Sulfur-Vacancy Induced NiMoS Catalyst for Direct Hydrodeoxygenation of Lignin into Aviation Fuel-Range Cycloalkanes

Abstract In the chemical pulping of lignocellulose, a substantial amount of black liquor (pH 14) is generated as a byproduct. Acid precipitation treatment can be used to convert black liquor into low-molecular-weight kraft lignin, which has potential for producing aviation fuel-range cycloalkanes. In this study, an Ni-doped MoS2/γ-Al2O3 catalyst, Ni0.3MoS/γ-Al2O3, was synthesized using incipient wetness impregnation. The catalyst enables the hydrodeoxygenation of various lignin dimers (including β–O–4, α–O–4, and 4–O–5) under mild conditions, producing the corresponding cycloalkanes. Additionally, Ni0.3MoS/γ-Al2O3 efficiently catalyzes the direct hydrodeoxygenation of kraft lignin at 300 °C under 3 MPa H2 for 12 h, achieving a high cycloalkane yield of 30.0 wt % and selectivity of 88.2%. Therefore, the Ni–Mo–S phase formed by doping Ni into MoS2 promotes the adsorption and dissociation of H2, thereby resulting in benzene ring hydrogenation. Concurrently, the catalyst with abundant sulfur vacancies facilitates the adsorption and activation of oxygen-containing reactants, thus promoting the cleavage of C−O bonds. This work presents a novel and efficient strategy for the direct hydrodeoxygenation of kraft lignin from black liquor to produce aviation fuel-range cycloalkanes.