Chemical Looping Combustion Performance Research Articles

Insights into the gas-solid hydrodynamics and thermochemical characteristics in a pilot-scale chemical looping combustion unit using MP-PIC

Chemical looping combustion (CLC) emerges as an efficient pathway for CO2 capture and storage, yet complex in-furnace phenomena are still far from being understood. Accordingly, the multiphase reactive flow during the CLC process in a pilot-scale dual circulation fluidized bed (DCFB) is numerically investigated by the multi-phase particle-in-cell method considering thermochemical sub-models. After model validations, the thermochemical behaviors and the impact of operating parameters on CLC performance are explored, followed by unveiling the underlying mechanisms of heat and mass transfer characteristics. The pressure gradient is explicitly correlated with the solid holdup in two reactors. Gas-solid flow in the fuel reactor (FR) is more heterogeneous than that in the air reactor (AR) due to complex reactions and large amounts of gas/particle exchanges with other parts of the DCFB, and the whole CLC unit shows good circulating and heat transfer performance. Higher temperatures improve fuel conversion and increase CO2 yield. Elevating the air/fuel ratio (ψ) significantly enhances CLC performance at ψ ≤ 1.0 but it insignificantly affects the CLC performance at ψ > 1.0. A higher total inlet flow rate leads to suppressed fuel conversion and a subsequent decline in CO2 yield. The particle heat transfer coefficient (HTC) in the AR is approximately 450 W/(m2·K), significantly higher than that in the FR of about 300 W/(m2·K).

Self-regulation of bed temperature field of the fixed-bed reactor unit by composite-filled oxygen carriers for chemical looping combustion of methane

Fixed-bed reactors (FBRs) are suitable for chemical looping combustion (CLC) of gaseous fuels. However, the non-uniform temperature field such as the formation of hotpots can easily lead to the deactivation of oxygen carriers (OCs), ultimately leading to the degradation of the CLC performance and the durability of the OCs. This work systematically investigates the effect of individual CuO/SiO2 and Fe2O3/Al2O3 OC-filled FBR units on the bed temperature field using a self-built experimental setup to monitor the real-time bed temperature evolution. In addition, a strategy for self-regulating the bed temperature field by composite OCs-filled FBR units is proposed based on the differences in the thermodynamic properties of different OCs, including CuO/SiO2, Fe2O3/Al2O3, Mn2O3/ZrO2 and NiO/ZrO2. It has been found that the radial bed temperature of a single CuO/SiO2 OC-filled FBR unit is significantly higher than that at the central axis, and the bed temperature fluctuates within a range of ± 50 °C throughout the CLC process. The bed temperature of a single Fe2O3/Al2O3 OC-filled FBR unit fluctuated within a range of ± 25 °C during the reduction stage, but the bed temperature increased by nearly 100 °C due to the strong exothermic reaction of the oxidative regeneration of the reduced Fe2O3/Al2O3 OCs. The use of composite OCs-filled FBR units not only improves the CH4 conversion and CO2 selectivity, but also maintains a stable bed temperature fluctuates within a range of ± 15 ℃ during the different reaction stages of the CLC process. The synergistic effect between the OCs contributes to the bed temperature field remaining in a relatively stable state. The results indicate that the rational distribution of composite-filled OCs in FBRs can achieve self-regulation of the bed temperature field to some extent by exploiting the OCs’ endothermic and exothermic properties.

Glycerin combustion through chemical looping

Greenhouse gas emissions and their consequences are one of the main environmental problems faced today. To mitigate the impacts caused by this phenomenon, Brazil seeks to reduce 43% of its CO2 emissions by 2030 in order to meet the Paris Agreement. To achieve this goal, it is possible to use technologies based on the Carbon Capture, Utilization and Storage (CCUS) concept, such as Chemical Looping Combustion (CLC). The CLC can use natural wastes and industrial residues as carbon sources such as biomass, biogas and heavy oils. Glycerin, a by-product that accounts for almost 10% of all products from the biodiesel industry, can be used in this process since its availability is increasing over the years. Glycerin has a heat of combustion higher than ethanol and methane. This study aims to evaluate the feasibility of using glycerin in Chemical Looping Combustion. The crude glycerin was synthesized considering water, methanol and ethanol as the main contaminants. The fuel reactor temperature (TFR), oxygen-to-fuel molar ratio (ϕ) and H2O/Glycerin molar ratio, as well as the influence of methanol and ethanol on the performance of CLC were assessed. It was shown that the optimal performance of CLC was ϕ = 7, H2O/Glycerin = 0.75 and TFR = 1023 K, with a combustion efficiency (ηC) of 90% and complete carbon capture (carbon capture efficiency, ηCC = 100%). At these conditions, was noted that ethanol addition increased the combustion efficiency, while adding methanol caused a loss in efficiency.

