Oxygen Uncoupling Research Articles

Evaluation of CuO/MgAl2O4 in Biomass Chemical Looping Gasification with Oxygen Uncoupling

Chemical looping gasification (CLG) is a promising method for the utilization of biomass to produce syngas. However, its realization is largely dependent on the use of an oxygen carrier with a high and stable reactivity in cyclic reduction and oxidation. This work focused on the improvement of reactivity and stability of CuO in chemical looping gasification via the addition of MgAl2O4 as an inert material. First, the stability and reactivity of synthesized Cu-based oxygen carriers were studied in a thermogravimetric analyzer (TGA). Then, the characteristics of CLG of biomass and the oxygen carrier in syngas production were investigated by testing gas components, syngas production, and oxygen carrier sintering performance. The results show that CuO supported on MgAl2O4 has a better capacity for oxygen release than pure CuO and a superior stability and gasification activity in the cyclic chemical looping gasification with biomass. A higher operating temperature led to the production of more syngas from biomass gasification with CuO/MgAl2O4 as the oxygen carrier, particularly for CO and H2. CuO/MgAl2O4 also demonstrated a much better effect on methane reforming in CLG. It is believed that CuO/MgAl2O4 is a suitable oxygen carrier for the chemical looping with oxygen uncoupling (CLOU) and CLG of biomass.

Sulphur, nitrogen and mercury emissions from coal combustion with CO2 capture in chemical looping with oxygen uncoupling (CLOU)

Chemical looping with oxygen uncoupling (CLOU) is a chemical looping combustion (CLC) process for the combustion of solid fuels with the use of a solid oxygen carrier that releases gaseous oxygen inside the fuel reactor. The aim of this work was to study the fate of pollutant elements present in fuel, i.e. S, N and Hg, during CLOU combustion. Experiments using lignite as fuel were carried out in a 1.5kWth unit operating continuously for more than 35h of coal combustion. Novel particles containing 50wt.% CuO, 10wt.% Fe2O3 and 40wt.% MgAl2O4 prepared by spray drying were used as the oxygen carriers in the CLOU process. Most of the sulphur introduced with the fuel exited as SO2 at the fuel reactor outlet, although a small amount of SO2 was measured at the air reactor outlet. Most of the nitrogen present in coal was found as N2 at the outlet of the fuel reactor, although 20wt.% of N in the coal was converted to NO. Mercury speciation was also analyzed. The major mercury species in the fuel reactor was Hg0 (g), and the Hg0 (g)/Hgtotal (g) ratio in the air reactor was 0.5.

Screening of different manganese ores for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU)

Oxygen carriers based on manganese oxides have recently shown great promise for use in chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). In this work, eleven different manganese ores have been investigated for application in CLC and CLOU. The reactivity towards methane and synthesis gas (50% CO in H2) and the oxygen uncoupling behaviour at 900, 950 and 1000°C have been investigated. The mechanical stability and integrity of the ores were also evaluated in a jet-cup attrition rig. It was found that some of the ores could convert approximately 70–80% of the added methane to carbon dioxide, and most of them provided almost complete conversion of synthesis gas. In these experiments the bed mass was 15g for experiments with methane and 2g for experiments with syngas, corresponding to a specific solids inventory of 57 and 25kg/MW, respectively. All of the oxygen carrier materials released small amounts of gas phase oxygen via CLOU, between 0.01 and 0.03mass% of the oxygen carrier during the inert period. Some of the investigated ores also exhibited low rates of attrition. The combination of high reactivity with different fuel gases, relatively low attrition rates and low cost make some of these manganese ores highly interesting for a CLC process based on interconnected fluidized beds.

Thermodynamic analysis of in situ gasification-chemical looping combustion (iG-CLC) of Indian coal

Chemical looping combustion (CLC) is an inherent CO2 capture technology. It is gaining much interest in recent years mainly because of its potential in addressing climate change problems associated with CO2 emissions from power plants. A typical chemical looping combustion unit consists of two reactors-fuel reactor, where oxidation of fuel occurs with the help of oxygen available in the form of metal oxides and, air reactor, where the reduced metal oxides are regenerated by the inflow of air. These oxides are then sent back to the fuel reactor and the cycle continues. The product gas from the fuel reactor contains a concentrated stream of CO2 which can be readily stored in various forms or used for any other applications. This unique feature of inherent CO2 capture makes the technology more promising to combat the global climate changes. Various types of CLC units have been discussed in literature depending on the type of fuel burnt. For solid fuel combustion three main varieties of CLC units exist namely: syngas CLC, in situ gasification-CLC (iG-CLC) and chemical looping with oxygen uncoupling (CLOU). In this paper, theoretical studies on the iG-CLC unit burning Indian coal are presented. Gibbs free energy minimization technique is employed to determine the composition of flue gas and oxygen carrier of an iG-CLC unit using Fe2O3, CuO, and mixed carrier-Fe2O3 and CuO as oxygen carriers. The effect of temperature, suitability of oxygen carriers, and oxygen carrier circulation rate on the performance of a CLC unit for Indian coal are studied and presented. These results are analyzed in order to foresee the operating conditions at which economic and smooth operation of the unit is expected.

