Flexible NiCo-based catalyst for direct hydrodeoxygenation of guaiacol to cyclohexanol

Article abstract of DOI:10.1039/d0nj02929g

The catalytic hydrodeoxygenation (HDO) of lignin-derived phenols is an important step for bio-oil upgrading. Herein, a novel HDO system was established in the presence of nitrogen, instead of traditional hydrogen. A series of CNT-supported Ni-based catalysts was prepared and introduced in the HDO of guaiacol and other lignin-derived phenolic compounds. The bimetallic NiCo/CNT catalysts exhibited better catalytic performance during the HDO reaction, in comparison with monometallic Ni/CNT and Co/CNT catalysts. Among these catalysts, the (15 + 5)% NiCo/CNT catalyst afforded the highest guaiacol conversion (up to 100%) with cyclohexanol as the main product in isopropanol. The effects of process parameters on guaiacol conversion and product distribution were studied in detail, finding that the presence of nitrogen could help to suppress the generation of byproducts, while the presence of hydrogen would facilitate the occurrence of side reactions. The HDO reaction of guaiacol occurred possibly in two consecutive steps: the demethoxylation of guaiacol to phenol and the further hydrogenation of the aromatic ring to cyclohexanol.

Full text of DOI:10.1039/d0nj02929g

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Page 1 of 33
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DOI: 10.1039/D0NJ02929G
Flexible NiCo Based Catalyst for Direct Hydrodeoxygenation of
Guaiacol to Cyclohexanol
ac
bd*
ac
d
Changzhou Chen , Minghao Zhou , Peng Liu , Brajendra K Sharma ,
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Jianchun Jiang ac*
a. Institute of Chemical Industry of Forest Products, Chinese Academy of
Forestry; Key Lab. of Biomass Energy and Material, Jiangsu Province;
National Engineering Lab. for Biomass Chemical Utilization; Key and Open
Lab. on Forest Chemical Engineering, SFA, Nanjing 210042, China
b. School of Chemistry and Chemical Engineering, Yangzhou University,
Yangzhou 225002, China
c. Co-Innovation Center of Efficient Processing and Utilization of Forest
Resources, Nanjing Forestry University, Nanjing 210037, China
d. Illinois Sustainable Technology Center, Prairie Research Institute, one
Hazelwood Dr., Champaign, University of Illinois at Urbana-Champaign,
IL 61820, USA
* Corresponding Author: E-mail: zmhzyk19871120@163.com (Minghao Zhou)
jiangjc@icifp.cn (Jianchun Jiang)
Abstract
The catalytic hydrodeoxygenation (HDO) of lignin-derived phenols is an important
step for bio-oil upgrading. Herein, a novel HDO system was established with the
presence of nitrogen, instead of traditional hydrogen. A series of CNT supported
Ni-based catalysts were prepared and introduced in the HDO of guaiacol and other

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DOI: 10.1039/D0NJ02929G
lignin-derived phenolic compounds. The bimetallic NiCo/CNT catalysts exhibited
better catalytic performance during the HDO reaction, in comparison with
monometallic Ni/CNT and Co/CNT catalysts. Among those catalysts, (15+5)%
NiCo/CNT catalyst afforded the highest guaiacol conversion (up to 100%)with
cyclohexanol as the main product in isopropanol. The effects of process parameters
on the guaiacol conversion and products distribution were studied in detail, finding
that the presence of nitrogen could help to suppress the generation of byproducts,
while the presence of hydrogen would facilitate the occurrence of side reactions. The
HDO reaction of guaiacol occurred possibly in two consecutive steps: the
demethoxylation of guaiacol to phenol and the further hydrogenation of aromatic ring
to cyclohexanol.
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Keywords: Guaiacol; lignin-derived phenols; hydrodeoxygenation; Ni-based
bimetallic catalysts; isopropanol.
Introduction
Biomass has been widely regarded as a promising alternative for the generation
of liquid fuel (bio-oil). However, bio-oil is not suitable for large-scale utilization due
to its high oxygen content, poor stability and low heating value, which makes it an
inappropriate fuel [1, 2]. The removal of oxygen is becoming a challenge for the
bio-oil upgrading to transport fuels [1-4]. Therefore, it is of great importance to
improve the bio-oil quality through catalytic hydrodeoxygenation (HDO). According
to previous studies, HDO catalysts can be generally classified into three groups: metal
hybrids (sulfides, carbides, nitrides, etc.) [5-9], noble metals [10-13] and transition

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metals [14-17]. Although metal hybrids exhibited satisfactory catalytic activity during
the HDO reaction, those catalysts always deactivated quickly in the presence of water
[
4]. Furthermore, the deactivation and regeneration process for those metal sulfides or
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other carbides, nitrides were also complicated, despite of their high catalytic behavior.
Noble metal catalysts showed great potential due to their high activity and stability in
mild HDO reaction conditions, but the high cost added the difficulty for noble metal
catalysts in industrial reactions [18, 19]. Transition metal catalysts have received
increasing attentions for the HDO reactions due to their lower price and satisfactory
activity, compared with noble metal catalysts. Therefore, it is urgent to explore
affordable and active HDO catalysts for bio-oil upgrading.
Bio-oil is a complicated mixture of different oxygen-containing compounds,
such as reactive phenols, which accounts for a large amount of lignin fraction in
bio-oil [18, 20, 21]. Thus, model compounds are promising alternatives for the
screening of catalysts for the bio-oil upgrading. Guaiacol and phenol are always
chosen as model compounds of lignin-derived phenols, due to the presence of
representative groups (e.g. -OH and -OCH ) [22, 23]. Ni-based transition metal
3
catalysts were widely reported effective for the catalytic conversion of phenolic
compounds to cyclohexanol and its derivatives, while cyclohexanol is an important
chemical used in industry [14, 24-28]. Kordouli et al reported the HDO of phenol in
decalin over reduced Ni/ASA and NiMo/ASA in a flow reactor at 310℃ with a
hydrogen pressure of 3 MPa, and confirmed the promoting action of Mo in
NiMo/ASA due to the highest Ni dispersion and largest acidity [14]. Fang et al.

