D. I. Kochubei

Activity of Rh/TiO2 catalysts in NaBH4 hydrolysis: The effect of the interaction between RhCl3 and the anatase surface during heat treatment

The reaction properties of Rh/TiO2 sodium tetrahydroborate hydrolysis catalysts reduced directly in the reaction medium depend on the temperature at which they were calcined. Raising the calcination temperature to 300°C enhances the activity of the Rh/TiO2 catalysts. Using diffuse reflectance electronic spectroscopy, photoacoustic IR spectroscopy, and chemical and thermal analyses, it is demonstrated that, as RhCl3 is supported on TiO2 (anatase), the active-component precursor interacts strongly with the support surface. The degree of this interaction increases as the calcination temperature is raised. TEM, EXAFS, and XANES data have demonstrated that the composition and structure of the rhodium complexes that form on the titanium dioxide surface during different heat treatments later determine the state of the supported rhodium particles forming in the sodium tetrahydroborate reaction medium.

(CuO-CeO2)/glass cloth catalysts for selective CO oxidation in the presence of H2: The effect of the nature of the fuel component used in their surface self-propagating high-temperature synthesis on their properties

The potential of surface self-propagating high-temperature synthesis (SSHS) for obtaining (CuO-CeO2)/glass cloth catalysts is demonstrated. The dependence of the structural and catalytic properties of the catalysts on their preparation conditions (nature of the fuel component) is considered. X-ray diffraction, electron microscopy, and EXAFS data suggest that the short-term action of high temperature in the SSHS leads to the complete decomposition of the precursors and has an effect on the distribution of the resulting phases. According to H2 TPR and XPS data, the degree of dispersion of CuO and the electronic state of the reacting CuO and CeO2 phases depend on the choice of fuel. This is likely due to fuels varying in the amount of heat released in their combustion. The degree of dispersion of CuO and the total contribution from Cu1+ and Ce4+ to the electronic state of the active component increase as the standard enthalpy of combustion increases in the urea < glycerol < citric acid order. This leads to an increase in the catalytic activity of the (CuO-CeO2)/glass cloth system in selective CO oxidation.

Nanocomposites Based Upon Alumina and Zirconia Pillared Clays Loaded with Transition Metal Cations and Clusters of Precious Metals: Synthesis, Properties and Catalysis of NO x Selective Reduction by Hydrocarbons

Thermally stable alumina and zirconia pillared clays loaded with copper and cobalt cations and silver nanoparticles were synthesized. The structural and surface features of these nanosystems were studied and compared with those of bulk analogs -partially stabilized zirconias and γ-alumina loaded with the same active components. Specificity of the catalytic properties of nanocomposites in the reactions of nitrogen oxides reduction by propane, propylene and decane in the excess of oxygen appears to be determined both by the degree of interaction between pillars and active components and the type of reducing agent.

Specificity of the Local Structure of Nanocrystalline Doped Ceria Solid Electrolytes

This work presents results of studies of the structural features of nanocrystalline doped Ce1xMexO2-y samples (Me = Sm, Bi, Gd; x = 0-0.5) prepared via the polymerised precursor (Pechini) route by using a combination of diffraction (XRD, TEM, WAXS on SR) and spectroscopic (EXAFS, Raman, FTIRS of lattice modes, XPS, SIMS) methods.

Structure and Thiophene Hydrodesulfurization Activity of MoS2/Al2O3 Catalysts

It was found that, in MoS2/Al2O3 catalysts prepared by exfoliation, the structure of MoS2 is strongly distorted. The catalytic activities of these catalysts and traditionally prepared catalysts toward the hydrodesulfurization of thiophene were compared. It was established that the stacking dimension of MoS2 in the catalysts prepared by exfoliation was 200 Å, whereas it was 20 Å in a standard catalyst. It was demonstrated that, although the number of molybdenum atoms in the edge plane per gram of MoS2 in the catalysts prepared by exfoliation was 10 times smaller than that in the standard catalyst, the activity of these catalysts was close to the activity of the standard catalyst. On this basis, it was suggested that the hydrodesulfurization of thiophene can occur on the basal plane of MoS2 that has a defect-free structure with a distorted environment of molybdenum.

The microstructure and properties of framework zirconium phosphates based nanocomposites : catalysts of alkane isomerization

Abstract Nanocomposites based upon framework zirconium phosphates with supported WO3, MoO3 and Pt nanoparticles were synthesized via the incipient wetness impregnation of high-surface-area mesoporous phosphate samples with water solutions of corresponding salts followed by drying and calcination. The structure and surface properties of nanocomposites were studied by using combination of structural and spectral methods. Due to a strong interaction between supports and supported species, the structure of the latter differs considerably from that of the bulk phases. Surface acid centers typical for zirconium phosphates disappear suggesting their participation in bonding nanoparticles of promoters. Instead, new types of strong acid sites associated with tungsten oxide clusters emerge. The effect of these promoters on performance of zirconium phosphates in the reaction of pentane and hexane isomerization is considered.

