Fine-Tuning of Ni/NiO over H-NbO for Enhanced Eugenol Hydrogenation through Enhanced Oxygen Vacancies and Synergistic Participation of Active Sites.

The hydrogenation of lignin-derived phenolics to produce valuable chemicals is a promising but challenging task. This study successfully demonstrates the use of sustainable transition metal-based catalysts to hydrogenate lignin-derived phenolics. A defect-induced oxygen vacancy containing H-NbO prepared from commercial NbO was employed as a catalyst. H-NbO exhibited higher oxygen vacancies (158.21 μmol/g) than commercial NbO (39.01 μmol/g), evaluated from O-TPD. Upon supporting 10 wt % Ni, a Ni/NiO interface was formed over H-NbO, which was intrinsically active for the hydrogenation of phenolics. 10Ni/H-NbO exhibited a two-fold increase in activity than 10Ni/NbO, achieving >99% eugenol conversion and affording ∼94% 4-propyl cyclohexanol selectivity, wherein ∼63% eugenol conversion and ∼73% 4-propyl cyclohexanol selectivity were obtained over 10Ni/NbO. The Ni/NiO formation was confirmed by X-ray photoelectron spectroscopy, HR-TEM, and H-TPR analysis, while the oxygen vacancies were verified by Raman spectroscopy and O-TPD analysis. The resulting interface enhanced the synergy between Ni and H-NbO and facilitated hydrogen dissociation, confirmed by H-TPD. Remarkably, 10Ni/H-NbO maintained its catalytic activity for five tested cycles and demonstrated exceptional activity with various phenolics. Our findings highlight the potential of a sustainable transition metal catalyst for the hydrogenation of lignin-derived phenolic compounds, which could pave the path to producing valuable chemicals in an environmentally friendly manner.