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.