Multicomponent Oxide Systems Research Articles

Hydrogen technologies for decarbonization of ferrous metallurgy: scientific background and technical capabilities

To date, the use of ferrous hydrogen in metallurgy is considered from several positions. First, the partial or complete replacement of carbon with hydrogen reduces greenhouse gas emissions of CO2. Secondly, due to the different chemical affinity for oxygen, it becomes possible to selectively (selectively) extract components from complex complex ores and man-made materials. Thirdly, the absence of carbon in the reaction zone will make it possible to obtain a metal with a low content of carbides, which in many cases increases the demand for the product. Thermodynamic calculations of a multicomponent oxide system (Ni, Fe, P, Zn, Mn, V, Cr, O) in the presence of various reducing agents: carbon, hydrogen are performed using the TERRA software package, and their combined effects are considered. It is shown that the type of reducing agent affects the temperature of the beginning of the reduction of metals and the degree of their metallization. Thus, by selecting the type of reducing agent, its quantity, and the temperature of the process, it is possible to selectively extract some metals, and leave others in an oxidized state. Ilmenite concentrate in the form of a briquette was used in laboratory tests. The analysis of the iron reduction process using carbon or hydrogen as a reducing agent has been carried out. In comparison with the results obtained using carbon, the kinetics of iron reduction with hydrogen is higher. At the same time, the reduction proceeds with the formation of metallic iron, rutile (TiO2) and residual ilmenite. Whereas, in a carbothermic process occurring at higher temperatures (1000–1300 ℃), the reduction products are iron and iron ditanate (FeTi2O5). In addition, an important advantage of selective reduction by gas is the possibility of subsequent separation of the metallic and oxide phases by melting, without fear of secondary reduction due to solid carbon residues.

(Invited) Design of Photoactive Inorganic Nanomaterials for Environmental Challenges

Nowadays, one of the main technological challenges that we are facing is the ability to provide a sustainable supply of clean energy and, among all renewable sources, solar energy displays the greatest potential. Recently, the development of novel synthetic strategies has led to the preparation of nanostructured materials displaying unique properties compared to the bulk counterpart systems, with controlled and tunable morphologies able to enhance the activity and selectivity of a catalytic process. In particular, nanostructured materials synthesized via the bottom–up approach present an opportunity for future generation manufacturing of devices.This talk will focus on the importance of tuning the morphological features of a catalyst as a strategy to improve its optical and photocatalytic properties, focusing on how rationally designing inorganic materials at the nanoscale can lead to morphologies and structures suitable to enhance the performance of industrially and environmentally important processes. The talk will discuss some environmental applications that can be addressed by photoactive multi-component oxide systems synthesized via the bottom–up approach, highlighting their structure-reactivity relationship. Water contamination, in particular, is one of the upfront issues to be solved and complex organic molecules and pharmaceuticals, including antibiotics, are gaining attention due to their abuse and their low degradability. Photocatalytic drugs degradation will be presented as a successful case history [1-3] to provide inspiration to produce cheap, environmentally friendly, stable, and efficient photocatalysts, which hold a great potential for the development of new technologies not only for water remediation applications but also for energy applications in the field of solar fuel production.[1] E. Moretti, L. Storaro, A. Talon, P. Riello, A. Infantes Molina, E. Rodríguez-Castellón, Appl. Catal. B: Environmental 168 (2015) 385.[2] M. Telkhozhayeva, B. Hirsch, R. Konar, E. Teblum, R. Lavi, M. Weitman, B. Malik, E. Moretti, G.D. Nessim, Appl. Catal. B: Environmental 318 (2022) 121872.[3] L. Liccardo, M. Bordin, P.M. Sheverdyaeva, M. Belli, P. Moras, A. Vomiero, E. Moretti, Adv. Funct. Mater. 33 (2023) 2212486.

Unraveling the Structural and Compositional Peculiarities in CTAB-Templated CeO2-ZrO2-MnOx Catalysts for Soot and CO Oxidation.

Structure-performance relationships in functional catalysts allow for controlling their performance in a wide range of reaction conditions. Here, the structural and compositional peculiarities in CTAB-templated CeO2-ZrO2-MnOx catalysts prepared by co-precipitation of precursors and their catalytic behavior in CO oxidation and soot combustion are discussed. A complex of physical-chemical methods (low-temperature N2 sorption, XRD, TPR-H2, Raman, HR TEM, XPS) is used to elucidate the features of the formation of interphase boundaries, joint phases, and defects in multicomponent oxide systems. The addition of Mn and/or Zr dopant to ceria is shown to improve its performance in both reactions. Binary Ce-Mn catalysts demonstrate enhanced performance closely followed by the ternary oxide catalysts, which is due the formation of several types of active sites, namely, highly dispersed MnOx species, oxide-oxide interfaces, and oxygen vacancies that can act individually and/or synergistically.

