The Sr2TiO4 samples were synthesized by mechanical activation (MA) from a mixture of SrCO3 and TiO2 precursors followed by calcination at 900 and 1100 degrees C. The accumulation of internal energy stresses in the mechanical mixture of precursors was controlled by varying the mechanical activation time (10, 20 and 25 min) through the use of mills of different power. Powder mixtures of precursors as-blend, after MA, and after calcinations were studied using XRD, FTIR, thermal analysis, and SBET methods. The energy impact in Sr2TiO4 synthesis is more pronounced at calcination temperature of 900 degrees C, the increase in the energy load at a temperature of 1100 degrees C is levelled out, due to the formation of practically single-phase Sr2TiO4.

Методами растровой электронной микроскопии (РЭМ), рентгенофазового анализа (РФА) и дифракции отраженных электронов (ДОЭ) была исследована микро- и наноструктура на поверхности поликристаллической фольги платины (Pt(poly)) после отжига в атмосфере О2 при РО2=0.2 и 1 бар и Т = 1000−1400 К. С ростом температуры от 1000 до 1400 К основная часть зерен сохраняла структуру поверхности близкую к (110) грани, и при этом обнаруживалась перестройка поверхности зерен со ступенчатой структурой (311) в поверхностную структуру (100) и отчасти в структуру (111). При этих температурах величины параметра ячейки α и области когерентного рассеивания D практически не изменяются и оказаются близкими к полученными для исходной Pt(poly) (3.925 Å, 25 нм). РЭМ изображения в интервале увеличений от ×100 до ×300k при Е0 равном 5, 10 и 20 кэВ в режиме вторичных (ВЭ) и отраженных электронов (ОЭ) показывают микрозернистую структуру с зернами размером от 10 до 150 мкм (~30 мкм) и различным уровнем яркости, а также фасетки высотой от 10 до 100 нм на поверхности зерен. Соседние зерна с различной яркостью содержат фасетки с различающейся формой, размерами и ориентацией. После отжига при 1100 К, на поверхности ярких зерен обнаруживаются слоистые структуры с толщиной слоев до 100 нм, тогда как на поверхности зерен с серым и темным уровнем яркости фиксируются фасетки с квадратной и прямоугольной формой с высотой ступеней до 100 и 25 нм, соответственно. Зафиксированный уровень яркости и структура фасеток могут быть связаны со структурой поверхности зерен близкой к (111), (100) и (110) кристаллографическим плоскостям, соответственно. При высокой температуре (1000−1400 К) и давлении О2 (~1 бар) может формироваться высокое покрытие поверхности адсорбированными атомами Оадс, стимулирующими выделение из объема на поверхность адсорбированных атомов Ptадс. Высокая концентрация подвижных, мобильных атомов Ptадс вызывает перестройку поверхности, включающую формирование фасеток на поверхности зерен, которые понижают поверхностную энергию и образуют стабильную поверхностную структуру.

The micro- and nanostructure of the surface of polycrystalline platinum foil (Pt(poly)) after annealing in the O2 atmosphere at PO2 = 0.2 bar and 1 bar and T = 1000-1400 K is analyzed by scanning electron microscopy (SEM), powder X-ray diffraction, and electron backscatter diffraction (EBSD). With an increase in the temperature from 1000 K to 1400 K the main part of grains maintains the surface structure close to the (110) face, with the grain surface rearranging from the (311) stair structure to the (100) surface structure, and partially to (111). At these temperatures the values of unit cell parameter a almost do not change in coherence scattering region D and appear to be close to those obtained for initial Pt(poly) (3.925 Å, 25 nm). In the electron secondary and backscatter mode, SEM images in the magnification range from ×100 to ×300k at E0 of 5 keV, 10 keV, and 20 keV demonstrate the microgranular structure with 10-150 µm ( 30 µm) grains and different brightness levels, as well as the 10-100 nm high facet on the grain surface. The neighboring grains with different brightness contain facets of different shapes, sizes, and orientations. After annealing at 1100 K layered structures with a layer thickness up to 100 nm are found on the surface of bright grains while square and rectangular facets with step heights up to 100 nm and 25 nm respectively are observed on the surface of grains with gray and dark levels of brightness. The fixed level of brightness and the structure of facets can be related to the grain surface structure close to (111), (100), and (110) crystallographic planes respectively. At high temperatures (1000-1400 K) and O2 pressure ( 1 bar) the surface can be densely covered with adsorbed Oads atoms stimulating the release of adsorbed Ptads atoms from the bulk to the surface. The high concentration of mobile Ptads atoms causes the surface rearrangement involving the formation of facets on the grain surface, which decrease the surface energy and form the stable surface structure.

