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

Abstract

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 x prepared from commercial Nb2O5 was employed as a catalyst. H-NbO x exhibited higher oxygen vacancies (158.21 μmol/g) than commercial Nb2O5 (39.01 μmol/g), evaluated from O2-TPD. Upon supporting 10 wt % Ni, a Ni/NiO interface was formed over H-NbO x , which was intrinsically active for the hydrogenation of phenolics. 10Ni/H-NbO x exhibited a two-fold increase in activity than 10Ni/Nb2O5, 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/Nb2O5. The Ni/NiO formation was confirmed by X-ray photoelectron spectroscopy, HR-TEM, and H2-TPR analysis, while the oxygen vacancies were verified by Raman spectroscopy and O2-TPD analysis. The resulting interface enhanced the synergy between Ni and H-NbO x and facilitated hydrogen dissociation, confirmed by H2-TPD. Remarkably, 10Ni/H-NbO x 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.

The cooperative effect of Co and CoO in Co/CoO enabled efficient catalytic hydrogenation and demethoxylation of guaiacol to cyclohexanol

“…7a). 14 Only the guaiacol conversion was considered for the kinetic study because the solvent and H 2 gas were in large excess than guaiacol, and the catalyst amount remained constant during the catalytic reaction, suggesting the rationale behind the pseudo first order reaction. The slope of the ln(1 − x ) versus time plot, corresponding to the rate constant, was calculated, resulting in the following values: k 150 = 0.00195 min −1 , k 160 = 0.00333 min −1 , and k 170 = 0.00522 min −1 .…”

“…To address these challenges, effectively design catalysts, and gain a deeper understanding of the reaction mechanisms, researchers have turned to lignin model compounds such as benzyl phenyl ether, diphenyl ether, phenethyl phenyl ether, eugenol, vanillin, guaiacol, and phenol in their studies. [9][10][11][12][13][14][15][16][17] Guaiacol, a signicant component of lignin pyrolysis oil, features a methoxy group positioned ortho to the phenolic unit. 18 Researchers have extensively utilized guaiacol in their studies to successfully obtain various valuable products, including phenol, catechol, ocresol, benzene, cyclohexane, and cyclohexanol, through heterogeneous catalytic processes.…”

The Synergy of Alloyed Pd and Ni Over H-NbOx: Enhancing Hydrogenation of Lignin Derivatives and Lignin Bio-Oil into Cyclic Hydrocarbons and Alcohols

“…The transformation of the Nb 2 O 5 into H-NbO x was accomplished via hydrothermal and subsequent acid treatment. The binding energies at 204.8 and 207.5 eV attributed to Nb 3d 5/2 and Nb 3d 3/2 for Nb in H-NbO x , which was thoroughly investigated in our earlier report . Notably, in the metal-decorated H-NbO x , the peaks shift toward higher binding energies (∼0.5 eV).…”

“…The synthesis process of H-NbO x involves hydrothermal treatment of Nb 2 O 5 under basic conditions to produce NaNbO x , which was then subjected to acid treatment to yield H-NbO x . Subsequently, H-NbO x was decorated with the desired amounts of Pd and Ni through impregnation, followed by reduction using NaBH 4 under an N 2 atmosphere.…”

“… Over 50% of β-O-4 linkage is present in the native lignin, which is crucial to cleave for efficient depolymerization via breaking C–O or C–C bonds . In this instance, the cleavage of C–O and C–C bonds found within β-O-4 linkages has been explored using a range of model compounds with metal-based catalysts, − leading to the transformation of lignin monomers into valuable chemicals. − The conversion of these model compounds and lignin bio-oil into hydrocarbon presents a promising and straightforward way to lignin valorization.…”