Effect of alkali earth metal doping on the CuO/Al2O3 oxygen carrier agglomeration resistance during chemical looping combustion

The influence of alkali earth metals (AEMs, including Ca, Sr and Ba) doping on the performance of CuO/Al2O3 oxygen carrier (OC) in chemical looping combustion (CLC) was investigated. The OCs using solid-state synthesis method were evaluated in a fluidized bed reactor using municipal solid waste (MSW) syngas as fuel for 50 redox cycles. It was found that the doping of AEMs enhanced the CLC performance on CuO/Al2O3. XRD characterization and TGA analysis showed that aluminates of AEMs were formed in the doped OCs leading to the segregation of CuO from CuAl2O4 spinel, thereby promoting the redox kinetics. The OCs doped with AEMs exhibited enhanced stability and agglomeration resistance throughout multiple redox cycles in the fluidized bed experiments. CuO/Al2O3 containing 40 wt% CuO suffered from severe agglomeration and deactivation during initial 5 cycles, while the OCs with Ba, Sr and Ca doping respectively deferred the agglomeration to 15-20th, 20-25th and >50th cycle. 5–10 wt% Ca-doping content exhibited great stability without deactivation or agglomeration issues during 50 cycles, but excess Ca doping (≥20 wt%) showed severe agglomeration. The agglomeration was attributed to the outward migration of Cu/CuO, leading to the segregation from CuAl2O4 and surface enrichment. The enhanced agglomeration resistance with AEM doping was mainly attributed to outward migration of AEM species and inward migration of Cu species during the synthesis process.

Recent progress in the development of synthetic oxygen carriers for chemical looping combustion applications

Continuously rising concentrations of CO2 in the atmosphere has led to significant negative impacts on the environment which propelled research efforts to replace fossil fuel-based energy with clean energy sources. However, the reliance on fossil fuel as the main energy source is projected to stay for many years to come, and therefore developing cleaner pathways to utilize fossil fuels for energy generation is paramount. Chemical looping combustion (CLC) has emerged in recent years as a promising technology for CO2 capture in power plants and other CO2 intensive industries. A key cornerstone for CLC is the development of efficient oxygen carriers with high oxygen capacity, fast kinetics, cyclic stability, mechanical strength, and low cost. The research progress in this field is rapidly growing to tackle the major materials and operational challenges to advance the knowledge toward a commercial scale CLC application. This work provides an overview of the significant advancements achieved over the past seven years in the development of synthetic metal oxide-based oxygen carriers. A summary of key performance indicators used to evaluate oxygen carriers is presented in this study to enable for a systematic assessment of the oxygen carriers’ properties and performance. This work is focused on summarizing and critically reviewing the literature on the development of oxygen carriers such as Ni, Cu, Fe, Mn, Co-based metal oxides and combined/mixed oxygen carriers in the past seven years. Studies of naturally occurring materials and waste materials used as oxygen carriers are excluded from this review which is mainly focused on synthetically prepared materials. Significant efforts were dedicated to investigating the role of the supports, synthesis methods, promotors, and other factors affecting the CLC performance of synthetic oxygen carriers using solid, liquid, and gaseous fuels. This review also outlines the main challenges, research needs and opportunities for future progress to highlight potential pathways to develop synthetic oxygen carriers in an environmentally friendly, and cost-effective manner.

Boosting chemical looping combustion performances of red mud with transition metal oxides

Red mud (RM) is industrial solid waste that severely threatens environmental safety, and its resource utilization is significant both economically and ecologically. The presence of ferric oxides (Fe2O3) makes RM potential oxygen carriers (OC) for chemical looping combustion (CLC), which is a promising, novel and low-carbon combustion technology. This work examined the CLC performance of two kinds of RM using gaseous and solid fuels. Both Fe2O3 and alkali and alkaline-earth metals (AAEM) species within RM enhance carbon conversion during CLC. Nevertheless, the reactivity of original RM is unsatisfactory due to its low oxygen transporting capacity (R0, lower than 0.1), carbon conversion (XC, less than 0.8), CO2 selectivity (YCO2, less than 0.9) and instable performance. Transition metal oxides including CuO and NiO were used to modify the RM through wet impregnation. Both oxides notably improve RM performances, i.e., XC and YCO2 are notably increased. Still, deteriorations during redox cycles are observed because of particle agglomeration and sintering, especially for the RM modified with NiO. Considering the cost, potential environmental risk and efficacy, CuO is superior to NiO thanks to the enhanced performances of the modified RM-based OC including higher XC (about 0.9), YCO2(approximately 1) and stronger sintering resistance.