Intermetallic hydrides [TiFe0.95Zr0.03Mo0.02]Hx (0 ≤ x ≤ 2): The nature of the phase responsible for the selective reduction of CO2 1

Based on data obtained by X-ray diffraction and Mössbauer spectroscopy, it was concluded that tetragonal distortions appeared in the structure of cubic TiFe upon doping with Zr and Mo atoms and the intermetallide TiFe0.95Zr0.03Mo0.02 is formed, which can absorb ∼1 mol of H2 per mole of the intermetallide. The heating of the hydrogen-saturated intermetallide in Ar to 185°C released ∼0.80–0.82 mol of H2 per mole of the intermetallide. This hydrogen was the constituent of cubic [TiFe0.95Zr0.03Mo0.02]H1.93 and orthorhombic [TiFe0.95Zr0.03Mo0.02]H, which are the hydride phases of the parent [TiFe0.95Zr0.03Mo0.02]H2 hydride. The remainder of the hydrogen (∼0.18 mol per mole of the intermetallide), which was released only at 700–920°C, entered the γ solution of nonstoichiometric TiH2 – x. EXAFS and XANES data indicate an increase in the signal intensity in the Ti–Ti direction and a decrease in electron density on titanium atoms for [TiFe0.95Zr0.03Mo0.02]H0.36. These results were interpreted in terms of a scheme according to which hydrogen atoms in an interstitial solid solution are arranged closer to titanium atoms and coordinated to them. It was found that a phase of [TiFe0.95Zr0.03Mo0.02]H0.36, which is a constituent of the γ solution, is responsible for the selective reduction of CO2 to CO (90–98%).

Genesis of the active-component precursor in the synthesis of Pt/Al2O3 catalysts: II. Synthesis of platinum hydroxo complexes on the alumina surface as precursors of the active component of Pt/Al2O3 catalysts

The thermal hydrolysis of chloroplatinate adsorbed on γ-Al2O3 is a possible approach to the synthesis of surface platinum hydroxo complexes as precursors to the active component of supported platinum catalysts. It is demonstrated by EXAFS and diffuse reflectance spectroscopy that the surface chloro complexes undergo deep hydrolysis under hydrothermal conditions at various processing times and temperatures. The average oxygen coordination number of platinum in these complexes is as large as 4.5. According to gradient elution data obtained using both the competitive replacement of adsorbed complex anions and variation of the charged state of the oxide surface, the resulting hydrolyzed precursor differs from the conventional chloride precursor in the nature of binding to the surface and interacts with alumina via a coordination mechanism.

Structure Specificity of Nanocrystalline Praseodymia Doped Ceria

The features of the structure of nanorystalline Ce 1-x Pr x O 2-y system (0 ≤ × ≤ 0.5) prepared via a complex polymerized precursor (Pechini) route have been elucidated by using a combination of spectroscopic (XANES, XPS) and structural (TEM, neutron diffraction) methods. Within the studied range of composition, the structure of all samples air annealed at 500 °C corresponds to single-phase fluorite-like solid solution. The relative content of Pr 3+ both in the bulk and in the surface layer appears to be as high as 20–50%. The Rietveld refinement revealed non-monotonous variation of structural parameters (lattice parameter, domain size, microstrain density, Ce-O and O-O distances) and residual lattice hydroxyls concentration with Pr content. Clustering of defects along with variation of the mean Pr cation radius/charge state and disordering of the surface layer/ domain boundaries appear to be responsible for the observed features.

EFFECT OF LANTHANUM MANGANITE MODIFICATION BY CALCIUM AND/OR FLUORINE ON THE BONDING STRENGTH, MOBILITY AND REACTIVITY OF THE LATTICE AND SURFACE OXYGEN

Ca and/or F-modified samples of LaMnO 3 have been prepared by the Pechini method. The bulk structure of samples was characterized by TEM, EXAFS and XRD, while the surface composition was studied by SIMS. Thermal analysis, O 2 TPD, H 2 TPR and isothermal pulse/flow samples reduction by CO were applied to characterize the accessible surface/bulk oxygen mobility and reactivity. A reasonable description of the experimental energetic spectrum of the surface oxygen for various types of regular and defect surface sites on the perovskite faces was achieved by using semiempirical Interacting Bonds Method in the slab approximation with a due regard for the surface face termination and relaxation. Fluorine was found to decrease the surface coverage by reactive weakly bound oxygen forms while increasing the bulk oxygen excess and mobility. Calcium generated reactive weakly bound oxygen forms while decreasing the oxygen excess in the lattice and converting the regular M-O oxygen forms into the bridging ones through migration to the surface.