This study investigates phase transitions in CuO/Al 2 O 3 oxygen carriers during chemical looping combustion (CLC), aiming to understand performance and stability over extended redox cycles.

This study investigates phase transitions in CuO/Al2O3 oxygen carriers during chemical looping combustion (CLC), aiming to understand performance and stability over extended redox cycles. In situ quick X-ray assorption spectroscopy (QXAS) was employed to track the transformations of the copper aluminate phase (CuxAlyO4) over 50 redox cycles in various oxidizing (2.5 to 21% O2 in N2) and reducing (H2, CO, CH4) environments. The study reveals that the oxygen carrier undergoes significant phase transitions, reaching a threshold where CuxAlyO4 predominantly converts to copper oxide and alpha-Al2O3, leading to irreversible structural modifications. Complementary SEM analysis further highlights morphological changes, such as particle growth prior to alpha-Al2O3 formation. This cycle-dependent phase evolution provides new insights into accelerated ageing mechanism involving the interplay between copper phase transformations and alpha-Al2O3 formation, which is critical for enhancing the durability of oxygen carriers in CLC applications.

Solid sulfide electrolytes hold great promise for making all-solid state batteries a reality. Therefore, their wet chemical synthesis has become increasingly important in recent years due to various benefits such as scalability and versatility. The Li3PS4 electrolyte has a relatively high ionic conductivity (approximate to 10(-4 )S cm(-1) at 25 degrees C) and can be synthesized in various organic solvents by reacting Li2S and P2S5. It is well-known that the choice of the solvent is critical for the synthesis. Herein, we investigated several new organic polar solvents such as sulfur-based solvents (propanethiol, thiolane, and thiophene), amines, and carbonyls (esters, carbonates, ketones) for the synthesis of Li3PS4. The relationship between the ability to perform the reaction, the ionic conductivity, and the solvents' characteristics revealed that the electronic density of the polar function plays a key role. The results of this study can be used as a guideline to select new synthesis solvents. We also identify a particular solvent, isobutyl isobutyrate (IBIB), which allows the decomposition of the corresponding Li3PS4 solvato-complex below the boiling point of the solvent with one of the highest reported ionic conductivities for the wet chemical method (2.1 x 10(-4) S cm(-1) at room temperature).

Chemical Looping Combustion is a promising midterm solution to mitigate CO2 emission, by carrying out indirect fuel combustion and allowing inherent separation of CO2. During the CLC process, an oxygen carrying material is subjected to successive oxidation‐reduction reactions at high temperature which induce significant material degradation. CuO/Al2O3 based materials have been widely considered as promising oxygen carriers (OC). However, the oxygen carrier ageing mechanisms (active phase migration and interactions with the support, phase transitions) are not well understood. Herein, an in‐depth overview of the material evolution is achieved by employing a multi‐scale characterization approach. At the μm‐scale, copper migration within the alumina support has been observed using Scanning Transmission X‐ray Microscopy (STXM) and Scanning Electron Microscopy (SEM). The spatial distribution of the Cu−Al species provides information on copper mobility and the different phases interactions. A comprehensive mechanism is proposed concerning the redox behaviour of the CuO/Al2O3 system, relating the diffusion of the Cu‐species, the active phase‐support interactions, and the role of copper in the Al2O3 support phase transition to the temperature and the number of redox cycles. Understanding the ageing process of CuO/Al2O3 materials paves a way to design more stable oxygen‐carriers.

