Single-step conversion of lignin monomers to phenol: Bridging the gap between lignin and high-value chemicals

Article abstract of DOI:10.1016/S1872-2067(18)63132-8

Transformation of lignin into high-value chemicals is hampered by the complexity of monomers obtained from lignin depolymerization. Here we report a strategy, composed of hydro-demethoxylation and de-alkylation reactions, that is able to chemically converge various lignin-derived phenolic monomers into phenol in a single-step. Using 2-methoxy-4-propylphenol as a model compound, Pt/C exhibited the best performance in hydro-demethoxylation reaction affording >80% 4-propylphenol from 2-methoxy-4-propylphenol, while H-ZSM-5 was identified as the most suitable catalyst for de-alkylation, achieving 83% yield of phenol from 4-propylphenol. Since the two catalysts operate under compatible conditions, combining the two catalysts to simultaneously promote both hydro-demethoxylation and de-alkylation reactions was achieved. Configuration of how to organize the catalysts is a critical parameter, where the physical mixture of the two was most effective, providing over 60% phenol from 2-methoxy-4-propylphenol in a single-step.

Full text of DOI:10.1016/S1872-2067(18)63132-8

Chinese Journal of Catalysis 39 (2018) 1445–1452
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Single‐step conversion of lignin monomers to phenol: Bridging the
gap between lignin and high‐value chemicals
Jiaguang Zhang a,b,†, Loris Lombardoa,c,†, Gökalp Gözaydına, Paul J. Dysonc, Ning Yan a,*
a Department of Chemical and Biomolecular Engineering, National University of Singapore, 117585 Singapore
b School of Chemistry, University of Lincoln, Joseph Banks Laboratories, Green Lane, Lincoln, LN6 7DL, United Kingdom
c Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH‐1015, Switzerland
A R T I C L E I N F O
A B S T R A C T
Article history:
Transformation of lignin into high‐value chemicals is hampered by the complexity of monomers
Received 28 June 2018
Accepted 4 July 2018
Published 5 September 2018
obtained from lignin depolymerization. Here we report a strategy, composed of hy‐
dro‐demethoxylation and de‐alkylation reactions, that is able to chemically converge various lig‐
nin‐derived phenolic monomers into phenol in a single‐step. Using 2‐methoxy‐4‐propylphenol as a
model compound, Pt/C exhibited the best performance in hydro‐demethoxylation reaction afford‐
ing >80% 4‐propylphenol from 2‐methoxy‐4‐propylphenol, while H‐ZSM‐5 was identified as the
most suitable catalyst for de‐alkylation, achieving 83% yield of phenol from 4‐propylphenol. Since
the two catalysts operate under compatible conditions, combining the two catalysts to simultane‐
ously promote both hydro‐demethoxylation and de‐alkylation reactions was achieved. Configura‐
tion of how to organize the catalysts is a critical parameter, where the physical mixture of the two
was most effective, providing over 60% phenol from 2‐methoxy‐4‐propylphenol in a single‐step.
© 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Keywords:
Lignin
Phenol
Zeolite
De‐alkylation
Hydro‐demethoxylation
Published by Elsevier B.V. All rights reserved.
1. Introduction
is composed of three types of substituted phenols connected by
a number of C–O and C–C bonds, forming a three‐dimensional
Lignin, a main component of lignocellulosic biomass ac‐
counting for 15%–30% by weight and 40% by energy [1,2], is
still not sufficiently used in biorefineries. Despite the significant
advances in lignin depolymerisation via hydrogenolysis [3–21],
oxidation [22–27], hydrolysis [28–34], thermal [35–37], photo‐
[38–40] and electro‐chemical [41] transformations in the past
decade, the depolymerized lignin is most often a complex mix‐
ture of phenolic compounds hampering direct use as high‐value
chemicals. This is first of all attributed to the non‐uniform na‐
ture of lignin. Unlike cellulose [42] and chitin [43], the top two
biopolymers in nature—that contain only one monomer linking
together primarily by 1,4‐glycosidic bond in a liner form, lignin
amorphous, irregular polymer. Second, lignin polymers may
undergo non‐selective fragmentation and rearrangement dur‐
ing depolymerisation [13], further complicating the product
stream.
One solution to the problem is to produce lignin with a sim‐
pler structure via generic engineering. For instance, overex‐
pression of the ferulate 5‐hydroxylase gene in poplar (Populus
spp.) affords lignin with almost pure syringyl units and close to
90% β‐O‐4 linkages [4]. Nevertheless, this technique is cur‐
rently not widely applied and its economic viability remains to
be seen. Another solution is to develop strategies that are able
to converge complex monomers derived from lignin into a sin‐
* Corresponding author. E‐mail: ning.yan@nus.edu.sg
† These authors contributed equally to this work.
This work was supported by the Ministry of Education in Singapore Tier‐1 (R‐279‐000‐479‐112) and Tier‐2 (R‐279‐000‐462‐112) Projects.
