Highly selective ring rearrangement of 5-hydroxymethylfurfural to 3-hydroxymethylcyclopentanon catalyzed by non-noble Ni-Fe/Al2O3

Article abstract of DOI:10.1016/j.mcat.2021.111505

3-Hydroxymethylcyclopentanone (HCPN) has been regarded as a considerable intermediate for the synthesis of polymers, pesticides and fragrances, which is mainly produced from petrochemical refinery. In recent years, the preparation of HCPN from biomass has gradually attracted attention. HCPN can be obtained through the selective ring rearrangement of biomass-based 5-hydroxymethyl furfural (5-HMF). In this paper, the Ni-Fe/Al₂O₃ was fabricated and used as an efficient catalyst for the production of HCPN, giving a 5-HMF complete conversion with a high HCPN selectivity (86 %) at 160 °C under 4 MPa H₂ for 4 h. The optimized Ni-Fe/Al₂O₃ showed excellent activity towards the production of HCPN compared with monometallic catalysts, suggesting that there was a synergistic effect in Ni-Fe alloy. The introduction of Fe into Ni/Al₂O₃ improved the H₂ adsorption capacity and also changed the acidic/basic sites, which are beneficial for the formation of HCPN. Moreover, Ni-Fe/Al₂O₃ exhibited superb stability and could be successively used four times without obvious loss in catalytic activity.

Full text of DOI:10.1016/j.mcat.2021.111505

Molecular Catalysis 505 (2021) 111505
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.journals.elsevier.com/molecular-catalysis
Highly selective ring rearrangement of 5-hydroxymethylfurfural to
3-hydroxymethylcyclopentanon catalyzed by non-noble Ni-Fe/Al2O3
,
,
,
Jiachen Lia, Yunchao Fenga, Huiqiang Wanga, Xing Tanga b, Yong Suna b, Xianhai Zenga b,*,
,
b
Lu Lina
a College of Energy, Xiamen University, Xiamen, 361102, China
b Fujian Engineering and Research Center of Clean and High-valued Technologies for Biomass, Xiamen Key Laboratory of Clean and High-valued Utilization for Biomass,
Xiamen, 361102, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
3-Hydroxymethylcyclopentanone (HCPN) has been regarded as a considerable intermediate for the synthesis of
polymers, pesticides and fragrances, which is mainly produced from petrochemical refinery. In recent years, the
preparation of HCPN from biomass has gradually attracted attention. HCPN can be obtained through the se-
lective ring rearrangement of biomass-based 5-hydroxymethyl furfural (5-HMF). In this paper, the Ni-Fe/Al2O3
was fabricated and used as an efficient catalyst for the production of HCPN, giving a 5-HMF complete conversion
with a high HCPN selectivity (86 %) at 160 ◦C under 4 MPa H2 for 4 h. The optimized Ni-Fe/Al2O3 showed
excellent activity towards the production of HCPN compared with monometallic catalysts, suggesting that there
was a synergistic effect in Ni-Fe alloy. The introduction of Fe into Ni/Al2O3 improved the H2 adsorption capacity
and also changed the acidic/basic sites, which are beneficial for the formation of HCPN. Moreover, Ni-Fe/Al2O3
exhibited superb stability and could be successively used four times without obvious loss in catalytic activity.
5-Hydroxymethylfurfural
3-Hydroxymethylcyclopentanon
Ni-Fe alloy catalyst
Ring rearrangement
1. Introduction
using water as the solvent (Fig. 1). Ohyama et al. firstly reported the ring
rearrangement reaction for 5-HMF over Au/Nb2O5, achieving an HCPN
Biomass-derived platform compounds could be converted into many
high value-added chemicals, which can convert the unsustainable
economy derived from fossil resources to a sustainable one based on
renewable biomass. 5-hydroxymethylfurfural (5-HMF), one of the
principal biomass-derived platform compounds, can be converted into a
broad range of downstream products and derivatives such as 2,5-furan-
dicarboxylic acid, 2,5-bis(hydroxymethyl)tetrahydrofuran, 2,5-dihy-
droxymethylfuran, levulinic acid, 1,6-hexanediol, etc. [1–7].
yield of 86 % with 12 h at 140 ℃ and 8 MPa H2 [8]. Moreover, Pd and
Pt-based catalysts were also examined for HCPN production from 5-HMF
[12–14]. Recently, unremitting efforts have been devoted to design and
prepare non-noble catalysts with high activity for the synthesis of HCPN.
