DFT study of oxygen adsorption on Mo 2 C(001) and (201) surfaces at different conditions

Density functional theory (DFT) calculations were performed to investigate oxygen adsorption on Mo2C(001) and (201)surfaces at different coverage. The energies and structures of oxygen from lowest to saturated coverages were clearly identified on each surface. Thermodynamics method was introduced to reveal the roles of temperature, pressure as well as oxygen sources (O2, H2O and CO2) on the surface oxygen coverage, which is related to the surface oxidation. On the basis of phase diagram, we can easily identify the stable oxygen coverage at different defined conditions. In addition, it reveals that O2 is the strongest oxidant, which results in the full coverage of oxygen on both surfaces in a wide range of temperature and pressure. Then, H2O and CO2 are weaker oxidants, which could only cause partial oxidation of Mo2C surfaces. These results indicate the facile oxidation of Mo2C catalyst. The possible ways to avoid surface oxidation are keeping higher temperature and H2 pressure in the gas phase.