Screening of supported and unsupported Mn–Si oxygen carriers for CLOU (chemical-looping with oxygen uncoupling)

Oxygen carriers based on oxides of Mn and Si in combination with Mg, Al, Ca and Ti (Mn0.63Si0.27X0.1, X = Ca(OH)2, TiO2, MgO, AlOOH) were examined for CLOU (chemical-looping with oxygen uncoupling), in terms of oxygen uncoupling ability and ability to convert both methane and syngas. The focus was on the optimization of the production process to yield mechanically strong oxygen carrier particles with a reasonable activity. For this purpose, 15 types of oxygen carriers were produced by spray-drying and calcined for different time periods and at different temperatures.The oxygen uncoupling behavior and gas conversion of the materials were investigated in a batch fluidized-bed reactor under alternating oxidizing and reducing conditions in the temperature range 850–1050 °C. To determine attrition resistance and mechanical stability, a jet-cup attrition rig was used. Furthermore, physical and chemical properties such as specific surface area and crystal phase composition have been determined.For the oxygen carriers with additives of Mg, Al, Ca, Ti, some material combinations showed a significant increase in reactivity and improved mechanical stability compared to the unsupported Mn–Si particles. Changing the production process (milling process and calcination time) just caused slight difference in attrition resistance, gas conversion as well as oxygen release.

Kinetics of oxygen uncoupling of a copper based oxygen carrier

Here, an oxygen carrier consisting of 60wt% CuO supported on a mixture of Al2O3 and CaO (23wt% and 17wt% respectively) was synthesised by wet-mixing powdered CuO, Al(OH)3 and Ca(OH)2, followed by calcination at 1000°C. Its suitability for chemical looping with oxygen uncoupling (CLOU) was investigated. After 25 repeated redox cycles in either a thermogravimetric analyser (TGA) or a laboratory-scale fluidised bed, (with 5vol% H2 in N2 as the fuel, and air as the oxidant) no significant change in either the oxygen uncoupling capacity or the overall oxygen availability of the carrier was found. In the TGA, it was found that the rate of oxygen release from the material was controlled by intrinsic chemical kinetics and external transfer of mass from the surface of the particles to the bulk gas. By modelling the various resistances, values of the rate constant for the decomposition were obtained. The activation energy of the reaction was found to be 59.7kJ/mol (with a standard error of 5.6kJ/mol) and the corresponding pre-exponential factor was 632m3/mol/s. The local rate of conversion within a particle was assumed to occur either (i) by homogeneous chemical reaction, or (ii) in uniform, non-porous grains, each reacting as a kinetically-controlled shrinking core. Upon cross validation against a batch fluidised bed experiment, the homogeneous reaction model was found to be more plausible. By accurately accounting for the various artefacts (e.g. mass transfer resistances) present in both TGA and fluidised bed experiments, it was possible to extract a consistent set of kinetic parameters which reproduced the rates of oxygen release in both experiments.

Development Trends in Porous Adsorbents for Carbon Capture.

Accumulation of greenhouse gases especially CO2 in the atmosphere leading to global warming with undesirable climate changes has been a serious global concern. Major power generation in the world is from coal based power plants. Carbon capture through pre- and post- combustion technologies with various technical options like adsorption, absorption, membrane separations, and chemical looping combustion with and without oxygen uncoupling have received considerable attention of researchers, environmentalists and the stake holders. Carbon capture from flue gases can be achieved with micro and meso porous adsorbents. This review covers carbonaceous (organic and metal organic frameworks) and noncarbonaceous (inorganic) porous adsorbents for CO2 adsorption at different process conditions and pore sizes. Focus is also given to noncarbonaceous micro and meso porous adsorbents in chemical looping combustion involving insitu CO2 capture at high temperature (>400 °C). Adsorption mechanisms, material characteristics, and synthesis methods are discussed. Attention is given to isosteric heats and characterization techniques. The options to enhance the techno-economic viability of carbon capture techniques by integrating with CO2 utilization to produce industrially important chemicals like ammonia and urea are analyzed. From the reader's perspective, for different classes of materials, each section has been summarized in the form of tables or figures to get a quick glance of the developments.

