Tungsten-Based Bimetallic Catalysts for Selective Cleavage of Lignin C?O Bonds

Article abstract of DOI:10.1002/cctc.201701240

Tungsten-based bimetallic catalysts M–W/AC (M=Ru, Pt, and Pd; AC=activated carbon) exhibited high activity and selectivity in the hydrogenolysis of typical α-O-4 model compounds and deconstruction of lignin feedstock for the production of aromatic chemicals. Synergy effect was observed between tungsten and noble-metal species, which on the one hand modulated the hydrogenolysis activity of tungsten and improved the activity of catalyst, and on the other hand suppressed overhydrogenation that avoided the formation of cycloalkanes. The conversion of α-O-4 model compounds with different substituents showed that electronic effects play an important role in stabilizing the reaction intermediates, and the electron-donating methoxy group on the aromatic ring accelerated the hydrogenolysis efficiency. Solvent effect was another factor that determined hydrogenolysis efficiency; dipolar aprotic solvents such as n-hexane provided the high yields of target aromatics. In the conversion of realistic lignins, the bimetallic catalyst showed excellent activity not only in α-O-4 cleavage but also in the hydrogenolysis of other major linkages such as β-O-4 and β?β between aromatic units, so that a high yield of liquid oil was obtained from lignin.

Full text of DOI:10.1002/cctc.201701240

Accepted Article
Title: Tungsten-based Bimetallic Catalysts for Selective Cleavage of
Lignin C-O Bonds
Authors: changzhi li, jianwei ji, Haiwei Guo, Zaojuan Qi, Bo Zhang, Tao
Dai, Min Jiang, Chuanqing Ren, Aiqin Wang, and tao zhang
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201701240
Link to VoR: http://dx.doi.org/10.1002/cctc.201701240
A Journal of
www.chemcatchem.org

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
Tungsten-based Bimetallic Catalysts for Selective Cleavage of
Lignin C-O Bonds
Jianwei Ji,[a, b] Haiwei Guo,[a, c] Changzhi Li,*[a] Zaojuan Qi,[a,d] Bo Zhang,[a] Tao Dai,[a, c] Min Jiang,[b]
Chuanqing Ren,[b] Aiqin Wang [a] and Tao Zhang*[a]
Abstract: In this paper, tungsten based bimetallic catalysts M–W/AC
(M = Ru, Pt and Pd) exhibited high activity and selectivity in the
hydrogenolysis of typical α-O-4 model compounds and
deconstruction of lignin feedstock for the production of aromatic
chemicals. Synergy effect was observed between tungsten and
noble metal species, which on the one hand modulated the
hydrogenolysis activity of tungsten and improved the active of
catalyst, on the other hand suppressed over-hydrogenation that
avoided the formation of cycloalkanes. The conversion of α-O-4
model compounds with different substituents showed that electronic
effects played an important role in stabilizing the reaction
intermediates and electron-donating methoxy group on aromatic ring
accelerated the hydrogenolysis efficiency. Solvent effect was
another factor that determined hydrogenolysis efficiency; dipolar
aprotic solvents such as n-hexane provided the high yields of target
aromatics. In the conversion of realistic lignins, the bimetallic catalyst
showed excellent activity not only in α-O-4 cleavage but also in the
hydrogenolysis of other major linkages such as β-O-4 and β-β
between aromatic units, so that high yield of liquid oil was obtained
from lignin.
Among the various reported strategies for chemical
disassembly of lignin,[4] one of the most popular approach is
hydrocracking using supported noble metal catalysts under high
temperature and high hydrogen pressure.[5] While promising, the
high activity of noble metal along with harsh reaction condition
leads to undesired concurrent hydrogenation of aromatic rings
and typically affords a mixture of low depolymerized lignin
products, phenols, cyclanes and some other repolymerization
products.[3a, 3b] To deal with the above problems, we recently
developed a method for the chemoselective C-O cleavage of
typical β-O-4 model compounds and deconstruction of lignin
feedstock over tungsten carbide catalyst in virtue of its platinum-
like catalytic behavior.[6] Though this non-noble metal catalyst
shows high activity in β-O-4 cleavage, owing to the relatively low
hydrogenation ability, it exhibits very poor performance in
activating α-O-4 and other linkages. Therefore, new catalyst with
higher activity for the selective cleavage of the stubborn aryl C-O
bonds such as α-O-4 is highly desirable.
