xNi _x On precursors (x = 0, 0.2, 0.4, 0.6, 0.8, 1) synthesized by a ceramic method. According to X-ray powder diffraction, when reacting with an equimolar CH₄/CO₂ mixture at 800–900°С, the precursors are converted into a mixture of neodymium and calcium oxides and cobalt and nickel metals. The catalyst based on NdCaNiO _n at 850°С has ensured high conversions of methane (91%) and CO₂ (86%) at СО and hydrogen yields of 88 and 78%, respectively. At 940°С, the yield of CO is close to the quantitative one (97%).     

Study of the factors affecting the formation of copper–chromium/aluminum oxide compounds with a spinel structure

The effect of the Cr³⁺/Al³⁺ ratio on the crystallization temperature of mixed oxide compounds with a spinel structure and their structural features and morphological characteristics have been studied using a combination of physicochemical methods: thermal analysis, IR spectroscopy, X-ray powder diffraction, and electron microscopy. The role of temperature of synthesis and drying of Cu–Cr/Al hydroxy precursors in the formation of copper-containing spinels CuCr _x Al_2–x O₄, where x = 0–2, has been elucidated. The results are of interest for selection of the optimal composition and conditions of synthesis and formation of copper-containing spinels for their practical use.     

Highly efficient mesoporous WO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/KIT-6 catalysts for oxidative desulfurization of dibenzothiophene with hydrogen peroxide

Oxidative desulfurization (ODS) of organic compounds containing sulfur element from a model oil was performed using tungsten oxide catalysts supported on mesoporous silica with cubic Ia3d mesostructure, well-defined mesopores (7.2 nm), high surface area (719 m²/g), and three-dimensional pore network (WO _x /KIT-6). The prepared WO _x /KIT-6 catalysts (5–20 wt% WO _x ) were characterized by X-ray diffraction analysis, N₂ sorption measurements, electron microscopy, H₂-temperature programmed reduction, Raman spectroscopy, and thermogravimetric analysis. Among the mesoporous catalysts, 10 wt% WO _x /KIT-6 exhibited the best catalytic performance. Sulfur-containing organic compounds, such as dibenzothiophene, 4,6-dimethyldibenzothiophene, and benzothiophene, were completely (100 %) removed from the model oil over 10 wt% WO _x /KIT-6 catalyst in 2 h. In addition, the catalyst could be reused several times with only slight decrease in catalytic activity.     

Preparation of Pt-MO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> systems via oxidation of alloys

Supported platinum systems Pt-MO _x (M = Mo or Ce) were prepared by oxidizing Pt-Mo or Pt-Ce alloys of various compositions. The phase composition and crystal structure of samples before and after oxidative treatment were characterized by powder X-ray diffraction (XRD). Morphology was studied using scanning electron microscopy (SEM). The oxidation of Pt-Mo alloys or Pt-Ce intermetallic compounds yields Pt-MO _x systems in which nanosized platinum particles are homogeneously supported on metal oxide. This method can be used to synthesize Pt-MO _x systems with other transition or rare-earth elements and with various component concentrations.     

Preparation of mesoporous Ce<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> mixed oxides and their catalytic properties in methane combustion

Mesoporous Ce_{1 ? x} Fe _x O₂ mixed oxide catalysts of different molar ratios (x = 0.1–0.5) were prepared by the citric acid sol-gel method and the microwave technique. The activities of Ce_{1 ? x} Fe _x O₂ mixed oxides on methane combustion were investigated, and the structure and reductive properties were characterized by XRD, BET, DRS, and TPR. The data showed that Ce_{1 ? x} Fe _x O₂ mixed oxides prepared were mesoporous material. When x ≤ 0.2, the transition metal Fe incorporated into the lattice of CeO₂ to form cubic Ce_{1 ? x} Fe _x O₂ solid solutions, and mixed phases of cubic Ce_{1 ? x} Fe _x O₂ solid solutions and α-Fe₂O₃ existed when x > 0.2. Ce_{1 ? x} Fe _x O₂ solid solutions show higher activity for methane combustion than pure CeO₂, especially for Ce_0.9Fe_0.1O₂.     