The La 1– x Ca x Mn 0.5 Co 0.5 O 3 solid solutions ( x = 0.2-0.6) are prepared by the Pechini method and characterized by a number of physical and chemical methods. It is shown that the oxygen nonstoichiometry in the samples significantly increases with increasing number of calcium cations in the La sublattice. The thermal analysis of the samples shows that the lattice oxygen is released at ~600 °C for all samples and that its amount increases with increasing calcium content. The in situ powder XRD data obtained in the He atmosphere indicate that the studied solid solutions with x ≥ 0.4 are unstable under these conditions and may exhibit partial structural destruction and that the AB O 3 complex oxide in the system with x = 0.6 transforms into a phase characterized by the A 2 B O 4 structural type of the Ruddlesden–Popper series.

The catalytic performance of LaFe1-xNixO3 perovskites prepared by the Pechini method was studied in the high-temperature decomposition reaction of nitrous oxide at temperatures of 750-900 degrees C. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), adsorption (S-bet) and hydrogen thermo-programmed reduction (H-2-TPR) methods. The prepared single-phase solids with specific surface areas of 4.7-8.4 m(2) g(-1) are porous particles (aggregates) of 10-100 mu m composed of microblock crystallites. The surface of all samples is enriched with lanthanum. Increasing the Ni content increases the normalized per m(2) catalytic activity of LaFe1-xNixO3 perovskites, their reducibility in hydrogen, the ratio of Fe + Ni/La and the content of low bond oxygen forms on the sample surface. The correlation of activity and low bond oxygen forms was revealed, which is consistent with the mechanism of reaction of nitrous oxide decomposition. For future industrial applications the LaFe0.4Ni0.6O3 perovskite is proposed due to its higher stability in the reaction medium as compared with samples with x > 0.6.

Твёрдые растворы La1-xCaxMn0.5Co0.5O3 (х = 0.2-0.6) были синтезированы методом Пекини и охарактеризованы комплексом физико-химических методов. Показано, что увеличение количества катионов кальция в подрешетке La приводит к значительному росту кислородной нестехиометрии в образцах. Термический анализ образцов показал выделение решёточного кислорода в районе температуры 600 oС для всех образцов, причём количество выделяемого кислорода увеличивалось при росте содержания кальция в структуре. Исследование образцов in situ РФА в атмосфере He показало, что твёрдые растворы, начиная с х = 0.4, нестабильны в данных условиях и могут претерпевать частичное разрушение структуры, а для состава х = 0.6 сложный оксид типа ABO3 превращается в фазу со структурным типом A2BO4 ряда Раддлесдена-Поппера.

Using the methods of X-ray, thermal, microscopic, adsorption and chemical analyzes, the possibility of obtaining aluminum-copper mixed oxide catalysts by preliminary hydrothermal treatment of a suspension of the product of centrifugal thermal activation of gibbsite with an aqueous solution of copper nitrate and subsequent heat treatment of the obtained precursor was studied. The heat treated in the range of 450-750 degrees C catalysts are mainly mixtures of CuO and CuAl2O4 phases in different ratio. The different ratio of active phases allows them to be used as catalysts for low-temperature purification of NH3 and high-temperature combustion of NH3 as a fuel at various power plants. Testing of catalysts in the process of selective oxidation of ammonia (NH3-SCO) showed that prepared aluminum-copper catalysts are not inferior in their catalytic properties to known catalysts, including aluminum-platinum ones, and the proposed synthesis method is resource-saving compared to known methods, including those with many options for preparing these systems by "sol-gel" technology.

