Unlocking the Hydrodeoxygenation Pathway: Synergy between Single-Atom Fe and N-Doped Carbon for Direct Conversion of Unsaturated Aldehydes to Alkenes

The selective hydrodeoxygenation (HDO) of α,β-unsaturated carbonyl compounds to alkenes offers an atom-economical route for upgrading bioderived molecules but remains challenging due to competing reaction pathways. Herein, we present an Fe single-atom site anchored in an N-doped carbon matrix catalyst (Fe1/NC), synthesized by immobilizing [Fe(bpy)3]2+ complexes into a ZIF-8-derived nitrogen-doped carbon followed by pyrolysis. Structural characterizations reveal atomically dispersed Fe–N4O moieties that, together with the Lewis-basic N sites of the support, create a bifunctional architecture. In the transfer HDO of cinnamaldehyde, Fe1/NC achieves complete conversion and 89.4% selectivity toward alkenes (1-propenylbenzene/allylbenzene) under mild conditions (170 °C, isopropanol as hydrogen donor, 1 MPa N2), surpassing both supported Fe-nanoparticle catalysts and the previously reported Zn-based analogue. Control experiments and theoretical analysis elucidate the detailed reaction pathway, demonstrating that the Fe–N4O sites selectively catalyze carbonyl hydrogenation via the Meerwein–Ponndorf–Verley mechanism with an energy barrier of 1.40 eV, while both the Fe center and adjacent basic N sites on the NC support collaboratively facilitate C–O bond cleavage and subsequent low-barrier hydrogen transfer to form alkenes. This synergistic mechanism between single-atom sites and the functional support enables efficient tandem HDO across a broad substrate scope. The work establishes a rational design strategy for engineering synergistic single-atom catalysts tailored for complex multistep transformations in sustainable chemistry.