DOI: 10.1016/S1872‐2067(18)63132‐8 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 39, No. 9, September 2018

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Jiaguang Zhang et al. / Chinese Journal of Catalysis 39 (2018) 1445–1452
gle stream. An elegant biological funnelling strategy was pro‐
posed and developed, in which a lignin liquor stream was con‐
verted to polyhydroxyl acid, forming the foundation of various
end uses [44]. As far as we are aware, one‐step chemical trans‐
formation that convert, or conceptually that are able to convert,
OH
One step
OH
Lignin
H2
derived
phenolic
monomers
Multifunctional catalyst
OMe
0~2
Demethoxylation + Dealkylation
R
R = ethyl or propyl
lignin
derived
monomer
mixtures
such
as
Scheme 1. The strategy to truncate lignin derived phenolic monomers
to phenol, together with methanol and alkenes as valuable
side‐products.
2‐methoxy‐4‐propylphenol and 2,6‐dimethoxy‐4‐propylphenol
into a single value‐added product is very rare.
Despite the complexity of decomposed lignin, the structures
of the products are not without patterns. A common feature for
the monomers obtained from lignin under neutral or reductive
conditions is that they are substituted phenols bearing zero to
two methoxyl groups in the ortho‐position and an alkyl group
in the para‐position. If highly selective de‐methoxyl [45–53]
and de‐alkyl [54–61] chemistry could simultaneously occur,
one may anticipate that a mixture of substituted phenols to be
converted into a single‐compound phenol (Scheme 1). Notably,
phenol is one of the most important aromatic chemicals utilized
in industry reaching an annual production of 8.9 million tons
[51], mainly used as synthetic polymer precursors such as bi‐
sphenol‐A and nylon [62,63], as well as pharmaceuticals and
herbicides. Its current production is mainly through the Hock
Process based on petroleum feedstock, including oxidation of
cumene with oxygen and then cleavage of the cumene peroxide
formed in the first step to afford phenol and acetone in a 1:1
ratio [62]. One disadvantage of the process, among others, is
that the demand for phenol far exceeds the demand for ace‐
tone. Previously, converting alkyl phenols into phenol has been
reported, but the substrates are limited to non‐methoxyl group
containing ones [54–58].
methane (HPLC grade) and ethanol (HPLC grade) were from
VWR Chemicals. Multiwall carbon nanotubes (MWCNT) (ø:
20–40 nm; 70–120 m2/g) were purchased from Shenzhen
Nanotech Port Co., Ltd. Pt1/m‐Al2O3 [64], 5 wt% Pt/MWCNT
[65] and Mn‐P‐ZSM‐5 [55] were prepared following literature
methods. In the above, Pt1 refers to the single‐atom identify of
Pt species, whereas m‐Al2O3 stands for mesoporous alumina
[64].
2.1. Hydro‐demethoxylation
In a typical experiment, 2‐methoxy‐4‐propylphenol was in‐
jected at a defined flow rate by a syringe pump (Harvard Ap‐
partus, PHD 2000 Infusion, or LongerPump, LSP04‐1A) into a
stainless steel reactor tube (outer diameter of 10 mm) con‐
taining the catalyst. The catalyst was fixed in the middle of the
reactor tube using silica wool. Hydrogen gas or a mixture of
hydrogen/nitrogen gas was delivered to the tubular reactor at
a precise flow rate by using a mass flow controller. The liquid
products were trapped by bubbling through ice‐water cooled
DCM (25 mL), and then analyzed by GC‐FID and GC‐MS tech‐
niques. The reactant conversion and product yield were deter‐
mined using dodecane as an internal standard. Several cata‐
lysts were tested under different reaction conditions by chang‐
ing the temperature, the gas composition, gas and substrate
flow rate, as well as catalyst amount.
In this work, we developed a single‐step route to convert
lignin
2‐methoxy‐4‐propylphenol as a model compound. To identify
proper catalyst combination, we first optimized
derived
monomers
into
phenol
using
2‐methoxy‐4‐propylphenol conversion into 4‐propylphenol
over noble metal catalysts in the presence of hydrogen. Then
de‐alkylation of 4‐propylphenol into phenol was evaluated and
optimized using zeolite catalysts. We further demonstrated a
single‐step protocol to convert 2‐methoxy‐4‐propylphenol into
phenol, by physical mixing Pt/C and H‐ZSM‐5 catalysts. Catalyst
screening, reaction condition optimization, effect of water, as
well as the effect of the way to mix the two catalysts in sin‐
gle‐step conversion were studied. We also studied the deacti‐
vation mechanism for de‐alkylation, and propose possible ways
to regenerate the catalysts.
2.2. De‐alkylation
For the de‐alkylation of propylphenol, the same stainless
steel tubular reactor as the hydro‐demethoxylation reaction
was employed. Zeolite catalysts were tested and placed in the
middle of the furnace. Substrate and water were fed by using
two syringe pumps (Harvard Appartus, PHD 2000 Infusion, and
LongerPump, LSP04‐1A). A mass flow controller was again
used to control the flow rate of the gas (hydrogen/nitrogen
mixture with 20% hydrogen, nitrogen or purified hydrogen).
Products were trapped by bubbling through ice‐water cooled
DCM (25 mL) and analyzed by GC‐FID or GC‐MS using dodec‐
ane as an internal standard.