Cesium-promoted cobalt spinel is promising as a catalyst for the low-temperature decomposition of nitrous oxide for use in the second stage of a single-reactor unit for the combined removal of nitrogen oxides. This work studied the effect of the conditions for the preparation of granular and block bulk catalysts based on Co 3 O 4 by extrusion molding.

This study revealed an increased reactivity of centrifugally thermoactivated products of gibbsite toward aqueous solutions of nickel nitrate at room temperature as well as under hydrothermal conditions. X-ray, thermal, microscopy, adsorption and chemical analysis methods were used to investigate and demonstrate the possibility of obtaining highly loaded mixed aluminum–nickel oxide systems, with a nickel content of ca. 33 wt.%, using a hydrochemical treatment at room temperature or a hydrothermal treatment of suspensions of the product of the centrifugal thermal activation of gibbsite in aqueous solutions of nickel nitrate. It was shown that the thermal treatment of xerogels—hydrochemical interaction products—in the range of 350–850 °C led to the formation of NiO phases and highly dispersed solid solutions of nickel based on the NiAl2O4 spinel structure, with different ratios and a high specific surface area of 140–200 m2/g. A hydrochemical treatment of suspensions at room temperature ensures that the predominant formation of the NiO phase is distributed over the surface of the alumina matrix after calcination, whereas hydrothermal treatment at 150 °C leads to a deeper interaction of the suspension components at the treatment step, which occurs after the thermal treatment of the formed xerogel in the predominant formation of poorly crystallized NiAl2O4 spinel (“protospinel”). The considered method makes it possible to obtain complex aluminum–nickel oxide systems with different phase ratios, decreases the number of initial reagents and synthesis steps, completely excludes waste and diminishes the total amount of nitrates by 75 wt.% compared to the classical nitrate scheme for the coprecipitation of compounds with a similar elemental composition.

X N2O , % Time contact, sec ExperimentalThe 2%Cs/Co 3 O 4 сatalysts were prepared from excellent pastes by extrusion molding through feliers of different geometries.The dried catalysts were calcined in air at 400°С for 2 h.The catalysts were characterized by XRD, ТGA, BET, H 2 -TPR.The N 2 O decomposition was carried out at 150-450 o C, at atmospheric pressure and space velocity about 9000 h -1 , under real conditions (1500 ppm N 2 O, 3.6% O 2 , 3% H 2 O in He).The Co 3 O 4 (S bet ~ 100м 2 /г) was obtained by decomposition of 2Co(OH) 2 ×CoСО 3 ×H 2 O in a muffle in air at 300 С for 4 hours Paste preparation (by mixing at least 20-60 minutes) Molding (by forcing pastes through a die)

LaFe0.4Ni0.6O3/CeO2 (1:1) two-phase composite materials were prepared by mechanochemical (MC) and Pechini routes. The catalytic properties of the composites in methane and CO oxidation reactions strongly depend on their preparation conditions. In low-temperature (<600 °C) catalytic CO oxidation the composites demonstrate a higher activity compared with LaFe0.4Ni0.6O3 perovskite. The highest activity was observed for the composite prepared by mechanical treatment of perovskite and fluorite precursors. There is a correlation between activity and the content of weakly bound surface oxygen species. Catalytic activity in high-temperature (>750 °C) catalytic methane oxidation correlates with the reducibility of samples. The highest activity was observed for the composite prepared by the one-pot Pechini route with higher reducibility of the sample up to 600 °C.

