OD-Cu slab built by removing surface oxygen gradually until no oxygen appears on the surface in 1 ns. A pure Cu surface with the base of Cu2O was finally formed, and the results show that the planarsquare and convex-square sites are selectivity to ethylene. However, the simulations fail to observe the diffusion of oxygen due to the short simulation time and thus did not explain the complete reduction of Cu2O to Cu observed in many of the experiments.