The authors explore the possibility of synthesizing highly loaded mixed aluminum–cobalt spinels via the hydrochemical treatment of suspensions of a powder of the product of the centrifugal thermal activation of gibbsite in aqueous solutions of cobalt nitrate under room-temperature or hydrothermal conditions via X-ray diffraction, thermal, microscopic, adsorption, and chemical analysis. It is found that the heat treatment of products of hydrochemical interaction (xerogels) in the range of 350–850°C produces Co3O4 and CoAl2O4 spinel phases with different phase ratios, depending on the conditions of synthesis. The hydrochemical treatment of suspensions at room temperature ensures the dominant formation of a Co3O4 phase after calcination, while hydrothermal treatment at 150°C results in deeper interaction between the suspension components during treatment, ensuring the formation of CoAl2O4 after heat treatment. It is shown that the maximum content of CoAl2O4 spinel (90

The effect of gadolinium additives on the morphology, phase composition, and catalytic properties of MoVSbNbGdOx/SiO2 catalysts in the oxidative dehydrogenation of ethane to ethylene (ODE) is studied. It is shown that gadolinium concentration has a significant effect on the catalytic properties. At an optimum gadolinium content (Gd/Mo = 0.01–0.015), an increase in catalytic activity and ethylene selectivity is observed: at a temperature of 400°C, the ethylene yield achieves 72

Using high-resolution X-ray diffraction and synchrotron radiation, as well as scanning electron microscopy, it is shown that the observed high reactivity of commercial aluminum alloys activated with the Ga–In eutectic is associated with the formation of the Al–Ga–In eutectic along the grain boundaries in the entire material volume. The loss of material activity during storage under atmospheric conditions is due to oxidation of the eutectic components. Activation with pure gallium leads to the formation of AlGax solid solution, which has low activity in the reaction with water under neutral pH.

Barium aluminate BaAl2O4 of spinel structure was prepared by hydrothermal treatment at 150°С of a suspension of a gibbsite thermal activation product in an aqueous barium nitrate solution, followed by heat treatment of the precursors obtained. The product composition was studied by X-ray diffraction, thermal, microscopic, adsorption, and chemical analysis methods. Heat treatment of the hydrothermal reaction products at 850°С leads to the formation of single-phase barium aluminate BaAl2O4 with the specific surface area of ~50 m2 g–1 in the form of disk-shaped porous particles forming aggregates. The surface of BaAl2O4 particles is enriched in barium cations, which are relatively uniformly distributed over particles. The procedure allows reduction of the amount of the starting reactants and of the number of preparation steps, and also minimization or complete exclusion of the wash water formation.

The feasibility of the reactivation of CoMo/Al2O3 hydrotreating catalysts poisoned by Si compounds has been studied. CoMo/AAl(2)O(3) catalysts poisoned with 3, 4 and 5 wt.% of silicon were obtained during hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane. Catalysts poisoned by different amount of silicon were regenerated by oxidative treatment and subsequently reactivated using citric acid solution. The catalysts were studied by nitrogen adsorption-desorption method, CHNS analysis, UV-vis, thermal analysis, SEM, HRTEM, XPS. It was shown that the hydrodesulfurization activity of regenerated catalysts decreased with increasing silicon content. According to UV-vis results, the increase in Si content on the spent catalyst leads to the formation of CoOx oxides after oxidative regeneration. Probably, cobalt oxides do not promote MoS2 slabs during sulfidation, convert to inactive Co species and decrease hydrodesulfurization activity. After reactivation procedure, there was the increase in active component particles dispersion, while catalytic activity in hydrodesulfurization of dibenzothiophene and hydrodenitrogenation of quinoline increased. It was established that hydrodesulfurization and hydrodenitrogenation activities of CoMo/Al2O3 catalyst with less than 3 wt.% of Si could be completely restored by reactivation.

