A nitrogen-doped carbon modified nickel catalyst for the hydrogenation of levulinic acid under mild conditions

Article abstract of DOI:10.1039/d1gc01732b

The conversion of levulinic acid (LA) to γ-valerolactone (GVL) is one of the most important reactions from biomass-derived platform chemicals to value-added chemicals. In this work, nitrogen-doped carbon was introduced into a Ni/Al₂O₃catalyst and was employed for the hydrogenation of LA to GVL with a full conversion and equivalent yield under mild conditions, at as low as ambient hydrogen pressure and 130 °C for 6 h. The doping of nitrogen introduced NiNx species and the imperfection of modified nitrogen-doped carbon were beneficial for the selective hydrogenation of carbonyl groups. This catalyst showed excellent activity and selectivity in various solvents and could be recycled for at least 6 runs with little deactivation. In addition to LA, various substrates with both carbonyl and carboxyl groups could also be selectively hydrogenated to the corresponding lactones. This study offers both theoretical foundation and practical instructions for the high-efficiency conversion of LA to GVL over non-noble metal catalysts under mild conditions, especially ambient H₂pressure.

Full text of DOI:10.1039/d1gc01732b

View Article Online
View Journal
Green
Chemistry
Cutting-edge research for a greener sustainable future
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: L. Jiang, G. Xu
and Y. Fu, Green Chem., 2021, DOI: 10.1039/D1GC01732B.
Volume 20
This is an Accepted Manuscript, which has been through the
Number
May 2018
Pages 1919-2160
9
7
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
rsc.li/greenchem
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1463-9262
PAPER
Paul T. Anastas et al.
The Green ChemisTREE: 20 years after taking root with the 12
principles
rsc.li/greenchem

Please do not adjust margins
Page 1 of 8
Green Chemistry
View Article Online
DOI: 10.1039/D1GC01732B
ARTICLE
Nitrogen-doped carbon modified nickel catalyst for the
hydrogenation of levulinic acid under mild conditions
Liang Jiang‡1, Guangyue Xu‡1, Yao Fu*1
Received 00th January 20xx,
Accepted 00th January 20xx
The conversion of levulinic acid (LA) to γ-valerolactone (GVL) is one of the most important reactions from biomass-derived
platform chemicals to value-added chemicals. In this work, nitrogen-doped carbon was introduced to Ni/Al2O3 catalyst and
was employed for the hydrogenation of LA to GVL with full conversion and equivalent yield at mild conditions, as low as
ambient hydrogen pressure and 130 oC for 6 h. The doping of nitrogen introduced NiNx species, as well as the imperfection
of modified nitrogen-doped carbon, were beneficial for the selective hydrogenation of carbonyl groups. This catalyst showed
excellent activity and selectivity in various solvents and can be recycled for at least 6 runs with little deactivation. In addition
to LA, various substrates with both carbonyl and carboxyl groups can also be selectively hydrogenated to corresponding
lactones. This study offers both theoretical foundation and application instructions for high-efficiency conversion of LA to
GVL over non-noble metal catalysts under mild conditions, especially ambient H2 pressure.
DOI: 10.1039/x0xx00000x
The previously reported nickel catalysts as well as their
performances were listed in Table S1. Nickel supported on
Al2O3, SiO2, ZnO, MgO, TiO2, ZrO2, NiO, AC or N-doped carbon
Introduction
With the speeding development of modern industrial society,
the urgent demand of green chemistry has become a significant
issue. Biomass is an abundant, inexpensive, renewable and
carbon-neutral resource that could be an available alternative
of fossil resources for the green industry. In the past decades,
over 300 bio-chemicals as well as various catalytic valorization
microspheres were reported to convert LA to GVL under 120-
270 °C and 10-65 bar H2, as shown in Scheme 1. [7]
Since the employment of nitrogen doped Fe catalyst in
2013, [8] nitrogen doping has been widely used as an effective
modification method to promote the catalytic activity of various
[9]
non-noble metal catalysts.
The doping of nitrogen could
[1]
processes have been studied in biomass conversion. Among
change the activity of valence orbital in surface metal and
therefore improve the catalytic performance. In our previous
studies, nitrogen doped catalysts were employed for the
selective conversion of nitrobenzene to aniline, carboxylic acids
to hydrocarbons, and 5-hydroxymethylfurfural to 2,5-
dimethylfuran. [10] The doping of nitrogen will introduce nitride
species with special catalytic activities. Moreover, the nitrogen
will interrupt the formation of undesired spinel during the
calcination or pyrolysis process of the catalyst preparation.
In this paper, nitrogen-doped carbon was introduced to
Ni/Al2O3 catalyst and was employed for the hydrogenation of LA
to GVL at ambient pressure and low temperature. A series of
characterizations such as XRD, XPS, Raman and TEM were used
to study the structure and component of the catalysts. Various
solutions were used to reveal the compatibility of the catalysts.
Some other feedstocks with both carbonyl and carboxyl groups
were also tested.
which, selective conversion of levulinic acid (LA) to gamma-
valerolactone (GVL) is a key reaction of platform compounds to
value-added chemicals or fuels. LA is a kind of ketonic acid
[2]
that can be producted from cellulose and hemicellulose, and
was honored as one of the most important twelve biomass-
[3]
derived platform chemicals.
LA can be converted to fuel
molecules, polyester monomers, or value-added chemicals,
such as methyltetrahydrofuran, levulinate esters, angelica
[4]
lactone, 1,4-pentanediol, succinic acid, GVL, etc.
