Effect of Metal–Support Interface During CH4and H2Dissociation on Ni/γ-Al2O3: A Density Functional Theory Study

Methane and hydrogen dissociation are important reactions in carbon nanotube (CNT) and hydrogen production. Although there is extensive literature on theoretical studies for CH 4 and H 2 dissociation on Ni, little is known about the effect of the oxide support, especially the metal–support interface, on the dissociation properties of CH 4 and H 2 . In this study, the dissociations of CH 4 and H 2 on Ni cluster supported on γ-alumina were investigated using density functional theory (DFT) calculations. Two systems: Ni 4 cluster supported on the spinel model of γ-Al 2 O 3 (100) surface, S(Ni 4 ), and on the nonspinel model of γ-Al 2 O 3 (100) surface, NS(Ni 4 ), have been used to model Ni 4 /γ-Al 2 O 3 . For both models, it was found that CH 4 and H 2 dissociations are kinetically preferred at the Ni 2 site located at the nickel–alumina interface when compared with the top of the Ni cluster. Also, the study of CH 3 and H adsorption on different sites of the S(Ni 4 ) and NS(Ni 4 ) show that CH 3 and H bonded with the Ni 2 atom at Ni 4 /γ-Al 2 O 3 interface are more stable than at the top site adsorption. Moreover, the calculation of the metal–support interaction indicates that molecular adsorption on the Ni particle weakened its interaction with the oxide. Hirshfeld charge analysis showed that the surface Al atom works primarily as a charge donation partner when CH 3 and H are bonded with the Ni 2 atom at the interface. This also resulted in an upshift of the d-orbital around the Fermi energy of the Ni 2 atom, which finally stabilized the interface adsorption by this Al (donor)–Ni–adsorbates (acceptor) effect. The results obtained from the DFT calculations indicate that the metal–oxide interface plays an essential role in the dissociation of CH 4 and H 2 .