In situ hydrogenation of phenolic compounds over Ni-based catalysts: Upgrading of lignin depolymerization products

Article abstract of DOI:10.1039/c9nj05395f

A series of Ni-based catalysts, including Ni/SiO₂-ZrO₂, Ni/HZSM-5, Ni/Al₂O₃, Ni/SiO₂, Ni/AC and Ni/CMK-3, were prepared to produce H₂ from the aqueous phase reforming (APR) of methanol. This H₂ was then used in the in situ hydrogenation of phenolic compounds for bio-fuel. The effect of different promoters was investigated with the addition of Co, La, Fe and Cu to the Ni/CMK-3 catalyst coupled with analysis using BET, XRD and SEM. The results showed that Ni/SiO₂, Ni/AC and Ni/CMK-3 yielded the most hydrogen and they were chosen for further investigation in the in situ hydrogenation of phenol, guaiacol and lignin depolymerization products (LDP). Using these Ni-based catalysts, the APR of methanol provided hydrogen for the hydrogenation of the phenolic compounds. Of the modified Ni/CMK-3 catalysts, La-Ni/CMK-3 exhibited the highest activity for the conversion of phenol (80.88%) with a satisfactory cyclohexanol yield (76.64%) at 240 °C for 4 h without an external H₂ source. When using La-Ni/CMK-3, the content of the phenolic compounds in LDP decreased from 75.25% to 25.38% while the content of saturated alcohols increased from 1.34% to 31.19%. It has been shown that it is possible to use the APR of methanol for the hydrogenation of LDP over a series of Ni/CMK-3 catalysts.

Full text of DOI:10.1039/c9nj05395f

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In-situ hydrogenation of phenolic compounds over Ni-based catalysts:
upgrading of lignin depolymerization products
Ying Xu a,b,c,*, Zifang Penga ,Yuxiao Yua,d ,Dongling Wanga, Jianguo Liua,b,c,Qi Zhanga,b,c
Received 00th January 20xx,
Accepted 00th January 20xx
Chenguang Wang a,b,c
DOI: 10.1039/x0xx00000x
A series of Ni-based catalysts were prepared to obtain H2 from the aqueous phase reforming (APR) of methanol for the in-
situ hydrogenation of phenolic compounds for bio-fuel, including Ni/SiO2-ZrO2, Ni/HZSM-5, Ni/Al2O3, Ni/SiO2, Ni/AC and
Ni/CMK-3. The promotion effect was investigated with the addition of Co, La, Fe and Cu in Ni/ CMK-3 catalyst and which
were analyzed using BET, XRD and SEM. The results showed that Ni/SiO2, Ni/AC and Ni/CMK-3 exhibited better
performance on the yield of hydrogen, which were chosen for further investigation on the in-situ hydrogenation of phenol,
guaiacol and lignin depolymerization products (LDP). Over these Ni-based catalysts,the APR of methanol could provide
hydrogen for the hydrogenation of phenolic compounds.. Among the modified Ni/CMK-3 catalysts, La-Ni/CMK-3
exhibited the highest activity for the conversion of phenol (80.88%) with the satisfactory cyclohexanol yield (76.64%) at
240℃ for 4h without H2. Over La-Ni/CMK-3, the content of phenolic compounds in LDP decreased from 75.25% to
25.38%, while the content of saturated alcohols increased from1.34% to 31.19%. It’s possible to use the APR of methanol
for the hydrogenation of LDP over Ni/CMK-3 catalysts.
a
solvent solution (acetic acid or ethanol).Organosolv
pretreatment affords sulfur-free lignin with high purity, which
makes it a suitable precursor for depolymerization[7-9].Owing
to the corrosivity, instability and other drawbacks, the
Introduction
Inedible plant biomass in the form of lignocellulose, as one kind
of bioenergy, could meet these essential criteria including being unprocessed bio-oil need further upgrading for utilization.
Because there are many kinds of phenolic compounds in the
liquid product from the lignin and the content of each is not high,
there are a lot of study on the hydrogenation of phenolic
compounds to high-grade biofuels [10, 11].
renewable, CO2-neutral, widely available, and not competing
with food production [1]. Lignin, as one of the main components
of biomass and for its methoxylated phenylpropane structure, is
a kind of potential fossil fuels’ resource [2, 3]. However, as a
kind of three-dimensional amorphous polymer [4], the
Phenols, specially phenol and guaiacol, are popular model
compounds for phenolic monomer valorization study [12,13].
