O. A. Bulavchenko

Cobalt boride catalysts for hydrogen storage systems based on NH3BH3 and NaBH4

The catalytic activity of cobalt borides forming in situ under conditions of NH3BH3 and NaBH4 hydrolysis have been investigated. The reaction properties of the catalysts depend on the nature of the hydride. According to high-temperature X-ray diffraction, thermal analysis, high-resolution transmission electron microscopy, IR spectroscopy, and chemical analysis data, the nature of the hydride determines the particle size, chemical composition, and crystallization properties of the cobalt borides.

Effect of the Ni/Cu ratio on the composition and catalytic properties of nickel-copper alloy in anisole hydrodeoxygenation

The activity of NiCu-SiO2 catalysts with a metal content of 90% and different Ni/Cu ratios has been investigated in the hydrodeoxygenation of anisole, a model compound of bio-oil, at 280°C and 6 MPa. A homogeneous phase composition of the active component has been synthesized by the co-decomposition of nickel and copper nitrates followed by the introduction of SiO2 as a stabilizer. The resulting catalysts have been characterized by temperature-programmed reduction, X-ray powder diffraction, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy combined with energy-dispersive microanalysis. The bulk and surface composition of active-component particles has been determined by XPS and X-ray diffraction. In all of the catalysts containing 15–85 wt % Ni, there are two types of solid solutions. One has a constant composition, Cu0.95Ni0.05, which is independent of the Ni/Cu ratio in the catalyst; in the other, the nickel stoichiometry increases with an increasing Ni content of the active component. A correlation has been established between the Ni/Cu ratio and the rate constants of the reaction examined and between the Ni/Cu ratio and the degree of hydrodeoxygenation for all samples. The most active catalyst is Ni85Cu5-SiO2.

Low-temperature oxidation of carbon monoxide over (Mn1 − xMx)O2 (M = Co, Pd) catalysts

Abstract(Mn1 − xMx)O2 (M = Co, Pd) materials synthesized under hydrothermal conditions and dried at 80°C have been characterized by X-ray diffraction, diffuse reflectance spectroscopy, electron microscopy, X-ray photoelectron spectroscopy, and adsorption and have been tested in CO oxidation under CO + O2 TPR conditions and under isothermal conditions at room temperature in the absence and presence of water vapor. The synthesized materials have the tunnel structure of cryptomelane irrespective of the promoter nature and content. Their specific surface area is 110–120 m2/g. MnO2 is morphologically uniform, and the introduction of cobalt or palladium into this oxide disrupts its uniformity and causes the formation of more or less crystallized aggregates varying in size. The (Mn,Pd)O2 composition contains Pd metal, which is in contact with the MnO2-based oxide phase. The average size of the palladium particles is no larger than 12 nm. The initial activity of the materials in CO oxidation, which was estimated in terms of the 10% CO conversion temperature, increases in the following order: MnO2 (100°C) < (Mn,Co)O2 (98°C) < (Mn,Co,Pd)O2 (23°C) < (Mn,Pd)O2 (−12°C). The high activity of (Mn,Pd)O2 is due to its surface containing palladium in two states, namely, oxidized palladium (interaction phase) palladium metal (clusters). The latter are mainly dispersed in the MnO2 matrix. This catalyst is effective in CO oxidation even at room temperature when there is no water vapor in the reaction mixture, but it is inactive in the presence of water vapor. Water vapor causes partial reduction of Mn4+ ions and an increase in the proportion of palladium metal clusters.

