Effect of Metal-Support Interface During CH4 and H2 Dissociation 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 CH4 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 CH4 and H-2. In this study, the dissociations of CH4 and H-2 on Ni cluster supported on gamma-alumina were investigated using density functional theory (DFT) calculations. Two systems: Ni-4 cluster supported on the spinel model of gamma-Al2O3 (100) surface, S(Ni-4), and on the nonspinel model of gamma-Al2O3 (100) surface, NS(Ni-4), have been used to model Ni-4/gamma-Al2O3. For both models, it was found that CH4 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 CH3 and H adsorption on different sites of the S(Ni,) and NS(Ni-4) show that CH3 and H bonded with the Ni-2 atom at Ni-4/gamma-Al2O3 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 CH3 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 CH4 and H-2.