Successive Dehydrogenation of Methane On Cu/Ni (111) Bimetallic System: A DFT Study

We present a density-functional theory study on the dehydrogenation of methane and CH_x (x = 1–3) on a Cu/Ni(111) surface, where Cu atoms are substituted into the Ni surface at a coverage of 1/4 monolayer. As compared to the results on other metal surfaces, including Ni(111), a similar activation mechanism with different energetics is found for the successive dehydrogenation of CH₄ on the Cu/Ni(111) surface. In particular, the activation energy barrier (E_act) for CH →C+H is found to be 1.8 times larger than that on Ni(111), while E_act for CH₄ → CH₃+H is 1.3 times larger. Considering the proven beneficial effect of Cu observed in the experimental systems, our findings reveal that the relative E_act in the successive dehydrogenation of CH₄ plays a key role in impeding carbon formation during the industrial steam reforming of methane. Our calculations also indicate that previous scaling relationships of the adsorption energy (E_ads) for CH_x (x = 1-3) and carbon on pure metals also hold for several M/Ni(111) alloy systems (M=Cu, Ag, Au, Co, and Bi).