GVL is a
naturally occurring chemical, and is nontoxic and
biodegradable. It was reported to be useful as food flavor, fuel
additive or green solvent, or be further upgraded to
pharmaceuticals, fragrances or nylon materials. [5]
The conversion of LA to GVL required selective
hydrogenation of carbonyl group without hydrodeoxygenation
or hydrodecarboxylation. It has been reported by hundreds of
different catalytic systems during the past ten years. [6] Among
them, some ruthenium-based catalysts have been reported to
References:
50
40
30
20
10
0
7a-Ni/NiO
7b-Ni/MgO
7c-Ni/Mg2Al2O5
(7f)
catalyze the conversion of LA to GVL at room temperature with
7d-Ni/γ-Al2O3
[6f,g]
high H2 pressure.
In consideration of both catalytic
7e-Ni/NCMs
7f-Ni/Al2O3
(7e)
efficiency and catalyst cost, nickel was proved to be a suitable
non-noble metal catalyst compare with noble-metal catalyst.
(7d)
(7c)
This work:
Ni/Al2O3-CN
(7a)
(7b)
This work
140
1. Anhui Province Key Laboratory of Biomass Clean Energy, CAS Key Laboratory of
Urban Pollutant Conversion, University of Science and Technology of China, Hefei
230026. Institute of Energy, Hefei Comprehensive National Science Center, Hefei
230031.
120
160
180
200
Temperature (oC)
Scheme 1. The comparison of levulinic acid hydrogenation
E-mail for Y. Fu: fuyao@ustc.edu.cn
performance over various Ni-based catalysts.
‡ These authors contributed equally to this work
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 8
View Article Online
DOI: 10.1039/D1GC01732B
Scheme 2. Schematic procedure of the Ni/Al2O3-CN-T catalysts.
Catalyst characterization
XRD patterns of the different catalysts were measured by an
X’pert (PANalytical) diffractometer, using Cu Kα radiation at 40
kV and 40 mA, with a 2θ range of 10-70°. TEM images were
collected with a JEM 2100Plus apparatus operating at a voltage
of 200 kV. ESCALAB250 spectrometer (Thermo-VG Scientific,
USA) and 10-8-10-9 Torr pressure using monochromated Al Kα
radiation (1486.92 eV) was employed for XPS measurement.
The binding energies were calibrated relative to the carbon 1s
band at 284.6 eV. Raman spectra were measured by a confocal
Raman system (FST2-Ahdx-DZ) with 532ꢀnm laser excitation and
200 μW with X50 microscope objective lens. To increase Raman
signal strength, the catalysts were pretreated with dilute
hydrochloric acid before test. ICP analyses were carried out to
measure the leaching of catalysts by using Optima 7300 DV ICP-
OES from PerkinElmer Corporation. Nitrogen adsorption
measurements were performed using a TriStar II 3020
adsorption analyser from Micromeritics Instrument
Corporation.
Experimental
Materials
In this study, the chemicals were supplied from Aladdin
Chemicals Co. Ltd. (Beijing, China) and the solvents were
obtained from Sino pharm Chemical Reagent Co., Ltd.
(Shanghai, China). All the commercially available chemicals and
solvents were used directly without any treatment step.
Catalyst preparation
NiAl-OH/melamine composite precursor was synthesized by a
coprecipitation method. Melamine as the carbon and nitrogen
source was combined with metal precursors. First, 4 g of
melamine was dispersed in 70 mL deionized water under
continuously stirring at room temperature for 30 min to form a
homogeneous solution A. After that, 7.37 g of Al(NO3)3·9H2O,
0.55 g of Ni(NO3)2·6H2O were dissolved in 30 mL of deionized
water under ultrasound to form
a clear solution B.
General procedures of the hydrogenation of levulinic acid
Subsequently, solution B was slowly dripped into solution A
under continuously stirring. Afterwards, the above mixed
solution was titrated by a certain amount of base solution of 0.2
M NaOH until the pH value of solution reached 10.0 and
maintained for 30 min. Then the suspension was heated to 70
oC and kept for 12 h in an oil bath before cooling to room
temperature. The light blue solid slurry was filtered, washed
several times with deionized water to neutral and then dried at
80 oC for 12 h in oven to obtain NiAl-OH/melamine.
Nitrogen-doped carbon (abbreviated as CN) modified Ni/Al
mixed oxide (NiO/Al2O3-CN-air) was prepared by the following
steps. The NiAl-OH/melamine composite precursor was
calcined at 500 oC for 4 h in a muffle furnace to get NiO/Al2O3-
CN-air. Then, the NiO/Al2O3-CN-air sample was reduced under a
H2 flow at different temperature for 2 h with a heating rate of 3
oC/min in a tubular furnace. After allowing the system to cool
down to room temperature in a continuous H2 flow, the final
dark solid powder was named as Ni/Al2O3-CN-T, while T
represents the reduction temperature.
All levulinic acid conversion experiments were performed in a
25 mL NSC-type reactor purchased from Anhui Kemi Machinery
Technology Co., Ltd. Typically, the Ni catalyst (40 mg), levulinic
acid (1 mmol) and THF (10 mL) were charged into the autoclave.
The air in the autoclave was removed by flushing with H2 for six
times. Then the autoclave was charged with 1 MPa H2. The
autoclave was then heated from room temperature to 130 °C
within 10 minutes. Then the reaction was started at 130 °C for
1 h with a magnetic stirring at a rate of 700 rpm. After cooling
the autoclave to room temperature, n-hexanol was added to
the mixture as internal standard and the mixture was diluted
with THF, followed by filtration and analyzed by GC and GC-MS.
The solid catalysts were collected by centrifugation and then
washed with deionized water and THF for the catalysts recycling
test.
