Catalytic Hydrogenolysis Of Lignin Research Articles

Catalytic Hydrogenolysis of Lignin into Propenyl-monophenol over Ru Single Atoms Supported on CeO2 with Rich Oxygen Vacancies

Catalytic Hydrogenolysis of Lignin into Propenyl-monophenol over Ru Single Atoms Supported on CeO₂ with Rich Oxygen Vacancies

Catalytic hydrogenolysis of lignin over Ni/CeO2-Al2O3 catalysts with formic acid as hydrogen source

Lignin is an aromatic polymer with prospects for producing high value-added chemicals. In this study, hydrogenolysis of alkaline lignin was carried out at 240 °C for 8 h in a hydrothermal kettle using Ni/xCeO2-yAl2O3 as catalyst and formic acid as hydrogen source. Compared with Ni catalysts supported by single oxides, the results showed that Ni/xCeO2-yAl2O3 composite-supported catalysts exhibited better catalytic depolymerization performance with higher bio-oil yields. Among them, Ni/1CeO2–3Al2O3 exhibited the most outstanding catalytic activity, with a bio-oil yield of 52.77 wt% and a phenolic compound yield of 7.21 wt%.

Unraveling the mechanisms underlying lignin and xylan dissolution in recyclable biphasic catalytic systems

Despite the exceptional performance of recyclable biphasic pretreatment systems (i.e., p-toluenesulfonic acid (TsOH)/pentanol, H2SO4/butanol, and AlCl3/MTHF) in the holistic fractionation of lignocellulosic biomass (LCB), there remains a significant gap in understanding of the intricate mechanisms governing the rapid dissolution of lignin and xylan from LCB. This study conducts comparative analyses using laboratory experiments and computational simulations to gain insights into the mechanism behind removing lignin and xylan in these systems. Under identical pretreatment conditions (140 °C, 45 min), three systems exhibited distinct levels of delignification and xylan removal. TsOH/pentanol showcased the highest levels of both delignification (83.3%) and xylan removal (98.1%), followed by H2SO4/butanol (77.9% delignification and 83.0% xylan removal), and AlCl3/MTHF (73.5% delignification and 97.2% xylan removal). Lignin characterization revealed that TsOH/pentanol and AlCl3/MTHF lignin samples boasted well-preserved β-O-4 bonds (42.4/100 Ar, 40.4/100 Ar, respectively), uniform molecular weights, and <1% sugar content. This led to high yields of phenolic monomers (TsOH/pentanol, 33.9%; AlCl3/MTHF, 33.7%) after catalytic hydrogenolysis of lignin. Furthermore, mechanistic analyses revealed that the TsOH/pentanol and AlCl3/MTHF systems exhibited the most significant interaction energy formation with the lignin model (veratrylglycerol-b-guaiacyl ether) and D-xylan model due to robust hydrogen bonding interactions, yielding energy values of −2460 kJ/mol and −2385 kJ/mol, respectively. These interactions could play pivotal roles in accomplishing notable lignin and xylan extraction.

Catalytic hydrogenolysis of lignin in isopropanol as hydrogen donor over nickel-cobalt supported on zeolite to produce aromatic and phenolic monomers

Due to its high catalytic activity and good hydrogenating properties, bimetallic catalysts are gaining increasing attention for lignin valorization. Herein, transition bimetallic catalysts Ni-Co/HZSM-5 were proposed to investigate the catalytic hydrogenolysis reaction of lignin. The activity was demonstrated in an 80 mL stainless-steel reactor. At 250 ℃ temperature in 4 h of reaction using isopropanol as the hydrogen donor solvent. 45 wt% yields of total monomer products and 91% lignin conversion were obtained with Ni-Co/HZSM-5 catalysts. This is superior to the catalytic activity of Ni/HZSM-5 and Co/HZSM-5 monometallic catalysts. BET, SEM, XPS, and EDX techniques were used to characterize the catalysts. The results revealed that the synergistic effect between the two metal species (Ni-Co) was the major cause of their high catalytic activity, which resulted in better hydrogen transformation and better hydrogenolysis activity. The electronic interactions between Co and Ni enhanced the transfer of electrons and accelerated catalytic reactions. Also, well-dispersed Ni and Co on HZSM-5 support enhanced the surface area, providing more active sites for lignin to adsorb and participate in hydrogenolysis reactions. In addition, a series of measurements such as FT-IR, GPC, and GC-MS were performed to examine the hydrogenolysis reaction products. A total of 19 monomer products were successfully identified in GC-MS analysis. These results confirmed the great potential of bimetallic catalysts Ni-Co/HZSM-5 due to their synergistic effect.

Ni5Fe5/Al2O3 catalytic hydrogenolysis of lignin: mechanism investigation and selectivity regulation

The development of novel catalysts to regulate product selectivity and insight into the mechanism of lignin hydrogenolysis are important for the comprehensive utilization of lignocellulose.

Catalytic Hydrogenolysis of Lignin into Phenolics by Internal Hydrogen over Ru Catalyst

AbstractLignin is a by‐product of biorefineries and pulp and paper manufacturers. Lignin is a renewable source of phenolic precursors for fuels and chemicals. Hydrogenolysis of lignin cleaves the abundant β‐O‐4 bonds and releases phenolics. However, selective hydrogenolysis of lignin's β‐O‐4 bonds is challenging because it requires high‐pressure H2. Here we show efficient hydrogenolysis of lignin model compounds and technical lignin by Ru/C catalyst and internal hydrogen. The aliphatic hydroxyl groups (Cα−OH) in lignin enabled Ru‐catalyzed dehydrogenation of internal hydrogen and the formation of reactive keto intermediate, which facilitated the β‐O‐4 cleavage into phenolic monomers. Furthermore, solvents that had a high donor number (Lewis basicity) enhanced the yield of phenolic monomers, equal to 27.9 wt.% from technical lignin. These findings offer a novel approach for biorefineries to design lignin isolation processes and/or solvent systems to maximize phenolic monomers and to control product selectivity/stability.

Catalytic hydrogenolysis of lignin and model compounds over highly dispersed Ni-Ru/Al2O3 without additional H2

Selective hydrogenolysis of lignin is an attractive strategy for valorizing lignin to fuels/value-added chemicals and developing novel and highly active heterogeneous catalysts is crucial. Herein, a highly dispersed Ni-Ru/Al2O3 catalyst prepared by a coprecipitation method using layered double hydroxide as precursor was reported. Various lignin model compounds were used to evaluate the catalyst activity. The results show that all the model compounds can be completely transformed into arenes and phenol below 150 °C using isopropanol as hydrogen source, and the latter was easily reduced to cyclohexanol. Kinetics study reveals that apparent activation energies increase in the order: benzyl phenyl ether (90.6 kJ/mol) < phenethoxybenzene (126.7 kJ/mol) < diphenyl ether (172.2 kJ/mol). 2D HSQC NMR analysis exhibits that most of C–O linkages in lignin were cleaved during hydrogenolysis over Ni-Ru/Al2O3. The results indicate that the bimetallic Ni-Ru catalyst has a high activity for catalyzing hydrogenolysis of lignin and model compounds. The catalyst was characterized with multiple tools. The results suggest that Ni and Ru nanoparticles in the catalyst are highly dispersed and a strong interaction exists between Ni and Ru, which should be responsible for promoting the hydrogenolysis of lignin and model compounds.

Cover Feature: Catalytic Hydrogenolysis of Lignin: The Influence of Minor Units and Saccharides (ChemSusChem 23/2021)

The Cover Feature shows a representative native structure of lignin with several minor units. When the structure is reductively cleaved into aromatic monomers the focus is normally on the products on the right-hand side as these are the main products. However, the monomers shown on the left-hand side can also become a significant part of the product mixture depending on the parent lignin structure. Detailed analysis of the product mixture and the structure of the lignin can reveal the origin of these minor products. More information can be found in the Full Paper by Z. Wang and P. J. Deuss.

Catalytic Hydrogenolysis of Lignin: The Influence of Minor Units and Saccharides.

The precise elucidation of native lignin structures plays a vital role for the development of “lignin first” strategies such as reductive catalytic fractionation. The structure of lignin and composition of the starting material has a major impact on the product yield and distribution. Here, the differences in structure of lignin from birch, pine, reed, and walnut shell were investigated by combining detailed analysis of the whole cell wall material, residual enzyme lignin, and milled wood lignin. The results of the 2D heteronuclear single quantum coherence NMR analysis could be correlated to the product from Ru/C‐catalyzed hydrogenolysis if monomeric products from ferulate and p‐coumaryl and its analogous units were also appropriately considered. Notably, residual polysaccharide constituents seemed to influence the selectivity towards hydroxy‐containing monomers. The results reinforced the importance of adequate structural characterization and compositional analysis of the starting materials as well as distinct (dis)advantages of specific types of structural characterization and isolation methods for guiding valorization potential of different biomass feedstocks.

Catalytic hydrogenolysis of alkali lignin in supercritical ethanol over copper monometallic catalyst supported on a chromium-based metal–organic framework for the efficient production of aromatic monomers

The catalytic hydrogenolysis of lignin has been reported as an effective approach for lignin depolymerization owing to its high efficiency for aromatic monomer production. In this study, a series of copper monometallic catalysts over an MIL-101(Cr) support were synthesized and used for the catalytic hydrogenolysis of alkali lignin using supercritical ethanol. First, the optimal copper catalyst for lignin hydrogenolysis was selected. Subsequently, the reaction conditions for catalytic hydrogenolysis were systematically optimized to maximize the total monomer yield. The optimal conditions were determined to be 6 h of reaction time, 20 min of sonication pretreatment, 50% catalyst loading, and 5% lignin loading. Under these conditions, an aromatic monomer yield of 38.5% was obtained; this depolymerized lignin stream, which is mainly composed of G-type monomers, can serve as a promising aromatic feedstock and carbon source for further microbial upgrading and bioconversion to produce various value-added products.

Catalytic hydrogenolysis of lignin in ethanol/isopropanol over an activated carbon supported nickel-copper catalyst

Lignin is the renewable and abundant source of aromatics on earth, and the depolymerization of lignin provides significant potential for producing valuable monophenols. In this work, catalytic hydrogenolysis of organosolv poplar lignin (OPL) in ethanol/isopropanol solvent over monometallic and bimetallic nonprecious catalysts was investigated. Ni/C and a series of NiCu/C catalyst with different Cu loadings were prepared and applied for depolymerization of OPL. The highest yield of phenolic monomers was 63.4 wt% achieved over the Ni10Cu5/C catalyst at 270 °C without external H2. The introduction of Cu in catalysts further promoted the hydrogen donor process of ethanol/isopropanol solvent and facilitated the cleavage of lignin linkages, resulting in the decreased molecular weight of bio-oil. The possible lignin dimer type structures, such as diphenylethane (β-1) type, phenylcoumaran (β-5) type, and pinoresinol (β-β) type structures, were proposed and identified by MALDI-TOF MS, giving a better understanding of the NiCu/C catalyzed lignin depolymerization.

Catalytic hydrogenolysis of lignin β-O-4 aryl ether compound and lignin to aromatics over Rh/Nb2O5 under low H2 pressure

The increasing risk of fossil fuels depletion due to surging energy demand has accelerated the search of alternative renewable sources. Lignin, one of the major components of lignocellulosic biomass, is the only abundant renewable natural resource for aromatic compounds. In this work, the effects of metals and process parameters were discussed via the catalytic hydrogenolysis of β-O-4 lignin model compound, 2-phenethyl phenyl ether. The best results were obtained over Rh/Nb2O5 with an overall conversion of 99.3% and exceptional selectivity of 98.9% to aromatic products when the hydrogenolysis was carried out at 260 °C and 0.1 MPa H2 for 4 h. The high efficiency is mainly attributed to the cooperation between Rh and NbOx at the perimeter sites, in which Rh particles are responsible for the dissociation of H2 and NbOx for activating CO bonds. With respect to depolymerize of ash wood lignin, the liquid products were mostly aromatics over Rh/Nb2O5 under 0.1 MPa H2. The results achieved in this work provide a promising prospect towards valorization of lignin into production of valuable aromatic compounds under low hydrogen pressure.

Catalytic Hydrogenolysis of Lignin for the Synthesis of Biokerosene

In this work, catalyst consisting of Ru deposited on hypercrosslinked polystyrene (HPS) was investigated in the process of hydrogenolysis of lignin isolated from different substrates. For sawdust, the maximum yield of the desired products was achieved with the use of acetic acid lignin, sunflower husk, and buckwheat husk when using the Klasson lignin. Analysis of hydrogenolysis products showed that the main substances formed in the process are benzene, phenol and their derivatives. In the process of hydrogenolysis of lignins at a pressure of 1 MPa hydrocarbons containing up to 9 hydrocarbon atoms were mainly obtained (78 %). Such hydrocarbons can be used as motor fuels. To increase the yield of hydrocarbons C9+, experiments were conducted to vary the temperature and pressure. The optimal reaction conditions allowing obtaining the highest yield of the target products (C9+ hydrocarbons) were found to be the following: the processing time 1 h, the temperature of 300 °C, the partial pressure of hydrogen of 4 MPa, the stirring speed of 1500 rpm. The 3 % Ru/HPS catalyst showed high stability during hydrogenolysis (up to 5 consecutive cycles without regeneration).

Investigation on the Catalytic Hydrogenolysis of Lignin over NbOx–Ni/ZnO–Al2O3

The catalytic hydrogenolysis of lignin was an important route to depolymerize lignin into aromatic monomer products and other high added value chemicals. Herein, the catalytic hydrogenolysis of pop...