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investigated the conversion of guaiacol to phenol or cyclohexane over bimetallic
Ni-Fe catalysts, and revealed the relationship between the Ni/Fe ratio and the products
selectivity [25]. Zhao et al reported similar phenomenon, while mesoporous carbon
spheres supported Ni-Fe bimetallic catalysts exhibited higher phenol conversion rate
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with cyclohexane as the primary products (250 ℃, 5 MPa H ) [26]. The synergistic
2
effect was revealed as Fe-containing sites helped to adsorb the hydroxyl species while
Ni sites performed the hydrogen activation during the HDO reaction. Guan et al
explored the catalytic activity of Ni Co @C/ZrO catalyst in the HDO of phenol,
x
y
2
finding that Ni Co @C/ZrO showed the best catalytic performance with a
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cyclohexanol selectivity of 91.14% (200 ℃, 2 MPa H ) [29]. In general, catalytic
2
HDO reaction is always conducted at relatively high temperature (200-400 ℃) and
high hydrogen pressure (4-20 MPa) [30]. Furthermore, commercial hydrogen is an
expensive energy resource, and the utilization of hydrogen might lead to several
inherent hazards, such as transportation, storage [31]. Thus, it was imperative to
explore Ni-based catalysts with high catalytic activity for the hydrodeoxygenation of
phenols at relatively mild reaction conditions without the use of hydrogen.
In this work, guaiacol was firstly chosen as a model compound for lignin-derived
phenolic compounds, and a novel method for HDO reaction in the presence of
nitrogen was reported, which could greatly improve the economic feasibility and
safety, compared with traditional HDO reaction with the presence of external
hydrogen. The catalytic activity of CNT supported monometallic and bimetallic
catalysts (containing Ni and/or Co) was investigated for the HDO of several

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lignin-derived phenols. The promotional effect of Co was observed and confirmed, as
bimetallic NiCo/CNT catalysts could give much higher cyclohexanol yield with
almost no byproducts. The catalysts were well characterized by XRD、TEM and XPS,
and the synergistic effect between active metals and support were also discussed
based on the characterization results. This work may provide a novel for researches
for the hydrodeoxygenation of phenols and the upgrading of bio-oil in the absence of
external hydrogen.
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Experimental
Chemicals
All reagents (analytic purity grade) were purchased from local Sinopharm
Chemical Reagent, which were used directly without any treatment.
Catalyst preparation and characterization
CNT supported Ni, Co and bimetallic catalysts were synthesized according to
previous studies [32, 33], and all catalysts were reduced in hydrogen atmosphere
before use. In a typical run, (15+5)% NiCo/CNT catalyst was prepared by
.
impregnating CNT (2 g) with an aqueous solution of Ni (NO ) 6H O (1.5g) and Co
3
2
2
.
(
NO ) 6H O (0.5g). Then the mixed solution was stirred for 24 h at room temperature
3 2 2
to ensure a high dispersion. After drying at 105 ℃ for 6 h, the dried sample was
calcined in a furnace at 500 ℃ for 5 h. The final (15+5)% NiCo/CNT catalyst was
obtained after reducing at 500 ℃ for 3 h under a hydrogen atmosphere. Different
ratios of NiCo/CNT catalysts were synthesized by the same method.
The prepared CNT supported monometallic and bimetallic catalysts were

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characterized by XRD on a Rigaku D/max-A instrument with a scanning speed of
2
°/min. Transmission electron microscopy (TEM) images were acquired on a TEM
Tecnai G2 20 instrument. The XPS measurements were performed on an
ESCALAB-250 (Thermo-VG Scientific, USA) spectrometer with Al Kα (1486.6 eV)
irradiation source. The specific surface area and pore volume were evaluated from the
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N adsorption-desorption isotherms using a Micromeritics Tristar II 3000 analyzer.
2
Catalytic hydrodeoxygenation of guaiacol in aqueous medium
All the guaiacol hydrodeoxygenation reactions were conducted in a 25 ml
stainless autoclave with a magnetic stirrer. For each run, 500 mg guaiacol, 50 mg
catalyst and 10 g isopropanol were added into the autoclave and purged with N gas
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for three times in order to exhaust air. Then the reaction was carried out under a
certain temperature and reaction time, with/without the presence of nitrogen. After
reaction, the reaction mixture was filtered to collect the catalyst and the filtrate was
analyzed by the Gas Chromatograph/Mass Spectrometer (GC/MS, Agilent 7890)
using n-dodecane as an internal standard. And GC-MS conditions were listed as
follows: column, a capillary (60 m × 0.25 mm i.d.) coated with 0.25m film 5% phenyl
.
−1
methyl siloxane; carrier gas, high purity helium; flow-rate, 1.0 ml min ; inlet mode
and temperature, pulsed splitless at 190 ℃; the column temperature was set at 60 ℃
.
−1
and held for 2 min for injection, then programmed at 5 ℃ min to 145 ℃ and held
.
−1
for 25 min at the temperature of 145 ℃, then at 5 ℃ min to 200 ℃, and finally, at
.
−1
20 ℃ min to 280 ℃, and held for 3 min at the temperature of 280 ℃. The product
yield and selectivity are calculated and defined as follows:

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n
 nGUA
0
n
Yi
GUA
i
XGUA
Where

100% (1) Y 
100% (2) Si 
100% (3)
i
0
n
n
XGUA
GUA
GUA
0
n
and nGUA depict the amounts of guaiacol before and after reaction,
GUA
respectively, in mol; and ni is the amount of reaction product, in mol. The mass
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balance of carbon was evaluated by the sum of reaction products and unreacted
materials in comparison with raw materials, which was round 93-95%. All the
experiments were conducted at least two times and the results agreed within 5%.
Results and discussion
Catalyst characterization
Physicochemical properties of the catalysts
The physicochemical properties of Ni/CNT and Co promoted NiCo/CNT
catalysts were presented in Table 1. The ICP results suggested that the metal loading
amounts were in good accordance with the theoretical calculating value before
catalysts preparation, as very marginal differences were observed. The BET surface
2
area of Co/CNT catalyst was relatively larger than Ni/CNT (150.5 m /g and 142.3
2
m /g respectively), indicating that Co particles were better dispersed on the CNT
support surface. Similar phenomena were also observed in bimetallic NiCo catalysts,
while the BET surface areas of Co promoted NiCo/CNT catalysts increased with the
addition of Co in catalysts, in comparison with monometallic Ni/CNT or Co/CNT
catalyst. The above results indicated that the introduction of Co in Ni/CNT could not
only help to improve the dispersion of metal particles, but also contribute to
restraining the aggregation of Ni/Co particles during the preparation, which was also
reported in Martin and Ma’s studies that the presence of Co could help to decrease the

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average metal particle size [34, 35]. Furthermore, the pore volume also increased to
some extent after the introduction of metal Co in NiCo/CNT catalysts. The average
metal particle sizes obtained from XRD and TEM also confirmed the promotional
effect of Co in the bimetallic catalysts, as the average metal particle size decreased
with the introduction of Co. These changes in catalyst properties would definitely
influence the catalytic activity during the guaiacol hydrodeoxygenation reaction,
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which will be studied in detail in the following sections.
Table 1 Chemical and physical properties of CNT supported Ni and/or Co catalysts
Composition (wt.%)a
Average
metal
Average
metal
b
b
S
BET
V
p
Catalysts
2
3
(m /g)
(cm /g)
Ni
Co
c
d
size (nm)
size (nm)
2
0% Ni/CNT
19.32
14.55
9.66
4.68
/
/
142.3
154.6
158.8
157.4
150.5
0.80
0.84
0.86
0.83
0.78
17.12
13.67
13.88
15.16
18.03
17.88
13.18
13.50
15.25
17.53
(15+5)% NiCo/CNT
(10+10)% NiCo/CNT
4.76
9.72
15.02
19.46
(
5+15)% NiCo/CNT
2
0% Co/CNT
a-measured by ICP analysis; b-evaluated from N adsorption-desorption isotherms; c-estimated by
2
XRD; d-measured by TEM
Structural properties and morphology of the catalysts
The XRD patterns of reduced Ni/CNT, Co/CNT and Co promoted NiCo/CNT
were shown in Fig. 1. It could be seen from Fig. 1 that, characteristic peaks
corresponding to metallic Ni and Co were clearly observed in monometallic Ni/CNT
and Co/CNT. The peaks at 2θ=44.5°, 52.1° and 76.3° could be ascribed to (111),
(
200), and (220) planes of metallic Ni, while the peaks at 44.6° and 76.4° could be
assigned to the diffraction of (111) and (220) planes of metallic Co [32,33].
Differently, the intensity corresponding to metallic Ni and Co varied, as much sharper

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peaks in Ni/CNT were observed than that in Co/CNT, suggesting the lower dispersion
of metal particles in Ni /CNT. In comparison with the XRD patterns of monometallic
and bimetallic catalysts in Fig. 1, the intensity corresponding to metallic Ni and/or Co
decreased gradually with the introduction of Co to Ni/CNT catalyst, suggesting the
improvement in dispersion of metal particles on the CNT support. Furthermore, no
NiO and CoO species (2θ=38.2°, 45.3°) in reduced catalysts were observed,
indicating good stability of CNT supported catalyst.
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Fig. 1 XRD spectra of CNT supported Ni and/or Co catalysts
The average metal particle size in Table 1 indicated that monometallic Ni/CNT
and Co/CNT showed relatively larger mean particle size (17.88 nm and 17.53 nm)
respectively. With the addition of Co in the bimetallic catalysts, the average particle
size decreased obviously to around 13.67 nm in NiCo/CNT catalysts with different
Ni/Co ratio. The particle size distributions for different catalysts were also presented
in Fig. 2 (Fig.2-a-Fig.2-d), and it could be found that the particle size distributions for
monometallic catalysts (Fig.2-a, Fig.2-b) were much wider than bimetallic NiCo/CNT
catalysts (Fig.2-c, Fig.2-d). Especially in (15+5)% NiCo/CNT, it showed best particle

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size distribution, as most of the particle sizes focused in the range of 10 nm-15 nm
(
Fig.2-d). TEM- EDX mapping was conducted, as it was suitable for the analysis of
two or more elements in catalysts. EDX mapping of the HAADF-STEM image and
elemental mapping images for (15+5)% NiCo/CNT were presented in Fig. 2-e-Fig. 2
0
1
2
3
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0
-
h, respectively. The elemental mapping images of NiCo/CNT catalyst showed that Ni
particles (blue colored) and Co (green colored) particles dispersed homogeneously on
the support surface, and Co was in close contact with Ni particle in the catalyst. In
summary, the TEM results confirmed that the addition of Co could help to increase
the dispersion and decrease the average metal size of catalysts, which was very
consistent with the XRD results in Fig. 1-b.
Fig. 2 TEM micrographs of different CNT-supported catalysts: a-20% Ni/CNT, b-20%
Co/CNT, c-(10+10)% NiCo/CNT, d-(15+5)% NiCo/CNT, e-f-EDX mapping images
Surface element compositions and reducibility of the catalysts

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The surface element compositions of reduced Ni/CNT, Co/CNT and NiCo/CNT
were analyzed by XPS. The corresponding binding energy information and surface
atomic ratios were presented in Table 2, and the Ni2p and Co2p XPS spectra of
reduced catalysts were exhibited in Fig. 3. The Ni2p XPS spectra of Ni/CNT
exhibited four main peaks with binding energy at 873.8 eV, 870.2 eV, 855.8 eV and
1
1
1
1
1
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1
1
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0
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0
2
+
0
2+
0
852.8 eV, corresponding to Ni (2p ), Ni (2p ), Ni (2p ) and Ni (2p )
1
/2
1/2
3/2
3/2
respectively, indicating the presence of oxidized Ni species. Binding energies at 780.1
0
eV, 782.7 eV and 796.7 eV corresponded to the main line of Co (2p ) and
3
/2
2
+
0
Co (2p ) and Co (2p ), respectively, suggesting the presence of both metallic Co
3
/2
1/2
0
2+
and CoO species in Co/CNT. The Ni (2p ) and Ni (2p ) peaks in NiCo/CNT
1
/2
3/2
catalyst shifted to relatively higher binding energy by 0.35 eV and 0.3 eV
0
2+
respectively, and the Co (2p ) and Co (2p ) peaks also shifted to higher binding
3
/2
3/2
energy by 0.6 eV and 2.8 eV. By comparing these two samples, one could clearly see
that the BE values of Co(0) and Ni(0) in (15+5)% NiCo/CNT catalyst were higher
than those in Ni/CNT and Co/CNT, indicating the stronger interaction between the
2
+
0
2+
0
metal species and the support. A subtle decrease of Ni /Ni ratio and Co /Co in
Table 2 ratio was observed in comparison with monometallic and bimetallic catalysts.
The XPS results confirmed the addition of Co in catalyst was beneficial for the
reduction of NiO and/or CoO species to metallic Ni and/or Co, which was consistent
with the characterization results from TPR analysis. Furthermore, the Bronsted acid
and Lewis acid distributions were measured by Py-IR (Fig. S7). It could be clearly
seen in Table S1 that NiCo/CNT showed a higher total acid amount than Ni/CNT

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catalyst. The results in Table S1 also indicated that very weak Bronsted acid was
observed in Ni/CNT, and Ni/CNT showed very low B/L ratio (0.016). Table S1
showed that the amount of Lewis acid increased obviously after the introduction of
element Co in Ni-based catalysts, which followed the order: (15+5)% NiCo/CNT >
0
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(
10+10)% NiCo/CNT > (5+15)% NiCo/CNT. The improvement in catalyst acidity
was further confirmed to be useful for the hydrodeoxygenation of guaiacol to
cyclohexanol, since partially reduced cobalt species provided Lewis acid sites for the
reaction.
Fig. 3 XPS pattern of CNT-supported Ni and/or Co catalysts: a-Ni analysis; b-Co analysis
2
p
2p
Table 2 Binding energies and atomic ratios of reduced catalysts obtained from XPS analysis
Binding energy (eV)
Catalysts
Atomic ratio
0
2+
0
2+
0
2+
0
2+
0
2+
0
Ni 2p3/2
Ni 2p3/2
Ni 2p1/2
Ni 2p1/2
Co 2p3/2
Co 2p3/2
Co 2p1/2
Ni /Ni
Co /Co
2
0% Ni/CNT
15+5)% NiCo/CNT
0% Co/CNT
852.8
852.85
/
855.8
856.1
/
870.2
870.55
/
873.8
873.9
/
/
/
/
0.38
0.36
/
/
(
780.7
780.1
785.5
782.7
796.7
796.7
0.20
0.25
2
H -TPR profiles of the 20% Ni/CNT, 20% Co/CNT and different ratios of
2
NiCo/CNT catalysts were shown in Fig. 4-(a). It could be seen from TPR profiles of
the Ni/CNT catalysts that peak occurred around 380 ℃ and 500 ℃. The reduction
peak at relatively low temperature ascribed to the reduction of superficial metal oxide

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(herein NiO) with very weak interaction with CNT support; and the reduction peak at
relatively high temperature ascribed to the reduction of metal oxide which was highly
dispersed with smaller size and strongly interacted with the support. The Co/CNT
catalyst had three overlapping broad reduction peaks, which were around 300 ℃, 400 ℃
and 500 ℃ respectively. Among them, the reduction peak that appeared in the low
temperature (300 ℃) corresponded to the hydrogen consumption peak where Co O
1
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4
was reduced to CoO, and the reduction peak that appeared in the high temperature
500 ℃) corresponded to the hydrogen consumption peak where CoO was reduced to
(
Co. In addition, The TPR spectra of 20% Co/CNT at about 400 °C moved to
relatively higher temperature compared with 20% Ni/CNT, which indicated that
metallic Co had much stronger interaction with CNT in Co/CNT catalyst than
Ni/CNT catalysts. The NiCo/CNT catalyst had two overlapping broad reduction
peaks, which were around 400 ℃ and 500 ℃ respectively. With the addition of Co,
the hydrogen consumption peak in the low temperature section of the NiCo/CNT
catalyst tended to move to the high temperature. The increase in the reduction
temperature indicated that the interaction between the metal in the catalyst and the
supported CNT has increased. Therefore, NiCo/CNT catalysts presented a higher
reducibility.
In addition, the acidity of 20% Ni/CNT, 20% Co/CNT and different ratios of
NiCo/CNT catalysts were investigated by NH -TPD in Fig. 4-b. We could find that
3
the 20% Ni/CNT catalyst showed a broad NH desorption peak at 120-250 ℃,
3
suggesting the presence of weak acid sites. And 20% Co/CNT catalysts exhibited two

New Journal of Chemistry
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NH desorption peaks at 200-300 ℃ and 320-400 ℃, indicating the presence of both
3
weak acid and medium strong acid sites. With the introduction of element Co to
Ni/CNT catalyst, (15+5)% Co/CNT catalysts exhibited two NH desorption peaks at
3
0
1
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150-270 ℃ and 320-400 ℃, indicating the presence of both weak acid and medium
strong acid sites. When the metal Co increased from 5 wt.% to 10 wt.%, the weak acid
centers (150 ℃-270 ℃) on the surface of the NiCo/CNT catalyst increased, while a
small amount of medium strong acid centers (320 ℃-400 ℃) appeared. When the
metal Co increased to 15 wt.%, the weak acid center (200 ℃-300 ℃) was further
strengthened, while the medium strong acid center (320 ℃-400 ℃) disappeared. The
results above showed that the ratio of the two metals had a certain effect on the
distribution of acid sites on the catalyst surface, which in turn affected the catalytic
activity of the catalyst. Combining the NH -TPD characterization results and the
3
experimental results in Fig. 5 and 6, it could be seen that the acidity of the catalyst
and the strength of the acidity had a great impact on its catalytic activity. Under the
action of the (15+5)% NiCo/CNT catalyst with lower acidity, the conversion of
guaiacol is high, up to 100%, and the selectivity of cyclohexanol was also over 90%.
Fig. 4 (a) H -TPR of different ratios of NiCo/CNT catalysts, and (b) NH -TPD of different ratios
2
3
NiCo/CNT catalysts

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Catalytic hydrodeoxygenation of guaiacol
Effect of metal composition in catalysts
Herein, the catalytic hydrodeoxygenation of guaiacol was conducted over
monometallic catalysts (Ni/CNT, Co/CNT) and bimetallic NiCo/CNT catalysts for the
screening of catalysts. The promotional effect in bimetallic catalysts was obviously
observed, considering both the guaiacol conversion rate and cyclohexanol selectivity,
which was exhibited in Fig. 5. As can be seen in Fig. 5 that, both the guaiacol
conversion and cyclohexanol selectivity were highly dependent on the active metal
components in catalysts. For catalysts of Ni/CNT and Co/CNT, the guaiacol
conversion rate was very low (around 40%), and the HDO products turned out to be a
mixture of phenol and cyclohexanol. Phenol mainly came from the demethoxylation
of guaiacol, and it was reasonable for the presence of methanol in the liquid. The
promotional effect of Co in catalysts was clearly confirmed, as the guaiacol
conversion rate increased dramatically to about 100% when the HDO reaction was
carried out over bimetallic NiCo/CNT catalyst. Interestingly, NiCo/CNT could afford
higher cyclohexanol selectivity with almost no presence of other byproducts, and only
very subtle amount of phenol and cyclohexane was detected in the liquid products.
This result was quite different from previous studies, while different kinds of
byproducts were detected and reported previously, such as o-cresol, catechol,
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1
-methyl-1,2-cyclohexanediol [31, 36-42]. Herein, methanol was generated from the
demethoxylation step from guaiacol, which was also observed in the
hydrodeoxygenation of other lignin-derived phenols [39]. And cyclohexane was the

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Page 16 of 33
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further hydrogenation of cyclohexanol after a dehydroxylation process. It was widely
believed that catalysts with good dispersion would help to facilitate the catalytic
reaction, which was regarded as the particle size effect [41]. In this work,
monometallic and bimetallic catalysts with the same metal loading amount were
investigated, and it was clearly observed that the catalytic activity was closely
associated with the metal composition and average metal particle size of catalysts. It
was presented in Table 1 and Fig. 2 that, the order of CNT supported catalysts with
different metal components was given as below: 20% Ni/CNT > 20% Co/CNT >
(5+15)% NiCo/CNT > (10+10)% NiCo/CNT > (15+5)% NiCo/CNT. The above
results confirmed that the introduction of Co could obviously help to suppress/ the
growth of metal particles in NiCo/CNT catalysts. The XRD patterns of Ni/CNT,
Co/CNT and NiCo/CNT with a total metal loading amount of 20% also confirmed
that, bimetallic NiCo/CNT exhibited better dispersion with smaller average metal
particle sizes, as the peak intensities corresponding to metallic Ni/Co decreased
obviously with the addition of Co. These changes could definitely affect the catalytic
activity during the guaiacol HDO reaction, which was confirmed in Fig. 5 that,
Co-promoted catalysts exhibited much higher guaiacol conversion rate and better
selectivity toward cyclohexanol. As the best catalytic performance was observed over
(15+5)% NiCo/CNT, therefore further studies for optimal conditions were conducted
using (15+5)% NiCo/CNT. Considering the activities of (15+5)%, (10+10)% and
(5+15)% NiCo/CNT were quite similar. It was not clear that if it was the effect of
particle size or it is due to incorporation of Co to change the active sites. So, 20 %
0
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Ni/CNT catalyst with smaller particle size (15.8nm) were prepared by ultrasound and
the TEM micrograph was shown in Fig. S4. Parallel experiment was carried with
different particle sizes (Fig. S5). Slight increase of the selectivity of cyclohexanol was
observed when the hydrogenation of guaiacol was carried over 20% Ni/CNT (15.8
nm). In addition, the selectivity of cyclohexanol achieved up to 90% when Co was
introduction to Ni/CNT catalyst. Therefore, both the effect of particle size and the
incorporation of Co were two key factors contributing to a high activity.
1
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Fig. 5 Guaiacol conversion and products distribution over different catalysts
Reaction condition: T = 220 ℃, p = 2 MPa, t = 2 h; catalyst: A-20% Ni/CNT, B-20% Co/CNT,
C-(15+5)% NiCo/CNT, D-(10+10)% NiCo/CNT, E-(5+15)% NiCo/CNT
Total loading amount was an important influence on catalyst activity and product
distribution. Herein, the catalytic hydrodeoxygenation of guaiacol was conducted over
NiCo/CNT catalysts with different total loading amounts ((7.5+2.5)% NiCo/CNT,
(
15+5)% NiCo/CNT, (22.5+7.5)% NiCo/CNT). As could be seen in Fig. 6 that, both
the guaiacol conversion and cyclohexanol selectivity increased with the total metal
load gradually increased from (7.5+2.5)% to (22.5+7.5)%. And the selectivity of

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cyclohexanol was increased in the order of (15+5)% NiCo/CNT > (22.5+7.5)%
NiCo/CNT > (7.5+2.5)% NiCo/CNT. The result was consistent with TEM
micrographs of (7.5+2.5)% NiCo/CNT, (15+5)% NiCo/CNT, (22.5+7.5)% NiCo/CNT
in Fig. S6, in which, (15+5)% NiCo/CNT showed best particle size distribution, as
most of the particle sizes focused in the range of 10 nm-15 nm (Fig.2-d). In
comparison, low loading amount of (7.5+2.5)% NiCo/CNT led to a poor conversion
and yield of the reaction, and high loading amount of (22.5+7.5)% NiCo/CNT could
result in metal agglomeration. It was verified again that good dispersion would help to
facilitate the catalytic reaction, which was regarded as the particle size effect [41].
Taken together, optimal catalyst was (15+5)% NiCo/CNT, which could be clearly
seen in Fig. 5 and 6.
0
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9
0
Fig. 6 Guaiacol conversion and products distribution over different catalysts
Reaction condition: T = 220 ℃, p = 2 MPa, t = 2 h; catalyst: none, (7.5+2.5)% NiCo/CNT,
(15+5)% NiCo/CNT, (22.5+7.5)% NiCo/CNT
Products distribution studies over NiCo/CNT catalyst
Reaction temperature always had a great effect on the hydrodeoxygenation
reaction and the specific products distribution. So in this study, we firstly investigated

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the influence of temperature with an initial nitrogen pressure of 2 MPa. It could be
seen in Fig. 7 that the conversion rate of guaiacol improved from 43.5% to about
1
00%, while the HDO reaction temperature increased from 180 ℃ to 220 ℃.
1
1
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Simultaneously, the selectivity of cyclohexanol exhibited a similar trend with the
increase of reaction temperature, as the cyclohexanol selectivity improved from about
59.8% to 93.9% with correspondingly decreased phenol selectivity. And the highest
cyclohexanol selectivity was obtained at 220 ℃, which was regarded as the optimal
reaction temperature as no improvement was observed with the continuous increase of
temperature. This was also observed in previous studies that, the HDO of guaiacol to
cyclohexanol always happened over different catalysts under a relatively higher
temperature (>200 ℃). Tomishige et al. reported that higher reaction temperature
would facilitate the HDO of guaiacol to afford cyclohexanol over Ru/C and MgO at
an initial hydrogen pressure of 1.5 MPa [40]. Sels et al. also reported higher
temperature (e.g. 250 ℃ or 300 ℃) and higher Ni loading amount (65 wt.%) could
help to achieve the conversion of guaiacol to cyclohexanol, confirmed the
promotional effect of higher reaction temperature during the HDO reaction of phenols
[
41, 42]. Furthermore, in Sels’s studies, they also reported the generation of
1
-methyl-1,2-cyclohexanediol (trans- and cis-) as the byproducts at higher
temperature (>200 ℃), leading to the decrease of cyclohexanol selectivity. In this
work, the HDO of guaiacol could afford a higher cyclohexanol selectivity (about
94%) with a nearly 100% conversion rate, catalyzed over (15+5)% NiCo/CNT
catalyst at 220 ℃.

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Fig. 7 Guaiacol conversion and products distribution over different temperatures
Reaction condition: (15+5)% NiCo/CNT catalyst, p = 2 MPa, t = 2 h
In this work, the HDO of guaiacol was conducted in a nitrogen atmosphere
instead of hydrogen. Herein, the effect of nitrogen pressure at a range of 0 MPa to 3
MPa was investigated over NiCo/CNT, which was obviously lower compared with
previous studies [37, 38, 43]. It could be clearly observed in Fig. 8 that the initial
nitrogen pressure had a great effect on the guaiacol conversion rate and product
selectivities. The HDO reaction showed a poor guaiacol conversion (33.5%),
affording a mixture of phenol and cyclohexanol, while no extra nitrogen was added in
the system. The guaiacol conversion improved from 33.5% to nearly 100%, with the
increase of the initial nitrogen pressure from 0 MPa to 2 MPa. The HDO reaction was
also conducted at a much higher initial pressure (e.g. 3 MPa), and there was almost no
change in conversion and cyclohexanol selectivity compared with that obtained with
the presence of 2 MPa nitrogen. In comparison with previous studies, this work
provided a novel method for the hydrodeoxygenation reaction of phenols without the
presence of extra hydrogen in the system, which would reduce the production cost and

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suppress the side reactions. Tomishige et al. found that increased hydrogen pressure in
the HDO system would help to suppress the conversion of guaiacol to cyclohexanol,
thus lead to the generation of byproducts, such as 2-methoxy-cyclohexanol [40]. In
our previous study, we also found that extra hydrogen in the system could lead to the
decrease of cyclohexanol selectivity, and instead, the selectivity of
1-methyl-1,2-cyclohexanediol (trans- and cis-) increased with the presence of extra
hydrogen [43]. Maybe this could well explain why our HDO system showed excellent
selectivity toward cyclohexanol (up to 94%) with almost no byproducts. Finally, 2
MPa of nitrogen was found to be suitable, taking guaiacol conversion and products
1
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distribution into consideration. As well known, H was an excellent hydrogen source
2
and often used to carry out most of the hydrogenation reactions. It could be clearly
seen that H and N achieved a similar result for the selectivity generation of
2
2
cyclohexanol (Fig. S1). In addition, only 60% selectivity of cyclohexanol was
obtained in the absence of external gas. This may be because isopropanol served as
the hydrogen source during the reaction. Furthermore, the use of hydrogen-donor
molecules could reduce security risks and cut the costs associated with transportation
and storage of hydrogen. Hence, the application of isopropanol as the hydrogen
source in guaiacol hydrogenation had been known as an efficient and novel alternative
to traditional hydrogenolysis procedures. Taken together, nitrogen was a
cost-effective choice in the selectively hydrogenation of guaiacol.