Chemical looping combustion (CLC) technology has emerged as one of the most important clean fossil fuel combustion technologies, because it allows for sequestration of CO2 with a minimal increase in energy requirements and fuel demand in comparison to traditional plants. In the framework of the Chinese-European Emission-Reducing Solutions project, the core technology of the CLC process is being developed in a 3 MWth system prototype for demonstration in an operational environment using petcoke as fuel. One of the main objectives is the selection of the oxygen carrier because it will impact the design and sizing of the demonstration unit as well as the nominal power of the unit. Two minerals, ilmenite T1 and LY Mn ore, with high potential for a well-performing oxygen carrier were tested in a 10 kWth continuous pilot unit. The collected fines were analyzed by scanning electron microscopy and X-ray fluorescence analysis to characterize the compositional and morphological evolution of the particles during operation. The performance of both oxygen carriers was compared with respect to solid fuel conversion, capacity for oxygen transfer, and particle lifetime in continuous circulation. A higher methane conversion can be obtained using ilmenite, while LY Mn is better at converting petcoke. Where the reduction potential of oxygen carriers is concerned, it was observed that LY Mn ore has a high initial R-0 Delta X value (R-0 Delta X = 0.8), which leads to a shorter activation period in comparison to ilmenite T1, which requires a longer activation period to reach its full potential. LY Mn ore is however more sensitive to attrition than ilmenite, under similar operating conditions, which is a critical characteristic for large-scale deployment. Finally, key operating parameters were identified for large-scale unit operation, including fuel reactor temperature, oxygen carrier flow rate, and fuel flow rate.

Despite the broad relevance of copper nanoparticles in industrial applications, the fundamental understanding of oxidation and reduction of copper at the nanoscale is still a matter of debate and remains within the realm of bulk or thin film-based systems. Moreover, the reported studies on nanoparticles vary widely in terms of experimental parameters and are predominantly carried out using either ex situ observation or environmental transmission electron microscopy in a gaseous atmosphere at low pressure. Hence, dedicated studies in regards to the morphological transformations and structural transitions of copper-based nanoparticles at a wider range of temperatures and under industrially relevant pressure would provide valuable insights to improve the application-specific material design. In this paper, copper nanoparticles are studied using in situ Scanning Transmission Electron Microscopy to discern the transformation of the nanoparticles induced by oxidative and reductive environments at high temperatures. The nanoparticles were subjected to a temperature of 150 °C to 900 °C at 0.5 atm partial pressure of the reactive gas, which resulted in different modes of copper mobility both within the individual nanoparticles and on the surface of the support. Oxidation at an incremental temperature revealed the dependency of the nanoparticles' morphological evolution on their initial size as well as reaction temperature. After the formation of an initial thin layer of oxide, the nanoparticles evolved to form hollow oxide shells. The kinetics of formation of hollow particles were simulated using a reaction-diffusion model to determine the activation energy of diffusion and temperature-dependent diffusion coefficient of copper in copper oxide. Upon further temperature increase, the hollow shell collapsed to form compact and facetted nanoparticles. Reduction of copper oxide was carried out at different temperatures starting from various oxide phase morphologies. A reduction mechanism is proposed based on the dynamic of the reduction-induced fragmentation of the oxide phase. In a broader perspective, this study offers insights into the mobility of the copper phase during its oxidation-reduction process in terms of microstructural evolution as a function of nanoparticle size, reaction gas, and temperature.

A promising copper based oxygen carrier produced using industrially-relevant manufacturing equipment has been aged in IFPEN's 10 kW(th) Chemical Looping Combustion pilot plant. Methane combustion was performed at 900 degrees C for 160 h with an OC/fuel ratio of 1.2. While full methane conversion to CO2 and water was achieved in the early stage of the experiment, fast deactivation was observed. The oxygen carrying particles were thoroughly characterized at various stages of the ageing experiment, from which a pathway leading to deactivation is proposed.