Liu[14] studied selective hydrogenation of phenol to
cyclohexanone over dual supported Pd-Lewis acid catalysts.
Long[15] used Ni/MgO as catalyst to hydrogenate guaiacol for
cyclohexanol production. The research group of Kou[16, 17]
found that guaiacol could be completely converted into
cycloalkane with Pd/C and H3PO4 catalysts. Yinet[18] reported
that Ru/CMK-3 showed superior catalytic performance on the
hydrogenation of levoglucosan, which gave essentially
quantitative yields of sugar alcohols. Huang[19] reported that
over Pd/N-CMK-3, various nitroarenes could be hydrogenated
highly efficiently and selectively to the corresponding aromatic
amines. Besides, the Pd/N-CMK-3 catalyst could be recovered
easily for multiple recycling reactions without a loss of catalytic
performance. Pang[20] used sulfonated CMK-3 as a catalyst, the
results showed that the cellulose could be selectively hydrolyzed
into glucose and the yield of glucose reached 74.5%.
depolymerization of lignin is a hot and difficult topic.
Lignocellulosic biomass is composed of cellulose (50%),
hemicellulose (25%) and lignin (25%)[5]. One of the most
prevalent strategies for lignin utilization is the direct
hydrogenolysis of native lignin in biomass. However, the single
lignin depolymerization has been shown to be higher in
efficiency. Lignin extracted by Organosolv methods are among
the most user-friendly and economically, because many solvents
can be easily recycled[6]. The lignin extraction process depends
on their chemical solubilization in the presence of an acid (proton
donor). The process is generally carried out in hot situation to
promote hydrolysis reactions between the ligno-cellulosic sub-
fractions. Finally, the extracted lignin fractions are solubilized in
a. Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences,
Guangzhou 510640, PR China.
But among the hydrogenation researches, hydrogen energy,
b. Key Laboratory of Renewable Energy, Chinese Academy of Sciences, Guangzhou
510640, PR China.
as a kind of very expensive and high-level energy, must be used
during the hydrogenation process. Is there any other lower cost
chemical could afford hydrogen without hydrogen? In our
previous work, we found that raw bio-oil could be converted into
saturated alcohol at 220°C over Raney Ni catalyst in the
methanol-water solvent without hydrogen. We also found that
the conversion of methanol in aqueous phase reforming (APR)
c. Guangdong Provincial Key Laboratory of New and Renewable Energy Research
and Development, Guangzhou 510640, PR China.
d. Tianjin Alta Scientific Co.,Ltd,Tianjin,PR China
e. E-mail: xuying@ms.giec.ac.cn
†Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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reaction, hydrogen selectivity were promoted and the side In this paper, different carriers, such as SiO2-ZrO2, HZSM-5,
View Article Online
DOI: 10.1039/C9NJ05395F
reaction for producing methane was restrained while the in-situ Al2O3, SiO2, AC and CMK-3, were chosen to load Ni activity in
hydrogenation happened in the same reactor[9]. Later, Guan[21] the APR of methanol for the hydrogen. The catalysts of Ni/SiO2,
found that in the upgrading fast pyrolysis bio-oil reaction, 0.25- Ni/AC, Ni/CMK-3 and the Ni/CMK-3 with different promoters
10wt.% Mg doping in Al-MCM-41 could improve the in- were chosen for further investigation on the in-situ
situ catalytic activity.
hydrogenation of model compounds and LDP.
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CuKα radiation source. Scan step was 0.02°, scanning in 5-
80° over catalysts. Scanning electron microscopy (SEM)
images were recorded on a Hitachi S-4800 instrument
operated at 20 kV.
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Experimental
Materials
Methanol (P99.5%, analytical reagent) was purchased from
Tianjin Fuyu Fine Chemical Co. Ltd. Phenol (P99.5%,
analytical reagent) and guaiacol (P99.5%, analytical
reagent) were purchased from Tianjin Fuchen Chemical
Reagents Factory. Co(NO3)2·6H2O and Ni(NO3)2·6H2O
were purchased from Guangzhou Chemical Co. Ltd.
