In the process of biomass chemical looping gasification using calcium ferrite as an oxygen carrier, H₂O or CO₂ can be injected into the oxidation reactor to produce H₂ or CO with high purity while oxidizing the reduced oxygen carrier, which is a new technology that has attracted wide attention in recent years. However, the splitting reaction mechanism of H₂O or CO₂ is still unclear. Therefore, based on density functional theory (DFT) calculations, the adsorption behavior of H₂O and CO₂, the electronic structure, and the splitting reaction path of H₂O and CO₂ on the surface of the reduced CaFe₂O₄ were systematically studied to deeply understand the reaction mechanism. The results show that H₂O and CO₂ form stable complexes on the CaO(111)/Fe(110) surface by chemisorption. H₂O is splitted to H₂ and adsorbed O* through a two-step reaction. In this process, the step of H₂O cracking to HO* and H* is the rate-determining step. CO₂ is splitted into CO* and O* through a one-step reaction, in which the desorption of CO from the surface is a rate-determining step. The total charges of H₂O and CO₂ after adsorption are –0.743 |e| and –0.954 |e|, respectively, and the total charges of Fe atoms on the surface are 0.931 |e| and 0.433 |e|, respectively. H₂O and CO₂ are electron acceptors, and Fe atoms on the surface are electron donors. The splitting of H₂O or CO₂ and the oxidation of reduced oxygen carriers are generally exothermic reactions, which can realize the oxidation of the reduced oxygen carrier and provide heat for the system.

Reduced oxygen carrier,Chemical looping gasification,CO2 splitting,H2O splitting,DFT calculation