Selective hydrodeoxygenation of lignin-derived phenolics to cycloalkanes over highly stable NiAl2O4 spinel-supported bifunctional catalysts

Hydrodeoxygenation (HDO) of lignin-derived bio-oil offers a promising route for the production of advanced biofuels. However, the conventional HDO of lignin-derived bio-oil faces serious problems, such as low hydrocarbon yield and easy deactivation of catalysts. Herein, a novel reaction system consisting of a highly stable bifunctional catalyst (i.e., Ni−WO x /NiAl 2 O 4 ) and a dodecane solvent was developed for the HDO of lignin-derived phenolics. The Ni 0 species, derived from NiWO 4 precursors on the NiAl 2 O 4 , were of small crystallite size and high dispersion, together with the strong oxophilicity of W, thereby exhibiting high activity. The use of a highly stable NiAl 2 O 4 spinel support and the replacement of common solid acid with more stable WO x for the cleavage of C O bond accounted for excellent stability. The optimized 10Ni−15WO x /NiAl 2 O 4 exhibited a high guaiacol conversion of 97.8% with a high cycloalkane yield of 83.8% under the optimum conditions (250 °C, 5 MPa H 2 , and 4 h). Cycloalkanes with a high yield over 90% were also obtained by the HDO of other complex lignin-derived compounds. More importantly, the catalyst always retained its initial activity for the HDO of guaiacol in five runs, with negligible coke formation. Subsequently, the HDO behavior of the bio-oil obtained from walnut shell pyrolysis was also studied. The relative content of cycloalkanes in the products reached 44.3% after the reaction. This study highlights the prospect of a highly stable catalyst consisting of hydrogenation metal and oxophilic promoter, and dodecane solvent to enable efficient production of cycloalkanes from the HDO of lignin-derived phenolics.