A. N. Shmakov

Alkene and thioether oxidations with H2O2 over Ti- and V-containing mesoporous mesophase catalysts

Abstract Well-organized Ti- and V-containing silicate mesoporous mesophase materials (MMM) were synthesized using C 16 H 33 N(CH 3 ) 3 Br and characterized by elemental analysis, IR, DRS-UV, XRD, and N 2 adsorption. Catalytic properties of these materials in alkene and thioether oxidations with aqueous H 2 O 2 were examined. The structure–activity study was performed for the C16-(Ti,Si)-MMM catalysts with the Si/Ti atomic ratio ranged from 19 to 166. The samples with the Si/Ti atomic ratio in the range of 49–124 showed the highest catalytic activities. Both structure perfection of the silicate matrix and degree of isolation of titanium ions in it appeared to be crucial factors determining catalytic activity of C16-(Ti,Si)-MMM in alkene oxidation. For efficient oxidation of more nucleophilic substrates (thioethers) the structural perfection of the C16-(Ti,Si)-MMM catalysts was less important. No titanium leaching occurred even in 1.1 M H 2 O 2 solution at 353 K, whereas vanadium leaching was already pronounced at [H 2 O 2 ]=0.05 M and room temperature. The oxidation processes proved to be true heterogeneous for C16-(Ti,Si)-MMM and mostly homogeneous for C16-(V,Si)-MMM.

Comparative textural study of highly ordered silicate and aluminosilicate mesoporous mesophase materials having different pore sizes

Abstract Honeycomb structure model was applied for describing surface properties in the MCM-41 and SBA-15 types of highly ordered silicas and aluminosilicates with different nominal mesopore diameters: about 4 nm and about 10 nm. As shown, calculations of internal specific surface area A me require a heterogeneity of this surface to be taken into account, the latter being quantified by the roughness coefficient β . These calculations at the condition β =1.0 will allow to estimate the lower limit of specific surface area of the materials only, which will correspond to the perfectly smooth walls of mesopores. This description seems to be valid for the MCM-41 type systems, for which β is about 1.1–1.2. On the contrary, β is found to exceed 1.5 for the SBA-15 type materials. This fact is probably due to an essential non-smoothness of the mesopore surface in these systems and may be associated with their synthesis conditions.

Highly-ordered aluminosilicate mesoporous mesophase materials: physico-chemical properties and catalytic behaviour

Abstract Structural and textural characteristics as well as coordination states of aluminium and some catalytic properties are studied for highly-ordered (with very narrow XRD reflections) aluminosilicate mesoporous mesophase materials ((Si,Al)-MMM) prepared with different aluminium concentrations by hydrothermal synthesis in the presence of C 16 H 33 N(CH 3 ) 3 Br. As shown, all physico-chemical parameters measured for these systems including their structural hydrostability are strongly influenced by the aluminium content. Based on analysis of the results obtained, a description of probable transformations during formation of mesoporosity in the C16-(Si,Al)-MMM is considered.

Synthesis of aluminum oxides from the products of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor: II. Physicochemical properties of the products obtained by the centrifugal thermal activation of hydrargillite

A variety of physicochemical methods were used to characterize the product of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor under the following conditions: the average particle size of the reactant, 80–120 μm; the temperature of the solid heating surface (plate or cylinder), 300–700°C; hot-zone residence time, ∼1 s; transfer of the product to the cooled zone of the reactor. The composition of the product and the extent of decomposition of hydrargillite were determined as a function of the processing temperature. The centrifugal thermal activation (CTA) of hydrargillite affords an X-ray-amorphous, highly reactive product with a developed surface and a disordered and inhomogeneous porous structure. This structure is capable of forming different modifications of aluminum hydroxide and oxide. The properties of the CTA product are compared with the properties of the earlier reported hydrargillite rapid decomposition products obtained using a gaseous heat-transfer agent (thermochemical activation product) or a fluidized bed of a granular heat-transfer agent (thermal dispersion product).

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.

Structure characteristics of disordered zirconium hydroxoxides

The structural characteristics of low-temperature zirconium hydroxoxide and zirconium dioxide obtained from zirconyl nitrate and treated at 383 and 653 K have been studied by the X-ray method of distribution of radial electron density. It is shown that the low-temperature hydroxide contains a ∼10 to 15-Å nucleus of the crystalline phase with a structure of short-range order similar to the short-range order in ZrO2. An increase in treatment temperature of zirconium hydroxide results in the formation of a mixture of cubic and monoclinic zirconium dioxide with a particle size of ∼60 Å.

A study of the local structure of aluminas obtained by different methods

The local structure of aluminas obtained from hydroxides (pseudo-boehmites) synthesized by different methods is studied using the radial density distribution function,. The occupancy of the cation sites of different types (tetrahedral and octahedral, spinel and non-spinel) in the structure of the studied oxides is analyzed.

Synthesis of titanium oxide structures on mesoporous silicon dioxide surface by molecular layering

The formation of titanium oxide structures through the repeated successive treatment of SBA-15 mesoporous silicon dioxide with vapors of TiCl4 and H2O at 200°C is investigated. The influence of the number of synthesis cycles on the character of the buildup of the surface titanium oxide structures and changes in the adsorption and structural characteristics of modified silica is shown.

Comparison of growth mechanisms of undoped and nitrogen-doped carbon nanofibers on nickel-containing catalysts

Abstract The growth mechanisms of carbon nanofibers on Ni catalysts and nitrogen-doped carbon nanofibers on Ni and Ni-Cu catalysts were studied. The growth of both types of nanofibers was found to occur by a mechanism that included the formation of surface non-stoichiometric nickel carbide followed by the dissolution and diffusion of carbon, or carbon and nitrogen into the bulk of the catalyst particles.

High precision X-ray diffraction studies of polycrystalline materials on synchrotron radiation

The review is devoted to application of synchrotron radiation (SR) for studying the structure of polycrystalline materials. The main emphasis is made on the equipment and techniques for acquiring high precision structural information — high angular resolution powder diffractometry and the use of anomalous scattering effect in structural studies. Various schemes of recording the high resolution X-ray patterns are presented, diffractometers operating in the world’s leading synchrotron radiation centers are described, and examples of particular applications are reported.