N. A. Rudina

Preparation and study of porous uranium oxides as supports for new catalysts of stream reforming of methane

Abstract We describe the method of synthesis of the porous uranium oxides (U 3 O 8 and UO 2 ) with specific surface area as high as 10–15 m 2 /g. Physico-chemical structure and properties of these materials were studied by X-ray diffraction, scanning electron microscopy and adsorption techniques. Porous U 3 O 8 was used as a support for Ni- and Ru-catalysts for steam reforming of methane for new ICAR-process of direct nuclear-to-chemical energy conversion (Int. J. Hydrogen Energy 18 (1) (1993)) Catalytic activity as a function of the metal (Ni or Ru) content, temperature and contact time was studied in non-gradient catalytic reactor at P =1 atm and T =600–780°C. The catalysts studied were shown to be very active in methane reforming by steam and allow to reach at these conditions the hydrogen production rate as high as 17–18 n cm 3 /s per 1 gram of the catalyst. The reaction rate obeys the law r = k 0 exp(− E a / RT)(p m - p m ∗ ), where p m is a partial pressure of methane, p m ∗ is close to the equilibrium pressure of methane at temperature T . The activation energy E a was found to be 54 kJ/mol for Ru/U 3 O 8 catalysts. To reduce the expected contamination of the produced syn-gas by radioactive products of nuclear splitting under application in the ICAR process we build up a thin oxide (MgO, Al 2 O 3 ) layer, coating the porous uranium particle. The results of the coating study are also presented.

Formation of a nickel catalyst on the surface of aluminosilicate supports for the synthesis of catalytic fibrous carbon

Conditions for the homogeneous precipitation of nickel hydroxide in the presence of urea onto the surface of aluminosilicate honeycomb monoliths, which were prepared based on clay, talc, and amorphous aluminum hydroxide, were examined. Factors affecting the concentration of supported nickel (synthesis time, starting solution concentrations, loaded amount of the support, and support calcination temperature) were studied. The possibility of supporting nickel hydroxide onto the surface of cellular ceramic foam, glass foam, and haydite was demonstrated. The morphology of nickel hydroxide particles, nickel metal particles on support surfaces, and carbon coatings synthesized in the course of the catalytic pyrolysis of a propane-butane mixture was studied by scanning electron microscopy.

Nickel catalysts based on porous nickel for methane steam reforming

The influence of synthesis conditions on the phase composition and texture of porous nickel supports as plates with a magnesium oxide underlayer were investigated by X-ray diffraction, low-temperature nitrogen absorption, and electron microscopy combined with X-ray microanalysis. Nickel catalysts supported on these plates were studied. Thermal treatment of Mg(NO3)2 in nitrogen yields a magnesium oxide underlayer with a small specific surface area (support I). The replacement of nitrogen with hydrogen leads to a larger surface area (support II). The formation of MgO is accompanied by the incorporation of Ni2+ cations from the oxide film into the underlayer. Upon subsequent reduction with hydrogen or under the action of the reaction medium, these cations form fine crystallites of nickel. The supports having an oxide underlayer show a higher activity in methane steam reforming than the initial metallic nickel. Nickel catalysts on supports I and II show similar activities. The activity of the catalysts was stable throughout 50-h-long tests; no carbon deposits were detected by TEM.

Synthesis of catalytic filamentous carbon on a nickel/graphite catalyst and a study of the resulting carbon-carbon composite materials in microbial fuel cells

The carbon-carbon composite materials obtained via the synthesis of catalytic filamentous carbon (CFC) on a Ni/graphite supported catalyst in the process of the pyrolysis of C3–C4 alkanes in the presence of hydrogen were systematically studied. The effects of the following conditions on the catalytic activity expressed as the yield of carbon (g CFC)/(g Ni) and on the character of CFC synthesis on graphite rods were studied: procedures for supporting Ni(II) compounds (impregnation and homogeneous precipitation), the concentrations of impregnating compouds (nickel nitrate, urea, and ethyl alcohol) in solution, graphite treatment (oxidation) conditions before supporting Ni(II) compounds, and the pyrolysis temperature of C3–C4 alkanes in the range of 400–600°C. Optimum conditions for preparing CFC/graphite composite materials, which are promising for use as electrodes in microbial fuel cells (MFCs), were chosen. The electrochemical characteristics of an MFC designed with the use of a CFC/graphite electrode (anode) and Gluconobacter oxydans glycerol-oxidizing bacteria were studied. The morphology of the surfaces of graphite, synthesized CFC, and also bacterial cells adhered to the anode was studied by scanning electron microscopy.

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).

Catalytical properties of Arthrobacter nicotianae cells, a producer of glucose isomerase, immobilized inside xerogel of silicium dioxide

Arthrobacter nicotianae cells, producers of glucose isomerase, were immobilized inside xerogel of silicium dioxide, and properties of the resulted heterogeneous biocatalysts were investigated in the process of isomerization of monosaccharide (glucose and fructose). The glucose isomerase activity of the resulted biocatalysts was shown to be 10 U/g, on average, taking into account the loss of the activity upon the immobilization, which amounted to 50% of the cell activity in suspension. The rate of the fructose isomerization increased linearly in the range of 55–80°C with the temperature coefficient 1.3. The biocatalysts were stable in this range; they were rapidly inactivated, however, at increasing temperature. The half-pife time of inactivation was six to seven h and five min or less at 80 and 85°C, respectively. The half-pife time of inactivation of heterogeneous biocatalysts was 50–90 h in the periodic process of isomerization of 2 M monosaccharides at 60°C in the presence of the immobilized Arthrobacter nicotianae cells.

