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.

Sn₃O₄ are promising semiconductor materials due to their visible light absorption ability. In this work, a series of materials, such as SnO₂, Sn₃O₄ and Sn₃O₄/SnO₂ heterostructures, with different phase ratios were prepared using hydrothermal synthesis. The materials were characterized using X-ray diffraction (XRD), Raman and diffuse reflectance spectroscopy (DRS), high resolution transmission electron microscopy (HRTEM), nitrogen adsorption (BET). Flat-band potentials (E_FB) of the samples were determined using the photocurrent onset potential (POP) method. It was shown that the potentials obtained with open circuit potential measurements versus illumination intensity (OCP) likely corresponded to the E_FB of SnO₂ nanoparticles in heterostructures due to interfacial electron transfer from the conducting band of Sn₃O₄ to that of SnO₂. The photo-electrooxidation processes of a series of organic substrates were studied in the potential range of 0.6–1.4 V vs. RHE under irradiation with ultraviolet (λ = 370 nm) and visible (λ = 450 nm) light. The Sn₃O₄ sample showed high activity in the photo-electrooxidation of acetone and formic acid in visible light. The Sn₃O₄/SnO₂ samples exhibited noticeable activity only in the oxidation of formic acid. The presence of the SnO₂ phase in the Sn₃O₄/SnO₂ samples increased the photocurrent values under ultraviolet illumination, but significantly reduced the oxidation efficiency in visible light.

The activation of a series of catalysts with the general formula Ni_0.9M_0.1O (M = Co, Ce, Mn, and Zr) synthesized by coprecipitation and the effect of modifying additives on the phase composition and structure of these catalysts were studied. The effect of additives on the initial state of the samples was studied by X-ray diffraction (XRD) analysis, and their role in the process of NiO reduction was studied using in situ XRD analysis and temperature-programmed reduction with hydrogen (TPR-H₂). It was found that the modifiers changed the structure and microstructure of the initial samples to increase the specific surface area and decrease the average coherent scattering region (CSR) sizes of NiO. The introduction of Mn and Co led to the formation of substitutional solid solutions with the oxide NiO. For Ce and Zr, the release of the oxide CeO₂ and X-ray amorphous ZrO_x was observed. The use of these additives led to an increase in the temperature of NiO reduction to a metallic state compared to that of the massive oxide. In addition, the effect of modifying additives on the particle size of the final metal was revealed. The use of Ce and Mn decreased the average CSR size of Ni by a factor of 2–5 compared to that of massive NiO.

In this work, NiO and NiO–SiO₂ are studied using X-ray diffraction and the method of atomic-pair radial distribution. Using X-ray phase analysis, it is determined that the sizes of NiO particles have a coherent-scattering region of more than 100 nm, while the NiO–SiO₂ sample has particle sizes of about 2–3 nm. However, full-profile simulation using the Rietveld method does not allow one to describe the effects observed during diffraction: asymmetry of the peaks, the appearance of an additional shoulder of peak 111 in the region of small angles; therefore, the method of atomic-pair radial distribution is used to analyze the structure. When simulating the experimental curve of the atomic-pair radial distribution, 3 different models are used: pure NiO, a mixture of NiO and Ni₂SiO₄, as well as a modified NiO model with Si embedded into the crystal lattice. The latter model is created based on the assumption of the incorporation of silicon into the NiO structure, as can be evidenced by the X-ray diffraction data. According to the results of simulation of the curve of the atomic-pair radial distribution, it is the latter model that provides the best description of the observed effects: a significantly increased unit-cell parameter in comparison with the sample without the addition of SiO₂, as well as decreased cation–oxygen distances in the structure while the distances between cations are increased.

In the present work NiO and NiO–SiO2 were investigated by X-ray diffraction and radial atomic pair distribution methods. By X-ray diffraction method, it was determined that the NiO particle sizes have coherent scattering region of more than 100 nm, while the NiO–SiO2 sample has a particle size of about 2–3 nm. At the same time, full-profile Rietveld simulation does not describe the effects observed on diffraction: the asymmetry of peaks, the appearance of an additional shoulder of peak 111 in the area of small angles, so the radial atomic pair distribution method was used to analyze the structure. During the simulation of the experimental atomic pair distribution curve, 3 different models were used: pure NiO, a mixture of NiO and Ni2SiO4, and a modified NiO model with Si embedded in the lattice. The latter model was created based on the assumption of silicon incorporation into the NiO structure, which can be evidenced by X-ray diffraction data. According to the results of radial atomic pair distribution modeling it is the latter model that gives the best description of the observed effects: significantly increased unit cell parameter, compared to the sample without SiO2 addition, as well as decreased metal cation–oxygen distances in the structure, while cation–cation distances are increased.

In this work the activation process and the effect of modifying additives on the phase composition and structure of a series of catalysts with the general composition Ni0.9M0.1O (M = Co, Ce, Mn, Zr) synthesized by co-precipitation were studied. The influence of the additives on the initial state of the samples was investigated by XRD, and their influence on the NiO reduction process was studied by in situ XRD and TPR-H2. It was shown that the introduced modifiers influence on the structure and microstructure of the initial samples, increasing the value of the specific surface and decreasing the average size of NiO CSR. Introduction of Mn, Co leads to formation with NiO oxide of solid solutions of replacement. For Ce and Zr the release of CeO2 oxide and X-Ray-amorphous ZrOx is observed. The use of these additives leads to an increase in the temperature of NiO reduction to the metallic state compared to the massive oxide. In addition, the effect of modifying additives on the particle size of the final metal is observed. The introduction of Ce and Mn decreases the average size of the NiO CSR in 2–5 times compared to the massive NiO.