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Review

Research Progress and Perspectives of the Reaction Kinetics of Fe-Based Oxygen Carriers in Chemical Looping Combustion

by
Jiakun Mei
1,
Shangkun Quan
1,
Hairui Yang
2,3,
Man Zhang
2,3,
Tuo Zhou
2,3,
Xi Yang
4,
Mingyu Zhang
4,
Tae-young Mun
5,6,
Zhouhang Li
1,
Ryang-Gyoon Kim
7,
Xing Zhu
1,
Hua Wang
1 and
Dongfang Li
1,*
1
State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650031, China
2
State Key Laboratory of Power Systems, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
3
Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
4
Yunnan Energy Research Institute Co., Ltd., Kunming 650100, China
5
Climate Change Research Division, Korea Institute of Energy Research (KIER), Daejeon 34129, Republic of Korea
6
Graduate School of Energy Science and Technology, Chungnam National University, Daejeon 305764, Republic of Korea
7
Research Institute of Industrial Science & Technology (RIST), Gwangyang 37673, Republic of Korea
*
Author to whom correspondence should be addressed.
Energies 2025, 18(9), 2313; https://doi.org/10.3390/en18092313
Submission received: 31 March 2025 / Revised: 23 April 2025 / Accepted: 28 April 2025 / Published: 30 April 2025
(This article belongs to the Section D1: Advanced Energy Materials)
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Abstract

:
Chemical looping combustion (CLC), a promising technology employing oxygen carriers to realize cyclic oxygen transfer between reactors, represents a transformative approach to CO2 capture with near-zero energy penalties. Among oxygen carriers, Fe-based materials have emerged as the predominant choice due to their cost-effectiveness, environmental compatibility, and robust performance. The reaction kinetics of oxygen carriers are crucial for both material development and the rational design of CLC systems. This comprehensive review synthesizes experimental and theoretical advances in kinetic characterization of Fe-based oxygen carriers, encompassing both natural and synthetic materials, while different models corresponding to specific reaction stages and their intrinsic relationships with microstructural transformations are systematically investigated. The kinetic characteristics across various reactor types and experimental conditions are analyzed. The differences between fixed bed thermogravimetric analysis and fluidized bed analysis are revealed, emphasizing the notable impacts of attrition on the kinetic parameters in fluidized beds. Furthermore, the effects of temperature and gas concentration on kinetic parameters are profoundly examined. Additionally, the significant performance variation of oxygen carriers due to their interaction with ash is highlighted, and the necessity of a quantitative analysis on the competing effects of ash is emphasized, providing actionable guidelines for advancing CLC technology using kinetics-informed material design and operational parameter optimization.

