Theoretical DFT Study on the Mechanisms of CO/CO₂ Conversion in Chemical Looping Catalyzed by Calcium Ferrite

The CO/CO₂ conversion mechanism on the calcium ferrite (CFO) surface in chemical looping was explored by a computational study using the density functional theory approach. The CFO catalytic reaction pathway of 2CO + O₂ → 2CO₂ conversion has been elucidated. Our results show that the Fe center in CFO plays the key role as a catalyst in the CO/CO₂ conversion. Two energetically stable spin states of CFO, quintet and septet, serve as the effective catalysts. The presence of the triplet O₂ molecule caused the conversion of these two spin-state structures into each other along the catalytic reaction pathway. A double release of CO₂ was predicted following this reaction mechanism. The rate-determining step is the formation of the 2CO₂-CFO complex (P4) in the quintet state (19.0 kcal/mol). The predicted energy barriers for all the steps suggest that the proposed pathway is plausible.