- Depolymerization of lignin: Via a non-precious Ni-Fe alloy catalyst supported on activated carbon
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Lignin primarily composed of methoxylated phenylpropanoid subunits is an abundant biomass that can be used to produce aromatics. Herein, a series of non-precious bimetallic Ni-Fe/AC catalysts were prepared for efficiently depolymerizing lignin. When organosolv birch lignin was used to determine the efficiency of the catalysts in methanol solvent, the Ni1-Fe1/AC (the ratio of Ni and Fe was 1 : 1) achieved the highest total yield of monomers (23.2 wt%, mainly propylguaiacol and propylsyringol) at 225 °C under 2 MPa H2 for 6 h. From GPC analysis, it is also proved that lignin was efficiently depolymerized. The Ni-Fe alloy structure was formed according to XRD, HRTEM, H2-TPR and XPS characterization. Based on the model compounds' tests, the Ni1-Fe1/AC catalyst showed high efficiency in ether bond cleavage without hydrogenation of aromatic rings which could be attributed to the synergistic effect of Ni and Fe on the alloy structure. The total yield of monomers by using the Ni1-Fe1/AC catalyst reached 39.5 wt% (88% selectivity to PG and PS) when birch wood sawdust was used as the substrate.
- Zhai, Yongxiang,Li, Chuang,Xu, Guangyue,Ma, Yanfu,Liu, Xiaohao,Zhang, Ying
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- Controlling lignin solubility and hydrogenolysis selectivity by acetal-mediated functionalization
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Existing lignocellulosic biomass fractionation processes produce lignin with random, interunit C-C bonds that inhibit its depolymerization and constrain its use. Here, we exploit the aldehyde stabilization of lignin to tailor its structure, functionality,
- Dick, Graham R.,Komarova, Anastasia O.,Luterbacher, Jeremy S.
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supporting information
p. 1285 - 1293
(2022/02/17)
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- Understanding the regioselectivity in the oxidative condensation of catechins using pyrogallol-type model compounds
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Catechins are found in many foods, including tea. These compounds are bioactive. Previous studies have shown that catechins form dimers on oxidation, and there seem to be distinct regioselective effects. However, the dimerization mechanism and regioselectivity are not well understood. Therefore, we investigated the oxidation of four pyrogallol-type model compounds of epigallocatechin (EGC) having various substituents with 1 equiv of copper chloride and 30% dioxane in water. Compounds having 2C-2C or 2C-4C bonds in the B-ring were obtained in different product ratios. Comparison of the oxidation rates of each compound revealed that the model compounds having an oxygen atom corresponding to the 1-position of the C-ring of EGC underwent slow oxidation. In addition, using density functional theory calculations, we found that the highest occupied molecular orbital energies of these compounds were higher than those of the others. Further, the 2C-2C-bonded oxidation product having an A-ring and an oxygen atom at the C-ring 1-position was confirmed to have the highest thermodynamic stability. From these results, it is suggested that the regioselective condensation reaction of the catechin B-ring is related to interactions between the A-rings, as indicated by earlier studies, and the presence of oxygen at the 1-position of the C-ring in EGC.
- Yanase, Emiko,Ochiai, Yuto,Hirose, Sayumi
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supporting information
p. 12359 - 12366
(2020/11/10)
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- Chemodivergent hydrogenolysis of eucalyptus lignin with Ni@ZIF-8 catalyst
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Reductive catalytic fractionation (RCF) of lignocellulosic biomass, that is depolymerization of the native lignin component into well-defined monomeric phenols in the first step, offers an opportunity to utilize entire biomass components. Herein, we report that Ni@ZIF-8 can serve as a chemodivergent catalyst in RCF of eucalyptus sawdust, thus selectively producing phenolic compounds having either a propyl or propanol end-chain under different reaction conditions. In both cases, high yields of lignin monomers and a high degree of delignification were achieved, next to well-preserved carbohydrate pulp suitable for further processing. A mechanistic study using model compounds indicated that the dehydroxylation at the γ-position of the β-O-4 structure may be involved in the selectivity-controlling step.
- Liu, Xue,Li, Helong,Xiao, Ling-Ping,Sun, Run-Cang,Song, Guoyong
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supporting information
p. 1498 - 1504
(2019/03/26)
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- Mechanistic investigation of the Zn/Pd/C catalyzed cleavage and hydrodeoxygenation of lignin
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While current biorefinery processes use lignin only for its heat value, the conversion of lignin to high value chemicals is an area of increasing interest. Herein we present a detailed mechanistic study of the hydrodeoxygenation (HDO) of lignin by using a synergistic Pd/C and ZnII catalyst through use of both lignin model compounds and lignocellulosic biomass. Spectroscopic data coupled with the study of lignin model compounds suggest that ZnII activates and facilitates removal of the hydroxyl group at the Cγ position of the β-O-4 ether linkage. Activation is proposed to occur through formation of a six-membered ring complex of ZnII coordinated to the oxygen atoms at Cα and Cγ of the lignin model compound guaiacylglycerol-β-guaiacyl.
- Klein, Ian,Marcum, Christopher,Kentt?maa, Hilkka,Abu-Omar, Mahdi M.
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supporting information
p. 2399 - 2405
(2016/05/19)
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- Isolation of functionalized phenolic monomers through selective oxidation and CO bond cleavage of the β-O-4 linkages in Lignin
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Functionalized phenolic monomers have been generated and isolated from an organosolv lignin through a two-step depolymerization process. Chemoselective catalytic oxidation of β-O-4 linkages promoted by the DDQ/tBuONO/ O2 system was achieved in model compounds, including polymeric models and in real lignin. The oxidized β-O-4 linkages were then cleaved on reaction with zinc. Compared to many existing methods, this protocol, which can be achieved in one pot, is highly selective, giving rise to a simple mixture of products that can be readily purified to give pure compounds. The functionality present in these products makes them potentially valuable building blocks.
- Lancefield, Christopher S.,Ojo, O. Stephen,Tran, Fanny,Westwood, Nicholas J.
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supporting information
p. 258 - 262
(2015/02/19)
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- Catalytic conversion of biomass using solvents derived from lignin
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We report an approach by which the hemicellulose and cellulose fractions of biomass are converted through catalytic processes in a solvent prepared from lignin into high value platform chemicals and transportation fuels, namely furfural, 5-hydroxymethylfurfural, levulinic acid and γ-valerolactone. The Royal Society of Chemistry.
- Azadi, Pooya,Carrasquillo-Flores, Ronald,Pagan-Torres, Yomaira J.,Guerbuez, Elif I.,Farnood, Ramin,Dumesic, James A.
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supporting information
p. 1573 - 1576
(2013/02/23)
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