Methane dissociation on Ni (1 0 0), Ni (1 1 1), and Ni (5 5 3): A comparative density functional theory study

Abstract

Density functional theory (DFT) calculations were performed to study the dissociation properties of CH4 on Ni (100), Ni (111), and Ni (553) surfaces. The transition states for methane sequential dissociations on the three surfaces were identified. The adsorption properties of the CHx (x=0–3) and H species on Ni (100), Ni (111), and Ni (553) surfaces were also studied. The results show that the adsorption of CHx (x=1–3) and H species is favored on less packed surfaces, e.g., Ni (100) and Ni (553). Among the surface species, carbon atom shows the most significant differences in adsorption energies between the different surfaces investigated; its adsorption strength follows the order Ni (100)>Ni (553)>Ni (111). Projected density of state for the carbon and surface Ni atoms on the three surfaces revealed that this decrease in atomic C adsorption strength for Ni (100), Ni (553), and Ni (111) originates from the reduction in the average energy of the d-band center of the surface Ni atoms. The analysis of the energetics for CH4 successive dehydrogenations on the various surfaces shows that on Ni (111), CH dehydrogenation proceeds with a barrier of 1.38eV and was found to be the rate-determining step for CH4 dissociation on Ni (111). On Ni (100) and Ni (553), CH4 dissociative adsorption, CH4→CH3+H, was found to be the rate-determining step with barrier heights of 1.23eV and 1.08eV, respectively. The results showed that the Ni (553) and Ni (100) promote the dissociation of CHx species by lowering the activation barriers when compared to Ni (111) due to their high average energy of the d-band center.