Structural, magnetic, and optical properties of nickel oxide supported on .eta.- and .gamma.-aluminas

Morphology-controlled synthesis of NiO films: the role of the precursor and the effect of the substrate nature on the films' structural/optical properties

NiO thin films were grown through MOCVD on quartz and LaAlO₃ (001) single crystal substrates. The relationship between the precursor/substrate nature and film properties allowed to define the best conditions to grow good quality NiO films.

Structural and optical characterization of metal tungstates (MWO4; M=Ni, Ba, Bi) synthesized by a sucrose-templated method

Background

Metal tungstates have attracted much attention due to their interesting structural and photoluminescence properties. Depending on the size of the bivalent cation present, the metal tungstates will adopt structures with different phases. In this work, three different phases of metal tungstates MWO₄ (M= Ba, Ni and Bi) were synthesized via the sucrose templated method.

Results

The powders of BaWO₄ (tetragonal), NiWO₄ (monoclinic) and Bi₂WO₆ (orthorhombic) formed after calcination temperatures of 750, 650 and 600°C for 4 h respectively are found to be crystalline and exist in their pure phase. Based on Scherrer estimation, their crystallite size are of nanosized. BET results showed NiWO₄ has the highest surface area. BaWO₄ exhibited less Raman vibrations than the NiWO₄ because of the increased lattice symmetry but Bi₂WO₆ showed almost the same Raman vibrations as BaWO₄. From the UV-vis spectra, the band gap transition of the metal tungstates are of the order of BaWO₄ > Bi₂WO₆ > NiWO₄. Broad blue-green emission peaks were detected in photoluminescence spectra and the results showed the great dependence on morphology, crystallinity and size of the metal tungstates.

Conclusion

Three different phases of metal tungstates of BaWO₄ (scheelite), NiWO₄ (wolframite) and Bi₂WO₆ (perovskite layer) in their pure phase were successfully prepared by the simple and economical sucrose-templated method. The highest surface area is exhibited by NiWO₄ while largest band gap is shown by BaWO₄. These materials showed promising optical properties.

The Feasibility of Ni-Alumina Catalysts in Oxidative Dehydrogenation of Ethane

The contribution deals with the development on the efficient Ni-alumina catalyst for the oxidative dehydrogenation (ODH) of ethane to ethene. The performance of Ni-alumina catalysts with varying nickel loadings and with thermal pretreatment was studied. We contribute to the understanding of the relationship between the activity of nickel species in ODH of ethane and its distribution. To analyze this effect, Ni-alumina catalysts were analyzed by UV-VIS spectroscopy, and H2-TPR profile. Ni-alumina catalysts were highly active and selective (ca. 80%) in the ODH of ethane. The catalysts contained both tetrahedral and octahedral nickel species, suggesting that nickel aluminate represented a partial spinel, where Ni(II) ions occupy both octahedral and tetrahedral sites of the oxygen lattice. It was suggested that the octahedral nickel species were more active than the tetrahedral ones.