1. Introduction

Global warming has drawn significant attention worldwide. Studies have shown that the increase in the concentration of greenhouse gases in the atmosphere is the primary cause of the ongoing global warming [1]. Among them, CO2 is the main greenhouse gas, accounting for more than 60% of the greenhouse effect [2].
Chemical looping combustion (CLC) technology has advantages such as near-zero energy consumption CO2 capture [3,4,5]. The concept of CLC technology was first introduced by Richter et al. [6] in 1983. However, it was not until 1987 that Ishida et al. [7] formally named this new combustion method as CLC and proposed that CLC technology could be used to achieve CO2 capture with extremely low energy consumption. The CLC system breaks down the process of the conventional fuel-air reaction into reduction and oxidation reactions, and the direct contact of the fuel with air is avoided by using an oxygen carrier to transfer the oxygen from the air into the fuel, achieving high-concentration CO2 emissions in the flue gas for CO2 capture [8,9]. Subsequently, Ishida et al. [7,10], for the first time, proposed the concept of combining a gas-turbine cycle to produce power with CLC while enabling CO2 capture. The significant milestones in the development of CLC technology are summarized in Table 1.
CLC systems are classified into two categories based on fuel type: gas fuel CLC and solid fuel CLC [22]. For gas fuel CLC, Lyngfelt et al. [13] introduced the concept of employing a dual fluidized bed for CLC and validated it using both cold and hot state tests, realizing chemical looping combustion with gaseous fuel. Lyngfelt [23] and colleagues at Chalmers University of Technology designed a 10 kWth gas fuel CLC system. In this system, a fast fluidized bed served as the air reactor, and a bubbling fluidized bed served as the fuel reactor. With NiO used as the oxygen carrier, following a 100-h continuous operation, the system attained a fuel conversion rate exceeding 98%, and no CO2 was detected at the outlet of the air reactor [14]. Korea Institute of Energy Research designed and constructed a 50 kWth gas fuel CLC system, employing a circulating fluidized bed as the air reactor and a bubbling bed as the fuel reactor. Experimental results showed that the fuel conversion rate and CO2 capture rate attained values as high as 99.7% and 98%, respectively [15]. The Spanish National Coal Institute devised and set up a 10 kWth gas fuel CLC system with a dual bubbling bed configuration and conducted evaluations of various oxygen carriers [24]. Bolhàr et al. [25] at the Vienna University of Technology constructed a 120 kW gas fuel CLC system with dual fast bed reactors. This system employed Ni-based oxygen carriers, demonstrating 98% CH4 conversion and 94% CO2 capture efficiency.
For solid fuel CLC, Lyngfelt et al. [26,27] explored the current state of the art, performance characteristics, and pilot scale experience of this process, and conclusions were drawn regarding oxygen carrier materials suitable for solid fuels, suggesting that the technology is ready for scale up. The research team led by Laihong Shen from Southeast University carried out CLC experiments using coal as the fuel, achieving a CO2 capture efficiency of 80% at 960 °C with NiO as the oxygen carrier [28]. Thon et al. utilized a two-stage bubbling bed as the fuel reactor and a circulating fluidized bed riser as the air reactor, with lignite used as the solid fuel and ilmenite used as the oxygen carrier. They discovered that the two-stage fuel reactor performed well, and CO2 concentrations in the dry off-gas exceeded 90 vol.% [29]. The investigations into solid fuel CLC systems are summarized in Table 2.
Through the study of oxygen carriers, a critical component in CLC, Henrik Thunman et al. [36] introduced the concept of oxygen carrier-assisted combustion (OCAC) in 2013. They suggested that ilmenite’s capacity to cyclically absorb and release oxygen could enhance oxygen distribution in circulating fluidized bed boilers. This approach replaces part or all of the bed material in solid fuel boilers with oxygen carriers to improve combustion efficiency. OCAC has been validated across fluidized bed boilers at laboratory, semi-industrial, and full-industrial scales [36,37,38,39,40,41].
Oxygen carriers are undoubtedly critical components in CLC technology [42]. Fe-based oxygen carriers exhibit significantly lower costs than other transition metal-based oxygen carriers due to their abundant reserves as well as mature mining and production technologies. Notably, many iron ores can be directly utilized as oxygen carriers following simple treatment [43]. Furthermore, due to the significant advantages of Fe-based oxygen carriers in terms of cost-effectiveness and environmental friendliness, they are widely applied in CLC technology. Leion et al. [44] confirmed the viability of natural ilmenite as an oxygen carrier in a small-scale fluidized bed using CO and H2 as reactant gases. Furthermore, they utilized petroleum coke, wood chips, and two types of lignite as solid fuels to investigate the CLC efficiency of hematite when serving as an oxygen carrier. The results demonstrated that hematite maintained high reactivity. Moreover, its activity did not decrease as the reaction time increased [31]. Gu et al. [45,46] studied the feasibility of using hematite as an oxygen carrier for biomass and coal fuels in both a small-scale fluidized bed and a 1 kWth continuous fluidized bed reactor. The experimental results demonstrated that hematite displayed high reactivity. Fraga-Cruz et al. [47] investigated the combustion mechanism of ilmenite with syngas as the fuel and compared the air stream under varying temperature conditions. Berguerand et al. [16] conducted solid fuel CLC experiments using ilmenite in a 10 kWth reactor, indicating that natural ilmenite can be employed as an oxygen carrier for continuous 22 h experiments in a 10 kWth reactor. It displayed high reactivity, with the CO2 capture efficiency ranging from 82.5% to 96%. Abad et al. [48] tested the performance of an Fe-based oxygen carrier at 800–950 °C for 40 h. The results showed that there was no decrease in particle reactivity, and agglomeration and carbon deposition were not observed. However, the relatively low mechanical stability of Fe-based oxygen carriers remains a bottleneck, limiting their large-scale application, and efforts to improve this reaction rate have been a key focus of research on CLC technology [49]. Wang et al. [50] studied the reaction characteristics of the synthesized CuO/Al2O3 and Fe2O3/Al2O3 oxygen carriers by combusting them with Chinese anthracite. It can be concluded that the CuO/Al2O3 is more suitable for the combustion process of anthracite. Shen et al. [51] demonstrated that potassium- and nickel-doped iron ore oxygen carriers enhance solid-fuel gasification in fluidized beds. Ni-doped Fe-based carriers also maintained high CO2 capture efficiency in a 1 kWth reactor [52]. Pérez-Méndez et al. [47] compared the performance of the ilmenite with other oxygen carriers used in CLC. It was concluded that ilmenite was the best available oxygen carrier for CLC processes due to its cost-effectiveness, environmental friendship, high methane conversion efficiency, and abundant natural availability. Ilmenite is among the most promising Fe-based oxygen carriers for commercial CLC deployment [30,53,54,55]. In addition, the attrition of the oxygen carrier represents another essential property that needs to be taken into account for its practical implementation in CLC systems [56]. The attrition resistance of the oxygen carrier directly affects its lifespan, which is a vital determinant in the scalability and economic viability of CLC technology. For Fe-based oxygen carriers in a fluidized bed reactor, as the reaction proceeds, the active components on the surface of the oxygen carrier are susceptible to attrition. This leads to a decrease in the content of these active components and subsequently modifies the reaction kinetics of the Fe-based oxygen carrier. Li et al. [57] explored the attrition characteristics of hematite under diverse conditions and observed that increasing the temperature can enhance the wear resistance of hematite under fluidized bed conditions. Hatanaka et al. [58] observed increasing ilmenite attrition rates over 150 redox cycles in a fluidized bed reactor. Unlike other Fe-based carriers, SEM revealed particle surface aggregation after 100–150 cycles, which was absent at 50 cycles. The observations of the samples using scanning electron microscopy and measurements of their tapped density and reduction rate showed that this rapid increase arises from changes in the surface morphology, including the migration of iron to the particle surfaces. Nelson et al. [59] explored the effects of temperature, fuel gas concentration, and flow rate on the properties of ilmenite and found that the fuel gas concentration affects the particle morphology evolution, and higher fuel gas concentration promotes the migration of iron to the surface of the ilmenite particles. Shen et al. [60] conducted long-term redox cycles of ilmenite using FB-TGA and found that during the reaction, iron migrates toward the particle surface, resulting in the formation of an iron-rich external shell.
Moreover, the reaction kinetics of the oxygen carrier are closely related to parameters such as the solid circulation rate between reactors and the solid inventory in each reactor. The solid circulation rate affects the contact time between the oxygen carrier and the fuel, which in turn influences the reaction rate. A proper solid circulation rate needs to be determined based on the reaction kinetics to achieve efficient combustion. Similarly, solid inventory governs the overall reaction rate and fuel conversion efficiency. Insufficient solid inventory results in inadequate oxygen carrier-fuel interaction, causing incomplete combustion. Conversely, excessive inventory can lead to challenges such as poor fluidization and elevated pressure drops. Therefore, a comprehensive understanding of the reaction kinetics of the oxygen carrier is vital for the successful operation and development of CLC systems [61]. Furthermore, kinetic parameters are crucial for reactor design and reaction mechanism prediction. The redox reaction kinetic models of the oxygen carrier are key tools for exploring the underlying mechanisms of the carrier reaction and are essential for optimizing the oxygen carrier reaction process [22]. Investigating the redox kinetics of the oxygen carrier is critical for advancing CLC technology. Ei-Geassy [62] and Et-Tabirou [63] carried out experimental investigations to determine the activation energy for the reaction between Fe2O3 single crystals and CO. Wang et al. [64] analyzed the reduction behavior of Fe2O3/Al2O3 using thermogravimetric analysis (TGA). Breault et al. [65] conducted kinetic experiments regarding the reaction of hematite with CO in a TGA reactor to acquire the relevant kinetic parameters. Chen et al. [66] utilized a micro-fluidized bed reactor to investigate the reaction characteristics and kinetics of the reaction between hematite and CO. Zhang et al. [67] used an innovative pressurized fluidized bed reactor to obtain activation energies and pre-exponential factors for the reaction of Fe2O3 and Fe2O3/Al2O3 with CO. Garcia-Labiano et al. [68] studied the reaction kinetics of Cu-based, Fe-based, and Ni-based oxygen carriers with CO, H2, and CH4. Abad et al. [69] utilized the unreacted shrinking core model to depict the reaction of Fe2O3/Al2O3 with syngas. Su et al. [70] determined the intrinsic reaction kinetics of hematite by altering the temperature and gas concentrations in a TGA and a batch fluidized bed reactor.
Understanding the kinetics of oxygen carrier redox reactions is crucial for the modeling and the detailed design of CLC reactors. At present, a substantial amount of research has been conducted on the kinetics of Fe-based oxygen carrier reactions. However, different researchers have reached diverse conclusions, and there is a scarcity of articles that classify the kinetics of Fe-based oxygen carrier reactions based on distinct experimental conditions. Therefore, this review emphasizes the research progress regarding the reaction kinetics of Fe-based oxygen carriers, summarizing the effects of temperature, gas species, and gas concentration on their reaction kinetics. Additionally, the impacts of different reactors and various types of Fe-based oxygen carriers (both natural and synthetic) on the reaction kinetics are analyzed. Finally, the interactions between different fuel ashes and Fe-based oxygen carriers are also summarized. The present review may provide a theoretical foundation for the design of reactors based on Fe-based oxygen carriers.

2. Reaction Kinetics of Fe-Based Oxygen Carriers

In the study of CLC, the investigation of the reaction kinetics of the chemical reactions involved in the oxygen-carrying particles is helpful in revealing the main factors affecting the reaction performance of the oxygen carrier, enabling effective prediction of its reaction rate and providing the basic parameters required for numerical simulation using kinetic analysis, thereby guiding reactor design and simulation [68,71,72,73,74]. In practical CLC reactor systems, reactions involving oxygen carriers primarily involve gas–solid interactions. Gas–solid reactions can be categorized into catalytic and non-catalytic types. In catalytic gas–solid reactions, the primary chemical changes occur in the gas phase, while the solid phase acts as a catalyst. In non-catalytic gas–solid reactions, the solid reactants are gradually consumed as the reaction progresses, forming a solid product layer on their surface. These processes are collectively termed gas–solid reactions [75].

