Hydrodeoxygenation Performance of Lignin-Derived Phenolics to Cycloalkanes: Insights into the Crystal Structures of the Nb2O5 Support

Hydrodeoxygenation (HDO) of lignin-derived phenolics is promising to produce high-value-added chemicals and liquid fuels. As a strong oxophilic support, Nb2O5 maintains high catalytic activity for the deoxygenation of oxygen-rich reactants, while few studies have clarified the influence of crystal structures on reactivity. In this study, the Nb2O5 supports with three crystal structures (pseudohexagonal-TT, orthorhombic-T, and monoclinic-H) were successfully prepared and used for the HDO of lignin-derived phenolics after loading bimetal Ni and Co. The structural properties and acidity of the supports and catalysts gradually deteriorated with the increase in calcination temperatures. The oxygen vacancy content and the interaction strength between supports and active metals followed the rule of Nb2O5-TT > Nb2O5-T> Nb2O5-H. In addition, oxygen vacancy content also had a volcanic relationship with the catalyst reduction times. Then, the catalytic activity of the catalysts was studied in the HDO reaction of guaiacol. The 10Ni-10Co/Nb2O5-TT (450 degrees C) catalyst exhibited the best catalytic performance with a complete conversion of reactant and a high cycloalkane selectivity of 98.6% under optimal conditions (250 degrees C, 3 MPa H-2, and 3 h). More importantly, recycle tests indicated that it also had excellent stability. Moreover, other typical lignin-derived monomers and dimers were selected to test the reactant adaptability of the catalyst, and the selectivities of cycloalkanes also verged on the theoretical value. Therefore, the bifunctional catalyst composed of oxophilic Nb2O5-TT (450 degrees C) support and high-efficiency active metals possessed strong competitiveness in the HDO of lignin-derived phenolics.