Role of Oxygen Species toward the C–C Bond Cleavage in Steam Reforming of C<sub>2+</sub> Alkanes: DFT Studies of Ethane on Ir(100)
Ruitao Wu, Kaitlyn R. Wiegand, Longmei Ge, Lichang Wang
Abstract
Understanding C–C bond cleavages has become important in developing a cost-effective technology for the steam reforming of natural gas, the primary form of hydrogen production. Previous studies of C–C bond cleavages in C2+ steam reforming have focused solely on the C2+Hx species. Here, we report the density functional theory (DFT) studies of 10 C–C bond cleavages of ethane decomposition (C2Hx, x = 0–6) on Ir(100). We also investigated the effects of O and OH species that are present in steam ethane reforming (SER) on these cleavages. The DFT results demonstrate that coupling O with the C2Hx species decreases activation energy, from >1 to 0.3 eV. Therefore, the C–C bond rupture in SER, along the minimum energy pathway, is likely to take place in C2HxO. The findings suggest that a good steam reforming catalyst also needs to facilitate the C2Hx and O coupling, which would not only improve C–C bond cleavage but also prevent C deposition, a major cause of catalyst deactivation. Furthermore, the activation energy and reaction energy surfaces were constructed for 34 C–C bond cleavage reactions, which allow for direct performance comparisons among catalysts and the selection of a catalyst of interest beyond the minimum energy path.