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Chemical looping combustion (CLC) is a clean and efficient flame-free combustion technology, which combust the fuels by lattice oxygen from a solid oxygen carrier with inherent CO2 capture. The development of oxygen carriers with low cost and high redox performance is crucial to the whole efficiency of CLC process. As the solid by-product from the sulfuric acid production, pyrite cinder presented excellent redox performance as an oxygen carrier in CLC process. The main components in pyrite cinder are Fe2O3, CaSO4, Al2O3 and SiO2 in which Fe2O3 is the active component to provide lattice oxygen. In order to systematic investigate the functions of supports (CaSO4, Al2O3 and SiO2) in pyrite cinder, three oxygen carriers (Fe2O3-CaSO4, Fe2O3-Al2O3 and Fe2O3-SiO2) were prepared and evaluated in this study. The results showed that Fe2O3-CaSO4 displayed high redox activity and cycling stability in the multiple redox cycles. However, both Fe2O3-Al2O3 and Fe2O3-SiO2 experienced serious deactivation during redox reactions. It indicated that the inert Fe-Si solid solution (Fe2SiO4) was formed in the spent Fe2O3-SiO2 sample, which decreased the oxygen carrying capacity of this sample. The XPS results showed that the oxygen species on the surface of Fe2O3-CaSO4 could be fully recovered after the 20 redox cycles. It can be concluded that CaSO4 is the key to the high redox activity and cycling stability of pyrite cinder.

The characterization of the active structure of water-splitting catalysts is crucial to evolve to a sustainable energy future based on hydrogen. Such information can only be obtained by operando methods. We present a diffuse reflectance UV-vis (DRUV) spectroelectrochemical study that allows tracking the changes of solid oxygen evolution catalysts under working conditions. The versatility of our approach is demonstrated on two cobalt-containing catalysts, Zn0.35Co0.65O and CoAl2O4. The changes the catalysts undergo during the oxygen evolution reaction can be tracked by probing the electronic structure using UV-vis spectroscopy. These findings are compared to ex situ analyses, which support the assignments of the structures stabilized under different potentials. Thus, structure–activity correlations can be proposed, and deeper insights into the catalytically active structures can be obtained.

Conventional fiber reinforced plastics (FRPs) have compatibility issues with solid oxygen while used as a fuel tank, which might cause combustion and explosion. To study the compatibility of different epoxy resins with liquid oxygen, molecular dynamics was used to simulate the phase changes of cross-linked epoxy resins under the impact of solid oxygen. Three curing resin systems, which are bisphenol A epoxy resin (DGEBA), bisphenol F epoxy resin (DGEBF), and tetrahydrophthalate diglycidyl ester (epoxy resin 711), are modeled to investigate the rational material system for the application of fuel tanks in launching vehicles. The simulation results show that the order of solid oxygen compatibility of these epoxy resins is DGEBA > DGEBF > epoxy resin 711 at the same density of crosslinking. The selection of curing agent also has an impact on the compatibility, with the same epoxy, diaminodiphenyl methane (DDM) has more advanced performance comparing to diaminodiphenyl sulfone (DDS). Keywords: Molecular dynamics, ReaxFF, Epoxy resin, Oxygen compatibility

Mn-based solid oxygen carriers supported on MgAl2O4 were prepared by the microwave-assisted combustion method followed by wet impregnation of the active phase. The oxygen carriers were characterized by X-ray diffraction, temperature-programmed reduction and scanning electron microscopy with energy-dispersive spectroscopy of the surface. The study aimed to evaluate the influence of the thermal treatment on the structure and reactivity of the oxygen carriers. Reactivity tests using coal as fuel were carried out in a thermobalance at temperatures of 750–850 °C to evaluate the behavior of the carriers. The results revealed that oxygen carriers, which were subjected to only a heat treatment after the impregnation step (MnC1), showed more reactive surfaces presenting a greater number of non-reactive and irreversible phase and thus displaying lower oxygen transport capacity as well as poorer reactivity. The carriers prepared by heat treating the support after the combustion reaction and again after the impregnation step (MnC2), showed higher oxygen transport capacity and greater reactivity with coal at 850 °C. The better reactivity is associated with the formation of Mg6MnO8 and Mn2O3 phases.

The interaction between chloride ions and passivate film of steel bars determines the corrosion resistance of iron materials. In this study, the molecular structure, dynamics properties and adsorption behavior of water molecules and ions on passivate film surface is systematically investigated by molecular dynamics simulation method. This interfacial model is constructed for NaCl solution with 1.5 mol/L near the γ-FeOOH [0 1 0] surface. The FeO6 octahedron, exhibiting strong hydrophilic nature within the surface, provides a large amounts of oxygen sites to form H-bonds with the neighboring water molecules. The surface water molecules, distributed in the first adsorbed layer, not only show a comparably high magnitude of dipole moment but also tend to develop an H-down orientation with respect to the γ-FeOOH substrate. Solid oxygen and hydrogen atoms in the γ-FeOOH substrate, which replace the surrounding water molecules, change the hydration structure of ions and the adsorbed ions mobility. Furthermore, the sodium and chloride ions can be adsorbed by the iron hydroxyl surface in different ways. On the one hand, by forming Na O bond with solid oxygen in the iron hydroxyl, the sodium ions can penetrate into the vacancy areas between the neighboring FeO6 octahedrons. On the other hand, chloride ions form H-bonds with the neighboring Fe OH groups and associate with sodium ions on the surface to form the cation-anion ionic pairs. Both H-bond connection and the cation-anion ionic pairs restrict the chloride ions in the γ-FeOOH substrate. Additionally, due to the attraction of the solid substrate, the diffusion coefficient of solution species within the surface dramatically decrease by 70% and the resident time of water and ions in the vicinity of γ-FeOOH substrate is elongated more than twice as compared with that in bulk solution. Hopefully, this paper can provide valuable insights and interpret the corrosion mechanism of iron materials at the molecular level.