Analytic methods
The Shimadzu Nexis 2030 gas chromatography (GC) instrument
was used for the products analysis, which equipped with a RTX-
65 column (30 m×0.32 mm×0.25 μm) and a flame ionization
detector. The analytic conditions of experimental results were
as follows: The flow rate of the N2 carrier gas, H2, and air was 40
mL·min-1, 32 mL·min-1 and 200 mL·min-1, respectively. The
Ni/Al2O3-600-cp catalyst was obtained by using the same
method as above without adding melamine. Ni/CN-600 catalyst
was prepared by using active carbon instead of Al(NO3)3·9H2O,
with other details the same as above. Ni/Al2O3-600-im catalyst
was prepared on the basis of an impregnation method.
Please do not adjust margins

Page 3 of 8
Green Chemistry
Please do not adjust margins
Journal Name
ARTICLE
injection port temperature was 250 °C. The GC oven
temperature program was conducted as follows: The
temperature program ranges from 50 °C to 190 °C at a heating
rate of 10 °C·min-1 and then heated to 250 °C to keep for 3 min
with a heating rate of 20 °C·min-1. The flame ionization detector
temperature was set to 270 °C. The conversion of substrates
and the yield of products were determined by internal standard
method.

View Article Online
DOI: 10.1039/D1GC01732B
 C
 Ni
 Al2O3


Ni/CN-600






Ni/Al2O3-600-cp
Results and discussion
Ni/Al2O3-600-im
Ni/Al2O3-CN-600
Catalyst characterization results
A series of Ni/Al2O3-CN-T (T=500, 600 and 700) catalysts were
prepared, as described in Experimental section. Ni/Al2O3-cp
catalyst synthesized by coprecipitation method, Ni/Al2O3-im
catalyst synthesized by impregnation method, as well as Ni/CN
catalyst were employed as comparison. All the preparation
weight ratio of Ni to Al2O3 were 10%. The actual Ni content of
Ni/Al2O3-CN-T were tested by ICP-OES to be 7.1%, 7.9% and
8.3% with T=500, 600 and 700, respectively, as shown in Table
S2.
20
30
40
50
60
70
2 Theta (degree)
Figure 1. XRD pattern of the different Ni catalysts.
From XRD patterns (shown in Figure 1), the Ni/CN catalyst
showed obvious diffraction peaks of Ni nanoparticle, while the
Ni/Al2O3-im, Ni/Al2O3-cp, and Ni/Al2O3-CN mainly showed
signals of Al2O3 support. It was because that Al2O3 could offer
better dispersion capacity that active carbon. The better
dispersion of Ni could increase the specific surface active area
of metal to improve the catalytic performance.
Different reduction temperature will also affect the size of
Ni nanoparticles, as shown in Figure S1. The diffraction peak of
Ni increased with the increasing of reduction temperature. It
indicated that the Ni nanoparticle would grow larger at higher
reduction temperature. This result agreed with TEM images. As
shown in Figure 2 and Figure S2, the average sizes of Ni
nanoparticles were 8.26 nm, 11.03 nm and 17.60 nm when the
reduction temperature was 500 °C, 600 °C and 700 °C,
respectively. The area-selected EDS mappings of the Ni/Al2O3-
CN-600 are shown in Figure 2, suggesting a uniform dispersal of
Ni, Al, C and N elements in the Ni/Al2O3-CN-600 catalyst. The
nickel nanoparticles aggregated seriously in Ni/CN-600 (Figure
S3), which showed that Al2O3 was beneficial to the dispersion of
nickel.
The XPS spectra of Ni 2p was shown in Figure 3. For
Ni/Al2O3-CN, besides Ni0, Ni2+ and satellite peaks, there was also
a non-integer valence state of Ni species at binding energy of
854.3 eV (Ni 2p3/2). It indicated that there was a kind of NiNx
species instead of traditional Ni-O species [11]. This NiNx species
did not exist in any other catalysts. The surface atomic
composition of the Ni/Al2O3-CN-T catalysts were counted in
Table S3. The slight decrease of nitrogen and carbon was related
to the reduction temperature. However, there was no obvious
difference in the content of surface elements at different
reduction temperatures. The Ni 2p patterns of Ni/Al2O3-CN-T at
different reduction temperatures were shown in Figure S4. The
NiNx intensity of Ni/Al2O3-CN-600 was obviously higher than
Ni/Al2O3-CN-500 and Ni/Al2O3-CN-700. It indicated that the
formation of NiNx required proper preparation conditions. The
oxidation state of nickel was also detected by XPS, which was
owing to the oxidation of surface metallic Ni nanoparticles with
O2 in air. Two peaks were detected in the N 1s XPS pattern of
Ni/Al2O3-CN-T, which were apportioned to pyridinic N and
graphitic N (Figure S5).
Figure 2. TEM images (a, b) and average size distribution (inset
of b) of nickel nanoparticles of the Ni/Al2O3-CN-600; HAADF-
STEM image (c) and the element mapping of Ni/Al2O3-CN-600
(d-g).
To better understand the texture properties of these
catalysts, further characterization was carried out. According to
the N2 adsorption-desorption isotherms (Figure S6), the
Brunauer−Emmett−Teller (BET) surface areas, pore volumes
and pore diameter were calculated and summarized in the
Table S4. It could be clearly observed that when NiO/Al2O3-CN-
air was reduced at 500 °C, the BET surface area rapidly
increased to 240.29 m2/g from 67.70 m2/g and the average pore
volume increased to 0.18 cm3/g from 0.10 cm3/g. The possible
reason was that a small amount nitrogen doped carbon
materials decompose during the reduction process. As the
reduction temperature increases, the BET surface area
decreased to 145.12 m2/g, and the average pore diameter
increased to 5.49 nm from 4.51 nm. It could be caused by the
further decomposition of nitrogen doped carbon and the
agglomeration of nickel at high reduction temperature.