Modification of Metal (Fe, Al) Doping on Reaction Properties of a NiO Oxygen Carrier with CO during Chemical Looping Combustion

Oxygen carriers can significantly enhance the performance of chemical looping combustion at low energy-cost CO2 capture. Based on the density functional theory, a microscopic model of the metal Fe, Al-doped NiO oxygen carrier was established. The results indicate that the intermediate state energy and the reaction energy reduce due to electronic interaction of the Al-doped surface. With the progress of the reaction, the NiO–Al surface promotes the oxidation process of CO, indicating that the activity of the NiO surface enhanced, which is attributed to the electronic and steric effects of the Al–O structure. For the decomposition of CO on the OC surface, doping with other atoms is beneficial to suppress the carbon deposition, which is related to the steric hindrance caused by doping with other atoms. Besides, doping with iron and aluminum atoms is more conducive to the movement of OC bulk crystal lattice oxygen to the surface, thereby promoting subsequent reactions. Therefore, it is feasible to improve the reactivity of the Ni-based OC by doping metal Al, and its modification effect is closely related to the characteristics of the components.

Correlating electronegativity in bimetallic oxygen carriers for chemical looping combustion

Metallic tailoring of oxygen carrier plays a crucial role within chemical looping combustion (CLC) applications, which can be correlated to the redox reaction enhancement and sustainability. Such attributes arise from the electric valence of the material constituents, which can bring about superior oxygen vacancy and structural stability. In the concurrent study, the role of electronegativity of the bimetallic carriers upon CLC performance was scrutinized based on various bimetallic metal oxides composition. Two metallic systems were examined in the current study: Iron based oxides and copper-based oxides, where the secondary metallic element within each of the examined oxide carrier is composed of one of the 5 metallic elements, predefined for the purpose of electronegativity variation. The secondary metallic element include: Calcium, Lanthanum, Magnesium, Manganese, and Chromium. Several gas byproducts were monitored during the course of the CLC reaction, via mass spectrometer, in order to quantify the variations incurred as a result of different metallic composition inclusion. Additionally, electron microscopic techniques, such as the SEM, were utilized in the study, so as to visualize the structural alteration of sintered materials. The experimental results indicate a higher reactivity with the fuel at a higher electronegativity difference within the bimetallic structure, in the case of iron-based oxide system. Also, copper-based oxide system was associated with higher carbon dioxide production with higher selectivity, relative to iron-based oxide systems.

Stable Mixed Fe-Mn Oxides Supported on ZrO2 Oxygen Carriers for Practical Utilization in CLC Processes

The objective of the research was to prepare Fe-based materials for use as oxygen carriers (OCs) and investigate their reactivity in terms of their applicability to energy systems. The performance of ZrO2 supported Fe-Mn oxide oxygen carriers with hydrogen/air in an innovative combustion technology known as chemical looping combustion (CLC) was analyzed. The influence of manganese addition (15–30 wt.%) on reactivity and other physical properties of oxygen carriers was discussed. Thermogravimetric analyses (TGA) were conducted to evaluate their performance. Multi-cycle tests were conducted in TGA with oxygen carriers utilizing gaseous fuel. The effect of redox cycle number and temperature on stability and oxygen transport capacity and redox reaction rate were also evaluated. Physical-chemical analysis such as phase composition was investigated by XRD, while morphology by SEM-EDS and surface area analyses were investigated by the BET method. For screening purposes, the reduction and oxidation were carried out from 800 °C to 1000 °C. Three-cycle TGA tests at the selected temperature range indicated that all novel oxygen carriers exhibited stable chemical looping combustion performance, apart from the reference material, i.e., Fe/Zr oxide. A stable reactivity of bimetallic OCs, together with complete H2 combustion without signs of FeMn/Zr oxide agglomeration, were proved. Oxidation reaction was significantly faster than the reduction reaction for all oxygen carriers. Furthermore, the obtained data indicated that the materials have a low cost of production, with superior reactivity towards hydrogen and air, making them perfect matching carriers for industrial applications for power generation.

