Iron spin-state engineering modulates orbital-coupling to drive efficient transfer hydrogenation

The precise regulation of Fe spin states and correlation with catalytic activity remain a challenging frontier in heterogeneous catalysts. Herein, we report an Fe-based spinel oxide with iron atoms solely occupying octahedral sites, prepared from layered double hydroxide (MgFe-LDH) precursor. The Fe spin configuration has been precisely regulated from low- to high-spin states by controlling the calcination temperature. The catalyst prepared at 700 °C (MgFeO-700) exhibits a medium-spin Fe state, which optimally balances reactant activation and six-member-ring transition state formation, delivering superior catalytic transfer hydrogenation (CTH) performance with a stable 95% yield in the transformation of furfural (FF) to furfuryl alcohol (FOL). Combined in situ DRIFTs and density functional theory (DFT) calculations reveals that the hybridization strength of Fe 3d and O 2p orbitals governs the spin-dependent reaction kinetics. The moderate d-p orbital coupling in the medium-spin state reduces the six-membered-ring transition state barrier, driving higher catalytic efficiency This work uncovers a direct structure–activity correlation between Fe spin state and catalytic performance, providing a general strategy for spin-state engineering of Fe-based oxides toward economical and robust catalysts.