Chemical Looping Combustion (CLC) is a promising technique to achieve fuel combustion in a nitrogen free atmosphere, therefore giving the possibility to separate and store or use CO2. Several potential applications are considered in the field of power generation with gas, liquid and mostly solid fuels. In the Carbon Capture, Storage and Utilization (CCSU) context, energy penalty is reduced with CLC compared to other routes. In addition, other applications of Chemical Looping Technology are considered in the field of H-2 production or gasification for instance.In the past years, a huge effort has been conducted worldwide to investigate CLC materials and process issues. In 2008, IFPEN and Total have started an ambitious collaboration to develop CLC applications. Nowadays, the CLC concept is well demonstrated on the pilot scale. The next step is to demonstrate the technology over time on a larger scale. For further developments, some challenges should be addressed, both on market and technical aspects:Short term market is limited. Uncertainties around CO2 emission market (i.e. carbon credits) and storage issues are hindering policy and public acceptance and still must evolve in the right direction,Financing of industrial Carbon Capture and Storage units in this context is challenging and other applications of CLC may require to be investigated such as utilization of captured CO2 for FOR purpose,The industrial use of synthetic metal oxides or natural ores at large scale generates a lot of issues related to availability, price, waste disposal, health and safety, additionally to chemical and mechanical aging, reactivity, and oxygen transfer capacity,Chemical looping reactor and process technology concepts have to be explored, developed, modeled and scaled up in order to ensure adequate power production together with good gas solid contact and reaction requirement, controlled circulation of mixtures of particle (oxygen carrier, ash, solid fuel for instance). All these points should be considered on very large scales for carbon capture and storage (CCS) applications in order to minimize energy penalty and cost in severe operating conditions (temperatures above 800 degrees C and intense solid circulation).Technical challenges remain to be solved and proven with large demonstration over long periods of time. In this context, research in the field of fluidization technology is essential and we will address some key points investigated at IFPEN as related to control of solid circulation, oxygen carrier attrition, conceptual design of CLC reactors and process performance. (C) 2017 Elsevier B.V. All rights reserved.

This work was devoted to study experimentally and numerically the oxygen carrier (NiO/NiAl2O4) performances for Chemical-Looping Combustion applications. Various kinetic models including Shrinking Core, Nucleation Growth and Modified Volumetric models were investigated in a one-dimensional approach to simulate the reactive mass transfer in a fixed bed reactor. The preliminary numerical results indicated that these models are unable to fit well the fuel breakthrough curves. Therefore, the oxygen carrier was characterized after several operations using Scanning Electronic Microscopy (SEM) coupled with equipped with an energy dispersive X-ray spectrometer (EDX). These analyses showed a layer rich in nickel on particle surface. Below this layer, to a depth of about 10 µm, the material was low in nickel, being the consequence of nickel migration. From these observations, two reactive sites were proposed relative to the layer rich in nickel (particle surface) and the bulk material, respectively. Then, a numerical model, taking into account of both reactive sites, was able to fit well fuel breakthrough curves for all the studied operating conditions. The extracted kinetic parameters showed that the fuel oxidation was fully controlled by the reaction and the effect of temperature was not significant in the tested operating conditions range.

The influence of the preparation method of NiAl2O4 binders on their thermal stability was studied. For this purpose, the reactivity of two different NiAl2O4 binders with CO as fuel was studied in a fixed bed reactor device. Successive oxidation-reduction cycles were performed on the two binders to study their reactivity with the fuel and their structural modifications as cycles proceed. Results reveal that binders are not inert in reducing atmosphere; they both react with the fuel to produce CO2. The total reduction capacity (TRC) of the first binder (B1, synthetized by pyrolytic pulverization) increases during the first cycles and levels off after 20 cycles. However, the TRC of the second binder (B2, synthetized by calcination of a mixture of Ni(OH) and gamma-Al2O3), increases progressively and reaches a maximum after 80 cycles. The growing amount of available oxygen in the binders leads both binders to structural modifications. X-ray Diffraction studies performed on fresh and aged binders presented a shift of the peaks related to NiAl2O4. Moreover, quantitative X-ray Diffraction studies and Temperature Programmed Reduction measurements were performed in order to quantify the NiO present in each binder before and after oxidation-reduction cycles. These experiments revealed the presence of NiO in fresh binders due to the preparation method, and an increase of this amount after oxidation-reduction cycles. Therefore, NiAl2O4 in the binder is progressively decomposed producing NiO and Al2O3. Finally, the decomposition of the binder NiAl2O4 as cycles proceed was also observed in studies performed on the oxygen carrier NiO/NiAl2O4. This work showed that the binder reacts with the fuel and therefore it can contribute to the modification of the oxygen carrier reactivity. (C) 2016 Elsevier Ltd. All rights reserved.

