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In this paper, structural features of the NiO-SiO2 nanocrystalline catalyst synthesized by the sol-gel method were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and differential dissolution (DD). The XRD pattern of NiO-SiO2 significantly differs from the "ideal" NiO pattern: the peaks of the NiO-like phase are asymmetric, especially the 111 diffraction peak. The NiO-SiO2 nanocrystalline catalyst was investigated by means of XRD simulations based on two approaches: conventional Rietveld analysis and statistical models of 1D disordered crystals. Through a direct simulation of XRD profiles, structural information is extracted from both the Bragg and diffuse scattering. XRD simulations showed that the asymmetry of all the diffraction peaks is due to the presence of two NiO-like oxides with different lattice constants and different average sizes: ~90 wt% of mixed Ni-Si oxide (Ni:Si = 0.14:0.86) with average crystallite sizes (D ~ 27.5 Å) and ~10 wt% of pure NiO (D ~ 50 Å). The high asymmetry of the 111 diffraction peak is due to the appearance of diffuse scattering caused by the inclusion of tetrahedral SiO2 layers between octahedral NiO layers. Such methods as TEM and DD were applied as independent criteria to prove the structural model, and the results obtained confirm the formation of mixed Ni-Si oxide. [ABSTRACT FROM AUTHOR]

Nanostructured powders xFe/nano-Al2O3 with the Fe loading of x = 0.0 – 5.0 wt% were obtained using laser vaporization by CO2 laser. XRF, XRD, HRTEM, PL and UV–Vis DRS techniques were employed to investigate physicochemical, structural and optical properties of the synthesized nanopowders with the average particle size of 9 nm. Nanopowders xFe/nano-Al2O3 as model catalysts were tested in isobutane dehydrogenation reaction. The results obtained were compared with similar data for the xFe/γPb-Al2O3 systems synthesized by the conventional sol–gel method. According to XRD and UV–Vis DRS data, in the series of xFe/nano-Al2O3 samples a great part of Fe3+ ions is in the disordered environment of subsurface layers of Al2O3 nanocrystallites, predominantly in the tetrahedral coordination. In distinction to samples of the xFe/γPb-Al2O3 series, in the case of nanostructured xFe/nano-Al2O3 powders the formation of Fe2O3 phase does not occur at any concentrations of iron or conditions of testing. The analysis of the PL spectra of xFe/nano-Al2O3 powders also showed the presence of surface sites of Fe3+ ions, which were not detected for xFe/γPb-Al2O3. Catalytic testing of the xFe/nano-Al2O3 series samples in isobutane dehydrogenation revealed the formation of the iron active sites that ensure catalytic activity of the samples. Differences in the catalytic properties of FeOx/Al2O3 samples obtained by the sol–gel method and laser vaporization are related to different states of Fe3+ ions. Thus, the xFe/nano-Al2O3 nanopowders, in contrast to xFe/γPb-Al2O3, contain a large amount of active Fe3+ sites. These sites, being involved in the dehydrogenation reaction, are present predominantly on the surface of the nanopowders. [ABSTRACT FROM AUTHOR]

The nanoscale Co–Mg–O oxide sample (15 wt% in terms of Co 3 O 4) was prepared from the corresponding xerogel synthesized by the modified sol-gel method. The hydrolysis of as-prepared Mg(OCH 3) 2 was carried out using the aqueous solution of Co(NO 3) 2 precursor. The CoO x nanocrystallites of about 10–20 nm in size were shown to be uniformly distributed within the MgO matrix. The reduction of Co–Mg–O in H 2 flow was found to proceed in two separate stages within the temperature ranges of 200–350 °C and 350–600 °C. The prepared binary Co–Mg–O system was demonstrated to possess completely reproducible reduction behavior in the consecutive reduction/reoxidation cycles. The phase composition of the sample exposed to both the reducing and oxidative environment was followed by an in situ X-ray diffraction analysis performed at temperatures of 25, 300, 500 and 700 °C. The determined lattice parameters for MgO (a = 4.219 Å) and Co 3 O 4 (a = 8.110 Å) were found to be slightly increased as compared with the values from Powder Diffraction File, so that the formation of joint non-stoichiometric (Mg 1-x Co x)O and (Co 3-x Mg x)O 4 phases was suggested. The strong chemical interaction of cobalt oxide with MgO matrix was also evidenced by the data of a diffuse reflectance UV–vis spectroscopy. Image 1 • The nanoscale Co–Mg–O oxide system was prepared by the modified sol-gel method. • CoO x species of 10–20 nm in size are uniformly distributed within the MgO matrix. • The prepared Co–Mg–O system possesses completely reproducible reduction behavior. • Strong interaction between Co and Mg oxides was proved by DR UV–vis spectroscopy. [ABSTRACT FROM AUTHOR]

Influence of composition and heterogenization to titania matrix of Pd-Zn nanoparticles has been studied in selective hydrogenation of the triple bond of 2-methyl-3-butyn-2-ol (MBY). Pd-Zn bimetallic nanoparticles with the various molar ratios Pd/Zn have been obtained by chemical reduction method. Composition- controlled sol-gel technique was employed to synthesize Pd-Zn/TiO 2 catalysts. The structure properties of the bimetallic catalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Computer modeling for XRD patterns was first used to identify the composition of Pd-Zn alloy and to determine the particle size. For the colloidal and embedded nanoparticles dependences of physicochemical and catalytic properties on composition are different being determined respectively by geometric and electronic effects. The addition of zinc with Pd/Zn ratio of 1 increased selectivity to alkene at 99% conversion from 92.9% for the Pd catalyst to 96.9% for bimetallic catalysts, which is mainly caused by alloy formation. [ABSTRACT FROM AUTHOR]

Two-component Fe Mg O oxide system was prepared via sol-gel technique. An aqueous solution of iron nitrate was used to hydrolyze the magnesium methoxide instead of distilled water. The iron loading in a final sample was 15 wt% with respect to Fe 2 O 3 . The method was shown to provide a uniform distribution of iron oxide within MgO matrix. The sample was characterized by means of a low-temperature nitrogen adsorption and scanning electron microscopy. Reduction behavior of the sample was studied in a temperature-programmed regime using hydrogen as a reducing agent. In order to follow the possible phase transformations, the sample was examined by an in situ X-ray diffraction analysis in both reductive and oxidative atmospheres within the temperature range of 25–700 °C. It was found that after the first cycle of reduction/re-oxidation, the sample stabilizes in a novel state, and hydrogen uptake profiles of further cycles of reductive/oxidative treatment become completely reproducible. According to X-ray diffraction data, the sample consists of small particles (9 nm) of Fe 3 O 4 phase well-dispersed within the structure of nanocrystalline MgO. [ABSTRACT FROM AUTHOR]