The Raman spectra was used to identify the surface CN
species. To avoid the baseline jamming of the fluorescence of
Ni or Al species, the catalyst was washed by hydrochloric acid
before Raman test. The signal at around 1340 cm-1 and 1600 cm-
1
were assigned to the D-band and G-band of CN surface,
respectively. The D-band represented the imperfection of CN,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 8
ARTICLE
Journal Name
while the G-band represented the in-plane stretching vibration catalyst without the introduction of nitrogen and VciaewrbAortincl,egOinvlienes
of sp2-carbon. The intensity ratio of D- and G- bands were 32.5 % LA conversion and 93.1 % GVL selectivity (entry 5, Table
DOI: 10.1039/D1GC01732B
labelled in Figure 4. The ratio revealed a volcano-like trend with 1). The catalytic performances of Ni/Al2O3-600-cp and Ni/Al2O3-
respect to the reduction temperature.
600-im were significantly lower than that of the Ni/Al2O3-CN-
600 (entries 5 and 6 vs entry 3, Table 1). It indicated that the
nitrogen doped carbon played an important role in the reaction.
Compared with Ni/Al2O3-CN-600, the conversion of LA and the
selectivity of GVL were both very low on Ni/CN-600 catalyst, and
the yield of GVL was only 3.5% (entry 7 vs entry 3, Table 1). The
results indicated that alumina plays an important role in the
catalytic system. The agglomeration phenomenon of nickel
(Figure S3) in Ni/CN-600 without Al2O3 could effectively prove
that Al2O3 was beneficial to the dispersion of nickel, which
might be one of the main reasons that affect the catalytic
activity. [12]
Combining the catalytic reaction performance and the
characterization results, it indicated that there were the
following impact factors. Firstly, from the comparison of
NiO/Al2O3-CN-air and Ni/Al2O3-CN-500/600/700 catalysts, it
indicated that it was the reduced Ni species, instead of Ni oxide,
that acted as the significant catalytic site for the conversion of
LA to GVL. Secondly, from the comparison of Ni/Al2O3-600-
cp/im and Ni/Al2O3-CN-500/600/700 catalysts, it revealed that
the NiNx species introduced by N modification had higher
activity than metallic Ni. Thirdly, from the trend of NiNx intensity
(by XPS), ID/IG ratio and catalytic results with respect to catalyst
reduction temperature, it came up with the same trend that
proper reduction temperature will lead to more NiNx species as
well as surface imperfection of CN, with was benefit to catalytic
activity. To further understand the performance of the catalyst,
the optimized catalyst Ni/Al2O3-CN-600 was then tested in
various conditions.
NiNx
Ni
Ni2+
2p
Ni/Al2O3-CN-600
Ni/Al2O3-cp-600
Ni/Al2O3-im-600
Ni/CN-600
885
880
875
870
865
860
855
850
845
Binding Energy (eV)
Figure 3. XPS pattern of the different Ni catalysts.
ID/IG=1.18
Ni/Al2O3-CN-700
ID/IG=1.23
Ni/Al2O3-CN-600
ID/IG=1.05
Table 1. Catalytic performance of different catalysts on the
hydrogenation of levulinic acid.
Ni/Al2O3-CN-500
1200
1300
1400
1500
1600
-1
1700
Entry
Catalyst
Conversion (%) Yield (%)
Raman Shift (cm
)
Figure 4. Raman spectra of the catalysts for acid treatment.
1
2
NiO/Al2O3-CN-air
Ni/Al2O3-CN-500
Ni/Al2O3-CN-600
Ni/Al2O3-CN-700
Ni/Al2O3-600-cp
Ni/Al2O3-600-im
Ni/CN-600
0
0
Catalytic hydrogenation of levulinic acid in different catalysts
The catalytic performances of different catalysts have been
tested by hydrogenation of levulinic acid to GVL in THF under 10
bar H2 at 130 °C. As shown in Table 1, a control experiment in
the presence of NiO/Al2O3-CN-air showed that the oxidized Ni
could not catalyze the hydrogenation of levulinic acid. It
suggested that NiO was inert for this reaction (entry 1, Table 1).
All Ni/Al2O3-CN-T could efficiently catalyze the hydrogenation of
levulinic acid (entries 2, 3, 4, Table 1), but the catalytic
performance of Ni/Al2O3-CN-T showed a distinct difference due
to the different reduction temperatures. Under the same
reaction conditions, the conversion of LA was 38.6 %, 52.0 %,
and 37.5 % with almost equivalent selectivity of GVL for
Ni/Al2O3-CN-500, Ni/Al2O3-CN-600, and Ni/Al2O3-CN-700,
respectively. The reaction results of these catalysts proved that
Ni/Al2O3-CN-600 has the best catalytic activity for the
hydrogenation of LA, compared with Ni/Al2O3-CN-500 and
Ni/Al2O3-CN-700. When the reaction time extended to 3 h, the
reaction over Ni/Al2O3-CN-600 could get full conversion and
near-equivalent GVL yield.
38.6
52.0
37.5
34.9
13.8
4.3
38.3
51.6
36.9
32.5
11.6
3.5
3
4
5
6
7
8a
Ni/Al2O3-CN-600
>99
>99
Reaction conditions: levulinic acid (1 mmol), THF (10 mL), 40 mg
catalyst, 130 °C, 10 bar H2, 1 h. a. the reaction time extend to 3
h.