2.1. Kinetic Models of Fe-Based Oxygen Carrier Reaction

In order to predict the kinetic behavior of oxygen carrier reduction, different gas–solid reaction models have been proposed to explain the reaction mechanisms of oxygen carriers. At present, reaction models commonly used in CLC include the changing grain size model, the shrinking core model, and the nucleation and nuclei growth model. The particle/grain evolution described for these three different reaction mechanism models in the reaction is shown in Figure 1, as described in Ref. [8]. Furthermore, numerous scholars have proposed modified reaction models for different reaction conditions to be applied in actual experiments. Examples include the apparent model [76], grain model [77], pore model, and rate equation theory [75].
The selection of various kinetic models can significantly influence the kinetic parameters derived from reaction data. Habermann et al. [78] divided the reduction reaction of iron ore into two phases using a fluidized bed reactor: a first phase controlled by gas phase diffusion and a second phase dominated by the reduction reaction within the iron ore. Zhu [79] obtained the kinetic parameters of three models by choosing three different models at the same temperature. Mei et al. [80,81] researched the reaction between Fe2O3/Al2O3 and CO by dividing the reaction into two stages by converting the conversion rate, thus obtaining a mechanism model that was adapted to different stages. Ksepko et al. [82] determined the kinetic parameters of Fe2O3/TiO2 using three different models to obtain different kinetic parameters. Monzam et al. [83] proposed a kinetic model based on two parallel reactions to describe the reduction of Fe2O3 to FeO; however, this model was constrained by CH4 concentration and temperature conditions. Su et al. [70,84] examined the reduction kinetics of hematite with CO using TGA and a small-scale fluidized bed reactor. They found that the reduction of hematite occurs in two stages (Fe2O3 → Fe3O4, Fe3O4 → FeO), with the first stage being controlled by gas diffusion and the second stage by chemical reaction. Piotrowski et al. [85,86] researched the kinetics of the reduction reaction of hematite with syngas and obtained activation energies in the range of 25–125 kJ/mol using a two-dimensional nucleation and nuclei growth model. Consequently, for redox reactions, different models are required due to the different ways in which the structure of the solid particles changes. Notably, Li et al. [87,88] successfully predicted the kinetics of CaO carbonation under diverse experimental conditions by formulating a general rate equation theory. The approximate flowchart is shown in Figure 2. Moreover, based on the general rate equation theory, his team successfully predicted the H2 and CO reduction kinetics of CaMn0.775Ti0.125Mg0.1O2.9-δ at different temperatures and concentrations by applying the transition state theory and density functional theory. They also predicted the reduction kinetic of Fe2O3 with H2 at different temperatures and concentrations [89,90].

2.2. Reaction Kinetics of Fe-Based Oxygen Carriers in the TGA

Currently, the primary experimental devices for investigating the reaction kinetics of oxygen carriers include TGA [84,91], micro-fluidized bed reactor (MFB) [92,93], and fluidized bed thermogravimetric analysis (FB-TGA) [94,95]. The schematic diagrams of these experimental setups are illustrated in Figure 3. TGA, which is characterized by high measurement precision and excellent sensitivity, is the most representative and widely used analytical instrument for characterizing reaction kinetics [94]. The studies on the reaction kinetics of Fe-based oxygen carriers conducted using TGA are summarized in Table 3.

2.3. Reaction Kinetics of Fe-Based Oxygen Carriers in Fluidized Bed Reactors

As discussed in Section 2.2, TGA is the most prevalently employed instrument for characterizing reaction kinetics. However, due to its measurement principle and structural characteristics, TGA suffers from issues such as low mass and heat transfer rates, non-uniform temperature distribution, and high gas diffusion resistance [116,117]. Meanwhile, there is a significant gradient in both the temperature and gas concentration within the particulate sample, which increases the deviation in characterization and kinetic fitting. It is far from the CLC process under bubbling and turbulent conditions [118]. Therefore, the reaction kinetics of oxygen carriers measured using TGA are often lower than the true values [22]. The employment of fluidized bed reactors to characterize gas–solid reaction kinetics not only facilitates the establishment of gas–solid contact patterns under diverse flow regimes but also enables the attainment of diffusion-enhanced isothermal reaction zones, which can closely mimic the actual process of CLC [94]. Thus, studies on the reaction kinetics of Fe-based oxygen carriers using fluidized bed reactors as the experimental equipment are summarized in Table 4.
As shown in Table 3 and Table 4, taking ilmenite as an example, Liu et al. [100] obtained an activation energy of 169.6 kJ/mol for the reaction of ilmenite with CO using TGA. Purnomo et al. [126] determined an activation energy in the range of 51–92 kJ/mol for the reaction between ilmenite and CO in a fluidized bed batch reactor, while Perreault et al. [121] reported an activation energy of 51 kJ/mol using a small-scale fluidized bed reactor. Similarly, Schwebel et al. [120] determined activation energies in the range of 71.59–89.34 kJ/mol within a batch fluidized bed reactor. Conversely, Winayu et al. [131] reported an activation energy of 25.54 kJ/mol. It is evident that the activation energies vary significantly across different reactor types, particularly when comparing results from conventional fluidized beds and small-scale fluidized beds. Moreover, it can be observed that for the same type of Fe-based oxygen carriers, different researchers have determined different kinetic parameters using TGA and fluidized bed reactors. Consequently, it is not recommended to directly apply the kinetic parameters derived from TGA to simulations associated with fluidized bed reactors.
However, in fluidized bed reactors, the reaction process must be estimated by measuring the concentrations of outlet gas components and performing inversion calculations. Even with high-resolution and fast-responsive mass spectrometers, it is difficult to achieve real-time and accurate TGA mass measurements. As a result, this method is unable to effectively distinguish between gas phase reactions and gas–solid reactions. Moreover, in fluidized bed reactors, phenomena like gas back-mixing and axial diffusion occur. These phenomena have the potential to distort the gas signal, thereby hindering the obtainment of the true kinetic information of the oxygen carrier [135]. Consequently, some researchers have sought to balance the strengths and weaknesses of TGA and fluidized bed reactors. By employing a fluidized bed thermogravimetric analysis, they integrate the efficient heat and mass transfer within the fluidized bed with the precise process measurement capabilities of TGA. This approach enabled novel research pathways and advanced analytical techniques for characterizing gas–solid reactions in CLC [94].
The École Polytechnique de Montréal in Canada first proposed the design and construction of a fluidized bed thermogravimetric analyzer in 2014. They developed two distinct FB-TGA systems: one heated using an electric furnace and another with magnetic induction [136,137,138]. Despite the limited measurement precision, it has determined the basic configuration and testing methods of the FB-TGA. The team led by Zhenshan Li from Tsinghua University [139,140] developed a micro-fluidized bed reactor in 2018. They verified the measurement feasibility of the FB-TGA and emphasized the advantages of the FB-TGA in characterizing rapid gas–solid reaction processes. The team led by Laihong Shen from Southeast University [141,142] developed an FB-TGA capable of introducing steam using aerodynamic methods in 2020. Consequently, some scholars have initiated the study of the reaction kinetics of oxygen carriers using FB-TGA. Liu et al. [143] examined the oxygen uncoupling and redox reaction kinetics of perovskite-type oxygen carriers using a micro-fluidized bed thermogravimetric analyzer. They discovered that the oxidation reaction takes place only in the initial stage and is governed by the chemical reaction. The reduction reaction encompasses a fast phase and a slow phase, which are governed by the chemical reaction and the diffusion through the product layer, respectively. Wang et al. [144] explored the redox reaction kinetics of Fe/Cu-based oxygen carriers employing a micro-fluidized bed thermogravimetric analyzer. They characterized the redox reaction process in terms of the product island-based rate equation theory. Shen et al. [145] employed a fluidized bed thermogravimetric reactor to develop a multi-scale kinetic model for the analysis of the redox reaction kinetics of hematite.

