Location of the Spinel Vacancies in γ-Al O.

A non-spinel model for the structure of γ-Al O , with 25 % of the Al cations at tetrahedral positions, has been the subject of wide interest. However, O NMR measurements and, more recently, Al NMR measurements have shown that there are considerably more Al cations at tetrahedral positions. This means that the Al vacancies in γ-Al O are not at tetrahedral but at octahedral positions, as in isostructural γ-Fe O and in accordance with density functional theory predictions. This has consequences with regard to the surface structure of γ-Al O , and thus, for catalysis.