Synthesis-Controlled α- And β-Molybdenum Carbide for Base-Promoted Transfer Hydrogenation of Lignin to Aromatic Monomers in Ethanol

Molybdenum carbide catalysts over activated carbon with different crystal phases were synthesized under controllable carburization atmospheres and temperatures for transfer hydrogenation of Kraft lignin in ethanol to aromatic monomers. Single α-MoC_1-x and crystal transformation of α-MoC_1-x to β-Mo₂C are observed under a CH₄/H₂ mixture and H₂ carburization atmospheres, respectively. The mixed crystal phases of α-MoC_1-x and β-Mo₂C with different crystallinities under a N₂ carburization atmosphere exhibit higher activity with a maximum aromatic yield of 0.5163 g/g Kraft lignin when carburized at 700 °C. The dehydrogenation reaction and Kraft lignin hydrogenation are proposed to explain the synergistic effect of β-Mo₂C, base, and α-MoC_1-x for the base-promoted transfer hydrogenation process in ethanol, which is confirmed by in situ Fourier transform infrared analysis. This highly efficient process is suitable for the conversion of different lignin feedstock.