Hydrodeoxygenation of lignin-derived phenolic compounds over zero-valent iron nanoparticles

The development of efficient non-noble metal catalysts for the hydrodeoxygenation (HDO) of lignin-derived phenolic compounds is critical for biomass valorisation. In this work, unsupported Fe-based nanocatalysts were systematically investigated to uncover the intrinsic active sites and eliminate support-induced complexities during the HDO of phenolic compounds. It was found that catalytic activity is positively correlated with the relative fraction of the metallic Fe 0 phase. Among the catalysts evaluated, zero-valent nano-Fe (50 nm) exhibited the highest performance, achieving complete phenol conversion with a 97% cyclohexane yield at 300 °C and 4 MPa H 2 after 20 h. Based on the characterisation results, this superior activity is not solely dependent on the geometric surface area, but is intrinsically driven by the synergy of an ultrathin surface passivation layer and a high density of exposed zero-valent iron (Fe 0 ) defect sites. Furthermore, surface interactions were elucidated via density functional theory (DFT) calculations, revealing robust parallel adsorption and effective activation of the aromatic ring on the Fe (110) surface. Additionally, catalyst stability, phase evolution, and broad applicability for various lignin-derived substrates were systematically examined. These findings establish a fundamental baseline for the intrinsic activity of pure Fe nanoparticles, providing theoretical guidance for the rational design of support-free non-precious metal catalysts.