O. V. Komova

Effect of the nature of the active component and support on the activity of catalysts for the hydrolysis of sodium borohydride

The effect of the nature of an active component and a support on the rate of hydrolysis of aqueous sodium borohydride solutions was studied. It was found that the activity of supported catalysts, which were reduced in a reaction medium of sodium borohydride, decreased in the order Rh > Pt ≈ Ru ≫ Pd regardless of the nature of the support (γ-Al2O3, a Sibunit carbon material, or TiO2). The catalysts based on TiO2 exhibited the highest activity. As found by UV-vis diffuse reflectance spectroscopy, the composition and structure of the supported precursor of an active component depend on the nature of the support. It is likely that rhodium clusters with different reaction properties were formed on various supports under the action of a reaction medium.

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.

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.

Activity of Rh/TiO2 catalysts in NaBH4 hydrolysis: The effect of the interaction between RhCl3 and the anatase surface during heat treatment

The reaction properties of Rh/TiO2 sodium tetrahydroborate hydrolysis catalysts reduced directly in the reaction medium depend on the temperature at which they were calcined. Raising the calcination temperature to 300°C enhances the activity of the Rh/TiO2 catalysts. Using diffuse reflectance electronic spectroscopy, photoacoustic IR spectroscopy, and chemical and thermal analyses, it is demonstrated that, as RhCl3 is supported on TiO2 (anatase), the active-component precursor interacts strongly with the support surface. The degree of this interaction increases as the calcination temperature is raised. TEM, EXAFS, and XANES data have demonstrated that the composition and structure of the rhodium complexes that form on the titanium dioxide surface during different heat treatments later determine the state of the supported rhodium particles forming in the sodium tetrahydroborate reaction medium.

Immobilized glucoamylase: A biocatalyst of dextrin hydrolysis

Heterogeneous biocatalysts of starch saccharification based on glucoamylase and carbon-containing carriers were obtained, and their biocatalytic properties in the enzymatic hydrolysis of corn dextrins were studied. It was shown that the morphology of the surface carbon layer of carriers markedly affected the properties of biocatalysts. Glucoamylase immobilized by adsorption on the surface of carriers covered with a layer of catalytic filamentous or pyrolytic carbon had the maximum enzymatic activity and stability, whereas biocatalysts prepared on the basis of carriers that had no carbon layer or were covered with graphite-like surface carbon had a low activity and stability.

Immobilized yeast membranes as biocatalysts for sucrose inversion

Yeast membranes were obtained by autolysis of various strains with relatively high invertase activity. Heterogeneous biocatalysts for sucrose inversion were made of the yeast membranes and granulated carbon-containing supports made of common natural materials: expanded clay aggregate (ECA), sapropel, and lignin. The properties of these biocatalysts were studied. It was shown that the biocatalyst activity and stability of the immobilized yeast membranes increased with reference to the initial ECA, independent of the morphology of the carbon layer synthesized on the support surface. Heterogeneous biocatalysts prepared by adsorption of yeast membranes on sapropel had the greatest activity and stability, whereas lignin-based biocatalysts were relatively unstable.

Granulated rhodium catalysts of sodium borohydride hydrolysis for generators of high-purity hydrogen

Sodium borohydride hydrolysis in a flow reactor with turbulent mixing of reactants in a catalytic bed by the evolving hydrogen bubbles was studied. The stability of catalytic systems decreases in the order 1% Rh/Sibunit > 1% Rh/TiO2 > 1% Rh/γ-Al2O3. The decrease in the hydrogen generation rate is caused by the formation of a metaborate film on the catalyst surface, by the loss of the active component, and by disintegration of support granules and their removal with the flow of the spent liquid. High granule strength and macroporous structure of 1% Rh/Sibunit ensure stable generation of hydrogen.

Developing Effective Cobalt Catalysts for Hydrogen-Generating Solid-State NaBH4 Composite

Hydrogen-generating solid-state NaBH4 composite are promising systems for storing and transporting hydrogen intended for use in low-temperature proton-exchange membrane fuel cells. Catalysts are introduced into the composites to ensure the generation of hydrogen at ambient temperatures. In this work, the effect of the synthesis conditions for cobalt catalyst on the gas generation rate is analyzed. It is found that the efficiency of hydrogen generation depends on the nature of the cobalt salt and pH of the aqueous solution of the salt in which the active component precursor is reduced under the action of sodium borohydride because these factors determine the composition, degree of dispersion, and magnetic behavior of the cobalt systems. It is found that the highest rate of gas generation—505 cm3/min per gram of the composite with a hydrogen content of 8.4 wt %—is observed for a sample reduced with sodium borohydride in a hydrochloric acid solution of cobalt chloride with a pH of 1.3. The results can be used to develop effective inexpensive cobalt catalysts for the production of hydrogen from pelletized solid-state NaBH4 composite.

Solid-State Hydrogen-Generating Composites Based on Sodium Borohydride: Effect of the Heat Treatment of Boron–Cobalt Catalysts on the Hydrogen Generation Rate

Calcined boron–cobalt catalysts prepared by reduction of cobalt chloride in an aqueous sodium borohydride solution can be successfully used as components of pelletized solid-state hydrogen-generating composites based on sodium borohydride. Morphological changes and phase and chemical transformations occurring in the catalysts with an increase in the calcination temperature were studied. The catalyst performance in hydrolysis of sodium borohydride was determined. The hydrogen generation rate depends on the specific surface area of the calcined sample.