Ionic liquid [OMIm][OAc] directly inducing oxidation cleavage of the β-O-4 bond of lignin model compounds

Article abstract of DOI:10.1039/c7cc04209d

We explored the oxidation reactions of lignin model compounds directly induced by ionic liquids under metal-free conditions. In this work, it was found that ionic liquid 1-octyl-3-methylimidazolium acetate as a solvent could promote the aerobic oxidation of lignin model compound 2-phenoxyacetophenone (1) and the yields of phenol and benzoic acid from 1 could be as high as 96% and 86%, respectively. A possible reaction pathway was proposed based on a series of control experiments. An acetate anion from the ionic liquid attacked the hydrogen from the β-carbon thereby inducing the cleavage of the C-O bond of the aromatic ether. Furthermore, it was found that 2-(2-methoxyphenoxy)-1-phenylethanone (4) with a methoxyl group could also be transformed into aromatic products in this simple reaction system and the yields of phenol and benzoic acid from 4 could be as high as 98% and 85%, respectively. This work provides a simple way for efficient transformation of lignin model compounds.

Full text of DOI:10.1039/c7cc04209d

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: H. Fan, Y. Yang, Q.
Meng, Z. Zhang, G. Yang and B. Han, Chem. Commun., 2017, DOI: 10.1039/C7CC04209D.
This is an Accepted Manuscript, which has been through the
Volume 52 Number
1 4 January 2016 Pages 1–216
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Accepted Manuscripts are published online shortly after
Chemical Communications
www.rsc.org/chemcomm
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
first methanofullerene derivatives of Sc N@D5h-C80
=
3
rsc.li/chemcomm

Please do not adjust margins
ChemComm
Page 1 of 4
View Article Online
DOI: 10.1039/C7CC04209D
Journal Name
ARTICLE
Ionic liquid [OMIm][OAc] directly inducing oxidation cleavage of
β‐O‐4 bond of lignin model compounds †
Yingying Yanga,b, Honglei Fan*a, Qinglei Meng*a, Zhaofu Zhanga, Guanying Yanga, Buxing Han*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
We explored the oxidation reactions of lignin model compounds directly induced by ionic liquids under metal‐free condi‐
tions. In this work, it was found that ionic liquid 1‐octyl‐3‐methylimidazolium acetate as a solvent could promote the aero‐
bic oxidation of lignin model compounds 2‐phenoxyacetophenone (1) and the yields of phenol and benzoic acid from 1
could be as high as 96% and 86%, respectively. A possible reaction pathway was proposed based on a series of control ex‐
periments. Acetate anion from ionic liquid attacked the hydrogen from β‐carbon thereby inducing the cleavage of C‐O
bond of aromatic ethers. Further, it was found that 2‐(2‐methoxyphenoxy)‐1‐phenylethanone (4) with methoxyl group
could also be transformed into aromatic products in this simple reaction system and the yields of phenol and benzoic acid
from 4 could be as high as 98% and 85%, respectively. This work provides a simple way for efficient transformation of
www.rsc.org/
lignin
model
compounds.
Introduction
work21, [BnMIm][NTf2]/inorganic acid system was used to
promote the conversion of lignin β‐O‐4 model compound 2‐
phenoxyacetophenone into phenol and benzoic acid via a free‐
radical pathway.
Transformation of lignocellulosic biomass has attracted more
and more attention in order to obtain fuel and fine chemicals
sustainably.1,2 Lignin, one of the main components of biomass,
is a kind of abundant renewable aromatic bioresource.3 It has
Dissolution of lignocellulosic biomass is a critical step22 to
been a great challenge4 to obtain value‐added chemicals make the material access to active sites of catalysts for the
especially aromatic compounds from lignin through efficient valorisation of biomass. In recent years, ionic liquids (ILs) have
methods in suitable solvents.
been used for the dissolution of biomass and high solubility of
lignin has been achieved23‐25. In addition, ILs with low vapor
pressure, recycling and high gas solubility have been used as
reaction media and catalysts.26 Through adjusting types of
anions and cations, the properties of ILs can be designed.
Moreover, ILs can catalyze some reactions such as aldol
condensation27 and Knoevenagel reactions28. So, using ILs as
reaction media can provide new opportunities for the
dissolution and degradation of lignin.
During the lignin valorisation, model compounds with
different linkages5 like β‐O‐4, α‐O‐4 and 4‐O‐5 are often
selected to study selective cleavage of the chemical bonds.
Among them, β‐O‐4 linkage is considered as the typical unit in
lignin.6 Usually, transformation of β‐O‐4 lignin model
compounds can be mainly divided into thermal cracking,7
hydrolysis reactions,8 catalytic reduction reactions9 and
catalytic oxidation reactions10. For selective oxidation
transformation, the model compounds can be cleaved by
In this work, we studied the catalytic performance of ILs for
insert of oxygen to form high value‐added chemicals like transformation of β‐O‐4 lignin model compounds under metal‐
aldehydes, ketones, organic acids using various metal catalysts free conditions. It was found that [OMIm][OAc] were very
such as Pd,11 Cu,12,13 Co,14 Ir,15 V,16 Re17 and Ru18. Meanwhile, effective for the catalytic oxidation of lignin model compounds
lignin model compounds can also be transformed into 2‐phenoxyacetophenone(
1
)
and 2‐(2‐methoxyphenoxy)‐1‐
aromatic chemicals by the metal‐free catalysis methods.19,20 phenylethanone (
4) using O2 as the oxidant without any
Metal‐free catalysis has some attractive advantages, such as additional catalysts. This novel route has some obvious
low cost and no heavy metal contaminants. In our previous advantages such as metal‐free, mild reaction condition, high
yields of the products, easy recycling of the ILs.
Results and discussion
Transformation of 2‐phenoxyacetophenone (1) using ILs.
a. Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid
and Interface and Thermodynamics, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, China. E‐mail: hlfan@iccas.ac.cn;
mengqinglei@iccas.ac.cn; hanbx@iccas.ac.cn.
b. School of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, Beijing 100049, China
Electronic Supplementary Information (ESI) available: Structures of the ILs used,
Method for extracting lignin, GC data and HPLC data. See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 4
ARTICLE
Scheme
Journal Name
that the side reactions were accelerated at high temperature.
1
1
Oxidation depolymerization of lignin model
View Article Online
1
andDyOieI:l1d0s.1o0f39t/hCe7CpCr0o4d2u0c9tDs
compound
We first investigated the oxidation reaction of
phenol ( ) and benzoic acid ( ) in various ILs (scheme 1). The
The dependence of conversion of
on the pressure of oxygen is shown in Fig. 1B. The reaction
didn’t occur without oxygen, suggesting that oxygen is crucial
for the reaction. The conversion increased rapidly as the
oxygen pressure increased. The yields of phenol and benzoic
acid reached maximum at 1.5 MPa. At higher oxygen pressure,
the yield of phenol decreased slightly due to its further
oxidation. The amount of water added in the system affected
the reaction as illustrated in Fig. 1C. With increasing amount of
1
to produce
2
3
liquid products were analysed by HPLC. The results were
presented in Table 1, and the structures of the ILs used were
given in Supporting Information (Figure S1). [OMIm][OAc]
showed the best catalytic performance for the reaction, and
the yields of the main products phenol and benzoic acid could
be as high as 96% and 86%, respectively. Different ILs were
also tested (entries 2‐5), but they were not as efficient as
[OMIm][OAc]. On one hand, the ILs with weak nucleophilic
properties (entries 2‐4), could not cleave the C‐C/C‐O bonds
effectively leading to low conversion. On the other hand,
water, the conversion of 1 and yields of the products increased
at the beginning and then decreased when the amount of
water exceeded 0.025 mL. The main reason is that water is a
reactant, as shown in scheme 2 (in the following sections).
Thus, when the amount of water was not enough, the
conversion and yields increased with increasing amounts of
water. However, when the amount of water exceeded certain
value, the yields of the products decreased with increasing
water content. One possible reason is that the formation of
hydrogen bond between IL and water blocks the attacking of
acetate anion leading to low conversion and yields. In addition,
the reusability of [OMIm][OAc] was tested and the results
were illustrated in Fig. 1D. Obviously, the loss of the yields of
phenol and benzoic acid was not notable in the four cycles,
indicating excellent stability of the IL in the reaction.
strong nucleophilic IL (entry 5) favoured the conversion of 1,
but it resulted in more side reactions. Additionally, [HDBU][Im]
would react with the acidic products phenol and benzoic acid,
resulting in low yields of the target products. For comparison,
the common neutral IL 1‐butyl‐3‐methylimidazolium chloride
([BMIm][Cl]) and organic solvent toluene were also tested and
very poor conversion and yields were obtained (entries 6‐7).
To identify the role of the imidazolium cation, another IL and
salt with acetic acid anion were also investigated (entries 8‐9).
For [HDBU][OAc], its bad thermal stability led to [HDBU][OAc]
decomposing partly into DBU and HOAc. The basicity of DBU
can cause the occurrence of side reactions leading to low
yields of target products. Furthermore, we carried out this
transformation using KOAc. The conversion was very low
because KOAc cannot contact the lignin model compound
effectively due to its low solubility.
Table 1. Oxidation of lignin model compound
1 catalyzed by
different ILs.
Entry
IL
Conversion
Yield(
2
)(%)
Yield(3)(%)
1
2
3
4
5
6
7
8
9
[OMIm][OAc]
[HDBU][HCOO]
[BMIm][BA]
[BMIm][TFA]
[HDBU][Im]
[BMIm][Cl]
Toluene
>99
88
96
51
61
52
30
<1
<1
36
<5
86
15
60
29
18
<1
<1
20
0
70
Fig. 1 Effects of reaction parameters on the conversion and
yields in IL [OMIm][OAc] with 0.212 g reactant 1. (A) Effect of
62
>99
23
temperature, IL 1 g, H2O 0.025mL, O2 1.5 MPa, 2 hours; (
B
C
)
)
)
Effect of O2 pressure; IL 1 g, H2O 0.025mL, 100 oC, 2 hours; (
Effect of water amount, IL 1 g, O2 1.5 MPa, 100 oC, 2 hours; (
D
15
Reuse of the IL [OMIm][OAc] under the reaction condition of
entry 1 in Table 1.
[HDBU][OAc]
KOAc
>99
<5
Exploration of possible reaction path. It is very interesting
to explore how the IL catalyzes the transformation of lignin
model compound. Our previous work showed that
[BnMIm][NTf2]/inorganic acid system promotes cleavage of C‐
O bond of 2‐phenoxyacetophenone via a OOH free radical
pathway.21 In this work, we carried out experiments to study
whether the reaction proceeded by a free‐radical pathway
through adding free radical quenching agent 2,2,6,6‐
a The reactions were carried out in the solutions containing 0.212 g of
reactant
, 1 g of IL, 0.025 mL of H2O under 1.5 MPa of O2 at 100 oC for
2 hours. Yield ( ) = Yield of phenol; Yield ( ) =Yield of benzoic acid.
1
2
3
Investigation of effects of different parameters. The effects
of various reaction parameters were studied using
[OMIm][OAc] and the results are given in Fig. 1. Figure 1A
shows the variation of the conversion and yield with
temperature. The conversion of
benzoic acid increased with increasing temperature at the
beginning, and then decreased after 100 oC. The main reason is
tetramethylpiperidinyloxy
（TEMPO）into the reactor. When
1 and the yields of phenol and
0.052 g TEMPO was added, the yields of phenol and benzoic
acid were 98% and 78%, respectively. Furthermore, when
0.110 g TEMPO was added, the yields of phenol and benzoic
2 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 4
ChemComm
Please do not adjust margins
Journal Name
ARTICLE
acid were 96% and 75%, respectively. These results showed
that TEMPO had no obvious effects on transformation of the
lignin model compound. Therefore, it could be concluded that
the oxidation reaction catalyzed by the IL did not proceed via
OOH free radical pathway.
View Article Online
DOI: 10.1039/C7CC04209D
Additionally, it can be known from scheme 1 that a carbon
atom of
1 lost in the reaction to produce phenol and benzoic
acid. The gas chromatography (GC) analysis indicated that
gaseous products included carbon dioxide, hydrogen and
carbon monoxide. As an example, Fig. S2 gives the GC spectra
of the gaseous products in the reaction shown in entry 1 of
Table 1. Considering that formic acid can be decomposed into
carbon monoxide and water or into carbon dioxide and
hydrogen under heating,29 we speculated that the lost carbon
formed formic acid firstly in the reaction, which further
decomposed into these gases. In order to find the evidence for
this argument, we analyzed the liquid products of the reaction
mixture after a shorter reaction time (1 h) by HPLC, and the
peak of formic acid could be observed in the chromatogram
(Fig. S3), i.e., formic acid was formed during the reaction.
Meanwhile, we found an unknow compound from the HPLC
chromatogram. Consequently, we separated the unknow
Scheme 2 Possible reaction pathway for the oxidation of 2‐
phenoxyacetophenone catalyzed by [OMIm][OAc]
.
The pathway discussed above involves two intermediates,
phenylglyoxal and benzoylformic acid. In order to get more
evidence to support the reaction pathway discussed above, we
used the possible intermediates phenylglyoxal and
benzoylformic acid as reactants and carried out the
experiments under the condition in Entry 1 of Table 1 (scheme
3). These two intermediates were converted completely and
the liquid product was benzoic acid. Moreover, the
composition of the gaseous products from the reactions was
the same as that from 2‐phenoxyacetophenone. In addition,
the mixture of phenylglyoxal and phenol was used as the
reactant under the same conditions. The final products were
phenol and benzoic acid, which revealed that the reaction
pathway was not changed in the presence of phenol. The
experimental results supported our proposed reaction
mechanism.
compound and then analyzed
the IR spectra method. From Fig S4a, a band at 1708 cm‐1 was
assigned to the absorptions of C=O group of , and other
bands at 1598 cm‐1 1582 cm‐1 1499 cm‐1 and 1480 cm‐1
1 and the unknow compound by
1
、
、
belonged to vibration absorption of benzene rings. From the IR
spectra of the unknow compound (Fig. S4b), two bands at
1648 cm‐1 and 1600 cm‐1 were found and band strengthens
were similar, which showed that the unknow intermediate
product contained two adjacent carbonyl groups.
According to our experimental results and the knowledge in
literature, we proposed the possible reaction pathway
(scheme 2). First, under the strong electron withdrawing role
of carbonyl, the electron cloud density of C‐H bond of adjacent
methylene is reduced, leading to the easy cleavage of C‐H Scheme 3 Oxidation reactions of phenylglyoxal (Eq. 1),
benzoylformic acid (Eq. 2), and phenylglyoxal+phenol (Eq. 3)
catalyzed by [OMIm][OAc] under the condition shown in
bond. After attacked by the nucleophilic acetate anion, the
reactant loses a proton from methylene to form carbon
negative anion and acetic acid molecule is formed
simultaneously. Due to the conjugate effect between
methylene with the negative charge and carbonyl group, the
negative charge on the methylene can be transferred to
carbonyl group and enol structure is formed. During the
subsequent oxidation step, there is not hydroperoxide existing
in the reaction system from our experimental results. It can be
known from the literature30 that compounds with the enol
structure can react with oxygen and produce the unstable
epoxy compound intermediate. The C‐O bonds of the epoxy
compounds are cracked and form phenol and phenylglyoxal in
the presence of acetic acid. And then, phenylglyoxal with two
carbonyl groups can be oxidized into benzoylformic acid.
Finally, under the nucleophilic attack of water, benzoylformic
acid can be transformed into benzoic acid and formic acid.
Entry 1 of Table 1
.
Transformation of another lignin model compound. To
verify the generality of catalytic system, the transformation of
another
β‐O‐4
lignin
model
compounds
2‐(2‐
methoxyphenoxy)‐1‐phenylethanone (
4) with methoxyl group
was also studied (scheme 4), and the results were given in
Table 2. The IL [OMIm][OAc] could also promote the
transformation of
4 into guaiacol (5) and benzoic acid (3)
effectively, as could be known from the results in Table 2. As
expected, both temperature and pressure affected the
o
reaction significantly. At 100 C and 1.5 MPa, the yields of
5
and 3 could be as high as 98% and 85%, respectively (entry 2 in
Table 2). All these results revealed that the IL was efficient for
the transformation of β‐O‐4 lignin model compounds.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 4
ARTICLE
Journal Name
O
O
4. A. Rahimi , A. Ulbrich , J. J. Coon and S. S. Stahl, VNieawtAurrteic,le2O0n1lin4e,
O
O
DOI: 10.1039/C7CC04209D
O
HO
515, 249‐252.
[OMIm][OAc]
O2, H2O,
OH
+
5. J. Zakzeski, P. C. A. Bruijnincx, A. L. Jongerius and B. M.
Weckhuysen, Chem. Rev., 2010, 110, 3552‐3599.
6. T. vom Stein, T. den Hartog, J. Buendia, S. Stoychev, J.
Mottweiler, C. Bolm, J. Klankermayer and W. Leitner, Angew.
Chem. Int. Ed., 2015, 54, 5859‐5863.
4
3
5
Scheme
4
Transformation of 2‐(2‐methoxyphenoxy)‐1‐
phenylethanone (4) catalyzed by [OMIm][OAc].
Table 2 Oxidation of lignin model compound
4 catalyzed by
7. J. Kim, K. Kim and E. E. Kwon, Energy, 2016, 100, 51‐57.
8. B. J. Cox and J. G. Ekerdt, Bioresour. Technol., 2013, 134, 59‐65.
9. K. L. Luska, P. Migowski, S. E. Sayed and W. Leitner, Angew.
Chem. Int. Ed., 2015, 54, 15750‐15755.
10. G. R. Chatel and D. Rogers, ACS Sustainable Chem. Eng., 2014,
2, 322‐339.
11. Y. Zhu, L. C. zhao, M. Sudarmadji, N. H. Min, A. B. Ying, J. A.
Maguire and N. S. Hosmane, ChemistryOpen, 2012, 1, 67‐70.
12. H. Sun, X. Li and J. Sundermeyer, J. Mol. Catal. A: Chem, 2005,
240, 119‐122.
13. M. Wang, L. H. Li, J. M. Lu, H. J. Li, X. C. Zhang, H. F. Liu, N. C.
Luo and F. Wang, Green Chem., 2017, 19, 702‐706.
14. J. Zakzeski, P. C. A. Bruijnincx and B. M. Weckhuysen, Green
Chem., 2011, 13, 671‐680.
15. M. C. Haibach, N. Lease and A. S. Goldman, Angew. Chem. Int.
Ed., 2014, 53, 10160‐10163.
16. G. F. De Gregorio, R. Prado, C. Vriamont, X. Erdocia, J. Labidi, J. P.
Hallett and T. Welton, ACS Sustainable Chem. Eng., 2016, 4 (11),
6031‐6036.
17. B. Zhang, C. Li, T. Dai, W. H. George, A. Wang and T. Zhang, RSC
Adv., 2015, 5, 84967‐84973.
18. H. L. Fan, Y. Y. Yang, J. L. Song, G. D. Ding, C. Y. Wu, G. Y. Yang
and B. X. Han, Green Chem., 2014, 16, 600‐604.
[OMIm][OAc].a
entry
Pressure(MPa
）
Conversion(%)
Yield(
5
)(%)
Yield(3)(%)
Temp.(
℃)
1
2
3
4
5
6
7
8
90
1.5
1.5
1.5
1.5
1.5
0
0.5
1
2
90
>99
>99
>99
>99
0
80
95
>99
86
98
94
85
68
0
80
85
80
72
59
0
100
110
130
150
100
100
100
100
77
90
87
66
83
80
9
a
The reactions were carried out in the solution containing 0.242 g of 2‐(2‐
methoxyphenoxy)‐1‐phenylethanone, 1 g of IL and 0.025 mL of H2O under
certain oxygen pressure at certain temperature for 2 h. Yield (
guaiacol, Yield ( ) = yield of benzoic acid.
5) = yield of
3
And then, we have chosen another lignin model compound
2‐phenyloxy‐1‐phenethanol with Cα‐OH group and organosolv
lignin as reactants and they were depolymerized effectively
(data in the supporting information). Further, we selected 2‐(2‐
methoxyphenoxy)‐1‐phenylethanol as the reactant and
analyzed the product distribution using GC‐MS in the short
reaction time (supporting information). From the data, the
transformation of 2‐(2‐methoxyphenoxy)‐1‐phenylethanol
underwent to ketone first, and then proceeded via similar
reaction route of 2‐phenoxyacetophenone.
