Ab Initio Density Functional Calculations of Adsorption of Transition Metal Atoms on θ-Al2O3(010) Surface

The catalytic properties of metal clusters and particles depend on their environment; however, little is known so far about the subnanometer metal particles, the smallest being single atoms, supported on metal oxide substrates, in particular, the systems that can be experimentally synthesized. Employing the first-principles density functional theory approach, we have studied single metal atoms, Ni, Pt, Pd, Cu, Au, and Ag, adsorbed on a theta-Al2O3 (010) surface. We find that metal adsorption on a dry theta-alumina surface follows the binding strength order of Pd > Pt > Ni > Cu > Au > Ag. Interestingly, Ni, Pt, and Pd atoms, supported on theta-alumina, exhibit no magnetization, whereas Cu, Ag, and Au exhibit unpaired electrons. The bonding picture that emerges from this study shows that Ni, Pt, and Pd, are d(10) species with d-s hybrid character that are able to interact with the 2p orbital of surface oxygen. The interaction of Group 11 (Cu, Ag, Au) atoms with 010 surface of theta-Al2O3 is superficially similar to that of Group 10 metals. Group 11 metals with filled d orbitals have low tendency for d-s hybridization due to larger energy gaps than Group 10 metals. As a result of the overlap with 0 2p, the d orbital shifts to lower energy. The magnetization of Group 11 metals is primarily due to single electrons in s orbitals.