Low-Temperature Oxidation of Cobalt Nanoparticles with Water Vapor

The oxidation of Co nanoparticles with water vapor and molecular oxygen was studied over the temperature range 10–200°C. Cobalt particles reacted with water vapor at p _{H 2}O = 18 torr. Preadsorbed hydrogen and CO had no pronounced influence on the oxidation rate of cobalt nanoparticles. Temperature-programmed reduction showed that, after the oxidation of cobalt nanoparticles with water vapor, oxidized cobalt was in the divalent state.     

An equation for the rate of a first-order gas-liquid reaction

An equation is suggested for describing the kinetics of gas-liquid reactions first order with respect to the dissolved gas without assumptions on the reaction control mode (kinetic, diffusion, etc.). The equation was obtained with the use of the film model of gas-liquid reactions.     

Numerical simulation of the kinetics of ozone decomposition in an aqueous solution

The kinetic scheme for ozone decomposition in an aqueous solution in a wide pH interval was proposed on the basis of the known literature data. The apparent first-order rate constant for ozone decomposition at pH 1–14 was calculated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1151–1156, June, 2008.     

Catalytic properties of Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> prepared using a template in the oxidation of CO

The catalytic activity in CO oxidation of Ce _x Zr_1–x O₂ double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N₂ that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce: Zr = 4, regardless of the nature of the template; when Ce: Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce: Zr = 4, the conversion of CO on biomorphic oxide in the range of 100–350°C is higher than that observed for Ce _x Zr_1–x O₂ (CTAB); reducing the Ce: Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100–200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.     

Ozone production and losses in N<Subscript>2</Subscript>/O<Subscript>2</Subscript> mixtures in an ozone generator

Nonunique ozone concentrations at the output of an ozone generator under identical external conditions of barrier discharge activation of N₂/O₂ mixtures but with different prehistories of operating practice and employed gas mixtures are investigated theoretically. An analytical approach is developed to determine the ozone yield with regard for its heterogeneous loss. Plasma-chemical and electron kinetics in the N₂/O₂-mixtures are calculated numerically. The results of numerical calculations are compared to experimental data obtained by the authors. It is noted that the heterogeneous loss of ozone is the probable reason for the observed variety of behavior of О₃ concentrations, depending on prehistory of ozone generator operation, along with the N₂ and O₂ gas flow rates and the specific active power.     

Effect of cobalt weight content on the structure and catalytic properties of Co/CNT catalysts in the fischer–tropsch synthesis

Cobalt-based Fischer–Tropsch synthesis (FTS) catalysts containing 1 to 40 wt % cobalt supported on multi-walled carbon nanotubes (CNTs) have been investigated. The CNTs have been characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. All catalysts have been prepared by impregnating, with an ethanolic solution of cobalt nitrate, the CNTs preoxidized with concentrated nitric acid and have been tested in the FTS at 220°C and atmospheric pressure. Correlations have been established between the cobalt weight content of the catalyst and the Co particle size determined by transmission electron microscopy and X-ray diffraction. The Co content and particle size have an effect on the activity and selectivity of the catalyst and on the target fraction (C₅₊) yield in the FTS. The highest CO conversion is observed for the catalyst containing 20 wt % Co; the highest selectivity and activity, for the catalyst containing 5 wt % Co; the highest C₅₊ yield, for the catalyst containing 10 wt % Co.     

Effect of pretreatment conditions on the catalytic activity of coprecipitated Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> catalyst in soot oxidation

The temperature of soot oxidation and efficiency of Ce_0.5Zr_0.5O₂ catalyst depends on its morphology, which determines the area of intergranular contact between the solid substrate and the catalyst. The temperature-programmed reduction in hydrogen to 1000°C and oxidation at 500°C (redox cycles) cause the mobility of oxygen in oxide to be enhanced and decrease the temperature of soot combustion. Oxidation of soot in the air flow on the Ce_0.5Zr_0.5O₂ catalyst result in its activation. Reuse of the catalyst decreases the temperature of soot oxidation.     

The oxidative destruction of lignin in the ozonation of wood

The oxidative destruction of lignin in the ozonation of aspen wood was studied. The kinetic curves of ozone consumption for samples with different contents of water were obtained. The consumption of ozone increased as the content of water grew. The second derivatives of the UV absorption spectra of lignin were obtained to show that the principal direction of lignin transformations under the action of ozone was the destruction of its aromatic constituents with the formation of carboxyl- and carbonyl-containing compounds. Measurements of the UV diffuse reflectance and EPR spectra of wood showed that the ozonation of wood caused the destruction of lignin quinoid structures. Part of lignin remained unchanged under the action of ozone. A key role in the destruction of wood lignin was played by ozone dissolved in water. Varying the content of water in wood samples allows various lignin transformation products to be obtained through ozonation.     

Interaction between ozone and the chloride ion in sulfuric acid solutions up to 6-M concentration

The effect of sulfuric acid concentration on Cl₂ evolution in the reaction between O₃ and Cl^? has been investigated. The catalytic effects of metal ions in this reaction have been studied as a function of solution acidity. The chlorine evolution rate increases markedly with increasing acid concentration. At acid concentrations below 4 mol/l, the most effective catalyst is Co²⁺. The catalytic activities of Fe³⁺ and Cu²⁺ peak at $C_{H_2 SO_4 } $ = 4.8 mol/l. In passing to highly acidic solutions ( $C_{H_2 SO_4 } $ > 5 mol/l), the catalytic activity of the metal ions decreases, but the chlorine evolution rate remains high owing to the high acidity. Kinetics of VO²⁺ oxidation with ozone in acid media have been studied, and the ozone solubility in aqueous sulfuric acid has been measured.