Experimental investigation of binary and ternary combined manganese oxides for chemical-looping with oxygen uncoupling (CLOU)

Some binary and ternary combined manganese oxides of Mn with one or two additional metals or metalloids of Fe, Si, Ca and Mg were investigated as oxygen carriers for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). More specifically the following systems were investigated: (1) MnyMgOx, (2) CaMnO3–(Fe0.25Mn0.75)2O3, (3) CaMnO3–(Fe0.67Mn0.33)2O3, (4) CaMnO3–MnMgOx, (5) MnMgOx–(Fe0.25Mn0.75)2O3 and (6) Mn2SiOx–Fe2SiOx. The general trend was that the binary systems, where two metals are used in the formulation showed the most promising results in terms of oxygen uncoupling and reactivity. However, there are several ternary combinations which show a combination of high oxygen uncoupling, reactivity with methane and reasonable strength. A pseudo first-order effective rate constant was evaluated for the investigated particles. The measured rates are lower than for benchmark nickel oxide and calcium manganites, but higher than for ilmenite. The ternary System 6, Mn2SiOx–Fe2SiOx was investigated in more depth, including solid fuel experiments to determine the rate of oxygen release. At 850 and 900°C (Mn0.5Fe0.5)2SiOx had the highest average reactivity, with a maximum average yield of 91.5% at 850°C. On the other hand, at higher temperatures, the particles with the highest Mn content showed best behavior, i.e. (Mn0.67Fe0.33)2SiOx. Reactivity experiments with char in the FB reactor with this OC showed that the oxygen capacity for CLOU was high, 3.5wt% at 950°C, with a maximum release rate of 0.2gO2/kgOC,s. The low rate of uncoupling means that the experiments with gaseous fuel were likely dominated by the direct gas–solid reaction, and not CLOU. X-ray powder diffraction suggests that the main reaction path is via (MnxFe1−x)2O3 to (MnxFe1−x)3O4, although the reaction between Mn7SiO12 to MnSiO3 cannot be ruled out as a possible route of oxygen transfer. This was supported by thermodynamic calculations of this multi-component system.

Development of CaMn0.775Mg0.1Ti0.125O3-δ oxygen carriers produced from different Mn and Ti sources

Perovskite CaMn0.775Mg0.1Ti0.125O3-δ has attracted great interest as an oxygen carrier. To apply this material to a commercial scale chemical-looping unit, one key challenge is to find raw materials which are cheap and available in large quantities for production. Considering the content and price, Mn- and Ti-oxides are likely the raw materials having the major effect. Twelve Mn-oxide sources and four different TiO2 powders were evaluated for production of CaMn0.775Mg0.1Ti0.125O3-δ in this work. Particles with perovskite structure were successfully spray dried. All oxygen carriers showed oxygen uncoupling characteristics and most of them had a high reactivity, i.e. over 90% methane conversion already at 950°C with a bed mass corresponding to 57kg/MW, when examined in a batch fluidized-bed system at 900–1050°C. Furthermore bulk density, crushing strength and resistance against attrition were studied. Although the attrition index varied, materials with good attrition resistance were identified. The rates of reaction were analyzed using two pseudo-first order apparent rate constants. The rates varied in a wide range, and are generally lower than with optimized Ni-based materials, but higher than with ilmenite. Still, the added oxygen uncoupling likely has a large positive effect at high degrees of solid conversion, something not seen with Ni-based materials.

Chemical-Looping Combustion and Gasification of Coals and Oxygen Carrier Development: A Brief Review

Chemical-looping technology is one of the promising CO2 capture technologies. It generates a CO2 enriched flue gas, which will greatly benefit CO2 capture, utilization or sequestration. Both chemical-looping combustion (CLC) and chemical-looping gasification (CLG) have the potential to be used to generate power, chemicals, and liquid fuels. Chemical-looping is an oxygen transporting process using oxygen carriers. Recently, attention has focused on solid fuels such as coal. Coal chemical-looping reactions are more complicated than gaseous fuels due to coal properties (like mineral matter) and the complex reaction pathways involving solid fuels. The mineral matter/ash and sulfur in coal may affect the activity of oxygen carriers. Oxygen carriers are the key issue in chemical-looping processes. Thermogravimetric analysis (TGA) has been widely used for the development of oxygen carriers (e.g., oxide reactivity). Two proposed processes for the CLC of solid fuels are in-situ Gasification Chemical-Looping Combustion (iG-CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU). The objectives of this review are to discuss various chemical-looping processes with coal, summarize TGA applications in oxygen carrier development, and outline the major challenges associated with coal chemical-looping in iG-CLC and CLOU.