For example, Ramos et al. fabricated Cu-Al2O3 catalyst from the
hydrotalcite materials for the hydrogenation of 5-HMF. Under the
optimal conditions (180 ◦C, 2 MPa, 6 h), HCPN yield of 86 % at complete
5-HMF conversion was achieved [15]. Rosseinsky and co-workers re-
ported that Ni-Al layered double hydroxide, at 140 ◦C and 2 MPa H2,
showed an HCPN yield of 81 % after 6 h [16]. Xu et al. investigated the
ring rearrangement of HMF into HCPN over a NiCu MOF catalyst [17].
The yield of HCPN reached 70.3 % at 130 ◦C under the pressure of 2 MPa
H2. Despite the great advancement, there is still much work to be done to
overcome shortcomings such as poor recyclability and expensive pre-
cursors. Therefore, it’s quite desirable to develop robust and efficient
catalysts based on inexpensive and abundant 3d transition metals to-
wards 5-HMF conversion to HCPN.
HCPN is a versatile compound in the production of medicine, pes-
ticides, perfume, and other chemicals [8,9]. In the current process,
HCPN can not be directly obtained from cyclopentanone (CPO) because
it is the β-substituted equivalent of CPO, thus, mainly produced from
petrochemical resources (cyclization of 1,6-hexanediol, decarboxylation
of adipic acid or oxidation of cyclopentene) under harsh conditions [10,
11]. At this point, efficient production of HCPN from biomass-based
furanic compounds would be of great significance.
Typically, the conversion of 5-HMF into HCPN involves tandem
hydrogenation, hydrolysis, condensation and dehydration reaction
In general, bimetallic catalysts exhibited better activity and stability
* Corresponding author at: College of Energy, Xiamen University, Xiamen, 361102, China.
E-mail address: xianhai.zeng@xmu.edu.cn (X. Zeng).
https://doi.org/10.1016/j.mcat.2021.111505
Received 14 December 2020; Received in revised form 26 February 2021; Accepted 26 February 2021
Available online 8 March 2021
2468-8231/© 2021 Elsevier B.V. All rights reserved.

J. Li et al.
Molecular Catalysis 505 (2021) 111505
compared to monometallic materials due to the synergistic effect be-
tween two metals [18–20]. For instance, Christopher and co-workers
revealed that CuNi/TiO2 catalyst showed advanced catalytic perfor-
mance and stability as well as recyclability compared to Cu/TiO2 for
furfural hydrodeoxygenation [21]. Wang et al. found that NiCo/SiO2
catalyst was 2 and 20 times more active than Ni/SiO2 and Co/SiO2 for
the synthesis of tetrahydrofurfuryl alcohol via hydrogenation of furfuryl
alcohol [22]. Therefore, in terms of the reusability and selectivity for
catalyst, it would be a feasible scheme to design hydrogenation catalysts
with multi-metal.
different Ni/Fe ratios were remarked as Ni6-Fe1/Al2O3, Ni4-Fe1/Al2O3,
Ni3-Fe1/Al2O3. The catalysts were thoroughly ground before used.
2.3. Catalyst characterization
The X-ray diffraction (XRD) patterns of catalysts were performed on
a Rigaku Ultima IV diffractometer using a Cu Ka radiation with the
conditions: 30 mA, 40 kV, 2θ from 10◦ to 80◦ at a scanning speed of 10◦/
min.
The specific surface area, pore volume and pore size of the catalysts
were measured by N2 adsorption-desorption using a Micromeritics ASAP
2020 HD88. Before the adsorption test, the sample was degassed in a
vacuum atmosphere of 100 ◦C for 4 h, then treated in helium atmo-
sphere at 250 ◦C for 2 h. Finally, N2 was adsorbed by the catalyst at
ꢀ 196 ◦C to obtain N2 adsorption-desorption isotherm of. According to
the isotherm, the specific surface area, pore volume, and pore diameter
were identified by using the Brunauer-Emmett-Teller (BET) and Barrett-
Joyner-Halenda (BJH) methods, respectively.
Inspired by these cases, we prepared a bimetallic Ni-Fe alloy sup-
ported on Al2O3 towards the selective ring rearrangement of HMF to
achieve better selectivity towards HCPN and strengthen catalysts’ sta-
bility. The structures of the synthesized materials were investigated by
the powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy
(XPS), hydrogen temperature-programmed reduction (H2-TPR), and
transmission electron microscopy (TEM). HCPN was obtained with a
high yield of 86 % and 5-HMF conversion of 100 %. Moreover, the Ni-Fe
alloy catalyst could be easily separated and recycled without significant
activity declined after 4 runs.
The morphology of catalysts was observed by transmission electron
microscopy (TEM, FEI Tecnai G2 F20) with an accelerating voltage of
100 kV.
