Highly dispersed Mo2C/AC for gas-phase catalytic direct deoxygenation during lignin pyrolysis

Abstract

Lignin pyrolysis can efficiently produce renewable aromatic hydrocarbons, but the selective cleavage of lignin C–O bonds and the inhibition of intermediate polycondensation in solvent-free systems remain significant challenges. This work proposes a strategy coupling gas-phase lignin pyrolysis with online hydrodeoxygenation, employing highly dispersed Mo₂C to achieve targeted deoxygenation of lignin toward aromatics. Mo₂C/AC exhibits high direct deoxygenation selectivity over a wide temperature range (300–500 °C), which facilitates selective C–O bond cleavage while inhibiting catalyst coking and aromatic ring cracking. The aromatic hydrocarbon yield from guaiacol reached as high as 93 mol%, with 100% selectivity. Specifically, Mo₂C effectively mitigates the high-temperature condensation of guaiacol by removing oxygen-containing groups, thereby inhibiting the formation of oligomers. Compared with traditional zeolite-catalysed lignin pyrolysis at the same temperature, the yield of monocyclic aromatic hydrocarbons increased by 344%, while coke formation was reduced to only 20% of the original level. After birch lignin pyrolysis coupled with hydrodeoxygenation, the yield of monomeric aromatic hydrocarbons can reach up to 11.3 wt%. This study achieves selective deoxygenation of lignin in the gas phase at low temperature while significantly suppressing catalyst coking, offering a viable strategy for efficient solvent-free lignin conversion.