19. P. J. Deuss, M. Scott, F. Tran, N. J. Westwood, J. G. de Vries and
K. Barta, J. Am. Chem. Soc., 2015, 137, 7456‐7467.
20. a. G. Brunow, O. Karlsson, K. Lundquist and J. Sipilä, Wood Sci.
Technol., 1993, 27(4), 281‐286; b. S. Siankevich, Z. F. Fei, N. Yan,
and P. J. Dyson, Chimia, 2015, 69, 592‐596; c. Y. J. Gao, J. G.
Zhang, X. Chen, D. Ma and N. Yan, ChemPlusChem, 2014, 79,
825‐834.
Conclusions
We have found that IL [OMIm][OAc] could induce the aerobic
oxidation reactions of lignin model compounds to produce
aromatic chemicals under metal‐free conditions. During the
transformation of lignin model compounds, the yields of
phenol and benzoic acid from
86%, respectively; the yields of phenol and benzoic acid from
1 could be as high as 96% and
4
could be as high as 98% and 85%, respectively. Acetate, the
anion of the ILs, plays a key role in the catalytic reaction. Our
systematic studies revealed the novel IL reaction system was
simple and efficient for the transformation of β‐O‐4 lignin
model compounds. We expect that the simple reaction system
has great potential of application in a “one‐pot” dissolution‐
transformation‐separation process of lignocellulosic biomass.
21. Y. Y. Yang, H. L. Fan, J. L. Song, Q. L. Meng, H. C. Zhou, L. Q. Wu,
G. Y. Yang and B. X. Han, Chem. Commun., 2015, 51, 4028‐4031.
22. K. C. Badgujar and B. M. Bhanage, Bioresource Technol., 2015,
178, 2‐18.
23. N. Sun, M. Rahman, Y. Qin, M. L. Maxim, H. Rodríguez and R. D.
Rogers, Green Chem., 2009, 11 (5), 646‐5.
24. D. A. Fort, R. C. Remsing, R. P. Swatloski, P. Moyna, G. Moyna
and R. D. Rogers, Green Chem., 2007, 9 (1), 63‐69.
25. Y. Q. Pu, N. Jiang and A. J. Ragauskas, J. Wood Chem. Technol.,
2007, 27, 23‐33.
26. J. P. Hallett and T. Welton, Chem. Rev., 2011, 111, 3508‐3576.
27. S. Abello, F. Medina, X. Rodriguez, Y. Cesteros, P. Salagre, J. E.
Sueiras, D. Tichit and B. Coq, Chem. Commun., 2004, 9, 1096‐
1097.
Acknowledgments
The authors thank the National Natural Science Foundation of China
(21133009, 21173234, 21321063) and Chinese Academy of Sciences
(KJCX2. YW. H30).
References
1. C. Li, X. Zhao, A. Wang, G. W. Huber and T. Zhang, Chem. Rev.,
2015, 115, 11559‐11624.
28. C. Pauna, J. Barkliea, P. Goodricha, H. Q. N. Gunaratnea, A.
McKeowna, V. I. Pârvulescub and C. Hardacre, J. Mol. Catal. A:
Chem., 2007, 269, 64‐71.
29. T. M. McCollom, B. R. T. Simoneit and E. L. Shock, Energy Fuels,
1999, 13, 401‐410.
2. Y. Cai, K. Zhang, H. Kim, G. Hou, X. Zhang, H. Yang, H. Feng, L.
Miller, J. Ralph and C. Liu, Nature Commun., 2016, 7, 11989.
3. a. S. K. Hanson and R. T. Baker, Acc. Chem. Res., 2015, 48, 2037‐
2048. b. C. Zhang, H. Li, J. Lu, X. Zhang, K. E. MacArthur, M.
Heggen and F. Wang, ACS Catal., 2017, 7, 3419‐3429.
30. J. J. Havel and K. H. Chan, J. Org. Chem., 1976, 41(3), 513‐516.
4 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins