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 Al_V-ethanol complexes upon the adsorption of ethanol on the tetracoordinated Al_IV sites. This interaction significantly enhances synergy with adjacent Al_V-OH sites, resulting in a marked reduction of the activation energy barrier for ethene production. Furthermore, we reveal an interchange between Al_IV and Al_V-OH species, allowing hexacoordinated Al_VI-OH sites to participate in the dehydration pathway through the migration of ethanol between these coordination sites.