Theoretical insights into the size effect of α-Fe₂O₃ oxygen carrier on chemical looping reforming of methane

The regulation of the oxygen carrier size is crucial to the chemical looping reforming (CLR) of methane to syngas. However, there is still a lack of in-depth understanding of the relationship between oxygen carrier size and its catalytic performance. Herein, we perform density functional theory (DFT) calculations combined with microkinetic simulations to study the surface catalytic behavior and oxygen supply capacity of different sizes of (Fe₂O₃)_n clusters (n = 4, 13, 21, 40, ∞). Our results demonstrate that when the cluster diameter is ∼1.8 nm, that is, the (Fe₂O₃)₂₁ cluster, the CH₄ dissociation barrier is the lowest due to the more positive charge of the central Fe site. Meanwhile, the CH₄ dissociation barrier on this cluster is also close to the oxygen migration barrier, achieving a precise matching between oxygen migration rate and surface catalytic reaction rate, thereby rendering high production rate towards syngas.