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• Fe-based oxygen carriers is presented on attrition-resistance performance and reactivity. • The emphasis is on the design of Fe-based oxygen carrier. • The relationship between deactivation phenomenon and structural evolution is analyzed. Chemical looping combustion, as one of the key carbon capture technologies, employs oxygen carrier (OC) to transfer oxygen atoms between fuel and air to achieve the purpose of in-situ CO 2 enrichment during fuel combustion. The OC is the core element in the chemical looping combustion (CLC) process, and the design of OC is one of the main research directions in the field of chemical looping process. Fe-based OCs have attracted much attention due to the advantages of low cost and environmental friendliness. Most of the existing Fe-based OCs face the problems of short lifetime and poor reactivity, failing to meet the demands of industrial operation. In this study, to improve the attrition-resistance performance of Fe-based OCs, critical factors including attrition rate and crushing strength are discussed. To improve the reactivity of Fe-based OCs, oxygen transport capacity and reaction activation energy are discussed. Meanwhile, the deactivation of Fe-based OCs is revealed through the microstructural changes caused by the phase segregation in the reduction and oxidation processes. Methods to improve the attrition-resistance and reactivity performance are proposed as well. In addition, the applications of simulation methods including computational fluid dynamics (CFD), density functional theory (DFT), machine learning (ML) and artificial intelligence (AI) in the design of CLC system as well as OCs are presented. On this basis, a deep understanding of the property's regulation of Fe-based OCs is obtained. This provides theoretical guidance for the industrial design and application of Fe-based OCs. [ABSTRACT FROM AUTHOR]

Coal-based mercury pollution from power plants has received increasing attention. In a previous study, high iron and calcium coal ash (HICCA) was found as a promising oxygen carrier (OC) for chemical looping combustion (CLC). The purpose of this study was to investigate the catalytic effect of HICCA on Hg0 removal as well as the impacts of several gas impurities, such as HCl, SO2, and NO. Experiments on Hg0 removal efficiencies for different atmospheres were performed in the fixed-bed reactor at 850 °C. Based upon the characterization of BET, SEM, XRD, XPS, and EDS of reaction products, the reaction mechanisms of different gases with the HICCA samples were established. The mechanisms were further explained using the thermodynamic equilibrium calculations. The experimental results showed that the Hg0 removal efficiency using HICCA was 11.60%, while the corresponding value in the presence of 50 ppm HCl was 90.46%. Hg0 removal by HICCA involving HCl is mainly attributed to homogeneous reaction between Hg0 and HCl as well as the formation of reactive species (Cl, Cl2, Cl2O, O, S, and SCl2) through the reactions of HCl with Fe2O3 and CaSO4 in HICCA. The formation of C–Cl bond is not the main pathway for the promotional effect of HCl on Hg0 removal. SO2 played a negative role in Hg0 removal by HICCA. The inhibition of SO2 may be attributed to its effect on the reduction of Fe2O3 and its bonding with C–O, COOH, and C(O)–O–C. NO enhanced Hg0 removal by HICCA primarily through the homogeneous reactions of Hg0 with N2O and O. In addition, NO also interacted with HICCA and promoted the heterogeneous oxidation of Hg0 by producing more C–O, C=O, and COOH/C(O)−O−C on HICCA surface. This study proved the effectiveness of HICCA on Hg0 removal in iG-CLC and revealed the mechanisms of the interaction between HCl/SO2/NO and MxOy/CaSO4 as well as carbon-oxygen groups. [ABSTRACT FROM AUTHOR]

• Mercury emission from both air and fuel reactors for CLC of coal is summarized. • Mercury in coal, temperature, and water vapor promote the release of mercury in fuel reactor. • Oxygen carriers promote the conversion of Hg0 to Hg2+ and HgP. • The impacts of different gas components on mercury removal are discussed. Chemical looping combustion (CLC) of coal for carbon capture utilization and storage is an effective technology to reduce carbon emission due to smaller energy penalty and inherent low emission of pollutants. However, a large uncertainty exists in mercury emission from both air and fuel reactor for coal-fired chemical looping combustion. This paper attempts to reveal the underlining mechanisms for the transformation of mercury-related species both in combustion and post-combustion process. Mercury in coal, temperature, and water vapor promote the release of mercury in fuel reactor. Oxygen carriers (OCs) promote the conversion of Hg0 to Hg2+ and HgP. Both oxygen release and adsorption ability of reduced OCs contributes to the mercury removal efficiency. HCl is the dominant species for Hg0 oxidation. NO, SO 2 , CO, and H 2 have negative impacts on Hg0 oxidation; while O 2 promotes Hg0 oxidation; the influence of H 2 O on Hg0 oxidation depends on concentration. H 2 S may promotes Hg0 removal by formation metal sulfides. In the post combustion mercury removal by adsorption and catalytic oxidation process, O 2 , HCl, NO, and CO 2 promote the oxidation of Hg0, whereas SO 2 , CO, and H 2 inhibit the oxidation of Hg0. The impacts of H 2 S and H 2 O on Hg0 oxidation depends on their concentrations. Simultaneous removal of SO 2 , NO, and Hg0 by green oxidation-based absorption using free radicals or in the compression process have a good prospect due to potential low cost. This work will encourage wider discussion on flue gas treatment possibilities to reduce the cost of future CLC power plant. [ABSTRACT FROM AUTHOR]

• Iron-based oxygen carriers with different structures are prepared using compression molding. • Fe 2 O 3 /CuO@MgO oxygen carriers show superior cyclic stability due to precluding the diffusion of Fe3+ ions. • The ion diffusion mechanism during cyclic redox process for iron-based oxygen carriers is proposed. Iron-based oxygen carriers as one of the most commonly used oxygen carriers in chemical looping combustion, shows poor cycling stability. In this work, spinel-structured, Fe 2 O 3 @MgO core–shell structure, and Fe 2 O 3 /CuO@MgO core–shell structure oxygen carriers were prepared using compression molding. The effects of deep reduction and oxidative regeneration processes on the cyclic stability of oxygen carriers with different structures were investigated using thermal gravimetric analyzer. The mechanisms for the changes in the cyclic stability were explored through a series of characterization analyses. The results showed that the reduction process of spinel oxygen carriers generated Fe-Mg solid solution, which was unfavorable to deep reduction, and phase separation occurred during 5 cycles. Due to the migration of Fe3+ ions to the surface, surface was seriously sintered, deteriorating the cyclic stability of spinel oxygen carriers. For Fe 2 O 3 @MgO oxygen carrier, the deep reduction can be realized, but the interdiffusion phenomenon of Fe2+ and Mg2+ occurred after 5 reductions, and the generation of (MgO) x (FeO) 1−x solid solution impeded the deep reduction. The addition of CuO in the core of oxygen carriers to form Fe 2 O 3 /CuO@MgO could inhibit the interdiffusion of Fe2+ and Mg2+, and maintained the oxygen carrying capacity up to more than 95 % in 10 cycles. Meanwhile, CuO synergized with Fe 2 O 3 to enhance the reduction and oxidation reactivity of the oxygen carrier. On this basis, the ion diffusion mechanism during the deep reduction and oxidation of iron-based oxygen carriers with different structures was proposed. This study provides guidance for the modification of iron-based oxygen carriers with superior cycling stability. [ABSTRACT FROM AUTHOR]