In comparison with the monometallic catalyst, the use of
bimetallic catalyst offers the possibility to modify the catalyst
property and tailor the selectivity to a particular product.[7]
6b]
Building on our previous progress[6a,
that tungsten-based
catalysts have the ability to keep the aromaticity of feeds intact,
herein, we prepare a series of tungsten-based bimetallic
Introduction
catalysts, M–W/AC (M
= Ru, Pt and Pd) for selective
Harvesting chemicals from renewable feedstocks attracts
increasing attention due to the oil depletion and ecological
environment deterioration.[1] Lignin is an amorphous
tridimensional polymer of three primary units, namely, syringyl
(S), guaiacyl (G), and p-hydroxyphenyl (H) units, as well as
some noncanonical subunits joined by ether and C−C linkages.[2]
It is by far the most abundant renewable source composed of
aromatic units in nature, the chemical structure renders it a
sustainable candidate feedstock for aromatic chemicals.
However, due to the carbon-based inactive property and highly
heterogeneous nature of amorphous structure, it is big challenge
for the selectively conversion of lignin to a spectrum of aromatic
compounds.[3]
hydrogenolysis of the C-O bonds in α-O-4 lignin model
compounds. Clear synergy effect is observed between tungsten
and noble metal species, which significantly improved the yields
of the target aromatic chemicals. More importantly, the catalysts
possess good stability and can be applied in the catalytic
conversion of realistic lignin to afford aromatic liquid oil with the
yield up to 66.7%.
Results and Discussion
Preliminary study with α-O-4 model compound
Benzyl phenyl ether (BPE), a typical lignin model compound with
α-O-4 linkage, was initially selected to explore the activity of
monometallic and tungsten-based bimetallic catalysts for the
cleavage of C-O bonds. The reactions were typically conducted
in n-hexane under 0.7 MPa H2 at 260 °C for 10 h. Table 1 shows
that toluene and phenol are major products in all trials according
to GC-FID analysis. W/AC alone provided low yields of toluene
(40.3%) and phenol (33.8%) with BPE conversion of 79.5%
(entry 1). In virtue of the high intrinsic activity in hydrogenation
reaction, Ru/C (1wt%) afforded higher conversion of 94.2% with
toluene and phenol yields of 81.4% and 48.6% (entry 2); in
addition, aromatic ring overhydrogenation product cyclohexanol
was detected with the yield of 3.7%. In comparison, upon
performing the reaction using bimetallic Ru-W/AC catalyst, BPE
[a]
Dr. J. Ji, Dr. C. Li, H. Guo, Z.Qi, Dr. B. Zhang, T. Dai, Prof. A. Wang,
Prof. T. Zhang
State Key Laboratory of Catalysis, Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, Dalian 116023, China
E-mail: licz@dicp.ac.cn (C. Li), taozhang@dicp.ac.cn (T. Zhang)
Dr. J. Ji, M. Jiang, C. Ren
Shaanxi Key Laboratory of Catalysis, School of Chemical and
Environment science, Shaanxi University of Technology, Hanzhong
723001, China
[b]
[c]
[d]
H. Guo, T. Dai
University of Chinese Academy of Sciences, Beijing, 100049, China
Z. Qi
College of Chemistry, Xiangtan University, Xiangtan, Hunan,
411105, China.
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
was nearly completely consumed under the same condition and
afforded toluene and phenol in yields up to 92.6% and 61.5%,
respectively (entry 8). Interestingly, no cyclohexanol was formed
in Ru-W/AC catalyzed reaction. Apparently, higher BPE
conversion towards toluene and phenol formation was realized
over bimetallic catalysts as comparison to the reactions over
monometallic catalysts Ru/AC and W/AC, implying synergistic
effect exists between W and Ru in this reaction. In a like manner,
Pt-W/AC in contrast to Pt/AC and W/AC, gave improved BPE
conversion and higher yields of toluene and phenol without any
overhydrogenation product (entry 4 vs 1, 3). Specifically,
monometallic catalyst Pd/AC showed activity strong enough to
cleave α-O-4 linkage with the conversion of 99.7% and toluene
yield of 89%, however, cyclohexanol with the yield of 36.5% was
obtained instead of phenol, suggesting the significant
overhydrogenation of aromatic ring occurred (entry 5). To our
pleasant surprise, Pd-W/AC increased the yields of toluene and
phenol to 100% and 29.0%, respectively; equally important,
cyclohexanol yield distinctly decreased to 0.4% (entry 6).
Therefore, synergistic effect that target to aromatic products also
appeared in Pd-W/AC. In all the trails, it was found that the yield
of toluene was in excess of the yield of phenol. To explore the
reason, reaction using phenol as the substrate was conducted
under the condition of entry 5, phenol conversion of 26% with
benzene and diphenyl ether yields of 13% and 5%, respectively,
were detected (Figure S2). We therefore tentatively attributed
the lower yield of phenol to the side reactions of
hydrodeoxygenation and radical-induced polymerization.
Figure 2. Effect of the H2 pressure. Reaction conditions: BPE 100 mg, 1%Ru-
30%W/AC 20 mg, 260 oC, n-hexane 30 mL, 10 h.
the suitable ratio of Ru/W may play an important role in
improving the activity of the hydrogenolysis reaction in addition
to minimizing side reactions such as repolymerization of active
intermediate, and 1%Ru-30%W/AC emerged as the best choice.
Optimization of the reaction conditions showed that the
catalytic activity and the selectivity of the products highly
depended on the reaction temperature. As illustrated in Figure 1,
o
low temperature of 200 C could not activate C-O bond in BPE,
and no conversion was detected. Upon increasing the reaction
temperature to 220 oC, 240 oC and 260 oC, not only the
corresponding conversion of BPE, but also the selectivity of the
products increased sharply. For instance, the substrate was
nearly completely consumed at 260 oC and afforded toluene and
phenol in yields up to 92.6 and 61.4%, respectively, suggesting
that Ru-W/AC catalyzed C-O bond cleavage is a thermodynamic
controlling reaction[8], and the reaction temperature was one of
the key factors that controlling the overall rate. Taking economy
and energy consumption into consideration, 260 °C was
selected as the suitable reaction temperature.
The different loading amounts of Ru species in Ru-W/AC were
evaluated to optimize reaction performance. As shown in Table
1, Ru loading of 0.5% was sufficient for the transformation of
BPE (entry 7), when Ru loading was increased to 1% (entry 8),
the conversion of BPE showed no clear difference (>99.0%),
however higher selectivity on toluene and phenol was achieved.
Further increase Ru loading to 2% and 5% did not improve the
selectivity to the target products (entries 9-10), indicating that
The effect of hydrogen pressure on the conversion efficiency
was also explored. Figure 2 shows the products distribution
under different hydrogen pressures (0-1.5 MPa) keeping other
parameters constant. It was found that the conversion of the
substrate was almost unchanged (>97.0%), while the yields of
the products were different to a certain extent. Reaction without
any hydrogen afforded the yields of toluene and phenol 65.9%
and 47.1%, respectively. The presence of 0.1 MPa hydrogen
gas remarkably improved the yields of both products to 80.4%
and 61.9%, respectively; increasing hydrogen pressure to 0.7
MPa smoothly enhanced toluene yield to 92.6% with unchanged
phenol yield. However, further increasing hydrogen pressure to
1.5 MPa led to a slight decrease in both toluene and phenol,
which was probably due to over hydrogenation of the
products.[3b] Another possible reason is that the high coverage of
hydrogen on catalyst surface inhibiting the adsorption of the
substrate.[9]
Figure 1. Effect of the reaction temperature. Reaction conditions: BPE 100 mg,
1%Ru-30%W/AC 20 mg, H2 0.7 MPa, n-hexane 30 mL, 10 h.
Solvent effect on the conversion of BPE
This article is protected by copyright. All rights reserved.

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
Table 1. Cleavage of the α-O-4 linkage in BPE over different catalysts.[a]
Product Yields (%)[b]
Cyclohexanol
Conv. (%)b
Entry
Catalyst
Toluene
40.3
Phenol
33.8
2-benzylphenol
4-benzylphenol
1.2
30%W/AC
79.5
94.2
89.2
98.9
99.7
100
---
4.7
0.7
0.1
3.0
---
1
2
3
4
5
6
7
8
9
10
1%Ru/AC
81.4
60.5
82.4
89.0
100
48.6
36.5
50.6
0
3.7
0.9
---
---
1%Pt/AC
---
1%Pt-30%W/AC
1%Pd/AC
0.6
---
36.5
0.4
---
1%Pd-30%W/AC
0.5%Ru-30%W/AC
1%Ru-30%W/AC
2%Ru-30%W/AC
5%Ru-30%W/AC
29.0
52.9
61.5
56.0
49.8
---
---
99.1
99.7
99.1
99.2
79.7
92.6
90.5
82.3
3.3
3.2
3.0
1.5
0.7
0.6
0.6
0.1
---
---
---
[a] Unless otherwise specified, the reaction conditions were: a stainless-steel autoclave was charged with the substrate (100 mg), catalyst (20 mg), and n-hexane
(30 mL), and the vessel was pressurized with H2 (0.7 MPa) and then reacting at 260 oC for 10 h. [b] The conversion of BPE and yields of the products were
determined by GC-FID with mesitylene as an internal standard.
Table 2 reveals that the reaction performance depends heavily
on the nature of the solvent for Ru-W/AC-catalyzed BPE.
Moderate to poor conversions (entries 1-3) were obtained in
methanol (5.9%), 1,4-dioxane (43.6%) and THF (36.7%).
It is interesting to find that better results were achieved in
isopropanol (conversion of 62.7% with the yields of toluene and
phenol 55.7% and 41.3%, respectively) than above three
mentioned solvents (entry 4 vs entries 1-3). Besides, 1.5%
cyclohexanol was detected as a byproduct in the reaction
mixture, yet this byproduct was not found in other solvents.
The results are reasonable noting that isopropanol is an
excellent hydrogen-donor solvent that can in-situ supply active
hydrogen via H transfer from the solvent to the substrate.[10]
Notably, dipolar aprotic solvents such as n-hexane and
cyclohexane afforded best conversions over 90% with toluene
yields higher than 90% and phenol yields higher than 55%
(entries 5-6). Unlike aforementioned four solvents, alkanes show
no Lewis basicity, hence the strong interaction with Ru-W/AC is
not exist in such kind of solvents; moreover, n-hexane and
cyclohexane are not hydrogen-donor solvent, which thus avoids
Byproducts
diphenylmethane,
including
2-benzylphenol,
1,2-diphenylethane,
4-benzylphenol,
1-benzyl-4-
methylbenzene (Figure S1 in Supporting Information) were
detected. The relatively lower performance might due to the high
Lewis basicity of the solvents[10] which established a strong
interaction with Ru-W/AC. This surface interaction may reduce
the catalytic activity towards hydrogenolysis of C-O bonds.[10] In
addition, after reaction, the clear liquid mixture turned black,
suggesting that part of the intermediates, such as phenyl and
benzoxy radicals, converted into insoluble products by
polymerization.[11]
Table 2. Ru-W/AC-catalyzed BPE in different solvents.[a]
Product Yields (%)
Entry
Solvent
Conv. (%)
Toluene
Phenol
Cyclohexanol
2-benzylphenol
4-benzylphenol
1
2
3
4
5
6
Methanol
1,4 -Dioxane
THF
Isopropanol
n-Hexane
Cyclohexane
5.9
9.7
7.8
--
--
--
1.5
--
0.2
0.8
0.2
0.1
3.2
3.0
0.3
0.3
0
--
0.6
0.7
43.6
36.7
62.7
99.7
92.0
35.7
26.3
55.7
92.6
91.7
29.8
19.9
41.3
61.5
55.6
--
[a] Reaction conditions: unless otherwise specified, a stainless-steel autoclave was charged with the substrate (100 mg), 1%Ru-30%W/AC (20 mg), and solvent
(30 mL), and the reactions were conducted under an atmosphere of H2 (0.7 MPa) at 260 oC for 10 h.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
over-hydrogenation of aromatic ring. These features make n-
hexane and cyclohexane excellent solvents for Ru-W/AC
catalyzed hydrogenolysis of BPE.[4a, 10]
The reusability of the Ru–W/AC catalyst for the hydrogenolysis
of BPE was investigated. After the reaction was completed, the
catalyst was collected by simple filtration and was directly used
in the next cycle. As show in Figure 3, the conversion over the
catalyst maintained at 99.7% even in the fourth recycle; in
parallel, the selectivity pattern of the products was also without
notable change over the fourth recycle. STEM spectra and the
corresponding elemental mapping of the fresh catalyst showed
that both Ru and W atoms exist on the surface of the carbon
support and that they are evenly distributed on the support
(Figure S3). XRD patterns of the fresh and used catalysts
suggested that no obvious peaks of RuO2 and WOx were
observed for both catalysts (Figure S4), indicating that
ruthenium and tungsten was still highly dispersed on AC after
used four times. The results suggested that the stability of Ru–
W/AC catalyst was much better than that of W2C/AC alone[6b]
for liquid phase reactions.
Conversion of various lignin α-O-4 model compounds
To explore the scope of the application of Ru-W/AC catalyst,
aseries of BPE analogues with different substituents in the R1,
R2, and R3 positions (Table 3) were employed as the
substrates for the cleavage of α-O-4 bonds under the optimized
conditions. Asshown in Table 3, toluene and phenol derivatives
were the dominant products in all cases, which suggested that
aryl C-O bonds of the substrates were selectively cleaved and
the aryl rings were left intact in the products. The conversions
of all the substrates were higher than 99% in our reaction
system; however, the yields of the aromatics varied. The
substrates with electron-withdrawing hydroxyl substitution in R1
and R2 positions (substrates 2-3) resulted in distinctly poorer
yields than substrate 1 without any hydroxyl group; particularly
for substrate 2, the strong ortho-conjugative effect of hydroxyl
substitution resulted in the lowest yields of the target products,
whereas hydroxyl group in meta-position (substrate 3)
possesses no conjugative effect and the activity did not
decrease too much. The results also suggested that an
electron-donating methoxy group in R3 position accelerated the
hydrogenolysis efficiency of the substrate, which provided the
highest total yields of the target products (substrate 4). As
radical
mechanism plays an important role in the
transformation of lignin to functionalized aromatics, especially in
oxidative treatment and reducing reactions of lignin.[2, 11] It is
therefore logical that electron-donating methoxy group could
stabilize reaction intermediates and thus improve the
conversion efficiency. Taken together, Ru-W/AC in n-hexane
showed excellent activity in the cleavage of various α-O-4
linkages, and electronic effects played an important role in
determination of the reaction performance.
Figure 3. Recycle results of 1%Ru-30%W/AC in the conversion of BPE.
Reaction condition: BPE 100 mg, catalyst 20 mg, n-hexane 30 mL, H2 0.7
MPa, 260 oC, 10 h.
Table 3. Ru-W/AC-catalyzed C-O bond cleavage of various lignin α-O-4
model compounds.[a]
Conversion of realistic lignin feedstock
The excellent results obtained with the model compounds
encouraged us to apply the methodology to the conversion of
realistic lignin feedstock. Noting that the structure of
organolsolv lignin is close to natural lignin,[2] the organosolv
lignins from different plant botanical species of poplar
(hardwood), pinewood (softwood), and corn stalk (grass) were
selected as the substrates to be depolymerized by Ru-W/AC,
with the aim to explore the versatility of the catalyst.
Product yiled (%)
Con. (%)
Substrate
R1
R2
R3
B
A
1
2
3
4
H
OH
H
H
H
OH
H
H
H
H
OCH3
99.7
100
100
100
92.7
29.5
72.6
82.9
61.5
18.6
34.2
93.6
H
Table S1 illustrates the yields of the phenolic oils and the
monomer components of the oils. All organosolv lignins can be
effectively converted into aromatic liquid oils with the high yields
varying from 42.7 to 66.7 wt%. GC-MS characterization
suggested that no cycloalkane was detected in all the liquid oils,
implying that the catalyst is highly selective in activating the aryl
C-O bonds of isolated lignins. However, the oil yield from corn
stalk is higher than that from pinewood lignin and poplar lignin,
due to the looser structure, larger surface area and lower
[a] Reaction conditions: a stainless-steel autoclave was charged with the
substrate (100 mg), 1%Ru-30%W/AC (20 mg), and n-hexane (30 mL); the
reactions were conducted under an atmosphere of H2 (0.7 MPa) at 260 oC for
10 h.
Catalyst stability
This article is protected by copyright. All rights reserved.

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
molecular weight of corn stalk lignin (Table S2, GPC results)
that probably caused by its shorter growth period.[6b]
Additionally, inherent variability in the chemical composition of
different lignin resources may also result in the different oil
yields.
Regarding the monomer composition, the lignins fractionated
from poplar, pinewood, and corn stalk yielded a broad variety of
phenolic compounds, being 2,6-dimethoxyphenol, 4-ethyl-2-
methoxyphenol, 2-methoxy-4-(propenyl)phenol, 4-(2-
a. Side chain region
b. Aromatic region
c. Side chain region
d. Aromatic region
Figure 4. (a, b) 2D-HSQC-NMR spectra of organosolv poplar lignin in DMSO-d6/pyridine-d5 (4:1 v/v) before the reaction, and (c, d) poplar lignin oil.
hydroxyethyl)-2-methoxyphenol, 4-methoxyphenol and phenol,
as well as 4-ethylphenol the main products (Table S1), which
are derived from the lignin G, S and H primary units. Besides, a
which was much different from that in lignin material (0:98:2)
according to 2D-HSQC-NMR characterization (Figure S6b).
Similar phenomenon occurred on poplar lignin oil, G and H
units content increased from 34.1% to 41.3%, and 1.6% to
35.6%, respectively; while S units decreased from 64.3% to
23.1% in poplar bio-oil (Figure 4d vs Figure 4b). For the liquid
oil of corn stalk lignin, S:G:H molar ratio (32:52:16, Figure S6h)
was also different to the lignin material (59:40:1, Figure S6f).
Above results confirmed that different lignins exhibited various
activities in releasing different types of aromatic units, which
may due to their inherent structure difference, e.g. type and
amount of the linkages along with different primary units.
dramatically
higher
amount
of
oxydibenzene,
(benzyloxy)benzene, 2-(benzyloxy)phenol dipolymers were
detected in the liquid oils.
Typically, poplar lignin (hardwood lignin) belongs to type G–S
lignin, which comprises a mixture of S and G units along with a
trace amount of the H unit, pinewood lignin (softwood lignin)
essentially consists of G units, grass lignin is made up of H, G,
and S units. It is interesting to find that the bio-oil of pinewood
lignin provides S:G:H molar ratio of 36:50:14 (Figure S6d),
This article is protected by copyright. All rights reserved.

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
recorded with a PW3040/60 X’Pert PRO (PANalytical) diffractometer
equipped with a CuK a radiation source (l=0.15432 nm). STEM-EDX
analysis was performed on a JEM-2100F (JEOL) microscope with the
acceleration voltage of 200 kV. Detailed synthesis procedures and
characterization methods as well as supporting figures are provided in
the Supporting Information. 2D-HSQC spectra were recorded on a
Bruker AVAVCE III HD 700 MHz spectrometer at 25 oC. For
heteronuclear single quantum coherence (HSQC) spectra, the Bruker
standard pulse program hsqcetgpsi was used for HSQC experiments.
50 mg lignin was dissolved in 0.5 mL d6-DMSO and solvent peak was
used as internal reference.
In order to better estimate the structure change of the lignins
before and after reaction, 2D-HSQC-NMR spectra of poplar
lignin and corresponding oil products were deeply compared.
Figure 4a and 4c illustrate the side chain region of the lignin
and its liquid oil. It was found that cross signals of methoxyls
(OMe at δC/H = 55.85/4.07 ppm) and β-O-4 aryl ether (The Cα–
Hα, Cβ–Hβ, and Cγ–Hγ correlations in structure A (50.1%) were
observed at δC/H=72.57/5.67, 86.6/4.88, and 60.3/4.32 ppm,
respectively) were the dominant linkages in poplar lignin. In
addition, a small amount of β-5/α-O-4 linkages (resinol structure
B 13.7%) was observed with Cα–Hα, Cβ–Hβ, and Cγ–Hγ
correlations at δC/H=87.13/6.19, 53.38/4.19, and 63.32/4.38
ppm, respectively, whereas signals from phenylcoumaran (β-β,
Structure C 36.2%) were observed with Cα–Hα, Cβ–Hβ, and
double Cγ–Hγ correlations at δC/H=85.74/5.32, 54.23/3.72,
71.44/4.47, and 71.44/4.83 ppm, respectively. After reaction,
most A, B, C linkages of poplar lignin disappeared in the side-
chain region of the oil (Figure 4c), indicating that the three
major linkages of A, B, and C are attacked by the Ru-W/AC
catalyst. Similar results were obtained in the transformation of
pinewood lignin (Figure S6a vs Figure S6c) and corn stalk lignin
(Figure S6e vs Figure S6g). Taken together, Ru-W/AC catalyst
shows high activity not only in α-O-4 cleavage but also in the
cleavage of β-O-4 and β-β linkages of different lignins. It should
be noted that no cycloalkane was detected in the three types of
liquid oil, which further identified that Ru-W/AC is highly
selective in the activation aryl C-O bonds in lignin without
destroying aromatic ring.
Lignin Extraction. All lignins were prepared as described in our
previous literature.[6a] In short, the organosolv lignin was extracted as
follow: the sawdust (40 mesh) was treated with an ethanol-water
(7:3/v:v) mixture in 200 oC for 2 h. The solid: liquid ratio used was 1:6
(g/g) and held constant for all experiments. When the reaction was
stopped, the reactor was cooled to room temperature. The solid fraction
was separated by vacuum filtration from the liquid fraction. The liquid
fraction was treated to precipitate the lignin: two volumes of acidified
water (pH around 2) were added to a known volume of liquid fraction in
order to precipitate the lignin. The precipitated lignin was then separated
by filtration and was heated at 50 oC overnight for vacuum dryness.
Typical procedure for C-O cleavage of lignin model compounds.
The catalytic conversion of lignin model compound was performed in a
stainless-steel autoclave (Parr, 100 mL) with an initial H2 pressure of 0.7
MPa. Typically, the stainless-steel autoclave was charged with the lignin
model compound (100 mg), catalyst (20 mg), and n-hexane (30 mL),
and the autoclave was then charged with an initial H2 pressure of 0.7
MPa; the mixture was stirred (750 rpm) at 260 oC for 10 h. After the
reaction, the mixture was cooled to room temperature and filtered. The
liquid phase was analyzed by GC-FID and was quantified by the internal
standard method (standard: mesitylene, HP-5 column, 30 m×0.32
mm×0.25 μm).
Conclusions
In summary, we have developed a highly active and stable
catalytic system based on tungsten-based bimetallic catalysts
(M-W/AC, M = Ru, Pt and Pd) for selective hydrogenolysis of
various lignin α-O-4 model compounds and organosolv lignin
materials into monophenols and aromatic liquid oils. The
combination of noble metal species with W can on the one
hand modulate the hydrogenolysis activity of W and help to
improve the activity of the catalyst, on the other hand suppress
over-hydrogenation that avoid the formation of cycloalkanes.
Our results showed that tungsten-based bimetallic catalysts
showed excellent activity not only in α-O-4 cleavage but also in
the hydrogenolysis of various side-chain linkages in lignin.
Besides, this catalyst could be reused four times without
significant loss in activity. Therefore, this process might become
a highly promising route for selective hydrogenolysis lignin into
small molecules that can be further upgraded into fuel or high-
value chemicals.
Typical procedure for the Ru-W/AC-catalyzed depolymerization of
lignin feedstock. The catalytic conversion of lignin material was
performed in a stainless-steel autoclave (Parr, 100 mL) with an initial H2
pressure of 0.7 MPa and 260 oC for 10 h. Typically, the autoclave was
charged with lignin (100 mg), catalyst (20 mg), and methanol (30 mL),
and the mixture was stirred at a rate of 750 rpm. After the reaction, the
mixture was cooled to room temperature and filtered. The solid residue
was washed with methanol and dried at 50 oC under vacuum for 2D-
HSQC-NMR characterization. The filtrate was concentrated under
reduced pressure at 35 oC to obtain the liquid oil, which was weighed.
The liquid oil was then diluted to 2 mL with methanol, and the monomer
products in the liquid oil were analyzed and quantified by the internal
standard method (standard: mesitylene) with an HP 5973 GC–MS (HP-5
column, 30 m×0.32 mm×0.25 μm).
Acknowledgements
Support from the National Natural Science Foundation of China
(21473187, 21690083, 21690080, 21506214), the Strategic
Priority Research Program of the Chinese Academy of
Sciences (XDB17020100), China Postdoctoral Science
Foundation (2017M611279), Scientific research plan projects of
Shaanxi Education Department (16JS016), the Natural Science
Foundation of Shaanxi Province (2017JQ2029, 2015JM2060)
Experimental Section
Materials and analysis methods. (NH4)6H2W12O40·XH2O, PdCl2,
H2PtCl6·6H2O, RuCl3 were purchased from Aladdin Chemistry Co., Ltd.,
Shanghai, China. All lignin α-O-4 model compounds were purchased
from SA Chemical Technology (Shanghai) Co., Ltd. The M-W/AC (M =
Ru, Pt and Pd) catalyst were prepared as described in supporting
information. X-ray diffraction (XRD) patterns of the catalysts were
This article is protected by copyright. All rights reserved.

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
2015, 54, 258-262; h) J. C. Kong, M. Y. He, J. A. Lercher, C. Zhao,
Chem. Commun. 2015, 51, 17580-17583; i) S. Kasakov, H. Shi, D. M.
Camaioni, C. Zhao, E. Barath, A. Jentys, J. A. Lercher, Green Chem.
2015, 17, 5079-5090.
and Shaanxi University of Technology doctoral Foundation
(SLGQD13(2)-5, SLGKYQD-2) is gratefully acknowledged.
Keywords: lignin • bimetallic catalyst • tungsten • aromatics •
[5]
[6]
[7]
a) C. Peng, Q. Chen, H. W. Guo, G. Hu, C. Z. Li, J. L. Wen, H. S.
Wang, T. Zhang, Z. B. K. Zhao, R. C. Sun, H. B. Xie, ChemCatChem
2017, 9, 1135-1143; b) Y. B. Huang, L. Yan, M. Y. Chen, Q. X. Guo, Y.
Fu, Green Chem. 2015, 17, 3010-3017; c) C. Zhao, J. A. Lercher,
ChemCatChem 2012, 4, 64-68.
hydrogenolysis
[1]
a) Y. P. Huo, H. Q. Zeng, Y. G. Zhang, Chemsuschem 2016, 9, 1078-
1080; b) X. Chen, H. Y. Yang, N. Yan, Chem.-Eur. J. 2016, 22, 13402-
13421; c) Q. N. Xia, Z. J. Chen, Y. Shao, X. Q. Gong, H. F. Wang, X.
H. Liu, S. F. Parker, X. Han, S. H. Yang, Y. Q. Wang, Nature
Communications 2016, 7.
a) H. W. Guo, B. Zhang, Z. J. Qi, C. Z. Li, J. W. Ji, T. Dai, A. Q. Wang,
T. Zhang, Chemsuschem 2017, 10, 523-532; b) H. W. Guo, B. Zhang,
C. Z. Li, C. Peng, T. Dai, H. B. Xie, A. Q. Wang, T. Zhang,
Chemsuschem 2016, 9, 3220-3229; c) C. Z. Li, M. Y. Zheng, A. Q.
Wang, T. Zhang, Energy Environ. Sci. 2012, 5, 6383-6390.
a) D. M. Alonso, S. G. Wettstein, J. A. Dumesic, Chem. Soc. Rev.
2012, 41, 8075-8098. b) J. W. Zhang, Y. Cai, G. P. Lu, C. Cai, Green
Chem. 2016, 18, 6229-6235. c) J. Zhang, H. Asakura, J. van Rijn, J.
Yang, P. Duchesne, B. Zhang, X. Chen, P. Zhang, M. Saeys, N. Yan,
Green Chem. 2014, 16, 2432-2437. d) P. Zhang, T. Wu, T. Jiang, W.
Wang, H. Liu, H. Fan, Z. Zhang, B. Han, Green Chem. 2013, 15, 152-
159. e) J. Zhang, Y. Cai, G. Lu, C. Cai, Green Chem. 2016, 18, 6229-
6235. f) M. Kim, J. M. Ha, K. Y. Lee, J. Jae, Catal. Commu. 2016, 86,
113-118.
[2]
[3]
C. Li, X. Zhao, A. Wang, G. W. Huber, T. Zhang, Chem. Rev. 2015,
115, 11559-11624.
a) H. Konnerth, J. G. Zhang, D. Ma, M. H. G. Prechtl, N. Yan, Chem.
Eng. Sci. 2015, 123, 155-163; b) Q. Song, F. Wang, J. Xu, Chem.
Commun. 2012, 48, 7019-7021; c) R. Rinaldi, R. Jastrzebski, M. T.
Clough, J. Ralph, M. Kennema, P. C. A. Bruijnincx, B. M. Weckhuysen,
Angew. Chem. Int. Ed. 2016, 55, 8164-8215.
[4]
For recent examples, see: a) Z. W. Cao, J. Engelhardt, M. Dierks, M.
T. Clough, G. H. Wang, E. Heracleous, A. Lappas, R. Rinaldi, F.
Schuth, Angew. Chem. Int. Ed. 2017, 56, 2334-2339; b) G. Calvaruso,
M. T. Clough, R. Rinaldi, Green Chem. 2017, 19, 2803-2811; c) B.
Zhang, C. Z. Li, T. Dai, G. W. Huber, A. Q. Wang, T. Zhang, RSC Adv.
2015, 5, 84967-84973; d) R. Ma, W. Y. Hao, X. L. Ma, Y. Tian, Y. D. Li,
Angew. Chem. Int. Ed. 2014, 53, 7310-7315; e) P. J. Deuss, C. W.
Lahive, C. S. Lancefield, N. J. Westwood, P. C. J. Kamer, K. Barta, J.
G. de Vries, Chemsuschem 2016, 9, 2974-2981; f) C. W. Lahive, P. J.
Deuss, C. S. Lancefield, Z. H. Sun, D. B. Cordes, C. M. Young, F.
Tran, A. M. Z. Slawin, J. G. de Vries, P. C. J. Kamer, N. J. Westwood,
K. Barta, J. Am. Chem. Soc. 2016, 138, 8900-8911; g) C. S.
Lancefield, O. S. Ojo, F. Tran, N. J. Westwood, Angew. Chem. Int. Ed.
[8]
[9]
C. Z. Li, H. L. Cai, B. Zhang, W. Z. Li, G. X. Pei, T. Dai, A. Q. Wang, T.
Zhang, Chin. J. Catal. 2015, 36, 1638-1646.
J. G. Zhang, J. Teo, X. Chen, H. Asakura, T. Tanaka, K. Teramura, N.
Yan, ACS Catal. 2014, 4, 1574-1583.
[10] X. Y. Wang, R. Rinaldi, Chemsuschem 2012, 5, 1455-1466.
[11] J. He, C. Zhao, D. Mei, J. A. Lercher, J. Catal. 2014, 309, 280-290.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201701240
ChemCatChem
FULL PAPER
Entry for the Table of Contents
FULL PAPER
J. W. Ji, H. W. Guo, C. Z. Li,* Z. J. Qi, B.
Zhang, T. Dai, M. Jiang, C. Q. Ren, A.
Q. Wang and T. Zhang*
Page No. – Page No.
Tungsten-based Bimetallic Catalysts
for Selective Cleavage of Lignin C-O
Bonds
Tungsten based bimetallic catalysts M–W/AC (M = Ru, Pt and Pd) exhibited high
activity and selectivity in the hydrogenolysis of typical α-O-4 model compounds and
deconstruction of lignin feedstock for the production of aromatic chemicals. High
yields of C-O cleavage products from model compounds (up to 92.6%) and from
lignin feedstock (up to 66.7%) were obtained without destroying the aromatic rings.
This article is protected by copyright. All rights reserved.