High Coverage CO Adsorption and Dissociation on the Orthorhombic Mo2C(100) Surface

CO adsorption and dissociation on the Mo and C terminations of the orthorhombic Mo2C(100) surface at different coverage were systematically investigated on the basis of density functional theory. On the Mo termination, only molecular adsorption is likely for n(CO) = 9-16. Mixed molecular and dissociative adsorption becomes possible for n(CO) = 8, while only dissociative adsorption is favorable for n(CO) = 1-7. This indicates the coverage-dependent CO dissociation and equilibrium between dissociation and desorption. On the C termination, there is no dissociative adsorption, and only molecular adsorption is favorable at all coverages (n(CO) = 1-16). The computed CO stretching frequencies as well as the predicted desorption states from ab initio thermodynamic analysis agree well with the available experimental findings. The stable coverage as a function of temperature and partial pressure provides useful information not only for surface science studies at ultrahigh vacuum conditions but also for practical applications at high temperature and pressure in exploring reactions.