MECHANISMS OF ADAPTATION PERICLASE-SPINEL REFRACTORIES TO THERMAL SHOCKS

In the group of periclase spinel refractories, the dynamics of demand for magnesite-chromite and chromium-magnesite refractories, which contain MgCr2O4 – magnesia-chromium spinel – in their phase composition, is changing, due to the environmental hazard of any hexavalent chromium compounds. These reasons stimulate the search for alternative refractories to replace chromium-containing ones. Periclase-spinel refractories of the MgO – MgAl2O4 system are poorly wetted by cement clinker melt and the lining made of them does not gain a garnish (coating), which is a mandatory technical requirement. It was necessary to develop a new type of periclase-spinel refractories based on more multicomponent oxide systems. At the same time, the task of ensuring their high heat resistance should be solved. Thus, the study of the mechanisms of adaptation of materials of the MgO – Al2O3 – FeO – TiO2 system, which counteract thermal stresses in refractories, is relevant. A new periclase-spinel refractory material has been developed, the phase composition of which is modified by a FeO- and TiO2-containing pre-synthesized additive. Refractories made of the developed material meet the technical requirements that determine operational reliability when used for lining high-temperature zones of rotary kilns for firing Portland cement clinker. The thermal resistance of a material is determined by its ability to withstand thermal stresses caused by the involuntary expansion/contraction of individual structural blocks of the material and causing its breakdown and subsequent destruction. Some mechanisms of adaptation are demonstrated and discussed based on the results of the analysis of X-ray and electron microscopic studies. Some of the discussed mechanisms are unconventional for the technological practice of refractory nonmetallic materials and complement the toolkit of materials scientists. The achieved results and some technological methods of ensuring thermal stability have signs of universality and can be used for various types of heterophase refractory nonmetallic materials

Tuning the mechanical and thermal properties of (MgNiCoCuZn)O by intelligent control of cooling rates

The possibility of altering the phase equilibria of multicomponent oxide systems through precise control of configurational entropy has opened a platform with unlimited possibilities to fine-tune material properties. The current work is aimed at tailoring the mechanical and thermal properties of (MgNiCoCuZn)O by an intelligent design of constituent phase structure resulting from controlled cooling from the stabilization temperature. Based on the cooling rates, the amount of CuO nucleation was found to vary between 5.4 and 12.3 wt%, along with a corresponding decrease in Cu2+ content in the matrix. It was observed that with the decrease in Cu2+ ion concentration in the matrix, the Young’s modulus and hardness increased by 33% and 26%, respectively, along with a corresponding decrease in the coefficient of thermal expansion by 15%. Similarly, an increased nucleation of CuO precipitates led to the improvement of fracture toughness of the material by 15%, while its thermal conductivity remained unaltered.

A multicomponent equimolar proton-conducting quadruple hexagonal perovskite-related oxide system.

Since the high configurational entropy-driven structural stability of multicomponent oxide system was proposed Rost et al. in 2015, many experiments and simulations have been done to develop new multicomponent oxides. Although many notable findings have shown unique physical and chemical properties, high configurational entropy oxide systems that have more than 3 distinct cation sites are yet to be developed. By utilizing atomic-scale direct imaging with scanning transmission electron microscopy and AC-impedance spectroscopy analysis, we demonstrated for the first time that a multicomponent equimolar proton-conducting quadruple hexagonal perovskite-related Ba5RE2Al2ZrO13 (RE = rare earth elements) oxide system can be synthesized even when adding eight different rare earth elements. In particular, as the number of added elements was increased, i.e., as the configurational entropy was increased, we confirmed that the chemical stability toward CO2 was improved without a significant decrement of the proton conductivity. The findings in this work broaden the use of the crystal structure to which the multicomponent model can be applied, and a systematic study on the correlation between the configurational entropy and proton conductivity and/or chemical stability is noteworthy.

