Construction of the model radial distribution curves with regard to the features of X-ray diffraction experiment

A method to construct model radial distribution functions (RDFs) from the already known structural data is described. The method includes the procedures to calculate termination ripples that always appear on the experimental RDF because of the bounds of the integration limits in the Fourier transformation of the X-ray scattering curve. The introduction of this procedure increases the accuracy of the comparative RDF method used to elucidate the phase composition of nanodispersed materials and to determine the features of the local structure of the phases as compared to their well crystallized analogues. Cerium dioxide samples with different dispersion exemplify the applicability of this method to determine the features of the local structure.     

1H NMR Study of Zeolite Water Structure and Broensted Acid Centers in Chabazite

The disordered structure of absorbed water in a highly porous zeolite chabazite Ca₂[Al₄Si₈O₂₄]·nH₂O (2 ≤ n ≤ 12.8) is studied from motionally narrowed ¹H nuclear magnetic resonance spectra at room temperature. Concentration phase transitions were observed at n ≈ 8.3 and n ≈ 10.2. The transitions are accompanied by displacement of Ca²⁺ ions and variation of the Broensted acid centers at inner surface of zeolite pores.     

Effect of violations of the structure and layer packing on the diffraction pattern of gibbsite and bayerite

Using the simulation method for the diffraction patterns of one-dimensionally disordered materials, the effect of different violations in the layered structure of aluminum trihydroxides (gibbsite and bayerite) on their diffraction patterns is analyzed. The features of the diffraction patterns of a disordered gibbsite sample obtained by intercalation-deintercalation of lithium salts are considered.     

Nickel Reinforced Catalysts Over a Heat-Exchanging Surface for Benzene Hydrogenation

X-ray technique, mercury porosimetry and electron microscopy were used to study the regularities of formation of porous metallic nickel-aluminium supports reinforced with a steel grid and distributed over a heat-exchanging surface, and of nickel catalysts supported on them. Such catalysts are active in gas phase benzene hydrogenation and also possess high heat conductivity.     

Structure and stability of clusters on metal surfaces

Small clusters of 3d metals Ni/Ni(001), Cu/Cu(001), 4d-Pd/Pd(001), Ag/Ag(001), 5d-Pt/Pt(001), and Au/Au(001) are investigated by semiempirical methods using multiparticle interatomic interaction potentials. It is shown that the same magic numbers (4, 6, and 9) are characteristic for all metals indicated; these numbers are determined by the symmetry characteristics of the clusters, related to the morphology of the fcc (001) substrate. It is shown for Pt/Pt(111) that small clusters of seven, ten, and more atoms are stable for the fcc (111) surface. This confirms that the magic numbers are associated with the symmetry of the clusters. Fiz. Tverd. Tela (St. Petersburg) 41, 1329–1334 (July 1999)     

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.     

Copper Reinforced Catalysts on a Heat-Exchange Surface for Nitrobenzene Hydrogenation to Aniline

The methods of X-ray diffraction, mercury porosimetry, and electron microscopy are used to study the texture and phase composition of nickel–aluminum supports obtained by the sintering of nickel and aluminum powders reinforced by a stainless steel grid and distributed over a heat-exchange surface, as well as copper catalysts for nitrobenzene hydrogenation to aniline supported on these materials. The catalysts prepared using this procedure are active in this reaction and make it possible to carry it out without substantial overheatings of the surface.     

Method for determining the positions of sulfate groups in sulfated carbohydrates

A new method of determining positions of the sulfate groups in sulfated carbohydrate-containing compounds is described which consists in the direct replacement of the sulfate groups by formyl groups through the action on these compounds of chloromethylenediethylammonium chloride in dimethyl formamide. Subsequent chromatomass spectrometry permits the determination of the positions of the formyl groups and, consequently, of the initial sulfate groups. The replacement of sulfate groups by formyl groups under these conditions takes place both in sulfated monomeric and polymeric compounds. The stability of the formyl group in peracetylated monoformates under the conditions of acetolysis has been shown, and in the case of polymeric compounds this permits the determination of the positions of formyl and sulfate groups. Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 607–612, September–October, 1980.     

Manganese minerals from the Miassovo freshwater lake: Composition and structure

The mineral, chemical, and trace element composition and the microstructures of manganese minerals in bottom nodules and crusts collected from the Bolshoe Miassovo freshwater lake (South Urals) were studied. Freshwater manganese species were shown to have more diversified mineral compositions than in marine species. In addition to (9.6- and 7.2 Å) layered manganese mineral structures, various manganese-containing carbonates were frequently present in lacustrine samples. As opposed to marine samples, lacustrine samples were poor in trace elements, in particular rare-earth elements, but have higher contents of Sr, As, Ti, and V. A structural analysis of lacustrine manganese species showed their biomorphic nature, which manifested itself as organic bacterial species ranging from spherulitic to filamentary ones.