New Journal of Chemistry
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Fig. 8 Guaiacol conversion and products distribution over different N pressure
2
Reaction condition: (15+5)% NiCo/CNT catalyst, T = 220 ℃, t = 2 h
Li et al. reported that the hydrodeoxygenation/hydrogenation and
repolymerization reaction were always competing reactions, taking reaction
temperature and time into consideration [44]. So herein, the effect of reaction time
was also investigated in Fig. 9 after the study of the effect of reaction temperature. At
the very start, we conducted the HDO reaction for 1 h to figure out the possible
intermediates or byproducts, and the results turned out to be very low guaiacol
conversion rate and poor selectivity toward cyclohexanol (60.6% and 67.6%
respectively). Then we shortened the reaction to 30 min, unfortunately, we just
observed much lower conversion rate, without the observance of other byproducts
except phenol. Afterwards, we prolonged the reaction time to 2 h, 4 h and 6 h
respectively, and we found that the guaiacol conversion rates were all up to100%.
And the experimental results all exhibited very high selectivity of cyclohexanol
(
>94%), without any other byproducts. The high selectivity might benefit from the
nitrogen in the system, while Tomishige and Jiang Jianchun observed that extra

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hydrogen would lead to the increase of byproducts amount, such as
2
-methoxy-cyclohexanol [40] and 1-methyl-1,2-cyclohexanediol (trans- and cis-)
[
43]. In general, the introduction and presence of nitrogen in the system could help to
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improve the cyclohexanol selectivity and suppress other side reactions. Tomishige
and Sels reported that the process of guaiacol to cyclohexanol consisted of several
complex steps, such as demethoxylation, demethylation, etc., therefore the process
was always in need of proper reaction time and high temperature, with the presence of
different intermediates/byproducts (e.g. 2-methoxy-cyclohexanol). In comparison, our
system could afford much higher cyclohexanol selectivity within shorter reaction
time. Finally, 2 h was regarded as the optimal reaction time for the HDO of guaiacol,
considering the guaiacol conversion and cyclohexanol selectivity.
Of note is the mass balance of these reactions. The hydrogenolysis product was
obtained only as cyclohexanol and almost no starting materials could be easily
recovered by GC/MS when the product yield is very high (Fig. S2). The
representative chromatogram could be seen in Fig. S3.

New Journal of Chemistry
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Fig. 9 Guaiacol conversion and products distribution over different reaction time
Reaction condition: (15+5)% NiCo/CNT catalyst, p = 2 MPa, T = 220 ℃
Possible reaction pathway over NiCo/CNT catalyst
The hydrodeoxygenation of guaiacol to cyclohexanol was a complex progress,
involving several competitive reactions. As presented in Scheme 1, our previous study
reported that 1-methyl-1,2-cyclohexanediol (trans- and cis-) was detected as the
intermediate during the HDO of guaiacol in water (pathway I), followed by the
dehydration to afford 2-methyl-cyclohexanol (cis- and trans-). And pathway III was
another important competing reaction during the HDO process, affording phenol as
the main intermediate in our previous study, which was confirmed to be the main
reaction path in need of high external hydrogen pressure (5 MPa H ) [43]. Sels et al.
2
also reported two competitive pathways during the hydrodeoxygenation of guaiacol to
cyclohexanol (pathway II and pathway III in scheme 1), in which, high reaction
temperature and hydrogen pressure (300 ℃, 4 MPa) were needed in the HDO process
[
41, 42]. In comparison, this work provided a novel path for the conversion of
guaiacol to cyclohexanol in the absence of external hydrogen. Differently, nitrogen

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was introduced into the catalytic hydrodeoxygenation process, and turned out to have
positive effect for the conversion of guaiacol to cyclohexanol, while the HDO
reaction in this study exhibited much better selectivity toward cyclohexanol.
Furthermore, it was also confirmed that extra hydrogen in the HDO system would
lead to the formation of byproducts and then suppress the conversion of guaiacol to
cyclohexanol [40-43]. Different with previous reports, no other intermediates (e.g.
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1
-methyl-1,2-cyclohexanediol, 2-methyl-cyclohexanol, etc) were detected, and only
phenol was detected, which could be quickly hydrogenated into cyclohexanol [42].
The above results indicated the HDO process seemed impossible to take place
according to pathway I and pathway II, as no corresponding intermediates was
observed after reaction. According to the products distribution in Fig. 4-Fig. 7, we
deduced that the HDO of guaiacol over NiCo/CNT in isopropanol might undergo a
reaction path according to pathway IV in scheme 1, through the formation of phenol
as main intermediate. Also, very few amount of cyclohexane was observed in the
reaction products, which was the further hydrogenation product of cyclohexanol. In
general, the catalytic hydrodeoxygenation of guaiacol usually underwent several
competing steps, affording different intermediates and final products, so further
studies were needed for the thorough understanding of the catalytic HDO process in
the absence of external hydrogen.

New Journal of Chemistry
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Scheme 1 Possible reaction pathway for hydrodeoxygenation of guaiacol over NiCo/CNT
HYD-hydrogenation, DMO-demethoxylation, DME-demethylation HDO-hydrodeoxygenation)
(
Expanding the substrate scope for the HDO reaction and recyclability study
To confirm the above protocol, the catalytic hydrodeoxygenation of a series of
lignin-derived phenols were investigated under the optimum reaction conditions
(
220 ℃, 2 h, 2 MPa N ). It could be seen that NiCo/CNT exhibited good performance
2
for the hydrodeoxygenation of different lignin-derived phenols (Table 3). Phenol
could be easily converted to cyclohexanol under the optimum conditions, with a high
selectivity toward cyclohexanol (entry 2, 96%), which was in good accordance with
the HDO results of guaiacol. The HDO of catechol could afford a mixture of
1
,2-cyclohexanediol and cyclohexanol, and 1,2-cyclohexanediol was a possible
intermediate during the HDO of guaiacol to cyclohexanol [43]. For
E)-4-(3-hydroxyprop-1-en-1-yl)phenol, it seemed difficult for its HDO to
cyclohexanol in our catalytic system. Although the reaction was conducted at 240 ℃,
(

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the cyclohexanol selectivity was still very low (about 36%, entry 5), as it was much
difficult for the cleavage of C-C bond in our system. Based on all the above results,
we might conclude that NiCo/CNT catalyst exhibited good catalytic activity for most
of lignin-derived phenols, but further studies were still in need.
1
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Table 3 Evaluation of the substrate scope in the HDO process over NiCo/CNT
o
entry
1
substrates
T( C)/t(h)/P(MPa)
conversion
selectivity of products
OH
OH
OMe
100%
100%
100%
94%
220/2/2
OH
OH
96%
220/2/2
2
3
4
5
OH
OH
OH
OH
OH
OH
3
4%
45%
58%
36%
220/2/2
OH
OH
OH
OH
30%
220/2/2
240/2/2
100%
100%
OH
24%
OH
OH
The reusability of the NiCo/CNT catalyst was also explored, herein a batch of
NiCo/CNT catalysts were used repeatedly for the HDO of guaiacol at 220 ℃ for 2 h
with an initial nitrogen pressure of 2 MPa. The catalyst could be easily separated from
the mixture due to the magnetism of Ni. The results in Table 4 indicated that the
catalyst still showed good catalytic activity after three times use, with a subtle
decrease of cyclohexanol selectivity. And the ICP results suggested that the metal
leaching of both Ni and Co in catalyst happened during the reuse, which might
contribute to the loss of catalytic activity during the reaction.

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Table 4 Results of repeated use of (15+5)% NiCo/CNT catalysts
Selectivity (%)
phenol
Catalysts
Entry
Guaiacol con. (%)
cyclohexanol
93.9%
NiCo/CNT
1
2
3
100
95.1
92.4
3.2%
5.8%
9.4%
0
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91.2%
85.1%
Reaction conditions: reaction temperature-220 ℃, initial nitrogen pressure-2 MPa, reaction time-2
h.
Conclusion
In this work, catalytic hydrodeoxygenation of lignin-derived phenols was
conducted over CNT supported monometallic and bimetallic catalysts, and a novel
strategy was proposed over NiCo/CNT in the absence of external hydrogen. Among
those catalysts, NiCo/CNT catalysts afforded much higher guaiacol selectivity up to
9
4% with cyclohexanol as the main product, confirming the promotional effect of Co
in the catalyst. The introduction of nitrogen in the catalytic system could not only
facilitate the conversion of guaiacol to cyclohexanol, but also suppress the side
reactions during the hydrodeoxygenation process. The mechanisms for C-O bond
cleavage in guaiacol were also explored and proposed over NiCo/CNT in isopropanol
with the presence of nitrogen, suggesting that the HDO process happened in two
consecutive steps: the demethoxylation of guaiacol to phenol and the further
hydrogenation of aromatic ring to cyclohexanol. NiCo/CNT catalysts exhibited good
reusability during the hydrodeoxygenation process, which could provide possible
alternatives for those noble metal catalysts and the application of external hydrogen
for the upgrading of bio-oil.
Acknowledgments

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Authors are grateful for the financial support from the National Key R&D
Program of China (No. 2018YFB1501405-05), and the National Natural Science
Foundation of China (31700645).
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References
[
1] P. M. Mortensen, J. Grunwaldt, P. A. Jensen and A. D. Jensen, ACS Catal., 2013,
3, 1774-1785.
[
2] M. Ghadiryanfar, K. A. Rosentrater, A. Keyhani and M. Omid, Renewable
Sustainable Energy Rev., 2016, 54, 473-481.
[3] C. O. Tuck, E. Perez, I. T. Horvath, R. A. Sheldon and M. Poliakoff, Science,
012, 237, 695-699.
2
[4] M. Saidi, F. Samimi, D. Karimipourfard, T. Nimmanwudipong, B. C. Gates and
M. R. Rahimpour, Energy Environ. Sci., 2014, 7, 103-129.
[
[
[
5] P. M. Mortensen, D. Gardini, C. D. Damsgaard, J. Grunwaldt, P. A. Jensen, J. B.
Wagner and A. D. Jensen, Appl. Catal. A, 2014, 523, 159-170.
6] V. Itthibenchapong, C. Ratanatawanate, M. Oura and K. Faungnawakij, Catal.
Commun., 2015, 68, 31-35.
7] M. A. Machado, S. He, T. E. Davies, K. Seshan and V. T. Silva, Catal. Today,
2
018, 302, 161-168.
[8] Y. X. Yang, C. Ochoa-HernAndez, V. A. D. O’Shea, P. Pizarro, J. M. Coronado
and D. P. Serrano, Appl. Catal. B, 2014, 145, 91-100.
[9] X. Li, X. Luo, Y. Jin, J. Li, H. Zhang, A. Zhang and J. Xie, Renew. Sust. Energy
Rev., 2018, 82, 3762-3797.