Quantum Chemical Study Of CO Adsorption On The Fe(111) And Fe(100) Surfaces

Recently, as the fast development of the heterogeneous catalyst, the surface adsorption which is the key role in the heterogeneous catalyst show great foreground. CO adsorption on low index surfaces of transition metals has been the subject of numerous experimental and theoretical studies in recent years because of its crucial role in many catalytic processes, e.g., in car exhaust treatment or Fischer-Tropsch synthesis (FTS). The production of liquid fuel from coal via syngas through Fischer-Tropsch synthesis is of great significance based on the energy framework of abundance in coal and scarce in crude oil reserve of our country. Iron-based catalyst, due to its high F-T activity, low cost as well as high water-gas-shift (WGS) activity, is more preferable for F-T process of coal-derived syngas, which has a low H2/CO ratio. Though there are many theoretical and experimental studies on the F-T mechanism, a widely accepted agreement is not achieved. The theoretical study of CO adsorption on the iron surface, as the first step of the F-T mechanism, is of great importance.In this paper, a systematic study of CO adsorption on the Fe(111) and Fe(100) surfaces at different coverage is carried out with the density functional theory of the generalized gradient approximation (DFT-GGA). On the Fe(111) and Fe(100) surfaces, when the coverage is below 1/2 ML, the coverage effect on CO adsorption can be neglectable. The coverage effects mainly come from the adsorbed CO molecules lateral interactions through space. The nature of the interaction between CO and transition metals can be briefly summarized: the occupied 5a orbital of CO can readily overlap with the unoccupied d_z² and 4s orbitals of the transition metal atoms with electron donation; and the empty 2Ï€* orbitals of CO are also capable of overlapping with occupied d_xz and d_yz orbitals of the metal atoms with electron back donation. Some new adsorption configures are found included the bridge-like site on the Fe(111) surface and the 4-fold (1) site on the Fe(100) surface. The most stable adsorption site is the shallow-hollow on the Fe(111), but the the 4-fold (2) on the Fe( 100) surface.