Chemical-Looping with Oxygen Uncoupling of Different Coals Using Copper Ore as an Oxygen Carrier

Chemical-looping with oxygen uncoupling (CLOU) has been considered as a revolutionary technology for low-energy consumption CO2 capture. In this work, the performance of copper ore in the CLOU processes for diverse ranks of coal was examined in a batch-scale fluidized-bed at various temperatures. Typical Chinese coals (GaoPing anthracite, FuGu bituminous coal, and ShengLi lignite) were used as fuel. The effects of temperature and coal rank on the redox behavior, carbon conversion rate, and instantaneous rates of char conversion and oxygen generation were first investigated. It was found that both increasing the reactor temperature and decreasing the coal rank had beneficial effects on the carbon conversion rate, instantaneous rates of char conversion, and oxygen generation. In the CLOU processes of coal, the rate-limiting step was the burning of coal char with oxygen of low concentration if the oxygen carrier (OC) was excess to coal. And for higher-rank coals like anthracite, the rate-limitation effect wa...

Evaluation of Manganese Minerals for Chemical Looping Combustion

The use of mineral materials as oxygen carriers for Chemical Looping Combustion (CLC) is an attractive option due to their low cost. This paper reports an experimental study of four manganese minerals as potential oxygen carriers focusing on the behavior in CLC as well as in Chemical Looping with Oxygen Uncoupling (CLOU). Experiments were carried out in a thermogravimetric apparatus (TGA) and a fluidized-bed reactor. Repeated tests with all the minerals showed no sufficient CLOU properties. Then, they can only be used in CLC applications involving the redox pairs Mn3O4/MnO and Fe2O3/Fe3O4. Oxygen transport capacity and reactivity to the main fuel gases (H2, CO, and CH4) were determined in a TGA. Manganese minerals were also tested during 35–54 h in a fluidized-bed reactor to evaluate the evolution of reactivity to H2, CO, and CH4 as well as their attrition rate and mechanical strength. The reactivity of the materials decreased in the first 10 cycles with CH4 and then became quite stable for the rest of th...

Redox property and kinetics of copper oxygen carrier under different oxygen concentrations

Chemical looping with oxygen uncoupling and chemical looping air separation technologies all depend on the redox property of oxygen carrier. The present work investigated the redox properties of Cu/Zr oxygen carrier under different oxygen concentrations by TG technique. The durability and stability of oxygen carrier is also investigated under 1065°C reduction and 800°C oxidation temperatures. For reduction, the starting and ending temperatures and the peaks of DTG curves shift to high values with oxygen concentration increasing. The effect of oxygen concentration on oxidation is little and the regeneration of Cu/Zr oxygen carrier can be achieved in thin oxygen environment. For reduction and oxidation, times for complete conversion decrease with heating rates increasing. Kinetic models were proposed based on the nucleation and nuclei growth model. The reduction mechanism function is: and the oxidation mechanism function is: . For reduction, the values of E and A all increase as oxygen concentrations increase and heating rates decrease. For oxidation, the values of E and A are almost the same. The Cu/Zr oxygen carrier has high stability and it is a good candidate for chemical looping technologies at high temperatures. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 531–539, 2016

Performance of cement decorated copper ore as oxygen carrier in chemical-looping with oxygen uncoupling

Chemical-looping with oxygen uncoupling (CLOU) provides a revolutionary route for CO2 capture with low energy consumption. To address the CLOU process, the appropriate oxygen carrier should have the ability of releasing gaseous oxygen in the fuel reactor and regenerating itself in the air reactor at temperatures of interest for combustion. Copper ore, known for its low cost and abundant reserves, has been identified as an applicable oxygen carrier material for CLOU. However, Cu-based oxygen carriers share the common disadvantages of sintering and agglomeration at high temperatures. To enhance the sintering-resistant property of copper ore particles, four types of cement decorated copper ore oxygen carrier were prepared by mechanical mixing. Successive cyclic redox experiments at different temperatures in a thermogravimetric analyzer (TGA) were first conducted to investigate the oxidation and reduction properties of the newly prepared oxygen carriers. The TGA results showed that within 20 cycles, cement modified copper ore (CuC) particles performed better redox reactivity than single copper ore oxygen carrier, especially at elevated temperatures. Among the CuC oxygen carriers, CuC-20 (copper ore modified with 20wt.% of cement) was the best in redox reactivity. Cyclic redox reactivity of Cu-ore and CuC-20 were further tested in a batch-scale fluidized bed reactor with both synthesis gas and coal as fuel at 950°C. The results both indicated that CuC-20 showed little tendency toward agglomeration and no chemical interaction between the active phase of copper ore and cement, which maintained stable and good reactivity after the activation process.

