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 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 article is devoted to the experimental and theoretical study of regular and complex oscillations during ethylene oxidation on the nickel foil. The simplest mathematical model was based on the 14-stage mechanism of reaction including the stages of oxidation and reduction of the Ni catalyst. A precursor-mediated adsorption of CO and C2H4 was shown to be the crucial condition for the origin of the oscillatory behavior under reducing conditions. It was demonstrated that for real values of the parameters, the mathematical model can simulate both regular and irregular oscillations, as well as the “mixed-mode” oscillations observed in the experiment. For the first time oscillations with different properties and distinct mechanisms of their occurrence were detected in the same model. It was demonstrated that oscillations occurred as a result of a strong dependence of the reaction rate on the concentration of active sites due to a variation in the concentration of the surface oxide or the surface carbon.

The effect of the content of supported manganese on the structural properties and activity in the oxidation reactions of CO and propane for the MnОx/Zr0.4Ce0.6 catalysts prepared by the impregnation method has been studied. It was found that an increase in manganese content to 3.6% wt. (molar ratio Mn/(Zr + Ce) ≤ 0.1) leads to an increase in the catalytic activity of MnОx/Zr0.4Ce0.6 in oxidation reactions. In the case of a higher manganese concentration, the activity changes slightly. According to the XRD, TPR-H2, XPS and EPR, an increase in the amount of supported manganese for samples with Mn/(Zr + Ce) ≤ 0.1 is accompanied by a change in the lattice constant of the support, an increase in the amount of weakly bound oxygen, as well as the quantity of oxygen vacancies in the structure of cerium oxide. These changes are due to the incorporation of manganese into the structure of the support and the possible formation of highly dispersed particles of MnОx on its surface which ensures an increase in catalytic activity. Stabilization of catalytic activity with a further increase in the amount of supported manganese correlates with a slight change in the amount of weakly bound oxygen and oxygen vacancies of the support due to the appearance and subsequent increase in the content of the less active Mn2O3 phase.

When low molecular weight ammonium polyphosphate interacts with polyethylene polyamine, thermoplastic polymers containing fractions with glass transition temperatures Tglass ≥ –95°C are obtained. Their thermal and heat resistance, as well as moisture resistance, is measured at a humidity of 40–50

An Erratum to this paper has been published: https://doi.org/10.1134/S1990793124330017

The paper compares the properties and activity of palladium clusters deposited on aluminum oxides of different phase compositions obtained by different methods. The numbers of palladium atoms available for the adsorption of hydrazine were determined for each catalyst. A correlation was found between the number of such atoms and the rate of hydrogen formation in the decomposition reaction of hydrazine monohydrate. It was concluded that an active palladium catalyst for the decomposition of hydrazine can be obtained using a modified support with a large specific surface area. The specific surface area and its modification determined the surface coverage with the active reagent. Obviously, the study of the role of various properties of supports in the formation of the active phase should be continued.

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

A block spatially cross-linked silicon-oxide copolymer and silicon oxide modified with methyl groups were synthesized catalytically at room temperature using oligomeric methylmethoxysiloxane and zirconium oxychloride (ZOC) octahydrate. The mechanism of curing of siloxane is considered. The thermal stability of compositions containing 5, 10, and 15 wt

Catalytic activity of Co foil in ethylene oxidation was studied against oxidation degree of Co surface at stepwise foil oxidation. Experiments were conducted at temperatures of 500–800°C by a pulse method using alternative pulses of 0.2% C2H4–0.25% O2–1% Ar–He testing mixture and 1% O2–1% Ar–He oxidative mixture. Oxidation degree of Co foil varied from a totally reduced surface to an oxidation depth about a hundred of cobalt oxide “monolayers”. Using XRD, SEM and EDS, it was shown that CoO phase formed during a first stage of the stepwise oxidation (from 0 to ~60 oxide “monolayers”) at the all tested temperatures and modifications of surface morphology could be observed. At this stage the samples had a relatively high activity in both partial and total oxidation of ethylene at 500–600°C. On the contrary, at 700–800°C total oxidation was practically absent and the rate of partial oxidation was much lower than that at 500–600°C. During a second stage of Co surface oxidation (from ~60 to ~120 oxide “monolayers”) at 500–600°C also Co3O4 phase was found as well as a gradual ordering of the oxide crystals. In that state, the samples demonstrated a stationary (at 500°C) or an extremal (at 600°C) activity in total oxidation of ethylene. On the contrary, a temperature increase up to 800°C led to a sharp decrease of catalytic activity of the Co foil in this interval of oxidation degree.

Self-oscillatory reactions of ethane oxidation (I) or CO oxidation (II) over Co foil at a temperature of 620 or 660°C, respectively, for 1 h caused the formation of a microporous surface layer composed of CoO crystals with sizes of 0.2–0.4 μm. In reaction (I), the crystals formed agglomerates with a size of ~1 μm with pores of the same size between them. The thickness of the microporous layer after type I treatment was ~0.7 μm. On the contrary, the agglomerates and pores were almost absent after type II treatment. The catalytic activity of foil samples with the microporous surface layers in the reactions of deep ethylene oxidation, CO oxidation, and CO methanation was measured. It was found that a maximal increase in the catalytic activity took place after type I treatment. The stability of the resulting porous layers in an inert (He), reducing (H2), or oxidizing (O2) atmosphere was studied upon heating to 750°C. A significant recrystallization and cracking of the layer were observed upon the inert-gas treatment. After heating in hydrogen, a strongly fixed surface layer with stable catalytic activity was formed. Finally, as a result of heating in an oxidizing atmosphere, the thickness of the surface layer increased to 6–8 µm; the main component was Co3O4, and its catalytic activity was minimal among the three cases.

The paper is devoted to the experimental and theoretical studies of self-sustained oscillations and wave phenomena during CO oxidation on Ni foil. A new type of spatial structures arising due to the redox processes of the catalyst and observed under isothermal conditions at atmospheric pressure were studied. A 3D distributed mathematical model was constructed, which describes the color change and the propagation of kinetic waves of nickel oxidation–reduction in a flow-through reactor. The main reason for the wave phenomena and their propagation during CO oxidation on nickel was shown to be the presence of an oxygen concentration gradient in the flow-through reactor due to the effect of mass transfer on the reaction rate.

The effects of flame stretch as well as that of thermal and molecular diffusion on the scenario of flame acceleration in channels are quantified by means of computational and analytical endeavors. The analytical formulation incorporates the internal transport flame properties into the theory of flame acceleration due to wall friction by means of the Markstein number, which characterizes the flame response to curvature and stretch. Being a positive or negative quantity and a function of the thermal-chemical combustion parameters, such as the thermal expansion ratio as well as the Lewis and Zeldovich numbers, the Markstein number either moderates or promotes flame acceleration. While the Markstein number may provide a substantial impact on the flame acceleration rate in narrow channels, this effect diminishes with increase in the channel width. The analytical formulation is accompanied by extensive computational simulations of the reacting flow equations, which clarify the impact of the Lewis number on flame acceleration. It is noted that for Lewis numbers below a certain critical value, at the initial stage of flame acceleration, a globally convex flame front splits into two or more finger-like segments, accompanied by a drastic increase in the flame front surface area and associated enhancement of flame acceleration. Later, however, these segments of the flame front meet, promptly consuming cavities and pockets, which substantially decreases the flame surface area and moderates acceleration. Eventually, this dynamics results in a single, globally convex flame, which keeps accelerating. Overall, the thermal-diffusive effects substantially facilitate flame acceleration, thereby advancing a potential deflagration-to-detonation transition.

The self-oscillatory mode of methane oxidation over Pd foil at temperature of 400°C for 1 h caused the formation of a surface layer containing bulky porous agglomerates of nanocrystals. According to SEM data, the agglomerates with diameters of 1–20 μm consisted of crystals ~100 nm in size with pores of similar sizes between them. The agglomerates projected over the surface by 5–10 μm. The catalytic activity of the treated samples in a CO oxidation reaction was measured. The temperature of the onset of the catalytic reaction (CO conversion, 3%) decreased from 400°C for the initial Pd foil to 200°C for the Pd foil after the self-oscillatory oxidation of methane. Results of X-ray diffraction analysis and energy-dispersive X-ray spectroscopy (EDS) allowed us to conclude that the agglomerates observed consisted of the crystals of palladium oxide (PdO). On the contrary, the oxidation of Pd foil surface in a stationary mode was found to promote the formation of a smooth layer of palladium oxide without noticeable porous structures, and the catalytic activity of this layer was lower than that of the Pd sample after self-oscillations. The stability of the obtained porous layers in an inert (He), reducing (H2), or oxidative (air) atmosphere on heating to 700°C was studied. Under the inert or reducing conditions, both the disappearance of palladium oxide and the destruction of nanoparticle agglomerates took place to cause a decrease in the catalytic activity of Pd foil in the CO oxidation reaction. On the contrary, the oxidative treatment caused both an increase in the PdO content of the sample and a growth of the number of porous nanocrystal agglomerates on the surface to result in an additional increase in the catalytic activity of Pd foil.

