Surface morphology of Fe3C catalyst under different CO coverage from DFT and thermodynamics

High-coverage CO adsorption on seven surfaces of Fe3C catalyst has been systematically studied by density functional theory and thermodynamics. Results show that CO molecules prefer to bind on surface iron atoms of Fe3C catalyst, and the saturation coverage ranges from 0.5 to 0.833 monolayers (ML) on different surfaces. The equilibrium phase diagrams of CO adsorption on different Fe3C surfaces at different CO coverage are plotted, and the stable CO concentration on each surface of Fe3C at any CO partial pressure and temperature could be easily identified. CO adsorption/activation on Fe3C catalyst via an acceptance-donation mechanism can be explained by the projected density of states (PDOS) and charge density difference plots. Interestingly, stabilities of the Fe3C surfaces can be modified by adsorbed CO, and eventually the morphologies of Fe3C nanoparticle can also be changed. Our results provide essential information for selective synthesis of Fe3C catalyst with specific structures experimentally.