Regulation of M4/Nb2O5 catalysts toward directed product selectivity in guaiacol hydrodeoxygenation

Guaiacol hydrodeoxygenation (HDO), a key reaction in lignin valorization, enables the production of high-octane, low-oxygen compounds such as benzene and cyclohexane. However, precise control over product selectivity remains a main challenge due to the complex reaction network. In this work, density functional theory (DFT) calculations were employed to investigate the mechanism and product selectivity of guaiacol HDO over five metal clusters supported on Nb₂O₅ (M₄/Nb₂O₅, M = Ru, Rh, Pd, Ir, Pt). The results show that Ru₄ and Pt₄ clusters preferentially stabilize the adsorption of aromatic rings, thereby facilitating ring hydrogenation to form cyclohexanol. In contrast, Rh₄/Nb₂O₅ and Pd₄/Nb₂O₅ promote selective C–O bond cleavage with limited ring hydrogenation, favoring the formation of benzene. Notably, Ir₄/Nb₂O₅ enables complete ring hydrogenation and C–OH bond cleavage, resulting in the formation of cyclohexane as the main product. Experimental results confirmed that Pd/Nb₂O₅ and Ir/Nb₂O₅ catalyze the conversion of guaiacol to fully deoxygenated products (benzene and cyclohexane), with a conversion rate of 70 %. The correlation study has confirmed that the electronegativity of metal clusters strongly affects the activity and selectivity of the reaction through the synergistic effect between the metal and the support. These findings elucidate the structure–activity–selectivity relationships underlying HDO performance and offer valuable insights for the rational design of selective deoxygenation catalysts targeting lignin-derived compounds.