Cleavage of the βO4 linkage of lignin using group 8 pincer complexes: A DFT study

Liu, Cong; Wilson, Angela K.

doi:10.1016/j.molcata.2015.01.013

Cited by 19 publications

(6 citation statements)

References 49 publications

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“…More recently, some kinetic modeling and analysis has been carried out, particularly to model fast pyrolysis [45][46][47][48][49][50] . Both specific 51 and general catalysis of lignin depolymerization has been investigated computationally by studying the effect of transition metal catalysts [52][53][54][55] and ionic liquids [56][57] on lignin degradation. Few studies [58][59] have focused on the more complex chemistry of the other seven linkages in lignin, despite the fact that β-O-4 may comprise as little as 35% of the lignin linkages, depending upon the feedstock 60 .…”

Section: Introductionmentioning

confidence: 99%

“…Previous computational efforts have focused on studying model compounds that contain the abundant β-O-4 ether lignin linkage by evaluating homolytic bond dissociation energies, − mechanical properties, − and intramolecular hydrogen bonding . More recently, some kinetic modeling and analysis has been carried out, particularly to model fast pyrolysis. − Both specific and general catalysis of lignin depolymerization has been investigated computationally by studying the effect of transition metal catalysts − and ionic liquids , on lignin degradation. Few studies , have focused on the more complex chemistry of the other seven linkages in lignin, despite the fact that β-O-4 may comprise as little as 35% of the lignin linkages, depending upon the feedstock …”

Section: Introductionmentioning

confidence: 99%

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Depolymerization Pathways for Branching Lignin Spirodienone Units Revealed with ab Initio Steered Molecular Dynamics

Mar

Kulik

2017

J. Phys. Chem. A

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Lignocellulosic biomass is an abundant, rich source of aromatic compounds, but direct utilization of raw lignin has been hampered by both the high heterogeneity and variability of linking bonds in this biopolymer. Ab initio steered molecular dynamics (AISMD) has emerged both as a fruitful direct computational screening approach to identify products that occur through mechanical depolymerization (i.e., in sonication or ball-milling) and as a sampling approach. By varying the direction of force and sampling over 750 AISMD trajectories, we identify numerous possible pathways through which lignin depolymerization may occur in pyrolysis or through catalytic depolymerization as well. Here, we present eight unique major depolymerization pathways discovered via AISMD for the recently characterized spirodienone lignin branchinglinkage that may comprise around 10% weight of all lignin in some softwoods. We extract representative trajectories from AISMD and carry out reaction pathway analysis to identify energetically favorable pathways for lignin depolymerization. Importantly, we identify dynamical effects that could not be observed through more traditional calculations of bond dissociation energies. Such effects include thermodynamically favorable recovery of aromaticity in the dienone ring that leads to near-barrierless subsequent ether cleavage and hydrogen bonding effects that stabilize newly formed radicals. Some of the most stable spirodienone fragments that reside at most 1 eV above the reactant structure are formed with only 2 eV barriers for C-C bond cleavage, suggesting key targets for catalyst design to drive targeted depolymerization of lignin.2

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Depolymerization Pathways for Branching Lignin Spirodienone Units Revealed with ab Initio Steered Molecular Dynamics

Mar

Kulik

2017

J. Phys. Chem. A

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“…Besides the Ru-based homogeneous catalysts, in 2015, Wilson studied the β-O-4 linkage cleavage process over various group 8 pincer complexes (Figure ). The study finds that the C β –OAr bond activation by transition metal catalysts is essentially controlled by the ability of the metal center to donate electrons to the C β –OAr, and ligands that can donate electrons to the metal center tend to facilitate the C β –OAr bond cleavage.…”