2. Experimental
Technical grade H2 (99.99%), forming gas (20% H2), nitro‐
gen (99.99%), air (21% ± 1% O2), CO (99.8%) were acquired
from Air Liquide. 2‐methoxy‐4‐propylphenol (≥99%),
4‐propylguaiacol (≥99%), 4‐propylphenol (≥97%), platinum on
carbon (5 wt%), platinum on silica (1 wt%), platinum on alu‐
mina (5 wt%), palladium on carbon (10 wt%) were purchased
2.3. Combined hydro‐demethoxylation and de‐alkylation
reactions
Combined reactions were conducted in a similar manner as
that described for hydro‐demethoxylation and de‐alkylation
reactions. The major difference is that the two catalysts were
mixed using different configurations inside the reactor, as pro‐
vided in Section 3.3.
from Sigma‐Aldrich. H‐ZSM‐5 (SiO2/Al2O3
= 25), HUSY
(SiO2/Al2O3 = 14), and beta zeolite (SiO2/Al2O3 = 25) were ob‐
tained from the Catalyst Plant of Nankai University. Dichloro‐

Jiaguang Zhang et al. / Chinese Journal of Catalysis 39 (2018) 1445–1452
1447
2.4. Analysis methods
served for the alumina and silica supports, while MWCNT was
the second best support providing 20% 4‐propylphenol. It ap‐
pears that the interaction between 2‐methoxy‐4‐propylphenol
and the support is a key factor to initiate the reaction. Activated
carbon and MWCNT both have a porous structure with a small
amount of chemically bounded oxygen. The existence of both
hydrophobic carbon and hydrophilic oxygen regions plausibly
provide strong interactions with the substrate featuring a ben‐
zene ring that is hydrophobic, as well as hydroxyl and methoxyl
groups that are hydrophilic. The larger surface area of activated
carbon (>1000 m2/g) may be the reason for its superior per‐
formance compared with MWCNT support which has a surface
area of only 80 m2/g [66].
GC‐FID (Agilent 7890A) equipped with an HP‐5 capillary
column (30 m × 250 µm) was used to quantify the products.
GC‐MS (Agilent 7890A) was used to determined side products
of hydro‐demethoxylation and de‐alkylation reactions. Ther‐
mogravimetric analyses (TGA) were performed on Shimadzu
DTG‐60A. BET (Nova) was employed to determine the pore
volume of fresh and used H‐ZSM‐5. Fourier Transform infrared
spectroscopy (FTIR) was carried out on a Bio‐Rad Vertex 70.
3. Results and discussion
3.1. Hydro‐demethoxylation reaction
Further efforts to optimize the Pt/C catalyst were made. One
important parameter in flow rate reactions is the contact time
between catalyst and substrate, given by the weight‐to‐feed
ratio (W/F, mass of catalyst over mass flow rate). We evaluated
a series of W/F values, ranging from 0.1 to 0.25 h, by changing
the loading of Pt/C catalyst (Fig. S1). Not unexpectedly, the
conversion tends to increase with the increase of W/F, at an
expense of decreased selectivity to 4‐propylphenol. A W/F of
0.15 h was the best compromise between conversion and se‐
lectivity, at which point 84% conversion and 94% selectivity
were achieved, providing a 4‐propylphenol yield of ca. 80%. A
time on stream study was conducted at 350 °C, purposely se‐
lected to have a lower initial conversion than that obtained at
400 °C (Fig. S2). As can be seen, conversion and selectivity in‐
creased during the first 2 h and stabilized thereafter. Encour‐
agingly, there was no sign of deactivation under the applied
conditions for at least 4 h. The reaction could also be conducted
in a batch reactor at slighter lower temperature. Other sub‐
The hydro‐demethoxylation was carried out using
2‐methoxy‐4‐propylphenol as a model compound in a stainless
steel tubular flow reactor at 400 °C, using Pt/C, Pd/C and Ru/C
catalysts, respectively. The system requires some time to reach
steady state so that the substrate conversion and
4‐propylphenol selectivity during the second hour were com‐
pared (Fig. 1). Active carbon alone was inert, while the three
metal catalysts exhibited distinctively different activities. Pt/C
was most active (70% conversion), followed by Ru/C (55%
conversion) and Pd/C (<15% conversion). Pt/C was also the
most selective catalyst, enabling >95% selectivity towards
4‐propylphenol. The main side products as observed by GC‐MS
analysis
include
4‐propylcresol,
4‐propylcatechol,
4‐propylbenzene and benzene.
Other Pt catalysts, including Pt supported on Al2O3, meso‐
porous Al2O3 (m‐Al2O3), SiO2, and MWCNT, were tested to de‐
termine the effect of support in hydro‐demethoxylation reac‐
tion. Surprisingly, no or small formation of product was ob‐
strates,
including
2‐methoxy‐4‐ethylphenol
were converted
and
into
4‐methyl‐2,6‐dimethoxyphenol,
20%–50% alkylphenol under non‐optimized conditions, sug‐
gesting that the catalytic system developed is applicable to
other types of lignin monomers and should be applicable to
convert a mixture of lignin monomers (Table S1).
3.2. De‐alkylation of alkylphenol to phenol
De‐alkylation reaction has been widely investigated for sub‐
stituted benzene. Ethyl and propyl benzene readily undergo
de‐alkylation in gas phase on zeolites such as Re/ZSM‐5 [67].