11 Figures, 4 Tables.-- © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, The in-situ Gasification Chemical Looping Combustion (iG-CLC) process allows combustion with inherent CO2 capture. In this process, the oxygen for combustion is commonly supplied by a solid oxygen carrier based on a metal oxide thus avoiding direct contact between fuel and air. The oxygen carrier circulates between two reactors. In the fuel reactor, the fuel is oxidized to CO2 and H2O while the oxygen carrier is reduced. In the air reactor, the reduced oxygen carrier is regenerated in air. Ilmenite has been widely used as a low-cost oxygen carrier for the iG-CLC process, and it can be taken as a reference material. Recently, the Tierga iron ore has been identified as a promising candidate for further scale-up of the process due to the higher combustion efficiency achieved compared to the results using ilmenite. Modelling of the iG-CLC process with Tierga iron ore as oxygen carrier is a key step to determine the potential of this material. In order to model the iG-CLC process it is necessary to know the reactivity of both oxygen carrier and fuel used. In this paper, the kinetic determination for the reduction and oxidation reactions of the Tierga ore is presented. Reaction orders close to unity were obtained for the main reducing gases, i.e. H2, CO and CH4, as well as O2. The activation energy values obtained were 81.1 ± 7, 76.1 ± 6 and 257 ± 14 kJ/mol for H2, CO and CH4, respectively. The activation energy for oxidation was determined as 18.4 ± 0.5 kJ/mol. In addition, a simple method is used for a comparison of the performance of different oxygen carriers based on their kinetics., This work was supported by the Spanish Ministry of Economy and Competitiveness (projects ENE2014-56857-R, ENE2016-77982-R), by the European Regional Development Fund (ERDF), the EU project ACCLAIM (RFCP-CT-2012-00006). T. Mendiara thanks for the ‘‘Ramón y Cajal’’ post-doctoral contract awarded by the Spanish Ministry of Economy and Competitiveness. The authors also thank PROMINDSA for providing the iron ore used in this work.

Low-temperature thermal diffusivity of molecular cryocrystals (O₂, N₂, CO, N₂O and CO₂) has been investigated and some anomalies were found. The thermal diffusivity of these crystals vary by more than 4–6 orders of the magnitude in the temperature range from 1 K up to their triple points. The thermal diffusivity displays jumps at the phase transition points. It has been found that the thermal diffusivity of solid oxygen is nonmonotonic. Below 4 K, the temperature dependence shows a plateau which is due to the fact that both the heat capacity and the thermal conductivity have the cubic temperature dependence in this temperature range. For the cryocrystals of the nitrogen group, a similar plateau is shifted to lower temperatures. The temperature dependence of the equalization time for these crystals is studied. Досліджено низькотемпературну температуропровідність молекулярних кріокристалів (O₂, N₂, CO, N₂O і CO₂). Температуропровідність цих кристалів змінюється більш ніж на 4–6 порядків в області температур від 1 К до їх потрійних точок. В області фазових перетворень спостерігаються стрибки температуропровідності. Виявлено, що температуропровідність твердого кисню є немонотонною. Нижче 4 К на температурній залежності спостерігається плато, яке обумовлено тим, що як теплоємність, так і теплопровідність в цьому температурному діапазоні мають кубічну температурну залежність. Для кріокристалів азотної групи подібне плато зміщується в бік більш низьких температур. Вивчено температурну залежність часів вирівнювання температури для цих кристалів. Исследована низкотемпературная температуропроводность молекулярных криокристаллов (O₂, N₂, CO, N₂O и CO₂). Температуропроводность этих кристаллов изменяется более чем на 4–6 порядков в области температур от 1 К до их тройных точек. В области фазовых переходов наблюдаются скачки температуропроводности. Обнаружено, что температуропроводность твердого кислорода является немонотонной. Ниже 4 К на температурной зависимости наблюдается плато, обусловленное тем, что как теплоемкость, так и теплопроводность в этом температурном диапазоне имеют кубическую температурную зависимость. Для криокристаллов азотной группы подобное плато смещается в сторону более низких температур. Изучена температурная зависимость времен выравнивания температуры для этих кристаллов.

6 Figuras.- 3 Tablas.-"This is a post-peer-review, pre-copyedit version of an article published in Mitigation and Adaptation Strategies for Global Change. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11027-019-9840-5".-Título del post-print: Biomass combustion by Chemical Looping with Oxygen Uncoupling process: experiments with Cu-based and Cu-Mn mixed oxide as oxygen carriers., Bioenergy with carbon dioxide (CO2) capture and storage (BECCS) technologies represent an interesting option to reach negative carbon emissions, which implies the removal of CO2 already emitted to the atmosphere. Chemical looping combustion (CLC) with biomass can be considered as a promising BECCS technology since CLC has low cost and energy penalty. In CLC, the oxygen needed for combustion is supplied by a solid oxygen carrier circulating between the fuel and air reactors. In the fuel reactor, the fuel is oxidized producing a CO2-concentrated stream while the oxygen carrier is reduced. In the air reactor, the oxygen carrier is regenerated with air. Chemical looping with oxygen uncoupling (CLOU) is a CLC technology that allows the combustion of solid fuels as in common combustion with air by means of an oxygen carrier that release gaseous oxygen in the fuel reactor. In the last years, several Cu-based, Mn-based, and mixed oxide oxygen (O2) carriers have been tested showing good CLOU properties. Among them, copper (Cu)-based and Cu-Manganese (Mn) mixed oxides showed high reactivity, O2 release rate, and high O2 equilibrium concentration. The aim of this work is to study the viability of biomass combustion by CLOU process. The combustion of three types of biomass (pine sawdust, olive stone, and almond shell) were studied in a continuous 1.5 kWth CLC unit. Two O2 carriers were tested: a Cu-based oxygen carrier with Magnesium, Aluminum, Oxgen (MgAl2O4) as an inert prepared by spray drying (Cu60MgAl) and a mixed Cu-Mn oxide prepared by spray granulation (Cu34Mn66). These materials are capable of releasing gaseous oxygen when they are reduced in a different range of temperatures. CO2 capture and combustion efficiency were evaluated. Two fuel reactor operation temperatures were used: 775–850 °C for Cu34Mn66 and 900–935 °C for Cu60MgAl. High CO2 capture efficiencies and 100% combustion efficiency were reached with both oxygen carriers and with all the biomasses tested. Therefore, the CLOU technology with the Cu- and Cu-Mn-based oxygen carriers allowed avoiding CO2 emissions maintaining high combustion efficiencies. Results obtained demonstrate that this innovative biomass combustion technology combined with carbon storage lets an efficient BECCS process implementation., I. Adánez-Rubio acknowledges the MINECO and Universidad de Zaragoza (UZ) for the post-doctoral contract awarded (FJCI-2015-23862). A. Pérez-Astray thanks MINECO for the BES-2015-074651 pre-doctoral fellowship co-financed by the European Social Fund.This work was financially supported by the Spanish Ministry of Economy and Competitiveness (MINECO Project: ENE2014-56857-R) and the European Union ERDF funds.

