Adsorption and C–C bond cleavage of benzene on hematite α-Fe2O3 surfaces: a DFT mechanistic study

Reforming tar molecules into smaller gaseous molecules has been a critical challenge for biomass energy utilization. Hematite (α-Fe₂O₃) has been demonstrated as an effective catalyst for the catalytic reforming of tar, nevertheless, the detailed mechanism of α-Fe₂O₃ catalyzed tar reforming remains unclear. In this work, we apply the density functional theory method to investigate this problem. Specifically, we study both (0001) and (01[Formula: see text]2) surface structures of α-Fe₂O₃ and then use the structures to investigate the adsorption and C-C bond cleavage of benzene on these surfaces. Our results show that the dominant interactions between benzene and a single Fe-terminated (0001) surface are van der Waals forces, yet benzene could be chemisorbed on the Fe and O co-exposed (01[Formula: see text]2) surface via strong C-O interactions. As a result, the (0001) surface is not active towards benzene cleavage, whereas the (01[Formula: see text]2) surface can promote the aromatic C-C bond breaking. Furthermore, our calculations indicate that chain-like alkene species and carbonyl species are the two types of potential products that form after the C-C bond cleavage of benzene on the α-Fe₂O₃ (01[Formula: see text]2) surface, with the activation energy of 1.78 eV and 2.62 eV, respectively. In summary, we reveal the importance of co-adsorption on both Fe and O centers and oxidative addition on C-C bond cleavage of aromatic compounds on the α-Fe₂O₃ surface, which provides novel insights into the mechanisms of tar cracking on oxide catalysts.