Cu(NO3)2, La(NO3)3·6H2O and FeCl3 were purchased from
Guangzhou Chemical Reagents Factory. Other chemicals
were supplied by Jinhuada Chemical Reagent Co., Ltd.
CMK-3 was prepared in the way shown in the literatures [22,
23].
Typical procedure and products analysis
The APR of methanol was carried out in a 100 mL stainless
autoclave. 1.5g catalyst, 36g water and 16g methanol
(water/methanol =20/5, molar ratio) were charged into the
autoclave. After the air was changed with N2, the pressure
was set to 0.1 MPa and the reaction was set at 220°C for 4 h
with the revolution of 400rpm. After reaction, the autoclave
was cooled down to the room temperature and then sampled
the gas products for GC analysis with FID detector.
The in-situ hydrogenation of phenolic/gualacol and the
lignin depolymerization product was also carried out in the
100 mL stainless autoclave respectively. Based on the APR
reaction system of methanol, the reactants of 0.08mol(model
compounds) or 14 mL(raw lignin depolymerization product)
were added in the reactor. The in-situ hydrogenation reaction
was set at 240°C for 4 h under 1 Mpa pressure of N2
atmosphere. The gas product was sampled for analysis by
Shimadzu GC20B gas chromatograph and the liquid product
was sampled for analysis by Shimadzu GC 2010. The raw
lignin depolymerization product and the upgraded product
were also measured by gas chromatography/mass
spectrometry (GC–MS, Trace 2000, Thermo-Finnigan Inc.,
USA). The separation was realized on a column of HP-
INNOWAX, 30 m*0.25 mm*0.25 mm, and the oven
temperature program was 40 o C (holding for 8 min) at 6/min
to 280oC (holding for 30 min). The content of each
compound was evaluated based on GC data using the
internal standard method. The conversion of reactant (mol%)
was calculated as below.
The
lignin
depolymerization
product
was
depolymerized from organicsolve lignin in methanol over
0.5g organicsolve lignin, 0.12g MgCl2 (calcining before
using) and 40 mL methanol were charged into a 100 mL
316L stainless autoclave. After the air was changed with H2,
the pressure was set to 0.5 MPa and the reaction was set at
260 °C for 0.5 h. After reaction, the autoclave was cooled
down to the room temperature, the product mixture was
filtered, and the liquid product was obtained as feedstock in
the in-situ hydrogenation process.
Preparation of catalysts and characterization
The Ni/CMK-3 catalyst was prepared using wet
impregnating method. After impregnating CMK-3 in
Ni(NO3)2·H2O aqueous solutions, the water was evaporated
and the residue was dried at 120oC. The catalysts of 20 wt%
Ni was obtained after calcined at 450oC at N2 atmosphere
and reduced at 550℃ in the flow of 5vol% hydrogen mixed
with 95vol% nitrogen [24]. We also got the catalysts of
Ni/SiO2-ZrO2, Ni/HZSM-5, Ni/Al2O3, Ni/SBA-15, Ni/AC,
Ni/SiO2 and Ni/CMK-3 in the same method.
Co-Ni/CMK-3 catalyst was prepared by wet
impregnating method. The CMK-3 was impregnated in the
Ni(NO3)2·6H2O and Co(NO3)2·6H2O mixed aqueous
solution and the content of Ni and Co addition were 20wt%
and 1wt% respectively. After calcined at 450oC at N2
atmosphere and reduced at 550℃ in the flow of 5vol%
hydrogen mixed with 95vol% nitrogen, the Co-Ni/CMK-
3was obtained. In the same way, we got the catalysts of La-
Ni/CMK-3, Fe-Ni/CMK-3 and Cu-Ni/CMK-3.
Moles of reactants after reaction
Conversion= (1- Moles of reactants loaded initially) ×100% (1)
Moles of product
Selectivity of product= (∑ Moles of product) ×100% (2)
Results and discussion
Aqueous phase reforming of methanol
The APR of methanol was carried out over the Ni-based
catalysts with different carriers. The amount of each gas in
products was shown in Fig. 1.