A framework for evaluating the effect of oxygen carrier characteristics on the performance of industrial-scale CLC using solid fuels

In this work we present a framework to find the potential heat recovery from Chemical Looping Combustion (CLC) using different combinations of oxygen carriers and solid fuels, based on thermodynamic equilibrium calculations. This framework requires thermodynamic information of the reacting species, which is readily available, and no kinetic information for each oxygen carrier, which is scarcer, is required. As the results of this framework are independent of the configuration of the CLC reactor, this tool can aid in the preliminary evaluation of oxygen carriers with potential for CLC applications and relevant operating conditions.

Effective H2S control during chemical looping combustion by iron ore modified with alkaline earth metal oxides

Iron ore (IO) modified with alkaline earth metal (AEM) oxides were developed as oxygen carriers (OCs) for the chemical looping combustion (CLC) of simulated municipal solid waste (MSW) syngas to simultaneously reduce the H2S emission. The AEM oxides, especially BaO, were found to improve the CLC performance of IO greatly due to the formation of AEM ferrites, which promoted the lattice oxygen activity. When using the pristine IO, less than 10% of the input H2S could be removed with the remaining being released from the reactor mainly in the form of SO2. The loadings of CaO and MgO were also found to be ineffective in sulfur removal from the syngas, because the sulfur fixation reactions were kinetically and thermodynamically limited for CaO and MgO, respectively. By contrast, over 60% of the input H2S was effectively retained on the BaO-loaded OC in the form of sulfates/sulfites because of the high reactivity between BaCO3 and H2S in the presence of Fe2O3. This study indicates that the IO loaded with BaO showed superior performance both in CLC of syngas and control of sulfur species, which can be used in the CLC of sulfur containing fuels to realize a cleaner combustion process.

Characterisation of Australian ilmenite oxygen carrier during chemical looping combustion of Victorian brown coal

Chemical looping combustion (CLC) offers a low emission route for fossil fuel-based power generation. In this study, a compact fully looped chemical looping reactor was developed in-house, and operated continuously with a Victorian brown coal as fuel and an Australian ilmenite as oxygen carrier at 940–980 °C and atmospheric pressure for 36 h. The study found that the CLC performance increased with increasing operation time. The CO2/CO molar ratio, used to evaluate the CLC reaction degree, increased from 2.3 to 8.9 over the 36 h of operation. Specifically, this paper provides a comprehensive study and evaluation of the ilmenite characteristics on morphology changes and ash interaction, due to the continuous operation. No noticeable effect by ash interaction on the CLC performance or operation was observed during the continuous operation. The characterisation results revealed a clear segregation of iron species from the iron‑titanium matrix, its migration to and enrichment over the particle surfaces. Hematite (Fe2O3) formation became more pronounced while pores developed internal and external of the ilmenite particles. These changes are believed to improve the carrier reactivity, and so the CLC performance, but also to weaken the mechanical strength of the carrier, promoting particle attrition and leading to its loss by elutriation.

Dual-functional witherite in improving chemical looping performance of iron ore and simultaneous adsorption of HCl in syngas at high temperature

The synergetic effect in using witherite (BaCO3) and iron ore (IO) for simultaneous dechlorination and chemical looping combustion (CLC) of municipal solid waste (MSW) derived syngas was studied on a bench-scale fluidized bed reactor at the temperature range of 800–900 °C. For comparison, limestone a widely used HCl sorbent was also tested. It was found that the pristine IO had negligible HCl sorption capacity during CLC of syngas. The IO-witherite mixture demonstrated much higher HCl adsorption capacity than the pristine IO and IO-limestone mixture in the temperature range of 800 to 900 °C with the presence of 25–35 vol% H2O in syngas. At the loading ratio 10 wt% of sorbent, the HCl removal capacity of IO-witherite was 3 times higher than that of the IO-limestone at 900 °C. Though IO and sorbent were physically mixed, a strong solid-solid interaction between IO and witherite surface occurred to form interstitial solid solution, BaFe12O19. The hexagonal structure of the BaFe12O19 facilitated the lattice oxygen mobility and thus improved greatly the redox performance of the IO. With increasing the inlet HCl concentration, the CLC performance of IO-Ba was further improved mainly because the chlorination process made the witherite particles more porous, which benefits the solid-solid interactions. The bulk spent witherite particles after processing could be separated easily from the IO particles by magnetic separation to realize the recovery of the used sorbents, while IO particles could be refilled into the CLC process. This research highlights that the IO-witherite mixture could be a promising OC for the CLC of HCl containing syngas to accomplish cleaner combustion.