Reduction kinetics analysis of sol–gel-derived CuO/CuAl2O4 oxygen carrier for chemical looping with oxygen uncoupling

Chemical looping with oxygen uncoupling (CLOU) is a promising technology due to its potential to reduce energy efficiency penalty and cost associated with CO2 capture. In this work, a CuO/CuAl2O4 oxygen carrier (OC) prepared by sol–gel was investigated in its oxygen release kinetics (4CuO → 2Cu2O + O2). Based on several well-organized temperature-programmed reduction experiments which were conducted in a thermogravimetric analyzer, the activation energy E (343.7 kJ mol−1) and pre-exponential factor A (3.78 × 1012 s−1) were determined and the Avrami–Erofeev random nucleation and subsequence growth model fitted well with the reduction experimental data. The enhancement of OC reduction rate in real fluidized bed CLOU reactor using different types of solid fuels (petroleum coke, anthracite, bituminous, and lignite) was identified in terms of the chemical kinetics and thermodynamics for the first time. It was found that the CuO reduction rate is more sensitive to the local temperature change than the oxygen concentration driving force. The results could contribute to the design, operation, and performance prediction of real CLOU reactors.

Characteristics of Copper-based Oxygen Carriers Supported on Calcium Aluminates for Chemical-Looping Combustion with Oxygen Uncoupling (CLOU)

Eight different oxygen carriers (OC) containing CuO (60 wt %) and different mass ratios of CaO to Al2O3 as the support were synthesized by wet-mixing followed by calcination at 1000 °C. The method of synthesis used involved the formation of calcium aluminum hydrate phases and ensured homogeneous mixing of the Ca2+ and Al3+ ions in the support at the molecular level. The performance of the OCs for up to 100 cycles of reduction and oxidation was evaluated in both a thermogravimetric analyzer (TGA) and a fluidized bed reactor, covering a temperature range of 800 to 950 °C. In these cycling experiments, complete conversion of the OC, from CuO to Cu and vice versa, was always achieved for all OCs. The reactivity of the materials was so high that no deactivation could be observed in the TGA, owing to mass transfer limitations. It was found that OCs prepared with a mass ratio of CaO to Al2O3 in the support >0.55 agglomerated in the fluidized bed, resulting in an apparent deactivation over 25 cycles for all tempe...

Fuel Nitrogen Conversion in Chemical Looping with Oxygen Uncoupling of Coal with a CuO-Based Oxygen Carrier

The interest in chemical looping with oxygen uncoupling (CLOU) of coal as a method for CO2 enrichment has increased drastically during recent years. The objective of this work was to experimentally investigate fuel nitrogen conversion in the CLOU process of coal with a CuO-based oxygen carrier in a batch fluidized-bed unit. Three coals of different rank (anthracite, sub-bituminous, and bituminous) and their corresponding chars were used as fuels. Furthermore, experiments of coal combustion under air-fired conditions were performed to recognize the unique pathway of fuel nitrogen conversion in CLOU. Experimental results indicated that NO was formed in the largest amount of total NOx. For the Shenhua bituminous coal that was used, most of the NO, NO2, and N2O from fuel nitrogen was formed during the devolatilization stage of the coal. However, with Xuzhou sub-bituminous coal or Huaibei anthracite as fuels, a certain portion of NO was derived from char-N. Under the current experimental conditions (temperatur...