The surface area and pore size distribution of the
catalysts were determined by the Brunauer–Emmet–Teller
(BET) method using Quantachrome. The average pore
diameter and pore volume were calculated with the Barret–
Joyner–Halenda(BJH) model. X-ray diffraction(XRD)
patterns were recorded using a RigakuD/max-rC with a
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The BET of Ni/SiO2, Ni/AC and Ni/CMK-3 were shown in
DOI: 10.1039/C9NJ05395F
Table 1. The carbon carriers had relative higher specific
surface area. CMK-3, as one of typical mesoporous materials,
has the biggest specific surface area and average pore size
among the three catalysts, as well as high hydrothermal
stability and biocompatibility [29, 30].
View Article Online
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
CO
CO
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C
2+
C
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CH
4
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H
2
Ni/SiO -ZrO Ni/HZSM-5 Ni/Al O
Ni/SiO
2
Ni/AC Ni/CMK-3
2
2
2
3
Catalysts
Ni/SiO
2
Fig.1 The gas distribution from the APR of methanol over
Ni catalysts on different supports (0.1MPa (N2), 220 oC, 4 h,
1.5g catalyst, 36g water and 16g methanol)
Ni/CMK-3
Ni/AC
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40
50
60
70
80
2Theta/degree
In all the products, H2, CO2 and CH4 were the main products.
Over Ni/HZSM-5 catalyst, there was some C2H6 and C2+ in
the products. Grarcia[25] studied the APR reaction of
methanol, acetic acid and glycerol over Ni-La/Al2O3 catalyst,
the gas phase was made up of H2, CO2, CO and CH4.
Tsiakaras[26] used Ni/SiO2-Al2O3 as catalyst in the APR of
crude glycerol, the main gas products were H2, CH4 and CO2.
While using Pt/Al2O3 as catalyst [27], except for the three
kinds of gas, CO was one of the main gas products in the
products.
From Fig. 1, the gas product distributions over Ni/SiO2,
Ni/Ac and Ni/CMK-3 were quite similar with each other and
the amount of H2 was all above 0.03 mol. The distributions
of gas products varied greatly after APR reaction over
Ni/SiO2-ZrO2, Ni/HZSM-5 and Ni/Al2O3. Naito[28] used
NaY zeolite, Al2O3, SiO2, and SiO2-Al2O3 to load ruthenium
as catalysts for the aqueous phase reforming of acetic acid
and found that the amounts of products changed a lot over
different supports. The gas product distributions might
depend not only on the activity centers but also on the
supports. In consideration of the better performance on the
APR of methanol, the catalysts of Ni/SiO2, Ni/Ac and
Ni/CMK-3 were selected as the catalysts to investigate the
in-situ hydrogenation of lignin-derived compounds and the
raw lignin depolymerization products.
Fig. 2 XRD patterns of Ni/SiO2, Ni/Ac and Ni/CMK-3
The XRD patterns of Ni/SiO2, Ni/AC and Ni/CMK-3 were
shown in Fig. 2. In the three XRD patterns, the three strong
diffraction peaks were all in 44.51o, 51.85o, and 76.37o,
which belonged to the characteristics peak of Ni(111),
Ni(200) and Ni(220) respectively[31]. Although the Ni load
in the three catalysts was the same, the strength of the
diffraction peak varies greatly, which represented the
difference in Ni particle size[32]. Therefore, it can be
indicated that Ni dispersion varies greatly on different
carriers, and the order of approximate particle size is Ni/SiO2
was bigger than that of Ni/CMK-3 and Ni/AC.
Although in the three catalysts the position of the
characteristic diffraction peak was almost the same, the
intensity of the peaks varied greatly, which meant that the
crystal sizes of these three samples were quite different.
From the characteristics peak of Ni, the crystal size of Ni of
Ni/SiO2 >Ni/CMK-3>Ni/AC.
The characterization of Ni-based catalysts
Ni-Fe/CMK-3
Table 1 Textural and structural properties of the catalysts
Ni-Cu/CMK-3
Ni/CMK-3
Pore
Average pore
Catalysts
ABET/m2·g-1
volume
size/nm
/cc·g-1
Ni-Co/CMK-3
Ni-La/CMK-3
Ni/SiO2
450.75
1.06
0.31
10
20
30
40
50
60
70
80
Ni/AC
846.36
0.54
3.83
0.76
0.75
2Theta/(degree)
Ni/CMK-3
1001.15
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Fig.3 XRD patterns of Ni/CMK-3 catalysts with different
promoters
XRD patterns of Ni/CMK-3 with promoters were shown in
Fig. 3. Similar with the XRD pattern of Ni/CMK-3,
thetypical peaks indexed with 2
= 44.51o, 51.85o and 76.37o
were attributed to Ni(111), Ni(200) and Ni(220). The
characteristic peaks of promoters were not obvious for its
low content.
