Promoting the selective hydrogenolysis of C-O bond in lignin over molybdenum carbide by the modulation of MoC/Mo2C heterostructure

Catalysts for the selective cleavage of C-O bond in lignin are important for the synthesis of aromatic monomers. Herein we developed a promising strategy for preparation of dual phase MoxC (α-MoC/β-Mo2C) nano-catalyst embedded within nitrogen-doped carbon via temperature-programmed carburization of C-Mo-N precursor. The intrinsic activity of the molybdenum carbide is adjusted by varying the Mo: N ratio to maximize the exposed active sites. The Mo:N ratio during synthesis controls the relative formation of α-MoC and β-Mo2C by influencing the local carbon and nitrogen environment during carburization. The MoxC with the optimal composition of α-MoC/β-Mo2C (0.48/0.52) demonstrates that the real birch lignin could be completely converted at 260 °C after 3 h with 23.8 wt% aromatic monomers yield. Furthermore, the catalyst shows no significant loss of catalytic activity in five consecutive runs. Such prominent performance not only benefits from the presence of pyridine N that modulate the orbital structure of Mo to promote H2 activation, but also should be ascribed to the strong synergistic effect between α-MoC and β-Mo2C. The numerous hetero-interfaces offer abundant active sites with a strong H2 activation and the disassociation energy of Calkyl-O bond is significantly reduced on adsorption on α-MoC and β-Mo2C interface.