Niobium oxide supported on ZrO2 and mixed oxide of NbOx-ZrO2 was prepared and characterized. Mechanical treatment was followed by the microwave heating procedure of catalysts with more advanced textural parameters. The amount of Lewis (LAS) and Brønsted (BAS) acid sites rose with the increasing Nb content in the catalysts. The catalytic properties of samples of niobia-zirconia (NbZr samples, NbZr catalysts) were studied in a cellulose hydrolysis–dehydration reaction at 453 K under an inert Ar atmosphere in a batch reactor. Glucose and 5-hydroxumethylfurfural (5-HMF) were the major products. The initial reaction rate could be tuned by the density of acid sites on the surface of solid. At a low density of acid sites (0.1–0.3 µmol·m−2), the initial reaction rate had a pronounced inverse correlation. Increasing the LAS/BAS from 0.3 to 2.5 slightly stimulated the formation of the target products. The catalytic properties of NbZr catalysts prepared by microwave treatment were studied in cellulose transformation in a flow set-up. Glucose was found to be the major product. The maximum yield of glucose was observed in the presence of the sample of 17%Nb/ZrO2. Increasing Nb content resulted in the formation of Nb-associated acid centers and, in turn, increasing catalyst acidity and activity.

In this study, the modeling of the low-temperature catalytic abatement of NOX and N2O from tail gases in a weak nitric acid plant utilizing a single-pressure 0.716 MPa system was performed. A one-reactor concept assumes that in the first bed, NOX is reduced by ammonia on a commercial vanadia–alumina catalyst, and in the second bed, N2O is decomposed on a proprietary nickel–cobalt catalyst. The kinetics of N2O decomposition on a Cs/Ni0.1Co2.9O4 catalyst was experimentally studied in an isothermal flow reactor. The reaction rate constants were determined by varying the residence time and temperature; these data formed the basis for modeling kinetics and heat and mass transport in an adiabatic reactor in which the low-temperature mitigation of nitrogen oxides occurred. Taking into account the given spatial limitations inside the reactor and the allowable temperatures, the layer heights were evaluated to ensure a residual NOX and N2O content of less than 50 ppm. Catalyst loading using layers in a commercial reactor was estimated for the tail-gas flow rates of 46,040–58,670 m3/h. Simulations showed that the optimum inlet temperature was 260 °C; in this case, the NOX and N2O conversion targets were achieved in the range of 46,040–58,670 m3/h while adhering to catalyst bed height and outlet temperature limitations.

Platinum alloy gauzes are employed for the high-temperature oxidation of NH3 to NO used in the industrial production of HNO3 for application in agricultural fertilizers. To enhance the efficiency of NH3 oxidation, various Pt–Pd–Rh alloys are employed for the production of such catalytic gauzes. To understand the role of these metals in NH3 oxidation, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction were applied to investigate the morphology, composition and structure of Pt, Pd and Rh foils after annealing in O2 and oxidation of NH3 with air at 1133 K. After annealing in O2 and NH3 oxidation, the metallic microgranular structure was detected on Pt(poly), whereas oxide layers of Rh2O3 and PdO were observed on Rh(poly) and Pd(poly). At the onset of NH3 oxidation (t = 1 h), fibrous metal-oxide agglomerates of nanofibers formed on these oxide layers. The long-term (5–10 h) oxidation of NH3 led to the formation of a continuous layer of pyramidal crystals on Rh(poly) and palladium “cauliflowers” on Pd(poly). The highly exothermic reaction of NH3 with oxygen on metals and PdO or Rh2O3 initiates strong catalytic etching forming grains and facets on Pt, fibrous metal-oxide agglomerates, pyramidal crystals and metallic “cauliflowers” on Rh and Pd.

Mixed oxides MexCo3−xO4 (Me: Ni or Mg, x = 0–0.9) with a spinel structure were synthesized by precipitation from Me, Co nitrate solutions using (NH4)2CO3 as the precipitating agent with subsequent modification of the dry precipitate with cesium by the Pechini method and calcination. The samples were studied by XRD, TPR, and TPD methods. Their catalytic activity was studied in the low-temperature (150–350 °C) nitrous oxide decomposition process. It was shown that an increase in the degree of substitution of cobalt (x) leads to a significant decrease in the degree of crystallization of the oxides, an increase in the specific surface area, and the formation of surface weakly bound oxygen species. The highest activity was shown by the catalysts with a degree of substitution x = 0.1, especially by the nickel-substituted sample, which contained the maximum amount of weakly bound surface oxygen species. The difference in the influence of Mg and Ni on the MexCo3−xO4 properties is discussed.