Preparation,structure, and charge transport characteristics of BIFEVOX ultrafine powders

Existence boundaries, structure, and transport parameters of ultrafine powders were studied in Bi₄V_{2 ? x} Fe _x O_{11 ? x} (BIFEVOX) solid solutions. The details of synthesis of the solid solutions via liquid precursors are analyzed comparatively. In general, BIFEVOX formation via liquid precursors is similar to phase formation in solid-phase synthesis. With low iron levels (x = 0.05–0.1), solid solutions are formed in the monoclinic α phase (space group C2/m) The compositions with x = 0.125 and 0.15 are mixtures of α- and β phases. In the range 0.2 < x < 0.7, the Bi₄V_{2 ? x} Fe _x O_{11 ? x} solid solution has the structure of the γ phase of Bi₄V₂O₁₁ (space group I4/mmm). The β phase in the system in question has a very narrow existence range in the vicinity of x = 0.175. The average particle sizes of the powders prepared by various methods are within 0.5–3 μm. In the powders prepared via liquid precursors, however, the distribution peak shifts toward smaller sizes, to 0.3–1 μm. Mechanical activation conserves the structure of the γ phase of BIFEVOX, and unit cell parameters change only insignificantly; however, the crystal lattice is slightly distorted. The electrical conductivity of BIFEVOX was studied as a function of temperature, preparation technology, and composition using impedance spectroscopy. Equivalent circuits of cells were analyzed. The conductivity of samples prepared by solution technology is always higher than for samples prepared by the solid-phase process. Features of electrical conductivity versus temperature for various phases are noted. All transitions on the conductivity curves match the features of linear thermal expansion curves. Compositions with doping levels x= 0.1–0.3 have the highest total conductivities.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and LiCoO<Subscript>2</Subscript> composite cathode materials obtained by mechanical activation

New composite cathode materials xLiMn₂O₄/(1 ? x) LiCoO₂(x = 0.7, 0.6, 0.5 и 0.4) were obtained by mechanical activation. According to scanning electron microscopy data, the process was accompanied by pronounced dispersion and fine mixing of the initial components. In the course of the preparation and electrochemical cycling of the composites, LiMn₂O₄ and LiCoO₂ partially reacted, leading to the replacement of manganese with cobalt in the structure of spinel, which was detected by powder X-ray diffraction (XRD), IR and X-ray photoelectron spectroscopy (XPS), and cyclic chronopotentiometry. The specific discharge capacity of composites was ～100 mAh/g.     

Promotional effect of Ce on the SCR of NO with NH<Subscript>3</Subscript> at low temperature over MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> supported by nitric acid-modified activated carbon

Different amounts of Mn and Ce oxides were loaded onto nitric acid-modified activated carbon (ACN) by wet impregnation. The series of catalysts were employed for the selective catalytic reduction of NO _x by NH₃ at temperatures between 100 and 250 °C. Cerium-modified catalysts exhibited higher de-NO _x performance than those modified with Mn/ACN, even with the same total loadings. The precursor solution with a molar ratio for Ce/(Mn + Ce) of 0.4 exhibited the highest catalytic activity. Enhanced resistance to SO₂ and H₂O and better stability were observed for 10%Mn–Ce(0.4)/ACN relative to 10%Mn/ACN. The catalysts were further characterized by N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The N₂ physisorption and XRD results suggested that co-doping Ce with Mn increased the surface area and promoted the dispersion of Mn–Ce binary metal oxides. H₂-TPR the NH₃-TPD results demonstrated that the interaction between manganese oxide and cerium oxide species enhanced the redox and surface acidity of 10%Mn–Ce(0.4)/ACN.     

Effect of the cerium content on the activity of Cu-Ce-Al-O catalysts in the methanol steam reforming reaction in a flow reactor

The Cu_18.5Ce _x Al_{81.5 ? x} (where x = 2, 7.4, and 14) oxide catalysts were synthesized by coprecipitation and tested in the methanol steam reforming reaction in an integral flow reactor at 270°C. It was found that the activity of the catalysts increased with the calcination temperature and catalysts with intermediate cerium contents exhibited the highest activity; these catalysts exhibited the greatest values of S _BET and S _Cu. The phase analysis demonstrated that copper in these samples occurred almost entirely as a CuO-CeO₂ solid solution. The concentration of carbon monoxide at the reactor outlet decreased with the calcination temperature. For the most active sample with a cerium content of 7.4% calcinated at 700°C, the concentration of CO reached a minimum of no higher than 0.3%.     

Magnetic Methods in a Study of the Effect of the Pore Structure of Silica Gels on the Particle Size of Cobalt in Catalysts for the Fischer-Tropsch Synthesis

A magnetic method was proposed for evaluating the average particle size of cobalt metal in supported cobalt catalysts for the Fischer-Tropsch synthesis. This method includes a set of techniques such as in situ temperature-programmed reduction and in situ temperature-programmed oxidation with simultaneous magnetization measurements and the dependence of magnetization on magnetic field intensity (the field dependence method). It was found that cobalt supported on silica gel with a bimodal pore-size distribution exhibited a special behavior in topochemical processes: the majority of cobalt particles occurred in a superparamagnetic state, while a portion occurred in a multidomain state.     