7 figures, 5 tables.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical Looping Combustion (CLC) is a promising carbon capture technology to contribute to the development of BioEnergy with Carbon Capture and Storage (BECCS) technologies. In CLC, the oxygen needed for combustion is supplied by a solid oxygen carrier. During the last years, intensive research has been conducted to identify potential oxygen carriers. Iron and manganese-based minerals allowed obtaining high CO2 capture efficiencies, but lower values for the combustion efficiency, that is, high oxygen demand values, due to the high content of volatiles in biomass. Manganese-iron mixed oxides doped with titanium possess the capability of releasing molecular oxygen under specific conditions which would enhance volatile conversion. The objective of the present work was to evaluate the potential of one of these materials ((Mn66Fe)-Ti7) to improve the combustion efficiency of CLC with biomass in a 0.5 kWth continuous CLC unit. Almost 100% of CO2 capture efficiency was obtained in all the experiments. Once the operational conditions for the synthetic material (Mn66Fe)-Ti7 were optimized, it was possible to reach oxygen demand values about 10% with the advantage that the (Mn66Fe)-Ti7 oxygen carrier presented magnetic properties that would facilitate its separation from biomass ashes in the fuel reactor., This work was supported by ENE2017-89473-R AEI/FEDER, UE. A. Pérez-Astray thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for the BES-2015-074651 pre-doctoral fellowship co-financed by the European Social Fund. T. Mendiara thanks for the “Ramón y Cajal” post-doctoral contract awarded by MINECO.

Small : nano micro (2104356), (2021). doi:10.1002/smll.202104356, Published by Wiley-VCH, Weinheim

Chemical looping water splitting systems operate at relatively high temperatures (450-800 degree C) to produce, purify, or store hydrogen by the cyclic reduction and oxidation (redox) of a solid oxygen carrier. Therefore, to improve long-term operation, it is necessary to develop highly stable oxygen carriers with large specific surface areas. In this work, highly interconnected doped Fe2O3 foams are fabricated through the freeze-casting technique, and the aid of a submicrometric camphene-based suspension to prevent Fe sintering and pore clogging during redox operation. The influence of the dopant elements (Al and Ce) over the pore morphology evolution, and redox performances are examined. The use of an Fe2O3 porous structure with initial pore size above 100 microns shows a significant reduction of the sample densification, and the addition of Al2O3 by the co-precipitation process proves to be beneficial in preventing the generation of a core-shell structure following redox processing., 25 pages, 8 figures

The phase diagram of oxygen is investigated for pressures from 50 to 130 GPa and temperatures up to 1200 K using first-principles theory. A metallic molecular structure with the P63/mmc symmetry (η′ phase) is determined to be thermodynamically stable in this pressure range at elevated temperatures above the e(O8) phase. Crucial for obtaining this result is the inclusion of anharmonic lattice dynamics effects and accurate calculations of exchange interactions in the presence of thermal disorder. We present analysis of electronic, structural, and thermodynamic properties of solid oxygen at 0 K and finite temperature with hybrid exchange functionals, including a comparison with available experimental data.

This review aims to give more understanding of the selection and development of oxygen carrier materials for chemical looping. Chemical looping, a rising star in chemical technologies, is capable of low CO2 emissions with applications in the production of energy and chemicals. A key issue in the further development of chemical looping processes and its introduction to the industry is the selection and further development of an appropriate oxygen carrier (OC) material. This solid oxygen carrier material supplies the stoichiometric oxygen needed for the various chemical processes. Its reactivity, cost, toxicity, thermal stability, attrition resistance, and chemical stability are critical selection criteria for developing suitable oxygen carrier materials. To develop oxygen carriers with optimal properties and long-term stability, one must consider the employed reactor configuration and the aim of the chemical looping process, as well as the thermodynamic properties of the active phases, their interaction with the used support material, long-term stability, internal ionic migration, and the advantages and limits of the employed synthesis methods. This review, therefore, aims to give more understanding into all aforementioned aspects to facilitate further research and development of chemical looping technology.

