Effect of W Modification on MoS₂ Surface Edge in the Ethanolysis of Lignin into Platform Chemicals

A series of metal-doped MoS₂, including W-, V-, and Re-doped MoS₂, are prepared via a two-step hydrothermal method, which presents higher activity on the depolymerization of enzymatic hydrolysis lignin (EHL) in ethanol as compared to undoped MoS₂. At 320 °C for 6 h, the highest overall aromatic monomer yield of 231 mg/g EHL, including alkylphenols (A-Ps) as the main products with a yield of 126.5 mg/g EHL, is obtained over two-step hydrothermally prepared W-doped MoS₂ with the W/Mo molar ratio of 0.1 (Ts-W_0.1@MoS₂). The W-doped MoS₂ sample gives higher enhancement of EHL bio-oils' heating value to 37.1 MJ/kg as compared to Re and V modified MoS₂. Large distribution of W atoms on the MoS₂ surface in two-step hydrothermally synthesized samples leads to the higher activity of EHL depolymerization than one-step prepared samples. The reduction of W precursors on the MoS₂ surface in the preparation process promotes the generation of more Mo⁵⁺ and Mo⁶⁺, which plays important roles in the improvement of EHL depolymerization activity. The effect of the W-doping modification and the stability of W-doped MoS₂ are discussed. The anti-sulfur loss and antioxidant abilities are significantly enhanced after W-doping modification. In the recyclability test, the good incorporation of W atoms with MoS₂ surface and the gradual oxidation of W-based sites improve the balance of catalytic cycles among different Mo-based sites, which results in the increase of catalyst stability.