Ya. V. Zubavichus

Layered compounds assembled from molybdenum disulfide single-layers and alkylammonium cations

Abstract Intercalation compounds A x MoS 2 have been obtained by restacking aqueous MoS 2 dispersions in the presence of A-alkylammonium cations (A=R 4 N + or R(CH 3 ) 3 N + ). Varying the experimental conditions, the negative charge of the MoS 2 single-layers in the dispersions can be modified, which allows to control the content and packing geometry of the A guest layers in the resulting intercalation compounds. The value of the negative charge kept on the MoS 2 host layers of the intercalation compounds determines the degree of in-layer distortion of their Mo sublattice.

Short- and long-range order balance in nanocrystalline Gd2Zr2O7 powders with a fluorite-pyrochlore structure

A series of nanocrystalline Gd2Zr2O7 powders has been studied using a combination of X-ray diffraction and X-ray spectroscopy with synchrotron radiation. It has been shown that isothermal annealing of an X-ray amorphous mixed hydroxide first leads to the formation of an oxide nanomaterial with a defect fluorite structure and clearly pronounced nonequivalence of the local environment of the Gd3+ and Zr4+ ions. Increasing heat treatment temperature results in initiation and growth of nanodomains with pyrochlore-type superstructure ordering of cations inside bulkier crystallites of defect fluorite. To adequately describe the evolution of the real nanocrystalline structure of gadolinium zirconate, a combination of X-ray structural methods sensitive to the averaged crystal structure and local atomic structure should be used.

Cocatalytic effect of palladium and zinc in the condensation of alcohol carbon backbones into hydrocarbons

The results of the direct conversion of ethanol and its mixture with glycerol into a C4–C10+ alkane and olefin fraction in the presence of Pd-, Zn-, and Pd-Zn-containing catalysts, which were prepared by supporting homo- and heterometallic acetate complexes onto the surface of γ-Al2O3, are reported. It was found that, in the presence of mono- and bicomponent Pd-ZnO (Pd; ZnO)/γ-Al2O3 systems, selectivity in the formation of alkanes, olefins, or their mixtures in the target fraction can be controlled as a result of the cocatalytic effect of active components that are responsible for the catalyst activity in condensation and hydrogenation reactions. The structures of the active components were studied and the genesis of the catalytic systems was characterized using XAFS, XPS, and XRD analysis. It was found that the addition of glycerol considerably increased the yield of the target hydrocarbon fraction.

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.

Lanthanide effect on the formation and evolution of nanocrystalline structures in Ln2Hf2O7 compounds (Ln = Sm-Dy)

X-ray diffraction with synchrotron radiation has been used for comparative analysis of crystal structure evolution in Ln2Hf2O7 (Ln = Sm-Dy) complex oxides with a fluorite-pyrochlore structure, synthesized by isothermal annealing of mixed hydroxides. It has been shown that heat treatment of the precursor in the temperature range 600–700°C initiates the formation of nanocrystallites with a fluorite structure. Long-range cationic ordering of the pyrochlore type appears in Ln2Hf2O7 (Ln = Sm-Tb) samples once a definite crystal size has been achieved at temperatures ≥1200°C. In Dy2Hf2O7 samples, a defect fluorite structure persists in the entire range of heat-treatment temperatures.

Formation of Nanocrystalline Structures in the Ln 2 O 3 -MO 2 Systems (Ln = Gd, Dy; M = Zr, Hf)

The formation of (Ln3+)2(M4+)2O7 (Ln = Gd, Dy; M = Zr, Hf) nanocrystallites obtained by annealing mixed hydroxides LnM(OH)7 · nH2O (precursors) synthesized by coprecipitation has been studied by synchronous thermal analysis, X-ray diffraction (normal and anomalous diffraction of synchrotron radiation), and EXAFS. In the systems under consideration, heat treatment of the X-ray amorphous precursors leads to their dehydration, and at 600–700°C, nanocrystallites with an fcc structure of disordered fluorite start forming. A further increase in temperature is accompanied by crystallite growth (CDD) and considerable change in the local structure of the heat-treated compounds. The crystallization enthalpies and activation energies have been determined.

Structural diagnostics of functional nanomaterials with the use of X-ray synchrotron radiation

An experimental facility for the complex X-ray diagnostics of functional nanomaterials (Structural Materials Science beamline) installed at the Kurchatov Synchrotron Radiation Center is presented. The key structural elements of the beamline are described. The research capabilities of the facility are demonstrated by the example of transparent magnets and glasses with magnetic nanoparticles, which are promising for the design of magneto-optical data storage and spintronics devices.

New ferro-and antiferromagnetic complexes of tridentate azomethines with copper

Tridentate azomethine ligands with N2O4 and N3donor atoms and their copper complexes were synthesized and characterized. The dimeric structure of copper(II) chelates was confirmed by EXAFS studies. Complexes based on 2-tosylaminobenzaldehyde azomethines tend to undergo ferromagnetic exchange, whereas similar salicylaldehyde derivatives have antiferromagnetic exchange.

From single-layer dispersions of molybdenum disulfide towards ternary metal sulfides: incorporating copper and silver into a MoS2 matrix

Abstract Interaction of MoS 2 single-layer dispersions with Cu(II) or Ag(I) salts results in formation of ternary metal sulfides. Upon this, reduction of Cu(II) to Cu(I) and reduction of part of Ag(I) to Ag(0) occur. The structural features of the compounds are discussed on the basis of XRD, electron diffraction, EXAFS and XPS data.

Characteristic features of the nanocrystalline structure formation in Ln2Hf2O7 (Ln = Gd, Dy) compounds

A combination of modern locally sensitive methods of structure analysis based on the interaction of synchrotron radiation with condensed matter was used to study the formation and evolution of crystal structures, change in the size of crystallites, the type and degree of cationic ordering, and features of the local atomic structures of compounds Ln2Hf2O7 (Ln = Gd, Dy) prepared by heat treatment of X-ray amorphous precursors.