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Using Scherrer formula, the grain size of Ni particles in
catalyst samples modified by various additions were
calculated. The textural properties and the Ni particle grain
size of Ni/CMK-3 catalysts with different promoters were
shown in Table 2.
Table 2 Physical properties of Ni/CMK-3with promoters
Average
pore
Average
metal
a
Catalysts
ABET
/
FW
(m2·g-1)
sizea/nm HM sizeb/nm
Ni/CMK-3
Ni-
Fe/CMK-3
Ni-
La/CMK-3
Ni-
Co/CMK-3
Ni-
1001.15
3.83
3.86
3.84
3.83
3.85
0.18 46.15
0.13 63.47
0.23 36.26
0.22 39.05
0.15 56.39
922.68
925.95
955.84
1018.04
Cu/CMK-3
FWHM: full width half maximum;
a Evaluated from N2 adsorption-desorption isotherms.
b Estimated by XRD.
Fig.4 SEM imagines of Ni/CMK-3 with promoters
b:La, c:Cu, d:Co, e:Fe
（a:Non,
）
The surface area of the catalysts was all in the range of 920
to 1020 m2.g-1 and all the modified catalysts kept the
characteristic of high surface areas. The pore diameters of
the catalysts were all about 3.8 nm, which had little
difference with each other. The average Ni size in catalysts
with different additives were calculated by the Scherrer
formula estimated by XRD. The results exhibited that the
Ni/CMK-3 catalysts modified by La and Co, in which the
average Ni size was 36.26 nm and 39.05 nm, exhibited better
dispersibility with smaller metal particle size than the
Ni/CMK-3 catalysts with other promoters. The introduce of
La and Co would help to increase the dispersibility of metal
particles and contribute to restraining the aggregation of
metal particles during the thermal treatment which might be
due to the strong interaction between Co/La and/or Ni
species and support. Similar behaviors were reported in the
Ni catalysts after the addition of other metal components to
improve the dispersibility of metal particles [33-35]
The SEM of these Ni/CMK-3 catalysts were shown in Fig.
4. All the catalysts maintained the mesoporous rod structure
of CMK-3[36]. Moreover, the voids all kept well, even if the
Ni active center was loaded. The Ni activity was uniformly
dispersed in the surface and pore channels of the catalysts.
In Fig. 5,we could see a lot of white dots on the CMK-3
carrier which were the Ni particle. The difference between
Ni/CMK-3(Fig.4a), Ni-La/CMK-3(Fig.4b) and Ni-
Co/CMK-3 (Fig. 4d) was not particularly obvious, but the
dots in Fig. 4c(Ni-Cu/CMK-3) and Fig.4e (Ni-Fe/CMK-3)
were significantly larger than those mentioned above. The
results were consistent with the average metal size estimated
by XRD above.
The in-situ hydrogenation of model compounds over Ni-
based catalysts
The experimental results of the hydrogenation of phenol and
guaiacol over Ni-based catalysts were showed in Fig. 5.
From Fig.5, over different catalysts, the conversions of
model compounds, the selectivity and the yield of
cyclohexanol were quite different. The experimental results
indicated that, the in-situ hydrogenation rate of phenol and
guaiacol over Ni/CMK-3 was higher than Ni/SiO2 and
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DOI: 10.1039/C9NJ05395F
Ni/CMK-3. For phenol, there were two products including
cyclohexanol and cyclohexanone, the selectivity of
cyclohexanol was all above 75% over the three kinds of
catalysts. As for guaiacol, the selectivity of cyclohexanol
was the highest of 93.11% over Ni/AC, meanwhile the
conversion was up to 67.26% over Ni/CMK-3. For phenol
and guaiacol, cyclohexanol reached the maximum yield
under the action of catalyst Ni/CMK-3. The BET and XRD
results of Ni/CMK-3 catalyst were the most optimistic
among the three-characterization analysis of catalysts. The
higher specific surface area and smallest particle size might
lead to a higher adsorption capacity and a better catalytic
activity [37].