For comparison, Ni/Al2O3-600-cp catalyst, which prepared
by the same method as described for the Ni/Al2O3-CN-600
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 8
Green Chemistry
Please do not adjust margins
Journal Name
ARTICLE
Catalytic hydrogenation of levulinic acid in different solvents
100
80
60
40
20
0
View Article Online
DOI: 10.1039/D1GC01732B
Conversion of LA
Yield to GVL
As is well known, the solvent plays a vital role in the reaction. [13]
Therefore, the hydrogenation of levulinic acid in different
solvents was then performed. As shown in Table 2, the best
results were produced in THF, affording more than 99 % LA
conversion and GVL yield with 1 MPa H2 at 130 °C for 3 h (entry 1,
Table 2). In other solvents, such as H2O, toluene, methanol,
ethanol, isopropanol and dioxane, LA conversion and GVL yield
occurred as 82.1-99 % and 79.3-96.1 %, respectively, and the
selectivities of the target product were all more than 96.1 %
(entries 2-7, Table 2). These results indicated that the properties
of the solvents had no distinct relationship to the catalytic activity
of Ni/Al2O3-CN-600 in this system. The Ni/Al2O3-CN-600 catalyst
has excellent adaptation to various solvents. The comparison with
other previously reported catalysts were reviewed in Table S5. It
could be due to that the basic sites formed by nitrogen doping
were helpful in the adsorption of LA feedstock.
110
120
130
140
150
Temperature (oC)
Figure 5. Catalytic hydrogenation of levulinic acid in different
temperatures. reaction conditions: levulinic acid (1 mmol), THF
(10 mL), 40 mg Ni/Al2O3-CN-600 catalyst, 10 bar H2, 1 h.
Catalytic hydrogenation of levulinic acid in different
temperatures
With THF as the best solvent, the hydrogenation of levulinic acid
over the Ni/Al2O3-CN-600 was conducted at different
temperatures. As shown in Figure 5, the reaction temperature
showed a great effect on the catalysis performance of Ni/Al2O3-
CN-600 towards the hydrogenation of LA. Generally, the LA
conversion greatly increased with the increasing of reaction
temperature. For example, the LA conversion of 9.3 % and 21.1 %
were attained at 110 °C and 120 °C, respectively. When the
reaction temperature increase to 130 °C, the LA conversion
greatly increased to 52.0 %. Reactions were also conducted at
higher temperatures of 140 °C and 150 °C, the conversion of LA
increased to 74.8 % and 96.3 % with a low increase rate,
respectively.
100
Conversion of LA
Yield to GVL
80
60
40
20
0
Table 2. The effect of the reaction solvents on the hydrogenation
of levulinic acid.
1b
5
1a
10
20
30
1
H2 Pressure (bar)
Conversion
(%)
Yield
(%)
Selectivity
(%)
Figure 6. Catalytic hydrogenation of levulinic acid in different
Entry
Solvent
hydrogen pressure. Reaction conditions: levulinic acid (1 mmol),
a
THF (10 mL), 40 mg Ni/Al2O3-CN-600 catalyst, H2, 1 h, 130 °C,
Ni/Al2O3-CN-600, 6 h, b Ni/Al2O3-600-cp, 6 h.
1
2
3
4
5
6
7
THF
H2O
>99
96.2
93.7
>99
>99
94.5
91.2
85.7
96.1
91.9
79.3
>99
98.2
97.3
86.6
96.1
98.2
96.6
Catalytic hydrogenation of levulinic acid in different hydrogen
pressure
The effect of H2 pressure for the hydrogenation of levulinic acid
was also discussed at the reaction temperature of 130 °C in the
THF solvent, and the reaction results exhibited in Figure 6. The
yield of GVL was 25.4 % with 25.7 % LA conversion after 1 h under
1 bar H2 pressure, and then increased inconspicuously under
hydrogen pressure in the range from 5 to 30 bar. The selectivity
of GVL was kept to be more than 98 % in different hydrogen
pressure at the same time. These above results clearly illustrated
that the hydrogen pressure beyond 5 bar almost showed little
influence on the hydrogenation of levulinic acid in our catalytic
system. It revealed an excellent hydrogen activation ability of this
catalyst at low hydrogen pressure. Increasing the conversion of
LA by rising hydrogen pressure from 1 bar to 5 bar could be
attributed to the increase of hydrogen concentration in the
reaction, thus enhancing the reaction rate. To our delight, the full
conversion of LA was achieved by extending the reaction time to
6 h at 1 bar H2 catalyzed by Ni/Al2O3-CN-600. However, only 62.1
Toluene
Methanol
Ethanol
Isopropanol
Dioxane
>99
93.6
82.1
Reaction conditions: levulinic acid (1 mmol), Solvent (10 mL), 40
mg Ni/Al2O3-CN-600 catalyst, 130 °C, 10 bar H2, 3 h.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 8
ARTICLE
Journal Name
2-benzoylbenzoic acid over the Ni/Al O D-CONI:-1600.1003V9cie/awDtaA1GrltyiCcsl0et1O7an3ll2isnoBe
% conversion of LA catalyzed by Ni/Al2O3-600-cp was achieved at 100 °C for 3 h. The hydrogenation of 2-acetylbenzoic acid and
under the same reaction conditions.
2
3
proceeded successfully, affording the corresponding products
with an excellent yield. (entries 6 and 7, Table 3). It suggested that
the catalytic system can be applied to the selectively conversion
of a series of ketonic acid to relative lactones.