Chemical-looping combustion (CLC) is an attractive process in CO2 capture, especially when solid oxygen carriers are used in it. The main requirements for oxygen-transporting materials include appropriate oxidation (in air) and reduction (in the presence of fuel) ability. In the paper a conceptual proposition for CLC-related processes with the application of solid oxygen carriers oxidized in both air and CO2 atmosphere has been presented. The possibility of the “looping” process on the same carriers using both CO2 and air atmosphere as an oxidizing agent allows us to enrich the concept of CLC and related processes by proposing a cyclic recirculation of the produced CO2 back to the installation. The oxidizing of solid oxygen carrier in a CO2 atmosphere is accompanied by CO emission from the plant. This toxic gas could be transformed into a useful product in any chemical process. It is possible to combine the looping processes with manufacturing of any appropriate morphological form of carbon in the cyclic CO disproportionation process. The combined process could lead to a lower CO2 emissions to the environment. SrTiO3 doped by Cr (STO:Cr) and a mixture of TiO2- and Ni-based compounds (TiO2-Ni) were investigated as oxygen transporting materials. The experiment methodology based on thermogravimetric, diffraction and spectroscopic studies was shown. Thermogravimetric (TGA) and Powder Diffraction (XRD) measurements were provided in-situ during a few cycles in a reducing (Ar+3 % H2) and oxidizing environment. Moreover, the STO:Cr powders were characterized ex-situ by the X-ray Photoelectron Spectroscopy (XPS) method. It was found that in tested conditions the cyclic process of the investigated powders’ oxidation and reduction is possible. Satisfactory results considering the oxygen transport capacity was obtained for the TiO2-Ni sample.

The combustion of fuel in oxygen rather than in air is one route to allow for the large-scale capture and storage of CO2. An alternative to the conventional air separation to produce oxygen, which imposes a significant energy penalty, is chemical looping air separation (CLAS). CLAS exploits the cyclic oxidation and reduction of solid oxygen materials. Here, the equilibrium partial pressure curves and the redox behavior for two potential materials (the perovskites SrFeO3-δ and SrMn0.1Fe0.9O3-δ) are derived from experiments. For the redox tests, a low dead volume micro reactor, operated as a differential packed bed, was used. This system enabled measuring the process of reduction at the 10 ms scale. Experiments were carried out between 798 and 898 K, with pO2 varied between 0 and 0.21 atm. All perovskites showed good performance during experiments lasting 1000 cycles. Despite similar chemical composition, the measured oxygen chemical potential and reduction kinetics differed between the tested materials significantly.

The novel open-source flowsheet simulation software DYSSOL was used to simulate effects inside a system of interconnected fluidized bed reactors. The development of the needed models was done exemplary for the Chemical Looping Combustion process for solid and gaseous fuels. In CLC a solid oxygen carrier material is circulated between interconnected fluidized bed reactors. In the simulation, the focus is laid on the prediction of the dynamics of the whole system, especially the process start-up, shut-down and fuel load change. A dynamic model, which can be applied for bubbling beds and circulating fluidized beds was derived. Additionally, a cyclone was introduced for gas-solid separation. Loop seals ensure gas sealing between the reactors and were included into the modeling. Fluid mechanics inside the systems are modeled with empirical and semi-empirical, one-dimensional correlations, to enable fast calculations. These considerations allow real-time simulations of long-term effects in the system. The chemical reactions for gaseous and solid fuel combustions are included in the simulation. This has an effect on the solid oxygen carrier and so the oxidation and reduction of the carrier are regarded. The simulations were validated with experiments on a 25 kWth Chemical Looping Combustion facility at TUHH. The flowsheet models are able to predict the movement of the bed material between the units after operation changes as well as the time frames in which these changes occur. Besides, the gas and solids conversions in the fluidized bed reactors were simulated accurately.

High magnetic field x-ray diffraction experiments of solid oxygen have been performed at 10 K using DC magnetic fields of up to 5 T as well as pulsed magnetic fields of up to 25 T. The $\ensuremath{\alpha}$ phase of oxygen exhibits no magnetostriction greater than $\mathrm{\ensuremath{\Delta}}d/d={10}^{\ensuremath{-}4}$ at 5 T, where $d$ and $\mathrm{\ensuremath{\Delta}}d$ denote a lattice plane spacing and its magnetic field variation, respectively. The $\mathrm{\ensuremath{\Delta}}d/d$ at higher fields of up to 25 T is found to be smaller than $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. These results contradict the previously reported giant magnetostriction in the $\ensuremath{\alpha}$ phase where the volume magnetostriction $\mathrm{\ensuremath{\Delta}}V/V$ reaches ${10}^{\ensuremath{-}2}$ at 7.5 T [K. Katsumata et al., J. Phys.: Condens. Matter 17, L235 (2005)].

The paper provides an up-to-date review of the experimental and theoretical works on solid oxygen published over the past decade. The most important results presented in this review are the following: Detection of magnetic collapse in neutron studies under the delta–epsilon transition. Identification of the lattice structure of the ϵ phase. In this structure the O 2 molecules retain their individuality, but there is an additional link leading to the formation of clusters of molecular quartets with the structural formula (O 2 ) 4 . Discovery of the unique magnetic properties of the delta phase, which hosts three different magnetic structures in the domain of the same crystallographic structure. The extension of the phase diagram to the high-pressure high-temperature region which was previously beyond the reach for experiment; the molecular η and η ′ phases were found and their structures were identified. Behavior of the melting line up to 60 GPa (1750 K). Discovery of a new molecular θ phase in ultrahigh magnetic fields up to over 190 T and the construction of the thermodynamical magnetic-field–temperature H – T phase diagram on the base of the ultrahigh-field magnetization, optical magneto-transmission, and adiabatic magnetocaloric effect measurements. Prediction of the persistence of the molecular state of solid oxygen up to the pressure of 1.9 TPa which is significantly higher than the corresponding limits in solid hydrogen and nitrogen, other generic molecular solids.

Chemical looping-based approaches allow for the production of high purity hydrogen from methane with an inherent separation of the coproduced carbon dioxide. In such a process, first methane is oxidized using lattice oxygen from a solid oxygen carrier. In the second half-cycle, the reduced oxygen carrier is reoxidized with steam to yield hydrogen. In this work, we report on the development of an iron-based oxygen carrier with an excellent redox stability and probe the synergistic effect of adding Mn2O3 and ZrO2, leading to an enhancement of the reactivity of iron oxide with methane and increasing the hydrogen yield over multiple redox cycles. The promoting effects of Mn2O3 and ZrO2 in the oxygen carrier were elucidated by combining TPR, STEM-EDX, reactivity tests, and conductivity measurements complemented by SIMS analysis. The addition of ZrO2 promoted the oxidation reactivity of the material, whereas the addition of Mn2O3 accelerated the reduction of iron oxide. Conductivity measurements revealed that t...