Effect of the composition and structure of the precursor compound on the catalytic properties of cobalt-aluminum catalysts in the Fischer-Tropsch synthesis

The effect of preparation procedure on the anionic composition and structure of hydroxo compounds as precursors of Co-Al catalysts and on their catalytic properties in the Fischer-Tropsch synthesis was studied. The dynamics of changes in the composition and structure of the hydroxide precursors of Co-Al catalysts during thermal treatment and subsequent activation was studied by thermal analysis, IR spectroscopy, XRD analysis, and in situ XRD analysis with the use of synchrotron radiation. It was found that the precursor compounds prepared by deposition-precipitation of cobalt cations on γ- and δ-Al2O3 under urea hydrolysis conditions, which had a hydrotalcite-type structure and contained nitrate, carbonate, and hydroxyl groups, turtned into the oxide compounds Co3 − xAlxO4 (0 < x < 2) with the spinel structure in the course of thermal treatment in an inert atmosphere. The hydrogen activation of an oxide precursor led to the formation of cobalt metal particles through the intermediate formation of a cobalt(II)-aluminum oxide phase. The catalyst was characterized by high activity and selectivity for C5+ hydrocarbons in the Fischer-Tropsch synthesis.

MnOx-Al2O3 catalysts for deep oxidation prepared with the use of mechanochemical activation: The effect of synthesis conditions on the phase composition and catalytic properties

The catalytic activity of alumina-manganese catalysts in the oxidation of CO was studied. The MnOx-Al2O3 catalysts were prepared by an extrusion method with the introduction of mechanically activated components (manganese oxide and its mixtures with aluminum oxide, aluminum hydroxide, and a mixture of a manganese salt with aluminum hydroxide) into a paste of aluminum hydroxide followed by thermal treatment in air or argon at 1000°C. In the majority of cases, the catalysts contained a mixture of the phases of β-Mn3O4 (Mn2O3), α-Al2O3, and δ-Al2O3. The presence of low-temperature δ-Al2O3 suggested the incomplete interaction of manganese and aluminum oxides. It was found that the catalytic activity of MnOx-Al2O3 depends on the degree of interaction of the initial reactants, and its value is correlated with the amount of β-Mn3O4 in the active constituent. The intermediate thermal treatment of components at 700°C negatively affects the catalytic activity as a result of the formation of Mn2O3 and the coarsening of particles, which levels the results of mechanochemical activation. The greatest degree of interaction between Al- and Mn-containing components was reached in the selection of mechanochemical activation conditions by decreasing the size of grinding bodies, optimizing the time of mechanochemical activation, and using the mechanochemical activation of precursor mixtures. As a result of mechanochemical activation, the initial reactants were dispersed, the amounts of MnO2 and Mn2O3 changed, and defects were formed; this strengthened the interaction of components and increased catalytic activity.

Debye function analysis of nanocrystalline gallium oxide γ-Ga2O3

Abstract The metastable nanocrystalline γ-Ga2O3 with the particles’ dimensions about 2 nm was prepared by coprecipitation method and its structure was studied using X-ray powder diffraction. The corresponding diffraction pattern is characterized by a strong broadening of diffraction peaks. The Debye function analysis method (DFA) was applied to calculate the full profile of the XRD pattern for the first time. Earlier reported structural models of the γ-Ga2O3 were examined with respect to experimental diffraction data. The influence of crystallite sizes on the diffraction pattern was considered. The obtained structure of the disordered γ-Ga2O3 has vacancies in 8a and 16d spinel positions and additional atoms in 8b, 16c and 48f non-spinel positions. The proposed structure differs from those reported by the ratio between occupancies of the tetrahedral and octahedral gallium positions.

Effect of the mechanical activation of a mixture of MnCO3 · mMn(OH)2 · nH2O and AlOOH as a stage of the preparation of a MnOx-Al2O3 catalyst on its phase composition and catalytic activity in CO oxidation

The effect of the mechanical activation of a mixture of MnCO3 · mMn(OH)2 · nH2O and AlOOH as a stage in the preparation of a MnOx-Al2O3 catalyst on the characteristics of the resulting samples was studied. It was found that the catalytic activity of MnOx-Al2O3 increased even after mechanical activation for 5 min. It was established that a decrease in the concentration of manganese hydroxocarbonate within the limits of the tested ratios between the components exerted the greatest positive effect of mechanical activation on catalytic activity. This was likely because the dispersion of this compound increased and interactions between the components strengthened in the course of mechanical activation. This was evidenced by a considerable increase in the amount of the α-Al2O3 phase relative to δ-Al2O3 in the catalyst calcined at 950°C. According to the results of temperature-programmed reduction with hydrogen, the formation of a larger number of catalytically active, fine MnOx particles after high-temperature heat treatment was responsible for the strengthening of interactions between the initial components upon mechanical activation. Transmission electron-microscopic data also indicated an increase in the dispersity of manganese oxide particles with the use of mechanical activation as a stage of the preparation of the MnOx-Al2O3 catalyst.

