We use density functional theory to examine methane dissociative adsorption on lanthana to produce H and CH3 bonded to the surface. Previous work suggested that the binding energy of a Lewis base and a Lewis acid to an oxide exceeds by far the value expected from adding the binding energies of the same compounds chemisorbed alone. This rule suggests that the fragments (H and CH3) formed by the dissociative adsorption of methane on an oxide will adsorb so that they could benefit from this strong acid-base interaction. To do this, one fragment must bind to oxygen and the other to a cation. Such a configuration should have lower energy than the one obtained by binding both fragments to oxygen, even though each fragment prefers to bind to oxygen when it binds alone. We suggest that this behavior is encountered in most systems. (Chemical Equation Presented).

Previous work has proposed that two molecules that coadsorb on an irreducible oxide surface tend to choose their binding sites so that one is a Lewis acid and the other is a Lewis base. Here we examine whether this rule works in the case of the adsorption of two hydrogen atoms on lanthana. We find that when one hydrogen atom is adsorbed, it will bind to an oxygen atom and form a polaron by donating electron charge to a group of La atoms. When two atoms are adsorbed, one forms a hydroxyl and the other forms a hydride at the polaron site created by the adsorption of the first atom. Polaron formation in irreducible oxides is rather unusual, and so is the formation of a hydride. While the former is probably limited to lanthana, the latter is likely to be a general feature for all irreducible oxides if an electron donor is present on the surface. (Figure Presented).

Binary oxides catalyze a large number of interesting reactions, but often the performance is not good enough for commercialization. Attempts have been made to improve the catalytic properties of oxides by replacing some of the cations in the surface or the subsurface layer of the oxide with cations of a different kind. Here we use density functional theory to examine oxygen adsorption on La2O3(001) doped with higher valence dopants such as Ti, Zr, Nb, Ta, Ge, Sn, As, and Sb. La2O3 was chosen because it is representative of irreducible oxides. The choice of dopants allows us to study how the O2 adsorption energy and the nature of the adsorbed O2 depend on the valence of the dopants and on their place in the periodic system.