Time course of the hydrogenation of Levulinic acid
As hydrogenation of levulinic acid produced GVL with excellent
selectivity at 5 bar, the reaction time was extended to achieve a
higher GVL yield. Therefore, time course of the product
distribution was studied at 130 °C under 5 bar H2 pressure, as
Catalyst recycling experiments
shown in Figure 7. It was noted that the content of LA increasingly Heterogeneous catalyst’s reusability is of great important factors
decreased from 0 to 3 h, while the yield of GVL improved from 0 in view of practical application. Therefore, the recyclability of the
to 3 h with a high selectivity. Finally, GVL was produced at a yield Ni/Al2O3-CN-600 catalyst was studied in the LA hydrogenation
of 99 % after reaction 3 h. It was worth mentioning that no reaction. As a comparison, the recycle performance of Ni/Al2O3-
obvious by-products were detected during the different reaction 600-cp had also been studied. The experiments were proceeded
time points. It might be due to hydrogenation the carbonyl of at a non-full conversion stage to better show the recyclability of
levulinic acid to produced 4-hydroxy-pentanoic acid (HPA) and the catalysts. In order to achieve similar GVL yield in the first use,
then HPA would be rapidly dehydrated to produce GVL over the the reaction time was 1 h and 2.5 h over Ni/Al2O3-CN-600 and
Ni/Al2O3-CN-600 catalyst (Scheme 3).
Ni/Al2O3-600-cp, respectively. As shown in Figure 8, the catalyst
showed only slight decreasing on the basis of the catalytic activity
after successive reuses of up to six cycles. It might be due to the
leaching of a tiny amount of unstable surface nickel according to
ICP-OES (Table S6). It is worth mentioning that Ni/Al2O3-CN-600
still exhibited very good selectivity for GVL after using six times.
The catalytic activity of Ni/Al2O3-600-cp decreased rapidly after 5
cycles, which might be contribution to the etching of nickel (Table
S6). In summary, these results suggested that Ni/Al2O3-CN-600
has excellent reusability and stability during the reaction process,
and can be a promising candidate catalyst for hydrogenation of
LA to GVL.
100
0
Conversion of LA
Yield to GVL
80
20
40
60
80
100
60
40
20
0
Table 3. Substrate expansion over Ni/Al2O3-CN-600.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Entry
1
Substrate
Conversion (%)
>99
Yield (%)
>99
Time (h)
Figure 7. Time course of the hydrogenation of Levulinic acid.
Reaction conditions: levulinic acid (1 mmol), THF (10 mL), 40 mg
Ni/Al2O3-CN-600 catalyst, 5 bar H2, 130 °C.
O
OH
O
O
O
O
O
+H2
O
O
OH
2
3
>99
>99
>99
>99
>99
92.3
-H2O
O
LA
GVL
O
O
O
O
H
H
O
OH
H
O
H2
O
OH
4b
OH
Ni
O
OH
O
O
HPA
5b
6
>99
>99
84.6
85.1
OH
O
Al
CN
O
O
Scheme 3. Reaction route of the catalytic hydrogenation of
levulinic acid with H2 over the Ni/Al2O3-CN-600 catalyst.
OH
Substrates scope
O
O
Moreover, some other substrates with both carbonyl and
carboxyl groups were tested, as shown in Table 3. The levulinic
esters can be converted to GVL with almost full conversion and
near-equivalent yield (entries 2 and 3, Table 3). The aromatic
ketonic acids could also be efficiently catalyzed by Ni/Al2O3-CN-
600. 3-benzoylpropionic acid and 4-benzoylbutyric acid (entries 4
and 5, Table 3) could reach full conversion under mild conditions
HO
7
>99
82.9
Reaction condition: 1 mmol substrate, 10 mL THF, 40 mg Ni/Al2O3-
CN-600, 130°C, 3 h, 5 bar H2. b100 °C.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 8
Green Chemistry
Please do not adjust margins
Journal Name
ARTICLE
60
50
40
30
20
10
0
References
View Article Online
DOI: 10.1039/D1GC01732B
Ni/Al2O3-CN-600
Ni/Al2O3-600
[1] (a) Chheda, J., Huber, G. W., Dumesic, J. A. Liquid-phase
catalytic
processing
of
biomass-derived
oxygenated
hydrocarbons to fuels and chemicals. Angew. Chem., Int. Ed.
2007, 46, 7164−7183. (b) Corma, A.; Iborra, S.; Velty, A. Chemical
routes for the transformation of biomass into chemicals. Chem.
Rev. 2007, 107, 2411−2502. (c) Gallezot, P. Conversion of biomass
to selected chemical products. Chem. Soc. Rev. 2012, 41,
1538−1558. (d) Huber, G. W.; Iborra, S.; Corma, A. Synthesis of
transportation fuels from biomass: Chemistry, catalysts, and
engineering. Chem. Rev. 2006, 106, 4044−4098.
[2] (a) Deng, L., Zhao, Y., Li, J., Fu, Y., Liao, B., Guo, Q.-X.
Conversion of Levulinic Acid and Formic Acid into γ-Valerolactone
over Heterogeneous Catalysts. ChemSusChem. 2010, 3, 1172. (b)
Tukacs, J. M., Király, D., Strádi, A., Novodarszki, G., Eke, Z., Dibo,
G., Kegl, T., Mika, L. T., Efficient catalytic hydrogenation of
levulinic acid: a key step in biomass conversion. Green Chem.
2012, 14, 2057–2065. (c) Molinari, V., Antonietti, M., Esposito, D.
An integrated strategy for the conversion of cellulosic biomass
into γ-valerolactone. Catal. Sci. Technol. 2014, 4, 3626–3630.
[3] (a) Smeets, E. M. W., Faaij, A. P. C., Lewandowski, I. M.,
Turkenburg, W. C., A bottom-up assessment and review of global
bio-energy potentials to 2050. Prog. Energy Combust. Sci. 2007,
33, 56-106. (b) Werpy, T., Petersen, G., Top Value Added
Chemicals from Biomass. Volume I-Results of Screening for
Potential Candidates from Sugars and Synthesis Gas, U. S. D. o.