The possibility of preparing magnesium aluminate by the reaction of the product of centrifugal thermal activation of gibbsite with a saturated aqueous solution of magnesium nitrate at room temperature and 150°С was studied by X-ray diffraction, thermal, microscopic, adsorption, and chemical analysis methods. The reaction at 150°C between the components taken in the stoichiometric ratio with respect to the cations yields the phase of a layered double hydroxide [Mg0.33Al0.66(OH)2](NO3)0.6·0.013H2O. Its heat treatment at 550°C ensures the formation of stoichiometric spinel MgAl2O4 with the specific surface area of ~150 m2 g–1. Traditional impregnation of the product of centrifugal thermal activation of gibbsite with a concentrated magnesium nitrate solution, taken in an amount corresponding to the moisture capacity of the solid phase, at room temperature, followed by heat treatment at 550°С, yields a solid solution based on the low-temperature form γ-Al2O3 with the specific surface area of ~180 m2 g–1, containing ~4.55 wt % Mg. The samples obtained differ in the particle morphology and in the magnesium content on the surface. As compared to the traditional coprecipitation method, the suggested procedure allows considerable reduction of the reactant amounts and number of process steps and minimization or complete elimination of the wastewater formation.

The morphology, microstructure, and chemical composition of the surface and near-surface layers of polycrystalline wire of an industrial platinoid gauze composed of Pt (81 wt %), Pd (15 wt %), Rh (3.5 wt %), and Ru (0.5 wt %) are investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy. After oxidizing NH3 with air at T = 1133 K under a pressure of 3.6 bar for 50 h, a continuous rough layer of the cauliflower-type agglomerates formed during catalytic etching is detected on the frontal surface of the gauze. On the surface of wire fragments from 100 to 150 μm in size with a smooth micrograined structure, nanometer-size etch pits are detected at a concentration of 1.0 × 108–6.0 × 108 cm–2, which may be etching sites of the hotspot type. The growth of etch pits and the formation of crystalline terraces on the grain surface are caused by the surface diffusion of metal atoms. The continuous etching layer contains porous crystalline agglomerates (cauliflowers) with a linear size of 3 to 18 μm (mean size about 10 μm) at a concentration of 4.9 × 105 cm–2. Pores with a diameter of 0.1 to 1.7 μm are detected on the surface of agglomerates at a concentration of 1.3 × 107 cm–2. The specific surface area of the platinoid gauze, which is calculated from microscopic images taking into account the surface area of agglomerates and pores, is about 260 cm2/g. In the process of highly exothermic oxidation of NH3 with oxygen, on the surface of agglomerates with a low concentration of defects and in pore voids 5–15 μm in width and up to 10 μm in depth with an increased specific surface area and a high concentration of defects, vapor of volatile oxides and metals that are formed at hot regions of the bottom of pore voids can be condensed on the overlaying cold regions of the surface of agglomerates and single crystals. These processes give rise to the formation of a continuous etching layer of porous crystalline agglomerates, massive single crystals, and deep pore voids. The formed etching layer substantially increases the specific surface area of the catalyst, which leads to an increase in the volumetric rate of NH3 oxidation that accelerates the etching process.

The structure, morphology, and chemical composition of the surface and near-surface layers of platinoid wires of polycrystalline gauzes, containing Pt (81 wt %), Pd (15 wt %), Rh (3.5 wt %), and Ru (0.5 wt %) after treatment at 1133 K in various media—in air, in ammonia, and after NH3 oxidation in air—are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS). A thin film is found on the surface of the initial gauze containing an oxide layer of Rh2O3 with a thickness of ~2 nm, on the surface of which an inhomogeneous graphite-like layer 10–50 nm thick is located. It is shown that the heat treatment of gauzes in air leads to the partial removal of the surface graphite-like film that forms the reticulated structure on the wire surface. The treatment of gauzes in an ammonia atmosphere leads to the complete removal of the graphite-like and oxide layers and to the growth of metal grains of ~10 μm. After the catalytic reaction of NH3 oxidation, a deep structural rearrangement of the surface layer of the wire takes place, as a result of which crystalline metal agglomerates of ~10 μm are formed. It is supposed that the reaction of NH3 molecules with oxygen atoms penetrated on the defects leads to the local increase of temperature, due to which the metal atoms emerge on the surface and form large crystalline agglomerates and pores in the region of the grain boundaries.

Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to study microstructure, morphology and chemical composition of the surface and near-surface layers of polycrystalline wire of commercial platinoid gauzes containing Pt (81 wt %), Pd (15 wt %), Rh (3.5 wt %), and Ru (0.5 wt %) after ammonia oxidation (10 vol % NH3) by air at 1133 K for 50 h in the presence of these gauzes. Upon the completion of the catalytic reaction of ammonia oxidation, reconstruction (catalytic etching) of the surface layer on the backside of gauze wire (in the direction of the gas flow) was observed, in which the regions with different degrees of etching were identified. The analysis of these regions showed that the catalytic etching of the platinoid wire is initiated by etching the surface layer in the region of grain boundaries and dislocations in the course of highly exothermic catalytic reaction of ammonia oxidation by oxygen penetrated in the regions of defects. The regions with minimal etching contain smooth grains with crystalline terraces, 50 nm high, and with etching pits with size of ~72 nm in a concentration of 4.2 × 108 cm–2. The region with medium etching includes rough grains with etching pits with size of ~85 nm in a concentration of 2.5 × 108 cm–2. The regions with maximal etching consist of recrystallized grains with large pores with sizes of 350–400 nm in concentration of 8.9 × 106 cm–2. These grains are separated by voids with a width of 1–5 μm and a depth of 10 μm, which increases the specific surface area in the surface layer of wire. The growth of the specific surface area of the platinoid wire is accompanied by an increase in the volume rate of ammonia oxidation and, as a result, local overheating due to the high exothermicity of the reaction. With increasing temperature, the rate of diffusion of metal atoms increases, which, in turn, accelerates etching in this region. These processes lead to increasing the region of etching along the wire, which points to the autocatalytic regime of etching of platinoid gauzes in ammonia oxidation by oxygen.

The dissolution of oxygen in polycrystalline palladium Pd(poly) at an O2 pressure of 100 Pa and temperatures of 500–950 K has been investigated by temperature-programmed desorption. At 500 K, the process yields a surface palladium film that includes an oxide-like reconstructed structure on a rarefied metal surface layer. At this temperature, palladium sorbs ~2 monolayers (ML) of oxygen. At 600–800 K, palladium dissolves up to ~140 ML of oxygen as a result of O2 chemisorption on the surface of the oxide film, penetration of Oads atoms under the oxide film, and their diffusion into the metal bulk. The dependence of the amount of oxygen sorbed by Pd(poly) (n) on the time of exposure to an O2 atmosphere is described by a nearparabolic function, n = atb, indicating that oxygen atoms diffuse in the metal lattice. The activation energy of this diffusion, Еdif, is ~83.5 kJ/mol. At high temperatures (800–950 K), palladium sorbs much less oxygen (≤10 ML). This is due to the complete decomposition of the surface oxide film, a process that markedly hampers the insertion of Oads atoms under the surface layer of the metal.

The dissolution of oxygen in polycrystalline palladium Pd(poly) at an O2 pressure of 100 Pa and temperatures of 500–950 K has been investigated by temperature-programmed desorption. At 500 K, the process yields a surface palladium film that includes an oxide-like reconstructed structure on a rarefied metal surface layer. At this temperature, palladium sorbs ~2 monolayers (ML) of oxygen. At 600–800 K, palladium dissolves up to ~140 ML of oxygen as a result of O2 chemisorption on the surface of the oxide film, penetration of Oads atoms under the oxide film, and their diffusion into the metal bulk. The dependence of the amount of oxygen sorbed by Pd(poly) (n) on the time of exposure to an O2 atmosphere is described by a nearparabolic function, n = atb, indicating that oxygen atoms diffuse in the metal lattice. The activation energy of this diffusion, Е dif, is ~83.5 kJ/mol. At high temperatures (800–950 K), palladium sorbs much less oxygen (≤10 ML). This is due to the complete decomposition of the surface oxide film, a process that markedly hampers the insertion of Oads atoms under the surface layer of the metal.

