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

We present density-functional theory calculations of the dehydrogenation of CHx (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, CHx 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 CHx 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 CHx dissociation. Finally, we also demonstrate that the active center for CHx dissociation is dynamic with the variation of the Au concentration.