Lignin represents the most abundant source of renewable aromatic resources, and the depolymerization of lignin has been identified as a prominent challenge to produce lowmolecular-mass aromatic chemicals. Herein, we report a nanostructured MoO x /CNT, which can serve as an efficient catalyst in hydrogenolysis of enzymatic mild acidolysis lignins (EMALs) derived from various lignocellulosic biomass, thus giving monomeric phenols in high yields (up to 47 wt %). This catalyst showed high selectivity toward phenolic compounds having an unsaturated substituent, because the cleavage of C−O bonds in β-O-4 units is prior to reduction of double bonds by MoO x /CNT under a H 2 atmosphere, which was confirmed by examination of lignin model compound reactions. The effects of some key parameters such as the influence of solvent, temperature, reaction time, and catalyst recyclability were also examined in view of monomer yields and average molecular weight. This method constitutes an economically responsible pathway for lignin valorization, which is comparable to the performance of precious-metal catalytic systems in terms of activity, reusability, and biomass feedstock compatibility.

C-lignin is a homo-biopolymer, being made up of caffeyl alcohol exclusively. There is significant interest in developing efficient and selective catalyst for depolymerization of C-lignin, as it represents an ideal feedstock for producing catechol derivatives. Here we report an atomically dispersed Ru catalyst, which can serve as an efficient catalyst for the hydrogenolysis of C-lignin via the cleavage of C−O bonds in benzodioxane linkages, giving catechols in high yields with TONs up to 345. A unique selectivity to propenylcatechol (77%) is obtained, which is otherwise hard to achieve, because this catalyst is capable of hydrogenolysis rather than hydrogenation. This catalyst also demonstrates good reusability in C-lignin depolymerization. Detailed investigations by model compounds concluded that the pathways involving dehydration and/or dehydrogenation reactions are incompatible routes; we deduced that caffeyl alcohol generated via concurrent C−O bonds cleavage of benzodioxane unit may act as an intermediate in the C-lignin hydrogenolysis. Current demonstration validates that atomically dispersed metals can not only catalyze small molecules reactions, but also drive the transformation of abundant and renewable biopolymer.

Lignin is the largest renewable resource of bioaromatics, and the catalytic fragmentation of lignin into phenolic monomers is increasingly recognized as an important starting point for lignin valorization. Herein, we report that ZnMoO supported on MCM-41 can catalyze the fragmentation of biorefinery technical lignin, enzymatic mild acidolysis lignin, and native lignin derived from corncob to yield lignin oily products that contain 15-37.8 wt % phenolic monomers, in which the high selectivities towards methyl coumarate (1) and methyl ferulate (2) were obtained (up to 78 %). The effects of some key parameters such as the influence of the solvent, reaction temperature, time, H pressure, and catalyst dosage were examined in view of activity and selectivity. The loss of Zn from the catalyst is discussed as the primary cause of deactivation, and the catalytic activity and selectivity can be well preserved in at least six runs by thermal calcination. The high selectivity to 1 and 2 leads to their easy separation and purification from lignin oily product to provide sustainable monomers for the preparation of functional polyether esters and polyesters.

Catechyl lignin (C-lignin), a homobiopolymer usually existing in the seed coats of Vanilla and Cactaceae plants, was recognized as an “ideal lignin” archetype leading to well-defined aromatic compounds. Herein, we report that deep eutectic solvents (DESs) can serve as green and recyclable solvents to extract C-lignin from cheap and abundant castor seed coats for the first time, which led to C-lignin biopolymer in good yields with high purity. High abundance of benzodioxane structures in DES-extracted C-lignin samples was corroborated by HSQC NMR experiments. Catalytic depolymerization of ChCl/LA DES C-lignin with Pd/C resulted in monomeric catechol derivatives in 29.6 wt % (or 81 mol %) yields with 86% selectivity toward catechylpropanol. This study provided a green and cost-effective C-lignin extraction procedure from bulk sustainable feedstock, thus paving the way for C-lignin valorization into unique catechol compounds.

Lignin depolymerization into aromatic monomers with high yields and selectivity is essential for the economic feasibility of biorefinery. However, the relationship between lignin structure and its reactivity for upgradeability is still poorly understood, in large part owing to the difficulty in quantitative characterization of lignin structural properties. To overcome these shortcomings, advanced NMR technologies [2D HSQC (heteronuclear single quantum coherence) and 31P] were used to accurately quantify lignin functionalities. Diverse lignin samples prepared from Eucalyptus grandis with varying β‐O‐4 linkages were subjected to Pd/C‐catalyzed hydrogenolysis for efficient C−O bond cleavage to achieve theoretical monomer yields. Strong correlations were observed between the yield of monomeric aromatic compounds and the structural features of lignin, including the contents of β‐O‐4 linkages and phenolic hydroxyl groups. Notably, a combined yield of up to 44.1 wt % was obtained from β‐aryl ether rich in native lignin, whereas much lower yields were obtained from technical lignins low in β‐aryl ether content. This work quantitatively demonstrates that the lignin reactivity for acquiring aromatic monomer yields varies depending on the lignin fractionation processes.

Low-molecular-weight aromatics were selectively obtained from the catalytic hydrogenolysis of biorefinery corncob lignin with a non-precious Ni/AC catalyst.

A new family of protic NHC Ru complexes ligated with a phosphine-tethered imidazole moiety were prepared, which can act as excellent catalysts for acceptorless dehydrogenation of secondary alcohols and dehydrogenative coupling of primary and secondary alcohols, thus leading to the formation of a variety of carbonyl compounds with release of H.

The complete disassembly of C-lignin and G/S lignin coexisting in Euphorbiaceae seed coats was achieved for the first time.