T. V. Larina

Laser-induced luminescence of model Fe/Al2O3 and Cr/Al2O3 catalysts

The laser-induced luminescence of Cr3+ impurity ions in model Fe/Al2O3 and Cr/Al2O3 catalysts with different calcination temperatures was studied. It was found that an additional luminescence band at 770 nm appeared in the luminescence spectra of low-temperature samples as a result of the interaction of octahedrally coordinated Cr3+ ions with Fe3+ impurity ions. In the θ-Al2O3 phase with a concentration of Cr3+ ions higher than 0.1 wt %, the interaction of the Cr3+-Cr3+ ion pairs in the immediate surroundings resulted in the appearance of Nθ lines due to the splitting of Rθ lines. The differences of these lines from the Nα lines of α-Al2O3 were related to the individuality of the crystal lattice of the θ phase and the coordination of Cr3+ impurity ions in the immediate surroundings, which is different from that in the α phase. Based on the laser-induced luminescence spectroscopic data, it was found that regions with a local Cr3+ concentration higher than the average Cr3+ concentration in the bulk of a catalyst by one order of magnitude were formed in the α-Al2O3-Fe2O3 system with the bulk Fe and Cr concentrations of 2.5 and 0.04 wt %, respectively, which was calcined at 1220°C, as a result of the diffusion of chromium and iron ions.

Characterization of the nickel-amesite-chlorite-vermiculite system.

Synthetic TO (1 tetrahedral layer/1 octahedral layer) phylloaluminosilicates of Ni–Mg–Al with amesite (septechlorite) structure were synthesized and their evolution during calcination in inert and reducing media was studied. After treatment at 700–800 °C in hydrogen, the samples consisted of dispersed metallic nickel particles supported on TOT Mg-chlorite-vermiculite; none of the catalysts studied contained SiO2. The samples were stable in inert gas and hydrogen atmospheres at 850 °C, as well as in hydrogen plus steam at 20 bar and 650 °C. Thus, we consider Ni-containing amesite-like compounds to be suitable catalysts for the methane steam reforming process.

Physico-chemical study on the state of cobalt in a precipitated cobalt-aluminum oxide system

The evolution of Co–Al (1 ∶ 1) hydroxycarbonate with a hydrotalcite-like structure during its consequent calcination in an inert gas flow and reduction in H2 has been studied by means of X-ray diffraction, infrared spectroscopy, UV–VIS diffusive reflectance spectroscopy and magnetic susceptibility measurements. The oxidation of Co2+ species to Co3+ state during the calcination in the inert gas medium occurs simultaneously with the formation of a highly inverted anion-modified spinel-like structure. The samples reduced at 480°C and 620°C contain metallic cobalt particles. Ferromagnetic and paramagnetic contributions are distinguished and evaluated. The spontaneous magnetization of the sample reduced at 480°C increases monotonously with the temperature in the range of 78–300 K. The correlation of the results with earlier data on physico-chemical and catalytic properties has been discussed.

Formation of platinum sites on layered double hydroxide type basic supports: II. Effect of the nature of the interlayer anion of the layered aluminum-magnesium hydroxides on platinum binding and Pt/MgAlO x formation

The interaction of aqueous H2PtCl6 solutions with hydrotalcite-type aluminum-magnesium hydroxides differing in the nature of their interlayer anion is reported. In the case of CO32− as the interlayer anion, the introduction of the platinum(IV) chloro complex does exerts no significant effect on the structural properties of the support, on its thermal decomposition dynamics, and on the textural characteristics of the resulting oxide phase. The binding of the platinum complexes to “activated hydrotalcite” with interlayer OH− anions increases the interplanar spacing and enhances the thermal stability of the layered structure. This is accompanied by marked changes in textural characteristics of the material, leading to the formation of a nearly monodisperse mixed oxide phase. In the Pt/MgAlOx samples obtained by reductive treatment, a considerable proportion of platinum is in the form of planar particles, and this corroborates the hypothesis that the metal complex at the sorption stage is mainly localized in the interlayer space of this support. Platinum binds to the support as chloro complexes via rapid anion exchange, and these bound platinum species are characterized by a higher reduction temperature.

Nanoclusters as Precursors to (MoVW)5O14: In situ and chemical characterisation of the systems of a single phase oxidation catalyst

Abstract The ternary oxide (MoVW)5O14 is considered to be highly significant for catalytic, mild selective oxidation reactions. By using UV/Vis, ESR and 95Mo NMR spectroscopies the coordination chem-istry of the molybdate species in the precursor solutions was studied. This work has established that mixing the precursor solutions (ammonium hepta molybdate, ammonium meta tungstate and vanadyl oxalate) forms a polymeric network in which the vanadyl species act as a linker between the molybdate species. Addition of tungsten atoms significantly enhances the polymerisation proc-ess

Evolution of the structure of Co stevensite during its treatment in the air, inert gas flow and flowing hydrogen

Abstract Synthetic TOT (2 tetrahedron layers,1 octahedron layer) trioctahedral hydrosilicates (stevensites) of Zn, Mg, Co and Co-Zn were prepared by the deposition–precipitation technique. The evolution of both the structure and spectral properties of the silicates were studied during their treatment in various media. The position of the ν(OH) absorption band and the temperature of crystallization of the anhydrous silicate were found to be useful indicators of the cationic composition of stevensites. The data obtained are used to analyze and to review the earlier data on Co/SiO2 catalysts. It is concluded that the formation of Co stevensite occurs in the majority of cases when the pH of the maternal solution during the preparation of a catalyst is above four.

Effect of chromium content on the properties of a microspherical alumina-chromium catalyst for isobutane dehydrogenation prepared with the use of a centrifugal thermal activation product of gibbsite

The states of chromium in both promoted and unpromoted alumina-chromium catalysts with various chromium contents prepared with the use of a centrifugal thermal activation product of gibbsite were studied in detail. The presence of five chromium species was found in the catalysts of this type: two Cr6+ and three Cr3+ species. The concentration of each particular chromium species depends on the total chromium content of the catalyst. Based on the experimental data, we hypothesized that highly disperse Cr3+ particles, the formation of which was completed at a chromium content of ∼7–9 wt %, are responsible for the catalytic activity of alumina-chromium samples in the reaction of isobutane dehydrogenation.

The state of Cu2+ ions in concentrated aqueous ammonia solutions of copper nitrate

Stabilization of Cu2+ ions in concentrated aqueous ammonia solutions of copper nitrate in a wide range of ammonium ion concentrations has been studied by EPR and electronic absorption spectroscopy. Three types of Cu2+ associates with different types of orbital ordering have been identified. The ammonium ion concentration in a solution has a decisive effect on the type of orbital ordering of Cu2+ ions in associates. In all cases, Cu2+ ordering in associates is caused by the existence of bridging OH groups in the axial and equatorial positions of [Cu(NH3)n(H2O)6 − n]2+ complexes (n < 6). At a high concentration of ammonium ions, weakly bound associates of tetramminecopper with the

Cobalt-containing catalysts supported by synthetic Zn- and Mg-stevensites and their performance in the Fischer–Tropsch synthesis

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