摘要：
Background, Aims and Scope. With the rapid development of industry and transportation, the problems of environmental pollution and energy wastage come along with it. Carbon monoxide (CO) mainly comes from the metallurgical industry, chemical industry and automobile exhaust emissions, etc., which are discharged in large quantities and are harmful to the environment and human health. It has a great danger to the environment and human health. Therefore, it is urgent to develop an effectively approach to eliminate CO. Currently, CO elimination methods are mainly divided into physical adsorption and chemical conversion methods. CO catalytic combustion is currently the most effective and widely used method to eliminate CO, and has been studied more in automobile exhaust gas purification and fuel cells (selective catalytic oxidation).

Methods. In order to reduce CO₂ emission, and accelerate the achievement carbon peak in China, it is crucial to develop efficient CO combustion technologies. Chemical-looping combustion (CLC) is an innovative combustion technology with the inherent characteristics of CO₂ capture. Thus, it can be achieved the efficient elimination of CO by means of chemical looping combustion. In more details, CO can be oxidized to CO₂ by lattice oxygen in the oxygen carrier (M_xO_y) through the fuel reactor, which can facilitate the separation and capture of CO₂. Subsequently, in the air reactor, the reduced oxygen carrier (M_xO_y-1) is regenerated by reacting with O₂ from the air. Therefore, oxygen carriers are the foundation of CLC and are considered to be one of the determining factors for successful operation of CLC.

Results and Discussion. The transformation of oxygen species on CeO₂/Fe₂O₃ oxygen carrier are the main factor that determine the reactivity of CO CLC. According to the XPS results of fresh and used CeO₂/Fe₂O₃ oxygen carrier, the lattice oxygen of oxygen carrier was confirmed as the active oxygen to migrate to the surface and react with CO. Firstly, the lattice oxygen transfers from inside of oxygen carrier to surface and then react with CO. For CeO₂/Fe₂O₃-O_v oxygen carrier with oxygen vacancies (OVs), the lattice oxygen rapidly migrates to the surface to fill oxygen vacancies due to the oxygen chemical potential. The higher performance of CeO₂/Fe₂O₃-O_v oxygen carrier is an indication of the role of Ce and Fe in improving the mobility of lattice oxygen and re-oxidation after reduction by CO. In addition, the lattice oxygen is easily mobilized to replenishing the surface oxygen vacancies due to the reduced Ce (Ce⁴⁺ ↔ Ce³⁺) in CLC reaction. The circular switch of Ce³⁺/Ce⁴⁺ is conducive to the catalytic oxidation of CO. The CO CLC reaction process pathway on CeO₂/Fe₂O₃ oxygen carrier is shown in Fig. 1, which follows the Mars-van Krevelen (MvK) mechanism. That is, the CO is introduced, and reacts with oxygen species of CeO₂/Fe₂O₃ OC. Then, the metal oxides in the OC are reduced. Finally, the reduced OC is oxidized to replenish oxygen. A complete adsorption, deoxidation, desorption oxidation reduction reaction of oxygen supplement and regeneration. The CO CLC is a complete redox reaction process of adsorption, deoxygenation, desorption, oxygen supplement and regeneration of oxygen carrier.

Conclusion. In this study, CeO₂, Fe₂O₃ and CeO₂/Fe₂O₃ composite oxygen carrier (OCs) with oxygen vacancies were successfully synthesized via sol-gel and thermal treatment method, and the reactivity of OCs were evaluated in a fixed bed and thermogravimetric analyzer for carbon monoxide chemical looping combustion (CO-CLC). The morphology and crystalline phase of OCs were tested by SEM, XRD etc. characterization methods. The activity test results showed that the performance of CeO₂/Fe₂O₃ composite oxygen superior than CeO₂ and Fe₂O₃. The presence of Ce and Fe in CeO₂/Fe₂O₃ composite oxygen carrier can synergistically improve the activity of the reaction and confirmed by TGA analysis and DFT theoretical calculations. The EPR and Raman results indicate that the oxygen vacancies were formed in OCs, which can rapidly facilitate the migration of lattice oxygen to the surface to fill oxygen vacancies. Combined with the results of reactivity and characterization test of OCs, the CO CLC reaction abide by the Mars-van Krevelen (MvK) mechanism, which undergone the complete redox reaction process of adsorption, deoxygenation, desorption, oxygen supplement and regeneration of oxygen carrier in chemical looping reaction.

synergistic effect, oxygen vacancy, CeO2/Fe2O3 oxygen carrier, chemical looping combustion (CLC), reactivity