Characterisation of Electrochemical Properties for Molten Titanium(IV) Oxide - Sodium Oxide and Expansion into Other Binary Oxide Systems for the Electrolytic Reduction of Valuable Metals

Molten oxide electrolysis is a promising route to reduce harmful environmental effects that occur when compared to more common industrial metal extraction techniques. This method can provide a stepping stone to decarbonise metal production and to do this suitable supporting electrolyte ore combinations need to be found. For the application of extracting titanium metal, due to the lack of electrochemical information on complex multi-component titanium metal oxide systems, designing an electrolytic cell and predicting ultra-high temperature (above 1500°C) behaviours becomes difficult. Hence, to gain insight into this electrochemical information a binary system, TiO2 – Na2O, was investigated via experimentation and the use of FactSage 7.2 (a thermodynamic predictive software). This system was chosen as the phase diagram indicated deep eutectics either side of a congruently melting line compound situated at approximately 40 wt% TiO2, hence providing suitable operating temperature and composition ranges. Additionally, FactSage predicted that the relative potentials of the half-cell reactions 2Na2O → 4Na + O2 and TiO2 → Ti + O2, change order when the composition of TiO2 is increased from below the congruently melting line compound, to above, indicating that above approximate 40 wt% TiO2, titanium metal may be favourably reduced first when electrolytically reducing the melt. Lab scale experimental process conditions (temperature and composition) were studied to determine the feasibility of electrolytically reducing titanium metal from the molten oxide mixture. From our research, expansion into other binary oxide systems for different metals of interest, specifically neodymium and tantalum, will be discussed. Specifically, systems that contain congruently melting line compounds with adjacent eutectic reactions were hypothesised to have a similar reordering of the half-cell potentials, favouring the reduction of the desired metals (Nd or Ta). Understanding simplified binary systems will scaffold insight into more complex, industrially-relevant molten oxide mixtures at ultra-high temperatures, potentially contributing to the discovery of new and more sustainable electrochemical pathways for technology-critical metals.

Calculation of eutectics temperatures and compositions of multicomponent sections of the system (Mg, Ca, Sr, Ba)O—Al2O3—Cr2O3

With change in the structure of metallurgical production in Ukraine, the range of used refractory materials is expanding: the share of unshaped highquality refractories is growing, since this eliminates the time-consuming and energy-consuming operation of firing piece products, and also simplifies the operation of creating a lining layer. To establish the maximum possible operating temperature of materials developed on the basis of compositions of the optimal regions of multicomponent oxide system (Mg, Ca, Sr, Ba)O— Al2O3—Cr2O3, it was necessary to calculate the temperatures and compositions of the eutectics of binary, ternary and four-component sections, which was the purpose of this study.
 For calculations in binary sections, the Epstein — Howland method is most acceptable, and in three- and four-component sections — the solution of nonlinear equations system. It was found that to obtain a refractory unshaped material based on calcium aluminium chromite cement with periclase as a filler, it is necessary to adjust the phase composition of the cement towards an increased CaCr2O4 content, and the total composition must contains at least 75 wt. % periclase or magnesium spinel. In addition, in the case of alumina hydrates formation as a result of cement hydration processes, magnesium spinel will be synthesized as part of a refractory unshaped material during service. To obtain refractory unshaped materials based on strontium aluminium chromite cement and periclase as filler, it is necessary to increase the SrAl2O4 content and minimize the Sr3Al2O6 content in the cement composition, while the filler content in the composition can vary within wide limits, since the melting temperature of such compositions will be more than 1700 °C. To create refractory unshaped materials based on barium aluminium chromite cements, it is necessary to increase the content of BaAl2O4 in the cement composition as the most hydraulically active and refractory component and the composition of the composite material should be low- or ultra-low-cement in order to increase the operating temperature. In addition, in the case of chromium hydroxides formation during the hydration of aluminium chromite cement, chromium spinel will be synthesized in the composition during service, increasing the refractoriness of resulting composition. Thus, by varying the type and phase composition of cement and the ratio of cement and aggregates in the concrete composition, it is possible to obtain unshaped materials with a wide operating temperature range for use in heat-stressed areas of high-temperature aggregates.

Highly Reliable Implementation of Optimized Multicomponent Oxide Systems Enabled by Machine Learning-Based Synthetic Protocol.