The zeolite pore volume is the key parameter for the selectivity
and conversion of alkylbenzenes to benzene. On the other side,
de‐alkylation of substituted phenols into phenol remains hard‐
ly investigated. As we are aware, there were only a couple of
reports describing the process, where 4‐ethyl phenol was con‐
verted to phenol and ethylene over ZSM‐5 zeolite catalyst [55].
The system is only active for para‐substituted phenols, while
ortho‐ or meta‐ethyl phenols were not convertible because
they cannot diffuse into the zeolite pores due to their larger
molecular sizes. In a recent study, Sels et al. [54] reported the
excellent de‐alkylation performance of alkylphenols using a
simple acidic H‐ZSM‐5 zeolite as catalyst. They found that
co‐feeding water is crucial to avoid fast catalytic deactivation
and to obtain good selectivity.
Fig. 1. Catalyst screening for hydro‐demethoxylation of
2‐methoxy‐4‐propyl phenol. Reaction conditions: catalyst 75 mg, 400
°C, 2‐methoxy‐4‐propylphenol injection rate 3.01 mmol/h, H2 flow rate
20 ml/min. The data shown above are based on GC analysis of the sam‐
ple collected on stream for 1 h from the second hour onwards.

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Jiaguang Zhang et al. / Chinese Journal of Catalysis 39 (2018) 1445–1452
Fig. 2. De‐alkylation of 4‐propylphenol. (a) Effect of catalyst loading and catalyst activation. Reaction conditions: varied amount of un‐activated or
activated H‐ZSM‐5, 350 °C, 4‐propylphenol infusion rate 240 µL/h, water infusion rate 180 µL/h, 20/80 H2/N2 flow rate 50 mL/min. The data shown
above are based on GC analysis of the sample collected on stream for 1 h from the second hour onwards. (b) Effect of time on stream. Reaction condi‐
tions: H‐ZSM‐5 200 mg, 350 °C, 4‐propylphenol infusion rate 240 µL/h, water injection rate 180 µL/h, 20/80 H2/N2 flow rate 50 mL/min.
We initially conducted a catalyst screening using H‐ZSM‐5,
HUSY, beta zeolites and Mn‐P‐ZSM‐5 (Fig. S3). No reaction oc‐
curred at 300 °C or below. 350 °C was the minimum tempera‐
ture required to have any activity. At 375 °C, the activity follows
the order: H‐ZSM‐5 ≈ HUSY > Mn‐P‐ZSM‐5 > beta zeolite, while
H‐ZSM‐5 provided the highest selectivity towards phenol (Fig.
S3). Based on previous studies on de‐alkylation reaction of
alkylbenzenes [47,48], the reaction occurs after substrate dif‐
fusion into the zeolite pores, where Brønsted acid sites lead to
the formation of an arenium ion, followed by de‐alkylation to
form alkene and phenol. The propyl cation will donate a proton
to the zeolite to afford propylene, and regenerate the active
sites. H‐ZSM‐5 has the ideal combination of acidity and pore
size, and therefore gave the best performance in propylphenol
de‐alkylation.
H‐ZSM‐5 (SiO2/Al2O3 = 25) was selected to perform condi‐
tion optimization. First, the influence of the W/F was studied.
Water was co‐fed in the system as it plays a role by desorbing
phenol from the zeolite therefore inhibiting catalyst deactiva‐
tion [4]. The reaction is relatively slow and W/F appears to be a
critical factor to determine conversion and yield. At W/F = 0.5
h, merely 20% substrate conversion was achieved, which
sharply increased to 40% and 72%, respectively, when W/F
increased to 0.75 and 1.0 h. Next, pre‐activation of H‐ZSM‐5 at
540 °C was tested, but there was no substantial change in reac‐
tivity.
acterization techniques were employed to further understand
the deactivation of zeolite catalyst. During TGA measurement,
the brown H‐ZSM‐5 spent catalyst turned white again after
completion of the analysis, indicating the removal of carbon
deposit. Two distinct peaks can be observed at around 220 and
420 °C, respectively. The first peak can be attributed to the
burning of light coke (small to medium chain alkanes, aromat‐
ics) and chemisorbed molecules. The second one at higher
temperature could represent the burning of heavier coke (peak
approximately at the same temperature than carbon black
burning (Fig. 3(a)). A total weight loss of 20% was observed for
the entire process. FT‐IR analysis was conducted to compare
the fresh catalyst and the spent catalyst, but only peaks that
correspond to the zeolite were present [51]. FT‐IR analysis
demonstrated that the zeolite structure remained intact after
the reaction. From these data, it appears that the deactivation
of H‐ZSM‐5 is mainly due to formation of coke within the mi‐
cropores, due to secondary reactions or deposition of sub‐
strates on the surface. As known from the literature, coke for‐
mation affects the activity of zeolites by poisoning or blocking
the access to the active Brønsted acid sites [50]. Indeed, the
reactivity of H‐ZSM‐5 could be simply recovered by activation
at 400 °C in air for 1 h (data not shown).
