Methane dehydrogenation on Au/Ni surface alloys -a first-principles study

摘要

We present density-functional theory calculations of the dehydrogenation of CH_x (x = 1-4) on Au-alloyed Ni(211) surfaces, where the Au atoms are substituted on the Ni surface with the ratio of Au atoms to the total stepped Ni atoms being 1:4, 1:2 and 3:4, respectively. To evaluate the role of Au at the step-edge on the process of methane dehydrogenation, CH_x adsorption and dissociation on a pure Ni(211) surface is also conducted. Our results show that Au addition weakens the adsorbate-substrate interaction. With the increase of the Au concentration, the binding energies of CH_x gradually decrease and correlate well with the number of Au atoms on each model. On the Ni(211) surface, methane experiences a successive dehydrogenation process at the step-edge site in which carbon is eventually formed. As Au is introduced, the relative formation rate of carbon is greatly hampered even with a small amount of Au addition, while an appropriate amount of Au modification on the Ni catalyst has little effect on the activity of the CH_x dissociation. Finally, we also demonstrate that the active center for CH_x dissociation is dynamic with the variation of the Au concentration.