X-Ray diffraction study of the new ecdysteroid derivatives containing isoxazoline ring in the side chain

Crystal and molecular structure of (2β,3β,14α,20R,5′R)-14,20-dihydroxy-20-(3′-isopropylisoxazolin-5′-yl)-2,3-isopropylidenedioxy-5β-pregn-7-en-6-one and (2β,3β,14α,20R,5′R)-20-hydroxy-20-(3′-methylisoxazolin-5′-yl)-14-trimethylsilyloxy-2,3-isopropylidenedioxy-5β-pregn-7-en-6-one was investigated by XRD analysis. Compounds crystallize in the orthorhombic [space group P2₁2₁2₁; a 1.751(2), b 12.146(2), c 19.660(4) Å] and hexagonal [space group P6₁; a 14.138(3), b 14.138(3), c 27.597(7) Å] crystal systems, respectively. These compounds, which resulted from the 1,3-dipolar cycloaddition of isobutyronitrile oxide or acetonitrile oxide to the corresponding steroid olefin, have 5′R-stereochemistry of the formed chiral center. The conformation of the side chain of molecules is stable due to the intramolecular hydrogen bonds.     

An XPS study of the oxidation of noble metal particles evaporated onto the surface of an oxide support in their reaction with NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The interaction of the model catalysts Rh/Al₂O₃, Pd/Al₂O₃, Pt/Al₂O₃, and Pt/SiO₂ with NO _x (mixture of 10 Torr of NO and 10 Torr of O₂) was studied by X-ray photoelectron spectroscopy (XPS). Samples of the model catalysts were prepared under vacuum conditions as oxide films ≥100 Å in thickness on tantalum foil with evaporated platinum-group metal particles. According to transmission electron microscopic data, the platinum-group metal particle size was several nanometers. It was found by XPS that the oxidation of Rh and Pd nanoparticles in their interaction with NO _x occurs already at room temperature. The particles of platinum were more stable: their oxidation under the action of NO _x was observed at elevated temperatures of ～300°C. At room temperature, the interaction of platinum nanoparticles with NO _x hypothetically leads to the dissolution (insertion) of oxygen atoms in the bulk of the particles with the retention of their metallic nature. It was found that dissolved oxygen is much more readily reducible by hydrogen than the lattice oxygen of the platinum oxide particles.     

The oxygen nonstoichiometry,defect structure,and thermodynamic characteristics of disordering of nickel-and iron-substituted lanthanum cobaltites

The oxygen nonstoichiometry of nickel-and iron-substituted lanthanum cobaltites of the compositions LaCo_1?x Ni _x O_3?δ (x = 0.1, 0.3) and LaCo_0.9Fe_0.1O_3?δ was studied by high-temperature thermogravimetric analysis over the temperature and oxygen partial pressure ranges 1223–1473 K and 10^?3–0.21 atm. The partial replacement of cobalt with nickel (an acceptor impurity) in lanthanum cobaltite was found to increase the number of defects in the oxygen sublattice, whereas the replacement with iron (a donor impurity) decreased this number. Correlations between the experimental \(\log p_{O_2 } = f(\delta )\) dependences and the suggested models of formation of point defects were analyzed taking into account the formation of Schottky defects. Interrelation between the defect structure, partial molar thermodynamic characteristics of oxygen release from the crystal lattices of the oxides studied, and the nature of substituting impurities (Ni and Fe) in lanthanum cobaltite was demonstrated.     

Synthesis of an Ni<Subscript>2</Subscript>P catalyst supported on Na-MCM-41 with highly activity for dibenzothiophene HDS under mild conditions

A novel and simple method to synthesize supported Ni₂P/Na(x)-MCM-41 catalysts (where x is the mass fraction of Na-to-MCM-41 in terms of percentage) at a lower reduction temperature by incorporation of Na was described. The catalysts were characterized by H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD), N₂ adsorption–desorption, CO uptake, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The effect of Na on the structure of catalysts and catalytic properties for the dibenzothiophene (DBT) hydrodesulfurization (HDS) was investigated, which confirmed that a suitable amount of Na can promote highly dispersed Ni₂P particles. The Na preferentially interacts with phosphate to generate the sodium phosphate and therefore suppresses the formation of stronger P–O–P bonds, which enables the phosphide catalyst to be easily formed at a lower reduction temperature. Compared with conventional phosphate (973–1273 K), the reduction temperature of Ni₂P/Na(x)-MCM-41 catalyst was relatively low (773 K). The Ni₂P/Na(x)-MCM-41 catalyst with x?=?1.0 showed the maximum DBT conversion of 91.6%, which is higher than that of Ni₂P/M41 without Na (80.3%).     

