The C-H breaking of methane on the clean and the oxygen precovered palladium single crystal surfaces with the simplest orientations, namely, the dense (111), (100), the more open (110), and the stepped (111) surfaces, the corresponding O/Pd surfaces with different coverage of oxygen, as well as the palladium oxide PdO(100) and PdO(110) surfaces, has been studied with the density functional theory-generalized gradient approximation method using the repeated slab models. The adsorption energies under the most stable configuration of the possible species and the activation energy barriers of the reaction are obtained in the present work. Through systematic calculations for the C-H breaking of methane CH(4)-->CH(3)+H on these surfaces, it is found that such a reaction is structure sensitive on clean palladium and oxygen precovered palladium surfaces with lower oxygen coverage, but it is insensitive on oxygen precovered palladium surfaces with higher oxygen coverage and on palladium oxides. These results are in general agreement with the experimental observations.

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The C-N bond breaking of methylamine on clean, carbon ͑nitrogen, oxygen͒-modified Mo͑100͒ ͓denoted as Mo͑100͒ and Mo͑100͒-C͑N,O͒, respectively͔, Mo 2 C͑100͒, MoN͑100͒, and Pt͑100͒ surfaces has been investigated by the first-principles density functional theory ͑DFT͒ calculations. The results show that the reaction barriers of the C-N bond breaking in CH 3 NH 2 on Mo͑100͒-C͑N,O͒ are higher than that on clean Mo͑100͒. The calculated energy barrier can be correlated linearly with the density of Mo 4d states at the Fermi level after the adsorption of CH 3 NH 2 for those surfaces. Moreover, the DFT results show that the subsurface atom, e.g., carbon, can reduce the reaction barrier. In addition, We noticed that the activation energies for the C-N bond breaking on Mo 2 C͑100͒ and MoN͑100͒ are similar to that on Pt͑100͒, suggesting that the catalytic properties of the transition metal carbides and nitrides for C-N bond scission of CH 3 NH 2 might be very similar to the expensive Pt-group metals.