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Bond cleavage of lignin model compounds into aromatic monomers using supported metal catalysts in supercritical water

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ABSTRACT

More efficient use of lignin carbon is necessary for carbon-efficient utilization of lignocellulosic biomass. Conversion of lignin into valuable aromatic compounds requires the cleavage of C–O ether bonds and C–C bonds between lignin monomer units. The catalytic cleavage of C–O bonds is still challenging, and cleavage of C–C bonds is even more difficult. Here, we report cleavage of the aromatic C–O bonds in lignin model compounds using supported metal catalysts in supercritical water without adding hydrogen gas and without causing hydrogenation of the aromatic rings. The cleavage of the C–C bond in bibenzyl was also achieved with Rh/C as a catalyst. Use of this technique may greatly facilitate the conversion of lignin into valuable aromatic compounds.

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Product yield from bibenzyl after treatment for 1 h in supercritical water at 673 K and a water density of 0.5 g cm−3 with Pd/C, Pt/C, Rh/C, or Ru/C as a catalyst or with no catalyst.
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f6: Product yield from bibenzyl after treatment for 1 h in supercritical water at 673 K and a water density of 0.5 g cm−3 with Pd/C, Pt/C, Rh/C, or Ru/C as a catalyst or with no catalyst.

Mentions: The results of ethylbenzene decomposition indicated that the C–C bond could be cleaved using either Rh/C or Pt/C as a catalyst; we thus attempted to cleave the C–C bond of bibenzyl, a model lignin compound, using the supported metal catalysts in supercritical water (Fig. 6). Surprisingly, toluene and benzene could be obtained from bibenzyl using Rh/C, the indication being that the C–C bond in bibenzyl was cleaved. Cleavage of the C–C bonds in the linkages between the aromatic monomers of a model lignin compound has not been reported; this result can therefore open a new pathway for lignin decomposition research. Phenanthrene was obtained from bibenzyl, especially when Pt/C was the catalyst (Fig. 6), the indication being that Pt/C was an excellent catalyst for the dehydrogenation reaction. The Pd/C catalyst only slowly catalyzed the cleavage of the C–C bond in bibenzyl, the indication being that the species of metal was an important determinant of the behavior of lignin during its decomposition in supercritical water.


Bond cleavage of lignin model compounds into aromatic monomers using supported metal catalysts in supercritical water
Product yield from bibenzyl after treatment for 1 h in supercritical water at 673 K and a water density of 0.5 g cm−3 with Pd/C, Pt/C, Rh/C, or Ru/C as a catalyst or with no catalyst.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384005&req=5

f6: Product yield from bibenzyl after treatment for 1 h in supercritical water at 673 K and a water density of 0.5 g cm−3 with Pd/C, Pt/C, Rh/C, or Ru/C as a catalyst or with no catalyst.
Mentions: The results of ethylbenzene decomposition indicated that the C–C bond could be cleaved using either Rh/C or Pt/C as a catalyst; we thus attempted to cleave the C–C bond of bibenzyl, a model lignin compound, using the supported metal catalysts in supercritical water (Fig. 6). Surprisingly, toluene and benzene could be obtained from bibenzyl using Rh/C, the indication being that the C–C bond in bibenzyl was cleaved. Cleavage of the C–C bonds in the linkages between the aromatic monomers of a model lignin compound has not been reported; this result can therefore open a new pathway for lignin decomposition research. Phenanthrene was obtained from bibenzyl, especially when Pt/C was the catalyst (Fig. 6), the indication being that Pt/C was an excellent catalyst for the dehydrogenation reaction. The Pd/C catalyst only slowly catalyzed the cleavage of the C–C bond in bibenzyl, the indication being that the species of metal was an important determinant of the behavior of lignin during its decomposition in supercritical water.

View Article: PubMed Central - PubMed

ABSTRACT

More efficient use of lignin carbon is necessary for carbon-efficient utilization of lignocellulosic biomass. Conversion of lignin into valuable aromatic compounds requires the cleavage of C–O ether bonds and C–C bonds between lignin monomer units. The catalytic cleavage of C–O bonds is still challenging, and cleavage of C–C bonds is even more difficult. Here, we report cleavage of the aromatic C–O bonds in lignin model compounds using supported metal catalysts in supercritical water without adding hydrogen gas and without causing hydrogenation of the aromatic rings. The cleavage of the C–C bond in bibenzyl was also achieved with Rh/C as a catalyst. Use of this technique may greatly facilitate the conversion of lignin into valuable aromatic compounds.

No MeSH data available.