The structural features and a series of properties of Ca_xLa_1 - xAlO_3 (x = 0–0.3) aluminates have been studied. The limits of stability of the cubic perovskite Ca_xLa_1 - xAlO_3 structure under the isomorphic substitution La3+ → Ca2+ have been determined by X-ray diffraction analysis. The dependence of the state of oxygen on the surface of the obtained samples on their composition has been studied by X-ray photoelectron spectroscopy (XPS). Based on a comparison of the XPS data with the catalytic properties of Ca_xLa_1 - xAlO_3 samples in the oxidation of C1–C3 alkanes, it was concluded that point defects (oxygen radical ions O– and surface OH– groups) are involved in the activation of reactant molecules, hydrocarbons and oxygen.

A new hybrid complex of CdS nanocrystals with silicotungstic heteropolyacid has been synthesized through their equimolar interaction in an organic solvent. The silicotungstic heteropolyacid acts as an electrophile and interacts with the nucleophilic cadmium sulfide by replacing its surface ligands. When possessing semiconductive properties, silicotungstic heteropolyacid, in combination with CdS, provides the complex with new capabilities which could prove valuable for the development of photocatalyst with improved characteristics, such as activity, charge separation efficiency, and resistance to photocorrosion. The complex was studied by means of optical spectroscopy and photoluminescence methods in the UV and visible ranges. Significant changes in the photoluminescence spectrum of CdS indicate effective coupling of the electronic systems of the interacting components. The structure of the heterocomplex was investigated and confirmed using FTIR spectroscopy, energy-dispersive spectroscopy, and ICP-MS.

The kinetics of acetylene hydrogenation in the presence of supported catalysts containing transition metals (Fe, Co, Ni, Cu, Ag) and palladium has been studied. The catalysts have been synthesized by depositing palladium hexafluoroacetylacetonate from solution in a supercritical carbon dioxide medium onto a silicon-based support and subsequently subjecting the samples to heat treatment and reduction in a hydrogen stream at 500°C. The support has been preimpregnated with solutions of transition metal nitrates. The catalytic properties of bimetallic systems and monometallic systems containing the same components have been compared. It has been shown that palladium and the transition metal used affect the catalytic properties of each other. It has been found that the kinetics of formation of acetylene hydrogenation products (ethylene, methane) changes with an increase in temperature, and the changes are different in the presence of bimetallic catalysts containing Cu and Ag and the catalysts containing Fe, Co, and Ni. In the latter case, a minimum acetylene conversion rate is observed at a temperature of about 100°C, and the ethylene selectivity abruptly increases with a further increase in temperature. The observed relationships are interpreted in terms of the existence of various adsorbed species of reactants (hydrogen and unsaturated hydrocarbons), which differ in adsorption strength and reactivity, on the surface of complex multicomponent catalyst systems.

The structural features and some properties of aluminates of the composition LnAlO3 (Ln = La, Ce, Pr) are studied. All three aluminates obtained at the final calcination temperature of 900°C have a cubic perovskite structure. In Ce-containing systems, along with it, a highly dispersed CeO2 phase with a cubic fluorite structure is observed. The cubic perovskite structure is retained upon modification of La and Pr aluminates by substituting 10 at

Rare-earth tungstates Ln2WO6 (Ln = Eu, Gd, Tb, Dy) and their high-entropy analogues were synthesized by mechanical activation of oxides. For the first time, an orthorhombic α-modification of Dy2WO6 (sp. gr. Pm21n) was obtained and characterized. It was demonstrated that the replacement of a single rare-earth element with a combination of five cations (La, Nd, Gd, Tm, Y) leads to the stabilization of the tetragonal phase (sp. gr. P4̅21m) of the high-temperature polymorph, which does not stabilize as a ceramic at room temperature in single-component systems. The high-entropy tungstate (La0.2Nd0.2Gd0.2Tm0.2Y0.2)2WO6 was found to exhibit record oxygen-ion conductivity for this class of compounds (1.84 × 10-5 S/cm at 700 °C), which is an order of magnitude higher than that of α-Sm2WO6 and α-Dy2WO6, and more than twice as high as that of monoclinic Nd2WO6. In the catalytic reaction of oxidative methane condensation, the high-entropy composition provided the best balance of selectivity and activity (39%/12%) among ionic conductors, while monoclinic Eu2WO6, due to the ability of Eu to change its oxidation state, became the leader among electronic conductors (42%/14%), achieving the highest yield of target C2 products (5.9%).

The catalytic properties of palladium and a palladium–copper composite, both deposited on γ-Al2O3 from a supercritical carbon dioxide (SC CO2) medium, were studied in the selective hydrogenation of acetylene to ethylene. Complexes of palladium and copper with hexafluoroacetylacetone were used as precursors of the active component. The acetylene hydrogenation process was studied in a reaction mixture comprising 1.0 vol

The authors study the effect the means of synthesis and preliminary treatment have on the structural features of samples of mixed lanthanum and aluminum oxides with constant atomic ratio La : Al = 1 : 1, along with their catalytic properties during the oxidation of methane. Using organic substances (filter paper or starch) as structuring agents in synthesizing the samples and subjecting them to an aqueous or aqueous–ammonia fluid environment with high-temperature treatment at different stages allows the phase composition, structural characteristics, and morphology of the resulting systems to be varied. It is shown there is no direct correlation between the structural characteristics, morphology, and catalytic properties of La–Al oxides. It is suggested that the efficiency of systems during the oxidation of methane is associated exclusively with the type and concentration of point defects, primarily the state of surface oxygen anions. At the same time, the phase composition and morphology influence the number and type of active centers, and their accessibility to reagents.

The transformations of a series of simple oxides (Al2O3, SiO2, La2O3, CeO2, PrO2) during their treatment with isopropanol (i-C3H7OH) in an autoclave under supercritical (SC) conditions and with subcritical water vapor were studied. In the presence of water vapor at 350°C, the specific surface areas of oxides decrease most significantly, and some of them (aluminum, lanthanum, and praseodymium oxides) are converted into hydroxides. Praseodymium oxide PrO2 is almost completely converted within 6 h under the action of i-C3H7OH at 350°C, which is accompanied by its reduction and partial conversion into hydroxide. In the case of CeO2, there were no transformations (including hydration and reduction) in i-C3H7OH or water vapor, and the specific surface area did not change. The differences in the behavior of CeO2 and PrO2 are explained by the difference in the values of the fourth ionization potential of the Ce and Pr atoms and, as a consequence, in the binding energies of oxygen in higher oxides. The products of conversion of i-C3H7OH were detected, whose composition depends on the type of the oxide being treated. The transformation of i-C3H7OH is dominant in the presence of Al2O3 and mostly gives dehydration products (propylene, diisopropyl ether). In the presence of La, Ce, and Pr oxides, dehydrogenation is dominant, forming acetone and hydrogen (mostly in the presence of La2O3). The catalytic nature of isopropanol decomposition in the presence of the given simple oxides was established. Silica SiO2, which has no pronounced acid-base and redox properties, showed the least activity in the decomposition of i-C3H7OH. It was assumed that when treated with SC isopropanol, the oxides are structured under the action of water vapor, which is the product of the transformation of i-C3H7OH. The catalytic activity of the autoclave material (stainless steel 12Kh18N10T) in the decomposition of i-C3H7OH along both routes—dehydration and dehydrogenation—was noted.

The formation of mixed oxides in La2O3/MO–Al2O3 systems (M is a group IIA element: Mg, Ca, Sr, Ba) subjected to a high-temperature treatment and treatment in a water fluid (WF) medium is studied. It is shown that the high-temperature treatment of a group IIA element aluminate with supported lanthanum nitrate leads to the formation of LaAlO3 only in the case of an Mg-containing system. In other cases, original aluminates do not undergo transformations, and lanthanum oxide is formed. The treatment of La/M–Al ternary systems in a WF medium leads to the formation of LaAlO3 in all cases; in addition, in all samples, except for the Ba-containing system, phases of free oxides of group IIA metals appear. The increase in the activity and selectivity of La/M–Al ternary oxide systems in the oxidative coupling of methane compared to the respective parameters of M–Al binary systems is attributed to the presence of an individual La2O3 oxide phase.

The effect of the method used to synthesize Ln–Al (Ln = La, Ce, Pr) mixed oxide systems with an Ln : Al atomic ratio of 1 : 1 on the formation of their phase composition and their catalytic properties in the oxidative coupling of methane (OCM) is studied. The precursors are prepared by impregnating ashless filter paper with mixed solutions of nitrates of the respective metals by the incipient wetness impregnation method and subsequent drying and combustion of the resulting mass in air. Further treatment is conducted by combining calcination at 600 and 900°C with a treatment in a water fluid (WF) or water–ammonia fluid (WAF) medium. The laws governing the transformation of the amorphous precursor of Pr–Al oxides during treatment in WF and WAF media and high-temperature synthesis are similar to those observed for the La–Al system. In both cases, the amorphous precursor in a water-containing fluid is transformed into LnAlO3 with a cubic perovskite structure with an admixture of AlO(OH) (boehmite) and basic REE carbonate phases. The subsequent treatment in air at 900°C leads to the formation of a mixture containing LnAlO3 aluminates and free La2O3 or PrO2 oxides. Single-phase samples containing exclusively lanthanum and praseodymium aluminates are synthesized by heating amorphous precursors in air at 900°C. The treatment of the Ce–Al system in a WF or WAF leads to the formation of a well-crystallized CeO2 oxide instead of aluminate or Ce-containing hydroxides, while the Al-containing component remains X-ray amorphous. Cerium aluminate CeAlO3 is synthesized by treating a mixture of cerium and aluminum oxide precursors in a hydrogen stream. It is found that, due to differences in the 4th ionization potential (IP4) values of the La, Ce, and Pr atoms (49.9, 36.7, and 39.0 eV, respectively), completely different synthesis conditions are required to form LnAlO3 aluminates with a perovskite structure that contain REE in the (3+) oxidation state. The catalytic properties of the synthesized samples in the OCM are studied. The efficiency and stability of isostructural LnAlO3 aluminates in the OCM decreases in the following order: La > Pr > Ce. Despite the fact that PrAlO3 is the most active of these aluminates, LaAlO3 exhibits the highest selectivity for OCM products (ethane + ethylene).

The occurrence of dry reforming of methane (DRM) in a steady-state mode and partial oxidation of methane (POM) in a self-oscillating mode over a nickel foil sample and the simultaneous occurrence of these two reactions have been studied. It has been shown that during the cooccurrence of the DRM and POM reactions, a kinetic coupling of these reactions takes place; it is evident as a change in the self-oscillation period and a significant acceleration of the DRM reaction in certain phases of the self-oscillation cycle compared with the DRM rate over this Ni sample in a steady-state mode. The DRM acceleration effect is observed in a temperature range of 600–750°C. The maximum increase in the CO2 conversion value averaged over the oscillation period is a factor of 2.6 at a temperature of 700°C for a feed gas mixture composition of CH4 : CO2 = 1 : 1 + 3.5

Morphology of reactor polymer compositions based on ultrahigh molecular weight polyethylene (UHMWPE) with Mw = 1000 kg/mol and low molecular weight high density polyethylene (LMWPE) with Mw = 48 kg/mol obtained in single-stage ethylene polymerization in the presence of a binary catalytic system is studied. The content of the LMWPE fraction in the compositions ranged from 6.3 to 29 wt

The synthesis of mixed La–Al oxide systems with the atomic ratio La : Al = 1 : 1 was studied. At the first stage, a dried mass containing starch and La and Al nitrates was burned. Heat treatment of the resulting amorphous product at a temperature of ≥700°C gave LaAlO 3 aluminate with a cubic perovskite structure. The composition and morphology of the product formed by subsequent treatment in a water fluid (WF) medium (density 0.2 g/cm 3 , 415°C) depend on the degree of ordering of the precursor. Crystalline LaAlO 3 (cubic) in the WF medium undergoes additional ordering with a decrease in the specific surface area ( S sp ) while maintaining the crystalline structure; further calcination at 900°C did not lead to a change in either S sp or the structure. Treatment of an amorphous precursor in the WF medium increased S sp and produced a mixture of LaAlO 3 aluminates of cubic and orthorhombic structures and La and Al hydroxides. Further calcination at 900°C gave a mixture of LaAlO 3 (cubic), La 2 O 3 (hexagonal), and, possibly, X-ray amorphous Al 2 O 3 . The synthesized systems were studied as catalysts for methane oxidation. There was no correlation between activity and selectivity for oxidative coupling products (ethane + ethylene) with the S sp value; they were found to depend on the phase composition of the mixed La–Al oxide. The most efficient systems turned out to be those that underwent intermediate treatment in the WF medium and contained the LaAlO 3 (cubic) and La 2 O 3 (hexagonal) phases. The results obtained indicate the high structural sensitivity of the process characteristics.

The formation of mixed oxides in the Al2O3–MO (M = Mg, Ca, Sr, Ba) systems by heat treatment and treatment with water fluids (WFs) is studied. It is shown that during the high-temperature treatment of mixtures of aluminum hydroxide Al(OH)3 with group 2 metal nitrates, mainly MAl2O4 aluminates are formed, sometimes with an admixture of aluminates of a different composition. If the same mixtures are pretreated in WF (400°C, fluid density 0.2 g/cm3), the composition of the sample is more complex because of dehydration and partial structuring of the Al-containing component during the treatment in the WF medium. It is demonstrated that the addition of ammonia to WF has a stimulating effect on the formation of double oxides, primarily due to the alkaline hydrolysis of the Group II metal salts and the formation of their hydroxides; and the reduction of nitrates and nitrites with ammonia is likely to be a secondary process.

