Optimizing geometric configuration of single Zn-N₄ sites for boosting reciprocal transformation between aromatic alcohols and aldehydes

It is significant to optimize geometric configuration of metal catalytic sites and boost their catalytic activity. Herein, we synthesized isolated single Zn-N₄ sites on N-doped carbon (Zn-CN) by pyrolyzing zeolite imidazole framework-8 (ZIF-8) at different temperatures. For the reciprocal transformation between benzyl alcohol and benzaldehyde, the catalytic activities of Zn-CN catalysts exhibited a volcano-like trend as the pyrolysis temperatures increased. The optimal catalyst was Zn-CN-900, with outstanding catalytic activity exceeding commercial 20 wt.% Pd/C and 20 wt.% Pt/C, promising to substitute the noble metal-based catalysts. X-ray absorption near-edge structure (XANES) measurements and density functional theory (DFT) calculation revealed the gradual transformation from tetrahedral ZnN₄ sites of ZIF-8 into planar ZnN₄ sites above 700 °C, with the maximum planar ZnN₄ sites in Zn-CN-900. The stronger adsorption between reactants and planar ZnN₄ sites facilitated the activation of reactants compared with tetrahedral ZnN₄ sites. This work will provide valuable insight into rational design of efficient catalysts by optimizing geometric configuration of catalytic sites.