Crystal structure and properties of (1,5-cyclooctadiene) (η<Superscript>5</Superscript>-pentamethylcyclopentadienyl) iridium(I) [Ir(cod)Cp*]

Volatile iridium(I) complexes [Ir(cod)Cp^x] (Cp^x = pentamethylcyclopentadienyl Cp*, ethylcyclopentadienyl Cp^Et, cod = 1,5-cyclooctadiene) are synthesized and characterized by IR and NMR spectroscopy. The [Ir(cod)Cp*] complex is a solid and the [Ir(cod)Cp^Et] complex is a liquid (SATP). The XRD method is used to determine the structure of the [Ir(cod)Cp*] complex: chemical formula C₁₈H₂₇Ir, space group P2₁/c, a = 8,4418(2) Å, b = 9,4764(3) Å, c = 19.2682(5) Å, β = 96.128(1) °, V = 1532.61(7) ų, Z = 4, d _calc = 1.888 g/cm³, μ = 8.697 mm^–1. The cyclopentadienyl ligand is η⁵-type coordinated; 1,5-cyclooctadiene have a cis-cis conformation and is η⁴-type coordinated. The thermal properties of the complexes are studied by thermogravimetry.     

The solid solutions based on lanthanum manganite as the cathod materials for bismuth-containing solid electrolytes

Substituted lanthanum manganites with the general composition La_1–x Bi _x Mn_1–y Fe(Ni,Cu)yO_{3 + δ} and unit cells in rhombohedral (space group (sp. gr.) R-3c) and/or orthorhombic (sp. gr. Pnma) symmetry are synthesized and attested. They are characterized by permanent excessive oxygen nonstoichiometry within a single structure type at room temperature, independent of the dopant concentration. These materials are adequately mechanically compatible with bismuth niobates. The interval of their chemical compatibility with bismuth-containing compounds is limited by 700–800°C. In this region, the conductivity of composites of substituted lanthanum manganites and bismuth-containing electrolytes is higher as compared with individual compounds. The use of individual manganites or their composites as the electrodes in cells with bismuthcontaining electrolytes increases the total conductivity of the cells.     

Molecular Layer Deposition and Thermal Transformations of Titanium(Aluminum)-Vanadium Hybrid Organic-Inorganic Films

In this work Molecular layer deposition (MLD) technique used to synthesize titanium-vanadium (TiV _x C _y O _z ) and aluminum-vanadium (AlV _x C _y O _z ) hybrid organic-inorganic films via alternating surface reactions of titanium tetrachloride (or trimethylaluminum), vanadium oxochloride, and ethylene glycol. Using in situ monitoring it was found that the surface reactions were self-limiting at temperatures of 90 and 115°C. The coating thickness per molecular layer deposition cycle (growth rate) at 115°C on a silicon substrate varied from 5.8 to 11.4 Å/cycle, and the film densities, from 1.7 to 2.0 g cm^–3. An analysis of the samples obtained at 115°C revealed their amorphous structure. A thermal treatment of titanium-vanadium films at 450°C in air resulted in formation of highly structured coatings. These coatings were composed of nanowires of single-crystal vanadium oxide (V₂O₅) and mixed nanostructures of titanium and vanadium oxides. Increase in thermal treatment temperature to 500°C resulted in elongation of the V₂O₅ nanowires up to tens of micrometers and in their separation from the substrate. A thermal treatment of aluminum-vanadium films in air resulted in formation of a low-density film. Pyrolysis of the films in an inert gas yielded composite coatings containing domains of graphitized carbon. These films can be potentially useful in modern devices for energy storage, electronics, medicine and other promising fields of technology.     

Fischer—Tropsch synthesis in ionic liquids

A comparative evaluation of the activity of different catalysts in the Fischer—Tropsch synthesis was performed. The reaction was conducted under batch conditions (autoclave) with the catalysts suspended in nonpolar and polar media, viz., n-decane or ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. The fused Fe—K system, cobalt carbonyl, and pivalate complex [Co(Piv)_2–x OH] _n were used as catalysts. In the most cases, the use of the non-acidic ionic liquid decreases the activity of these catalytic systems. The formation of liquid hydrocarbons С₅—С₁₄ is observed only with the combination ionic liquid—Сo₂(CO)₈. When the Fe—К catalyst is modified with a cocatalyst in the form of the ionic liquid supported on the silica gel surface ([BMIM][BF₄](30%)/SiO₂), the conversion of carbon monoxide somewhat increases (by 5—7%). The ratio paraffins/olefins/iso-paraffins/aromatics in the reaction products was shown to change in a wide range.