The effect of ambient oxygen concentration on thermographic phosphor thermometry was investigated to uncover the “oxygen quenching” mechanism of Eu-based phosphors using a lifetime-based measurement system. The phosphors being studied were the Eu doped yttria stabilized zirconias (YSZs) with Y3+ concentrations of 0, 8, 12 and 57 mol%, having monoclinic, tetragonal, cubic and δ crystalline lattice, respectively. To vary the ambient oxygen concentration, three different gas phases (air, oxygen and nitrogen with methane) were used. It was found that the phosphorescent lifetimes and intensities of all four phosphors were sensitive to the ambient oxygen concentration, while the reference phosphor, Y2SiO5:Eu, was not influenced. The “oxygen quenching” phenomenon observed in Eu-doped YSZs was attributed to the oxygen vacancies in the phosphors. In addition, the four YSZ:Eu phosphors exhibited different sensitivity to ambient oxygen concentration. The oxygen sensitivity was found to be closely related to the site symmetry of Eu3+, which was previously determined by the phosphorescent spectra. The site symmetry of Eu3+ strongly affected the charge-transfer states and therefore determined the non-radiative decay rate. The current findings provided guidance for the phosphor selection and sensor design for oxygen/pressure sensing in high-temperature environment.

Black phosphorus was studied by state-of-the-art synchrotron X-ray diffraction in a Diamond Anvil Cell during room temperature compression in the presence of He, H2, N2 and Daphne Oil 7474. The data demonstrate that the existence of the pseudo simple-cubic (p-sc) structure above 10.5 GPa is an intrinsic feature of P independent from the pressure transmitting medium. In the case of He, the pressure evolution of the lattice parameters and unit cell volume of P across the A17, A7 and p-sc structures was obtained and the corresponding EOS derived, providing a deeper insight on the recently reported p-sc structure. The results presented in this letter highlight the key role of the s-p orbital mixing in the formation and stabilization of the p-sc structure up to ~30 GPa, solving apparent contradictions emerging from previous literature and finally bringing order to the sequence of the high pressure A7 layered structure in group 15 elements.

The effect of cobalt substitution by highly charged Mo⁶⁺ cations in SrCo0.8Fe0.2O3-δ (SCF) on the structure, microstructure, oxygen permeation performance and stability in the atmosphere containing carbon dioxide was systematically investigated by XRD, HT-XRD, Mossbauer spectroscopy, oxygen release technique and oxygen permeation experiments. The decrease in oxygen stoichiometry of SrCo0.8-xFe0.2MoxO3-δ (SCFM) materials was accompanied by nanostructuring with observed formation of nanosized domains with ordered oxygen vacancies. Equilibrium "3−δ−lg pO2−T" diagrams showed that SCF doping by molybdenum leads to broadening of the P1 (cubic perovskite phase) stability region. The obtained SCFM membrane materials possess improved phase stability in the intermediate temperature range (T < 700°C) and low oxygen partial pressure (pO2 < 0.06atm) compared to the undoped SCF oxide. The observed non-Arrhenius dependence of oxygen fluxes across SCFM disc membranes is related to combined control by bulk diffusion and surface exchange reactions.

Chemical looping combustion (CLC) processes have been shown to be promising and effective in reducing CO2 production from the combustion of various fuels associated with the growing global demand for energy, as it promotes indirect fuel combustion through solid oxygen carriers (SOC). Thus, this study aims to synthesize, characterize and evaluate mixed copper and titanium oxide as a solid oxygen carrier for use in combustion processes with chemical looping. The SOC was synthesized based on stoichiometric calculations by the polymeric precursor method and characterized by: X-ray fluorescence (XRF), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-FEG) with EDS, and Programmed Temperature Reduction (PTR). The oxygen carrying capacity (ROC) and the speed index of the reduction and oxidation cycles were evaluated by Thermogravimetric Reactivity (TGA). The main reactive phase identified was: The CuO phase for the mixed copper and titanium oxide were identified and confirmed by X-ray diffraction using the Rietveld refinement method. The reactivity of the CuO-TiO2 system was high, obtaining a CH4 conversion rate above 90% and a speed index of 40%/min. Due to the structural characteristics and the reactivity tests of this material, it is concluded that mixed copper and titanium oxide have the necessary requirements to be used in chemical looping combustion (CLC) processes. Se ha demostrado que los procesos de combustión por recirculación química (CRQ) son prometedores y efectivos para reducir la producción de CO2 a partir de la combustión de varios combustibles, asociada con la creciente demanda mundial de energía, ya que promueve la combustión indirecta del combustible a través de transportadores. Sólidos de oxígeno (TSO). Así, este estudio tiene como objetivo sintetizar, caracterizar y evaluar una mezcla de óxido de cobre y titanio como transportador sólido de oxígeno para su uso en procesos de combustión con recirculación química. El TSO se sintetizó en base a cálculos estequiométricos por el método del precursor polimérico y se caracterizó por: fluorescencia de rayos X (FRX), difracción de rayos X (DRX), Microscopía electrónica de barrido (SEM-FEG) con EDS, Reducción de temperatura programada (RTP). La capacidad de transporte de oxígeno (Roc) y el índice de velocidad de los ciclos de reducción y oxidación fueron evaluados por Reactividad Termogravimétrica (TGA). La principal fase reactiva identificada fue: La fase CuO para la mezcla de óxido de cobre y titanio se identificó y confirmó mediante difracción de rayos X utilizando el método de refinamiento de Rietveld. La reactividad del sistema CuO-TiO2 fue alta, obteniendo una conversión de CH4 superior al 90% y un índice de velocidad de 40% / min. De las características estructurales y las pruebas de reactividad de este material, se concluye que la mezcla de óxido de cobre y titanio tiene los requisitos necesarios para ser utilizada en procesos de combustión por recirculación química (CRQ). Os processos de combustão por recirculação química (CRQ), tem-se mostrado promissor e efeiciente na diminuição da produção de CO2 proveniente da combustão de diversos combustíveis , associada à demanda global crescente de energia, pois promove a combustão indireta do combustível por meio de transportadores sólidos de oxigênio (TSO). Desta forma, este estudo tem como objetivo sintetizar, caracterizar e avaliar óxido misto de cobre e titânio como transportador sólido de oxigênio para utilização em processos de combustão com recirculação química. O TSO foi sintetizado com base em cálculos estequiométricos pelo método dos precursores poliméricos e caracterizados por: Fluorescência de raio X (FRX), Difração de raio X (DRX), Microscopia Eletrônica de Varredura (MEV-FEG) com EDS, Redução à Temperatura Programada (RTP). A capacidade de transporte de Oxigênio (Roc) e o índice de velocidade dos ciclos de redução e oxidação foram avaliados por Reatividade por Termogravimetria (TGA). A principal fase reativa identificadas foi: A fase CuO para o óxido misto de cobre e titânio foram identificadas e confirmadas por Difratometria de raio X utilizando o método de refinamento Rietveld. A reatividade do sistema CuO-TiO2 foi elevada, obtendo uma conversão de CH4 acima de 90% e índice de velocidade de 40 %/mim. Pelas características estruturais e pelos testes de reatividade desse material, conclui-se que o óxido misto de cobre e titânio possuem os requisitos necessários para serem utilizados nos processos de combustão por recirculação química (CLC).

