D. A. Zyuzin

Nanosized Au/C catalyst obtained from a tetraamminegold(III) precursor: Synthesis, characterization, and catalytic activity in low-temperature CO oxidation

A method in which the water-soluble complex [Au(NH3)4](NO3)3 is used as the active-component precursor is suggested for preparing nanosized Au/C catalysts (C = Sibunit, a mesoporous carbon material). The complex is unreadily reducible by the carbon matrix and can be involved in cation exchange with proton-containing groups of the support. This method is referred to as cationic adsorption. It has been demonstrated by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy that the catalyst prepared in this way and treated with H2 at 400°C contains size-uniform gold metal particles with a dominant diameter of <5 nm. The greater part of the gold particles is located on the outer surface of the Sibunit granules; that is, an egg shell type distribution of the active component takes place. The catalyst containing 1.3 wt % Au shows high activity in CO oxidation with excess humid air at 40°C. In this respect, it is far superior to the Au/C catalysts prepared by conventional methods (deposition-precipitation and impregnation), in which the typical gold particle size is several tens of nanometers.

Influence of the temperature of calcination of bayerite-containing aluminum hydroxide pellets on the water vapor adsorption capacity and acid-base properties of alumina

The paper considers the influence of the temperature of calcination (350–550°C) of alumina-based water adsorbents prepared from bayerite-containing aluminum hydroxide on the static water sorption capacity at high and low relative air humidities and on the acid-base properties of the surface. The acid-base properties of aluminas have been determined by means of IR spectroscopy of adsorbed CO probe molecule (Lewis sites) and by the spin probe method, which was used to determine the concentrations of electron acceptor and electron donor sites. It has been demonstrated that, at a high relative air humidity (60%), there is no correlation between the static capacity of the drier and its acid-base properties, while at low relative humidities (1–1.5%), an increase in the concentration of electron donor sites and a decrease in the concentration of electron donor and Lewis acid sites enhance the water sorption capacity of alumina.

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.

Highly effective water adsorbents based on aluminum oxide

A method of preparation of a stable, high performance water adsorbent with the phase composition η-Al2O3 + γ-Al2O3 + χ-Al2O3 from thermally activated hydrargillite has been developed. The synthesis procedure does not involve a reprecipitation stage. The resulting adsorbent has a high specific surface area (400 m2/g) and a mean pore diameter of 3.5 nm or below. The static capacity of the adsorbent reaches 24.2 g H2O per 100 g of sorbent, and its dynamic capacity is 8.2 g H2O per 100 g of sorbent. Service life tests showed the stability of the adsorbent in multiple sorption-desorption cycles. The minimum dew point in drying is −58.8°C.

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.

Structural study of X-ray amorphous Fe-Zr-O materials

Radial-distribution-function analysis was used to study the structure of x-ray amorphous Fe-Zr-O materials prepared by heat treatment between 383 and 673 K. The chemical and structural formulas of the materials were established. The results demonstrate that the introduction of Fe3+ into ZrO2 favors the formation of vacancies and reduces interatomic distances in comparison with cubic ZrO2. The materials contain OH- groups, whose concentration decreases with increasing heat-treatment temperature.

Role of the support in the formation of the properties of a Pd/Al2O3 catalyst for the low-temperature oxidation of carbon monoxide

The Pd/Al2O3 catalysts were prepared by the impregnation of aluminum hydroxide, which was synthesized by precipitation in the presence of polyvinyl alcohol, with a solution of palladium nitrate and were heat-treated at different temperatures. The resulting samples were characterized by X-ray diffraction, electron microscopy, diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy and were tested in CO oxidation in two modes: in a temperature-programmed reaction and under isothermal conditions at 20°C in the absence and in the presence of water vapor. The activity of the catalysts in the former mode was almost independent of support preparation conditions, but it was different in the latter mode. The catalyst whose support was obtained in the presence of polyvinyl alcohol and treated at 300°C in an atmosphere of nitrogen exhibited the highest activity in CO oxidation at 20°C. In the absence of water vapor from the reaction mixture, the initial conversion of CO reached 40% and then decreased. In the presence of water vapor, a continuous increase in the conversion of CO to 88% was observed, and the activity was stabilized at this level. The smallest size of palladium metal nanoparticles, the nearly monolayer carbon surface coverage, and the presence of OH groups, which are formed upon the dissociation of water present in the reaction mixture, facilitate an increase in activity.

X-ray diffraction study of zirconia pillared clays

X-ray powder diffraction (XRPD) and X-ray radial electronic distribution density (RED) of initial and zirconia-pillared interlayered clays (Zr-PILC) were studied. After pillaring, the basal (001) spacing was found to increase from 11 Å in the initial clay kept under air to 17.7 Å in Zr-PILC. The structure of zirconium nanopillars was characterized. The interatomic distances with corresponding coordination numbers obtained from the RED curves were close to those in zirconium tetramers.

STRUCTURAL FEATURES OF THE COMPONENTS OF COPPER-CERIUM-ZIRCONIUM OXIDE CATALYSTS

The structure of supports (ceria and zirconia) for supported copper catalysts for the processes of hydrogen obtaining and purification is studied. The formation features of the structure of zirconia annealed at 300–1000°C are identified at different levels: the atomic one and the level of the structural arrangement of secondary particles when the formation of agglomerated block structures with large number of grain interfaces occurs. The formation process of copper oxides on different supports is studied.

Effect of surfactants on the structure and texture characteristics of aluminum oxide

The effect of surfactants (polyvinyl alcohol and cetyltrimethylammonium bromide), which were introduced at the aluminum hydroxide synthesis stage, on the structure and texture characteristics of aluminum oxide was studied by a set of physicochemical techniques. The introduction of the above surfactants did not cause considerable changes in the thermal transformations of aluminum hydroxides, but it affected the genesis of the formed carbon. An analysis of the diffuse reflectance spectra and electron micrographs indicated that the aluminum oxide obtained in the presence of polyvinyl alcohol and calcined at 300°C was covered with polyene-type coke. An increase in the treatment temperature to 550°C led to the formation of condensed aromatic coke; in this case, the specific surface area of the sample increased from 125 to 500 m2/g. The samples calcined at 550°C were γ-Al2O3 with a unit cell parameter of 7.933 Å and a crystallite size of no more than 30–40 Å. The pore size distribution was bimodal, with maximums at 35–65 and 380–415 Å, regardless of treatment temperature.