Rational highly dispersed ruthenium for reductive catalytic fractionation of lignocellulose

Producing monomeric phenols from lignin biopolymer depolymerization in a detachable and efficient manner comes under the spotlight on the fullest utilization of sustainable lignocellulosic biomass. Here, we report a low-loaded and highly dispersed Ru anchored on a chitosan-derived N-doped carbon catalyst (RuN/ZnO/C), which exhibits outstanding performance in the reductive catalytic fractionation of lignocellulose. Nearly theoretical maximum yields of phenolic monomers from lignin are achieved, corresponding to TON as 431 mol(phenols) mol(Ru)(-1), 20 times higher than that from commercial Ru/C catalyst; high selectivity toward propyl end-chained guaiacol and syringol allow them to be readily purified. The RCF leave high retention of (hemi)cellulose amenable to enzymatic hydrolysis due to the successful breakdown of biomass recalcitrance. The RuN/ZnO/C catalyst shows good stability in recycling experiments as well as after a harsh hydrothermal treatment, benefiting from the coordination of Ru species with N atoms. Characterizations of the RuN/ZnO/C imply a transformation from Ru single atoms to nanoclusters under current reaction conditions. Time-course experiment, as well as reactivity screening of a series of lignin model compounds, offer insight into the mechanism of current RCF over RuN/ZnO/C. This work opens a new opportunity for achieving the valuable aromatic products from lignin and promoting the industrial economic feasibility of lignocellulosic biomass. Lignin valorization becomes the spotlight on the full utilization of biomass. Here, the authors report a highly dispersed Ru catalyst for reductive catalytic fractionation of lignocellulose, which affords monophenols in theoretical maximum yields, along with high preservation of carbohydrate.

Automated summary

Producing monomeric phenols from lignin biopolymer depolymerization in a detachable and efficient manner has attracted significant attention for the fullest utilization of sustainable lignocellulosic biomass. In this study, a low-loaded and highly dispersed Ru anchored on a chitosan-derived N-doped carbon catalyst (RuN/ZnO/C) is reported. This catalyst exhibits outstanding performance in the reductive catalytic fractionation of lignocellulose, achieving nearly theoretical maximum yields of phenolic monomers from lignin. The selectivity towards propyl end-chained guaiacol and syringol allows for easy purification, and the process leaves high retention of (hemi)cellulose for enzymatic hydrolysis. The good stability and transformation of Ru species contribute to the effectiveness of the catalyst. Time-course experiments and reactivity screening shed light on the mechanism. Overall, this work opens up new possibilities for the valorization of lignin and the economic feasibility of lignocellulosic biomass.