2. Experimental part
X-ray photoemission spectroscopy (XPS) analysis was collected from
a Thermo Scientific ESCALAB 250Xi spectrometer employing mono-
2.1. Materials
chromatic Al Kα radiation. The binding energies (BE) of all elements
were tuned to the carbon tape (284.6 eV) with an uncertainty of ±0.2
eV.
All materials in this work were acquired from commercial sources
and used without further purification. 5-HMF (98 %) was purchased
from Shanghai Energy Chemical Industrial Co., Ltd. (Shanghai, China).
Ni(NO3)2⋅6H2O (AR, >99 %), Co(NO3)2⋅6H2O (AR, >99 %), Cu
(NO3)2⋅3H2O (AR, >99 %), Fe(NO3)3⋅9H2O (AR, >99 %), and γ-Al2O3
(10 nm) were acquired from Sino-pharm Chemical Reagent Company
Co., Ltd. (Shanghai, China). HCPN was provided by Aikon Biopharma-
ceutical R&D Co., Ltd (Jiangsu, China).
H2-Temperature Programmed Reduction (H2-TPR), NH3-Tempera-
ture Programmed Desorption (NH3-TPD), CO2-Temperature Pro-
grammed Desorption (CO2-TPD) and H2-Temperature Programmed
Desorption (H2-TPD) were tested on a Micromeritics AutoChem II 2920.
For H2-TPR, equipped with a thermal conductivity detector (TCD), 30
mg sample was first loaded into the quartz tube and preheated to 550 ◦C
with a heating rate of 20 ◦C minꢀ 1 in helium gas flow for 1 h to remove
adsorbed species on the surface of the sample. The temperature was then
reduced to 120 ◦C and H2/Ar (10 Vol % H2) mixture was introduced for
0.5 h. After H2 adsorption, the catalyst samples were treated at 120 ◦C
for another 1 h in argon to remove the remaining or weakly adsorbed H2.
In the case of CO2-TPD and NH3-TPD, 40 mg sample was first loaded
into the quartz tube and preheated to 550 ◦C with a heating rate of 20 ◦C
minꢀ 1 in helium gas flow for 1 h to remove adsorbed species on the
surface of sample. The temperature was then reduced to 120 ◦C and
CO2/NH3-He (10 Vol % NH3) mixture was introduced for 0.5 h. After
CO2/NH3 adsorption, the catalyst sample was treated at 120 ◦C for
another 1 h in helium to remove the remaining or weakly adsorbed CO2/
NH3. TPD test was conducted in helium flow by increasing the tem-
perature to 850 ◦C with a heating rate of 20 ◦C minꢀ 1 and then keeping
2.2. Catalyst preparation
All the catalysts were fabricated with incipient wet impregnation. In
a typical procedure, nickel nitrate and iron nitrate with different molar
ratios were dispersed in deionized water. Then, the resulting salt
aqueous solution was dripped slowly onto 1 g γ-Al2O3 support powders
until the surfaces soaked. The mixtures stood after 12 h at room tem-
perature followed by maintained at 100 ◦C for 8 h. After that, the pre-
cursor underwent calcination in the muffle furnace at 500 ◦C for 4 h,
further reduced under atmospheric pressure in a 10 % H2/N2 flow by
increasing the temperature to 600 ◦C and keeping for 3 h at 600 ◦C. (700
◦C for Co-based catalysts cases). The as-prepared Ni-Fe catalysts with
Fig. 1. Reaction pathway for the ring rearrangement of 5-HMF into HCPN.
2

J. Li et al.
Molecular Catalysis 505 (2021) 111505
at 850 ◦C for 0.5 h.
was used. Interestingly, pure alumina could also catalyze substrates to
produce small content of HCPN because of its abundant acid-base sites,
which is contributed to the synthesis of the desired product. Surpris-
ingly, when Fe was introduced to generate bimetallic Ni-Fe/Al2O3
catalyst, the yield of HCPN increased from 47.7% to 82.7% and the
by-products such as BHMTHF, humins decresed significantly (Table 1,
Entry 4). However, the application of Co or Cu showed poor selectivity
for HCPN (Table 1, Entry 5,6). When other supports such as ZrO2, Nb2O5
were used (Table 1, Entry 7–10), low HCPN selectivity was also
observed. These controlled experiments demonstrated the specific syn-
ergistic effect of Ni, Fe and Al2O3 support, which greatly facilitated the
selectivity for the production of HCPN from 5-HMF. In this work, the
bimetallic catalyst Ni-Fe/Al2O3 exhibited significant activity for the
production of HPCN under relatively mild reaction conditions. Mean-
while, compared with the reported catalysts, Ni-Fe/Al2O3 possesses
better economic performance due to its non-noble metal components
and low metal content, which would be practical by actual production.
2.4. Catalysts performance
All reactions were carried out in a Parr reactor (50 mL). In a typical
experiment, 0.63 g 5-HMF, 0.126 g catalyst powder and 30 mL H2O were
put into the reactor. The reactor was flushed by H2 several times and
pressurized to 2 MPa. Then the system was heated to the designated
temperature, under stirring for 4ꢀ 8 h. When the reaction terminated,
the reactor was fast cooled to ambient temperature and decompressed.
Finally, catalysts and liquid products were segregated by centrifugation.
The liquid product was qualitatively identified through GC–MS
(Thermo Trace 1300 and ISQ LT), and quantitatively analyzed by a high
performance liquid chromatography (HPLC, WATERS Alliance e4695)
equipped with a Bio-Rad Aminex HPX-87H column and a refractive
index detector (RID). The applied parameters were as follows: column
temperature was kept at 60 ◦C; mobile phase was H2SO4 aqueous solu-
tion (5 mM at 0.6 mL/min), every sample was detected for 45 min. 5-
HMF conversion (XH, %), product yield (YP, %) and selectivity (SP, %)
were calculated with as the following Eqs. (1)–(3):
3.2. Catalyst characterization
(
)
The XRD patterns of the catalysts with different atomic ratios of Ni/
Fe were presented in Fig. 2A. The diffraction lines belonging to Ni and
NiO for the monometallic Ni/Al2O3 sample were observed at 2θ = 44.5,
51.8, 76.2◦ and 2θ = 37.2, 43.2, 62.8◦ (JCPDS, no.04-0850 and 47-
1049), respectively. Indicating that the precursor of Ni/Al2O3 was
mainly converted into metallic Ni after reduction. As for the mono-
metallic Fe/Al2O3 catalyst, the diffraction peaks at 2θ = 30.4, 35.4,
43.3◦ were mainly attributed to Fe2O3 (JCPDS, no.39-1346). The char-
acteristic peaks of FeNi3 alloy (JCPDS, no.38-0419) can be observed at
2θ = 44.2, 51.5 and 75.86◦ in XRD patterns of the Ni-Fe/Al2O3 catalysts.
Moreover, miller indices corresponding to these three characteristic
peaks were 111, 200 and 220, indicating the nanoparticles were face-
centered cubic crystals. The XRD patterns of Ni-Fe/Al2O3 showed the
Ni-Fe alloy structure in these bimetallic catalysts. In addition, there was
no impurity peak observed in the samples with various Ni/Fe ratios,
further confirming a high level of Fe3Ni alloy in the catalysts.
m oles of HMF in products
m oles of HMF in the initial substrate
XH(%) = 1-
× 100%
(1)
m oles of P in products
m oles of HMF in the initial substrate
YP(%) =
× 100%
(2)
(3)
YProduct
XHMF
SP(%) =
× 100%
3. Results and discussions
3.1. Catalyst screening
Table 1 shows the catalytic effects of different catalysts towards the
ring rearrangement of 5-HMF to HCPN in this work as well as previous
relevant reports. It can be seen that monometallic Ni/Al2O3 exhibited a
moderate catalytic performance for the 5-HMF conversion (73.8 %), but
the selectivity of HCPN was only 47.7 % (Table 1, Entry 2), and 12.6 %
substrate converted into 2,5-Bis(hydroxymethyl)-tetrahydrofuran
(BHMTHF). This undesired situation may be due to the high activity
of nickel, which leads to the formation of other ring-opening products or
furan ring hydrogenation products [23,24]. At the same time, low
conversion and selectivity were observed when monometallic Fe/Al2O3
H2-TPR profiles of the Ni-Fe/Al2O3 catalyst before reduction were
performed subsequently. As shown in Fig. 2B, the reduction profile of
the monometallic Ni/Al2O3 precursor presented a broad peak ranging
from 470 to 680 ◦C, and the maximum peak appeared at 590 ◦C, which
was attributed to the reduction of NiO to Ni. As for Fe/Al2O3, two fea-
tures were observed (280 ◦C and 420 ◦C), suggesting that two kinds of
iron oxides underwent reduction. In general, the peak centered at 420 ◦C
Table 1
Catalyst screening for ring rearrangement of 5-HMF into HCPN.
Yield (%)
HCPN
X5-HMF (%)
Entry
Catalyst
Pres (MPa)
Temp (oC)
Time (h)
BHMTHF
Othes
1
γ-Al2O3
2
2
2
2
2
2
2
2
2
2
8
4
2
3
2
4
2
3
140
140
140
140
140
140
140
140
140
140
160
150
180
140
140
150
140
130
4
18.3
47.8
13.5
82.7
ND
0.4
12.6
2.9
1.8
15.3
4.1
17.2
1.4
0.7
0
26.1
13.4
40.2
2.1
44.8
73.8
56.6
86.6
77.3
48.4
86.7
78.0
39.7
55.9
99
2
Ni/γ-Al2O3
4
3
Fe/γ-Al2O3
4
4
Ni-Fe/γ-Al2O3
Cu-Fe/γ-Al2O3
Co-Fe/γ-Al2O3
Ni-Fe/ZSM-5
4
5
4
62
6
4
11.1
16.2
21.5
3.4
33.2
53.3
55.1
35.6
50.2
13
7
4
8
Ni-Fe/MCM-41
Ni-Fe/Nb2O5
4
9
4
10
11
12
13
14
15
16
17
18
Ni-Fe/ZrO2
4
5.7
Au/Nb2O5 [8]
Pd/Fe-MIL-100 [13]
Cu/Al2O3 [15]
Pt/SiO2+ Ta2O5 [14]
NiAl hydrate [16]
Pd/Cu-BTC [12]
Ni–Cu/C [17]
Cp*Ir + Al2O3 [25]
12
24
6
86
0
85.4
86
4
10.6
14
100
100
100
100
99.5
99.8
100
0
30
6
61
0
39
81
8
11
24
5
90.9
70.4
82
4
4.6
0
29.4
18
4
0
Reaction conditions for this work: 0.63 g 5-HMF, 0.126 g catalyst, 30 mL H2O, stirring rate=600 r/min.
3

J. Li et al.
Molecular Catalysis 505 (2021) 111505
Fig. 2. XRD patterns (A) and H2-TPR profiles (B) for the as-prepared Ni-Fe/Al2O3 materials.
was ascribed to the reduction of Fe2O3 to Fe3O4, and the other one was
attributed to the reduction of Fe3O4 to form FeO or Fe at about 700 ◦C
[26,27]. For Ni-Fe/Al2O3, it could be observed that hydrogen was
consumed massively, indicating the existence of an interaction between
Ni and Fe, which might be responsible for the high reducibility of the
Ni-Fe/Al2O3. The most intense peak at 362 ◦C could be attributed to the
formation of Ni-Fe alloy, and the other peak at 570 ◦C was ascribed to
the reduction of partial NiO to metallic nickel. Compared with mono-
metallic precursors, introducing Fe species transformed reduction peaks
to the lower temperature, revealing the enhancement of reducibility of
bimetallic Ni-Fe samples.
existence of iron oxide. The peaks of Fe species above were also observed
in the XPS spectra of bimetallic Ni-Fe/Al2O3 (Fig. 3B). However, XRD
spectra of Ni-Fe/Al2O3 showed no characteristic peaks of iron oxides
because of the formation of amorphous FeNi3. It was noteworthy that
there existed a Fe◦ peak located at 707.3 eV in Ni-Fe/Al2O3, indicating
that metallic Fe formed below 600 ◦C. It was much lower than the
theoretical reduction temperature (660 ◦C) of Fe, which means that the
alloying of Ni and Fe promoted the reduction of iron oxide in Ni-Fe/
Al2O3. In the Ni-Fe/Al2O3 samples (Fig. 3D), two types of Ni including
Ni◦ (852.6 and 856.0 eV) and Ni2+ (862.0, 873.8 and 879.5 eV) were
exhibited, indicating that Ni◦ species on the surface of the catalyst was
partially oxidized. Compared with the XPS spectra of monometallic Ni
sample, the peaks of Ni species and Fe species in Ni-Fe/Al2O3 occurred a
shift of binding energies. Such shifts of binding energy for Ni and Fe
species were probably characteristic of a charge transfer from support
XPS analysis was performed to clarify the species in Ni-Fe/Al2O3, Ni/
Al2O3 and Fe/Al2O3. Fig. 3 shows the Ni 2p and Fe 2p spectra for the
catalysts. The peaks of 711.4 and 724.4 eV were ascribed to Fe2O3, while
the peak of 710.8 eV was attributed to Fe3O4 in Fig. 3A. It illustrates the
Fig. 3. XPS spectras: A) Fe 2p spectra of Ni/Al2O3, B) Fe 2p spectra of Ni-Fe/Al2O3, C) Ni 2p spectra of Fe/Al2O3, D) Ni 2p spectra of Ni-Fe/Al2O3.
4

J. Li et al.
Molecular Catalysis 505 (2021) 111505
towards metal surface, making Ni electron-rich, which would be more
conducive to the adsorption and dissociation of H2 species [28,29]. The
findings supported the results obtained from XRD and H2-TPR analysis
that Ni-Fe alloy was generated through the interaction between Ni and
Fe species.
samples exhibited several H2 desorption peaks. The peak at around 110
◦C was attributed to the desorption of physically adsorbed hydrogen. For
Fe/Al2O3 catalyst, a large desorption peak was observed at 355 ◦C
probably due to the presence of iron oxides sites. Two H2 desorption
peaks were both found in Ni/Al2O3 and Ni-Fe/Al2O3 catalysts, revealing
that two types of active centers existed on the surface of catalysts. The
peaks at the low and high temperatures were attributed to the weak and
strong adsorption of H2 on the catalyst surface, respectively. In addition,
the adsorbed H species were both reversibly and had catalytic activity to
the reaction. Besides, H2 uptakes were calculated by the peak areas. The
Ni-Fe/ Al2O3 catalyst gave an adsorption amount of H2 up to 2.43 mmol/
g, which was higher than that on the monometallic Ni catalyst (2.06
mmol/g). Furthermore, the relative content of the desorption peak area
at low temperature (Ni-Fe/ Al2O3 catalyst) was higher than that of
monometallic Ni/Al2O3 (32.6 %, 27.7 %), namely more low-
temperature Ni active centers, which was more beneficial to the
To further investigate the morphology of catalyst, Ni-Fe/Al2O3
catalyst was analyzed through TEM and EDX. As shown in Fig. 4,
spherical particles with an average particle size of 7.5 nm were well
dispersed. From the enlarged view (Fig. 4B), a clear crystalline fringe of
Ni-Fe/Al2O3 can be observed. In addition, the distance of lattice fringes
in the image was 0.203 nm, which is ascribed to the (111) plane and the
result is approximate to the theoretical value of the FeNi3 alloy nano-
crystal (JCPDS, no 38-0419). The SEM-EDX elemental mappings further
suggest the high distribution of Fe and Ni elements on Al2O3 support.
The H2-TPD analysis was carried out to explore the effects of the
addition of Fe into monometallic Ni catalyst. As shown in Fig. 5A, all
Fig. 4. A) TEM image of the Ni-Fe/Al2O3 catalyst; B) high-resolution TEM image of the Ni-Fe alloy; C-D) SEM-EDX elemental mappings of Ni and Fe; (E) Modulation
of metallic Ni by forming FeNi3 alloy.
5

J. Li et al.
Molecular Catalysis 505 (2021) 111505
Fig. 5. A) H2-TPD profiles of Ni-Fe catalysts; B) effect of Ni/Fe ratios. Reaction conditions: 0.63 g 5-HMF, 0.12 g catalyst, 30 mL H2O, PH2 = 2 MPa, stirring rate=600
r/min, reaction temperature = 160 ◦C, reaction time=4 h.
hydrogenation rearrangement of 5-HMF.
specific surface area and pore size, which may be less related to the
activity. Further research is needed for factors that affected catalysts’
activity.
Given the superior activity of Ni-Fe/Al2O3, the influence of the Ni/Fe
ratios on the reaction was further explored (Fig. 5B). When the atomic
ratio of Ni/Fe was 3:1, the catalytic activity of the catalyst was relatively
low, providing only a 70 % HCPN yield. When the ratio of Ni/Fe
increased to 4:1, 5-HMF conversion increased to 100 %. Meanwhile, the
yield of HCPN was up to 86 %, showing excellent catalytic activity and
selectivity. However, the yield of HCPN decreased sharply from 86 % to
66 % when the Ni/Fe ratio continued to increase to 6:1. This may be that
active Ni-Fe alloy tends to form at the Ni/Fe atomic ratio of 4:1. How-
ever, the content of the Ni-Fe alloy decreased when the ratio was too
high. What’s more, the side reaction was easily occurred due to a large
number of nickel species, which led to the reduction of selectivity for-
ward HCPN.
Generally, the 5-HMF ring rearrangement process requires both
acidic sites and basic sites involved in the ring opening or closing and
aldol condensation step, respectively [14,25]. NH3-TPD and CO2-TPD
experiments were conducted to reveal the effect of Fe addition on cat-
alysts’ acid or base properties. As shown in Table 2, pure γ-Al2O3
possessed abundant acidic and basic sites so that it played a significant
impact on the reaction. Both the NH3 and CO2 adsorption amounts
increased significantly when Al2O3 was loaded with metals. This
improvement of acid sites came from nickel and iron oxides species [26,
27,30], which were detected by XPS. When Fe was introduced to form
metallic catalysts, the acidic and basic sites were slightly reduced
probably due to the formation of FeNi3 alloy. With the increase of Ni/Fe
ratio, catalysts’ acid sites show an increasing trend because of the
presence of NiO generated from excessive Ni precursors. The adequate
acid-base sites contribute to the ring opening and closing during ring
rearrangement, but an excess of acidity may cause polymerization and
deoxygenation of 5-HMF [31]. In addition, the catalysts without acidic
sites gave a high yield of HCPN under the slightly acidic condition
created by water, which implicates that less acidic sites could be also
effective for the reaction [17]. Thus, the Ni4-Fe1/Al2O3 catalyst with
appropriate acid-base sites exhibited the best catalytic activity for pro-
duction of HCPN.
The chemical compositions and textural properties of Ni-Fe/Al2O3
catalysts were listed in Table 2. The Ni-Fe catalysts were fabricated by
keeping metal elements content at 18 % with different Ni/Fe atomic
ratios. As determined by ICP-MS, the Ni loadings and Ni/Fe ratios were
similar to the corresponding theoretical values. Additionally, the spe-
cific surface areas of Ni-Fe/Al2O3 catalysts ranged from 119 to 122 m2/
g, which were slightly lower than that of pure Al2O3 support (146 m2/g),
implying that the Ni-Fe alloy nanoparticles were embedded into Al2O3
without leading the nanostructure collapse. Moreover, the pore volume
decreased which could be explained by the fact that most active com-
ponents dispersed on the surface rather than inside the supports. The
pore volume decreased with the Ni/Fe ratio increasing. High catalytic
activity was observed in Ni4-Fe1/Al2O3, offering a possibility that
different ratios of Ni/Fe had no significant effect on the catalysts’
3.3. Effects of the reaction conditions
The ring rearrangement of 5-HMF to yield HCPN also depended on
the reaction parameters. Fig. 6 illustrates the effects of reaction time and
temperature on the ring rearrangement of 5-HMF. The hydrogenation
rearrangement of 5-HMF was performed at varying reaction tempera-
tures (120ꢀ 180 ◦C). As shown in Fig. 6A, the reaction temperature
played a significant role in HCPN production. Along with the rise of
temperature, the 5-HMF conversion went up rapidly. Within 4 h, 5-HMF
conversion increased from 66.8% to 100% when the temperature
increased from 120 to 160 ◦C. The results could be explained by the fact
that the conversion of 5-HMF and the intermediate products were sen-
sitive to temperature, and a higher temperature caused a higher reaction
rate. As a result, the highest yield of HCPN (86 %) was achieved at 160
◦C. However, when the reaction temperature further increased, the yield
of HCPN decreased sharply, possibly due to subsequent hydrogenation
or of HCPN or polymerization of BHMF [15,32]. Therefore, 160 ◦C was
determined as the optimal temperature for the production of HCPN from
5-HMF over Ni4-Fe1/Al2O3 in this work.
Table 2
Physicochemical properties of Ni-Fe/Al2O3 catalysts.
b
c
Catalyst
Ma
SBET
[m2/
g]
Vpore
Dpore
Acid sites
Base sites
[wt%]
[cm3/g]
[nm]
[mmol/g]
[mmol/g]
γ-Al2O3
Ni/Al2O3
Fe/Al2O3
Ni6-Fe1/
Al2O3
–
146
131
138
120
0.75
0.59
0.60
0.57
20.6
19.7
17.5
18.8
0.47
0.98
0.88
0.99
0.53
0.67
0.60
0.68
17.3
18.1
15.0
(2.4)
14.2
(3.3)
13.5
(3.9)
Ni4-Fe1/
Al2O3
119
122
0.54
0.53
18.1
17.6
0.87
0.81
0.68
0.64
Ni3-Fe1/
Al2O3
a
Determined from ICP-MS; the data in parentheses stands for the Ni/Fe mass
ratio.
b
c
Total pore volume measured at P/P0 = 0.99.
Average pore width calculated by BJH method.
The time-determined product distribution during the process of 5-
6

J. Li et al.
Molecular Catalysis 505 (2021) 111505
Fig. 6. Effects of reaction time and temperature on the reaction. Reaction conditions: 0.63 g of 5-HMF, 0.12 g Ni-Fe/Al2O3 catalyst, 30 mL H2O, PH2 = 2 MPa, stirring
rate=600 r/min, reaction time=4 h for (A), reaction temperature = 160 ◦C for (B).
HMF ring rearrangement over Ni-Fe/Al2O3 catalyst was also investi-
gated. Under the conditions of the 160 ◦C and 2 MPa H2 pressure, the
products were collected and detected once an hour. Fig. 6 shows the
variations in main product yield during the process. Firstly, the con-
version of 5-HMF on the Ni-Fe bimetallic catalyst was rapid, about 90 %
substrate was consumed in the first 2 h, and complete conversion was
achieved in about 4 h. In the early stage, BHMF was detected as the
intermediate, and it sequentially transformed to other products in the
presence of hydrogen atmosphere, metal sites and acid sites. 1-Hydrox-
yhexane-2,5-dione (HHD), as a product of another ring-opening reaction
pathway, had also been detected as an intermediate product. But its
content was poor throughout the process, which was mainly because the
basic sites of the Ni-Fe/Al2O3 catalyst played a partial role in the sub-
sequent aldol condensation reaction of HHD. It was noteworthy that
BHMTHF was the product from BHMF by further hydrogenation of furan
ring, and it was competitive with the formation of HCPN. Nevertheless,
almost no by-product THFDM was detected during the whole process.
These results confirm that the bimetallic Ni-Fe catalyst tends to catalyze
reaction on the carbonyl group in 5-HMF rather than on the furan ring,
making the subsequent ring-opening and rearrangement possible, which
would be the source of its excellent selectivity for the targeted cyclo-
pentanone derivatives. The content of 3-Hydroxymethylcyclopentanol
(HCPL) gradually increased over time. This was because after the 5-
deactivation. Notwithstanding, the spent catalyst could be recovered by
calcination and reduction. Deng et al. observed aggregation of Pd
nanoparticles after five reaction runs [12], leading to a large decrease of
BET surface area for catalyst, which may be ascribed to the activity loss.
Perret et al. ascertained the deactivation of the Ni-Al hydrate catalyst
was due to the obstruction of the active sites by the organic molecules
chemisorbed on the surface and the formation of coke [16]. The organic
impurities could be removed sufficiently by a heat treatment at 773 K to
regenerate the spent catalyst.
In this work, the stability of catalyst and the reasons for activity loss
were investigated. The used catalysts were collected from the liquid
product centrifugally and then washed with ultrapure water and anhy-
drous ethanol several times, subsequently got dried at 80 ◦C for the next
run. As shown in Fig. 7, 5-HMF conversion remained approximately
constant and HCPN yield was still relatively high after 4 cycles. As
shown in Fig. S2, the XRD pattern of the spent Ni-Fe/Al2O3 catalyst
showed new peaks attributed to AlO(OH) (JCPDS, no.83-1506),
implying the transformation of Al2O3 by hydration of partial Al2O3
during the reaction course [34,35]. Moreover, the catalysts could be
collected easily with magnets after reaction because they were highly
magnetic(Fig. S3 D). The stable and easily-recyclable properties make
bimetallic Ni-Fe/Al2O3 act as an efficient and robust catalyst to produce
HCPN from 5-HMF.
–
HMF was rapidly consumed, the C O bond in HCPN would be hydro-
–
genated to a hydroxyl group. Therefore, the appropriate hydrogen
pressure was essential to prevent a successive reduction of the target
product HCPN. 3-hydroxymethyl-(2, 3, or 4)-cyclo-pentenone (HCPEN),
as an intermediate product of another route [33], had not been detected,
which may be because that the hydrogenation was very fast to convert it
to HCPN completely and revealed the high efficiency of the bimetallic
Ni-Fe/Al2O3 catalyst. In short, the ring rearrangement process of 5-HMF
over Ni-Fe/Al2O3 catalyst not only showed the high efficiency, reaching
an HCPN yield up to 86 % with complete consumption of 5-HMF in 4 h.
The excellent selectivity for cyclopentanone derivatives proves that
there exists a large difference in catalytic activity towards the carbonyl
and furan ring functional groups of 5-HMF.
3.4. Catalyst recycling
The catalysts’ stability is of importance for practical production, but
the catalysts of current researches are inefficient on this point. Ramos
et al. found that the used Cu/Al2O3 catalyst had a significant weight loss
(28 %) by TG/DTG detection, which indicated that organic compounds
were deposited on the catalyst surface [15]. Additionally, they demon-
strated that the aqueous phase reaction promoted hydration of support
Al2O3 to AlO(OH), and these structural changes could cause catalytic
Fig. 7. Recycled experiments for the ring-rearrangement of 5-HMF over Ni-Fe/
Al2O3. Reaction conditions: Reaction conditions: 0.63 g of 5-HMF, 0.12 g Ni-Fe/
Al2O3 catalyst, 30 mL H2O, PH2 = 2 MPa, stirring rate=600 r/min, reaction
temperature = 160 ◦C, reaction time=4 h.
7

J. Li et al.
Molecular Catalysis 505 (2021) 111505
3.5. Discussion
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editing. Xianhai Zeng: Supervision, Conceptualization, Resources,
Writing - review & editing. Lu Lin: Resources, Supervision.
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9