Energy, 2004. (c) Bozell, J. J., Petersen, G. R. Technology
development for the production of biobased products from
biorefinery carbohydrates-the US Department of Energy's "Top
10" revisited. Green Chem. 2010, 12, 539-554.
1
2
3
4
5
6
Runs
Figure 8. The recycling experiments of the Ni/Al2O3-CN-600 and
Ni/Al2O3-600 catalysts towards the hydrogenation of levulinic
acid. Reaction conditions: levulinic acid (1 mmol), THF (10 mL), 5
bar H2, 130 °C, 40 mg Ni/Al2O3-CN-600, 1 h or 40 mg Ni/Al2O3-600,
2.5 h, respectively.
Conclusions
In the work, nitrogen-doped carbon was introduced to Ni/Al2O3
catalyst and was employed for the hydrogenation of LA to GVL
with full conversion and equivalent yield at mild conditions, as
low as 1 bar hydrogen pressure and 130 °C for 6 h. The doping of
nitrogen introduced NiNx species, as well as the imperfection of
modified nitrogen-doped carbon, which were beneficial for the
selective hydrogenation of carbonyl groups. This catalyst showed
excellent activity and selectivity in various solvents and can be
recycled for at least 6 runs with little deactivation. In addition to
LA, various ketonic acid substrates with both carbonyl and
carboxyl groups can also be selectively hydrogenated to
corresponding lactones. Based on the above results, the nitrogen-
doped carbon modified Ni/Al2O3 catalyst has great potential for
the selective hydrogenation of LA to GVL in future biomass
industry.
[4] Yu, Z. H., Lu, X. B., Xiong, J., Ji, N. Transformation of levulinic
acid to valeric biofuels: a review on heterogeneous bifunctional
catalytic systems. ChemSusChem. 2019, 12, 3915-3930.
[5] (a) Horvath, I. T., Mehdi, H., Fabos, V., Boda, L., Mika, L. T. γ-
Valerolactone—a sustainable liquid for energy and carbon-based
chemicals. Green Chem. 2008, 10, 238-242. (b) Alonso, D. M.,
Wettstein, S. G., Dumesic, J. A. Gamma-valerolactone,
a
sustainable platform molecule derived from lignocellulosic
biomass. Green Chem. 2013, 15, 584-595. (c) Tang, X., Zeng, X. H.,
Li, Z., Hu, L., Sun, Y., Liu, S. J., Lei, T. Z., Lin, L. Production of γ-
valerolactone from lignocellulosic biomass for sustainable fuels
and chemicals supply. Renewable Sustainable Energy Rev. 2014,
40, 608-620. (d) Ye, L., Han, Y. W., Feng, J., Lu, X. B. A review about
GVL production from lignocellulose: Focusing on the full
components utilization. Ind. Crops Prod. 2020, 144, 112031.
[6] (a) Dutta, S., Iris, K. M., Tsang, D. C., Ng, Y. H., Ok, Y. S.,
Sherwood, J., Clark, J. H. Green synthesis of gamma-valerolactone
(GVL) through hydrogenation of biomass-derived levulinic acid
using non-noble metal catalysts: A critical review. Chem. Eng. J.
2019, 372, 992-1006. (b) Adeleye, A. T., Louis, H., Akakuru, O. U.,
Joseph, I., Enudi, O. C., Michael, D. P. A Review on the conversion
of levulinic acid and its esters to various useful chemicals. AIMS
Energy. 2019, 7, 165-185. (c) Yan, L., Yao, Q., Fu, Y. Conversion of
levulinic acid and alkyl levulinates into biofuels and high-value
chemicals. Green Chem. 2017, 19, 5527-5547. (d) Banerjee, B.,
Singuru, R., Kundu, S. K., Dhanalaxmi, K., Bai, L. Y., Zhao, Y. L.,
Reddy, B. M., Bhaumik, A., Mondal, J. Towards rational design of
core–shell catalytic nanoreactor with high performance catalytic
hydrogenation of levulinic acid. Catal. Sci. Technol. 2016, 6, 5102-
5115; (e) Dhanalaxmi, K., Singuru, R., Mandal, S., Bai, LY., Reddy,
B. M., Bhaumik, A., Mondal, J. Magnetic Nanohybrid Decorated
Corresponding Author
Yao Fu: fuyao@ustc.edu.cn.
Author Contributions
The manuscript was written through contributions of all authors.
All authors have given approval to the final version of the
manuscript.
‡These authors contributed equally.
Acknowledgment
This work was supported by the National Key R&D Program of
China (2018YFB1501604), the National Natural Science
Foundation of China (21875239, 51821006, 51961135104,
21905266), and the Fundamental Research Funds for the Central
Universities (WK3530000013).
Abbreviations
LA, levulinic acid; GVL, γ-valerolactone; CN, nitrogen doped
carbon; HPA, 4-hydroxy-pentanoic acid.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 8 of 8
ARTICLE
Journal Name
Porous Organic Polymer: Synergistic Catalyst for High [12] Liu, D. W., Zhang, L. N., Han, W. P., Tang, M. X., Zhou, L. G.,
Performance Levulinic Acid Hydrogenation. ACS Sustain. Chem. Zhang, Y., Li, X. K., Qin, Z. F., Yang, H.Q. One-step fabVriiecwatAiroticnleoOfnNlinie-
DOI: 10.1039/D1GC01732B
Eng. 2017, 5, 1033-1045. (f) Xiao, C. X., Goh, T. W., Qi, Z. Y., Goes, embedded hierarchically-porous carbon microspheres for
S., Brashler, K., Perez, C., Huang, W. Y. Conversion of Levulinic levulinic acid hydrogenation. Chem. Eng. J. 2019, 369, 386-393.
