High Catalytic Activity in Upgrading of Ethanol to Aromatic Alcohols over Zinc Hydroxyapatite

The direct conversion of ethanol to aromatic alcohols has attracted much attention as increasingly available biomass ethanol fermented from renewable sources. Herein, we present a highly efficient zinc hydroxyapatite for direct synthesis of aromatic alcohols from ethanol with a specific rate of 1.95 × 10–7 molaromatics gcatal–1 s–1, which is up to now the best in the literature. The γ-C of 2-butenal after deprotonation undergoes the nucleophilic attack to the carbonyl-C of another 2-butenal to form 2,4,6-octatrienal, which is subsequently cyclized to give ortho-aromatics, as the main pathway for the aromatization. Dynamic and theoretical studies reveal that the Zn site plays a role in hydrogen transfer for dehydrogenation and hydrogenation. The substitution of the Zn atom for the Ca atom was identified at the strong basic [Ca–O–P] site, and the Zn site lowers the energy barrier to ethanol dehydrogenation. The rate-determining step of this reaction is the coupling of two acetaldehyde molecules to form 2-butenal. This work provides a strategy to catalyze the efficient conversion of ethanol to high value-added aromatic alcohols and contributes to the development of protocols for sustainable synthesis of aromatic alcohols from biomass through heterogeneous catalysts.