3.3. Combination of HDO and de‐alkylation reactions
The H‐ZSM‐5 catalyst was continuously evaluated for a pe‐
riod of 4 h. A steady decrease of both activity and selectivity
was observed. After 4 h, substrate conversion dropped from
>90% to ca. 60%, while the selectivity dropped to a less extent,
from ca. 90% to 80%. The color of spent catalyst was brown
instead of white, indicative of carbon deposition. Several char‐
After exploration of suitable parameters for both hy‐
dro‐demethoxylation and de‐alkylation reactions, we recog‐
nized the possibility of combining the two steps into a sin‐
gle‐step to trim lignin derived monomers directly into phenol,
since the two reaction has similar working temperature, pres‐
sure, and W/F values. The single‐step transformation requires

Jiaguang Zhang et al. / Chinese Journal of Catalysis 39 (2018) 1445–1452
1449
Fig. 3. (a) DTA and TGA of spent H‐ZSM‐5 catalyst; (b) FT‐IR spectra of fresh and spent H‐ZSM‐5 catalysts.
substrate undergoing reactions on metal and zeolite catalyst
sequentially, and therefore how to place the two catalysts in the
reactor is a key factor.
Four configurations were evaluated (Fig. 4(a)) at 375 °C, in‐
cluding (A) placing the Pt/C catalyst on the top and H‐ZSM‐5 in
the bottom; (B) splitting Pt/C and H‐ZSM‐5 into three portions,
where for each portion Pt/C and H‐ZSM‐5 were alternately
packed and separated by silica wool; (C) physical mixture of
Pt/C and H‐ZSM‐5; and (D) ball‐milled mixture of the two cata‐
lysts. Indeed, the way that the two catalysts mix exhibited a
profound influence on reactivity. Physically mixed Pt/C and
H‐ZSM‐5 was the best, reaching 99% conversion and 66% se‐
lectivity, suggesting the benefit of placing the two catalysts in
close contact. The main side products as identified by GC‐MS
include p‐xylene, 3‐propylphenol, anisole and 4‐methyl phenol
(Fig. S4). The existence of these chemicals highlight the
non‐quantitative selectivity is due to the incomplete cleavage of
both methoxyl and alkyl chains, and the re‐alkylation reaction
between phenol and alkene. Ball‐milled catalysts were the least
active. This is mainly because the crystal structure of zeolite
Fig. 4. (a) Schematic representation of the four configurations of the two catalysts in the reaction tube. (A) Pt/C packed on the top of H‐ZSM‐5, sepa‐
rated by silica wool. (B) Pt/C and H‐ZSM‐5 alternatively packed and separated by silica wool with three double‐layers in total. (C) Physical‐mix of the
two catalysts. (D) Ball‐milling of the two catalyst. (b) One step conversion of 2‐methoxy‐4‐propylphenol into phenol with 4 catalysts’ configurations.
Reaction conditions: H‐ZSM‐5 300 mg, Pt/C 50 mg, 375 °C, 2‐methoxy‐4‐propylphenol injection rate 240 µL/h, water injection rate 240 µL/h, H2 flow
rate 10 mL/min. The data shown above are based on GC analysis of the sample collected on stream for 1 h from the second hour onwards.

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Jiaguang Zhang et al. / Chinese Journal of Catalysis 39 (2018) 1445–1452
extensively studied in the past decade, the process has the po‐
tential to upgrade lignin into phenol in a remarkable 25% yield
(lignin basis). The current study helps to address a long stand‐
ing challenge in lignin valorization, i.e., the depolymerized lig‐
nin is most often a complex mixture of phenolics whose trans‐
formation into a pure high value chemical is non‐trivial. A limi‐
tation of the present work is the deactivation of catalyst in the
de‐alkylation reaction. Identification of a new support for Pt is
underdoing in the laboratary, so that catalyst regeneration
could be achieved simply by thermal treating in air.
Acknowledgments
We thank the Ministry of Education in Singapore Tier‐1
(R‐279‐000‐479‐112) and Tier‐2 (R‐279‐000‐462‐112) pro‐
jects for the financial support.
Scheme 2. (a) Overview of the single‐step transformation of
4‐propylguaiacol to phenol. (b) proposed whole utilization of woody
biomass in which lignin is mainly converted into phenol.
References
[1] K. Sanderson, Nature, 2011, 474, S12–S14.
[2] C. Li, X. Zhao, A. Wang, G. W. Huber, T. Zhang, Chem. Rev., 2015,
115, 11559–11624.
[3] Y. Shao, Q. Xia, L. Dong, X. Liu, X. Han, S. F. Parker, Y. Cheng, L. L.
Daemen, A. J. Ramirez‐Cuesta, S. Yang, Y. Wang, Nat. Commun.,
2017, 8, 16104.
[4] L. Shuai, M. T. Amiri, Y. M. Questell‐Santiago, F. Héroguel, Y. Li, H.
Kim, R. Meilan, C. Chapple, J. Ralph, J. S. Luterbacher, Science,
2016, 354, 329–333.
[5] Q. Xia, Z. Chen, Y. Shao, X. Gong, H. Wang, X. Liu, S. F. Parker, X. Han,
S. Yang, Y. Wang, Nat. Commun., 2016, 7, 11162.
[6] M. Zaheer, R. Kempe, ACS Catal., 2015, 1675–1684.
[7] S. Van den Bosch, W. Schutyser, R. Vanholme, T. Driessen, S. F. Ko‐
elewijn, T. Renders, B. De Meester, W. J. J. Huijgen, W. Dehaen, C.
M. Courtin, B. Lagrain, W. Boerjan, B. F. Sels, Energy Environ. Sci.,
2015, 8, 1748–1763.