This reports recent advances on CO2 capturing methods, focusing on chemical looping combustion (CLC) as a promising technology to achieve this goal. Generally, there are three main methods to capture CO2 resulting from fossil fuel combustion: post-combustion, oxy-combustion, and pre-combustion. In CLC, which is either classified as a pre-combustion method or as the fourth capturing method, the solid oxygen carrier provides the oxygen needed for combustion. This technique helps to avoid diluting the combustion effluent stream with the N2 released from air and therefore, minimizes the requirement of CO2 separation, a major cost of CO2 capture. In addition, it minimizes the formation of NOx that results when N2 comes in contact with oxygen and fuels at high temperatures. The desired properties of oxygen carrier candidates for CLC are high reduction and re-oxidation rates, high oxygen capacity, good stability and fludiziability at high temperatures, friendly to the environment, and low cost. Transition metal oxides are common candidates for CLC. Most investigations in this field have examined the reactivity and stability of oxygen carriers but few investigations have focused on their reduction and re-oxidation reaction mechanisms. Researchers have proposed two mechanisms for these reactions, the nucleation-nuclei growth and unreacted shrinking core models. Despite numerous investigations of CLC, there is still a lack of knowledge in some of its aspects such as the underlying surface chemistry and the economic impact. This work critically reviewed all capturing methods of CO2 with focusing on CLC process as a promising technology due to its ability to concentrate the resulted CO2 and minimizes the separation cost. This work provides essential insight information into CLC technology and highlights its status and needs.

© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical looping combustion (CLC) involves the use of a solid oxygen carrier to transport the oxygen from the air to a fuel. Attention has recently been focused on oxygen carriers based on Mn-Fe mixed oxides because they are cheap materials that are able to release oxygen at high temperature, the so-called oxygen uncoupling step. The aim of this work was to assess the use of (Mn0.77Fe0.23)2O3 material as an oxygen carrier with the ability to transport oxygen both by reduction with gaseous fuels and by oxygen uncoupling, i.e. typical mechanisms in CLC and in Chemical Looping with Oxygen Uncoupling (CLOU), respectively. The particles prepared by mechanical mixing were screened to obtain particles of sufficient reactivity and mechanical strength for use in a fluidized bed reactor. The preparation methodology and calcining temperature were varied. The reactivity of one selected material was evaluated by performing redox cycles both in a TGA and a batch fluidized-bed reactor. Thus, its behaviour was assessed during both decomposition-regeneration of bixbyite phase [(Mn0.77Fe0.23)2O3] in CLOU and the reduction-oxidation of spinel phase [(Mn0.77Fe0.23)3O4] with gaseous fuels, i.e. H2, CO and CH4. Its oxygen uncoupling and re-oxidation capability was highly influenced by the reaction temperature and oxygen concentration. On the other hand, CLC redox cycles with gaseous fuels showed high reactivity with H2 and CO and high oxygen transport capacity by reduction to mangano-wüstite phase [(Mn0.77Fe0.23)O]. Good fluid-dynamic behaviour was observed for the oxygen carrier particles along the redox cycles without agglomeration problems, regardless of the operating conditions used in the batch fluidized-bed reactor. Thus, the selected material was considered a promising candidate for use in both in CLC with syngas and CLC with coal., This work was partially supported by the Spanish Ministry for Economy and Competitiveness via the ENE2013-45454-R, ENE2014-56857-R and ENE2016-77982-R projects, by the European Regional Development Fund (ERDF), and by the Spanish National Research Council (CSIC) via the 2014-80E101 project. R. Pérez-Vega is grateful to MICINN for the FPI Fellowship.

In the recent work, we study on the structural and electronic properties of the graphene like Pd monolayer with the adsorption of oxygen adatoms by using first-principles calculations. The electronic band structure and projected density of states investigate that Pd-surface with oxygen molecule adsorption gives metallic behaviour. We found that the behaviour changed at M -point in the electronic band structure as adding oxygen atoms. The oxygen adsorption was dissociative until the Pd surface immersed with oxygen atoms. The electron charge density increases as the number of oxygen atoms on Pd-surface increases. The noticeable observation is that by adding 7th oxygen atom, they started to ripple from fixed Pd-surface without making a bond due to oxygen coverage increases. The results show that Pd monolayer has different applications as a oxygen catalyst and it can be utilized as the pellet, surface, and film materials to safeguard sustenance from oxidation.