The dissolution of oxygen in polycrystalline palladium Pd(poly) at an O 2 pressure of 100 Pa and temperatures of 500–950 K has been investigated by temperature-programmed desorption. At 500 K, the process yields a surface palladium film that includes an oxide-like reconstructed structure on a rarefied metal surface layer. At this temperature, palladium sorbs ~2 monolayers (ML) of oxygen. At 600–800 K, palladium dissolves up to ~140 ML of oxygen as a result of O 2 chemisorption on the surface of the oxide film, penetration of O ads atoms under the oxide film, and their diffusion into the metal bulk. The dependence of the amount of oxygen sorbed by Pd(poly) (n) on the time of exposure to an O 2 atmosphere is described by a nearparabolic function, n = at b , indicating that oxygen atoms diffuse in the metal lattice. The activation energy of this diffusion, Е dif , is ~83.5 kJ/mol. At high temperatures (800–950 K), palladium sorbs much less oxygen (≤10 ML). This is due to the complete decomposition of the surface oxide film, a process that markedly hampers the insertion of Oads atoms under the surface layer of the metal.

The decomposition of thin surface oxide films on polycrystalline palladium Pd(poly) at 500–1300 K was investigated by mathematical modeling. This process was analyzed in terms of a model including O 2 desorption from the chemisorbed oxygen layer (O ads ) and the passage of oxygen inserted under the surface layer of the metal (O abs ) and oxygen dissolved in metal subsurface layers (O dis ) to the surface. O 2 desorption was modeled on a surface with a square lattice of adsorption sites, with account taken of the energy of the lateral repulsive interactions between adjacent O ads atoms (ε aa ). At ε aa = 10 kJ/mol and when the activation energy of O 2 desorption for a chemisorbed-oxygen surface coverage of θ ≈ 0 is E des 0 = 230 kJ/mol, the calculated spectra are in agreement with the oxygen temperature-programmed desorption (TPD) spectra obtained for Pd(poly) at θ ≤ 0.5. The passage of O abs and O dis atoms to the surface was calculated using a first-order equation, with account taken of the activation energy for these atoms coming out to the surface ( E 2 and E 3 , respectively). As the oxide film is heated, O 2 desorption is accompanied by the passage of O abs and then O dis to the surface, which leads to an increase in the O ads surface coverage and, accordingly, to a buildup of lateral surroundings in the adsorbed layer. Owing to this fact and to the repulsive interactions between O ads atoms, the bonds between O ads and the surface weaken and E des decreases. As a consequence, the O 2 desorption rate increases and a low-temperature peak with T max ≈ 710 K, which is due to the passage of O abs atoms to the surface, and then a high-temperature peak with T max ≈ 770 K, which is due to the passage of O dis atoms to the surface, appear in the TPD spectrum. At ε aa = 10 kJ/mol, E des 0 = 230 kJ/mol, E 2 = 145 kJ/mol, and E 3 = 160 kJ/mol and when the number of inserted oxygen monolayers is θ abs ≤ 0.3 and the number of oxygen monolayers dissolved in subsurface layers is θ dis ≤ 10, the TPD spectra calculated for the given model are in agreement with the O 2 TPD spectra that are observed for Pd(poly) and are due to the decomposition of surface oxide films.

White globules of solid sulfur modification are obtained from saturated aqueous solutions. The chemical composition, morphology, and structure of the white sediment are investigated by means of X-ray fluorescence analysis, scanning electron microscopy, and high resolution transmission electron microscopy. It is shown that the white sediment contains an unknown modification of globular hexagonal sulfur with globule sizes of 5–10 μm and interplanar distances of 0.45, 0.29, and 0.15 nm. A single absorption band at 880 cm −1 is found in the Raman scattering spectra of the saturated solutions above the sediment. It is suggested that the white sediment consists of condensed S 2 phase.