Insight into the general rule for the activation of the X-H bonds (X = C, N, O, S) induced by chemisorbed oxygen atoms.

Density functional theory calculations are presented for adsorption and dissociation of NH3, H2O, CH3OH, H2S and C2H4 on clean and oxygen atom pre-adsorbed metal surfaces (Cu, Ag, Au, Ni, Pd, Pt, Rh, Ru, Os and Ir). The calculation results indicated that the oxygen-promotion effect depends both on the metallic activity and the character of the X-H bond. On the one hand, for a given reaction on a series metals, a good linear correlation was found between the energy barrier difference of X-H bond breaking on clean and oxygen-covered metals and the binding strength of oxygen on metals, namely an oxygen-promotion effect was favorable to the less active metals but unfavorable to the more active metals. On the other hand, for a series of X-H bond breaking reactions on a given metal, it was found that the promotion effect follows the trend of O-H > N-H > C-H, that is, the O-H bond is most promoted by the oxygen atom. The possible reason is the O-H bond forms the strongest hydrogen bond in the transition state among the X-H bonds investigated in this work. Additionally, it was found that the oxygen coverage has little effect on the X-H bond scission.