3. Effect of Different Reaction Conditions on the Reaction Kinetics of Fe-Based Oxygen Carriers

3.1. Reaction Kinetics of Natural Fe-Based Oxygen Carriers

Natural ores represent a viable option due to their cost-effectiveness, availability, and satisfactory performance [146]. Ma et al. [147] utilized natural hematite as the oxygen carrier within a 50 kWth coal-fired CLC reactor. They discovered that the maximum CO2 capture efficiency attained 91%, with a combustion efficiency of 86% at 1000 °C. Berguerand et al. [16] conducted solid fuel CLC experiments using ilmenite in a 10 kWth reactor. The study indicated that natural ilmenite could serve as an oxygen carrier in a 10 kWth reactor. The ilmenite underwent a continuous operation for 22 h, exhibiting high reaction activity and CO2 capture efficiencies ranging from 82.5% to 96%. Huang et al. [148] used natural hematite as the oxygen carrier in a fluidized bed reactor for direct chemical looping reforming of biomass. Their research found that hematite was able to supply oxygen. However, as the number of circulation cycles increased, particle wear and agglomeration were observed, leading to a decline in the oxygen carrier’s reactivity. Ge et al. [149,150] employed hematite as the oxygen carrier in both a 25 kW intermittent reactor and a continuous reactor for chemical looping reforming of biomass to generate hydrogen. The research findings suggested that the presence of hematite accelerates the biomass gasification process, enhancing both the carbon conversion rate and the gasification rate. Consequently, numerous researchers have investigated the reaction kinetics of natural ores as oxygen carriers. Abad et al. [74] determined the reaction kinetics of pre-oxidized and activated ilmenite with H2, CO, and CH4 using TGA. Piotrowski et al. [86] and Feilmayr et al. [129] obtained the reaction kinetics of hematite with CO using TGA and a fluidized bed reactor, respectively. The research on the reaction kinetics of natural Fe-based oxygen carriers is summarized in Table 5.

3.2. Reaction Kinetics of Synthetic Fe-Based Oxygen Carriers

However, natural ores are unable to satisfy the mechanical stability requirements of pilot-scale CLC units. To acquire oxygen carriers with mechanical properties and stability, various oxygen carriers have been synthesized artificially, including Fe-based, Ni-based, Cu-based, Mn-based, and composite oxygen carriers [22]. Yang et al. [153] confirmed using TGA that a 20% mass ratio of copper ore to iron ore could produce a synergistic effect on the reaction between the oxygen carrier and coal. Ryden et al. [154] incorporated 0.6 wt% NiO into ilmenite and performed the reaction in a 100 kWth coal-fired CLC reactor. As a result, the combustion efficiency increased from 76% to 90%. Tobias et al. [155] added Ni to various types of Fe2O3 particles and subjected them to multiple redox cycles in CLC. They found that the type of inert carrier and the calcination temperature significantly influenced the reactivity of the oxygen carrier. Yang et al. [156] investigated the CLC cycle of coal using hematite modified with copper as the active component. They reported that the addition of 6% copper significantly enhanced the reactivity of hematite. Jiang et al. [157] synthesized an oxygen carrier using an admixture of hematite and CuO. It has been discovered that the reactivity of the new oxygen carrier increases with the number of cycles. Bao et al. [92,158] observed carbon deposition and slag formation in CLC experiments using pure Fe2O3 oxygen carriers, whereas no agglomeration occurred with the addition of 10 mol% Al2O3. In addition, a new ilmenite oxygen carrier was synthesized by impregnating the original ilmenite particles with K2CO3, Na2CO3, or Ca(NO3)2, and its cyclic reduction reactivity was investigated in a fluidized bed reactor. It was found that the addition of foreign ions significantly enhanced the reduction reactivity of ilmenite. Synthetic oxygen carriers often demonstrate superior performance compared to natural oxygen carriers, likely due to the synergistic effects among composite oxygen carriers [159], which enhance their reaction rates. Consequently, the reaction kinetics parameters of synthetic oxygen carriers differ from those of natural Fe-based oxygen carriers. As shown in Table 6, the reaction kinetics of Fe-based oxygen carriers synthesized using methods such as adding supporting materials are summarized. The materials currently employed for investigating the reaction kinetics of Fe-based oxygen carriers are illustrated in Figure 4.
Based on the data presented in Table 5 and Table 6, Abad et al. [74] obtained an activation energy of 65.0 ± 2.7 kJ/mol for the reaction between ilmenite and H2 using TGA. In contrast, Steiner et al. [102] reported an activation energy range of 15–80 kJ/mol for the reaction between synthetic ilmenite and H2. Zhu [97] conducted TGA experiments to determine the activation energy of pure Fe2O3 and Fe2O3/Al2O3. This study found that the addition of an inert support did not change the reaction model but increased the activation energy of the reaction. This indicates that the presence of the inert support may affect the reaction kinetics, possibly due to changes in the surface area, pore structure, or mass transfer characteristics of the oxygen carrier. Similarly, Luo et al. [105] investigated the reaction between Fe2O3/MgAl2O4 and methane using TGA and reported that the activation energy for this reaction was higher than that for pure Fe2O3. Thus, it is evident that while the incorporation of inert supports can mitigate issues such as the sintering of Fe-based oxygen carriers at high temperatures and improve their cycle stability, it may also reduce the activity of the active components in the reactants. This reduction decreases the amount of active species required for the reaction, consequently increasing the activation energy.

3.3. Effect of Temperature and Gas Concentration on Reaction Kinetics of Fe-Based Oxygen Carriers

In CLC, temperature significantly influences reaction rates and chemical equilibrium. Gas concentration affects the frequency of effective collisions between reactants, thereby influencing the reaction rate. Therefore, the effects of varying temperatures and reaction gas concentrations on reaction kinetic parameters are of great significance. The literature reviews indicate that CO is among the most extensively studied reduction gases in current research. Taking ilmenite as an example, Abad et al. [74] obtained an activation energy of 113.3 ± 3.0 kJ/mol for CO concentrations ranging from 5 to 50% and temperatures in the range of 800–950 °C. Liu et al. [100] and Perreault et al. [121] obtained activation energies of 169.6 kJ/mol and 51 kJ/mol, respectively, for CO concentrations of 10–30% and 15–30%, respectively, and temperature ranges of 850–1050 °C and 800–900 °C, respectively. Similarly, Purnomo et al. [126] gained an activation energy of 59.4 kJ/mol for a CO concentration of 50% and temperatures ranging from 850 to 975 °C. Winayu et al. [131] gained an activation energy of 25.54 kJ/mol for a CO concentration of 25% and temperatures of 900–1000 °C. This demonstrates that the influence of gas concentration and temperature variations on the kinetic parameters of Fe-based oxygen carriers is significant and cannot be overlooked. With increasing temperature, the kinetic energy of reactant molecules increases correspondingly. This enhances collision intensity and frequency, leading to higher reaction rates. At low gas concentrations, the likelihood of collisions between reactants and gas molecules is reduced, resulting in slower reaction rates. As the concentration increases, collision frequency between reactants and gas molecules rises, thereby accelerating the reaction rate. Therefore, the effects of temperature and gas concentration variations on the reaction kinetics of Fe-based oxygen carriers are summarized in Table 7, using CO as the reduction gas.
The reaction of oxygen carriers in CLC is a complex gas–solid non-catalytic reaction [22]. Therefore, the reactivity of oxygen carriers should be studied by taking into account the combined effects of their intrinsic chemical reaction factors and mass transfer factors. Intrinsic reaction kinetics refers to the reaction kinetics unaffected by fluid flow, mass transfer, and heat transfer. It describes the inherent laws governing the chemical reaction itself. Zhang et al. [67] conducted research using a pressurized fluidized bed reactor to investigate the reaction kinetics of Fe2O3 and Fe2O3/Al2O3 with CO. They established an intrinsic reaction kinetics model for this process. Piotrowski et al. [85,86] studied the reduction of hematite (Fe2O3) to magnetite (Fe3O4) and determined that the activation energy for this process ranges from 25 to 125 kJ/mol, with a reaction order of 1. They also concluded that a two-dimensional nucleation and growth model is more suitable for describing the overall reaction process. Pineau et al. [164] examined the reduction process of hematite with hydrogen at temperatures ranging from 220 to 730 °C. They reported that the activation energy for the first stage of the reaction, where Fe2O3 is reduced to Fe3O4, is 76 kJ/mol. For the second stage, where Fe3O4 is reduced to FeO, the activation energy was found to be 39 kJ/mol. Monazam et al. [65] used TGA to determine the reaction kinetic parameters for the reduction of hematite by CO. They found that the reduction process proceeds in two concurrent steps, with an activation energy of 19.0 ± 0.14 kJ/mol. Su et al. [70] investigated the intrinsic reaction kinetics of hematite reduction by CO. They determined that for temperatures ranging from 400 to 650 °C, the intrinsic activation energy for the first stage of the reaction, where Fe2O3 is reduced to Fe3O4, is 138.55 kJ/mol. This value implies a higher energy barrier for the initial reduction step compared to the findings of Monazam et al. [65], implying that the reaction kinetics may vary significantly depending on the specific experimental conditions and the nature of the reaction mechanism.

3.4. Research on the Interaction and the Effect of Properties of Ash with Fe-Based Oxygen Carrier

One of the most critical characteristics of an oxygen carrier is its ability to undergo oxidation and reduction, facilitating oxygen transfer within a chemical looping system. Highly reduced oxygen carriers may encounter various performance issues, such as reduced reactivity, agglomeration, and defluidization. Meanwhile, taking coal in solid fuels as an example, the accumulated coal ash deposited on the surface of the oxygen carrier not only blocks the pores and hinders gas–solid reactions but also causes sintering and agglomeration of the oxygen carrier [22]. Therefore, the interaction between ash and the oxygen carrier is an important issue in the CLC process. Thermodynamic calculations indicate that reactions between ash and the oxygen carrier can occur at high temperatures, but at a relatively low rate [165]. Additionally, in the CLC process, studies have shown that for Fe-based oxygen carriers, ash deposition on the oxygen carriers and the interactions between the ash and the carriers are inevitable, and the ash will react with the oxygen carriers [166,167,168,169], which exacerbates performance issues [170]. These interactions can lead to modifications in the physical and chemical properties of the oxygen carrier, potentially compromising its cyclic stability and efficiency. The reactions can alter the surface area, porosity, and mechanical strength of the oxygen carrier, which are all critical factors for the overall performance of the CLC system. However, the current CLC technology is unable to completely separate the oxygen carrier from the ash [171]. Zhou et al. [172] studied the influence of biomass ash on the performance of iron ore and found that the inorganic components present in biomass ash vary, leading to different effects on the reactivity of the iron ore. Ilyushechkin et al. [173] examined the interaction between two types of coal ash and Fe-based oxygen carriers. The results demonstrated that iron-rich ash enhances the oxidation and reduction kinetics of iron ore. While it does not affect the reduction kinetics of ilmenite, it significantly prolongs the oxidation time of ilmenite. Silica-rich ash reduces the oxidation rates of iron ore. Yan et al. [174] modified iron ore with rape stalk ash and wheat stalk ash and found that the cumulative CO conversion of biomass ash modified oxygen carriers was significantly higher than that of unmodified oxygen carriers. Gu et al. [175] confirmed the effect of adding biomass ash to the oxygen carrier on its performance and conducted experiments with the addition of 5%, 10%, 15%, and 20% ash. The results showed that the addition of only 5% of rape straw ash was effective in improving the reactivity of the iron ore oxygen carrier. Moreover, no decrease in reactivity was observed after adding 20% of the ash. Feng et al. [176] investigated the enhancement mechanism of alkali metal doping on the reactivity of Fe2O3 oxygen carriers using density functional theory (DFT) calculations. The results demonstrated that the smaller the ionic radius of alkali dopants and the stronger their electronegativity are, the higher the activity of surface oxygen at sites distal to the dopants. The surface oxygen adjacent to the dopants will show the better activity compared to the one away from the dopants. Gu et al. [45,177] first developed a K2CO3-modified Fe2O3 OC and reported that this modification significantly enhanced the carbon gasification rate and promoted the conversion of carbonaceous gases to CO2 in the CLC process. Subsequently, they evaluated the reactivity of a 6% K2CO3-modified Fe2O3 with CO and H2 in a TGA and demonstrated that K as an electric donor could weaken the Fe-O bond, enhancing its reactivity. Yang et al. [178] investigated the interaction between wheat straw ash (WSA) and ilmenite using a fixed bed reactor. The result revealed that ilmenite with 10 wt% wheat straw ash showed the best performance. It was inferred that KFeO2 phase formation as a result of the interaction between WSA and ilmenite promotes the reactivity of the oxygen carrier. Therefore, the ash-doping experiments on Fe-based oxygen carriers are summarized in Table 8 to illustrate the effects of different types of ash on the performance of these oxygen carriers.

4. Conclusions and Future Prospects

This paper comprehensively reviews the effects of various factors on the reaction kinetic parameters of Fe-based oxygen carriers in CLC. It categorizes the findings according to reactor type (including TGA, FB reactors, and FB-TGA), temperature, and atmosphere. The following conclusions and prospects can be drawn.
(1)
The measurement methods for characterizing the reaction kinetics of oxygen carriers primarily include TGA, FB reactors, and FB-TGA. For the Fe-based oxygen carriers, TGA determines kinetic parameters by tracking mass changes in real-time; however, it faces challenges such as low mass and heat transfer rates. In contrast, FB reactors evaluate the reaction process and derive kinetic parameters by measuring the concentration of gas components at the outlet. However, it is difficult to achieve real-time and accurate measurements compared with TGA. The activation energy derived from TGA could differ significantly from that obtained using fluidized bed reactors; hence, kinetic parameters obtained from TGA are not advisable for direct application in fluidized bed simulations.
(2)
A distinction exists between intrinsic and apparent reaction kinetics. Existing studies on intrinsic reaction kinetics primarily focus on pure Fe2O3, hematite, and ilmenite, and a broad investigation on the widely utilized materials is required.
(3)
Due to the relatively low mechanical stability of Fe-based oxygen carriers, a common strategy to enhance the reaction performance of Fe-based oxygen carriers is the incorporation of inert supports. The addition of inert supports can alleviate problems such as the sintering of Fe-based oxygen carriers at high temperatures and improve their cyclic stability. However, partially inert supports may impose a restrictive effect on the active component Fe2O3 in the Fe-based oxygen carrier, thereby influencing the amount of active components required for the reaction. Consequently, the apparent activation energy is generally higher than that of pure Fe2O3.
(4)
In FB reactors, attrition is a critical factor affecting the service life of Fe-based oxygen carriers. Specifically for ilmenite, during the reaction process, active iron components migrate to the surface, while particle collisions within the FB reactor may lead to attrition, resulting in a decrease in active component content and the reaction kinetics. However, research on the impact of attrition on the reaction kinetics of Fe-based oxygen carriers remains limited, necessitating the need for further investigation.
(5)
During the long-term operation of CLC, it is inevitable that solid fuel ash interacts with the oxygen carrier, leading to physical and chemical changes in the carrier. The interactions may affect the reaction kinetics of the oxygen carrier. Existing studies primarily focus on the mechanisms of ash–oxygen carrier interactions and their effects on the surface morphology of oxygen carriers, while investigations into their impact on reaction kinetics are required. Current studies on the interaction between ash and Fe-based oxygen carriers have primarily focused on two aspects: microstructural modifications after adding ash, which are analyzed using DFT calculations, and alterations in reaction mechanisms and reactivities after adding ash, which are evaluated using experimental studies. However, few studies have integrated the results based on DFT calculations with experimental results to explore the interactions of ash and oxygen carriers. It is recommended to combine experimental and DFT methodologies to systematically elucidate the influences of ash on the kinetics of Fe-based oxygen carriers in future work.

Author Contributions

Conceptualization, D.L.; investigation, S.Q., Z.L., T.-y.M. and R.-G.K.; writing—original draft preparation, S.Q., T.Z., J.M. and X.Y.; writing—review and editing, D.L., Z.L., H.Y., M.Z. (Man Zhang), T.-y.M., R.-G.K., X.Z. and H.W.; supervision, D.L. and H.W.; project administration, D.L. and M.Z. (Mingyu Zhang); funding acquisition, D.L. and X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work is supported by the National Natural Science Foundation (Grant No. 52266007), Yunnan Fundamental Research Projects (Grant No. 202201BE070001-011), and Yunnan Major Scientific and Technological Projects (Grant No. 202405AO120103).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

Authors Xi Yang and Mingyu Zhang were employed by the company Yunnan Energy Research Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Evolution of particles/grains as described by different reaction mechanism models: (A) changing grain size model; (B) shrinking core model; (C) nucleation and nuclei growth model.
Figure 1. Evolution of particles/grains as described by different reaction mechanism models: (A) changing grain size model; (B) shrinking core model; (C) nucleation and nuclei growth model.
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Figure 2. Flowchart of the derivation of the rate equation theory, as described in Ref. [75].
Figure 2. Flowchart of the derivation of the rate equation theory, as described in Ref. [75].
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Figure 3. Schematic diagram of experimental equipment: (A) TGA; (B) MFB; (C) FB-TGA.
Figure 3. Schematic diagram of experimental equipment: (A) TGA; (B) MFB; (C) FB-TGA.
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Figure 4. Materials commonly used in kinetic studies of Fe-based oxygen carriers.
Figure 4. Materials commonly used in kinetic studies of Fe-based oxygen carriers.
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Table 1. Significant milestones during the development of CLC technology.
Table 1. Significant milestones during the development of CLC technology.
Author/OrganizationYearResearch ContentsRef.
Lewis and Gilliland1954Reaction between metal oxides and carbonaceous fuels[11]
Richter and Knoche1983Proposition of the concept of splitting the conventional combustion reaction into two cyclic redox reaction processes[6]
Ishida and Jin1994Proposition of the concept of integrating CLC with a gas-turbine cycle for power generation while enabling CO2 capture[10,12]
Lyngfelt et al.2001Proposition of the concept of dual fluidized beds for CLC[13]
Lyngfelt et al.200410 kWth gas fuel CLC test rig[14]
Korea Institute of Energy Research200550 kWth gas fuel CLC test rig[15]
Lyngfelt et al.2008Experiments on CLC of solid fuels[16,17]
Shen et al.2008[18]
Alstom20123 MWth pilot-scale CLC units[19]
Technical University of Darmstadt 20141 MWth pilot-scale CLC units[20]
Tsinghua University2024Auto-thermal continuous operation of a 5 MWth CLC system[21]
Table 2. The investigations into solid fuel CLC.
Table 2. The investigations into solid fuel CLC.
Author/OrganizationFuelCLC System ScaleRef.
Berguerand and LyngfeltCoal10 kWth CLC unit[16]
Shen et al.Biomass10 kWth reactor[18]
Linderholm et al.Bituminous coal and coke10 kWth CLC unit[30]
Leion et al.Petroleum coke, etc. [31]
Bayham et al.Sub-bituminous coal25 kWth CLC unit[32,33]
University of Stuttgart
University of Hamburg		Coal10 kWth CLC unit
25 kWth CLC unit		[34]
Utah State UniversityCoal200 kWth CLC unit[35]
Technical University of DarmstadtCoal1 MWth CLC unit[20]
AlstomCoal 3MWth CLC unit[19]
Table 3. A summary of reaction kinetics of Fe-based oxygen carrier using TGA as an experimental device.
Table 3. A summary of reaction kinetics of Fe-based oxygen carrier using TGA as an experimental device.
AuthorOxygen CarrierReaction GasRef.
WangLow-grade iron oreCO, CH4[96]
ZhuPure Fe2O3, Fe2O3/Al2O3CO[97]
Zhao et al.Pure Fe2O3, hematite, steel slagO2/CO2[98]
Mei et al.Fe2O3/Al2O3CO[81]
Abad et al.IlmeniteH2, CO, CH4, O2[74]
LiuFe2O3/Al2O3CO[99]
Kespko et al.Fe2O3-CuO/Al2O3, Fe2O3/TiO2Air, H2[82]
Bao et al.Modified ilmeniteCO[61]
Liu et al.IlmeniteCO[100]
Piotrowski et al.HematiteCO, H2[85,86]
Su et al.HematiteCO[70,84]
Ksepko et al.Sinai oreCH4, O2[101]
Steiner et al.Synthetic ilmeniteH2[102]
Khakpoor et al.IlmeniteCH4[103]
DilmacIron oreCO[104]
Luo et al.Pure Fe2O3, iron ore, Fe2O3/MgAl2O4CH4[105]
Mendiara et al.Tierga iron oreH2, CO, CH4, O2[106]
Nasr et al.Iron oreCH4[107]
Cabello et al.Fe2O3/Al2O3CH4, H2, CO[108]
Li et al.Cu/Fe-based oxygen carrierH2[109]
Monazam et al.HematiteCO[65]
Abad et al.IlmeniteCH4, H2, CO, O2[74]
Moed et al.Fe2O3-CuO/Al2O3H2, CO[110]
Li et al.Mn-Fe2O3CO[111]
Wang et al.Fe2O3CO/CO2[112]
Choisez et al.Iron powderH2[113]
Chai et al.Iron powderH2[114]
Halim et al.Fe2O3 powderH2[115]
Table 4. A summary of the reaction kinetics of an iron-based oxygen carrier using a fluidized bed reactor as an experimental device.
Table 4. A summary of the reaction kinetics of an iron-based oxygen carrier using a fluidized bed reactor as an experimental device.
AuthorReactorOxygen CarrierReaction GasRef.
WuFluidized bedIron oreCO[119]
Schwebel et al.Fluidized bedIlmeniteCO, CH4, H2[120]
Su et al.Fluidized bedHematiteCO[70,84]
Perreault et al.Micro-fixed bedIlmeniteCO[121]
Yu et al.Micro-fluidized bedHematiteCO/CO2[122]
Zhang et al.Spouted bedFe2O3CO/CO2[123]
Alsabak et al.Fluidized bedLaterite oreH2[124]
Spreitzer et.alFluidized bedIron oreH2[125]
Purnomo et al.Fluidized bedIlmenite, iron sand, LD slagCO, H2, CH4[126]
Zhang et al.Pressurized fluidized bedFe2O3, Fe2O3/Al2O3CO[67]
Chiron et al.Micro-fluidized bedFe-, Fe/Cu-based oxygen carriersH2[127]
Cheng et al.Fluidized bedFe2O3/Al2O3H2O, air[128]
Feilmayr et al.Fluidized bedHematiteH2, CO, H2O, CH4, CO2[129]
Winayu et al.Fluidized bedFe2O3/Al2O3/SiO2H2, CO, CH4[130]
Habermann et al.Fluidized bedIron oreH2, H2O, CO, CO2[78]
Chen et al.Micro-fluidized bedIron ore finesCO[66]
Winayu et al.Fluidized bedIlmeniteCO, H2, CH4[131]
Chen et al.Micro-fluidized bedFe2O3CO/CO2[132]
Zeng et al.Homemade reactorFe2O3H2[133]
Liu et al.Honeycomb fixed bedFe2O3/Al2O3H2/CO[134]
Table 5. Summary of studies on the reaction kinetics of natural Fe-based oxygen carriers.
Table 5. Summary of studies on the reaction kinetics of natural Fe-based oxygen carriers.
AuthorOxygen CarrierReaction GasReactorKinetic ParametersRef.
Activation Energy (kJ/mol)Preexponential Factor
WangLow-grade iron oreCO, CH4TGACO: 56
CH4: 62		CO: 1.5 × 10−3
CH4: 2.7 × 10−4		[96]
Schwebel et al.IlmeniteCO
CH4
H2		Batch fluidized bedCO: 71.59–89.35
CH4: 146.90–186.75
H2: 16.02–17.52		CO: 0.23–1.4
CH4: 476.84–27,563.78
H2: 0		[120]
Piotrowski et al.HematiteCOTGA58.13 [86]
Perreault et al.IlmeniteCOMicro-fixed bed51 [121]
Yu et al.HematiteCO/CO2Micro-fluidized bed49.646.55 s−1[122]
Ksepko et al.Sinai oreCH4
O2		TGACH4: 35.3
O2: 16.7		CH4: 2.4 × 10−2 s−1
O2: 1.02 × 10−4 s−1		[101]
IlmeniteCH4
O2		TGACH4: 62.4
O2: 125.7		CH4: 2.21 × 10−3 s−1
O2: 129 s−1		[70]
Khakpoor et al.IlmeniteCH4
O2		TGA106.7 ± 10.69.43 × 10−1[103]
DilmacIron oreCOTGA40–65 [104]
Nasr et al.Iron oreCH4TGA2152.87 × 108 min−1[107]
Liu et al.IlmeniteCOTGA169.61328.4 L1.2 mol−1.2 s−1[100]
Luo et al.Iron oreCH4TGA183.63 [105]
Zhao et al.HematiteO2/CO2TGA78.431.04 × 104[98]
WuIron oreCOFluidized bed25.84–45.665.62 × 10−4–4.96 × 10−3[119]
Alsabak et al.Laterite oreH2Fluidized bed10.18–34.76 [124]
Spreitzer et al.Iron oreH2Fluidized bed11–55 [125]
Purnomo et al.IlmeniteCO
H2
CH4		Fluidized bedCO: 91.6
H2: 251
CH4: 211		CO: 0.003
H2: 1 × 105
CH4: 137		[126]
Feilmayr et al.HematiteH2
CO
H2O
CH4
CO2		Fluidized bed [129]
Habermann et al.Iron oreH2
CO
CO2
H2O		Fluidized bed [78]
Chen et al.Fire iron ore COMicro-fluidized bed29.1–60.8720.4053–18.681[66]
Winayu et al.IlmeniteCO
H2		Fluidized bedCO: 25.54
H2: 63.11		CO: 3.72 × 105
H2: 779		[131]
MonazamHematiteCOTGA19.0 ± 0.14 [65]
Abad et al.Activated ilmeniteCO
H2
CH4
O2		TGACO: 80.7 ± 2.4