This work aims to study the evolution of NiO/NiAl2O4 redox performance with CO as fuel for Chemical Looping Combustion (CLC) applications. The oxygen carrier (OC) was investigated under alternating oxidizing and reducing conditions in a fixed bed reactor simulating the cyclic conditions of CLC. The study of the operating temperature influence reveals that total reduction capacity increases with temperature, due to the reaction of the binder NiAl2O4. Regeneration step performed under low oxygen concentration (5 vol.%) shows that the decrease in total reduction capacity during multiple cycles is minimized and the purity of produced CO2 is higher. Therefore, carrying out the regeneration step at lower oxygen concentrations can increase oxygen carrier lifetime. Characterization studies revealed the formation of a nickel rich layer at the surface (up to 20 mu m thick at 900 degrees C) and a partial sintering of particles regenerated under 20 vol.% of oxygen. However, these phenomena are not observed on the particles regenerated under low oxygen concentration. The formation of this layer can be explained by the fact that nickel oxidation is carried out by migration of Ni2+ cations through the layer of NiO initially oxidized at the surface of the particle, the layer becomes thicker during cycles, because NiO does not return to its initial position. At higher temperature, the diffusion velocity increases and therefore the layer formed is thicker.Specific surface area of the oxygen carrier decreases as cycles number increases from 9.4 m(2)/g for the fresh material to 4.4 and 2.3 m(2)/g after thirty cycles at 750 degrees C and 900 degrees C respectively. The same trend is observed for porous volume. However, the decrease is lower when particles are regenerated under low oxygen concentration (6 m(2)/g). (C) 2015 Elsevier Ltd. All rights reserved.

Chemical Looping Combustion is a promising technology for clean power generation with integrated CO2 capture. In this process the oxygen required for combustion is provided by a metal oxide. This work deals with the development of an experimental procedure to study performances of an oxygen carrier during oxidation/reduction cycles and the influence of the oxidation step on its behaviour. Tests were performed in a laboratory fixed bed reactor, with NiO/NiAl2O4, a promising oxygen carrier, and CO as fuel. Two different protocols of oxidation were studied. Results reveal that the oxidation step conditions can change the performances of the oxygen carrier. A significant decrease in total reduction capacity was observed using the regeneration step at high temperature due to structural changes in particles. SEM analysis reveals that particle surface contains different crystallites according to this procedure. With the second procedure ( oxidation in temperature ramp), nickel is partially agglomerated.

The aim of this work is to investigate the contribution of the binder (NiAl2O4) on the performances of the oxygen carrier NiO/NiAl2O4. To this purpose, oxidation/reduction cycles have been performed in a fixed bed reactor using CO as a fuel. The results reveal that the binder can react with the fuel to form CO2, and that its total reduction capacity increases with temperature. XRD characterizations performed on the binder (on the fresh and after several cycles) show a shift of the diffraction peaks of NiAl2O4 toward the ones of gamma-alumina, which can be attributed to a progressive decomposition of NiAl2O4 to alumina and NiO. (C) 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Dimensional and phase changes of four candidate oxygen carrier materials for chemical looping combustion are investigated by dilatometry and high-temperature X-ray diffraction during four redox cycles. NiO/Ni2AlO4 does not exhibit significant dimensional changes during cycling, and it is shown that the support material also contributes to the oxygen carrying capacity. CaMn0.875Ti0.125O3 exhibited good chemical stability and small dimensional changes upon redox cycling. Cu0.95Fe1.05AlO4 showed a one-dimensional expansion of 9% after the experiments, and significant phase changes were seen. The complex set of reactions occurring during redox cycling of ilmenite (FeTiO3) was shown to be accompanied by dimensional changes, giving non-steady dimensional changes during the oxidation and reduction steps.

The physio-chemical stability of the oxygen carrier material during chemical looping combustion (CLC) operation is crucial. In the present paper we discuss the challenges connected to operating a metal oxide base material in a cyclic manner between oxidizing and reducing atmospheres. Especially, focus has been put on the phase changes occurring within the oxygen carrier particles leading to changes in particle volume during operation and consequently, with time, also particle disintegration. Particle sintering may also occur for some oxygen carrier materials in their reduced form. These challenges have been exemplified through lab-scale CLC experiments carried out both in fixed bed and fluidized bed reactors.