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

Density functional theory (DFT) calculations were performed to study the dissociation properties of CH4 on Ni (1 0 0), Ni (1 1 1), and Ni (5 5 3) 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 (1 0 0), Ni (1 1 1), and Ni (5 5 3) 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 (1 0 0) and Ni (5 5 3). 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 (1 0 0) > Ni (5 5 3) > Ni (1 1 1). 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 (1 0 0), Ni (5 5 3), and Ni (1 1 1) 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 (1 1 1), CH dehydrogenation proceeds with a barrier of 1.38 eV and was found to be the rate-determining step for CH4 dissociation on Ni (1 1 1). On Ni (1 0 0) and Ni (5 5 3), CH4 dissociative adsorption, CH4 → CH3 + H, was found to be the rate-determining step with barrier heights of 1.23 eV and 1.08 eV, respectively. The results showed that the Ni (5 5 3) and Ni (1 0 0) promote the dissociation of CHx species by lowering the activation barriers when compared to Ni (1 1 1) due to their high average energy of the d-band center.

Graphical abstractDensity functional theory (DFT) calculations were performed to study the dissociation properties of CH4 on Ni (1 0 0), Ni (1 1 1), and Ni (5 5 3) surfaces. The transition states for methane sequential dissociations on the three surfaces were identified. Analysis of the overall reaction pathways shows that the Ni (5 5 3) and Ni (1 0 0) promote the dissociation of CHx species by lowering the activation barriers when compared to Ni (1 1 1). The results indicate that the low-coordinated surfaces, e.g., Ni (5 5 3) step surface, are generally more reactive for methane dissociation when compared to Ni (1 1 1) due to their high average energy of the d-band center.Figure optionsDownload full-size imageDownload high-quality image (204 K)Download as PowerPoint slideHighlights► CHx (x = 0–3) fragments have high mobility on the highly packed Ni (1 1 1) surface. ► Low coordinated Ni (5 5 3) and Ni (1 0 0) surfaces promote CHx (x = 1–4) dissociation. ► CH dissociation is the rate determining step for CH4 dissociation on Ni (1 1 1). ► CH4 dissociative adsorption is the rate determining step on Ni (5 5 3) and Ni (1 0 0).