A. N. Salanov

Study of multiwalled graphite nanotubes and filaments formation from carbonized products of polyvinyl alcohol via catalytic graphitization at 600–800°C in nitrogen atmosphere

Abstract The catalytic graphitization of amorphous carbon matrix was carried out at the temperature range of 600–800°C in nitrogen atmosphere. Amorphous carbon matrix with uniformly distributed Fe particles was obtained via catalytic carbonization of polyvinyl alcohol (PVA) at temperatures up to 600°C in nitrogen atmosphere. Using transmission electron microscopy (TEM), selected area diffraction (SAD), scanning electron microscopy (SEM), and X-ray diffractometry (XRD), graphite structures of three types were found in products of catalytic graphitization of amorphous carbon matrix: multiwalled graphite shells wrapping the catalyst particles, cockle-shelled graphite filaments (CSF), and multiwalled graphite nanotubes (MWNT). We suppose that the formation of CSF proceeds through the dissolution of amorphous carbon in the metal, transformation of the catalyst particles into a liquid state, and transfer of dissolved carbon via intermediates to growing filaments. Graphite nanotubes nucleate at the matrix surface and then grow in the porous space of the matrix.

Honeycomb-supported perovskite catalysts for high-temperature processes

Pechini route [US Patent No. 3,330,697 (1967)] was used for supporting perovskite-like systems on thin-wall corundum honeycomb support to prepare catalysts for high-temperature processes of methane combustion and selective oxidation into syngas. In this preparation, the surface of corundum monoliths walls was shown to be covered by strongly adhering porous perovskite layer formed by rounded crystals. At high temperatures when pore diffusion is expected to affect catalysts performance in fast reactions, this spatial distribution of the active component could be attractive. In the kinetically controlled region of methane oxidation, samples prepared via Pechini route possess activity comparable with that of samples made via support wet impregnation with mixed nitrate solutions, when an active component is uniformly distributed across the wall thickness. Corundum-supported lanthanum manganite and ferrite are the most active in the reaction of methane combustion, while its selective oxidation into syngas effectively proceeds on supported lanthanum cobaltite and nickelates. Corundum-supported perovskites are more thermally stable as compared with those on γ-alumina support.

Novel glass crystal catalysts for the processes of methane oxidation

Novel catalysts were prepared from magnetic microspheres and cenospheres recovered from fuel ashes being formed in combustion of Irsha-Borodinskii lignite and Kuznetskii coal. The specific features of microsphere formation in the coal combustion were discussed. The morphology as well as composition of different magnetic microspheres and cenospheres were studied by SEM, electron probe microanalysis and Mossbauer spectroscopy. The morphology of globules, crystallite size and defect structure of active phase was established to depend on the basicity of the glass phase. It was shown that catalytic activity of magnetic microspheres and cenospheres in the reaction of deep oxidation of methane is determined by the spinel phase and depends on the extent of its accessibility and type of defect structure.

Physicochemical and catalytic properties of glass crystal catalysts for the oxidation of methane

Magnetic microspheres and cenospheres recovered from fuel ashes were studied by SEM, XRD, electron probe microanalysis, chemical analysis and Mossbauer spectroscopy. The magnetic microspheres were shown to consist of a ¨ crystal phase based on a solid solution of Fe O -Mg, Mn, Ca-ferrite, a-Fe O and a glass phase composed of calcium 34 2 3 ferrite, fayalite, wollastonite, ferrous olivines and mullite. The morphology of globules and size of crystallites of active phase were established to depend on the basicity of the glass phase. It was shown that catalytic activity of magnetic microspheres and cenospheres in oxidative conversion of methane is determined by component containing iron and depends on its accessibility and distribution on the surface. q 2000 Elsevier Science B.V. All rights reserved.

Mechanisms of oxygen adsorption and desorption on polycrystalline palladium

The adsorption and desorption of oxygen on a polycrystalline palladium (Pd(poly)) surface (10-to 100-μm crystallites; ∼32% (100), ∼18% (111), ∼34% (311), and ∼15% (331)) at PO2 ≤ 1.3 × 10−5 Pa and T = 500–1300 K have been studied by TPD and mathematical modeling. The kinetics of O2 adsorption and desorption on Pd(poly) are primarily governed by the formation and decomposition of oxygen adsorption structures on the (100) and (111) crystallite faces. The O2 adsorption rate is constant at ϑ ≤ 0.15–0.25 owing to the formation of the p(2 × 2) structure with an Oads-surface bonding energy of D(Pd-O) = 364 kJ/mol on the (100) and (111) faces. The adsorption rate decreases with increasing coverage at ϑ ≥ 0.15–0.25 because of the growth, on the (100) face, of the c(2 × 2) structure, in which D(Pd-O) is reduced to 324 kJ/mol by lateral interactions in the adsorption layer. A high-temperature (∼800 K) O2 desorption peak is observed for ϑ ≤ 0.25, which is due to O2 desorption from a disordered adsorption layer according to a second-order rate law with an activation energy of Edes = 230 kJ/mol. A lower temperature (∼700 K) O2 desorption peak is observed for ϑ ≥ 0.25, which is due to O2 released by the c(2 × 2) structure according to a first-order rate law with Edes = 150 kJ/mol. At ϑ ≥ 0.25, there are repulsive interactions between Oads atoms on Pd(poly) (εaa = 5–10 kJ/mol).

Design of medium–temperature solid oxide fuel cells on porous supports of deformation strengthened Ni–Al alloy

An approach was developed towards design of medium-temperature solid-oxide fuel cells based on a deformation strengthened Ni-Al alloy. Methods of sintering were described that allowed obtaining layers of complex oxides with ionic and mixed conductivity and with regulated porosity in the range of 40–1%. Power density of a fuel cell on a metallic support reaches 500 mW/cm2 already at 700°C when humid H2 was used as fuel and air was used as an oxidant. Analysis of fuel cell cross-section after tests showed absence of fractures, flaking, and new phases with low conductivity, which proves good compatibility of all materials used in fuel cell design.

Synthesis and properties of highly porous MeOX/Al2O3/Al composites (Me = Mg, Ca, La, Ti, Al)

The influence of various oxide additives, such as CaO, MgO, La2O3, TiO2, and alumina on the reactivity of aluminium particles during their hydrothermal oxidation as well as on the thermal decomposition of hydroxides during the composite preparation has been studied. For some promoters, these additives were found to affect the crushing strength of composite granules and their microporous structure.

Interaction between oxygen and polycrystalline palladium at O2 pressures of 10−6–10 Pa

AbstractThe interaction between oxygen and polycrystalline palladium (Pd(poly)) at

Physicochemical investigation of the copper and silver catalysts of the ethylene glycol oxidation

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