Waste to wealth: H2S-free fabrication of Fe-ZnS/NC by industrial lignin self S-doping for efficient lignin aerobic oxidation

Industrial lignin mostly contains sulfur, which poisons metal catalysts easily. Metal sulfides with good S-resistance could be used as efficient catalysts for lignin oxidation, while metal sulfides preparation involved corrosive H2S. Here in, we proposed H2S-free fabrication of bimetallic Fe-ZnS/NC by industrial lignin self S-doping. The Fe-ZnS/NC 650 exhibited efficient oxidation activity (> 99% conversion) for β-O-4 cleavage and good S-resistance for industrial lignin oxidation. Density functional theory revealed the synergistic effect of FeS and ZnS in lignin oxidation, where FeS tended to activate O2 into superoxide radical (O2-•) and ZnS contributed to the polarization of β-O-4. The dual sites greatly reduced the migration distance of O2-• to the polarized β-O-4, facilitating the C-O/C-C cleavage. Hence, Fe-ZnS/NC 650 selectively converted lignin into carbonyl-containing aromatics with up to 92% selectivity under alkaline-free condition. This work developed a novel strategy using lignin-derived metal sulfide without external sulfur source for efficient lignin degradation.