Biomass-derived lignin to jet fuel range hydrocarbons via aqueous phase hydrodeoxygenation

Article abstract of DOI:10.1039/c5gc01534k

A catalytic process, involving the hydrodeoxygenation (HDO) of dilute alkali extracted corn stover lignin catalysed by noble metal catalyst (Ru/Al₂O₃) and acidic zeolite (H⁺-Y), to produce lignin-substructure-based hydrocarbons (C₇-C₁₈), primarily C₁₂-C₁₈ cyclic structure hydrocarbons in the jet fuel range, was demonstrated.

Full text of DOI:10.1039/c5gc01534k

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Biomass-derived Lignin to Jet Fuel Range Hydrocarbons via
Aqueous Phase Hydrodeoxygenation
Received 00th January 20xx,
Accepted 00th January 20xx
Hongliang Wang,a Hao Ruan,a Haisheng Pei,a Huamin Wang,b Xiaowen Chen,c Melvin P. Tucker,c
John R. Cort,*b and Bin Yang*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
A catalytic process, involving the hydrodeoxygenation (HDO) of on the direct transformation of lignin-degraded oligomers, and
the dilute alkali extracted corn stover lignin catalysed by noble dimers to long chain hydrocarbons although these components
metal catalyst (Ru/Al2O3) and acidic zeolite (H+-Y), to produce represent a large portion of lignin-derived intermediates. The
lignin-substructure-based hydrocarbons (C7-C18), primarily C12-C18 predominant linkage between monomers in lignin is the C-O-C
cyclic structure hydrocarbons in the jet fuel range, was bond, which constitutes around two-thirds to three-quarters of the
demonstrated.
total linkages. Generally, C-O-C bonds have lower bond dissociation
energy (~ 218–314 kJ mol-1) than that of C-C single bonds (~ 384 kJ
Lignin, a main constituent of lignocellulosic biomass (15-30% by mol-1)11. Therefore, it is conceptually possible to selectively cleave
weight, 40% by energy), has a great potential in advanced biofuel C-O-C bonds in lignin without disrupting the C-C linkages under
production in view of its inherent phenylpropane-based structure.1 controlled reaction conditions. It was calculated that 30%~69% of
The current vision of biorefineries undervalues lignin’s potential to lignin would be released as dimers if C-O-C linkages in lignin were
address the world’s high quality liquid fuel requirements.2 Despite selectively cleaved without disrupting C-C bonds.9d, 12 HDO of these
the potential, selective conversion of lignin has proven to be lignin substructure-based dimers can directly generate
challenging, mainly due to the heterogeneous, non-hydrolyzable hydrocarbons in the jet fuel range from biomass (Scheme 1, route
cross-linked structure of lignin and the high reactivity of its II).
degradation intermediates.3 Several catalytic upgrading routes,3b, 4
In this study, the conversion of dilute alkali extracted corn
especially hydrodeoxygenation (HDO),5 have been extensively stover lignin into hydrocarbons with carbon numbers in the range
studied with the aim of producing fuel range hydrocarbons. Sulfided of 7~18 was achieved. A remarkable outcome of this approach is
CoMo and NiMo-based catalysts,6 as well as various supported the generation of relatively long chain alkyl cyclohexanes by
metal catalysts, such as Pt, Pd, Re, Rh, or Ru based catalysts,7 were retaining lignin substructures (e.g. dimers) and coupling of lignin-
previously used for lignin HDO conversion. Most HDO processes are derived monomers and smaller fragments including methyl groups.
accompanied by cleavages of both C-O-C and aliphatic C-C bonds in
lignin, which result in depolymerizing lignin to monomers that
generally contain 6-9 carbon atoms, which have a moderate value
8
in fuel usage.4a, Although long chain hydrocarbons could be
generated via coupling reactions of lignin-degraded monomers
(Scheme 1, route I),9 it requires additional specific catalysts and
processes that increase costs. In the process described here, long
chain hydrocarbons were produced by maintaining the aliphatic C-C
linkages but cleaving ether C-O linkages during HDO, using model
compounds as starting materials.9b,10 Less effort has been focused
Scheme 1 Proposed routes of depolymerization and Hydrodeoxygenation of
biomass-derived lignin to cyclic structure hydrocarbons
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standard. These products accounted for more than 50% of the total
integrated GC peak area for all the detected products derived from
lignin. The reaction products were found in three general groups:
aromatics, alkyl cyclohexanes, and linear alkanes. They can also be
divided into three different groups according to their carbon atom
numbers：C6~C11，C12~C18，and C>18
.
As shown in Figure 1 and Table 1 (entry 1), the products
catalysed by Ru/Al2O3 and H+-Y zeolite catalysts were mainly alkyl
cyclohexanes with carbon numbers ranging from 12 to 18. A small
fraction of aromatics and ring-opening products were also detected.
The total yield of the top 23~25 products was calculated to be
21.8 %, with the distributions of C12~C18 and alkyl cyclohexanes
being 84.6
% and 89.8 %, respectively. NMR spectroscopy
confirmed that the predominant class of lignin substructure in the
product mixture was alkyl cyclohexanes (Figure S1). In recent years,
various supported noble metals and their alloys were widely used in
aqueous phase reactions as effective non-sulfide-based HDO
Fig. 1 Product distribution of alkali lignin treated under HDO conditions
with Ru/Al2O3 and solid acid zeolite (H+-Y) at 250 °C. Each peak was
identified from the GC-MS library and peak areas were used to quantify the
products. Reaction conditions: alkali lignin 100 mg, solid acid zeolite 300 mg,
Ru/Al2O3 300 mg, water 30 mL, PH2 4MPa, 4 h, 250 °C.
catalysts for conversion of lignin based model phenolic substrates
9b, 10
to hydrocarbons.
However, our results show the existence of
characteristic structural features of biomass-derived lignin
hydrocarbons in C7–C18 jet fuel range through HDO conversion
process.
The NREL dilute alkali extracted corn stover lignin was generated
Two control experiments were carried out under identical HDO
conditions while using the Ru/Al2O3 and H+-Y acidic zeolite catalysts
separately. Results showed that lignin conversion and the total
product yield were relatively low (not exceeding 52% and 15%,
respectively) when both catalysts were applied individually (Table
1). The lignin conversion with H+-Y acidic zeolite was higher (52%)
than that found with Ru/Al2O3 (31%), showing that H+-Y acidic
zeolite was more efficient at depolymerizing the lignin polymer. The
products were also found to be different. The major products
resulting from catalysis with Ru/Al2O3 and acidic zeolite alone were
found to be monocyclic alkyl cyclohexanes and phenols,
respectively. These results clearly demonstrated that the combined
effects of Ru/Al2O3 and acidic zeolite enabled the conversion of the
alkali lignin to higher carbon number cyclohexanes in high yield.
Zeolite possesses high concentration of active acid sites, thus could
from
compositions and subsequent purification methods are described in
the supporting information section. high catalyst loading
a
pilot-scale dilute alkali deacetylation process.13 It’s
A
approach was applied in the heterogeneous solid-solid catalytic
HDO of lignin reactions in order to minimize mass transfer limits.5a,
9b, 13b, 14
In a typical reaction, 100 mg lignin, 300 mg acid zeolite (H+-
Y), 300 mg Ru/Al2O3, and 30 mL water were added into a 100 mL
Parr reactor and reacted at 250 °C under 4 MPa H2 for 4 hours.
After completion of the reaction, catalysts, together with the solid
residues, were separated from the liquid phase by centrifugation
and the organic products were extracted using ethyl acetate and
were characterized using gas chromatography-mass spectrometry
(GC-MS) and nuclear magnetic resonance (NMR).
More than 80 lignin HDO products were detected by GC-MS (Fig.
1). Among these products, the most significant 23~25 hydrocarbons
were identified and quantified using n-decane as an internal
Table 1. Hydrodeoxygenation of the alkali lignin under various conditions a
Reaction
Lignin
Product distribution (wt. %)
By chemical structure
Total
Yield
Entry
Catalyst (mg)
By carbon numbers
Temperature
Conversion
(%)
C6-11
C12-C18
C>18
Aromatics
Alkyl-
cyclohexane
89.79
Non-cycle
alkanes
6.18
(oC)
250
(wt.%) c
21.83
1
2
Ru/Al2O3+zeolite
Ru/Al2O3
81.03
30.84
10.48
63.66
84.60
31.76
4.92
4.58
4.03
9.61
250
250
200
220
280
79.10
2.02
11.29
7.81
9.83
3b
zeolites
52.11
45.98
67.56
92.73
34.08
27.85
23.04
3.31
46.57
65.47
75.01
70.41
19.35
6.68
90.17
16.64
5.72
13.66
10.64
13.29
12.25
4
Ru/Al2O3+zeolite
Ru/Al2O3+zeolite
Ru/Al2O3+zeolite
76.00
91.18
72.84
7.36
5
1.95
3.10
6
26.28
0.63
26.53
a Reaction conditions: alkali lignin100 mg, solid acid zeolite (H+-Y) 300 mg, Ru/Al2O3 300 mg, water 30mL, PH2 4MPa, 4 h, T=250 °C. b The main products were
found to be phenols with high oxygen content. c Refers to the total yield of the top 23~25 products.
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not only effectively depolymerize lignin into monomers and dimers
via hydrolysis of the C-O-C bonds, but also could couple the
monomers into dimers via alkylation or dimerization reactions.9a
Ruthenium-based catalysts, together with acidic zeolites, showed
promising synergistic activity and efficiency in the
hydrodeoxygenation reactions consistent with the conversion of
the monomer and dimer intermediates of lignin into cyclohexanes
via complete removal of oxygen groups and hydrogenation of the
aromatic rings observed in this study. 9a, 15
The molecular weight distribution of the alkali lignin was
calculated from the gel permeation chromatography (GPC) curves
based on pre-calibration with polystyrene standards. The alkali
lignin had a relatively broad MW distribution with apparent
estimated weight average (Mw) and number average (Mn)
molecular weights centered at 2590 Da and 1410 Da, respectively,
which were lower than that of ball-milled corn stover lignin
(typically >3850 Da).16 The corresponding polydispersity value
(Mw/Mn) of the alkali lignin was also found higher (1.84) than that
of ball-milled lignin (1.03) 13b, 17
a Reaction conditions: model compound 100 mg, solid acid zeolite (H+-Y) 300
mg, Ru/Al2O3:300 mg, water 30mL, PH2:4 MPa, t=4 h, T=250 °C
Two-dimensional heteronuclear single quantum coherence (2-
D1H-13C HSQC) NMR was used to elucidate the compositions and
structure of the alkali lignin, including different aromatic units and
inter-unit linkages (see supporting material Fig. S2). Results showed
the conservation of native mono-lignol components (G and S) with
abundance of cinnamyl alcohol end groups in the alkali lignin. The
ratios of the three aromatic units and the percentages of their inter-
unit linkages were calculated from the relative peak areas18 (Table
S2). Both the ball-milled lignin and alkali lignin were mainly
composed of S and G subunits, accounting for nearly 90% of the
total subunits found by NMR. However, the percentage of β-O-4
linkages in alkali lignin (43%) was lower than that in the ball-milled
lignin (58%), suggesting some β-O-4 linkages were cleaved during
the lignin extraction and purification processes. On the other hand,
β-5 linkages in the alkali lignin (44%) were found to be much higher
than that in ball-milled lignin (27%), indicating most of C-C bonds
remained stable.
that a small amount of rearrangement and C-C bond cleavage
occurred during the reaction. In addition, the total yield of all the
ring-opening products was approximately 1%, indicating the C-C
bonds in aromatic rings were less susceptible to cleavage. 2,2'-
biphenol, representing the 5-5' aryl-aryl linkages in lignin, was also
used as a substrate in the reaction. After HDO reaction, it was found
that not only the aromatic rings were saturated but also the
hydroxyl groups on the rings had been removed. The substrate was
converted to a bicyclohexane with high selectivity (83%). It further
demonstrates that the carbon skeleton structure of the starting
material could be preserved during the HDO catalysis process.
Results showed that HDO of dehydrodi-isoeugenol (Table 2, entries
3), which resembles phenylcoumaran linkages (β-5 linkage), led to
cleavage of C-O-C bonds, hydrogenation of aromatic rings and
removal of oxygen-containing groups, while leaving C-C bonds
mostly intact.
The reactivity and structural features of alkali lignin could be
considered as one of the key factors for selective production of the
obtained C12-C18 cyclohexanes.9d, 13b The β-5 structures in the alkali
lignin implied that dimers with C-C bond linkages could be released
after all the C-O-C bonds in lignin are cleaved, and then be ready to
be transformed into higher carbon number cycloalkanes that retain
some characteristics of the substructures of the original alkali lignin.
For example, 5-5' substructure of lignin can result in bi(cyclohexane)
derivative products; β-5 and β-1 substructures can be converted
into 1,2-dicyclohexylethane analogues; β-β substructures can form
1,4-dicyclohexylbutane. All these products were found in the
reaction shown in Figure 1.
The alkali lignin with lower molecular weight and higher ratios of
condensed structures (e.g. β-5) showed the tendency toward the
formation of higher carbon number alkyl cyclohexanes. Some of the
products, such as 1,5-dicyclohexylpentane and other cyclopentane
derivatives, did not have similar structures like the lignin-derived
dimers, implying that these products were not directly derived from
lignin substructures but required rearrangement, coupling, or
insertion reactions that presumably involved C-C bond formation
and cleavage. Guiacyl-(4-O-methyl)-beta-guiacylether (Table 2 entry
4) represents the key features of β-O-4 linkages encountered in
lignin. Its HDO products were much more complicated, including
various dicyclohexylalkanes and alkyl cyclohexanes. Almost all the
β-O-4 bonds were found cleaved after the reaction, suggesting that
this catalytic system could effectively break alkyl-aryl ether bonds.
More importantly, it was discovered that the majority of the
products were bicyclohexanes, which indicated that the coupling of
the monomers released from the cleavage of β-O-4 bonds occurred.
Results obtained from HDO of alkali lignin and model
compounds provided more insights in the lignin HDO process. First,
the most types of C-O-C bonds, especially the β-O-4 bond, were
To test this hypothesis, the mechanism of the HDO reaction was
explored using several lignin model compounds chosen to represent
C-C bonds (Table 2, entries 1−3) under the similar reacꢁon
conditions to the alkali-extracted lignin. Results showed high
selectivity (95.5%) for aromatic ring hydrogenation of 1,2-
diphenylethane to give the saturated product 1,2-
dicyclohexylethane with no C-C bond cleavage (Table 2, entry 1).
Bicyclohexane was detected as a minor product (3.4%), indicating
Table 2. Hydrodeoxygenation of lignin model compounds. a
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cleaved effectively either by hydrogenolysis over Ru/Al2O3 catalysis dimerization reactions to produce
a wide variety of alkyl
or by zeolite H+-Y hydrolysis, and the bulk lignin polymer structure cyclohexane species that are commonly found in jet fuel blend
was fragmented into lignin substructures based aromatic stocks. An advantage of this approach is that the carbon chain
monomers and dimers. Then, these monomers and dimers could substructures of lignin can be largely retained and new C-C bonds
undergo dehydration, demethoxylation, and hydrogenation can be also generated. Therefore, lignin-substructure-based C12-C18
reactions to remove oxygen and saturate the aromatic ring. During cyclohexanes are plausibly generated through the cleavage of C–O–
the oxygen removal and aromatic ring hydrogenation reactions, C bonds without disrupting the C–C linkages (β–β', β–5' and 5'–5'')
most of the C-C bonds remained stable and the carbon skeleton in the lignin structure and/or through coupling reactions of
structures of these products were largely unchanged. Moreover, degraded lignin monomer. The overall carbon yield was 38.3%
some of the monomers coupled to form dimers and some (Table S2). In addition, NMR spectroscopy revealed distributions of
methylation occurred presumably by methyl groups derived from aliphatic hydrocarbons rather than aromatic lignin intermediate
HDO of aryl methyl ethers. Thus, products obtained from HDO of structures in solid residues after product separation, indicating the
lignin were mainly alkyl cyclohexanes with 12~18 carbon atoms.
The resulting solid products residues were collected and
high efficiency of the HDO transformations.
analysed by 2-D HSQC NMR after dissolution in a DMSO solvent Acknowledgements
(Figure S3). The H and 13C chemical shifts suggest that the material
1
We are grateful to the DARPA Young Faculty Award # N66001-11-1-
is a saturated aliphatic hydrocarbon similar to the oil products
although it is probably solid and insoluble in ethyl acetate due to
polymerization. Additionally, the effects of reaction temperature on
alkali lignin conversion and product distribution were studied. As
shown in Table 1, the conversion of lignin was low at 200 °C, and a
relatively high portion of aromatics with carbon number ranging
from 6~12 was found in the oil products. Increasing the reaction
temperature significantly improved the lignin conversion.
Meanwhile, aromatic products, such as cresol and guaiacol, were
decreased and more cyclohexane derivatives with carbon number
between 12~18 were formed. However, the total calculated yield of
the products was found to decrease when the temperature was
raised to 280 °C. Meanwhile, more ring-opened products, mainly
linear alkanes, were detected at the higher reaction temperature
(280 °C). In order to better monitor the reaction, gases were
collected and analysed after the reaction. The main gas products
detected were CH4, CO and CO2. The total yield of these products at
250 °C was about 3.7 wt.%, and it increased significantly to 7.4 wt.%
when the reaction temperature increased to 280 °C, indicating that
higher reaction temperatures could promote C-C bond
hydrogenolysis reactions, thus resulting in low molecular weight
products. The carbon balance was calculated after analysing carbon
contents in oil, aqueous, solid and gas phases (Table S3). The
change of product distribution with reaction time was investigated
(Figure S5). Results suggested that C12~C18 cycloalkanes were the
dominant products at all stages of the HDO reactions.
414, The Sun Grant-DOT Award # T0013G-A- Task 8, the National
Science Foundation Award # 1258504, and National Renewable
Energy Laboratory for subcontract # XGB-2-22204-01 for funding
this research. Part of this work was conducted at the William R.
Wiley Environmental Molecular Sciences Laboratory (EMSL), a
national scientific user facility located at the Pacific Northwest
National Laboratory (PNNL) and sponsored by the Department of
Energy’s Office of Biological and Environmental Research (BER). B.
Yang thanks Dr. Hongfei Wang and Ms. Marie S. Swita for helpful
discussions.
Notes and references
[1] (a) A. J. Ragauskas, C. K. Williams, B. H. Davison, G. Britovsek, J.
Cairney, C. A. Eckert, W. J. Frederick, J. P. Hallett, D. J. Leak, C. L.
Liotta, J. R. Mielenz, R. Murphy, R. Templer and T. Tschaplinski,
Science, 2006, 311, 484; (b) W. Boerjan, J. Ralph and M. Baucher,
Annu. Rev. Plant Biol., 2003, 54, 519; (c) C. P. Xu, R. A. D. Arancon, J.
Labidi and R. Luque, Chem. Soc. Rev., 2014, 43, 7485; (d) A. J.
Ragauskas, G. T. Beckham, M. J. Biddy, R. Chandra, F. Chen, M. F.
Davis, B. H. Davison, R. A. Dixon, P. Gilna, M. Keller, P. Langan, A. K.
Naskar, J. N. Saddler, T. J. Tschaplinski, G. A. Tuskan and C. E. Wyman,
Science, 2014, 344, 709; (e) J. Zakzeski, P. C. A. Bruijnincx, A. L.
Jongerius and B. M. Weckhuysen, Chem. Rev., 2010, 110, 3552.
[2]
T. P. Vispute, H. Y. Zhang, A. Sanna, R. Xiao and G. W. Huber, Science,
2010, 330, 1222
[3]
(a) P. J. Deuss, M. Scott, F. Tran, N. J. Westwood, J. G. de Vries and K.
Barta, J. Am. Chem.Soc., 2015, 137, 7456; (b) P. Ferrini and R. Rinaldi,
Angew. Che. Int. Ed., 2014, 53, 8634; (c) X. Wang and R. Rinaldi,
Angew. Che. Int. Ed., 2013, 52, 11499.
[4]
[5]
(a) R. Ma, W. Y. Hao, X. L. Ma, Y. Tian and Y. D. Li, Angew. Che. Int. Ed.
2014, 53, 7310; (b) Alireza Rahimi, Arne Ulbrich, J. J. Coon and S. S.
Stahl, Nature, 2014, 515, 249; (c) X. Y. Wang and R. Rinaldi, Angew.
Che. Int. Ed., 2013, 52, 11499; (d) Q. Song, F. Wang, J. Y. Cai, Y. H.
Wang, J. J. Zhang, W. Q. Yu and J. Xu, Energy Environ. Sci., 2013, 6,
994; (e) D. D. Laskar, B. Yang, H. Wang and J. Lee, Biofuels Bioprod.
Bioref., 2013, 7, 602-626
(a) S. K. Singh and J. D. Ekhe, RSC. Adv., 2014, 4, 27971; (b) M. Saidi, F.
Samimi, D. Karimipourfard, T. Nimmanwudipong, B. C. Gates and M. R.
Rahimpour, Energy Environ. Sci., 2014, 7, 103; (c) T. H. Parsell, B. C.
Owen, I. Klein, T. M. Jarrell, C. L. Marcum, L. J. Haupert, L. M.
Amundson, H. I. Kenttämaa, F. Ribeiro and J. T. Miller, Chem.Sci.,
2013, 4, 806; (d) N. Yan, Y. A. Yuan, R. Dykeman, Y. A. Kou and P. J.
Dyson, Angew. Che. Int. Ed., 2010, 49, 5549; (e) Y. Hong, H. Zhang, J.
Sun, K. M. Ayman, A. J. Hensley, M. Gu, M. H. Engelhard, J.-S. McEwen
and Y. Wang, ACS Catal., 2014, 4, 3335; (f) J. Zhang, J. Teo, X. Chen, H.
Asakura, T. Tanaka, K. Teramura and N. Yan, ACS Catal., 2014, 4,1574.
Conclusions
Our results showed that characteristic structural features of
biomass-derived lignin permit conversion to C7–C18 jet fuel range
hydrocarbons through catalysis by noble metal catalyst (Ru/Al2O3)
and acidic zeolite (H+-Y). The H+-Y type of zeolites that possess
large-pore structure and contain high concentrations of active acid
sites could effectively disrupt the lignin polymer into oligomers via
selectively cleaving C-O-C bonds. Lignin deconstruction can also be
partially done on the metal catalyst. Ruthenium-supported Al2O3,
together with the H+-Y zeolite, showed promising activity and high
efficiency in HDO reactions, which could not only have a synergistic
effect on oxygen removal from lignin-degraded intermediates, but
also could couple the monomers into dimers via alkylation or
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[6]
(a) D. Meier, R. Ante and O. Faix, Bioresour. Technol., 1992, 40, 171;
(b) S. K. Singh and J. D. Ekhe, Catal. Sci. Technol., 2015, 5, 2117; (c) A.
Y. Bunch and U. S. Ozkan, J. Catal., 2002, 206, 177; (c) B. Yang and D.
D. Laskar, (Washington State University, USA). Application: WO, 2014,
p. 93pp.
[7]
(a) O. Jan, R. Marchand, L. C. Anjos, G. V. Seufitelli, E. Nikolla and F. L.
Resende, Energy Fuels, 2015, 29, 1793; (b) J. Yang, C. L. Williams, A.
Ramasubramaniam and P. J. Dauenhauer, Green Chem., 2014, 16,
675; (c) T. Omotoso, S. Boonyasuwat and S. P. Crossley, Green Chem.,
2014, 16, 645; (d) T. Parsell, S. Yohe, J. Degenstein, T. Jarrell, I. Klein, E.
Gencer, B. Hewetson, M. Hurt, J. Im Kim and H. Choudhari, Green
Chem., 2015, 17, 1492; (e) C. Michel and P. Gallezot, ACS Catal., 2015,
5, 4130.
[8]
[9]
(a) A. K. Deepa and P. L. Dhepe, ACS Catal., 2014, 5, 365; (b) J. A.
Onwudili, P. T. Williams, Green Chem., 2014; 16, 4740; (c) Z. Jiang, T.
He and J. Li, C. Hu, Green Chem., 2014, 16, 4257.
(a) J. S. Yoon, Y. Lee, J. Ryu, Y.-A. Kim, E. D. Park, J. W. Choi, J. M. Ha,
D. J. Suh and H. Lee, Appl. Catal. B-Environ., 2013, 142, 668; (b) C.
Zhao and J. A. Lercher, ChemCatChem, 2012, 4, 64-68; (c) J. He, L. Lu,
C. Zhao, D. Mei, J. A. Lercher, J Catal., 2014, 311, 41-51; (d) N. Yan, C.
Zhao, P. J. Dyson, C. Wang, L. t. Liu and Y. Kou, ChemSusChem, 2008, 1,
626; (e) P. Bi, J. Wang, Y. Zhang, P. Jiang, X. Wu, J. Liu, H. Xue, T. Wang
and Q. Li, Bioresour. Technol., 2015, 183, 10.
[10] W. Zhang, J. Chen, R. Liu, S. Wang, L. Chen and K. Li, ACS Sustain.
Chem. Eng., 2014, 2, 683.
[11] J. He, C. Zhao, D. Mei, J. A. Lercher, J.Catal., 2014, 309, 280.
[12] T. Kotake, H. Kawamoto and S. Saka, J. Anal. Appl. Pyrolysis, 2014, 105,
309.
[13] (a) X. Chen, J. Shekiro, M. A. Franden, W. Wang, M. Zhang, E. Kuhn, D.
K. Johnson and M. P. Tucker, Biotechnol. Biofuels, 2012, 5, 8; (b) D. D.
Laskar, M. P. Tucker, X. Chen, G. L. Helms and B. Yang, Green Chem.,
2014, 16, 897.
[14] K. Barta, T. D. Matson, M. L. Fettig, S. L. Scott, A. V. Iretskii and P. C.
Ford, Green Chem., 2010, 12, 1640.
[15] (a) J. Zhang, J. Teo, X. Chen, H. Asakura, T. Tanaka, K. Teramura and N.
Yan, ACS Catal., 2014, 4, 1574; (b) P. Tomkins, E. Gebauer-Henke, W.
Leitner and T. E. Mueller, ACS Catal., 2014, 5, 203; (c) J. Wildschut, M.
Iqbal, F. H. Mahfud, I. Melian-Cabrera, R. H. Venderbosch and H. J.
Heeres, Energy Environ. Sci., 2010, 3, 962.
[16] Z. Lin, H. Huang, H. Zhang, L. Zhang, L. Yan and J. Chen, Appl. Biochem.
Biotechnol., 2010, 162, 1872.
[17] P. Kaparaju and C. Felby, Bioresour. Technol., 2010, 101, 3175.
[18] (a) E. A. Capanema, M. Y. Balakshin, J. F. Kadla and J. Agric. Food
Chem., 2004, 52, 1850; (b) S. D. Mansfield, H. Kim, F. Lu and J. Ralph,
Nature Protoc. 2012, 7, 1579.
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