Characteristics of dopant distribution and surface oxygen vacancy formation for modified Fe2O3 in chemical looping combustion

The modification of Fe2O3 oxygen carriers (OCs) by introducing foreign dopants is an important strategy to improve the reduction performance in chemical looping combustion. The 27 potential dopants in the periodic table were employed to systematically analyze the correlation between the dopant distribution and its property, and the influence mechanism of the dopant on surface oxygen vacancy formation for modified Fe2O3 by combining density functional theory (DFT) calculations and H2-TPR experiment. It was found that atomic radius and valence of the dopant are two crucial factors for its distribution. In addition, the dopant could regulate surface oxygen vacancy formation energy (Evac) of Fe2O3 by affecting the charge distribution of surface oxygen and surface structure. All the dopants with the valence lower than substituted Fe (+3) could lower the Evac of Fe2O3. Among the 27 dopants, Li, Na, K, Rb, Cs, Mg, Ca, Ni, Cu, Zn, Ag, Au, La, Ce, Pb, Al, Ti, Cr, Mn and Zr could significantly decrease the Evac of Fe2O3 and were identified to be promising dopants for modification of Fe2O3 OCs in CLC technology, which was well corroborated by H2-TPR experiments.

Performance improvement of chemical looping combustion with coal by optimizing operational strategies in a 3 kWth interconnected fluidized bed

Chemical looping combustion (CLC) for industrial-scale applications is hindered by challenges of inefficient fuel conversion, auto-thermal operation, and complex system operation. To improve the CLC performance under low temperature, operational strategies were optimized in a 3 kWth CLC plant with the design criterion of a simplified circulation mechanism. The gas conversion efficiency was enhanced by employing internal distributors in a multistage fuel reactor (FR). The CO2 capture and carbon conversion efficiencies were improved by each of the following: optimizing the FR fluidization flow, utilizing staged fluidization, and optimizing the steam coal (S/C) ratio. The potential of each of the abovementioned operational strategies was evaluated by analyzing the axial distribution of the gas concentration in the FR. The staged fluidization was the most effective method among the three operational strategies. It could increase the particle residence time, FR bed inventory, and cyclone efficiency. The CO2 capture efficiency increased from 57.8% to 80.3%, the carbon conversion efficiency increased from 81% to 96%, and the OC lifetime was improved from 300 h to 342 h. The OC attrition behaviors were also evaluated under different operational conditions. The FR internals had a limited effect on the OC lifetime; however, increasing the inlet velocity of the cyclone would aggravate the OC abrasion.

Kinetics of CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite prepared at industrial scale and its implication on the performance of chemical looping combustion of methane

The reaction kinetics of a CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite, prepared at ton-scale to be used as an oxygen carrier in a CLC process with methane, was determined. The variation of the reaction rates, oxygen transport capacity, and oxygen uncoupling behaviour of the selected material with the number of cycles was evaluated in a thermogravimetric analyser.The perovskite was activated for the reduction reaction with all the combustible gases, i.e., H2, CO and CH4. On the contrary, the oxidation rate barely changed throughout the cycles. The oxygen transport capacity underwent a slight decrease during the activation period.Kinetics of reduction, oxidation and oxygen uncoupling reactions were determined for the fresh and activated material assuming a grain model controlled by chemical reaction at low values of solids conversion and diffusion through the product layer at high values of solids conversion. This model predicted correctly the solids conversion vs. time curves as a function of temperature and gas concentration for the oxygen carrier reactions evaluated in this kinetics study.The kinetics data were introduced in a validated mathematical model of a fuel reactor to analyse the amount of solids required to fully combust CH4. A solids inventory of 350 kg/MWth was estimated in the fuel reactor at a temperature of 1243 K. However, this value could be reduced to 160 kg/MWth if the material operates under activation conditions within the CLC unit.

A high-performance oxygen carrier with high oxygen transport capacity and redox stability for chemical looping combustion

Oxygen carrier with high oxygen transport capacity and redox stability can greatly decrease material usage and maintain the stable system operation in chemical looping combustion. However, the trade-off between two aspects must be considered because operating the material at the high oxygen transport capacity often leads to severe sintering. Herein, we reported NiFeAlOx material as an oxygen carrier and investigated its chemical looping combustion performance. The results showed that it had an average oxygen transport capacity of 2.37 mmol/g and good stability during 20 cycles. In contrast, conventional Fe2O3 and FeAlOx material exhibited the transport capacity of 1.07 mmol/g and 0.78 mmol/g respectively. The higher transport capacity and redox stability enable the CO2 yield of 2.37 mmol/g in terms of nearly 100% capture efficiency. Through various characterization techniques, we found the high performance of this material was due to reversible exsolution and dissolution between the active compounds and the parent spinel support.