Traditional chemical looping technologies utilize solid oxygen carriers and has some disadvantages, especially when solid fuels like coal are used. In this work, a novel chemical looping process using gaseous metal oxide as oxygen carrier was proposed. The reaction of activated charcoal with gas-phase MoO3 was studied for the first time. The experiments were conducted isothermally at different temperatures in a fixed-bed reactor. The apparent activation energy of the reaction was calculated and suitable kinetic models were determined. The results and analysis showed that the proposed concept has potential in both coal chemical looping combustion and gasification process.

Y 2 O 3 films have great application potential in high-temperature metal matrix composite and nuclear engineering, used as interface diffusion and reaction barrier coating owing to their excellent thermal and chemical stability, high melting point and extremely negative Gibbs formation energy, and thus their structural and mechanical properties at elevated temperature are especially important. Oxygen vacancies exist commonly in yttrium oxide (Y 2 O 3 ) thin films and act strongly on the phase structure and properties, but oxygen vacancies dependent phase transition at elevated temperature has not been well explored yet. Y 2 O 3 thin films with different oxygen vacancy concentrations have been achieved by reactive sputtering through varying substrate temperature ( T s ), in which oxygen vacancies increase monotonously with increasing T s . For as-deposited Y 2 O 3 films, oxygen vacancies present at high T s can promote the nucleation of monoclinic phase, meanwhile, high T s can induce the instability of monoclinic phase. Thus their competition results in forming mixed phases of cubic and monoclinic at high T s . During vacuum annealing at 1000 °C, a critical oxygen vacancy concentration is observed, below which phase transition from monoclinic to cubic takes place, and above which phase transfer from monoclinic to the oxygen defective phase (ICDD file no. 39-1063), accompanying by stress reversal from compressive to tensile and maintenance of high hardness.

The mechanism of influence of molecular oxygen on the probability of ortho-para conversion of water molecules and its relation to water magnetization are considered within the framework of the concept of paramagnetic spin catalysis. Matrix elements of the hyperfine ortho-para interaction via the Fermi contact mechanism are calculated, as well as the Maliken spin densities on water protons in H2O and O2 collisional complexes. The mechanism of penetration of the electron spin density into the water molecule due to partial spin transfer from paramagnetic oxygen is considered. The probability of ortho-para conversion of the water molecules is estimated by the quantum chemistry methods. The results obtained show that effective ortho-para conversion of the water molecules is possible during the existence of water-oxygen dimers. An external magnetic field affects the ortho-para conversion rate given that the wave functions of nuclear spin sublevels of the water protons are mixed in the complex with oxygen.

Density functional theory is used to calculate the energies of formation of oxygen vacancies and migration of oxygen in the monoclinic and rutile phases of vanadium dioxide. The results are compared to estimates of the parameters of activation diffusion of oxygen using data from the electron-beam modification of thin film structures of vanadium dioxide and their subsequent reduction in the temperature range of 20–100°C. It is shown that diffusion in both phases of vanadium dioxide has a preferential direction of oxygen migration along axis а in the monoclinic phase and axis с in the rutile phase. The difference between the rate of oxygen vacancy generation upon electron-beam exposure above and below the temperature of metal–semiconductor phase transition is explained by the jump (~150%) in the activation energy of oxygen diffusion upon the structural transition of rutile–monoclinic phase. The mobility of oxygen (oxygen vacancies) correspondingly changes by more than an order of magnitude.

In this work, TiO2-SiO2 composite films were grown on amorphous quartz substrate at different oxygen partial pressure by pulsed laser deposition technique. The influence of oxygen partial pressure on structural, optical and surface properties of films was examined. Grazing incidence X-ray diffraction showed the formation of TiO2 rutile phase and degree of crystallinity decreased with the increase of oxygen pressure. Energy band gap of the films increased from 3.3 to 3.6 eV with the increase of oxygen pressure from 13.33 × 10− 3 Pa to 20.00 Pa. Variation of surface morphology of films with increasing oxygen partial pressure was studied by Atomic Force Microscopy (AFM). AFM images are showing that grain size of deposited films is increasing with increasing oxygen pressure. Field effect scanning electron microscopy images also shows the similar surface morphology. X-ray Photoelectron Spectroscopy shows the evidence of oxygen defect and related Ti3 + states in composite films. Composite films showed blue photoluminescence (PL) emission by the excitation of 350 nm wavelength. Deconvoluted PL peaks showed emission originated from Ti3 + defect level associated with an oxygen vacancy. Oxygen vacancy decreased with increasing oxygen pressure. Intense blue emission with high luminous efficacy of radiation and maximum flux was achieved for 13.33 × 10− 3 Pa oxygen pressure. Deposited films might be used in the field of blue light emitting diode application.

WOS: 000388050700015, We calculate in this study the Raman frequencies of the two librons and one vibron at various pressures at constant temperatures of 10 K and also at the temperatures of 6 and 18 K by using the volume data from the literature through the mode Gruneisen parameter for the a phase of oxygen. The Raman frequency shifts calculated for the pressure-induced librons and vibron, agree with the experimental frequency shifts in most cases, in particular at low pressures for alpha-O-2. This shows that the Raman frequency shifts can be calculated adequately from the volume by means of the mode Gruneisen parameter using the method given here for the alpha-phase of oxygen or more generally for molecular solids. (C) 2016 Elsevier GmbH. All rights reserved.

We investigated the atomic and local electronic structures of Ca2AlMnO5+δ to assess its potential as an oxygen storage material. High-angle annular dark-field scanning transmission electron microscopy was used to investigate structural changes in the material during oxygen storage. We found that the AlO4 tetrahedra convert to AlO6 octahedra during such a process. According to the Mn L-edge electron energy-loss near-edge structure (ELNES) measurements, the Mn oxidation state increased from +3 to +4 on oxygen storage. The observed site-resolved oxygen K-ELNES and first-principles electronic structure calculations showed that each nonequivalent oxygen site has different characteristics, corresponding to local chemical bonding and oxygen intake and release. For Ca2AlMnO5, the prepeak intensity was higher at MnO6 octahedral sites, indicating covalent bonding between the oxygen and Mn atoms. After oxygen storage, the ELNES spectra revealed that the Jahn–Teller distortion of the Mn sites was suppressed by the in...

