Hydrogen Dissociative Adsorption on Lanthana: Polaron Formation and the Role of Acid Base Interactions

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.