Multicomponent oxide systems are one of the essential building blocks in a broad range of electronic devices. However, due to the complex physical correlation between the cation components and their relations with the system, finding an optimal combination for desired physical and/or chemical properties requires an exhaustive experimental procedure. Here, a machine learning (ML)-based synthetic approach is proposed to explore the optimal combination conditions in a ternary cationic compound indium-zinc-tin oxide (IZTO) semiconductor exhibiting high carrier mobility. In particular, by using support vector regression algorithm with radial basis function kernel, highly accurate mobility prediction can be achieved for multicomponent IZTO semiconductor with a sufficiently small number of train datasets (15-20 data points). With a synergetic combination of solution-based synthetic route for IZTO fabrication enabling a facile control of the composition ratio and tailored ML process for multicomponent system, the prediction of high-performance IZTO thin-film transistors is possible with expected field-effect mobility as high as 13.06 cm2 V-1 s-1 at the In:Zn:Sn ratio of 63:27:10. The ML prediction is successfully translated into the empirical analysis with high accuracy, validating the protocol is reliable and a promising approach to accelerate the optimization process for multicomponent oxide systems.

Phase-Property Diagrams for Multicomponent Oxide Systems toward Materials Libraries.

Exploring the vast compositional space offered by multicomponent systems or high entropy materials using the traditional route of materials discovery, one experiment at a time, is prohibitive in terms of cost and required time. Consequently, the development of high-throughput experimental methods, aided by machine learning and theoretical predictions will facilitate the search for multicomponent materials in their compositional variety. In this study, high entropy oxides are fabricated and characterized using automated high-throughput techniques. For intuitive visualization, a graphical phase-property diagram correlating the crystal structure, the chemical composition, and the band gap are introduced. Interpretable machine learning models are trained for automated data analysis and to speed up data comprehension. The establishment of materials libraries of multicomponent systems correlated with their properties (as in the present work), together with machine learning-based data analysis and theoretical approaches are opening pathways toward virtual development of novel materials for both functional and structural applications.

Laser-induced structural modification in calcium aluminosilicate glasses using molecular dynamic simulations

Glass structures of multicomponent oxide systems (CaO–Al2O3–SiO2) are studied using a simulated pulsed laser with molecular dynamics. The short- and intermediate-range order structures revealed a direct correlation between the transformation of Al(IV) to Al(V), regions of increased density following laser processing, inherent reduction in the average T–O–T (T = Al, Si) angle, and associated elongation of the T–O bonding distance. Variable laser pulse energies were simulated across calcium aluminosilicate glasses with high silica content (50–80%) to identify densification trends attributed to composition and laser energy. High-intensity pulsed laser effects on fictive temperature and shockwave promotion are discussed in detail for their role in glass densification. Laser-induced structural changes are found to be highly dependent on pulse energy and glass chemistry.

Термодинамика роста металлической фазы при твердофазном восстановлении металлов в комплексных оксидах

To improve the technologies of solid-phase reduction of metals in ores, it is necessary to study in detail the regularities of the growth of nuclei of the metal phase, taking into account the conditions existing in the reduction aggregates. At the first stage of the study, the general regular-ities of the growth of a new phase in a multicomponent oxide system were studied. Using the methods of non-equilibrium thermodynamics, a complex physicochemical description of the solid-phase reduction of metals in a multicomponent oxide phase was obtained, taking into account the thermal and diffusion processes occurring in this case. Additionally, using the methods of chemistry of imperfect crystals, the regularities of the influence of the movement of anionic vacancies on the thermodynamic state of the system were formulated. For the considered system the physicochemical equations for the balance of vacancies and entropy were written. The developed new theory made it possible to consider thermal and diffusion processes, as well as the processes of vacancy movement in a multicomponent oxide system in their complexity. For a practical study of the reduction of metals in ores, the case of the growth of a metal particle from the initial phase of the ore was considered, taking into account the additional effect of the reducing agent on the process. On the basis of an integrated approach, a general expression for the production of entropy in the system of a growing metal nucleus, an initial ore phase and a phase of reducer inclusions was obtained. The carried out research made it possible to develop a mathematical model of the growth of a metal crystal in the volume of the oxide phase, depending on the heating mode and the composition of complex oxides. In particular, the developed mathematical model made it possible to calculate the growth rate of the metal nucleus in the initial multicomponent oxide phase. The obtained technique also made it possible to evaluate the degree of influence of the movement of anionic vacancies on the regularities of the reduction process.

