Density Functional Theory Study of CO and Hydrogen Co-adsorption on the Fe(111) Surface

Spin-polarized density functional theory calculations have been carried out to characterize CO and H 2 co-adsorption on the Fe(111) surface. At 0.5 monolayer (ML) CO coverage, the most-stable adsorption configurations are close to those of individually adsorbed CO and H, and the interaction of adsorbed CO and H does not lead to any hydrogenated product. As the ratio of H 2 /CO increases, the most-table co-adsorption site of CO changes from the shallow-hollow site (sh) to the top site (t), while H maintains approximately at the top-shallow bridge site (tsb) or the quasi-fourfold site (qff). At 1 ML CO coverage, a similar trend is found where CO moves up to the first-layer Fe surface, while H prefers to diffuse into the subsurface when the H 2 /CO ratio increases. At very high H 2 /CO ratios, the most-stable configuration of CO has adsorption at the top site (t). In addition, formyl (CHO) is formed at H 2 /CO ratios of 1 / 2 and 1 / 1, deriving from hydrogenation of adsorbed CO in the bridge-like site (brl). The interaction nature of CO−H is also analyzed by the DOS analysis.