Catalytic roles of Mo-based sites on MoS₂ for ethanolysis of enzymatic hydrolysis lignin into aromatic monomers

The depolymerization of enzymatic hydrolysis lignin (EHL) is examined over one-step hydrothermal-synthesized MoS₂ in ethanol without hydrogen gas. Value-added aromatic molecules, mainly including alkyl-substituted phenols (A-Ps), are obtained without char or tar formation. The MoS₂ samples prepared with different Mo and S precursors have been tested and the highest aromatic monomer yield of 226.4 mg/g EHL is achieved over the MoS₂ prepared with thioacetamide and sodium molybdate as precursors (STA-MoS₂) at 320 °C for 12 h. Proper ratios of Mo⁶⁺/Mo⁵⁺ (~0.46–0.65) and (Mo⁶⁺+Mo⁵⁺)/Mo⁴⁺ (~0.47–0.62) on the surface of MoS₂ catalysts are found to be significant for the achievement of high overall aromatic monomer yield. MoO_xS_y species with Mo⁵⁺ and S₂^2- is proposed as the active site for the production of complex alkyl phenols via demethoxylation and alkylation. The carbon deposition and the exchanges of sulfur and oxygen atoms resulted from the oxidization are likely responsible for the deactivation of catalyst.