H2: 65.0 ± 2.7
CH4: 135.2 ± 6.6
O2: 25.5 ± 1.2		CO: 1.0 × 10−1 mol1−n m3n−2 s−1
H2: 6.2 × 10−2 mol1−n m3n−2 s−1
CH4: 9.8 mol1−n m3n−2 s−1
O2: 1.9 × 10−3 mol1−n m3n−2 s−1		[74]
Pre-oxidized ilmeniteCO
H2
CH4
O2		 CO: 113.3 ± 3.0
H2: 109.32 ± 2.3
CH4: 165.2 ± 12.4
O2:
Echr: 11.8 ± 0.1
Edif: 77.4 ± 0.3		CO: 2.1 × 10−1 mol1−n m3n−2 s−1
H2: 5.1 × 10−1 mol1−n m3n−2 s−1
CH4: 8.8 mol1−n m3n−2 s−1
O2:
ks0: 8.0 × 10−5 mol1−n m3n−2 s−1
De0: 1.37 × 10−5 mol1−n m3n−2 s−1
LiuWüstiteH2
CO		Fluidized bedH2: 62–79
CO: 66–83		H2: 0.63–1.8 s−1
CO: 0.099–2.7 s−1		[151]
Khani et al.HematiteH2TGA40.87 [152]
Table 6. Summary of studies on the reaction kinetics of synthetic Fe-based oxygen carriers.
Table 6. Summary of studies on the reaction kinetics of synthetic Fe-based oxygen carriers.
AuthorOxygen CarrierReaction GasReactorKinetic ParametersRef.
Activation Energy (kJ/mol)Preexponential Factor
ZhuFe2O3/Al2O3COTGA74.420.525 × 105[97]
Mei et.al Fe2O3/Al2O3COTGA131–2703.1 × 103–1.6 × 1012[81]
LiuFe2O3/Al2O3COTGA [99]
Kespko et al.Fe2O3-CuO/Al2O3
Fe2O3/TiO2		Air, H2TGA41.318–42.594
33.08–35.379		0.027–0.255
0.056–0.069		[82]
Bao et al.Modified ilmeniteCOTGA [61]
Steiner et al.Synthetic ilmeniteH2TGA15–80 [102]
Luo et al.Fe2O3/MgAl2O4CH4TGA79.96 [105]
Cabello et al.Fe2O3/Al2O3CH4
H2
CO
O2		TGACH4: 66
H2: 8
CO: 14
O2: 23		CH4: 4.34 × 101
H2: 1.45 × 10−1
CO: 1.59 × 10−1
O2: 3.64 × 10−1		[108]
Li et al.Cu/Fe-based oxygen carrierH2TGA59.076.69 × 102[109]
Moed et al.Fe2O3-CuO/Al2O3H2
CO		TGAH2: 32.2–54.1
CO: 6.6–17.1		 [110]
Li et al.Mn-Fe2O3COTGA315.4–907.89.65 × 1018–4.49 × 1048[111]
Zhang et al.Fe2O3/Al2O3COPressurized fluidized bed101 ± 141.8 × 10−3[67]
Chiron et al.Cu-Fe oxygen carrierH2Micro-fluidized bed46
51		 [127]
Cheng et al.Fe2O3/Al2O3H2O, AirFluidized bed reactor 0.0026–0.0118[128]
Winayu et al.Fe2O3/Al2O3/SiO2H2
CO
CH4		Fluidized bedH2: 41.4
CO: 79.2
CH4: 13.6		H2: 27.7
CO: 712
CH4: 0.947		[130]
Alberto et al.Fe2O3/Al2O3COTGA202.5 × 10−4 mol1−n m3n−2 s−1[69]
Jin et al.Ni-Fe-Zr oxygen carrierH2
CO2		TGAH2:
Fe2O3 → FeO:14.90–20.00
FeO → Fe:13.87–25.40
CO2: 46.22–55.28		H2:
Fe2O3 → FeO: 3.05–6.06
FeO → Fe: 0.45–1.55
CO2: 55.19–186.85		[160]
Zhang et al.Fe2O3/Al2O3COPressurized fluidized bedCycle 2: 110 ± 12
Cycle 3: 115 ± 11
Cycle 4: 97 ± 13
Cycle 5: 101 ± 14		Cycle 2: 104.6 (−11.7 + 113.2) m s−1
Cycle 3: 211.4 (−21.6 + 24.1) m s−1
Cycle 4: 17.8 (−2.2 + 2.5) m s−1
Cycle 5: 33.2 (−4.5 + 5.2) m s−1		[67]
Li et al.xwt%Ni-Fe2O3/Al2O3
(x = 0, 5, 10, 20, 50)		CH4TGAx = 0: 75.40
x = 5: 71.25
x = 10: 65.70
x = 20: 53.93
x = 50: 62.03		x = 0: 0.59 m3n mol−n s−1
x = 5: 0.75 m3n mol−n s−1
x = 10: 0.26 m3n mol−n s−1
x = 20: 0.11 m3n mol−n s−1
x = 50: 0.40 m3n mol−n s−1		[161]
Liu et al.Fe2O3/Al2O3H2/COHoneycomb fixed bed reactorFirst stage: 3.5
Second stage:33.2		First stage: 3.06 × 10−5
Second stage: 2.99 × 10−4		[134]
Table 7. Research on the reaction kinetics of Fe-based oxygen carriers by varying temperatures and gas concentrations with CO as the reducing gas.
Table 7. Research on the reaction kinetics of Fe-based oxygen carriers by varying temperatures and gas concentrations with CO as the reducing gas.
AuthorOxygen CarrierGas ConcentrationTemperature (℃)Kinetic ParametersRef.
Activation Energy (kJ/mol)Preexponential Factor
WangLow-grade iron ore10%, 20%850, 900, 950561.5 × 10−3 mol1−n m3n−2 s−1[96]
ZhuFe2O320%750, 850, 95052.460.7 × 106 min−1[97]
Abad et al.Ilmenite5–50%800, 850, 900, 950113.3 ± 3.02.1 × 10−1 mol1−n m3n−2 s−1[74]
Liu et al.Ilmenite10%, 20%, 30%850, 950, 1050169.61328.4 L1.2 mol−1.2 s−1[100]
Perreault et al.Ilmenite15%, 20%, 25%800, 850, 90051 [121]
WuIron ore5%, 7.5%, 10%, 12.5%750–800
800–850
850–900		45.66
34.58
25.84		0.00496 s−1
0.00143 s−1
0.000562 s−1		[119]
Su et al.Hematite15–50%
5–20%
5%, 7.5%, 15%		400–650
850, 900, 950, 1000
400–650		74.48
110.75
138.55		1.2 × 1012 s−1
88.55 m4.5 mol−1.5 s−1
6.8 × 1013 s−1		[70,84,162]
Mei et al.Fe2O3/Al2O350%1000131–2703.1 × 103–1.6 × 1012 s−1[81]
Bao et al.Modified ilmenite11%900 [61]
DilmacIron ore10%, 20%, 25%, 50%750, 800, 850, 90040–65 [104]
Wang et al.Fe2O30–38%, 42–65%, 68–88%800–90035–70 [112]
Mendiara et al.Tierga iron ore5–60%800–100076.1 ± 6
139 ± 5		1.45 × 10−1 mol1−n m3n−2 s−1
9.16·10−5		[106]
Cabello et al.Fe2O3/Al2O35–60%700–105014
204		1.59 × 10−1
2.29 × 109		[108]
Monazam et al.Hematite5%, 10%, 20%700–95019.0 ± 0.14 [65]
Moed et al.Fe2O3-CuO/Al2O320%850, 875, 900, 9256.6–13.8 [110]
Li et al.Mn-Fe2O3 750, 800, 850315.4–907.89.65 × 1018–4.49 × 1048[111]
Purnomo et al.Ilmenite
iron sand
LD slag		50%850, 875, 900, 925, 950, 97559.4
51.7
64.8		7.34 s−1
0.73 s−1
9.78 s−1		[126]
Winayu et al.Ilmenite Fe2O3/Al2O3/SiO225%900, 950, 100025.54
79.2		3.72 × 105
712 min−1		[130,131]
Bohn et al.Fe2O38.5–9.5%650–90075.0–94.0 [163]
Chen et al.Fe2O340%, 60%, 80%, 100%750–950Fe2O → Fe3O4: 30.60 ± 0.75 to 52.99 ± 0.78
Fe3O4 → FeO: 52.44 ± 0.10 to 80.83 ± 0.12
FeO → Fe: 45.74 ± 0.25–92.12 ± 0.27		Fe2O3 → Fe3O4: 1.84 ± 0.69 s−1–13.71 ± 5 34 s−1
Fe3O4 → FeO: 17.57 ± 0.87 s−1–426.47 ± 25.92 s−1
FeO → Fe: 3.28 ± 0.41 s−1–628.46 ± 84.40 s−1		[132]
Chen et al.Iron ore fines50%700–85029.1–60.8720.4053–18.681 s−1[66]
Table 8. Research on the interaction of iron-based oxygen carriers with ash.
Table 8. Research on the interaction of iron-based oxygen carriers with ash.
AuthorOxygen CarrierAshConclusionRef.
Zhang et al.Fe2O3/Al2O3Three types of coal ashWhen the oxygen carrier was in contact with coal ash having a high Ca content, its reactivity was significantly enhanced after several cycles. Coal ash with a high Si content had a detrimental effect on the oxygen carrier.[179]
Bao et al.Fe2O3/Al2O3Four types of coal ashAsh composed of CaSO4 enhanced the activity of oxygen carrier, and the effect of ash in decreasing carrier activity increased with the number of cycles.[167]
Zhou et al.iron oreBiomass ashThe K-rich ash generated K3FeO2, which improved the reducing activity of the iron ore.[172]
Guo et al.Fe2O3/Al2O3Coal ashThe presence of ash exerted an inhibitory influence on the reduction reaction process from Fe2O3 to Fe3O4.[180]
Ilyushechkin et al.iron ore, ilmeniteTwo types of coal ash (with Si, Fe, Mg)The ash rich in Fe augmented the redox kinetics of iron ore while having no impact on ilmenite.
The ash abundant in Si decreased the oxidation rate of iron ore.		[173]
Wang et al.Fe2O3/Al2O3Sludge ashWhen the number of cycles was fewer than 10, the activity of the oxygen carrier had the potential to increase. As the number of cycles increased, the ash decreased the reactivity of the oxygen carrier.[181]
Purnomo et al.Nature ores, waste materialsThree K saltsThe initial oxidation state of the surface of the oxygen carrier had only a limited influence on its interaction with K salts.[170]
Cheng et al.Pure Fe2O3Coal ash, biomass ashA small amount of ash promoted the reduction of Fe2O3. Moreover, Ca2+, K+, and Na+ in ash interacted with silica-aluminate to form low melting point compounds.[171]
Gu et al.Iron oreThree types of biomass ashAsh that was rich in K and had a low Si content served to enhance fuel conversion.[175]
Yang et al.IlmeniteBiomass ashThe reactivity of ilmenite first increased and then decreased as the amount of biomass ash added increased, reaching its peak at 10% biomass ash addition. The addition of 15% biomass ash led to severe particle sintering.[178]
Yilmaz et al.Pure Fe2O3Synthetic biomass-derived ash (with K, Na)The co-presence of K and Si in the ash increased agglomeration.[182]
Synthetic biomass-derived ash (with Mg, Ca)Under the same experimental conditions, it was observed that Mg led to more severe clumping phenomena than Ca. [183]
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Mei, J.; Quan, S.; Yang, H.; Zhang, M.; Zhou, T.; Yang, X.; Zhang, M.; Mun, T.-y.; Li, Z.; Kim, R.-G.; et al. Research Progress and Perspectives of the Reaction Kinetics of Fe-Based Oxygen Carriers in Chemical Looping Combustion. Energies 2025, 18, 2313. https://doi.org/10.3390/en18092313

