Catalytic transfer hydrogenation of furfural into furfuryl alcohol over Ni–Fe-layered double hydroxide catalysts

Article abstract of DOI:10.1002/jccs.201800477

Layered double hydroxides (LDHs) and their derivatives have been reported to be widely used as heterogeneous catalysts in various reactions. Herein, Ni-Fe LDHs with the controlled Ni/Fe molar ratios (2:1, 3:1, 4:1) were synthesized via an easy hydrothermal method, which were used to catalyze the selective reduction of biomass-derived furfural into furfuryl alcohol using 2-propanol as a H-donor under autogenous pressure and characterized using FT-IR, XRD, TGA, BET, SEM, NH₃-TPD, and CO₂-TPD. It was found that the LDH with a Ni/Fe molar ratio of 3:1 demonstrated the best catalytic activity among the LDHs with different Ni/Fe molar ratios, which showed 97.0% conversion of furfural and 90.2% yield of furfuryl alcohol at 140°C for 5 hr. This was attributable to the synergistic effect of acidic sites and basic sites of the catalyst.

Full text of DOI:10.1002/jccs.201800477

Received: 18 December 2018
DOI: 10.1002/jccs.201800477
Revised: 6 March 2019
Accepted: 15 March 2019
A R T I C L E
Catalytic transfer hydrogenation of furfural into furfuryl alcohol
over Ni–Fe-layered double hydroxide catalysts
Tao Wang1 | Aiyun Hu1 | Haijun Wang1
| Yongmei Xia2
1Key Laboratory of Synthetic and Biological
Colloids, Ministry of Education, School of
Chemical and Material Engineering,
Jiangnan University, Wuxi, China
2State Key Laboratory of Food Science &
Technology, Jiangnan University, Wuxi,
China
Layered double hydroxides (LDHs) and their derivatives have been reported to be
widely used as heterogeneous catalysts in various reactions. Herein, Ni-Fe LDHs
with the controlled Ni/Fe molar ratios (2:1, 3:1, 4:1) were synthesized via an easy
hydrothermal method, which were used to catalyze the selective reduction of
biomass-derived furfural into furfuryl alcohol using 2-propanol as a H-donor under
autogenous pressure and characterized using FT-IR, XRD, TGA, BET, SEM, NH3-
TPD, and CO2-TPD. It was found that the LDH with a Ni/Fe molar ratio of 3:1
demonstrated the best catalytic activity among the LDHs with different Ni/Fe molar
ratios, which showed 97.0% conversion of furfural and 90.2% yield of furfuryl
alcohol at 140ꢀC for 5 hr. This was attributable to the synergistic effect of acidic
sites and basic sites of the catalyst.
Correspondence
Haijun Wang, Key Laboratory of Synthetic
and Biological Colloids, Ministry of
Education, School of Chemical and Material
Engineering, Jiangnan University, Jiangsu,
Wuxi 214122, China.
Email: wanghj329@outlook.com
Funding information
K E Y W O R D S
Ministry of Education of the People's
Republic of China & SAFEA for the
111 Project, Grant/Award Number: B13025;
SAFEA; MOE, Grant/Award Number:
B13025
2-propanol, catalytic transfer hydrogenation, furfural, furfuryl alcohol, Ni–Fe (3/1) LDH
tetrahydrofurfural, tetrahydrofurfuryl alcohol, 2-methylfuran,
and 2-methyltetrahydrofuran.[9–13] Among these compounds,
1 | INTRODUCTION
The development of the global economy has led to the exces-
sive depletion of fossil resources and the further deterioration
of the environment, which has been paid much attention by
the world.[1] In the last few years, lignocellulosic biomass has
attracted strong interest due to its abundant, renewable, and
easily obtainable properties.[2] Consequently, the production
of biofuels and chemicals from lignocellulosic biomass
becomes an effective way to alleviate the energy crisis and
improve environmental issues.[3–5] Furfural (FF) can be pro-
duced from the lignocellulosic biomass through multistep
acid-catalyzed reactions, and has also been deemed as one of
the most significant biomass-derived platform molecules for
the synthesis of fine chemicals and liquids fuels.[6–8]
Hydrogenation of FF is a very interesting exploration idea
because many of its downstream products are value-added
FAOL is viewed as a very important compound, which has
wide applications in the manufacture of resins, lubricants,
adhesives, and synthetic fibers.[14]
With respect to the production of FAOL, it is normally
generated through chemoselective reduction of FF over vari-
ous homogeneous or heterogeneous catalysts. The industrial-
ized production of FAOL is mainly carried out from the
hydrogenation of furfural over copper chromate at high
hydrogen pressure.[8,15] It is clear that this catalyst is costly
and has carcinogenic chromium causing serious environ-
mental pollution. What is more, the high cost of hydrogen
transport and storage and its easy burning and explosiveness
are the key factors that must be considered in practical appli-
cations. Most of the production of FF occurs in China,
which provides cheap raw materials for downstream furan-
based products. With the rapid development of China's
chemicals,
such
as
furfuryl
alcohol
(FAOL),
© 2019 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2019;1–9.
http://www.jccs.wiley-vch.de
1