Self-assembly template combustion synthesis of a core–shell CuO@TiO2–Al2O3 hierarchical structure as an oxygen carrier for the chemical-looping processes

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are the most promising technologies for capture of CO2 at a low cost. CLC and CLOU involve cyclic reduction and oxidation of a solid oxygen carrier (OC) to transfer active oxygen from air to carbon-based fuels for combustion with the inherent feature of isolating CO2. One key issue with these technologies is to manufacture a high-performance, economical and practical OC material. In this paper, we propose a self-assembly template combustion synthesis (SATCS) method for preparing a hierarchical structure copper-based OC, Cu-rich, Al2O3-supported and TiO2-stabilized in a core–shell microarchitecture. The selection of raw materials and the rational design of OCs are based on the density functional theory (DFT) calculations and the classical Derjaguin–Landau–Verwey-Overbeek (DLVO) theory, respectively. The spontaneous aggregation between α-Al2O3 microparticles (μm-Al2O3) and rutile TiO2 nanoparticles (nm-TiO2) is driven by the van der Waals attractive and electrostatic attractive forces to form core(Al2O3)–shell(TiO2) hard templates in the wet precursor containing copper nitrate and urea. Upon calcination of the dried precursor in air, fewer nitrogen oxides (NOx) are released, demonstrating an environment-friendly fabrication process, whereby a highly dispersed and high-loading Cu-based crystalline layer is deposited on the nanostructured shell. A representative CuO@TiO2–Al2O3 OC (17.5wt% Al2O3, 5wt% TiO2) possesses hierarchical porosity and an interconnected framework and exhibits excellent performance of the reactivity, stability, oxygen release/uptake capacity and mechanical strength in the high-temperature redox cycles. The proper addition of TiO2 nanoparticles is effective in preventing the formation of copper aluminates (CuAl2O4 and CuAlO2) and inhibiting the sintering of active component grain. In addition, the rational design method and novel synthesis technique allow a mass production of various metal oxide composites used for chemical looping processes with CO2 capture and clean utilization of energy.

Mathematical modeling of a two-stage fuel reactor for chemical looping combustion with oxygen uncoupling of solid fuels

The success of a Chemical Looping Combustion (CLC) process for solid fossil fuel combustion is critically affected by the performance of the oxygen carrier and by proper design and operation of the fuel reactor.In this study, a novel configuration of the fuel reactor for chemical looping combustion with oxygen uncoupling of solid fossil fuels is proposed. The configuration is based on a two-stage reactor with the aim of overcoming the main drawbacks of the single-stage design: limited conversion, slip of unburnt volatiles, extensive elutriation of char fines. The two stages of the configuration operate in series and accomplish different tasks. The bottom bed is mainly devoted to conversion of the char, taking advantage of the full oxidative power of the oxygen carrier coming from the air reactor. The top reactor exploits the residual oxidative power of the oxygen carrier to oxidize volatile matter and gasification products as well as the unconverted char issuing from the bottom bed.A mathematical model has been developed with the aim of assessing the performances of the two-stage fuel reactor varying operating conditions in comparison with a benchmark case consisting of a single-stage fuel reactor. Two options were considered in the benchmark, depending on whether the single stage fuel reactor is or is not equipped with a carbon stripper at the exhaust. The operation of the fuel reactor has been simulated by considering chemical looping combustion of a bituminous coal with an oxygen carrier consisting of CuO supported on zirconia.

Highly Efficient Oxygen-Storage Material with Intrinsic Coke Resistance for Chemical Looping Combustion-Based CO2 Capture.

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are emerging thermochemical CO2 capture cycles that allow the capture of CO2 with a small energy penalty. Here, the development of suitable oxygen carrier materials is a key aspect to transfer these promising concepts to practical installations. CuO is an attractive material for CLC and CLOU because of its high oxygen-storage capacity (20 wt %), fast reaction kinetics, and high equilibrium partial pressure of oxygen at typical operating temperatures (850-1000 °C). However, despite its promising characteristics, its low Tammann temperature requires the development of new strategies to phase-stabilize CuO-based oxygen carriers. In this work, we report a strategy based on stabilization by co-precipitated ceria (CeO2-x ), which allowed us to increase the oxygen capacity, coke resistance, and redox stability of CuO-based oxygen carriers substantially. The performance of the new oxygen carriers was evaluated in detail and compared to the current state-of-the-art materials, that is, Al2 O3 -stabilized CuO with similar CuO loadings. We also demonstrate that the higher intrinsic oxygen uptake, release, and mobility in CeO2-x -stabilized CuO leads to a three times higher carbon deposition resistance compared to that of Al2 O3 -stabilized CuO. Moreover, we report a high cyclic stability without phase intermixing for CeO2-x -supported CuO. This was accompanied by a lower reduction temperature compared to state-of-the-art Al2 O3 -supported CuO. As a result of its high resistance towards carbon deposition and fast oxygen uncoupling kinetics, CeO2-x -stabilized CuO is identified as a very promising material for CLC- and CLOU-based CO2 capture architectures.