Acid to γ-Valerolactone over Few-Layer Graphene-Supported [13] Mamun, O., Saleheen, M., Bond, J. Q., Heyden, A.
Ruthenium Catalysts. ACS Catal. 2016, 6, 593-599. (g) Zhang, K. L., Investigation of solvent effects in the hydrodeoxygenation of
Meng, Q. L., Wu, H. H., Yuan, T. Y., Han, S. T., Zhai, J. X., Zheng, B. levulinic acid to γ-valerolactone over Ru catalysts. J. Catal. 2019,
X., Xu, C. Y., Wu, W., He, M. Y., Han, B. X. Levulinic acid 379, 164-179.
hydrogenation to gamma-valerolactone over single Ru atoms on
a TiO2@nitrogen doped carbon support. Green Chem. 2021, 23,
1621-1627.
[7] (a) Song, S., Yao, S. K., Cao, J. H., Di, L., Wu, G. J., Guan, N. J.,
Li, L. D., Heterostructured Ni/NiO composite as a robust catalyst
for the hydrogenation of levulinic acid to gamma-valerolactone,
Appl. Catal., B. 2017, 217, 115-124. (b) Lv, J. K., Rong, Z. M., Wang,
Y., Xiu, J. H., Wang, Y., Qu, J. P. Highly efficient conversion of
biomass-derived levulinic acid into gamma-valerolactone over
Ni/MgO catalyst. RSC Adv. 2015, 5, 72037-72045. (c) Jiang, K.,
Sheng, D., Zhang, Z. H., Fu, J., Hou, Z. Y., Liu, X. Y. Hydrogenation
of levulinic acid to gamma-valerolactone in dioxane over mixed
MgO-Al2O3 supported Ni catalyst. Catal. Today. 2016, 274, 55-59.
(d) Fu, J., Sheng, D., Lu, X. Y. Hydrogenation of Levulinic Acid over
Nickel Catalysts Supported on Aluminum Oxide to Prepare
gamma-Valerolactone. Catalysts. 2016, 6, 6. (e) Liu, D. W., Zhang,
L. N., Han, W. P., Tang, M. X., Zhou, L. G., Zhang, Y., Li, X. K., Qin,
Z. F., Yang, H. Q. One-step fabrication of Ni-embedded
hierarchically-porous carbon microspheres for levulinic acid
hydrogenation. Chem. Eng. J. 2019, 369, 386-393. (f) Hengst, K.,
Schubert, M., Carvalho, H. W. P., Lu, C. B., Kleist, W., Grunwaldt,
J. D. Synthesis of γ-valerolactone by hydrogenation of levulinic
acid over supported nickel catalysts. Appl. Catal., A. 2015, 502,
18-26.
[8] Jagadeesh, R. V., Surkus, A. E., Junge, H., Pohl, M. M., Radnik,
J., Rabeah, J., Huan, H. M., Schunemann, V., Bruckner, A., Beller,
M. Nanoscale Fe2O3-Based Catalysts for Selective Hydrogenation
of Nitroarenes to Anilines. Science. 2013, 342, 1073-1076.
[9] (a) Li, A., Nicolae, S. A., Qiao, M., Preuss, K., Szilágyi, P. A.,
Moores, A., Titirici, M. M. Homogenous meets heterogenous and
electro-catalysis: Iron-nitrogen molecular complexes within
carbon materials for catalytic applications. ChemCatChem. 2019,
11, 3600-3623. (b) Qin, R. X., Liu, K. L., Wu, Q. Y., Zheng, N. F.
Surface coordination chemistry of atomically dispersed metal
catalysts. Chem. Rev. 2020, 120, 11810-11899.
[10] (a) Li, J., Zhang, J. J., Liu, H. Y., Liu, J. L., Xu, G. Y., Liu, J. X., Sun,
H., Fu, Y. Graphitic Carbon Nitride (g-C3N4)-derived Fe-N-C
Catalysts
for
Selective
Hydrodeoxygenation
of
5-
Hydroxymethylfurfural to 2,5-Dimethylfuran. ChemistrySelect.
2017, 2, 11062-11070. (b) Li, J., Liu, J. L., Liu, H. Y., Xu, G. Y., Zhang,
J. J., Liu, J. X., Zhou, G. L., Li, Q., Xu, Z. H., Fu, Y. Selective
Hydrodeoxygenation of 5-Hydroxymethylfurfural to 2,5-
Dimethylfuran
over
Heterogeneous
Iron
Catalysts.
ChemSusChem. 2017, 10, 1436-1447. (c) Wang, H., Liu, XH., Xu,
GY., Guo, ZW., Zhang, Y. In situ synthesis of Fe-N-C catalysts from
cellulose for hydrogenation of nitrobenzene to aniline. Chin. J.
Catal. 2019, 40, 1557-1565. (d) Li, J., Zhang, J. J., Wang, S., Xu, G.
Y., Wang, H., Vlachos, D. G. Chemoselective Hydrodeoxygenation
of Carboxylic Acids to Hydrocarbons over Nitrogen-Doped
Carbon−Alumina Hybrid Supported Iron Catalysts. ACS Catal.
2019, 9, 1564−1577.
[11] Li, B., Nam, H., Zhao, J., Chang, J., Lingappan, N., Yao, F., Lee,
T. H., Lee, Y. H. Nanoreactor of Nickel-Containing Carbon–Shells
as Oxygen Reduction Catalyst. Adv. Mater. 2017, 29, 1605083.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins