Lignin‐First Depolymerization of Lignocellulose into Monophenols over Carbon Nanotube‐Supported Ruthenium: Impact of Lignin Sources

Abstract

Lignin‐first depolymerization of lignocellulosic biomass into aromatics is of great significance to sustainable biorefinery. However, it remains a challenge, owing to the variance between lignin sources and structures. In this study, ruthenium supported on carbon nanotubes (Ru/CNT) exhibits efficient catalytic activity toward lignin hydrogenolysis to exclusively afford monophenols in high yields. Catalytic tests indicate that the yields of aromatic monomers are related to lignin sources and decrease in the order: hardwoods > herbaceous plants > softwoods. Experimental results demonstrate that the scission of C−O bonds and the high selectivity to monomeric aromatic compounds over the Ru/CNT catalyst are enhanced by avoiding side condensation. Furthermore, the fabricated Ru/CNT shows good reusability and recyclability, applicability, and biomass feedstock compatibility, rendering it a promising candidate for lignin valorization. These findings pave the way for rational design of highly active and stable catalysts to potentially address challenges in lignin chemistry.

Toward Value-Added Arenes from Lignin-Derived Phenolic Compounds via Catalytic Hydrodeoxygenation

“…The DFT calculation analysis confirmed that the high selectivity of the catalyst for the target product arenes was due to strong adsorption, selective activation of C–O bonds in phenolic compounds, and the strong metal–support interaction between Ru and NbOx species. Along this achievement, several groups have also recently demonstrated effective methods and strategies for the conversion of lignin to BTX, leading to exciting initial developments in this field. ,,− Although some inspiring achievements have been furnished, some challenges that need further in-depth study still exist. It is noteworthy that the reaction pathway for the lignin depolymerization reaction and the subsequent phenolic HDO reaction depends on the structure of the feedstock, which largely determines the product selectivity.…”

Metal–Organic-Framework-Derived Copper Catalysts for the Hydrogenolysis of Lignin into Monomeric Phenols

“…Apart from its calorific value, lignin is the second most copious renewable resource after cellulose. − It retains great value-added potential for the synthesis of lucrative compounds due to its distinctive aromatic skeleton. − Converting lignin from agroforestry and paper industry wastes into high-value-added monomeric phenols not only helps the environment but also meets the development of biorefineries . For this reason, the ″lignin-first″ biorefining strategy, which incorporates lignin valorization into the design phase, has shown maximum utilization of lignocellulose. − In this case, the natural lignin is removed from wood flour and converted to soluble aromatic compounds, while retaining (hemi)­cellulose as the insoluble part. A series of metal catalysts have been developed in the reductive catalytic fractionation (RCF) of biomass.…”

“…A series of metal catalysts have been developed in the reductive catalytic fractionation (RCF) of biomass. For example, the noble-metal catalysts of Pd − and Ru ,− are used in the RCF of lignocellulose to produce monophenol compounds with a content in the range of 20–55 wt %. However, the frequent use of expensive precious metals is the main problem to be solved.…”

Catalyst choice impacts aromatic monomer yields and selectivity in hydrogen-free reductive catalytic fractionation

“…9,12,16 Choice of substrate also has major implications for both monomer identity and overall yields, with hardwoods being more amenable to depolymerization and high monomer yields compared to softwoods and grasses. 17,18 Investigations of the impact of catalyst identity have mainly focused on the selectivity to different product monomers, with comparably less emphasis on the rate of stabilization. Typically, Ru/C, Ni/C, and Rh/C are reported to form propyl substituted monomers through a combination of hydrodeoxygenation and hydrogenation, 7,10,15,19 whereas Pd/C forms propanol substituted monomers.…”

“…9,12,16 Choice of substrate also has major implications for both monomer identity and overall yields, with hardwoods being more amenable to depolymerization and high monomer yields compared to softwoods and grasses. 17,18…”