Abstract:

Density functional theory (DFT) was employed to predict the most stable structure of Pd-doped Ni(111), Ni(100), and Ni(211) surfaces, and the activity for CH₄ dissociation on pure and Pd-doped Ni surfaces. We predict that the thermodynamically most stable structures are the surface-doped Pd/Ni surfaces, where a surface Ni atom is replaced by a Pd atom; subsurface-doped Pd/Ni surfaces are thermodynamically unstable. Of the surface-adsorbed Pd/Ni surfaces, only the Pd/Ni(211) surface is thermodynamically stable. From the calculated adsorption energies of CH₄ dissociation intermediates (CH₄, CH₃, CH, C and H) on surface-doped Pd/Ni surfaces, we find Pd-doping to reduce the adsorption energy for all species except for CH₄. In addition, from the calculated activation barriers for CH₄ and CH dissociations, we predict CH₄ and CH to dissociate predominately on Ni(211) and Pd/Ni(211) step surfaces, followed by the broad Ni(100) and Pd/Ni(100) surfaces. Pd-doping raises the activation barriers for CH₄ and CH dissociations. For the most active Ni(211) surface, Pd-doping causes the CH dissociation step to have a higher activation barrier than the CH₄ dissociation step, which changes the rate limiting step, and helps reduce carbon deposition.

Key words: Methane reforming, Nickel catalyst, Palladium doping, Carbon deposition, Density functional theory