[8] V. Molinari, C. Giordano, M. Antonietti, D. Esposito, J. Am. Chem.
Soc., 2014, 136, 1758–1761.
[9] K. Barta, G. R. Warner, E. S. Beach, P. T. Anastas, Green Chem.,
2014, 16, 191–196.
[10] X. Huang, T. I. Korányi, M. D. Boot, E. J. M. Hensen, ChemSusChem,
2014, 7, 2051–2051.
[11] M. V. Galkin, S. Sawadjoon, V. Rohde, M. Dawange, J. S. M. Samec,
ChemCatChem, 2014, 6, 179–184.
was damaged by mechanical force, which is not uncommon
when treating crystalline materials with ball‐milling.
Physical mixtures of Pt/C and H‐ZSM‐5 at other tempera‐
tures (325 and 400 °C), as well as Pt/C combined with HUSY or
Mn‐P‐ZSM‐5, were further tested to confirm that the data pre‐
sented in Fig. 4(b), C provided the highest yield of phenol from
2‐methoxy‐4‐propylphenol. Notably, the first step, i.e., hy‐
dro‐demethoxylation over Pt/C does not require water vapor
while the second de‐alkylation step over zeolite does. Consid‐
ering that Pt/C catalyst is less affected by water (Fig. S6) than
zeolite without water, co‐feed of water vapour is beneficial for
a high yield of phenol.
Success in trimming lignin monomers to phenol prompts us
to propose a strategy to valorize wood for value‐added chemi‐
cals. Woody biomass could be first converted into a mixture of
phenolic monomers in ca. 40% yield via hydrogenolysis [68]
and then following the single‐step trimming chemistry shown
in this work, >60% of phenol would be obtained either via a
two‐step or a one‐step approach, giving a combined yield of ca.
25% from native lignin. Methanol and alkenes (in particular
propylene) as the major side products are also valuable. The
hemicellulose and cellulose fraction or derivatives could be
further upgraded following fermentation or chemical trans‐
formations.
[12] R. Ma, W. Hao, X. Ma, Y. Tian, Y. Li, Angew. Chem. Int. Ed., 2014, 53,
7310–7315.
[13] P. Ferrini, R. Rinaldi, Angew. Chem. Int. Ed., 2014, 53, 8634–8639.
[14] J. Zhang, H. Asakura, J. van Rijn, J. Yang, P. Duchesne, B. Zhang, X.
Chen, P. Zhang, M. Saeys, N. Yan, Green Chem., 2014, 16,
2432–2437.
4. Conclusions
[15] H. Konnerth, J. Zhang, D. Ma, M. H. G. Prechtl, N. Yan, Chem. Eng.
Sci., 2015, 123, 155–163.
[16] J. Zhang, J. Teo, X. Chen, H. Asakura, T. Tanaka, K. Teramura, N.
Yan, ACS Catal., 2014, 4, 1574–1583.
[17] Y. Hu, G. Jiang, G. Xu, X. Mu, Mol. Catal., 2018, 445, 316–326.
[18] Z. Luo, Z. Zheng, L. Li, Y. T. Cui, C. Zhao, ACS Catal., 2017, 7,
8304–8313.
[19] B. Ma, H. Cui, D. Wang, P. Wu, C. Zhao, Nanoscale, 2017, 9,
5986–5995.
In summary, we have established an effective way to con‐
vert lignin derived monomers into phenol, via hy‐
dro‐demethoxylation and de‐alkylation reactions. Pt/C is the
best catalyst for hydro‐demethoxylation, presumably due to the
strong interaction of carbon to the substrate, while H‐ZSM‐5 is
most effective in de‐alkylation. Notably, the two reactions are
able to occur in a single‐step by physical mixing the two cata‐
lysts, affording phenol in over 60% yield directly from
2‐methoxy‐4‐propylphenol, which has not been achieved be‐
fore. By combining with lignin depolymerization that has been
[20] J. Chen, F. Lu, X. Si, X. Nie, J. Chen, R. Lu, J. Xu, ChemSusChem, 2016,
9, 3353–3360.

Jiaguang Zhang et al. / Chinese Journal of Catalysis 39 (2018) 1445–1452
1451
Graphical Abstract
Chin. J. Catal., 2018, 39: 1445–1452 doi: 10.1016/S1872‐2067(18)63132‐8
Single‐step conversion of lignin monomers to phenol: Bridging the gap between lignin and high‐value chemicals
Jiaguang Zhang †, Loris Lombardo†, Gökalp Gözaydın, Paul J. Dyson, Ning Yan *
National University of Singapore, Singapore;
University of Lincoln, United Kingdom;
Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Lignin derived methoxyl alkyl substituted phenols were converted into phenol by hydro‐demethoxylation and de‐alkylation.
[21] H. Guo, B. Zhang, Z. Qi, C. Li, J. Ji, T. Dai, A. Wang, T. Zhang,
ChemSusChem, 2017, 10, 523–532.
[22] C. S. Lancefield, O. S. Ojo, F. Tran, N. J. Westwood, Angew. Chem. Int.
Ed., 2015, 54, 258–262.
[23] R. Ma, M. Guo, X. Zhang, ChemSusChem, 2014, 7, 412–415.
