High-Field NMR, Reactivity, and DFT Modeling Reveal the γ-Al₂ O₃ Surface Hydroxyl Network

Aluminas are strategic materials used in many major industrial processes, either as catalyst supports or as catalysts in their own right. The transition alumina γ-Al₂ O₃ is a privileged support, whose reactivity can be tuned by thermal activation. This study provides a qualitative and quantitative assessment of the hydroxyl groups present on the surface of γ-Al₂ O₃ at three different dehydroxylation temperatures. The principal [AlOH] configurations are identified and described in unprecedented detail at the molecular level. The structures were established by combining information from high-field ¹ H and ²⁷ Al solid-state NMR, IR spectroscopy and DFT calculations, as well as selective reactivity studies. Finally, the relationship between the hydroxyl structures and the molecular-level structures of the active sites in catalytic alkane metathesis is discussed.