Effect of the Calcination Temperature and Composition of the MnO x –ZrO 2 System on Its Structure and Catalytic Properties in a Reaction of Carbon Monoxide Oxidation

The effect of the calcination temperature and composition of the MnOx–ZrO2 system on its structural characteristics and catalytic properties in the reaction of CO oxidation was studied. According to X-ray diffraction analysis and H2 thermo-programmed reduction data, an increase in the calcination temperature of Mn0.12Zr0.88O2 from 450 to 900°C caused a structural transformation of the system accompanied by the disintegration of solid solution with the release of manganese ions from the structure of ZrO2 and the formation of, initially, highly dispersed MnOx particles and then a crystallized phase of Mn3O4. The dependence of the catalytic activity of MnOx–ZrO2 in the reaction of CO oxidation on the calcination temperature takes an extreme form. A maximum activity was observed after heat treatment at 650–700°C, i.e., at limiting temperatures for the occurrence of a solid solution of manganese ions in the cubic modification of ZrO2. If the manganese content was higher than that in the sample of Mn0.4Zr0.6O2, the phase composition of the system changed: the solid solution phase was supplemented with Mn2O3 and β-Mn3O4 phases. The samples of Mn0.4Zr0.6O2–Mn0.6Zr0.4O2 exhibited a maximum catalytic activity; this was likely due to the presence of the highly dispersed MnOx particles, which were not the solid solution constituents, on their surface in addition to an increase in the dispersity of the solid solution.

High-Temperature X-Ray Diffraction Investigation of the Decomposition Process in Manganese-Gallium Spinel Mn1.5Ga1.5O4

The stability of spinel-type mixed Mn1.5Ga1.5O4 oxide prepared in an inert medium (1000 °C, Ar) is studied by thermogravimetry and high-temperature X-ray diffraction in air in a wide temperature range 30–1000 °C. On heating, reversible decomposition processes of initial spinel are observed. From 30 °C to 600 °C oxygen atoms attach to the surface layer of initial Mn1.5Ga1.5O4 spinel to form a new phase distinct from parent oxide by the oxygen stoichiometry (cation vacancies are formed). The product of decomposition is two oxides: Mn1.5Ga1.5O4 and Mn1.5–xGa1.5–x[·]xO4. On the contrary, above 600 °C a loss of oxygen occurs, the concentration of cation vacancies decreases in Mn1.5–xGa1.5–x[·]xO4, and the reverse process of single phase oxide crystallization takes place. At 1000 °C the spinel phase forms again whose composition is similar to that of the initial parent phase Mn1.5Ga1.5O4. On cooling the decomposition of this phase is again observed due to oxygen attachment.

Effect of Calcination Temperature on the Structure and Catalytic Properties of MnO x /Ca 2 O 3 in the Reaction of CO and Ethane Oxidation

Effect of the calcination temperature of the MnOx/Ga2O3 system on its structural and catalytic properties in the reaction of oxidation of CO and hydrocarbons. The dependences of the catalytic activity of MnOx/Ga2O3 in the reactions of CO and ethane oxidation on the calcination temperature exhibit an extremal behavior. The maximum values of activity are observed upon calcination of the system at 700°C, i.e., at the temperature that is limiting for the existence of a solid solution of manganese ions in γ-Ga2O3. The structural changes occurring with increasing calcination temperature are accompanied by a substantial decrease in the specific surface area of a sample. The observed rise in the specific catalytic activity (by a factor of ~7 upon an increase in the preliminary-calcination temperature from 600 to 800°C) confirms that the thermal activation effect exists for the given system.