2
WANG ET AL.
economy, the amount of furan-based compounds increases
rapidly, and the market price of these substances is much
higher than that of FF. Therefore, it is very desirable to
improve the deep processing technology of FF to achieve
higher economic benefit.
Recently, catalytic transfer hydrogenation (CTH) of FF to
FAOL is of great interest to researchers. This process employs
inexpensive and abundant alcohol to avoid the large number
of problems caused by the use of hydrogen. For example, in
recent years, the application of Zr- and Hf-based catalysts to
CTH reaction has always been the focus, including Li-Zr-
BEA,[16] Hf-BEA,[17] PhP-Hf,[18] Zr-Has,[19] Zr-PhyA,[20]
ZrPN,[21] and Zr-FDCA-T[22] etc., which demonstrated good
catalytic performance. In addition, various metal oxides have
been discovered to catalyze the reduction of FF by hydrogen
transfer, such as MgAlOx,[23] La2O3,[24] and Al2O3.[25]
Although much effort has been devoted to this aspect of the
study, some disadvantages including low catalyst reactivity
and harsh reaction conditions remain. Based on the industrial
demand, it is very meaningful to develop cheap and efficient
catalysts in the conversion of FF to FAOL.
FIGURE 1 FT-IR spectra of LDHs with different Ni/Fe molar
ratios
2 | RESULTS AND DISCUSSION
2.1 | Characterization of catalysts
Since the last few years, the Zr- and Hf-based catalysts
have been widely reported for the reduction of the carbonyl
group, but the reports of other metals were few. Recently, a
series of Ni-based and Fe-based catalysts, such as NiO,[26]
Co/SBA-15,[27] γ-Fe2O3@HAP,[28] NiFe2O4,[29] Fe-L1/C-
800,[30] Fe(NiFe)O4-SiO2,[31] and NiFe/SiO2,[32] have been
applied to CTH of FF into FAOL. The catalysts prepared by
these metals with abundant reserves on the earth are of great
application value. Based on the above reports, we have stim-
ulated our enthusiasm for exploring non-noble-metal-based
catalyst systems.
Catalyst characterization methods can be seen in the Support
Information. The Fourier transform-infrared (FT-IR) spectra in
the 400–4,000 cm−1 range of the as-prepared catalysts are
included in Figure 1. A broad absorption band at around
3,460 cm−1 was attributed to the stretching vibration of the –
OH groups. The band at 1,625 cm−1 was assigned to the bend-
ing motion of interlayer water.[35] The absorption bands appe-
aring at 1,363 cm−1 and 834 cm−1 were assignable to the
asymmetric stretching mode and out-of-plane deformation
vibration of interlayer carbonate species.[36] The peaks at
800–400 cm−1 were due to metal oxygen vibrational modes
In this work, Ni-Fe LDHs with variable Ni/Fe molar ratios
were synthesized using a simple hydrothermal method. LDHs
3+
have the general formula [M1−x2+Mx (OH)2]x+ (An-)x/nