Oxidative conversion of lignin and lignin model compounds catalyzed by CeO2-supported Pd nanoparticles

Article abstract of DOI:10.1039/c5gc01473e

The oxidative transformation of lignin into aromatic compounds is an attractive route for chemical utilization of lignocellulosic biomass. Unlike hydrogenolysis, no consumption of expensive hydrogen is required for the oxidative transformation. However, only limited success has been achieved for the oxidative conversion of lignin. Here, we report that cerium oxide-supported palladium nanoparticles (Pd/ CeO₂) can efficiently catalyze the one-pot oxidative conversion of 2-phenoxy-1-phenylethanol, a lignin model compound containing a β-O-4 bond and a Cα-hydroxyl group, in methanol in the presence of O₂, producing phenol, acetophenone and methyl benzoate as the major products. Pd nanoparticles played a pivotal role in the oxidation of a Cα-hydroxyl group into a Cα-ketonic group, which was crucial for the transformation of the model compound. The presence of the Cα-ketonic group activated the β-O-4 bond, which was subsequently cleaved over the Pd/CeO₂ catalyst, affording phenol and acetophenone. At the same time, the Cα-Cβ bond also underwent oxidative cleavage catalyzed by CeO₂, producing benzoic acid and further methyl benzoate. The Pd/CeO₂ catalyst could also catalyze the oxidative conversion of organosolv lignin under mild conditions (458 K), producing vanillin, guaiacol and 4-hydroxybenzaldehyde.

Full text of DOI:10.1039/c5gc01473e

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ARTICLE
Oxidative conversion of lignin and lignin model compounds
catalyzed by CeO2-supported Pd nanoparticles
Weiping Deng,a Hongxi Zhang,b Xuejiao Wu,a Rongsheng Li,a Qinghong Zhang*a and Ye Wang*a
Received 00th January 20xx,
Accepted 00th January 20xx
The oxidative transformation of lignin into aromatic compounds is an attractive route for chemical utilization of
lignocellulosic biomass. Unlike hydrogenolysis, no consumption of expensive hydrogen is required for the oxidative
transformation. However, only limited successes have been achieved for the oxidative conversion of lignin. Here, we
report that cerium oxide-supported palladium nanoparticles (Pd/CeO2) can efficiently catalyze the one-pot oxidative
conversion of 2-phenoxy-1-phenylethanol, a lignin model compound containing β-O-4 bond and Cα-hydroxyl group, in
methanol in the presence of O2, producing phenol, acetophenone and methyl benzoate as major products. Pd
nanoparticles played a pivotal role in the oxidation of Cα-hydroxyl group into Cα-ketonic group, which was crucial for the
transformation of the model compound. The presence of Cα-ketonic group activated the β-O-4 bond, which was
subsequently cleaved over the Pd/CeO2 catalyst, affording phenol and acetophenone. At the same time, the Cα−Cβ bond
also underwent oxidative cleavage catalyzed by CeO2, producing benzoic acid and further methyl benzoate. The Pd/CeO2
catalyst could also catalyze the oxidative conversion of Organosolv lignin under mild conditions (458 K), producing vanillin,
guaiacol and 4-hydroxylbenzaldehyde.
DOI: 10.1039/x0xx00000x
www.rsc.org/
been treated as a waste product in the pulp and paper industry,
where it is simply burnt for heat supply.4 Lignin is an
amorphous three dimensional polymer consisting of
Introduction
The catalytic transformation of biomass into chemicals and
fuels is a promising route for establishing a sustainable
chemical society. Lignocellulosic biomass is the most abundant
biomass resource and is inedible. Although the high-
temperature gasification or pyrolysis has been developed for the
transformation of lignocellulosic biomass to syngas or bio-oils,
both processes suffer from the problems of high energy
consumption and low selectivity.1 The development of efficient
catalytic systems for the low-temperature transformation of
lignocellulosic biomass selectively to target products is very
attractive but also highly challenging.
Lignocellulosic biomass is mainly composed of cellulose,
hemicellulose and lignin. There are numerous studies on the
catalytic transformations of cellulose and hemicellulose into
platform chemicals such as glucose, xylose and their
derivatives.2 However, only limited studies have been devoted
to the conversion of lignin to value-added products.3 Lignin has
methoxylated phenylpropane structures, making it a promising
renewable carbon resource for the production of aromatic
compounds. p-Coumaryl, coniferyl and sinapyl alcohols have
been identified as three primary monomers in lignin, and they
are linked by various C−O (e.g., β-O-4, α-O-4 and 4-O-5) and
C−C (e.g., β-5 and 5-5) bonds. The β-O-4 bond is the
predominant linkage in lignin and accounts for 50-60% of all
the C−O linkages (Scheme 1).3 It can be expected that the
selective cleavage of these linkages, in particular the β-O-4
bond, is crucial for the transformation of lignin to aromatics.
Due to the complexity of lignin, many current attempts are
focused on the catalytic conversion of lignin model compounds
a.State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative
Innovation Centre of Chemistry for Energy Materials, National Engineering
Laboratory for Green Chemical Production of Alcohols, Ethers and Esters, College
of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005,
China. E-mail: wangye@xmu.edu.cn, zhangqh@xmu.edu.cn; Fax: +86 592
2183047; Tel: +86 592 2186156
b.Department of Chemistry and Applied Chemistry, Changji University, Changji
831100, Xinjiang, China
†
Electronic Supplementary Information (ESI) available: [XPS spectra, H2-
chemsorption results, HPLC spectra of products from Organosolv lignin conversion,
effects of O2 pressure for the conversion of PP-ol, conversion of PP-one under N2
and O2, conversion of methanol under N2, and the catalytic performances of CeO2
supported Au and Pt catalysts]. See DOI: 10.1039/x0xx00000x
Scheme 1 Structures of a representative lignin fragment and lignin model
compound.
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mimicking the C−O linkages in lignin.
N-oxyl) and HNO3 were employed for the aerobic oxidation of
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DOI: 10.1039/C5GC01473E
Hydrolysis of lignin or lignin model compounds under Cα alcohol, providing Cα ketone with a yield of 94%. The
hydrothermal conditions can lead to the cleavage of C−O bonds, oxidized lignin could easily be hydrolyzed in the presence of
producing phenol derivatives. Acids (e.g., indium triflate) and formic acid/sodium formate, producing low-molecular-mass
bases (e.g., alkali hydroxides, carbonates and hydrotalcites) aromatics with a yield of more than 60 wt%.21 Westwood and
have been reported to catalyse the hydrolysis,5,6 but harsh co-workers reported another catalytic system by combining
reaction conditions (453−673 K) are frequently employed. This DDQ/t-BuONO/O2 (DDQ
=
2,3-dichloro-5,6-dicyano-1,4-
may cause repolymerisation of cleaved products or benzoquinone) for the pre-oxidation of Cα hydroxyl groups in
intermediates, forming a large amount of undesirable chars as lignin and Zn/NH4Cl for the subsequent cleavage of β-O-4
by-products. Moreover, the separation of homogeneous linkages.22 This catalytic system could be applied to the
catalysts from the products is also a problem.
conversions of various lignin model compounds containing β-
Hydrogenolysis is another promising method for the O-4 linkages, providing monomer yields of 80-92%. Moreover,
production of aromatics from lignin and its model compounds this system could catalyze the transformation of birch lignin,
in the presence of H2 or hydrogen sources. Efficient offering phenolic monomers with a yield of 5%.
homogeneous catalytic systems such as Ni,7 Fe,8 and Ru9
Inspired by the encouraging results achieved with
complexes have been reported for the hydrogenolysis. These multicomponent homogeneous catalytic systems, we have been
homogeneous catalysts showed encouraging performances for working for the development of efficient heterogeneous
the activation and cleavage of the C−O bonds under mild catalysts for one-pot oxidative cleavage of β-O-4 linkages in
reaction conditions. However, they suffered from the problems lignin and lignin model compounds under O2. Here, we report
of recovery and recycling uses. Moreover, some catalytic for the first time that a simple Pd/CeO2 can efficiently catalyse
systems are sensitive to air or moisture because of the use of the conversion of a lignin model compound, 2-phenoxy-1-
LiAlH4 or t-BuONa in these systems. Heterogeneous catalysts phenylethanol (Scheme 1), which contains β-O-4 linkage and
have also been investigated for the hydrogenolysis of lignin and Cα-hydroxyl group, into aromatic compounds. This catalyst is
its model compounds.10 For example, by using activated also active for the conversion of Organosolv lignin. The
carbon-supported Ni catalysts, Wang, Xu and their co-workers reaction mechanism for the conversion of lignin model
succeeded in the catalytic conversion of lignosulfonate into compounds with Pd/CeO2 has also been discussed to
phenol products at 473 K.11 Yan and co-workers pointed out accumulate knowledge for the rational design of efficient
that the addition of noble metals such as Au and Ru into Ni heterogeneous catalytic systems for the oxidative
could markedly enhance the catalytic performances for the transformation of lignin into aromatic compounds.
cleavage of C−O bonds in lignin.12 Beside Ni, other metal
catalysts including Cu,13 Mo,14 Pt,15 and Pd16 have also been
demonstrated to be efficient for the catalytic transformations of
Results and discussion
lignin and its model compounds into phenol derivatives via
hydrogenolysis. Although promising, the efficiencies of these
catalytic systems are still low for the transformation of lignin.
Expensive hydrogen or a hydrogen source must be consumed in
the hydrogenolysis. Furthermore, the cleavage of the C−O
bonds may be accompanied by the hydrogenation of aromatic
rings, resulting in mixtures of cyclohexane derivatives.10e,f
As compared to hydrogenolysis, the oxidative transformation
of lignin does not require the consumption of hydrogen or
hydrogen sources and may also produce aromatic compounds.3
Thus, the selective oxidation has also been considered as a
promising strategy for the conversion of lignin. Perovskite-type
composite metal oxides, i.e., LaFe1-xCuxO3 (x = 0, 0.1 and 0.2),
and Pd/Al2O3 catalysts were reported to catalyze the oxidative
conversion of alkaline lignin, forming vanillin and
syringaldehyde,17,18 but the product yields were quite low.
Homogeneous catalysts such as Mn(NO3)2 in combination with
an ionic liquid and Co(salen) exhibited high performances for
the cleavage of the C−O bonds in lignin.19,20 Very recently,
Stahl and co-workers presented a novel strategy for the
selective transformation of lignin into low-molecular-mass
aromatics under mild conditions.21 This strategy involves the
oxidation of the hydroxyl group at the Cα position in lignin into
a ketonic group and the subsequent hydrolysis of the β-O-4
linkage. 4-Acetamido-TEMPO (2,2,6,6-tetramethylpiperidine-
Metal oxide-catalyzed conversion of lignin model compounds
We first investigated the catalytic behaviours of several typical
metal oxides for the oxidative conversion of the lignin model
compound, i.e., 2-phenoxy-1-phenylethanol (denoted as PP-ol
Table 1 Catalytic conversion of 2-phenoxy-1-phenylethanol
over several metal oxidesa
O
O
OH
HO
O
3

Catalyst
O
4
2
1

+
+
methanol
O2
PP-one
AP
5
Phol
6
O
O
2-phenoxy-1-phenylethanol
OCH3
MB
OH
PP-ol
+
BA
Entry
Catalyst
Conv.
(%)
0
9.4
2.1
9.1
5.1
Yieldb (%)
PP-one
BA
0
MB
0
AP
Phol
1
2
3
4
5
blank
Al2O3
SiO2
CeO2
MgO
0
0
0
0
0
0
0
0
0
0
0
2.4
0
0.24
0
3.6
0
0.26
0.18
3.2
3.4
0
0.96
a Reaction conditions: PP-ol, 0.125 g (0.6 mmol); catalyst, 0.2 g; MeOH, 50 mL;
O2, 1 MPa; 458 K; 24 h. b PP-one, BA, MB, AP and Phol denote 2-phenoxy-1-
phenylethanone, benzoic acid, methyl benzoate, acetophenone and phenol,
respectively.
2 | J. Name., 2012, 00, 1-3
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hereafter), in methanol under O2. Methyl benzoate and/or
ARTICLE
Table 2 further shows that the prolonging of theVrieewacAtritioclne Otinmlinee
phenol could be obtained over Al2O3, CeO2 and MgO (Table 1). in the presence of CeO2 from 2 h to 4 h DsiOgIn: 1if0i.c10a3n9tl/yC5iGnCc0re14a7s3eEs
However, the conversions of PP-ol and the yields of aromatic the conversion of PP-one from 76% to 96% (entries 5-7). After
compounds were quite low.
4 h of reaction, the yields of major products, i.e., methyl
We found that 2-phenoxy-1-phenylethanone (denoted as PP- benzoate and phenol, increased to 77% and 87%, respectively.
one hereafter), which contains also β-O-4 bond but Cα-ketonic A further extension of the reaction to 8 h did not significantly
group instead of Cα-hydroxyl group in PP-ol, could be increase the yields of these products. Benzoic acid and
transformed facilely under our reaction conditions. PP-one acetophenone, a product without Cα−Cβ bond cleavage, were
could even be transformed in methanol under O2 at 443 K in the formed as minor products over CeO2. The yield of
absence of a catalyst with a conversion of 21%, producing acetophenone increased gradually with reaction time to 9.1%
benzoic acid, methyl benzoate and phenol as the major products after 8 h of reaction.
(Table 2). This is in agreement with the idea that the cleavage
of β-O-4 bond becomes easier when the Cα-hydroxyl group is
converted to Cα-ketonic group. The formations of benzoic acid
and methyl benzoate instead of acetophenone as the major
products indicated that the Cα−Cβ bond in PP-one also broke
facilely. As displayed in Table 2, SiO2 and Al2O3 provided
similar results to that without a catalyst, suggesting that these
two oxides did not play catalytic roles in the oxidative cleavage
of β-O-4 linkage. On the other hand, the use of MgO or CeO2
considerably accelerated the conversion of PP-one. In particular,
CeO2 exhibited significantly enhanced yields to methyl
benzoate (56%) and phenol (58%) after a reaction at 443 K for
2 h (entry 5). As compared to other metal oxides, the ratio of
methyl benzoate to benzoic acid over CeO2 was significantly
higher, suggesting that CeO2 also catalyzed the esterification of
benzoic acid with methanol efficiently. Although MgO also
showed a high PP-one conversion, the yields to aromatic
compounds were much lower. This is possibly because of the
side-reactions over this solid base. Moreover, because of the
strong basicity, MgO may react with the acidic product, i.e.,
benzoic acid, making the catalyst not recyclable.
Metal oxide-supported Pd-catalyzed conversion of lignin model
compounds and Organosolv lignin
We have clarified that CeO2 was an efficient catalyst for the
cleavage of the β-O-4 linkage in PP-one with Cα-ketonic group.
However, this catalyst could not activate the β-O-4 linkage in
PP-ol with Cα-hydroxyl group. Inspired by recent work using
homogeneous catalytic systems,21,22 we expect that the
promotion of the oxidation of Cα-hydroxyl group to ketonic
group would facilitate the conversion of PP-ol.
Noble metal nanoparticles, in particular Pd nanoparticles, are
known to be efficient for the aerobic oxidation of alcohols to
aldehydes under mild conditions.23 Thus, we exploited CeO2-
supported Pd nanoparticles for the oxidative conversion of PP-
ol. The supported Pd catalysts were prepared by
a
formaldehyde-reduction technique, which was known to
provide highly dispersed metallic Pd nanoparticles loaded on a
support.24 Our XPS studies revealed that the binding energies of
Pd 3d5/2 for supported Pd catalysts were 335 eV (Fig. S1, ESI†).
This confirmed that palladium existed in metallic Pd0 state over
our catalysts.25 We attempted to measure the size of Pd
nanoparticles by TEM, but we failed to obtain high-quality
TEM images due to the poor contrast between Pd and Ce.
Instead, we measured the dispersion of Pd, i.e., the fraction of
surface Pd atoms in all of the Pd atoms, by H2 chemisorption
and estimated the size of Pd particles from the dispersion of Pd.
The results showed that the dispersions of Pd particles over the
metal oxides except for MgO were ~50% (Table S1, ESI†).
Thus, Pd nanoparticles were highly dispersed on these metal
oxides. The dispersion of Pd on MgO was 27%, about half of
those on other oxides. By assuming a spherical-particle model,
the mean diameter of Pd can be roughly estimated by using the
following equation: Pd diameter = 1.12/Pd dispersion (nm).26
The mean diameter of Pd particles was 2.1 nm over CeO2
(Table S1, ESI†). The mean diameters of Pd particles loaded on
SiO2 and Al2O3 were similar, being 2.1 and 2.4 nm,
respectively, while that on MgO was about twice larger (Table
S1, ESI†).
Table 2 Catalytic conversion of 2-phenoxy-1-phenylethanone
over several metal oxidesa
O
O
HO
O
OH
3
+
+

Catalyst
O
4
2
1

acetophenone
benzoic acid
phenol
Phol
methanol
5
BA
AP
6
O
2
O
2-phenoxy-1-phenylethanone
OCH
3
PP-one
methyl benzoate
MB
Entry
Catalyst
Conv.
(%)
21
23
26
Yieldb (%)
MB
3.8
4.2
4.6
BA
9.2
8.2
13
AP
Phol
1
2
3
blank
Al2O3
SiO2
0
0
0
2.3
4.7
5.1
7.2
9.1
15
20
19
27
58
75
87
84
4
5
MgO
CeO2
CeO2
CeO2
CeO2
67
76
92
96
11
4.0
56
69
77
2.8
4.9
7.5
5.5
Table
3 displays the catalytic performances of Pd
6c
7d
8e
nanoparticles loaded on metal oxides for the oxidative
conversion of PP-ol at 458 K under 0.1 MPa O2. As compared
to the results shown in Table 1, it becomes clear that the
introduction of Pd into metal oxides significantly accelerated
the conversion of PP-ol. PP-one was a major product over
Pd/SiO2, Pd/Al2O3 and Pd/MgO catalysts. In particular, the
99
80
a Reaction conditions: substrate, 0.125 g (0.6 mmol); catalyst, 0.1 g; MeOH, 25
mL; O2, 1 MPa; 443 K; 2 h. b BA, MB, AP and Phol denote benzoic acid, methyl
benzoate, acetophenone and phenol, respectively. c 3 h. d 4 h. e 8 h.
This journal is © The Royal Society of Chemistry 20xx
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Table 3 Catalytic conversion of 2-phenoxy-1-phenylethanol
View Article Online
DOI: 10.1039/C5GC01473E
over Pd nanoparticles loaded on several metal oxidesa
O
O
OH
HO
O
3

Catalyst
O
4
2
1

+
+
methanol
O2
PP-one
AP
5
Phol
6
O
O
2-phenoxy-1-phenylethanol
OCH3
MB
OH
PP-ol
+
BA
Entry
Catalyst
Conv.
(%)
34
10
22
Yieldb (%)
PP-one
30
6.0
12
12
BA
0
0
MB
0
0.34
0
AP
Phol
1
2
3
Pd/Al2O3
Pd/SiO2
Pd/MgO
Pd/CeO2
Pd/Al2O3
+ CeO2
Pd/CeO2
Pd/CeO2
Pd/CeO2
Pd/CeO2
3.9
3.8
6.0
38
3.0
3.6
4.0
48
0
4
64
0.03
14
5c
25
2.0
0
18
5.0
20
6d
7e
8f
68
67
70
68
15
14
13
12
0.1
0.1
20
23
27
25
33
31
27
27
40
40
38
39
Fig. 1 Effect of Pd loadings on catalytic behaviours of Pd/CeO2 for the conversion of 2-
phenoxy-1-phenylethanol (PP-ol). (A) PP-ol conversion and PP-one yield. (B) Cleaved
product yields. PP-one, Phol, AP and BA denote 2-phenoxy-1-phenylethanone, phenol,
acetophenone and methyl benzoate, respectively. Reaction conditions: PP-ol, 0.6
mmol; catalyst, 0.2 g; MeOH, 50 mL; O2, 0.1 MPa; 458 K.
0.08
0.07
9g
a Reaction conditions: PP-ol, 0.125 g (0.6 mmol); catalyst (Pd loading, 1.5 wt%),
0.2 g; MeOH, 50 mL; O2, 0.1 MPa; 458 K; 24 h. b PP-one, BA, MB, AP and Phol
denote 2-phenoxy-1-phenylethanone, benzoic acid, methyl benzoate,
acetophenone and phenol, respectively. c Pd/Al2O3 (0.1 g) was mixed with CeO2
and methyl benzoate increased significantly. The increases in
the PP-ol conversion and product yields slowed down as the Pd
loading exceeded 1.5 wt%. These observations further suggest
that Pd nanoparticles play crucial roles in the conversion of PP-
ol by catalysing the oxidation of Cα-hydroxyl group, forming
PP-one intermediate, which undergoes subsequent cleavage of
the β-O-4 and Cα−Cβ bonds. It should be noted that, over CeO2
alone, methyl benzoate was a major product in addition to
phenol during the conversion of PP-one, while acetophenone
was a minor product. The presence of Pd onto CeO2
significantly increased the selectivity of acetophenone, a
product with β-O-4 cleavage but without Cα−Cβ cleavage. This
indicates that the loading of Pd nanoparticles onto CeO2
accelerated the cleavage of β-O-4 bond more than the Cα−Cβ
bond.
The stability of the Pd/CeO2 catalyst for the oxidative
conversion of PP-ol was investigated. After each run, the
catalyst was simply recovered by centrifugation, washing and
drying, and then was used for the next run. The catalytic
performances for the second run were somewhat different from
those for the first run; the PP-ol conversion and the yield to
methyl benzoate increased, whereas the yields to acetophenone
and phenol decreased slightly (Table 3, entries 4 and 6). From
the second to the fifth repeated run, the change in catalytic
behaviours was less significant (Table 3, entries 6-9). The
conversion of PP-ol kept at 67−70%. The yields to phenol and
acetophenone decreased and that of methyl benzoate increased
slightly. After 5 cycles, the yields to phenol, acetophenone and
methyl benzoate was 39%, 27% and 25%, respectively.
(0.1 g). Repeated use in the second run. e Repeated use in the third run.
d
f
Repeated use in the fourth run. g Repeated use in the fifth run.
yield of PP-one reached 30% over the Pd/Al2O3 catalyst. The
yield to the aromatic compounds with β-O-4 bond cleaved over
these catalysts was low. On the other hand, Pd/CeO2 showed
not only a higher PP-ol conversion but also significantly higher
yields to monomeric aromatic compounds. Methyl benzoate,
acetophenone and phenol were the major products over
Pd/CeO2, and their yields were 14%, 38% and 48%,
respectively. The formation of methyl benzoate also indicates
the breakage of the Cα−Cβ bond accompanying with the
cleavage of the β-O-4 linkage. The yield of acetophenone
(38%), which was a β-O-4 cleavage product, was also enhanced
remarkably as compared to that from conversion of PP-ol over
CeO2 (Table 1). In addition, the formation of PP-one was
observed on the Pd/CeO2, indicating the occurrence of the
oxidation of Cα-hydroxyl group to ketonic group. We measured
the catalytic performance of a physical mixture of Pd/Al2O3 and
CeO2 (Table 3, entry 5). As compared to Pd/Al2O3 alone, the
mixture showed higher yields of methyl benzoate and phenol
but a lower yield of PP-one. This is probably because CeO2
catalyzes the conversion of PP-one formed on Pd/Al2O3 (Table
2). However, the physical mixture exhibited significantly lower
PP-ol conversion and lower yields to aromatic compounds (in
particular acetophenone and phenol) than the Pd/CeO2 catalyst.
Thus, synergistic effects exist between Pd and CeO2 in the
Pd/CeO2 catalyst for the oxidative conversion of PP-ol.
It is known that the native lignin contains not only abundant
β-O-4 linkages but also various functional groups (in particular
CH3O-) in aromatic units, and the functional groups may affect
the activation of β-O-4 bonds. Hence, we investigated the
catalytic behaviours of Pd/CeO2 for oxidative conversions of
substituted 2-phenoxy-1-phenylethanol at 458 K. As displayed
We examined the effect of Pd loadings on catalytic
performances of Pd/CeO2 catalysts. The conversion of PP-ol
increased significantly with increasing the Pd loading to > 0.5
wt% (Fig. 1). The formation of PP-one became considerable at
the same time. Meanwhile, the yields of phenol, acetophenone
4 | J. Name., 2012, 00, 1-3
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Table 4 Catalytic performances of Pd/CeO2 for conversion of
Table 5 Catalytic conversion of Organosolv lignin over Pd/CeO
View Article Online
DOI: 10.1039/C5GC01473E
2
substituted 2-phenoxy-1-phenylethanol model compoundsa
catalysta
O
O
H3CO
HO
+
HO
Catalyst
Vanillin
4-Hydroxylbenzaldehyde
Organosolv lignin
methanol
OCH3
O
2
+
+
Unknown
OH
Guaiacol
Entry
Substrate
Conv.
(%)
Yieldb (%)
Phenol Ketone Ether
MB
26
AP
34
Yield (wt%)
OH
O
Vanillin
5.2
Guaiacol
0.87
4-Hydroxylbenzaldehyde
2.4
Unknownb
n.d.
1
2
3
4
86
90
90
88
64
82
68
72
0
0
22
0
OH
O
40
25
28
38
38
34
a
Reaction conditions: Organosolv lignin, 0.10 g; catalyst, 0.20 g; MeOH, 50 mL;
O2, 0.1 MPa; 458 K; 24 h. b Not detected.
O
OH
OH
O
O
O
O
11
13
6.4
3.2
Reaction mechanism for the conversion of lignin model
compounds
a Reaction conditions: substrate, 0.6 mmol; Pd/CeO2, 0.2 g; MeOH, 50 mL; O2, 0.1
MPa; 458 K; 24 h. b MB, AP, Phenol, Ketone and Ether denote methyl benzoate,
acetophenone, substituted phenol, substituted ketone and ether, respectively.
The elucidation of reaction mechanism for the conversion of
lignin model compounds is useful for the design of efficient
catalysts for the transformation of lignin to aromatic
compounds. To clarify the reaction pathways for the present
system, we investigated the time course for the conversion of
PP-ol over the Pd/CeO2 catalyst at 458 K under O2 atmosphere.
As displayed in Fig. 2, PP-one was formed as a major product
at the initial stage under our reaction conditions. The PP-one
selectivity was ~80% at a reaction time of 0.5 h. With
increasing the reaction time, the selectivity to PP-one decreased
sharply and those to phenol, acetophenone and methyl benzoate
increased. After 12 h of reaction, the change of product
selectivity became less significant. These observations confirm
our speculation that the conversion of PP-ol proceeds through a
tandem pathway via PP-one intermediate over the Pd/CeO2
catalyst.
in Table 4, the Pd/CeO2 could catalyse the oxidative
transformations of all these model compounds. As compared to
PP-ol, the substituted PP-ol was more reactive with our system,
and higher yields to the aromatic compounds could be obtained.
For instance, for the conversion of 2-(4-methoxyphenoxy)-1-
phenylethanol with a methoxy group at 458 K for 24 h, the
conversion was 90% and the yields to methyl benzoate,
acetophenone and 4-methoxyphenol were 40%, 38% and 82%,
respectively (Table 4, entry 2). This result indicates that the
presence of an electron-donor group such as CH3O-, which is
usually contained in the native lignin, facilitates the cleavage of
the β-O-4 bond and favours the formation of aromatic
compounds.
A few recent studies have pointed out the key roles of the
pre-oxidation of Cα-hydroxyl group to the corresponding
carbonyl group in the transformation of lignin or its model
We further performed the oxidative transformation of
Organosolv lignin in methanol under O2 using the Pd/CeO2
catalyst at 458 K for 24 h. The products were complicated and
some of them were still unknown (Fig. S2, ESI†). We identified
the formations of several monomeric aromatic compounds
including vanillin, guaiacol and 4-hydroxylbenzaldehyde, and
the yields of these compounds were 5.2 wt%, 0.87 wt% and 2.4
wt%, respectively (Table 5). The analyses of the solid residue
recovered from the reaction system indicated no significant
deposition of chars on the solid catalyst. A perovskite-type
LaFe0.8Cu0.2O3 catalyst was reported to catalyse the wet
oxidation of lignin, but a corrosive strong base such as NaOH
was required.17 This system provided maximum yields to
vanillin and 4-hydroxylbenzaldehyde of 4.56 wt% and 2.49
wt%, repsctively.17 The oxidative conversion of alkaline lignin
could be catalysed by a Pd/Al2O3 catalyst, producing vanillin
with a yield of 1.6 wt%.18 Our present result demonstrate that
Pd/CeO2 is a promising catalyst for the oxidative conversion of
lignin to aromatic compounds without using corrosive additives.
Fig. 2 Time course for the conversion of 2-phenoxy-1-phenylethanol (PP-ol)
catalyzed by Pd/CeO2. (A) PP-ol conversion. (B) Product selectivity. PP-one, Phol, AP
and MB denote 2-phenoxy-1-phenylethanone, phenol, acetophenone and methyl
benzoate, respectively. Reaction conditions: PP-ol, 0.6 mmol; catalyst, 0.2 g;
MeOH, 50 mL; O2, 0.1 MPa; 458 K.
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ARTICLE
Journal Name
compounds.21,22 The pre-oxidized lignin or its model CO could be formed with concentrations of 4 mol% and 2
View Article Online
compounds becomes more reactive and could be facilely mol%, respectively, at 458 K for 2 h (DTOabI:l1e0.1S043,9/ECS5GI†C)0.14T7h3Ee
transformed to aromatic compounds. This has been confirmed result confirms the occurrence of methanol dehydrogenation
by DFT calculations, which reveal that the β-O-4 bond over Pd/CeO2 under our reaction conditions. Taking all these
dissociation enthalpy decreases from 69.5 to 60.6 kcal mol-1 by facts into account, we propose that, in the absence of O2,
changing the Cα-OH into Cα=O.27 However, relatively Pd/CeO2 activates methanol, which affords active H species for
complicated systems such as 4-acetamido-TEMPO/HNO3 and the hydrogenolysis of the β-O-4 bond, producing phenol and
DDQ/t-BuONO/O2 have been exploited to perform the pre- acetophenone.
oxidation of lignin or its model compounds.21,22 Our present
Then, we discuss the mechanism under O2 atmosphere. O2
work has demonstrated that Pd nanoparticles loaded on CeO2 favours the formation of the Cα=O group, which can lower the
can catalyse the oxidation of the Cα-OH into Cα=O, resulting in energy barrier for breaking the β-O-4 bond. Our studies confirm
significant enhancement in the conversion of 2-phenoxy-1- that PP-one is much more reactive than PP-ol in the absence of
phenylethanol, a lignin model compound. We speculate that O2 (Tables S2 and S3, ESI†). Thus, the hydrogenolysis step
such a pre-oxidation reduced energy barrier for the cleavage of would be accelerated. Furthermore, our results have suggested
the β-O-4 bond.
that O2 is also involved in the oxidative cleavage of Cα−Cβ
To further understand the role of O2, we examined the effect linkage, resulting in the formation of benzoic acid or methyl
of O2 pressure on the conversion of 2-phenoxy-1-phenylethanol benzoate (Tables S2 and S3, ESI†). To gain further insights into
over the Pd/CeO2 catalyst. We observed a 6.7% conversion of the cleavage of Cα−Cβ bond, we performed catalytic
PP-ol in the absence of O2 (Table S2, entry 1, ESI†). The major conversions of several possible intermediates under O2
products were phenol and acetophenone. Neither benzoic acid atmosphere over Pd/CeO2 at 458 K. Table 6 shows that
nor methyl benzoate was formed in the absence of O2. This acetophenone is very stable under our reaction conditions (entry
suggests that only the cleavage of the β-O-4 bond can occur in 1). Thus, benzoic acid and methyl benzoate, two products with
the absence of O2. The presence of O2 not only promoted the Cα−Cβ cleaved, could not be formed by a consecutive oxidation
conversion of PP-ol, but also led to the formation of methyl of acetophenone. We have considered the possibility of direct
benzoate (Table S2, entry 2, ESI†). An increase in the O2 hydrogenolysis of the Cα−Cβ bond. If the hydrogenolysis of the
pressure increased the efficiency for the cleavage of both β-O-4 Cα−Cβ bond of PP-ol occurs, anisole and benzyl alcohol or
and Cα−Cβ linkages (Table S2, entry 3, ESI†).
benzyl aldehyde are expected to be formed. Although benzyl
We further performed the conversion of PP-one over the alcohol and benzyl aldehyde could be easily converted to
Pd/CeO2 catalyst. Similarly, acetophenone and phenol, the benzaldehyde, benzoic acid or methyl benzoate over Pd/CeO2
products with β-O-4 bond cleaved, were mainly formed in the catalyst under O2 atmosphere (Table 6, entries 3 and 4,), anisole
absence of O2 (Table S3, entry 1, ESI†). The yields of the two could not be oxidized under our reaction conditions (Table 6,
products reached 20% and 18% after a reaction at 458 K for 2 h, entry 2). However, during the conversion of PP-ol, we could
which were significantly higher than those obtained for the not observe the formation of anisole. Thus, we could exclude
conversion of PP-ol at 458 K for 24 h. The presence of O2 also the possibility of the direct hydrogenolysis to cleave the Cα−Cβ
increased the conversion of PP-one and the yields of linkage in PP-ol.
acetophenone and phenol (Table S3, entry 2, ESI†). Moreover,
methyl benzoate, the product with Cα−Cβ linkage cleaved, was intermediates
We further investigated the conversions of three possible
including 1-phenylethane-1,2-diol, 2-
also formed with a considerable yield under O2. These hydroxyacetophenone and methyl benzoylformate (Table 7),
observations further confirm that PP-one, an intermediate for which contained Cα−Cβ linkage, under the oxidative reaction
PP-ol conversion, is much more reactive than PP-ol. conditions to gain information on the cleavage of Cα−Cβ bond.
Acetophenone and phenol can be formed facilely from PP-one
via the cleavage of β-O-4 bond over Pd/CeO2 even in the
absence of O2, and the presence of O2 accelerates the breakage
of the Cα−Cβ linkage.
Table 6 Catalytic conversions of possible intermediates under
a
O2 atmosphere over Pd/CeO2
Entry
Substrate Conv. (%)
Yield (%)
Here, we first discuss possible reaction mechanism in the
absence of O2. Xu and co-workers once pointed out that
methanol can be used as an ideal hydrogen source for
hydrogenolysis of lignin model compounds over supported Ni
catalyst.11 We speculate that methanol can facilely be activated
over our catalyst to generate active hydrogen species. Actually,
Yee et al.28 already demonstrated that CeO2 alone was capable
of catalysing the dehydrogenation of alcohol owing to its
reducibility and basicity. The introduction of Pd could greatly
decrease the activation energy for methanol dehydrogenation,
and hence the reaction rate was increased by one order of
magnititude.28 Our studies for the conversion of methanol in the
absence of O2 over the Pd/CeO2 catalyst revealed that H2 and
O
O
O
OH
OCH3
1
O
1
2
3
0
0
0
0
0
0
-
0
0
O
0
0
-
O
69
OH
59
31
28
8.1
4
16
12
21
2.1
a Reaction conditions: substrate, 0.6 mmol; Pd/CeO2, 0.1 g; MeOH, 50 mL; O2, 0.1
MPa; 458 K; 2 h.
6 | J. Name., 2012, 00, 1-3
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Journal Name
Table 7 Catalytic conversions of possible intermediates with
ARTICLE
O
O
OH
3
6
Pd
O2
Pd/CeO2
View Article Online
HO

O
O
4
a
2
1

DOI: 10.1039/C5G+C01473E
Cα−Cβ linkage under O2 atmosphere over Pd/CeO2
CH3OH
5
O2
CeO2
Yield (%)
Entry Substrate
Conv.
(%)
CH3OH
O
O
O
O
OH
O
O
O
O
O
OCH3
OH
OH
+
HO
O
O
1
O
+
+
+
OH
O
100
100
45
54
24
18
1.2
6.8
3.8
17
23
OH
1
2
3
CO2
O
O
CeO2
3.2
OH
O
O
O
CH3OH
OCH3
OH
74
-
51
1.3
0
0
O
Scheme 2 Proposed reaction mechanism for the oxidative conversion of 2-phenoxy-1-
phenylethanol
.
a Reaction conditions: substrate, 0.6 mmol; Pd/CeO2, 0.1 g; MeOH, 50 mL; O2, 0.1
MPa; 458 K; 2 h.
Our results and mechanism have clearly pointed out the
crucial role of the pre-oxidation of Cα-OH. Thus, it can be
expected that any catalysts that can oxidize the Cα-OH may
enhance the oxidative transformation of lignin or its model
compounds. Beside Pd nanoparticles, we have also loaded other
metal (such as Au and Pt) nanoparticles onto CeO2. All these
catalysts could catalyse the transformation of 2-phenoxy-1-
phenylethanol into monomeric aromatic compounds (Table S5,
ESI†). Although the conversions over the Au/CeO2 and
Pt/CeO2 were lower than that over Pd/CeO2, the results
confirmed that the use of the present CeO2-supported metal
nanoparticles is a simple and effective strategy for one-pot
oxidative transformation of lignin model compounds into
monomeric aromatics. We expect that the further design of
more efficient heterogeneous catalysts using this strategy may
contribute to increasing the yield of aromatic compounds from
lignin.
As displayed in Table 7, 1-phenylethane-1,2-diol and 2-
hydroxyacetophenone were very reactive under our reaction
conditions (entries 1 and 2). After 2 h of reaction, the
conversions of both compounds reached 100%. The hydroxyl
group at the terminal carbon atom was oxidized into carboxyl
group and converted to methyl ester in methanol. Meanwhile,
approximately half of the C−C bonds in both compounds were
cleaved, forming corresponding monomeric aromatics (Table 7,
entries 1 and 2). Methyl benzoylformate, which can be obtained
from 1-phenylethane-1,2-diol or 2-hydroxyacetophenone, could
also be facilely converted, producing C−C cleaved products
under O2 within 2 h (Table 7, entry 3). As compared to PP-ol,
these compounds exhibited relatively high reactivity even
though the reaction was performed for a much shorter reaction
time and a lower catalyst/substrate ratio. The larger steric-
hindrance of PP-ol is probably a main reason for its lower
reactivity. In other words, due to the presence of bulky benzyl
groups, the C-C bond in PP-ol may be accessed by the active
site more difficultly.
Conclusions
Based on the results and discussion described above, we
propose a reaction mechanism for the conversion of 2-phenoxy-
1-phenylethanol (PP-ol) over Pd/CeO2 in methanol under O2
atmosphere in Scheme 2. In brief, the Cα-OH of PP-ol is first
oxidized owing to the catalytic function of Pd nanoparticles,
forming PP-one, whose β-O-4 bond becomes weakened
because of the presence of Cα=O. DFT calculations pointed out
that the bond dissociation energy of the β-O-4 bond was much
lower than that of the Cα−Cβ bond.13e Thus, it is reasonable to
consider that the cleavage of β-O-4 bond occurs prior to the
cleavage of Cα−Cβ bond. The subsequent hydrogenolysis of the
β-O-4 bond of PP-one could produce acetophenone and phenol
over the Pd/CeO2 catalyst. On the other hand, the oxidative
cleavage of the β-O-4 bond on CeO2 may mainly result in the
formations of phenol and an oxidized intermediate such as 2-
hydroxyacetophenone. A small fraction of acetophenone may
also be formed in this process. The oxidized intermediate would
undergo rapid oxidative C−C bond cleavage (Table 7), forming
benzoic acid and further methyl benzoate.
We found that Pd/CeO2 was an efficient and stable
heterogeneous catalyst for the oxidative transformation of
lignin and lignin model compounds into monomeric aromatic
compounds. Phenol, acetophenone and methyl benzoate were
produced with yields of 48%, 38% and 14%, respectively, for
the transformation of 2-phenoxy-1-phenylethanol at 458 K
under 0.1 MPa O2 atmosphere for 24 h. The presence of a
−OCH3 substituent, which usually exists in the native lignin,
further increased the performance. The yields of 4-
methoxyphenol, acetophenone and methyl benzoate reached
82%, 38% and 40%, respectively, for the conversion of 2-(4-
methoxylphenoxy)-1-phenylethanol. The present catalyst could
also be applied to the direct transformation of Organosolv
lignin in methanol under O2 atmosphere, providing vanillin,
guaiacol and 4-hydroxylbenzaldehyde with good yields. We
clarified that Pd nanoparticles played a crucial role in the
oxidation of Cα-OH group into Cα=O and this weakened the β-
O-4 bond. Our mechanistic studies suggest that the activated β-
O-4 bond may either be cleaved via hydrogenolysis forming
acetophenone and phenol or undergo oxidative cleavage,
forming phenol, oxidized intermediates such as 2-
hydroxyacetophenone as well as
a
small fraction of
acetophenone. The oxidized intermediate could undergo rapid
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C
−
C bond cleavage, producing benzoic acid and further methyl (0.6 mmol) or Organosolv lignin (0.1 g) were added into the
View Article Online
DOI: 10.1039/C5GC01473E
benzoate.
Teflon-lined stainless-steel reactor (70 mL) pre-charged with
methanol (25 or 50 mL). After purging and introduction of O2
with a pressure of 1.0 or 0.1 MPa, the reactor was placed in an
oil bath. The amount of O2 contained in the system was
estimated to be ~8 or ~0.8 mmol. When the desired temperature
(443 or 458 K) was reached, the reaction was started by
vigorous stirring with a magnetic stirrer. After a fixed time, the
reaction was stopped by cooling the reactor to room
temperature. Note that the co-presence of fine noble metal
particles and high-pressure oxygen in methanol may cause
strong exothermic reactions at a high temperature. The catalyst
was recovered by filtration and the liquid products were
analyzed by a HPLC (Shimazu LC-20A) equipped with RI and
UV-vis detectors and a C18 column (7 mm, 8×300 mm). A
mixture of water and acetonitrile (volume ratio of 4/6) was used
as a mobile phase with a flow of 0.5 cm3 min-1. The conversion
of a model compound is defined as: the mole of converted
substrate/the mole of total substrate × 100 (%). The yield of a
bond-cleaved product is defined as: the mole of the product/the
total mole of the substrate × 100 (%).
Experimental
Materials
SiO2, CeO2, Al2O3 and MgO were the commercial products of
Alfa Aesar. PdCl2, H2AuCl4 and H2PtCl6 were purchased from
Sinopharm Chemical Reagent Co., Ltd. 2-bromo-1-
phenylethanone (98%), guaiacol (98%), 4-methoxyphenol
(98%), 4-methylphenol (98%), guaiacol (98%) were purchased
from J&K Chemical company without further purification.
2-Phenoxy-1-phenylethanone (PP-one) was synthesized by a
modified procedure published in literature.13e Typically, 2-
bromo-1-phenylethanone (11.8 g, 49 mmol) and phenol (8 g, 85
mmol) were dissolved in 250 mL acetone, mixed with K2CO3
(12.3 g, 89 mmol) and refluxed at 343 K for 12 h. After cooling
down to room temperature, K2CO3 was separated by filtration.
Then, the product was obtained by recrystallization from
ethanol.
2-Phenoxy-1-phenylethanol (PP-ol) was synthesized by
selective reduction of the carbonyl group in 2-phenoxy-1-
phenylethanone. 2-Phenoxy-1-phenylethanone (1.5 g, 6.8 mmol)
was first dissolved in 35 mL mixture of tetrahydrofuran and
water (4/1, v/v). NaBH4, which was used as a reductant, was
added into the solution and the solution was then stirred at
room temperature for 6 h. A saturated solution of ammonium
chloride (50 mL) followed by 50 mL water was added into the
reaction mixture. Then, the product was extracted by ethyl ether,
washed with saturated NaCl and recrystallized from ethanol.
Similar procedures were also employed for the synthesis of
other β-O-4 lignin model compounds.
The supported Pd catalysts were prepared by a formaldehyde
reduction method.24 For example, for the preparation of the
Pd/CeO2 catalyst, 1.0 g of CeO2 was added in an aqueous
solution of H2PdCl4 (0.05 M) under stirring. After the pH value
of the suspension was adjusted to 10 by adding NaOH aqueous
solution, the mixture was heated to 333 K. Then, 100 mL of
formaldehyde solution (1 wt%) was added dropwise into the
mixture. After stirring for 1 h, the Pd/CeO2 was obtained by
thoroughly washing, followed by drying at 308 K in vacuum.
Acknowledgements
This work was supported by National Natural Science
Foundation of China (21173172 and 21473141), the Research
Fund for the Doctorial Program of Higher Education
(No.20130121130001), and the Program for Innovative
Research Team in University (No. IRT_14R31).
Notes and references
1
(a) J. O. Metzger, Angew. Chem. Int. Ed., 2005, 45, 696; (b) G.
W. Huber, S. Iborra and A. Corma, Chem. Rev., 2006, 106
4044; (c) B. Kamm, Angew. Chem. Int. Ed., 2007, 46, 5056.
(a) J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew.
Chem. Int. Ed., 2007, 46, 7164; (b) R. Ranaldi and F. Shuth,
,
2
ChemSusChem, 2009,
P. A. Jacobs and B. F. Sels, ChemCatChem, 2011,
Shimizu and A. Satsuma, Energy Environ. Sic., 2011,
2
, 1096; (c) S. Van de Vyver, J. Geboer,
, 82; (d) K.
, 3140;
3
4
(e) C. Zhou, X. Xia, C. Lin, D. Tong and J. Beltramini, Chem.
Soc. Rev., 2011, 40, 5588; (f) W. Deng, Q. Zhang and Y. Wang,
Dalton Trans., 2012, 41, 9817; (g) A. Wang and T. Zhang, Acc.
Chem. Res., 2013, 46, 1377; (h) M. Yabushita, H. Kobayashi
and A. Fukuoka, Appl. Catal. B: Environ., 2014, 145, 1; (i) P.
Mäki-Arvela, T. Salmi, B. Holmbom, S. Willför and D Y.
Murzin, Chem. Rev., 2011, 111, 5638;
Characterization
X-ray photoelectron spectra (XPS) were recorded with a
Quantum 2000 Scanning ESCA Microprobe instrument
(Physical Electronics) using Al Kα radiation. The binding
energy was calibrated using C1s photoelectron peak at 284.6 eV
as a reference. The H2 chemisorption was measured with a
Micromeritics ASAP 2010C instrument.
3
(a) J. Zakzeski, P. C. A. Bruijnincx, A. L. Jongerius and B. M.
Weckhuysen, Chem. Rev., 2010, 110, 3552; (b) 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, 124683.
4
5
M. Kleinert and T. Barth, Chem. Eng. Technol., 2008, 31, 736.
Catalytic reaction
L. Yang, Y. Li and P. E. Savage, Ind. Eng. Chem. Res., 2014, 53
,
2633.
The conversions of lignin model compounds and Organosolv
lignin were performed in a batch-type high-pressure autoclave
reactor, in which the reaction could proceed in a solvothermal
manner. Typically, the catalyst (0.1 g) and 2-phenoxy-1-
phenylethanol (0.6 mmol) or other β-O-4 model compounds
6
(a) J. E. Miller, L Evans, A. Littlewolf and D. E. Trudell, Fuel,
1999, 78, 1363; (b) V. M. Roberts, V. Stein, T. Reiner, A. A.
Lemonidou, X. Li and J. A. Lercher, Chem. Eur. J., 2011, 17
,
5939; (c) V. M. Roberts, S. Fendt S, A. A. Lemonidou, X. Li and
J. A. Lercher, Appl. Catal. B: Environ., 2010, 95, 71; (d) V. M.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 9 of 10
Green Chemistry
Journal Name
ARTICLE
Roberts, R. T. Knapp, X. Li and J. A. Lercher, ChemCatChem, 22 C. S. Lancefield, O. S. Ojo, F. Tran and N. JV.ieWw Aertsictlwe Oonolidne,
2010, , 1407; (e) M. R. Sturgeon, M. H. O’Brien, P. N. Angew. Chem. Int. Ed., 2015, 54, 258.
Ciesielski, R. Katahira, J. S. Kruger, S. C. Chmely, J. Hamlin J, K. 23 (a) D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu, A.
2
DOI: 10.1039/C5GC01473E
Lawrence, G. B. Hunsinger, T. D. Foust, R. M. Baldwin, M. J.
Biddy and G. T. Beckham, Green Chem., 2014, 16, 824; (f) S.
Dabral, J. Motweiler, T. Rinesch and C. Bolm, Green Chem.,
2015, doi: 10.1039/c5gc00186b.
(a) A. G. Sergeev and J. F. Hartwig, Science, 2011, 332, 439;
(b) A. G. Sergeev, J. D. Webb and J. F. Hartwig, J. Am. Chem.
Soc., 2012, 134, 20226; (c) P. Kelley, S. Lin, G. Edouard, M. W.
Day and T. Agapie, J. Am. Chem. Soc., 2012, 134, 5480.
Y. Ren, M. Yan, J. Wang, Z. Zhang and K. Yao, Angew. Chem.
Int. Ed., 2013, 52, 12674.
F. Carley, A. A. Herzing, M. Watanabe, C. J. Kiely, D. W.
Knight and G. J. Hutchings, Science, 2006, 311, 362. (b) A. H.