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Ni/SiO2
Ni/AC
Ni/CMK-3
Catalysts
100
Conversion
Selectivity
(a)
Fig.5 The in-situ hydrogenation results of phenol(a,c) and
guaiacol(b,d) over Ni/SO2, Ni/Ac and Ni/CMK-3
(1MPa (N2), 240 C, 4 h; 1.5g catalyst, 36g water, 16g
35
80
30
o
methanol and 0.08mol model compounds)
25
60
20
The gas products after the in-situ hydrogenation of
model compounds were also quite different. Compared with
the gas products after the APR of methanol (Fig. 1), the yield
of H2 was 0.03mol over Ni/SiO2. After the process of the in
in-situ hydrogenation of phenol, this amount deceased from
0.03 mol to 0.0076mol, dropping more than 0.02mol. But
from the conversion of phenol (7.7%) and the selectivity of
cyclohexanol (74.5%), the consumption was only 0.014mol.
Therefore, the addition of phenol might inhibit the Ni/SiO2
catalytic activity of APR. Meanwhile, for the catalysts of
Ni/AC and Ni/CMK-3, the consumption of H2 for the
hydrogenation of phenol was comparable to the difference
of the H2 yield between Fig. 1 and Fig. 5. For the
hydrogenation of guaiacol, the yield of H2 in the in-situ
hydrogenation was higher than that in the APR of methanol,
which might because the detached methoxy group may
further happen APR reaction on the surface of Ni/CMK-3,
providing more hydrogen for the reaction system. The
catalytic capacity of the catalyst to produce hydrogen after
the addition of phenolic compounds might be another factor
affecting the activity of in-situ hydrogenation of phenolic
compounds.
40
15
10
20
5
0
Ni/SiO2
Ni/Ac
Ni/CMK-3
Catalysts
(b)
100
80
60
40
20
0
60
50
40
30
20
10
0
Conversion
Selectivity
Ni/SiO2
Ni/Ac
Ni/CMK-3
Catalysts
(c)
0.05
CO
CO2
0.04
0.03
0.02
0.01
0.00
The gas product after in-situ hydrogenation of phenol under
Ni/CMK-3 catalysts was shown in Fig. 6. From Fig. 6, the
yields of the gas products were quite different and all
increased compared with the catalyst of Ni/CMK-3 after the
addition of Co, Cu and La, except for adding Fe in Ni/CMK-
3. The conversion of phenol and the selectivity of
cyclohexanol over Ni/CMK-3 catalysts were shown in Fig.
7.
CH4
H2
Ni/SiO2
Ni/AC
Ni/CMK-3
Catalysts
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2
3
4
La/CMK-3 > Ni-Co/CMK-3 > Ni/CMK-3 > NVi-ieCwuA/rCticMle OKn-lin3e>
DOI: 10.1039/C9NJ05395F
Ni-Fe/CMK-3 and from Table 2, the Ni particle size order of
the catalysts followed the sequence of Ni-La/CMK-3 < Ni-
Co/CMK-3 < Ni/CMK-3 < Ni-Cu/CMK-3 < Ni-Fe/CMK-3.
The change in activity might be related with the size of Ni
particles. Furthermore, the reason why the activity of Ni-
Fe/CMK-3 decreased might be that the hydrogen production
during the in-situ hydrogenation process does not provide
enough H2 for the hydrogenation of phenol. Abdullah[38]
found Ni-La-co-impregnated Al2O3 catalyst had excellent
activity for the production of hydrogen. Feed conversion of
88.53% was achieved over 10% Ni/Al2O3 catalyst which
increased to 95.83% in the case of 10% Ni-5% La/Al2O3
catalysts with a H2 selectivity of 70.44%. As shown in Fig,
6, the catalytic capacity of the Ni-La/CMK-3 catalyst to
produce hydrogen in the in-situ hydrogenation process was
the best among all the catalysts with the amount of H2
product was more than 0.05 mol. While enough hydrogen
was one of the important factors in the hydrogenation of
phenol. Bahari[39] also found that after adding La in
Ni/Al2O3, Ni particles were finely dispersed on the catalyst
surface. Meanwhile, the particle size was not only
importance on the activity, but also on the stability and the
production distributions [40, 41].
5
6
7
8
0.10
0.08
0.06
0.04
0.02
CO
CO
9
2
C
H
6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
CH
4
H
2
0.00
Ni/CMK-3
Ni-Co/CMK-3
Ni-La/CMK-3 Ni-Cu/CMK-3
Ni-Fe/CMK-3
Catalysts
Fig.6 Gas product after in-situ hydrogenation of phenol
under Ni/CMK-3 catalysts
Compared with Ni/CMK-3, the addition of Co and La
enhanced the catalysts’ in-situ hydrogenation performance
both on the conversion of phenol and the selectivity of
cyclohexanol. Especially over La-Ni/CMK-3, the
conversion of phenol increased from 37.56% to 80.88% and
the selectivity of cyclohexanol increased from 88.59% to
94.76%. From the gas products, we might foresee this result
for the highest H2 yield. Over Cu-Ni/CMK-3 and Fe-
Ni/CMK-3 catalyst, the conversion of phenol decreased. The
selectivity of cyclohexanol was nearly 100% over Ni-
Fe/CMK-3 but the conversion of phenol was only 1.40%,
which might be for the lower yield of H2.
The in-situ hydrogenation of raw lignin depolymerization
products over Ni-La/CMK-3
The GC-MS spectra of the lignin depolymerization product
before and after in-situ hydrogenation over Ni-La/CMK-3
were shown in Fig.8 and the main composition of
liquefaction products were shown in Table 3.
(a)
100
conversion
selectivity of cyclohexanol
90
100
80
70
80
60
50
40
30
20
10
0
60
40
20
0
5
10
15
20
25
time(min)
(b)
Ni/CMK-3
Ni-Co/CMK-3 Ni-La/CMK-3 Ni-Cu/CMK-3 Ni-Fe/CMK-3
Catalysts
Fig.7 The conversion of phenol and the selectivity of
cyclohexanol over Ni/CMK-3 with different promoters
(1MPa (N2), 240 C, 4 h; 1.5g catalyst, 36g water, 16g
o
methanol and 0.08mol phenol)
5
10
15
20
25
We observed that in general, the catalysts active order of the
yield of cyclohexanol followed the sequence of Ni-
time(min)
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Fig.8 GC-MS spectra of the lignin depolymerization
products before(a) and after(b) in-situ hydrogenation over
Ni-La/CMK-3
ARTICLE
1
2
3
4
5
6
7
8
15.55 Phenol, 2,4-dimethyl-
Phenol,2-methoxy-4-
1.04
7.02
80
View Article Online
-
DOI: 10.1039/C9NJ05395F
64
15.83
16.54
16.89
propyl-
Phenol,2,3,5,6-
tetramethyl-
Phenol, 2,3,5-
trimethyl-
2.62
1.44
0.89
1.68
3.10
58
68
From Fig. 8 we could observe that the two spectrograms
were quite different before and after the in-situ
hydrogenation. The retention time (R.T.) of the most
depolymerization products from lignin was between 13.30
min and 20.00 min, and after the in-situ hydrogenation
reaction, the retention time of the products mainly
concentrated from 7.80 min to 15.00 min.
From Table 3, the type of compounds, whose contents were
above 0.8 %, was more than 20. After the in-situ
hydrogenation reaction, the type of compounds, whose
retention time concentrated from 13.30 min to 20.00 min,
was nearly 10.
-
-
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
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27
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29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Phenol, 2,6-
90
17.27
18.01
dimethoxy-
1.83
Phenol,2-methoxy-4-
(1-propenyl)-, (E)-
Phenol,2,3,5,6-
tetramethyl-
76
-
18.71
19.86
0.85
0.89
82
96
-
Vanillin
-
others
19.76 21.62
Several high chromatographic peaks appeared between
7.80min and 8.60 min, most of which were ascribed to
saturated alcohols. The depolymerization products of lignin
were mainly phenolic compounds with little acids and
alcohols. The content of methoxyphenol (such as guaiacol)
was 32.42%, while that of other substituted phenols was
about 30%. After in-situ hydrogenation reaction, the content
of phenolic compounds decreased significantly, and the
structure of phenolic compounds was simplified. The
saturated alcohols’ contents increased obviously, which
mainly concluded cyclohexanol and methyl cyclohexanol.
According to the quantitative analysis of the internal
standard method, the content of phenolic compounds
decreased from 75.25% to 25.38%, meanwhile the content
of saturated alcohol increased from1.34% to 31.19% over
Ni-La/CMK-3.
