Synthesis of ethanol from aryl methyl ether/lignin, CO2 and H2

Article abstract of DOI:10.1039/c9sc03386f

Currently, ethanol is produced via hydration of ethene or fermentation of foods. Lignin and CO₂ are abundant, cheap and renewable feedstocks. Synthesis of ethanol using the lignin or its derivatives is of great importance, but is a great challenge and has rarely been reported. Herein, we propose a route to synthesize ethanol from CO₂, H₂, and lignin or various aryl methyl ethers, which can be derived from lignin. The reaction could be effectively conducted using Ru-Co bimetallic catalyst and the TON of ethanol could reach 145. Interestingly, ethanol was the only liquid product when lignin was used. A series of control experiments indicate that ethanol was formed via cleavage of aryl ether bond, reverse water gas shift (RWGS) reaction, and C-C bond formation. This protocol opens a way to produce ethanol using abundant renewable resources.

Full text of DOI:10.1039/c9sc03386f

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Synthesis of ethanol from aryl methyl ether/lignin,
CO2 and H2†
ab
Cite this: Chem. Sci., 2019, 10, 10640
ac
ab
*
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
Jingjing Zhang,
Qingli Qian,
Ying Wang,
Bernard Baffour Asare
ab
abcd
Jiang Yanab and Buxing Han
*
Bediako,
Currently, ethanol is produced via hydration of ethene or fermentation of foods. Lignin and CO2 are
abundant, cheap and renewable feedstocks. Synthesis of ethanol using the lignin or its derivatives is of
great importance, but is a great challenge and has rarely been reported. Herein, we propose a route to
synthesize ethanol from CO2, H2, and lignin or various aryl methyl ethers, which can be derived from
lignin. The reaction could be effectively conducted using Ru–Co bimetallic catalyst and the TON of
ethanol could reach 145. Interestingly, ethanol was the only liquid product when lignin was used. A
series of control experiments indicate that ethanol was formed via cleavage of aryl ether bond, reverse
water gas shift (RWGS) reaction, and C–C bond formation. This protocol opens a way to produce
ethanol using abundant renewable resources.
Received 9th July 2019
Accepted 1st October 2019
DOI: 10.1039/c9sc03386f
rsc.li/chemical-science
involves several key steps including cleavage of ether bond,
reverse water gas shi (RWGS) reaction, and C–C bond forma-
Introduction
Lignin and CO2 are abundant renewable carbon resources.1
Transformation of lignin and/or CO2 into value-added chem-
icals has attracted great interest.2–15 Lignin is a major compo-
nent of lignocellulosic biomass, and its valorization remains
a challenge because of the complex and robust structure.16 Aryl
methyl ethers are commonly used as model compounds to
study lignin conversion, which has been successfully trans-
formed into various chemicals, such as benzene, phenol, ter-
ephthalic acid, cyclohexanone, cyclohexane, methanol,
methane, acetates, acetic acid, etc.17–26 Ethanol is an important
bulk chemical and is widely used in human life, especially as an
alternative motor fuel. Recently, several important works on
converting cellulose to ethanol have been published.27,28
However, synthesis of ethanol using lignin or its derivatives has
rarely been reported so far.29,30 Without doubt, synthesis of
ethanol using lignin is highly desirable, but is challenging.
In this paper, we report the protocol to produce ethanol from
lignin or its derivatives, CO2, and H2 (Fig. 1). The reaction
tion. The reaction could be effectively accelerated by Ru–Co
bimetallic catalyst and the TON of ethanol could reach 145.
To the best of our knowledge, this is the rst work of ethanol
synthesis by combining lignin or its derivatives, and CO2, which
are abundant renewable feedstocks.
Results and discussion
Catalytic system
We started the catalyst screening with the simplest aryl methyl
ether (anisole) as the lignin model compound. The results are
revealed in Table 1. The reaction could be effectively accelerated
by Ru–Co bimetallic catalyst with 1,1,1-tris(diphenylphosphi-
nomethyl)ethane (triphos) ligand and LiI promoter in 1,3-
dimethyl-2-imidazolidinone (DMI) solvent (entry 1). The TON of
ethanol based on Ru catalyst was 73. The byproducts of the
reaction were phenol, CO, methane and trace propanol. Only
minor ethanol could form when single [RuCl2(CO)3]2 was used
as catalyst, while no ethanol was observed when Co2(CO)8
aBeijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid,
Interface and Chemical Thermodynamics, CAS Research/Education Center for
Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, China. E-mail: qianql@iccas.ac.cn; hanbx@iccas.ac.cn
bSchool of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, Beijing 100049, China
cPhysical Science Laboratory, Huairou National Comprehensive Science Center, No. 5
Yanqi East Second Street, Beijing 101400, China
dShanghai Key Laboratory of Green Chemistry and Chemical Processes, School of
Chemistry and Molecular Engineering, East China Normal University, Shanghai
200062, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c9sc03386f
Fig. 1 Synthesis of ethanol from aryl methyl ethers (a)/lignins (b), CO2
and H2.
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Table 1 Different catalytic systems of ethanol synthesis from anisole, CO2 and H2
Entry
Catalyst
Promoter
Ligand
Solvent
TONb
1c
2
3
4
5
6
7
8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2
Co2(CO)8
CuCl2, Co2(CO)8
IrCl3, Co2(CO)8
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
—
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
—
Dppe
PPh3
Imidazole
PPNCl
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
Triphos
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
73
3
0
0
0
0
4
0
36
46
46
41
0
32
11
1
0
4
32
0
0
51
59
57
40
48
32
39
0
0
0
0
0
Fe2(CO)9, Co2(CO)8
[RuCl2(CO)3]2, Fe2(CO)9
[RuCl2(CO)3]2, NiBr2
Ru(acac)3, Co2(CO)8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
Ru3(CO)12, Co2(CO)8
[RuCl2(CO)3]2, Co(PPh3)3Cl
[RuCl2(CO)3]2, CoCl2
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
[RuCl2(CO)3]2, Co2(CO)8
NaI
KI
MgI2
ZnI2
LiCl
LiBr
I2
LiBF4
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
DMI
DMI
NMP
NEP
Water
TMU
Toluene
THF
Acetonitrile
Squalane
0
a
Reaction conditions: 20 mmol Ru catalyst and 60 mmol Co catalyst (based on the metal), 20 mmol ligand, 2.2 mmol promoter, 2 mL solvent,
b
3.6 mmol anisole, 3 MPa CO2 and 5 MPa H2 (at room temperature), 190 ꢀC, 10 h. TON denotes moles of ethanol produced per mole of Ru
catalyst. The yield of ethanol based on anisole was 40.6%. Acronyms: 1,3-dimethyl-2-imidazolidinone (DMI), ruthenium(III) acetylacetonate
c
(Ru(acac)3), 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos), triphenylphosphine (PPh3), 1,2-bis(diphenylphosphino)ethane (dppe),
bis(triphenylphosphoranylidene)ammonium chloride (PPNCl), tetrahydrofuran (THF), 1-methyl-2-pyrrolidinone (NMP), 1-ethyl-2-pyrrolidinone
(NEP), tetramethylurea (TMU).
catalyst was applied separately (entries 2, 3). This suggested that the reaction rate further decreased remarkably (entry 16).
Ru complex was the major catalyst and Co complex was the Whereas the transition metal iodide (ZnI2) could not promote
cocatalyst. The TON of ethanol rose signicantly by combining the reaction at all (entry 17). The anionic counterpart of the
Ru and Co catalysts, indicating their synergy during the reac- promoter also played an important role in the reaction. When
tion. No ethanol was detected aer the reaction when we LiI was substituted by other lithium halides (LiCl, LiBr), the
combined other transition metal complexes (Cu, Ir, Fe) with TON of ethanol diminished by the sequence: LiI > LiBr > LiCl
Co2(CO)8 (entries 4–6). We also combined [RuCl2(CO)3]2 with (entries 1, 18, 19). Further experiment using iodine (I2)
other transition metal complexes (Fe, Ni), but the reaction rate demonstrated that ionic halogen was needed to promote the
had little increase or the reaction did not occur at all (entries 7, reaction (entry 20). We also tried LiBF4, but the reaction did not
8). Thus Ru–Co bimetallic catalyst rendered better catalytic take place (entry 21). The superiority of LiI as the promoter
performance. We also tested other combinations of Ru/Co could be ascribed to the stronger Lewis acidity and smaller size
complexes and found that [RuCl2(CO)3]2 and Co2(CO)8 were t of the Li+, and the better nucleophilicity of the IÀ.31,32
for the reaction (entries 1, and 9–12).
As a tridentate phosphine ligand, triphos could effectively
The promoter was necessary for the catalysis because no accelerate the reaction activity (entries 1, 22). To study the role
ethanol was produced without it (entry 13). When NaI or KI were of different phosphine ligands, we adopted the bidentate ligand
utilized instead of LiI, ethanol could also form but the catalytic dppe and monodentate ligand PPh3 in the experiment respec-
activity dropped by the order: LiI > NaI > KI (entries 1, 14, 15). tively, but they were less effective than triphos (entries 1, 23, 24).
When alkaline earth metal iodide (MgI2) was used as promoter The sequence of their promoting effect was as follows: triphos >
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dppe > PPh3. We also tried other ligands, such as imidazole and
PPNCl, but they inhibited the reaction (entries 22, 25, 26).
Hence triphos was a suitable ligand for the reaction. It is re-
ported that triphos displayed eminent role in converting
renewable molecules including CO2.33,34
Besides DMI, cyclic amides of similar structure (NMP, NEP)
could be used as reaction solvent, but they are not as good as DMI
(entries 1, 27, 28). Ethanol could not be detected when the
reaction was conducted in other solvents, such as water, TMU,
toluene, THF, acetonitrile or squalane (entries 29–34). The
solvent effect of the cyclic amides has been discussed else-
where.32 In short, the catalytic system consisting of [RuCl2(CO)3]2,
Co2(CO)8, LiI, triphos, and DMI was appropriate for the reaction.
Fig. 3 Time course of the reaction. Reaction conditions: 20 mmol
[RuCl2(CO)3]2 and 60 mmol Co2(CO)8 (based on the metal), 20 mmol
triphos, 2.2 mmol LiI, 2 mL DMI, 3.6 mmol anisole, 3 MPa CO2 and
5 MPa H2 (at room temperature), 190 ꢀC.
Impact of reaction conditions
Based on the above catalytic system, we studied the impact of
the reaction temperature (Fig. 2). The reaction began to occur at
140 ꢀC. The catalytic activity enhanced quickly with elevating
temperature. At 190 ꢀC, the TON of ethanol reached 73 and the
increase of reaction rate became minor when the temperature
instead of CO2 (entry 23 of Table S1†). The CO was generated via
RWGS reaction catalyzed by Ru catalyst (Fig. S1†). The Ru
catalyzed RWGS reaction has been reported in the literature.35,36
Propanol was also observed aer 6 h and it grew very slowly with
time. The propanol may be formed via ethanol homologation.37
Methane was observed at the start of the reaction and it
increased steadily during the reaction. Aer 10 h, the rise of
ethanol was less obvious, indicating that 10 h was the appro-
priate reaction time.
As a substrate, anisole was indispensable for the reaction,
because little ethanol was detected without it (entry 11 of Table
S1†). The anisole decomposed gradually during the reaction
and its aryl part was converted to phenol (Fig. S2†). The phenol
was stable at reaction condition and did not experience further
transformation (Fig. S3†). The stability of phenol was further
veried by the control experiment using phenol as substrate
instead of anisole (Fig. S4†). The LiI was responsible for the
decomposition of the anisole, while other catalytic components
ꢀ
was further raised. At 190 C, we investigated the inuence of
other reaction parameters, i.e., dosage of each catalyst compo-
nent and pressure of each reactant gas. The results and detailed
discussion were provided in the ESI (Table S1†). The suitable
dosages of the catalytic components were 20 mmol Ru catalyst
and 60 mmol Co catalyst (based on the metal), 20 mmol triphos,
and 2.2 mmol LiI. The appropriate gas pressure was 3 MPa CO2
and 5 MPa H2 (at room temperature). In brief, the condition in
entry 1 of Table 1 was the best for the reaction.
Reaction mechanism
Fig. 3 displayed the time course of the reaction. CO formed at
the beginning of the reaction and it increased quickly with time.
With the fast production of ethanol, the CO content in the
reactor stopped growing and kept at a constant level, suggesting
that CO was an intermediate for ethanol synthesis. This
assumption was conrmed by the control experiment using CO
Fig.
2 The TON of ethanol at different temperatures. Reaction
conditions: 20 mmol [RuCl2(CO)3]2 and 60 mmol Co2(CO)8 (based on
the metal), 20 mmol triphos, 2.2 mmol LiI, 2 mL DMI, 3.6 mmol anisole,
3 MPa CO2 and 5 MPa H2 (at room temperature), 10 h.
Fig. 4 The proposed reaction pathway.
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Table 2 Synthesis of ethanol from different aryl methyl ethers/lignins, CO2 and H2
Entry
1
Substrates
TON of ethanol
74
Yield of ethanolc (%)
Yield of propanolc (%)
1.4
Conversion of substrated (%)
100
41.1
2
126
35.0
1.3
100
3
4
5
72
40.0
40.3
40.0
<1
71.2
74.3
79.2
145
72
1.0
1.2
6
69
38.3
<1
76.4
7
8
61
71
33.9
39.4
<1
<1
74.7
77.5
9
68
72
37.8
40.0
<1
76.1
100
10
1.1
11
12
51
60
28.3
33.3
<1
<1
100
100
13
58
65
32.2
36.1
<1
100
14
1.1
83.3
15b
16b
Eucalyptus lignin
Willow lignin
38
41
37.3
38.1
0
0
76.5
77.8
a
Reaction conditions: 20 mmol [RuCl2(CO)3]2 and 60 mmol Co2(CO)8 (based on the metal), 20 mmol triphos, 2.2 mmol LiI, 2 mL DMI, 3.6 mmol
b
c
substrate, 3 MPa CO2 and 5 MPa H2 (at room temperature), 190 ꢀC, 10 h. 0.4 g lignin was added before the reaction. The yield was
calculated based on the mole of methoxyl group in the substrate. The aryl part of the aryl methyl ether was converted into the corresponding
d
phenol, thus the yield of phenol was equal or very close to the conversion of the corresponding substrate.
and reactant gases could assist this step (Table S2†). The LiI LiI (entry 2), while they greatly accelerated the decomposition
itself could decompose the anisole (entry 1). All the other (entries 1, 3). The gases could also markedly help the LiI to
catalytic components could not decompose the anisole without decompose the anisole (entries 1, 4). As for the transition metal
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catalysts, the Ru catalyst was more effective than Co catalyst in that the presence of the alkyl groups on the aryl methyl ether
promoting the anisole decomposition (entries 4–6). The ligand slightly decreased the reactivity. Furthermore, the aryl methyl
triphos was also benecial to the anisole decomposition ethers with methyl substituent at different positions had
(entries 3, 7). The LiBF4 was more efficient than LiI in decom- different reactivity, and they followed the order: para > meta >
posing the anisole (entry 8), but no ethanol was observed aer ortho (entries 5–7). The substrates with electron-withdrawing
the reaction (entry 21 of Table 1). Therefore the LiI could not groups, such as 4-triuoromethyl anisole, 3-triuoromethyl
only cleave the ether bond of anisole but also was essential to anisole, and 3,5-diuoroanisole, were also tested in the reaction
ethanol formation.
(entries 11–13). It was found that the electron-withdrawing
Aer anisole decomposition, trace CH3I was detected and groups on substrates lowered the reactivity more obviously
further converted to ethanol in the presence of CO and H2 (Fig. S5 than electron-donating groups. As for the impact of the position
and S6†). CH3I is a common intermediate of ethanol synthesis via of the triuoromethyl group, the substrate with the substituent
methanol homologation with CO and H2.32,38,39 Therefore, in this on para position was less reactive than that on meta position
work CH3I should be a key intermediate generated by decom- (entries 11, 12). When 2-methoxynaphthalene, which had one
posing anisole, which subsequently took part in the ethanol more fused aromatic ring than anisole, was used as substrate
formation via reductive carbonylation reaction. This deduction the reaction also occurred efficiently (entry 14). The GC-MS
13-
was further supported by the 13CO2 labeling test, where CH3
graphs of the reaction solutions in Table 2 are provided in the
CH2OH was formed in the reaction (Fig. S7†). This suggested that ESI (Fig. S12–S25†). The results demonstrate that the aromatic
the methyl group (–CH3) in ethanol was from anisole and the part of each substrate was converted into corresponding
–CH2OH group was derived from CO2. Methane in the product phenols. The catalytic system could also apply to lignin, where
was generated by further hydrogenation of CH3I and/or CO the methoxyl group took part in generating ethanol (entries 15,
(Fig. S8 and S9†). The control experiment using D2 revealed that 16). The contents of methoxyl groups in eucalyptus lignin and
obvious H–D exchange occurred in the reaction (Fig. S10†). During willow lignin used in this work were 15.8 wt% and 16.7 wt%
the transfer of CH3 group from anisole substrate to ethanol and/or respectively, which was determined by iodine stoichiometry
propanol, the H atoms on CH3 could be totally substituted by the titration method.41 The eucalyptus lignin and willow lignin
D atoms. As for the unreacted anisole, the H atoms on the CH3 could produce 87.5 and 94.4 mg(ethanol) g(lignin)À1, respectively.
were intact at the reaction condition. The H–D exchange reactions Interestingly, ethanol was the only liquid product aer the
have been investigated elsewhere.40
reaction using lignin as substrate.
Based on above discussion, we proposed the possible reaction
pathway (Fig. 4). The generation of ethanol mainly involves three
cascade reactions: cleavage of ether bond to form CH3I (1), RWGS
Conclusions
reaction to generate CO (2), and subsequent ethanol synthesis via In summary, we have developed the way to synthesize ethanol
reductive carbonylation (3). It is possible that the carbonyls in the from Aryl methyl ethers/lignin, CO2 and H2. The reaction could
catalyst precursors participated in forming the ethanol, but the proceed effectively using Ru–Co bimetallic catalyst, LiI
impact could be neglected because of the following reasons. promoter and triphos ligand. Ethanol could form at above
ꢀ
Firstly, no ethanol was observed without CO2 or H2 (entries 12, 13 140 C, and at optimized condition the TON of ethanol was as
of the Table S1†). Secondly, the 13CO2 labeling test indicated that high as 145. The catalytic system has good adaptability to
CH313CH2OH was the product in the reaction (Fig. S7†). This various aryl methyl ethers and lignin of different sources. The
indicated that CO2 rather than the carbonyls in the catalyst reactions using eucalyptus lignin and willow lignin as substrate
precursor formed ethanol. Finally, the HR-ESI-MS characteriza- could produce 87.5 and 94.4 mg(ethanol) g(lignin)À1, respectively,
tion of the catalyst aer the reaction suggested that the carbonyls moreover, ethanol was the only liquid product. The generation
were mainly retained on the catalyst (Fig. S11†).
of ethanol mainly involves three cascade reactions, i.e., cleavage
of ether bond to form CH3I, RWGS reaction to generate CO, and
subsequent ethanol formation via C–C bond formation. Ru was
responsible for the RWGS reaction. Ru and Co cooperatively
Substrate extension
We also tested other aryl methyl ethers as substrate to produce accelerated the ethanol synthesis. The catalytic system could
ethanol (Table 2). Guaiacol and syringol are naturally-occurring apply to various aryl methyl ethers and lignin of different
organic compound, which can be derived from lignin. They sources. To our knowledge, this is the rst report of ethanol
were both suitable substrates for producing ethanol (entries 1 production using aryl methyl ethers/lignin and CO2. It provides
and 2). When another hydroxyl substituted aryl methyl ether, 4- a new strategy of ethanol production, biomass and CO2 valori-
methoxyphenol was tested, the reaction also proceeded well zation. We believe that this work will trigger more research on
(entry 3). Based on the results of reactions using syringol and bulk chemicals synthesis by combining CO2 and biomass.
1,4-dimethoxybenzene, we can deduce that two methoxyl
groups on each substrate molecule participated in forming
ethanol (entries 2, 4). The TON of ethanol using 1,4-dimethox-
ybenzene as substrate was as high as 145. We also tried aryl
Experimental
Chemicals
methyl ethers with different alkyl substituents, which are Dichlorotricarbonyl ruthenium dimer ([RuCl2(CO)3]2, 98+%),
electron-donating groups (entries 5–10). The results indicated ruthenium(III) acetylacetonate (Ru(acac)3, 98%), ruthenium(III)
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iodide, iridium(III) chloride, anhydrous (IrCl3, 99.99%), cobal- calculated from the GC data. The gaseous samples were detec-
t(III) 2,4-pentanedionate (Co(acac)3, 98%), cobalt(II) chloride ted by a GC (Agilent 4890D) equipped with a TCD detector and
(CoCl2,
99.9%),
chlorotris(triphenylphosphine)cobalt(I) a packed column (carbon molecular sieve TDX-01, 3 mm in
(Co(PPh3)3Cl, 97%), cobalt(II) bromide (CoBr2, 97%), diiron diameter and 1 m in length) using Argon as the carry gas.
nonacarbonyl (Fe2(CO)9, 99%), copper(II) chloride (CuCl2, 98%),
lithium iodide (LiI, 99.95%), 1,1,1-tris(diphenylphosphino-
methyl)ethane (triphos, 97+%), triphenylphosphine (PPh3,
99+%), sodium iodide (NaI, 99.95%), bis(triphenylphosphor-
Extraction of lignin
The procedure was similar to that reported previously.42 To
eucalyptus or willow (200 g) was added 1,4-dioxane (1440 mL)
followed by 2 N HCl (160 mL) and the mixture was heated to
a gentle reux under a N2 atmosphere for 1 hour. The mixture
was then cooled and the lignin containing liquor was collected
by ltration. The collected liquor was partially concentrated in
vacuo to give a gummy residue which was taken up in acetone/
water (9 : 1, ꢁ250 mL) and precipitated by addition to rapidly
stirring water (2.5 L). The crude lignin was collected by ltration
and dried under vacuum. The dried crude lignin was taken up
in acetone/methanol (9 : 1) and precipitated by dropwise addi-
tion to rapidly stirring Et2O (2 L). The precipitated lignin was
collected by ltration and dried under vacuum to give a puried
eucalyptus or willow lignin (about 20 g). The lignin extracted by
above procedure was used in subsequent catalytic reactions
without further processing.
anylidene)ammonium chloride (PPNCl, 98+%), potassium
iodide (KI, 99.9%), magnesium iodide (MgI2, 99.996%), lithium
tetrauoroborate (LiBF4, 98%), 1-methyl-2-pyrrolidinone (NMP,
99%), imidazole (99%), tetramethylurea (TMU, 99%) and 4-tert-
butylanisole (98%) were purchased from Alfa Aesar China Co,
Ltd. Dicobalt octacarbonyl (Co2(CO)8, stabilized with 1–5%
hexane) and lithium chloride (LiCl, 98%) were supplied by TCI
Shanghai Co., Ltd. Lithium bromide (LiBr, 99.5%), 1,4-dime-
thoxybenzene (99+%), 2-methylanisole (98+%), 3-methylanisole
(98+%), 4-methylanisole (99+%), 3,5-diuoroanisole (98+%), 4-
methoxybenzotriuoride (98+%), 3-methoxybenzotriuoride
(98+%) and 1-methoxynaphthalene (97+%) were purchased
from Adamas Reagent Co., Ltd. 1,3-Dimethyl-2-imidazolidinone
(DMI, 99%), 3,5-dimethylanisole (98+%), 2,6-dimethoxyphenol
(98%), 2-methoxy-4-methylphenol (98+%) and guaiacol (98%)
were provided by Aladdin Reagent. Zinc iodide (ZnI2, 98%),
nickel bromide (NiBr2, 99%), anisole (99%), acetonitrile
(99.9%), iodine (I2, 99.5%) and squalane (99%) were bought
from Acros Organics. 1-Ethyl-2-pyrrolidinone (NEP, 99%),
tetrahydrofuran (THF, 99.5%) and 1,2-bis(diphenylphosphino)
ethane (dppe, 97%) were supplied by J&K Scientic Ltd. Toluene
(99.5+%) was obtained from Beijing Chemical Works. CO2
(99.99%), H2 (99.99%) and CO (99.99%) were provided by Bei-
jing Analytical Instrument Company. Deuterium gas (D2,
99.999%) was offered by Zhengzhou Xingdao Chemical Tech-
nology Co., Ltd. Carbon dioxide-13C (13CO2, 99% 13C) was
bought from Beijing Gaisi Chemical Gases Center.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
The authors thank the National Natural Science Foundation of
China (21875262, 21733011, 21533011), Beijing Municipal
Science
&
Technology Commission (Z181100004218004),
National Key Research and Development Program of China
(2017YFA0403102), and the Chinese Academy of Sciences
(QYZDY-SSW-SLH013).
Catalytic reaction
All the experiments were carried out in a 16 mL Teon-lined
stainless steel reactor equipped with a magnetic stirrer. The
inner diameter of the reactor was 18 mm. In a typical experi-
ment, certain amounts of the Ru–Co catalyst, promoter, ligand,
the substrates, and 2 mL solvent were added into the reactor. At
room temperature, CO2 and H2 were charged sequentially into
the reactor to desired pressure aer the reactor was purged with
1 MPa CO2 for three times. The reactor was placed in an air bath
of constant temperature, and the magnetic stirrer was set at
800 rpm. Aer the reaction, the reactor was cooled in an ice-
water bath. Then the residual gas was released slowly and
collected in a gasbag. Using toluene as the internal standard,
the reaction solution was analyzed by GC (Agilent 7890B)
equipped with a ame ionization detector and a DB-5 capillary
column (0.25 mm in diameter, 30 m in length). The liquid
products were identied using GC-MS (Agilent-7890B-5977A)
and/or GC-MS (Shimadzu-QP2010) with electron impact (EI)
ionization, as well as by comparing the retention times with the
standards in the GC traces. The yields of the products were
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