Samples of model CuO, NiO and CuO–NiO catalysts were synthesized by calcination of individual copper and nickel hydrated nitrates, and according to a technique of their co-calcination. They were ...characterized by XRD, Raman spectroscopy, TEM and XPS. Solid solutions of Cu2+ in NiO and Ni2+ in CuO in the CuO–NiO sample were shown to be formed. Reduction of CuO, NiO and CuO–NiO oxides as model catalytic systems was studied by in situ XRD and TPR-H2. Reduction of CuO–NiO system was found to take place at notably lower temperatures than in the case of individual CuO and NiO. In situ XRD studies showed that the NiO–CuO reduction begins from copper oxide reduction evidenced by a sharp hydrogen uptake peak in the TPR-H2 curve. Kinetics of reduction of CuO, NiO and CuO–NiO oxides by H2 was investigated in detail. It was shown that apparent activation energy and pre-exponential factor obtained by Kissinger method for copper oxide reduction in CuO–NiO, compared to pure copper oxide, increased from 38 to 54 kJ mol−1 and from 6.4 to 13.0 (ln A) correspondingly. This is connected with formation of solid solution of Ni2+ in CuO that results in a significant growth of nucleation sites. As compared to individual nickel oxide, reduction of NiO in CuO–NiO is characterized by considerably lower activation energy. This is most probably caused by changes of chemical state of Ni2+ as a result of copper introduction into nickel oxide structure and formation of solid solution of Cu2+ in NiO.
•Kinetics of CuO, NiO and CuO–NiO oxides reduction by H2 was investigated in detail.•Solid solutions of CuO and NiO in the mixed sample were shown to be formed.•Solid solutions formation affects the kinetics of CuO and NiO reduction with hydrogen.
In vitro and in vivo methods of Raman spectroscopy have been developed to assess the degree of mineralization of the enamel of different functional groups. This article presents comparative studies ...that were carried out using scanning Raman microspectroscopy with various sources of laser excitation with wavelengths of 532, 785, and 1064 nm. It is shown that the intensity of Raman scattering of enamel can be a measure of its thickness. The obtained dependence of the Raman scattering intensity on the distance from the incisal edge is in good agreement with the literature data, where two independent methods (computer tomography and electron microscopy) are used to determine the enamel thickness values. The proposed methods can be considered as potential quantitative methods for express diagnostics of the state of tooth enamel in vivo.
In the current study, we evaluated the solubility of a number of organometallic species and showed that it is noticeably improved in diiodomethane when compared to other haloalkane solvents. The ...better solvation properties of CH2I2 were associated with the substantially better σ‐hole‐donating ability of this solvent, which results in the formation of uniquely strong solvent–(metal complex) halogen bonding. The strength of the halogen bonding is attenuated by the introduction of additional halogen atoms in the organometallic species owing to the competitive formation of more favourable intermolecular complex–complex halogen bonding. The exceptional solvation properties of diiodomethane and its inertness towards organometallic species make this solvent a good candidate for NMR studies, in particular, for the acquisition of spectra of insensitive spins.
The unique solvation properties of diiodomethane towards halide‐containing organometallic species are associated with its enhanced σ‐hole‐donating ability, which leads to stronger solvent–(metal complex) halogen bonding. The introduction of additional halogen atoms in the organometallic species attenuates the strength of the halogen bonding.
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