Table 3 Main Composition of liquefaction products before
and after in-situ hydrogenation
Content (%)
Possibility
from GC-
MS (%)
Ni-
La/CM
K-3
Raw
R.T.
(min)
3.04
oil
Compound
1-Propanol
1.34
1.74
80
62
-
Cyclopentanone,2-
methyl-
4.99
6.37
7.82
2.07
2.84
-
-
72
90
Cyclohexanone
Cyclohexanol
Cyclohexanol,2-
methyl-, cis-
Cyclohexanol,4-
methyl-, cis-
Cyclohexanol, 3-
methyl-
25.08
-
-
-
-
83
43
40
62
8.05
8.31
8.46
0.96
0.87
0.79
Conclusions
Cyclohexanol, 4-
methyl-
8.53
8.57
1.41
9.84
3.79
2.56
1.91
50
67
48
80
97
91
In this paper, a series of Ni-based catalysts were prepared to
use in the in-situ hydrogenation of lignin derived compounds
and lignin depolymerization products. Among these
catalysts of Ni/SiO2-ZrO2, Ni/HZSM-5, Ni/Al2O3, Ni/SiO2,
Ni/AC and Ni/CMK-3, the relative higher hydrogen yield
was obtained in the APR of methanolover the catalyst of
Ni/SiO2, Ni/AC and Ni/CMK-3, which were used in the in-
situ hydrogenation of phenol and guaiacol. For phenol and
guaiacol, cyclohexanol reached the maximum yield under
the action of catalyst Ni/CMK-3. The catalyst of Ni/CMK-3
and Ni/CMK-3 modified by Co, La, Cu and Fe were studied
in the in-situ hydrogenation of phenol to investigate the in-
situ hydrogenation activity. The results showed that the
activity of catalysts might be related with the size of Ni
particles in the catalysts and including the yield of H2
production during the reaction. After adding La to Ni/CMK-
3, the conversion of phenol increased from 37.56% to 80.88%
and the selectivity of cyclohexanol increased from 88.59%
to 94.76%, meanwhile the Ni partial size decreased from
46.15 nm to 36.26 nm. After upgrading the lignin
depolymerization product over La-Ni/CMK-3, the content of
phenolic compounds decreased from 75.25% to 25.38%,
Acetic acid
Propanoic acid
Butanoic acid
-
-
9.65
10.72
11.02
13.34
-
Acetophenone
Phenol, 2-methoxy-
32.42
0.92
15.59
13.84 Phenol, 2,6-dimethyl-
Phenol,2-methoxy-4-
14.33
3.18
-
95
94
68
methyl-
cis-1,2-
Cyclohexanediol
Phenol, 2,4,6-
trimethyl-
2.06
2.79
14.41
14.76
0.99
-
14.79
14.83
14.92
Phenol, 2-methyl-
0.97
5.44
97
94
78
-
3.28
-
Phenol
Diphenyl ether
Phenol, 2,4,6-
trimethyl-
12.22
1.40
0.80
68
82
15.20
-
-
15.52 Phenol, 2,5-dimethyl-
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modelling and quantitative structure-activity relationships.
while the content of saturated alcohol increased from 1.34%
to 31.19%.
Chemical Engineering Journal,2019, 359:30V5ie-w32A0rt.icle Online
DOI: 10.1039/C9NJ05395F
11 Y.X. Yu, Y. Xu, T.J. Wang, L.L. Ma, Q. Zhang, X.H.
Zhang, et al. In-situ hydrogenation of lignin
depolymerization model compounds to cyclohexanol.
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Selective production of cyclohexanol and methanol from
guaiacol over Ru catalyst combined with MgO. Green
Chemistry 2014, 16: 2197-203.
Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
The authors gratefully acknowledge the financial support of
Natural Science Foundation of China(No. 51676191),
Strategic Priority Research Program of the Chinese
Academy of Sciences(XDA 21060102), Local Innovative
and Research Teams Project of Guangdong Pearl River
Talents Program (No. 2017BT01N092), the Youth Science
and Technology Innovation Talents of Guangdong
Province(No.2015TQ01N652) and the Youth Innovation
Promotion Association of Chinese Academy of
Sciences(2016313).
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