New high-entropy oxide phases with the perovskite structure

Results of studying the structure and chemical composition of perovskite phases synthesized by solid-state sintering in multicomponent oxide systems: (Ba,Sr,Ca,Mg,Pb)(Ti,Zr)O3, (Ba,Sr,Ca,Mg,Pb)(Ti,Zr,Hf)O3, (Ba, Sr, Ca,Mg,Pb)(Ti,Zr,Hf, Sn)O3, and (Ba,Sr,Ca,Mg,Pb)(Ti,Zr,Hf,Sn,Mn)O3 are presented. The chemical composition of the obtained samples was investigated using a JEOL JSM7001F scanning electron microscope equipped with an Oxford INCA X-max 80 energy-dispersive X-ray fluorescence spectrometer. The structure was studied with a Rigaku Ultima IV powder X-ray diffractometer. It was demonstrated the possibility of obtaining a high-entropy perovskite phase. Elements (Ba, Sr, Ca, Ti, Zr, Hf, Sn), which can form the high-entropy perovskites have been determined, as well as the elements (Pb, Mg, Mn), which, for various reasons, are hardly incorporated in the high-entropy perovskites.

К 125-летию со дня рождения лауреата Нобелевской премии академика Николая Николаевича Семенова Полуэмпирические методы расчета температур ликвидуса в оксидных системах

In the present study, two semi-empirical methods (geometric and polynomial) were proposed to calculate liquidus temperatures in ternary and quaternary systems using the data on the equilibria in the corresponding binary systems. Advantages, limitations, and peculiarities of application of the semi-empirical methods proposed were considered. The reliability of the results of calculating the liquidus temperature values in the Gd2O3-Y2O3-ZrO2 system was illustrated by comparison with the available data on the phase equilibria. The capacity to evaluate the eutectic line position in the temperature-composition coordinates was shown in multicomponent oxide systems. It was mentioned that the semi-empirical approaches proposed may find a further use to evaluate the liquidus temperature values in multicomponent systems with the aim of reducing the amount of experimental investigations of phase equilibria at high temperatures.

Subsolidus structure of the ZnO–SrO–Al2O3–SiO2 system as a base for designing radio-transparent ceramics

Designing new materials with unique properties requires scientifically substantiated approaches to problem-solving. Applying a physical-chemical analysis of oxide systems to devise the formulation for a material makes it possible to determine the conditions of phase formation and assess the manufacturability of compositions. Given the enormous number of experiments required to build the state diagrams of multi-component oxide systems, the physical-chemical modeling is the most appropriate method to study their structure. This paper substantiates the selection of the basic oxide system ZnO‒SrO‒Al 2 O 3 ‒SiO 2 to design radio-transparent ceramics and reports the results of studying its subsolidus structure using modern data on splitting the system into elementary volumes. The main geometric-topological characteristics of the system's internal tetrahedra have been defined and analyzed; the minimum temperatures for melt occurrence have been calculated, as well as the eutectic compositions. To design radio-transparent ceramics with a predefined level of dielectric characteristics (e<10, tgd<10 -2 ), a region of the formulations has been selected within the tetrahedron SiO 2 –ZnAl 2 O 4 –ZnSiO 4 –SrAl 2 Si 2 O 8 concentrations, which ensure the synthesis of the target phases of willemite and strontium anorthite. By using the new data, heat-resistant polyphase ceramics have been obtained, whose dielectric characteristics (e=5.98‒8.96; tgd=0.004‒0.008) meet the requirements for radio transparent materials. The optimal ratio of phases (ZnSiO 4 :SrAl 2 Si 2 O 8= 1:1) has been established, which makes it possible to reduce dielectric permeability (e=5.98) and minimize dielectric losses (tgd=0.004). Scanning electron microscopy and X-ray analysis were used to determine the structural and phase features of the new ceramic materials

Encapsulation of Co3 O4 Nanocone Arrays via Ultrathin NiO for Superior Performance Asymmetric Supercapacitors.

Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co3 O4 nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co3 O4 nanocones are hydrothermally grown over NF following the precision controlled deposition of shell NiO considering Co3 O4 nanocone as host. NiO thickness of 5 nm exhibits the highest specific capacity of 1242 C g-1 (2760 F g-1 ) at current density 2 A g-1 , which is greater than pristine Co3 O4 @NF (1045.8 C g-1 or 2324 F g-1 ). The rate capability with 5 nm NiO/Co3 O4 @NF nanocone structures is about 77% whereas Co3 O4 @NF retains 46 % of capability at 10 A g-1 . The ultrathin ALD 5 nm NiO accelerates both rate capability and 95.5% cyclic stability after 12 000 charge-discharge cycles. An asymmetric device fabricated between 5 nm NiO/Co3 O4 @NF (positive) || activated carbon (negative) achieves an energy density of 81.45 Wh kg-1 (4268 W kg-1 ) with good cycling device stability. Additionally, LEDs can be energized by two ASC device in series. This work opens the path in both advanced electrode material and surface modification of earth-abundant systems for efficient and real-time supercapacitor applications.

