A. A. Veligzhanin

Alumina-platinum catalyst in the reductive dehydration of ethanol and diethyl ether to alkanes

The reductive dehydration of ethanol and diethyl ether selectively occurs with the formation of alkanes to C10+ on an AP-64 alumina-platinum catalyst (0.6 wt % Pt/γ-Al2O3) after its reduction with hydrogen at 450°C for 12 h in Ar. It was found that one of the main reaction paths is the insertion of ethylene into substrate intermediates with the predominant formation of normal alkanes. It was found by XAFS spectroscopy that Pt2Al intermetallide particles were formed along with platinum metal clusters after long reduction. The ammonia TPD data indicated a change in the acid properties of the surface after the long reduction of the catalyst: the concentration of medium-strength surface aprotic acid sites increased by a factor of 2. It was found that the interaction of aprotic sites with water vapor resulted in the formation of strong proton acid sites. It is likely that these latter are responsible for the growth of a carbon skeleton in the course of alkane formation from ethanol.

Energy-transfer luminescence of a zinc oxide/ytterbium oxide nanocomposite

A newly structured nanocomposite material based on nanocrystalline ZnO/Yb2O3 has been prepared by thermal decomposition of Yb-doped zinc carbonate hydroxide. Transmission electron microscopy has revealed that the prepared nanopowder consists of ZnO nanocrystals of about 50 to 100 nm size decorated by attached smaller Yb2O3 nanocrystals of about 10 to 15 nm size. X-Ray absorption spectroscopy, in particular XANES and EXAFS, indicate the charge of Yb ions equals to +3 and their coordination is oxygen octahedral with the Yb–O and Yb–Yb interatomic distances the same as in bulk Yb2O3. Photoluminescence spectroscopy unambiguously proves an efficient excitation energy transfer from the ZnO nanocrystals to the Yb3+ ions. The energy transfer from the ZnO nanocrystals (absorption range from 250 to 400 nm) to the Yb3+ ions (emission range from 950 to 1100 nm) has been explained by a model, which considers the quantum cutting effect. The prepared nanocomposite is promising for application as a down-conversion layer for enhanced solar cells.

Trends in formation of the nanocrystalline structure and cationic ordering in the Dy2O3-HfO2 (1: 1) system

Evolution of the nanocrystalline structure of the complex oxide Dy2HfO5 in the course of thermal annealing at temperatures to 1600°C has been studied by a combination of X-ray and synchrotron methods, including traditional and anomalous X-ray diffraction, PDF, EXAFS, and SAXS. The changes in crystallite size upon annealing of the as-synthesized amorphous precursor have been analyzed in detail. The systematic distortions of a fluorite-type perfect crystal structure (space group

Structure and properties of precipitation-hardening ceramic Ti-Zr-C and Ti-Ta-C materials

Fm\bar 3m

Crystal structure and electronic states of Co and Gd ions in a Gd0.4Sr0.6CoO2.85 single crystal

) related to the nonequivalence of the local environment of the Dy and Hf cations but not resulting in formation of a pyrochlore-type cationordered structure in this system have been examined.

Mechanisms of formation of near-edge fine structure of K X-ray absorption spectra of metallic Cu, Ni, Co (HCP and FCC phases), and Cr

Abstract The cerium effective valence was investigated by means of CeL3-XANES spectroscopy in some intermediate valence Ce-based systems with different magnetic ordering mechanisms: CeNi doped with Nd, Pr and Gd in the temperature range 5–300 K, and Ce3Fe17–xMnx intermetallics. The dependences obtained are considered within the frames of generally accepted mechanisms of rare-earth ions intermediate valence states. Possible correlations between the cerium effective valence and the magnetic properties of compounds are also noted.

Studying processes of crystallization and cation ordering in Eu2Hf2O7

Precipitation hardening alloys of the Ti-Ta-C and Ti-Zr-C systems produced by self-propagating high-temperature synthesis (SHS) have been studied. Optimum compositions of the alloys and heat-treatment conditions, under which the decomposition of supersaturated solid solution accompanied by the precipitation of fine particles both inside carbide grains and at their boundaries occurs, have been determined. The precipitation hardening ceramic materials exhibit high hardness (∼15–23 GPa) and heat resistance (the mass increase of the Ti-9.4% Ta-10.5% C alloy is less than 8 g/m2 during a 50-h exposure in air at 800°C) and can be recommended for the application as materials for deposited multifunctional coatings, high-temperature contacts, evaporation crucibles, and abrasion-resistive tools.

Structural features of green cobalt(III) hydroxide

Single crystals of ludwigite Ni2MnBO5 were synthesized by flux growth technique. The detailed structural and magnetic characterizations of the synthesized samples have been carried out. The cations composition of the studied crystal was determined using X-ray diffraction and EXAFS technique, the resulting composition is differ from the content of the initial Mn2O3 - CuO components of flux. Magnetic susceptibility measurements and the calculations of the exchange integrals in frameworks of indirect coupling model revealed strong antiferromagnetic interactions and appearance of magnetic ordering phase at the temperature T=85 K. The hypothesis of the existence of several magnetic subsystems was supposed.