Section: Organic Molecular Intermediatesmentioning

confidence: 99%

Catalytic Strategies and Mechanism Analysis Orbiting the Center of Critical Intermediates in Lignin Depolymerization

et al. 2023

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Lignin, as a precious resource given to mankind by nature with abundant functional aromatic structures, has drawn much attention in the recent decade from academia to industry worldwide, aiming at harvesting aromatic compounds from this abundant and renewable natural polymer resource. How to efficiently depolymerize lignin to easy-to-handle aromatic monomers is the precondition of lignin utilization. Many strategies/methods have been developed to effectively degrade lignin into monomers, such as the traditional methods of pyrolysis, gasification, liquid-phase reforming, solvolysis, chemical oxidation, hydrogenation, reduction, acidolysis, alkaline hydrolysis, alcoholysis, as well as the newly developed redox-neutral process, biocatalysis, and combinatorial strategies. Therefore, there is a strong demand to systemically summarize these developed strategies and methods and reveal the internal transformation principles of the lignin. Focusing on the topic of lignin depolymerization to aromatic chemicals, this review reorganizes and categorizes the strategies/methods according to their mechanisms, orbiting the center of critical intermediates during the lignin linkage transformation, which includes the critical anionic intermediates, cationic intermediates, organometallic intermediates, organic molecular intermediates, aryl cation radical intermediates, and neutral radical intermediates. The corresponding introduction involves the generation and the transformation chemistry of the critical intermediates via the corresponding C–H/O–H/C–C/C–O chemical bond transformations, leading to the cleavage of the C–C/C–O linkage bonds. Accompanying the brief introduction of lignin chemistry and the final concluding remarks and perspectives on lignin depolymerization, this review aims to provide a current research process of lignin depolymerization, which may provide useful suggestions for this vigorous research field.

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“…The latter increase was probably due to cleavage of aryl ether linkages to produce Phe-OH and alkane, one of the main reactions of lignin depolymerization. 33 It has been well known that supercritical ethanol is effective as a hydrogen donor via hydride transfer of α-hydrogen through a hydrogen shuttling mechanism. 34,35 The decrease of Aliph-OH results from dehydration and hydrogenation or hydrodeoxygenation in the presence of alcohol as was found by previous researchers.…”

Section: Comparison Of Chemical Properties Of Oils Before and After Amentioning

confidence: 99%

Premethylation of Lignin Hydroxyl Functionality for Improving Storage Stability of Oil from Solvent Liquefaction

Hafezisefat¹,

Cady²,

Smith³

et al. 2019

Energy Fuels

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In this study, we methylated hydroxyl groups (phenolic hydroxyl: Phe-OH and aliphatic hydroxyl: Aliph-OH) in soda lignin (SL) prior to solvent liquefaction to improve storage stability of the resulting oil. We investigated two methylating reagents, dimethyl sulfate (DMS) and dimethyl carbonate (DMC), for selective Phe-OH and total hydroxyl group (Phe-OH and Aliph-OH) blocking. Samples of SL, DMS-SL, and DMC-SL were depolymerized into oils under supercritical ethanol (350 °C). Both methylated lignins produced higher amounts of oils and smaller amounts of char compared to untreated SL due to suppressed charring reactions. Oil produced from SL had relatively higher functional group contents than other oils from methylated lignins. Simulated one-year aging of oils was carried out and this revealed Mw increase of oil was the highest in SL (11.8 %), followed by DMC-SL (6.8 %) and DMC-SL (4.6 %). Interestingly, these increases showed linear correlation with decrease in Phe-OH after accelerated aging. Meanwhile, compositional difference in monomeric phenols in the oils were observed by GC/MS analysis. For example, methoxylated aromatics such as 4-ethylveratrole, 4-vinylveratrole, methylisoeugenol, and veratryl-2-propanone were detected only in oils from DMS-SL, and DMC-SL. Interestingly, there was no significant difference in monomeric compounds yields before and after accelerated aging among the oils, which suggests that repolymerization mainly occurred between oligomeric lignin fragments.

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Cleavage of the βO4 linkage of lignin using group 8 pincer complexes: A DFT study

Cited by 19 publications

References 49 publications

Depolymerization Pathways for Branching Lignin Spirodienone Units Revealed with ab Initio Steered Molecular Dynamics

Depolymerization Pathways for Branching Lignin Spirodienone Units Revealed with ab Initio Steered Molecular Dynamics

Catalytic Strategies and Mechanism Analysis Orbiting the Center of Critical Intermediates in Lignin Depolymerization

Premethylation of Lignin Hydroxyl Functionality for Improving Storage Stability of Oil from Solvent Liquefaction

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