Dynamic Self-Modification of γ-Al2O3 Driven by Alkaline-Metal Promotion and Carbocation-Mediated β-H Transfer for Efficient α-Olefin Synthesis.

The surface acidity of solid acids─a key determinant of their catalytic performance─is considered as an intrinsic nature, generally modulated via precursor and synthesis chemistry. Herein, we report a strategy for in situ reactive atmosphere-induced reconstruction of surface acidic sites on γ-Al2O3, enabling a pronounced enhancement of α-olefin selectivity during higher-alcohol dehydration. Specifically, γ-Al2O3 with a low Na content of 0.06 wt % after pretreatment under a reactive atmosphere delivers octanol conversion and 1-octene selectivity comparable to those of γ-Al2O3 with a high Na content of 0.4 wt %, but at a reaction temperature 80 °C lower. Using solid-state 1H NMR with H-D exchange of octanol hydroxyl groups as a molecular probe, together with DFT calculations, we unravel the mechanism: carbocation-mediated β-hydride transfer during long-chain alcohol dehydration triggers reconstruction of Lewis acid-base sites on γ-Al2O3. In contrast, exposure to ethanol or water shows no such effect and serving as control experiments. Key factors governing 1-octene selectivity are the Na content in pristine γ-Al2O3 and the acid-base properties of the reconstructed catalyst. This reactant-induced self-modification strategy provides key insights into the rational design of versatile γ-Al2O3 catalysts and supports.