Unveiling Active Al3+ Sites for Ethanol Dehydration on γ‑Al2O3 with Solid-State Nuclear Magnetic Resonance Spectroscopy

γ-Al2O3 is a crucial catalyst widely used in industrial alcohol dehydration processes. However, the specific nature of its active sites has remained unclear. In this study, we utilize two-dimensional heteronuclear correlation solid-state nuclear magnetic resonance and density functional theory calculations to uncover the active Al sites on the surface of γ-Al2O3 that facilitate ethanol dehydration. We show the formation of stable pentacoordinated AlV−ethanol complexes upon the adsorption of ethanol on the tetracoordinated AlIV sites. This interaction significantly enhances synergy with adjacent AlV−OH sites, resulting in a marked reduction of the activation energy barrier for ethene production. Furthermore, we reveal an interchange between AlIV and AlV−OH species, allowing hexacoordinated AlVI−OH sites to participate in the dehydration pathway through the migration of ethanol between these coordination sites.