Lu, W. C. Li, Z. Hou and F. Schüth, Chem. Commun., 2007,
1038; (c) Y. Chen, G. Zhen, T. Chen and Y. Yang, J. Catal.,
2010, 275, 11; (d) Q. Zhang, W. Deng and Y. Wang, Chem.
Commun., 2011, 47, 9275; (e) G. Chem, S. Wu, H. Liu, H. Jiang
and Y. Li, Green Chem., 2013, 15, 230; (f) R. B. Nasir Baig, M.
N. Nadagouda and R. S. Varma, Green Chem., 2014, 16, 4333;
(g) Z. Guo, B. Liu, Q. Zhang, W. Deng, Y. Wang and Y. Yang,
Chem. Soc. Rev., 2014, 43, 3480.
7
8
9
(a) J. M. Nichols, L. M. Bishop, R. G. Bergman and J. A. Ellman, 24 B. Hu, W. Deng, R. Li, Q. Zhang, Y. Wang, F. Delplanque-
J. Am. Chem. Soc., 2010, 132, 12554; (b) T. vom Stein, T.
Weigand, C. Merkens, J. Klankermayer and W. Leitner,
Janssens, D. Paul, F. Desmedt and P. Miquel, J. Catal., 2014,
319, 15.
25 J. F. Moulder, W. F. Stickle, P. E. Sobol and K. D. Bomben,
Handbook of X-ray Photoelectron Spectroscopy, Physical
Electronics, Inc., Eden Prairie, 1995.
ChemCatChem, 2013,
5
, 439.
10 (a) X. Wang and R. Rinaldi, ChemSusChem, 2012,
5, 1455; (b)
J. He, C. Zhao and J. A. Lercher, J. Am. Chem. Soc., 2012, 134
,
20768; (c) V. Molinari, C. Giodano, M. Antonietti and D. 26 N. Mahata and V. Vishwanathan, J. Catal., 2000, 196, 262.
Esposito, J Am Chem Soc, 2014, 136, 1758; (d) M. Zaheer, J. 27 S. Kim, S. C. Chmely, M. R. Nimlos, Y. J. Bomble, T. D. Foust, R.
Hermamsdorfer, W. P. Kretschmer, G. Motz and R. Kempe,
ChemCatChem, 2014, , 91. (e) J. He, L. Lu, C. Zhao, D. Mei
S. Paton and G. T. Beckham, J. Phys. Chem. Lett., 2011, 2,
2846.
6
and J. A. Lercher, J. Catal., 2014, 311, 41; (f) J. He, L. Lu, C. 28 A. Yee, S. J. Morrison and H. Idriss, J. Catal., 1999, 186, 279.
Zhao, D. Mei and J. A. Lercher, J. Catal., 2014, 309, 280.
11 (a) Q. Song, F. Wang and J. Xu, Chem. Commun., 2012, 48
7019; (b) Q. Song, F. Wang, J. Cai, Y. Wang, J. Zhang, W. Yu
and J. Xu, Energy Environ. Sci., 2013, , 994.
12 (a) J. Zhang, J. Teo, X. Chen, H. Asakura, T. Tanaka, K.
Teramura and N. Yan, ACS Catal, 2014, , 1574; (b) J. Zhang,
,
6
4
H. Asakura, J. van Rijn, J. Yang, P. Duchesne, B. Zhang, X.
Chen, P. Zhang, M. Saeys and N. Yan, Green Chem., 2014, 16
,
2432.
13 (a) G. S. Macala, T. D. Matson, C. L. Johnson, R. S. Lewis, A. V.
Iretskii and P. C. Ford, ChemSusChem, 2009, 2, 215; (b) K.
Barta, T. D. Matson, M. L. Fettig, S. L. Scott, A. V. Iretskii and
P. C. Ford, Green Chem, 2010, 12, 1640; (c) T. D. Matson, K.
Barta, A. V. Iretskii and P. C. Ford, J. Am. Chem. Soc., 2011,
133, 14090; (d) K. Barta, G. R. Warner, E. S. Beach and P. T.
Anastas, Green Chem., 2014, 16, 191; (e) Z. Strassberger, A. H.
Alberts, M. J. Louwerse, S. Tanase and G. Rothenberg, Green
Chem., 2013, 15, 768; (f) X. Huang, T. I. Koranyi, M. D. Boot
and E. J. M. Hensen, ChemSusChem, 2014, 7, 2276.
14 (a) A. L. Jongerious, R. Jastrzebski, P. C. A. Bruijnincx and B.
M. Weckhuysen, J. Catal., 2012, 285, 315; (b) A. L. Jongerious,
P. C. A. Bruijnincx and B. M. Weckhuysen, Green Chem., 2013,
15, 3049; (c) D. J. Rensel, S. Rouvimov, M. E. Gin and J. C.
Hicks, J. Catal., 2013, 305, 256; (d) R. Ma, W. Hao, X. Ma, Y.
Tian and Y. Li, Angew. Chem. Int. Ed., 2014, 53, 7310.
15 (a) M. Chatterjee, T. Ishizaka, A. Suzuki and H. Kawanami,
Chem. Commun., 2013, 49, 4567; (b) W. Xu, S. J. Miller, P. K.
Agrawal and C. W. Jones, ChemSusChem, 2012,
16 (a) M. V. Galkin, S. Sawadjoon, V. Rohde, M. Dawange and J.
S. M. Samec, ChemCatChem, 2014, , 179; (b) T. H. Parsell, B.
5, 667.
6
C. Owen, I. Klein, T. M. Jarrell, C. L. Marcum, L. J. Haupert, L.
M. Amundson, H. I. Kenttamaa, F. Ribeiro, J. T. Miller and M.
M. Abu-Omar, Chem. Sci., 2013, 4, 806.
17 J. Zhang, H. Deng, and L. Lin, Molecules, 2009, 14, 2747.
18 F. G. Sales, L. C.A. Maranhão, N. M. Lima Filho and C. A.M.
Abreu, Chem. Eng. Sci., 2007, 62, 5386.
19 K. Stark, N. Taccardi, A. Bosmann and P. Wasserscheid,
ChemSusChem, 2010, 3, 719.
20 C. Canevali, M. Orlandi, L. Pardi, B. Rindone, R. Scotti, J. Sipila,
F. Morazzoni, J. Chem. Soc. Dalton Trans., 2002, 3007.
21 (a) A. Rahimi, A. Azarpira, H. Kim, J. Ralph and S. S. Stahl, J.
Am. Chem. Soc., 2013, 135, 6415; (b) A. Rahimi, A. Ulbrich, J.
J. Coon and S. S. Stahl, Nature, 2014, 515, 249.
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Green Chemistry
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DOI: 10.1039/C5GC01473E
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Oxidative conversion of lignin and lignin model compounds
catalyzed by CeO2-supported Pd nanoparticles
Weiping Deng,a Hongxi Zhang,b Xuejiao Wu,a Rongsheng Li,a Qinghong Zhang*a and Ye Wang*a
Pd/CeO2 efficiently catalyzes the oxidative conversion of 2ꢀphenoxyꢀ1ꢀphenylethanol, a lignin
model compound with βꢀOꢀ4 linkage, in methanol, producing monomeric aromatics.