Effect Of Inert Metal Ion Substitution On Structure Of Iron-based Perovskite Oxygen Carrier And The Performance Of Chemical Looping Dry Reforming Of Methane

Different from traditional dry reforming of methane（DR）,chemical looping reforming of methane（CLDR）decoupled the traditional gas-gas reaction into two gas-solid reactions by recycling oxygen carriers（usually metal oxides）,which can convert greenhouse gases CH₄ and CO₂ into syngas with H₂/CO ratio of 2 and CO,respectively.It can also inhibit carbon accumulation of oxygen carrier and the reverse water-gas shift reaction.The rational design of oxygen carrier is the key of CLDR research.Iron-based perovskite oxygen carrier has good oxygen storage capacity and structural stability,and can improve the performance of oxygen carrier by doping A/B ions,so it is considered as an ideal oxygen carrier.In order to improve the redox performance,the doped B-site metals are mostly active metals with redox ability,and the doped A-site metals are mostly heterovalent metals,in order to improve the performance by regulating the chemical state of the B-site ions through charge compensation.The A/B site ion doping will inevitably bring about multiple changes such as oxygen vacancy concentration,ion valence state,number of active centers,crystal structure,etc.The lack of clear understanding of the intrinsic correlation between the redox and corresponding microstructures in turn limits the design and development of efficient oxygen carriers.In this paper,we focus on the geometric effects of non-reductive metal substitution and the modulation of the performance of iron-based perovskite oxygen carriers,which provides helpful guidance for rational design of advanced oxygen carriers.In this paper,the iron-based perovskite LaFeO₃ oxygen carrier is used as the intrinsic material,and metal ions（Al,Ga,Sc）,LaFe_0.8M_0.2O₃（M=Al,Ga,Fe and Sc）oxygen carriers were prepared by sol-gel method,and the geometric effects and microstructures of oxygen carriers（Fe O₆ octahedral distortion,inclination angle,Fe-O bond strength,oxygen vacancy formation energy,etc.）,combined with XRD,XPS,SEM,HRTEM,M（?）ssbauer,Raman and other experimental characterizations and density functional theory calculations to investigate the effect of non-redox metals doped with different ionic radii onFeO₆ in LaFeO₃ oxygen carriers The effect of facet distortion and CLDR reaction performance.It was found that the inclination angle ofFeO₆ octahedron decreased from 9.5°(LaFe_0.8Sc_0.2O₃)with the decrease of B-site doping ionic radius(Al³⁺=0.0535nm,Ga³⁺=0.062nm,Fe³⁺=0.0645nm,Sc³⁺=0.0745nm)To 6.6°(LaFe_0.8Al_0.2O₃),the oxygen vacancy formation energy and charge transfer energy are reduced,which significantly improves the redox performance of the oxygen carrier and greatly increases the syngas yield,while exhibiting more excellent CO₂ conversion rate and cycle stability.A series of perovskite LaFe_1-xAl_xO₃（x=0、0.25、0.5、0.75）oxygen carriers were prepared to investigate the effect of Al on the redox performance of iron cations and lattice oxygen activity in LaFe_1-xAl_xO₃ oxygen carriers.The results show that Al doping reduces the strength of Fe-O bond in Fe-O-Fe bond,promoting the release of lattice oxygen and reducing the temperature towards methane activation.