Lignin Compounds to Monoaromatics: Selective Cleavage of C−O Bonds over a Brominated Ruthenium Catalyst

Abstract

The cleavage of C−O linkages in aryl ethers in biomass‐derived lignin compounds without hydrogenation of the aromatic rings is a major challenge for the production of sustainable mono‐aromatics. Conventional strategies over the heterogeneous metal catalysts require the addition of homogeneous base additives causing environmental problems. Herein, we propose a heterogeneous Ru/C catalyst modified by Br atoms for the selective direct cleavage of C−O bonds in diphenyl ether without hydrogenation of aromatic rings reaching the yield of benzene and phenol as high as 90.3 % and increased selectivity to mono‐aromatics (97.3 vs. 46.2 % for initial Ru) during depolymerization of lignin. Characterization of the catalyst indicates selective poisoning by Br of terrace sites over Ru nanoparticles, which are active in the hydrogenation of aromatic rings, while the defect sites on the edges and corners remain available and provide higher intrinsic activity in the C−O bond cleavage.

Iodine‐Modified Pd Catalysts Promote the Bifunctional Catalytic Synthesis of 2,5‐Hexanedione from C6 Furan Aldehydes

“…The inferior synergism of bifunctional catalysis is a common phenomenon for many tandem reactions in biomass conversion. [12,14,[37][38][39] The design of powerful catalysts is extremely important for controlling multiple reactions under a same reaction condition.…”

“…The low proximity of hydrogenation sites and acid sites, and the long‐distance transport of intermediates between different active sites in the abovementioned physical‐mixed or simply assembled tandem catalysts results in unsatisfactory catalytic conversion and selectivity. The inferior synergism of bifunctional catalysis is a common phenomenon for many tandem reactions in biomass conversion [12,14,37–39] . The design of powerful catalysts is extremely important for controlling multiple reactions under a same reaction condition.…”

Selectivity Control of C-O Bond Cleavage for Catalytic Biomass Valorization

“…Nevertheless, various cross-linking side reactions (predominantly Friedel-Crafts) take place to produce larger fragments, due to the high reactivity of phenolic intermediates and products at high temperatures (Zakzeski et al, 2010). Also, the appropriate design of metal catalysts with enhanced capability to destroy the C-O bonds by hydrogenolysis while inhibiting the hydrogenation of the aromatic rings is highly challenging and in need of solution (Wu et al, 2021). Developing novel strategies like pre-modification of active groups and stabilization of in situ formed active species to obstruct the repolymerization of lignin fragments and the occurrence of over-hydrogenation is essential for comprehensive utilization of lignocellulosic biomass.…”

“…The three main monomers in lignin have been identified as p-coumaric acid, coniferous alcohol, and mustard alcohol (Jampa et al, 2019). Different monomers are connected by various C-O (e.g., α-O-4, β-O-4 and 4-O-5) and C-C bonds (Figure 1) (Wu et al, 2021). Among these bonds, the β-O-4 bond is dominant (Enright et al, 2019;Huang et al, 2020).…”

Hydrogenolysis cleavage of Csp2-Csp3 bond over a metal-free NbOPO4 catalyst

“…2,9 In the supported metal catalysts, the metals (Pt, Pd, Ru, Ni, Co) usually play a key role in activating hydrogen molecule, which is considered to be necessary in the hydro-processing. [10][11][12][17][18][19][20][21][22][23] However, recently, Huang et al reported that ceria with oxygen vacancies (Ov) can produce H δspecies via the heterolytic pathway and showed good activity in hydrogenation reactions 24 , where the oxygen vacancies played an important role in the formation and stabilisation of hydride species (CeOv 4+ -H -). 25 .…”