A density functional theory analysis on syngas adsorption on NiO (100) surface

Oxygen carrier (OC) design can effectively improve the performance of chemical looping combustion (CLC) and realize fossil fuel combustion at low energy-cost CO2 capture. This study describes the adsorption principles of syngas (i.e. CO and H2) on a clean nickel oxide (100) surface under single and multiple nearest neighbor effects. The results show that the adsorption stability of CO and H2 is mostly weakened by the first neighbor compared to the rest. With the same species as nearest neighbors (uniform adsorption), syngas adsorption stability is reduced when the number of neighbors increases. Similarly, when compared to uniform adsorption, the adsorption stability of CO and H2 is slightly stronger with neighboring sites occupied with different species (hybrid adsorption). In addition, a lower degree of symmetry tends to strengthen CO and H2 adsorption. Results from this analysis show that the adsorption stability of CO and H2 with neighbors are highly related to steric, hybrid and symmetry effects. An electronic property analysis was performed to further support the key role of hybrid neighboring effects in the adsorption process of syngas on the nickel oxide (100) surface.

Thermodynamic analysis of plant-wide CLC-SESMR scheme for H2 production: Studying the effect of oxygen carrier supports

Sorption enhanced steam methane reforming (SESMR) integrated with chemical looping combustion (CLC) is one of the most capable greener technologies that allows co-generation of H2 from natural gas together with CO2 capture. The performance of CLC mainly depends on the sustained reactivity, strength and durability of oxygen carriers (OCs). A suitable combination of active OCs with optimal inert composition is essential to meet the overall thermal demand of integrated CLC-SESMR process. In this work, the effect of inert OC supports on the performance of CLC-SESMR has been studied through thermodynamic analysis based on steady-state plant wide models developed using ASPEN plus. Ni-based OCs are considered with two different support materials, SiC/Al2O3 and MgAl2O4 at different inert compositions ranging from 0 to 70% by weight. The sensitivity analysis results revealed that H2 purity and CO2 captured are directly proportional to the inert composition while H2 yield is inversely proportional. The optimal inert compositions are found to be 30% and 40% by weight for the respective cases of SiC/Al2O3 and MgAl2O4. In both the cases, the overall performance of CLC-SESMR is found to be nearly same, i.e., with 97% overall methane conversion, 96% CO2 captured, 98.3% H2 purity, 2.24 H2 yield, and 71.4% net plant efficiency.

Enhanced performance of chemical looping combustion of methane by combining oxygen carriers via optimizing the stacking sequences

Combination of different types of oxides is a general strategy to prepare high performance oxygen carriers (OCs) for chemical looping combustion (CLC) technology. However, the possible chemical interactions among different components during the long-term redox cycling may reduce the stability of OCs. In the present work, we physically combine different types of OC sticks (i.e., CuO/SiO2, Fe2O3/Al2O3, Mn2O3/ZrO2 and NiO/ZrO2) in particular stacking sequences in a fixed bed reactor to improve the CLC performance. The reaction between methane and CuO is exothermic and the CuO/SiO2 OC exhibits very high activity for methane oxidation and superior resistance to carbon deposition. It is suitable to place the CuO/SiO2 in the front of the sequence which can sufficiently convert methane, and the heat releasing from this reaction will promote the following endothermic reactions. NiO/ZrO2 OC also represents very high activity for CH4 oxidation but results in serious carbon deposition. Since the reduced metallic Ni is an active catalyst for methane activation, it is suggested to place NiO/ZrO2 in the middle of the sequence to enhance the further conversion of methane and to provide enough space to remove the carbon deposition via the gasification by CO2 or H2O generated from the front reaction. Mn2O3/ZrO2 OC possesses poor activity for methane conversion but high resistance to carbon deposition, which can be used to convert unreacted methane in the end of the sequence. Fe2O3/Al2O3 OC is not an important issue due to the low activity and reaction rate. As a result, the combined OCs with a stacking sequence of CuNiFeMn or FeCuNiMn show high performance in CH4 conversion (>97%), CO2 selectivity (>96%), redox stability and resistance to carbon deposition. These results make a certain reference for using the combined OCs in the large-scale CLC system.