Reactive flash sintering (RFS) in oxide systems: kinetics and thermodynamics

The literature of the reactive flash sintering (RFS) in multi-component oxide systems nowadays consists of different types of binary phase diagrams, which were used here for analysis. Kinetic analysis of the reaction and simultaneous densification of the product phase via the liquid-film-assisted flash sintering is in agreement with a few seconds time scale of RFS. Capillarity and osmotic driving forces under the applied electric field are responsible for the ultrafast reaction and compound formation. Thermodynamic analyses of model systems with characteristic eutectic and peritectic reactions and congruent solidification show that all systems have to undergo local melting for the observed ultrafast reaction and the resultant microstructures. While the liquid film subjected to the external electric field has a transient nature, its homogenous composition is in the equilibrium state. The fragile nature of the major oxide melts imposes crystallization and growth during the cooling with partition coefficient of 1. Therefore, equilibrium phase diagrams can be used to predict the final product phases and microstructures according to the precursor powder composition and the flash conditions.

Моделирование, разработка и создание сегнетоактивных материалов на основе многокомпонентных сложнооксидных систем

Моделирование, разработка и создание сегнетоактивных материалов на основе многокомпонентных сложнооксидных систем

A Study of Nickel and Iron Reduction Silicothermic Process by Thermodynamic Simulation

The results of studying the effect of silicon concentration of ferrosilicon: FeSi5 (5% Si), FeSi20 (20% Si), FeSi35 (35% Si), FeSi50 (50% Si), FeSi65 (65% Si) on the degree of nickel (ηNi) and iron (ηFe) reduction of the CaO-SiO2-MgO-Al2O3-FeO-NiO-P2O5 multicomponent oxide system at a temperature of 1500 °C by thermodynamic simulation are given2. The HSC Chemistry 6.12 software package developed by Outokumpu (Finland) was used for the simulation. The chemical compounds Ni3Si and Ni5Si2 with the corresponding thermodynamic characteristics are entered into the database. The calculations were performed by the “Equilibrium Compositions” subroutine at a gas pressure of 1 atm, containing 2.24 m3 N2, as a neutral additive. The obtained modeling results indicate the thermodynamic possibility of nickel and iron reduction from the CaO-SiO2-MgO-Al2O3-FeO-NiO-P2O5 oxide system by silicon of ferrosilicon. The degree of iron reduction increases from 88.8 to 91.4%, with an increase in the silicon concentration of ferrosilicon [Si]FeSi from 5 to 65%. The degree of nickel reduction with an increase in the silicon concentration of ferrosilicon remains almost unchanged and amounts to 99.8-99.7%. The degree of use of silicon is 92.1–94.5%. The chemical composition of the complex alloy – ferrosiliconickel is determined. The obtained simulation results can be used to develop the technology for producing ferrosiliconickel from nickel ore by silicothermic method.

Cu-Mg-Fe-O-(Ce) Complex Oxides as Catalysts of Selective Catalytic Oxidation of Ammonia to Dinitrogen (NH3-SCO)

Multicomponent oxide systems 800-Cu-Mg-Fe-O and 800-Cu-Mg-Fe-O-Ce were tested as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO) process. Materials were obtained by calcination of hydrotalcite-like compounds at temperature 800 °C. Some catalysts were doped with cerium by the wet impregnation method. Not only simple oxides, but also complex spinel-like phases were formed during calcination. The influence of chemical composition, especially the occurrence of spinel phases, copper loading and impregnation by cerium, were investigated. Materials were characterized by several techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption (BET), cyclic voltammetry (CV), temperature programmed reduction (H2-TPR), UV-vis diffuse reflectance spectroscopy and scanning electron microscopy (SEM). Examined oxides were found to be active as catalysts of selective catalytic oxidation of ammonia with high selectivity to N2 at temperatures above 300 °C. Catalysts with low copper amounts (up to 12 wt %) impregnated by Ce were slightly more active at lower temperatures (up to 350 °C) than non-impregnated samples. However, when an optimal amount of copper (12 wt %) was used, the presence of cerium did not affect catalytic properties. Copper overloading caused a rearrangement of present phases accompanied by the steep changes in reducibility, specific surface area, direct band gap, crystallinity, dispersion of CuO active phase and Cu2+ accessibility leading to the decrease in catalytic activity.