Glucose isomerase activity in suspensions of Arthrobacter nicotianae cells and adsorption immobilization of the microorganisms on inorganic carriers

Kinetics of monosaccharide isomerization has been studied in suspensions of intact, non-growing Arthrobacter nicotianae cells. Under the conditions of the study, glucose and fructose were isomerized at the same maximum rate of 700 μmol/min per 1 g dried cells, which increased with temperature (the dependence was linear at 60–80°C). The proposed means of adsorption immobilization of A. nicotianae cells involve inorganic carriers differing in macrostructure, chemical nature, and surface characteristics. Biocatalysts obtained by adsorbing the cells of A. nicotianae on carbon-containing foamed ceramics in the coarse of submerged cultivation were relatively stable and retained original activity (catalysis of monosaccharide isomerization) throughout 14 h of use at 70°C. Maximum glucose isomerase activity (2 μmol/min per 1 g) was observed with biocatalysts prepared by adsorption of non-growing A. nicotianae cells to the macroporous carbon-mineral carrier Sapropel and subsequent drying of the cell suspension together with the carrier.

Carbon-in-silica matrices for the preparation of heterogeneous biocatalysts: The synthesis of carbon nanofibers on a Ni/SiO2 catalyst and the characterization of the resulting adsorbents for the immobilization of thermostable lipase

Comparative studies of nanocarbons and nanocarbon-in-silica adsorbents for the immobilization of enzymes, for example, thermostable lipase from Thermomyces lanuginosus, were performed. Carbon nanotubes (CNTs) with different diameters, specific surface areas, and concentrations of surface carboxy groups were studied as the nanocarbon adsorbents. The nanocarbon-in-silica adsorbents were prepared by the synthesis of carbon nanofibers (CNFs) in SiO2 xerogel in the course of the pyrolysis of C3-C4 alkanes on Ni catalysts; their physicochemical and textural characteristics were studied by thermal analysis, scanning electron microscopy, and nitrogen porosimetry. It was found that carbon nanofibers of different diameters were synthesized in the bulk of a silica matrix only at Ni contents higher than 1–1.5%. The CNFs-in-silica supports were nanoporous: the mean pore diameter and the specific surface area were ∼10 nm and 250–300 m2/g, respectively. The heterogeneous biocatalysts prepared by the adsorption of thermostable lipase on the CNTs and CNFs-in-silica supports were investigated in the reaction of triglyceride (tributyrine) hydrolysis; the physicochemical properties of biocatalysts and their enzymatic activity and stability were studied depending on the hydrophobicity-hydrophilicity of the support/matrix.

Reinforced nickel and nickel-platinum catalysts for performing the thermally coupled reactions of methane steam reforming and hydrogen oxidation

The formation of composite nickel and nickel-platinum catalysts reinforced with steel gauze was studied. The catalysts were prepared by sintering powdered nickel metal and a supported nickel catalyst (GIAP-3 or NIAP-18) with a chromium oxide additive in the case of nickel-containing composite catalysts or by sintering powdered nickel, aluminum, and a supported platinum catalyst in the case of catalysts containing nickel-platinum. With the use of electron microscopy, mercury porosimetry, and X-ray electron probe microanalysis, it was found that a metal matrix, in the pores of which supported catalyst particles were distributed, was formed in the composite catalysts. The reinforced nickel catalysts prepared were active in the reaction of methane steam reforming, and the catalysts containing nickel-platinum were active in the reaction of hydrogen oxidation. An increase in the activity of reinforced nickel catalysts in the course of the reaction was found. It is believed that the increase of the activity was due to the reduction of nickel oxide from an inactive difficult-to-reduce oxide film containing nickel and chromium oxides under the action of the reaction atmosphere.

Preparation and characterization of supports with a synthesized layer of catalytic filamentous carbon: III. Synthesis of carbon nanofibers on nickel supported onto aluminum oxide

The synthesis of catalytic filamentous carbon (CFC) on catalysts prepared by supporting Ni2+ compounds onto the surface of various alumina modifications (macroporous α-Al2O3 and mesoporous ϑ-Al2O3 and δ-Al2O3) using two procedures (impregnation and homogeneous precipitation) was studied. The texture characteristics (specific surface area and pore structure) of the parent supports and adsorbents with a CFC layer were compared. The effect of the supporting procedure on the surface morphology of Ni/Al2O3 catalysts and the synthesized CFC layer was studied by scanning electron microscopy. It was found that the carbon yield on a macroporous catalyst prepared by homogeneous precipitation was higher than that on a catalyst prepared by impregnation by a factor of ∼2. The CFC layer exhibited a mesoporous structure because of a chaotic interlacing of carbon nanofibers, and the synthesis of CFC on macroporous supports resulted in the formation of a bidisperse pore structure of the adsorbent. Active and stable heterogeneous biocatalysts were prepared by the adsorptive immobilization of enzymatically active substances (glucoamylase and nongrowing baker’s yeast cells) on CFC.