[24] Y. Gao, J. Zhang, X. Chen, D. Ma, N. Yan, ChemPlusChem, 2014, 79,
825–834.
Catal., 2018, 8, 4761–4771.
[40] N. Luo, M. Wang, H. Li, J. Zhang, H. Liu, F. Wang, ACS Catal., 2016, 6,
7716–7721.
[41] D. Shao, J. Liang, X. Cui, H. Xu, W. Yan, Chem. Eng. J., 2014, 244,
288–295.
[42] L. T. Mika, E. Cséfalvay, Á. Németh, Chem. Rev., 2018, 118,
505–613.
[25] R. Lu, F. Lu, J. Chen, W. Yu, Q. Huang, J. Zhang, J. Xu, Angew. Chem.
Int. Ed., 2016, 55, 249–253.
[26] W. Deng, H. Zhang, X. Wu, R. Li, Q. Zhang, Y. Wang, Green Chem.,
2015, 17, 5009–5018.
[27] M. Wang, X. Zhang, H. Li, J. Lu, M. Liu, F. Wang, ACS Catal., 2018, 8,
1614–1620.
[28] P. J. Deuss, M. Scott, F. Tran, N. J. Westwood, J. G. de Vries, K. Barta,
J. Am. Chem. Soc., 2015, 137, 7456–7467.
[43] N. Yan, X. Chen, Nature, 2015, 524, 155–157.
[44] J. G. Linger, D. R. Vardon, M. T. Guarnieri, E. M. Karp, G. B. Hun‐
singer, M. A. Franden, C. W. Johnson, G. Chupka, T. J. Strathmann, P.
T. Pienkos, G. T. Beckham, Proc. Natl. Acad. Sci. USA, 2014, 111,
12013–12018.
[45] J. Sun, A. M. Karim, H. Zhang, L. Kovarik, X. S. Li, A. J. Hensley, J. S.
McEwen, Y. Wang, J. Catal., 2013, 306, 47–57.
[46] T. Omotoso, S. Boonyasuwat, S. P. Crossley, Green Chem., 2014, 16,
645–652.
[29] T. D. H. Nguyen, M. Maschietti, T. Belkheiri, L. E. Åmand, H. Theli‐
ander, L. Vamling, L. Olausson, S. I. Andersson, J. Supercrit. Fluids,
2014, 86, 67–75.
[47] T. Prasomsri, M. Shetty, K. Murugappan, Y. Roman‐Leshkov, Ener‐
gy Environ. Sci., 2014, 7, 2660–2669.
[30] L. Yang, Y. Li, P. E. Savage, Ind. Eng. Chem. Res., 2014, 53,
2633–2639.
[48] A. L. Jongerius, R. W. Gosselink, J. Dijkstra, J. H. Bitter, P. C. A.
Bruijnincx, B. M. Weckhuysen, ChemCatChem, 2013, 5,
2964–2972.
[49] N. Joshi, A. Lawal, Ind. Eng. Chem. Res., 2013, 52, 4049–4058.
[50] R. R. Barton, M. Carrier, C. Segura, J. L. G. Fierro, S. Park, H. H.
Lamb, N. Escalona, S. W. Peretti, Appl. Catal. A, 2018, 562,
294–309.
[31] J. A. Onwudili, P. T. Williams, Green Chem., 2014, 16, 4740–4748.
[32] A. Toledano, L. Serrano, J. Labidi, Fuel, 2014, 116, 617–624.
[33] J. Pan, J. Fu, S. Deng, X. Lu, Energy Fuels, 2013, 28, 1380–1386.
[34] J. Hu, D. Shen, S. Wu, H. Zhang, R. Xiao, Energy Fuels, 2014, 28,
4260–4266.
[35] S. Adhikari, V. Srinivasan, O. Fasina, Energy Fuels, 2014, 28,
4532–4538.
[51] K. B. Jung, J. Lee, J. M. Ha, H. Lee, D. J. Suh, C. H. Jun, J. Jae, Catal.
Today, 2018, 303, 191–199.
[36] G. T. Neumann, B. R. Pimentel, D. J. Rensel, J. C. Hicks, Catal. Sci.
Technol., 2014, 4, 3953–3963.
[37] G. Jiang, Y. Hu, G. Xu, X. Mu, H. Liu, ACS Sustain. Chem. Eng., 2018, 6,
5772–5783.
[38] J. D. Nguyen, B. S. Matsuura, C. R. J. Stephenson, J. Am. Chem. Soc.,
2013, 136, 1218–1221.
[39] H. Liu, H. Li, J. Lu, S. Zeng, M. Wang, N. Luo, S. Xu, F. Wang, ACS
[52] L. Nie, B. Peng, X. Zhu, ChemCatChem, 2018, 10, 1064–1074.
[53] M. S. Jang, T. N. Phan, I. S. Chung, I. G. Lee, Y. K. Park, C. H. Ko, Res.
Chem. Intermed., 2018, 44, 3723–3735.
[54] D. Verboekend, Y. Liao, W. Schutyser, B. F. Sels, Green Chem., 2016,
18, 297–306.
[55] K. Kase, T. Idai, K. Ishii, E. Takahashi, EP0296582 (A2), 1988.

1452
Jiaguang Zhang et al. / Chinese Journal of Catalysis 39 (2018) 1445–1452
[63] J. Wallace, S. Updated by, Phenol, in: Kirk‐Othmer Encyclopedia of
Chemical Technology, 2005.
