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.     

Isotope exchange of molecular nitrogen on barium nitride

The activity of barium nitride in the isotope exchange of nitrogen is 2–3 orders of magnitude higher than that of Fe and Ru. In the temperature range from 373 to 673 K the activation energy of exchange is 40 kJ/mol.

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2–3 Fe Ru. 373–673 40 /.

     

Proton mobility in complex [RhL4Cl2]HSO4 · nH2SO4 · mH2O salts (L = Py, γ-picoline)

The method of deposition from solutions was used to synthesize [RhL ₄Cl₂]HSO₄ · nH₂SO₄ · mH₂O complex salts (L = Py, γ-picoline), n ≈ 0.5−0.6, m ≈ 5−6. According to the data of X-ray phase analysis, the crystal structure of these salts is formed by layers of cations separated by layers consisting of anions molecules of sulfuric acid and water connected through a system of hydrogen bonds. Calorimetric methods were used to study phase transitions and the range of thermal stability of salts. The method of ¹H NMR spectroscopy discovered that protons within the {HSO₄⁻ · nH₂SO₄ · mH₂O} subsystem featured enhanced conductivity. Conductivity studies showed that trans-[RhL ₄Cl₂]HSO₄ · nH₂SO₄ · mH₂O samples had high proton conductivity.     

The properties of 4′-N,N-dimethylaminoflavonol in the ground and excited states

The mechanism of protonation of 4-N,N-dimethylaminoflavonol and the structure of its protolytic forms in the ground and excited states were studied by electron absorption and fluorescence (steady-state and time-resolved) spectroscopy and with the use of the RM1 quantum-chemical method. A comparison of equilibrium constants and the theoretical enthalpies of formation showed that excitation should be accompanied by the inversion of the basicity of the electron acceptor groups of this compound and, as a consequence, changes in the structure of its monocationic form. An analysis of the spectral parameters of the protolytic 4-N,N-dimethylaminoflavonol forms, however, showed that their structure and the sequence of protonation in the excited state were the same as in the ground state. Changes in the structure of the monocation in the excited state were not observed because of the fast radiationless deactivation of this form and the occurrence of excited state intramolecular proton transfer in aprotic solvents.     

The state of the components in Cu-CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> catalysts for selective oxidation of CO

Cu-CeO₂ catalysts deposited on a commercial ZrO₂ support have been investigated. The catalyst composition has been optimized: the optimum copper content was found to be 5–10 wt % at a cerium oxide content of 23 wt %. The catalysts were investigated by X-ray diffraction analysis and X-ray photoelectron spectroscopy. According to the X-ray diffraction data, the support consists of the monoclinic ZrO₂ phase and cubic CeO₂ phase with an enlarged lattice parameter, while the catalysts contain CuO. The X-ray photoelectron data indicate the presence of a highly dispersed CuO₂ phase interacting with cerium oxide and zirconia on the surface of the catalyst having the optimum copper content.     

Zirconium-Containing Compositions with a Component Ratio Characteristic of the Garnet Structure: Physicochemical and Catalytic Properties

The possibility for the formation of garnet structures in the Mn–Fe–Zr–O and Ca–Sm–Zr–O systems obtained by the precipitation of the corresponding salts is studied. It is shown that, in the Mn–Fe–Zr–O system, garnet is crystallized at 860–920°C, for which probable cation distribution is estimated to be {Zr_2.5 ⁴⁺Mn_0.5 ²⁺}[Mn₂ ²⁺](Fe_2.5 ³⁺Mn_0.5 ³⁺)O₁₂. In the Ca–Sm–Zr–O system, the perovskite CaZrO₃, pyrochlore Sm₂Zr₂O₇, and CaO are formed at 900–1200°C, but compounds with garnet structures are not found. The reported systems are characterized by surface areas of 300–450 m²/g at 450°C, and they have the polydisperse distribution of pores over sizes. The introduction of surfactants at the stage of component mixing enables an increase in the overall pore volume and mechanical strength of these systems. The Mn–Fe–Zr and Ca–Sm–Zr compositions are active catalysts for the complete oxidation of hydrocarbons.     

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.