High-temperature oxidation of NH3 on Pt alloy gauzes to NO is widely employed in industry for the production of HNO3, which is used to obtain agricultural fertilizers. Particular attention is paid now to the investigation of the chemical composition of gauzes used in NH3 oxidation. X-ray photoelectron and energy-dispersive X-ray spectroscopies with the depth of analysis ca. 5 nm and ca. 500 nm were applied to investigate the chemical composition of surface and subsurface layers of the new and used in NH3 oxidation with air at T = 1133 K Pt–Pd–Rh–Ru catalytic gauzes (81, 15, 3.5, 0.5 wt.%, respectively). For all the gauzes, adsorption (OHad, COad), graphitic (Cgr) and oxide (Rh2O3) films were found on the surface of the metallic alloy. Under these films, Cab, Nab and Oab atoms absorbed in the subsurface layers were detected on the gauzes used in NH3 oxidation. The obtained data testify to the penetration of Oab and Nab atoms into deeper layers of the alloy during etching with elevation of the catalyst temperature. Oab atoms were accumulated predominantly on dislocations, etch pits and grain boundaries, whereas Nab atoms intercalated mostly into interstitial sites of the alloy lattice.

Methane oxidative coupling (OCM) is considered a potential direct route to produce C2 hydrocarbons. Layered perovskite-like Sr2TiO4 is a promising OCM catalyst. Mechanochemical activation (MA) is known to be an environmentally friendly method for perovskite synthesis. Sr2TiO4 were synthesized using MA of the mixtures containing SrCO3 or SrO and TiO2 or TiO(OH)2 and annealing at 900 and 1100 °C. XRD and FT-IRS showed that MA leads to the starting component disordering and formation of SrTiO3 only for SrO being pronounced when using TiO(OH)2. After annealing at 900 °C, Sr2TiO4 was mainly produced from the mixtures of SrCO3 or SrO and TiO(OH)2. The single-phase Sr2TiO4 was only obtained from MA products containing SrCO3 after calcination at 1100 °C. The surface enrichment with Sr was observed by XPS for all samples annealed at 1100 °C depending on the MA product composition. The OCM activity of the samples correlated with the surface Sr concentration and the ratio of the surface oxygen amount in SrO and perovskite (Oo/Op). The maximal CH4 conversion and C2 yield (25.6 and 15.5% at 900 °C, respectively), and the high long-term stability were observed for the sample obtained from (SrCO3 + TiO2), showing the specific surface morphology and optimal values of the surface Sr concentration and Oo/Op ratio.

Based on La2TiO5 layered perovskite, the complex oxide materials Sr2aLa2-2aTiO5-5 and Mg2aLa2-2aTiO5-5 (a = 0-1) were synthesized by sol-precipitation method. The X-ray diffraction analysis, the specific surface area, and scanning electron microscopy techniques showed that Sr-substituted samples contain phases of the 'layered' perovskite (SrLa)2TiO5-5 as well as La2O3, La(OH)3 and TiO2. The Mg-substituted samples contain the phases of the 'double' perovskites (Mg,La)TiO3-5, and La(OH)3. The specific surface area of as prepared samples varied within 0.5-4.2 m2/g. The catalytic properties of the materials were investigated by the reaction the oxidative coupling of methane to ethane in a fixed-bed microcatalytic reactor at temperatures from 600 to 950 degrees C. Most active in the OCM reaction were the samples in which the substitution degree of lanthanum a was equal to 0.1-0.3. Sr-substituted samples showed higher activity than Mg-substituted ones. The best activity was revealed for Sr2aLa2-2aTiO5-5 (a = 0.1). (c) 2022 Elsevier Ltd. All rights reserved.

A study is performed of the main ways of preparing aluminum oxides; the advantages of products of the thermal activation of hydrargillite (gibbsite) for preparing catalysts, supports, and sorbents; factors that influence the products of thermal activation and aluminum oxides according to the technology of thermal activation; and examples of effectively using products of the centrifugal thermal activation of hydrargillite to prepare catalysts, supports, and sorbents.