AMA Style

Mei J, Quan S, Yang H, Zhang M, Zhou T, Yang X, Zhang M, Mun T-y, Li Z, Kim R-G, et al. Research Progress and Perspectives of the Reaction Kinetics of Fe-Based Oxygen Carriers in Chemical Looping Combustion. Energies. 2025; 18(9):2313. https://doi.org/10.3390/en18092313

Chicago/Turabian Style

Mei, Jiakun, Shangkun Quan, Hairui Yang, Man Zhang, Tuo Zhou, Xi Yang, Mingyu Zhang, Tae-young Mun, Zhouhang Li, Ryang-Gyoon Kim, and et al. 2025. "Research Progress and Perspectives of the Reaction Kinetics of Fe-Based Oxygen Carriers in Chemical Looping Combustion" Energies 18, no. 9: 2313. https://doi.org/10.3390/en18092313

APA Style

Mei, J., Quan, S., Yang, H., Zhang, M., Zhou, T., Yang, X., Zhang, M., Mun, T.-y., Li, Z., Kim, R.-G., Zhu, X., Wang, H., & Li, D. (2025). Research Progress and Perspectives of the Reaction Kinetics of Fe-Based Oxygen Carriers in Chemical Looping Combustion. Energies, 18(9), 2313. https://doi.org/10.3390/en18092313

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