[56] Y. Liao, M. d’Halluin, E. Makshina, D. Verboekend, B. F. Sels, Appl.
Catal. B, 2018, 234, 117–129.
[64] Z. Zhang, Y. Zhu, H. Asakura, B. Zhang, J. Zhang, M. Zhou, Y. Han, T.
Tanaka, A. Wang, T. Zhang, N. Yan, Nat. Commun., 2017, 8, 16100.
[65] W. Deng, Y. Wang, S. Zhang, K. M. Gupta, M. J. Hülsey, H. Asakura, L.
Liu, Y. Han, E. M. Karp, G. T. Beckham, P. J. Dyson, J. Jiang, T.
Tanaka, Y. Wang, N. Yan, Proc. Natl. Acad. Sci. USA, 2018, 115,
5093–5098.
[66] B. Zhang, H. Asakura, J. Zhang, J. Zhang, S. De, N. Yan, Angew. Chem.
Int. Ed., 2016, 55, 8319–8323.
[67] J. M. Serra, E. Guillon, A. Corma, J. Catal., 2004, 227, 459–469.
[68] N. Yan, C. Zhao, P. J. Dyson, C. Wang, L. T. Liu, Y. Kou, ChemSus‐
Chem, 2008, 1, 626–629.
[57] T. Sato, T. Adschiri, K. Arai, J. Anal. Appl. Pyrolysis, 2003, 70,
735–746.
[58] F. P. Daly, J. Catal., 1980, 61, 528–532.
[59] Y. Chen, K. Wang, J. Y. Yang, P. Q. Yuan, Z. M. Cheng, W. K. Yuan, Ind.
Eng. Chem. Res., 2016, 55, 9578–9585.
[60] S. Kamiguchi, K. Kondo, M. Kodomari, T. Chihara, J. Catal., 2004,
223, 54–63.
[61] D. Li, H. Zhang, M. Usman, Z. Li, L. Han, C. Li, S. Zhang, J. Renew.
Sustain. Energy, 2014, 6, 033132/1–033132/15.
[62] M. Weber, M. Weber, M. Kleine‐Boymann, Phenol, in: Ullmann's
Encyclopedia of Industrial Chemistry, 2004.
催化一步转化木质素单体为苯酚: 建立木质素到高附加值化学品的通道
张佳光a,b,†, Loris Lombardo a,c,†, Gökalp Gözaydın a, Paul J. Dyson c, 颜 宁a,*
a新加坡国立大学化学与生物分子工程系, 新加坡
b林肯大学化学学院, 英国
c瑞士洛桑联邦理工化学科学与工程所, 瑞士
摘要: 木质素是地球上产量最大的芳香类有机高分子, 其有效转化利用在近年来备受关注. 催化降解木质素制备酚类单体
在过去十年取得了长足进步, 目前已开发出氢解、水解、热解、氧化、光解等一系列方法. 通过加氢脱氧法可以将木质素
的降解产物转化为烃类燃料, 但该过程耗氢量大, 并且芳香环在加氢气氛下被破坏. 另一个可能的应用是将木质素衍生物
进一步转化为高附加值的芳香族化合物, 但解聚产物成分复杂, 成为木质素高效转化为单一高附加值化学品的瓶颈.
在加氢条件下, 木质素解聚产物主要为酚类混合物, 多在羟基临位带有一至两个甲氧基, 并在对位带有C2或C3的取代
基(多为烷基). 针对这一结构特点, 我们设计了新反应路径, 通过分别去除甲氧基和烷基得到苯酚. 该过程保留了苯酚的基
本结构而将其他取代基去除, 原理上可以有效的将木质素降解的混合物转化为单一产物苯酚. 通过催化剂的筛选和优化,
Pt/C催化剂对脱甲氧基显示出最好的活性和选择性, 在400 °C, 常压下脱除效率>80%. 在流动气氛下连续工作4 h, Pt/C催
化剂无失活迹象. H-ZSM-5为最有效的脱烷基催化剂, 最优效率83%左右. H-ZSM-5在反应过程中逐渐失活. 通过热重差
热及红外光谱分析, 失活主要原因为积碳. 在400 °C空气中煅烧后, 催化剂可以再生.
通过简单的物理混合, Pt/C和H-ZSM-5一步将木质素单体转化为60%的苯酚, 显示了该方法直接转化木质素到高附加
值苯酚的巨大潜力. 这是同时将木质素中甲氧基、烷基选择性脱除的首例报道. 经过估算, 从原生木质素出发, 通过加氢解
聚, 耦合本文开发的一步脱甲氧基、烷基路径, 可将木质素转化为约25%的苯酚. 木质素中的甲氧基、烷基将分别转化为甲
醇和烯烃, 提高了木质素碳资源的利用效率.
关键词: 木质素; 苯酚; 分子筛催化剂; 脱甲氧基; 脱烷基
收稿日期: 2018-06-28. 接受日期: 2018-07-04. 出版日期: 2018-09-05.
*通讯联系人. 电子信箱: ning.yan@nus.edu.sg
†共同第一作者.
基金来源: 新加坡教育部资助项目(R-279-000-479-112, R-279-000-462-112).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).