Self-oscillatory methane oxidation over Ni foil at 750°C for 1 h resulted in the formation of a porous layer with a depth of 10–12 μm. The layer depth did not increase as the self-oscillatory reaction time was increased to 2–3 h. The porous layer consisted of nickel oxide crystals 100–200 nm in size or metallic Ni crystallites (indistinct crystals) of the above size in an oxidative gas atmosphere or a reducing atmosphere, respectively. The formation of the layer caused a great increase in the catalytic activity of nickel in the carbon dioxide conversion of methane (CDCM). Immediately after the self-oscillatory reaction, the crystals in the porous layer were in an oxidized state. In this state, they can remain at 750°C in a flow of an inert gas or CO2 without catalytic activity losses. On the contrary, the oxide crystals were reduced to the metal in a reducing atmosphere (H2, CH4), and they gradually stuck together to form a spongy structure whose surface area was much lower than that of the initial oxidized sample. A decrease in the catalytic activity of nickel after reducing pretreatment and in the course of the catalytic CDCM (where the catalyst was also reduced) confirmed the above conclusion. The porous layer on the Ni surface was similar to a Ni foam sample with pores of ~1 μm (metallic membrane) in catalytic and reactive properties, but it differed in a limited depth on the surface of the bulk metal.

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.

Propagation of a premixed flame from a closed to an open end in micro-channels with smooth non-slip isothermal walls is considered in the context of flame extinction dynamics. Powerful exponential flame acceleration in micro-channels with adiabatic walls has been demonstrated at the initial quasi-isobaric stage of the process [Bychkov et al., Phys. Rev. E 72, 046307 (2005)]. In contrast to the previous studies, here we investigate flame propagation in channels with isothermal walls. The problem is solved by means of high-fidelity laminar numerical simulations of the complete set of the Navier–Stokes combustion equations. For most of the problem parameter sets chosen, we obtain initial flame acceleration after ignition at the closed channel end. This acceleration resembles qualitatively the adiabatic case, but it develops noticeably slower, in an approximately linear regime instead of the exponential one and persists only for a limited time interval. Subsequently, heat loss to the walls reduces the temperature and hence the volume of the burnt gas behind the flame front, which produces a reverse flow in the direction of the closed channel end. When the amount of the burnt gas becomes sufficiently large, the reverse flow stops the acceleration process and drives the flame backwards with modifications of the flame front shape from convex to concave. Eventually, the flame extinguishes. Qualitatively, the process obtained reproduces a possible combustion failure during deflagration-to-detonation transition observed in previous experiments. We investigate the key characteristics of initial flame acceleration such as the acceleration rate and the maximum speed of the flame tip.

The effect of the oxidation degree of a nickel foil surface on the rate of catalytic oxidation of ethylene was studied by a pulse method at 600 and 700°C. It was shown that a reduced metallic surface demonstrated a high activity in partial ethylene oxidation, whereas a partially oxidized surface with an oxidation degree of ~24 formal O2 monolayers, in the total oxidation of C2H4. A SEM investigation has revealed that the oxidized surface was partially coated with nickel oxide nanocrystals. A further increase in the surface oxidation degree led to a continuous coverage of the Ni surface with oxide crystals and a dramatic decrease of catalytic activity. In addition, a low maximum of total ethylene oxidation was observed at 700°C in the range of surface oxidation degree of 95–135 O2 monolayers.

The NOvA long-baseline neutrino experiment uses a pair of large, segmented, liquid-scintillator calorimeters to study neutrino oscillations, using GeV-scale neutrinos from the Fermilab NuMI beam. These detectors are also sensitive to the flux of neutrinos which are emitted during a core-collapse supernova through inverse beta decay interactions on carbon at energies of O(10 MeV). This signature provides a means to study the dominant mode of energy release for a core-collapse supernova occurring in our galaxy. We describe the data-driven software trigger system developed and employed by the NOvA experiment to identify and record neutrino data from nearby galactic supernovae. This technique has been used by NOvA to self-trigger on potential core-collapse supernovae in our galaxy, with an estimated sensitivity reaching out to 10 kpc distance while achieving a detection efficiency of 23% to 49% for supernovae from progenitor stars with masses of 9.6 M-circle dot to 27 M-circle dot, respectively.

Ethoxy groups, acetate complexes, and condensation products were detected on the surface of a 5% CuO/ZrO 2 catalyst using in situ IR spectroscopy under conditions of ethanol conversion. Formate complexes were not observed under the reaction conditions. Acetaldehyde, acetone, CO 2 , and ethylene were detected as the main reaction products of ethanol conversion; hydrogen, butane, and toluene were also formed in small amounts. Acetaldehyde was formed by the interaction of ethoxy groups and surface hydroxyl groups. Acetone, butane, and toluene resulted from the conversion of condensation products. The low rate of hydrogen formation on this catalyst was due to the absence of a high-temperature formate complex from the catalyst surface.