摘要
Spin-polarized periodic density functional theory calculations have been performed to study the adsorption, diffusion, and oxidation of carbon on the Mo-terminated beta-Mo2C(001) surface as well as on a model Ni-doped beta-MO2C(001) surface with a surface Ni:Mo ratio of 1:2. The most stable adsorption sites for 0 and CO were found to be similar on the two surfaces, whereas those for C are different in that C prefers to adsorb at the step interface on the model Ni-doped surface. The adsorption energies for all three species were found to be less negative on the Ni-doped surface. The energy barriers and reaction energies for the diffusion and oxidation of carbon on the above beta-Mo2C(001) surfaces were calculated. On the pure beta-Mo2C(001) surface, C diffusion from its most stable adsorption site has a much smaller energy barrier of similar to 1.0 eV than C oxidation of similar to 2.6 eV, with both processes being quite endothermic. Upon Ni doping, the lowest energy barrier for C diffusion from its most stable adsorption site remains similar to 1.0 eV, whereas the lowest energy barrier for C oxidation is similar to 1.6 eV, much lower than that of similar to 2.6 eV on the pure beta-Mo2C(001) surface. The energy barrier difference between C diffusion and oxidation of similar to 0.6 eV on the Ni-doped surface is much smaller than that of eV on the pure beta-Mo2C(001) surface, and this can be beneficial for preventing carbon deposition and increasing CO selectivity.