The catalytic properties in the oxidative coupling of methane (OCM) and the structural features of a series of lanthanum aluminum mixed oxides with a constant La : Al atomic ratio of 1 : 1 were studied. Samples were prepared from precursors containing lanthanum and aluminum nitrates and an organic component: filter paper or starch. After drying and burning of the organic component, the samples were subjected to additional heat treatment and treatment with water fluid (WF) with a density of 0.2 g/cm 3 at 415°C. After calcination at 900°C, all the samples contained a phase of lanthanum aluminate LaAlO 3 with a cubic perovskite structure. Varying the type of organic component and the sequence of procedures and treatment conditions gave samples with different morphologies and catalytic properties. The minimum activity, selectivity for OCM products, and stability over time was demonstrated by the sample obtained under conditions conducive to the formation of the most ordered structure, namely, the sample sequentially calcined at 900°C, treated in a WF medium, and recalcined at 900°C. The most efficient and stable sample turned out to be the one whose crystal structure was formed mainly in the WF medium. It was noted that there is no correlation between the morphology of the particles and the specific surface area of the samples, on the one hand, and their catalytic properties, on the other. It was assumed that the catalytic properties are determined by the type and number of point defects in the crystal structure—primarily cation vacancies and, as a consequence, hole sites of the [O – ] type in the anion sublattice.

The effect of the synthesis method on the formation of the structure and composition of composites produced by the deposition of lanthanum oxide compounds on porous alumina is studied. The effect of the morphology of porous alumina (α-modification) on the formation of various compounds (La 2 O 3 oxide, as well as LaAlO 3 and La 10 Al 4 O 21 aluminates) during the thermal treatment of a support impregnated with a solution of lanthanum nitrate is shown. It is found that when systems are treated in a water fluid (WF), the processes of structuring and phase formation proceed at a much lower temperature and more intensely than during the thermal treatment, which is due to the mobility of the structural elements in the hydrated state. It is shown that the formation of LaAlO 3 aluminate is limited by the hydration of the initial aluminum oxide, which proceeds more intensely in the case of its γ-modification. Varying the sequence and conditions of the stages of the treatment in a WF and the thermal treatment makes it possible to obtain composites that have different morphologies and contain various oxide compounds and phases.

The regularities of the formation of the phase composition of crystalline silica during the processing of amorphous precursors in the aqueous fluid media below and above the critical point of water aimed at the formation of optimal support for the methane oxidative coupling (OCM) catalyst were studied. It was shown that the phase composition of SiO2 and the rate of phase formation strongly depend on the processing conditions (temperature, time, phase state of the water fluid) and the presence of trace amounts of impurities in the initial amorphous material. Nevertheless, for different precursors, the phase formation occurs, apparently, via the formation of the same bulk-hydrated structures. Optimization of the processing in the water fluid and subsequent heat treatment made it possible to obtain an OCM catalyst that is significantly more efficient than the one obtained by the conventional procedure using an amorphous support. It was concluded that the catalytic properties are entirely determined by chemical and phase transformations occurring in the active component (Na2WO4–Mn2O3) on the support surface and do not depend on the doping of the support with the ions composing the active phase.

The effect of the density of water fluid in the range of ~10–3–0.25 g cm–3 on the structuring of amorphous silica gel was studied at 380°C that exceeds the temperature of critical point of water. It was shown that a decrease in the specific surface area (Ssp) is observed already at the lowest density. As the latter increases, Ssp decreases further, and starting from the density of ~0.01 g cm–3, the formation of crystalline silica phases (cristobalite, keatit) was observed in the sample. Based on the observed regularities in the change in the morphology and crystallinity of SiO2, as well as on the data on the variations in the properties of the water fluid with temperature and pressure below and above the critical point, it was concluded that the increase in the structuring rate with an increase in the density of the water fluid is more likely due to the kinetic factor (mass action law) than with a change in the physical state of water (intermolecular interaction forces action). Using the obtained samples of treated silica gel as a support for the NaWMn/SiO2 catalysts it was shown that their efficiency in the oxidative coupling of methane decreases with increasing degree of crystallinity of the support. However, when supports that have undergone processing in the water fluid of relatively low densities (<0.05 g cm3) were used, the catalysts were more active and selective than the one prepared using the untreated silica gel.

Strontium and barium titanates deposited on a porous support (α-Al2O3) are synthesized by the treatment of previously deposited precursors (titanium oxide, strontium nitrate, or barium nitrite) in a water fluid medium at 400°C. The obtained samples are characterized by X-ray powder diffraction (XRD) analysis and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy. It is found that, in the presence of titanium oxide, α-Al2O3 is partially hydrated to form basic aluminum hydroxide AlO(OH) (boehmite), which is not detected by XRD after the treatment of α-Al2O3 in a water fluid. SEM with EDX spectroscopy demonstrates that strontium ions under the conditions of the treatment in a water fluid preferably interact with titanium oxide to form SrTiO3, although the aluminum oxide content in the samples is much higher. The conditions are determined for obtaining systems with different spatial distributions of the supported component inside the granules of the support by varying the procedure of its preliminary impregnation with the titanium oxide precursor.