Surface engineering to construct low-coordination high-valence FLP on ZnFe₂O₄ with excellent stability and catalytic activity

Frustrated Lewis pair (FLP) in metal oxides (e.g., spinel) show catalytic promise but face a trade-off between strong acidity and steric hindrance. Herein, we develop a high-temperature molten alkali etching strategy for engineering tetracoordinate iron sites (Fe³⁺_Td) in ZnFe₂O₄, while using the Zn→O→Fe electron transport chain as a structural stabilizer. This spatially segregated FLP system features electron-deficient Fe³⁺_Td (Lewis acid) and electron-rich O^2- (Lewis base) sites that enhance substrate adsorption synergistically and reduce activation barriers in catalytic transfer hydrogenation (CTH). When applied to biomass-derived carbonyl compounds and representative aldehydes/ketones, the catalyst achieves >95% conversion of furfural to furfuryl alcohol (120 °C, 2 h), outperforming conventional systems. Furthermore, it maintains >95% activity over five cycles, demonstrating exceptional stability. Density Functional Theory calculations confirmed that the constructed, low-coordination, high-valent FLP has a stronger adsorption capacity for substrate and exhibits high hydrogenation ability with an activation energy of only 0.17 eV, which is far lower than that of the unconstructed sample (0.88 eV). This work breaks down the conflict barriers between high-valence and low-coordination states and provides a scalable novel strategy for designing strongly acidic, low-resistance FLP catalysts for sustainable chemistry.