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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Perovskite samples of the LaMn1−xFexO3 (x = 0–1) series were prepared by the Pechini method; their physicochemical properties were studied using XRD, HRTEM, XPS, and BET, and their catalytic activity was estimated in nitrous oxide decomposition and methane and CO oxidation reactions. In methane and CO oxidation reactions, all intermediate (0 < x < 1) samples of the series exhibited a lower catalytic activity normalized to the unit surface area as compared to the extreme terms, whereas in the nitrous oxide decomposition all intermediate samples were more active than extreme terms of the series. Different dependences of activities on the composition obtained in the study for the tested reactions involving the catalyst oxygen are caused by differences in the reaction mechanisms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The study showed that the interaction of the product of centrifugal thermal activation of gibbsite with an aqueous solution of magnesium nitrate at a cationic ratio Mg:Al = 1:2 leads to the formation of mixed double hydroxides both under hydrothermal treatment at 150 °C and at room temperature. The subsequent thermal treatment at 550 °C of the product of mild interaction leads to ~90% alumina-magnesia spinel and ~10% MgO, while the treatment of the hydrothermal interaction product leads to ~100% spinel with the stoichiometric composition MgAl2O4. The obtained spinel samples possess a high specific surface area (above 100 m2/g) and a hierarchical pore structure formed by the micron-level particles of different sizes (1–2 and 10–20 μm) consisting of ~70 nm crystallites with ~3 nm pores; the samples differ mostly in the total volume and quantitative ratio of the pores. The samples have Lewis acid sites of moderate strength on the surface, the amount of which is much lower to how it is when compared with a sample prepared by precipitation in that they also differ by quantity from each other as well (503 μmol/g for stoichiometric spinel and 304 μmol/g for sample with admixture of MgO). As the calcination temperature is raised to 850 °C, the acidity decreases—only weak Lewis acid sites are observed, the amount of which is also higher for stoichiometric spinel (161 and 39 μmol/g, respectively). The method proposed for the synthesis of alumina-magnesia systems provides a high dispersion and a much lower surface acidity for the oxides; in addition, it minimizes or completely excludes wash water, in distinction to the precipitation method. [ABSTRACT FROM AUTHOR]

The dynamic capacity of the commercial desiccant (NaX zeolite) and the adsorbent, synthesised based on low-temperature modifications of aluminium oxide, obtained from bayerite-containing hydroxide, was determined with respect to water vapour. Experimental studies were carried out using a pilot installation at the atmospheric pressure and increased pressure (up to 0.6 MPa) and high humidity. The increase in the height of the layer of the adsorbents leads to an increase of their dynamic capacity with respect to water vapour and the protective power (action) time of the layer. It was shown that at the atmospheric pressure and the pressure of up to 0.3 MPa, the dynamic capacity of NaX is greater; at a higher pressure, the adsorption capacity of the developed adsorbent Al2O3 becomes greater than the zeolite capacity, which allows recommending it as a desiccant at increased pressure. [ABSTRACT FROM AUTHOR]

Interaction between the water adsorption ability of aluminium-oxide-based sorbents and their chemical composition, acid-base properties of the surface, and textural characteristics has been analysed. Alumina desiccants were synthesized with the centrifugal–thermal activation of gibbsite followed by the hydration of the gibbsite under mild conditions. It was demonstrated that the multicyclic adsorption regeneration of samples under realistic conditions results in structural transformations and changes in the acidity of their surfaces and water adsorption ability. The modification of pseudoboehmite with alkali ions increases surface basicity and the dynamic capacity of adsorbents relating to water vapours. Equations have been presented that describe the adsorption and desorption processes taking place during water vapour adsorption with the materials studied. [ABSTRACT FROM AUTHOR]

The one-pot hydrolysis-dehydration of activated microcrystalline cellulose was studied in pure hydrothermal water at 453 K over ZrO2 catalysts produced by thermodegradation, microwave treatment, mechanical activation, and sol–gel methods and spent without any co-catalyst. ZrO2 prepared by microwave treatment was more active compared to ones derived by other methods. The catalyst calcination temperature also impacted reactivity. The cellulose conversion increased simultaneously with acidity and SBET, which in turn were set by the preparation method and calcination temperature. Phase composition did not affect the activity. Yields of glucose and 5-HMF reaching 18 and 15%, respectively, were over the most promising ZrO2 prepared by microwave treatment at 593 K. To our knowledge, this ZrO2 sample provided the highest activity in terms of TOF values (15.1 mmol g−1 h−1) compared to the pure ZrO2 systems reported elsewhere. High stability of ZrO2 derived by microwave irradiation was shown in five reaction runs. [ABSTRACT FROM AUTHOR]

The effect of alkali metal (Li, Na, K) incorporation on the morphology and water vapor uptake properties of mesoporous Al2O3 has been studied. The modification of the raw material, pseudoboehmite, represented a mixture of low-temperature phases (γ + η + χ)-Al2O3, and has been done at low-temperature that does not change the phase ratio. A decrease in specific surface values and an average pores size increase were observed as a result of the introduction of metal cations by impregnation and subsequent thermal treatment. The influence of the content of the modifying metal on the adsorption ability of the obtained samples in relation to water vapours has been studied. It has been established that alkaline modification Al2O3 with the lithium cations did not result in adsorption ability improvement, whereas samples that were modified with sodium or potassium in the amount of 1.2 weight % and 2.6 weight %, respectively, possess a higher equilibrium capacity (by ~40%), as compared to that of the initial sample (Al2O3), and a sufficiently high adsorption rate. [ABSTRACT FROM AUTHOR]

This article attempts to study changes in the microstructure of solid solutions with the perovskite structure La0.5Ca0.5Mn0.5Fe0.5O3 under the action of the methane oxidation reaction medium. By the methods of XRD, XPS and HRTEM the initial condition of the structure and the surface of the perovskite were both investigated. A feature of the structure of this solid solution is the presence of planar defects in the direction of the planes (101). After the methane oxidation reaction, a similar study of perovskite structure was conducted to obtain the changes. It was shown that under the action of the reaction medium, Ca1−xMnxO particles form on the surface of the perovskite phase, while planar defects in La0.5Ca0.5Mn0.5Fe0.5O3 structure remain. In situ XRD experiments on perovskite calcination in helium current up to 750 °C showed the formation of a similar Ca1−xMnxO phase on the perovskite surface. [ABSTRACT FROM AUTHOR]