The oxygen absorption and diffusion properties are studied in γ-TiAl and TiAl3 alloys within density functional theory using projector augmented wave method in the plane-wave basis. It is shown that the octahedral site inside the Ti-rich octahedron is preferable for oxygen in case of γ-TiAl alloy whereas the Al-rich octahedron is more favorable environment for oxygen in TiAl3. It is shown that the energy barriers for oxygen jumps between different sites in bulk alloys depend significantly on the local environments of oxygen and increase for its jump from Ti-rich sites. The trajectories with minimum energy barriers are determined for both Ti-Al alloys. It is shown that the increase of Al content in alloy leads to the decrease of barriers for oxygen jumps.

Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxide separation. A solid oxygen carrier circulates between the fuel reactor, where it provides oxygen for fuel oxidation, and the air reactor, where it is reoxidized. In this study a 10 kWth pilot reactor was used to examine a calcium manganite based oxygen carrier in continuous operation with natural gas as fuel during 99 h. The composition of the oxygen carrier can be described by the formula CaMn0.775Ti0.125Mg0.1O3-δ. The main part of the material forms a perovskite crystal structure which has oxygen releasing properties. The fuel conversion was generally above 95% and full conversion was reached for certain operating conditions. The elutriation of fines, defined as particles smaller than 45 μm, decreased over time to eventually be below detection limit. That suggested a loss of fines of less than 0.011 wt%/h, indicating a lifetime of over 9000 h. A high fuel conversion with no thermodynamic limitation, good mechanical strength, low cost and very low toxicity shows that this calcium manganite material qualifies as a very promising oxygen carrier.

International audience; Condensed O2 tends to form clusters, even with a long-range order. In particular, in solid oxygen, strong intermolecular charge transfer at high pressures leads to the formation of (O2)4 tetramers above 10 GPa, in the ε-O2 phase, with weak O2–O2 chemical bonds. Indeed, ε-O2 is entirely made of these tetramers. We conducted experimental investigations on strongly densified O2 in a different environment, that is to say in the form of a subnano phase build up within the 1D microchannels of a purely siliceous, inert zeolite, TON, at pressures of 0.5–20 GPa, by means of diamond anvil cells. Our X-ray diffraction and infrared and Raman spectroscopy results consistently show that oxygen forms clusters in this nanophase, above 10 GPa, similar to ε-O2, except that the clusters are rather of the type of weakly bonded (O2)2 dimers in this case. Also, by analogy with bulk oxygen, we show that the O2 spin within the dimers departs from S = 1 toward lower values, upon increasing pressure. Our findings thereby add to the general view on essential properties of highly dense oxygen.

Strontium-doped lanthanum manganite thin films were deposited by pulsed laser deposition on yttria-stabilized zirconia single crystals for a comprehensive electrochemical characterization of the material acting as a cathode. A physically-meaningful electrical model was employed to fit the electrochemical impedance spectroscopy results in order to extract the main oxygen mass transport parameters as a function of the temperature and oxygen partial pressure. The oxygen diffusion and surface exchange coefficients extracted from the analysis showed several orders of magnitude of enhancement with respect to the bulk values reported in the literature and an unexpectedly low dependence with the oxygen partial pressure. Different observations were combined to propose a mechanism for the enhanced incorporation of oxygen in interface-dominated thin films mainly based on the high concentration of oxygen vacancies expected in the grain boundaries.

The people of the Kakap River area live and open businesses along the river while they directly dispose of waste into the river. The people also use the river as a source of clean water to meet their daily needs. The purpose of this study was to determine the condition of the Kakap River water quality against dissolved oxygen with BOD, COD, pH, and DO parameters. This research used purposive sampling, starting from determining the sample point to be selected. The sample points used were three locations along the Kakap River. The results of the water quality analysis of the Kakap River from the first location in the estuary: COD parameter is 5.0 mg/L, the BOD parameter is

Chemical looping can provide attractive alternative process routes in which solid oxygen carriers function as lattice oxygen transfer agents, for example for the partial oxidation of methane. We report on the development of a perovskite-based oxygen carrier (La0.85Sr0.15Fe0.95Al0.05O3-δ) that enables the complete conversion of CH4 to a synthesis gas (a mixture of H2 and CO, selectivity > 99 %) through donation of its lattice oxygen (up to 9 wt%) at temperatures > 900 °C. The thermodynamic properties of the oxygen carrier permit its lattice oxygen to be replenished with CO2 or H2O, of which > 94 % is converted into CO or H2, respectively. The potential of this compositionally and structurally flexible oxygen carrier is demonstrated in a continuous experiment lasting more than 45 days (∼ 4050 redox cycles), in which all CH4 (reductant) and all CO2 (oxidant) is converted into a synthesis gas without CO2 contamination., Applied Catalysis B: Environmental, 278, ISSN:1873-3883, ISSN:0926-3373

The results of the study of the spectral characteristics and photo cathodoluminescence zinc tungstate crystals subjected to heat treatment in an oxygen atmosphere, or flows of high-energy irradiation of oxygen ions. It was observed that additional introduction of oxygen leads to decline in luminescence’s effectiveness. It was discovered, that introduction of oxygen by thermal processing leads to changes in excitation spectrum. Decline of excitation effectiveness proportional to increase of excitation quanta energy from 4.5 to 6.5 eV was observed; in the meantime, in the unprocessed crystals it declined by only 25-30%. The effect can be explained by destruction of complex defects with luminescence centers during introduction of additional oxygen. It was demonstrated, that characteristic oxygen’s depth of entry during thermal processing is 20 nm.