High-field NMR, reactivity, and DFT modeling reveal the gamma-Al2O3 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 gamma-Al2O3 is a privileged support, whose reactivity can be tuned by thermal activation. This study provides an qualitative and quantitative assessment of the hydroxyl groups present on the surface of gamma-Al2O3 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 1H and 27Al 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.