Hydrodeoxygenation of lignin-derived phenolics to cycloalkanes over Ni–Co alloy coupled with oxophilic NbOx

Hydrodeoxygenation (HDO) of lignin-derived bio-oil is a promising route to produce advanced biofuels. However, the removal of oxygen-containing functional groups with high bond strength in bio-oil challenges the development of efficient, stable, and inexpensive catalysts. In this study, a series of bifunctional catalysts were synthesized by coupling Ni–Co alloy with an oxophilic NbOx support, which was used for the HDO of lignin-derived phenolics to produce cycloalkanes. The Ni–Co alloy formed on the bimetallic catalysts during calcination and reduction was verified by TEM, XPS, and H2-TPR measurements, which showed excellent hydrogenolysis activity. The composition of the Ni–Co alloy was the most uniform with a Ni/Co molar ratio of 1, and the catalyst achieved the highest catalytic activity. The oxygen vacancies provided by the NbOx support also enhanced the adsorption of phenolics and promoted the removal of oxygen-containing functional groups by forming a specific configuration. The synergistic catalysis of Ni–Co alloy and oxygen vacancies achieved complete conversion of guaiacol with a high cycloalkane selectivity of 98.9 % under optimal conditions (300 °C, 3 MPa H2, and 2 h). More importantly, only marginal deactivation occurred on the 5Ni–5Co/NbOx catalyst after 5 cycles and it was also successfully applied to the efficient conversion of other complex lignin-derived phenolics. Therefore, an efficient and economical strategy of coupling the Ni–Co alloy with an oxophilic NbOx support to catalyze the HDO of lignin-derived phenolics to produce cycloalkanes was prospective.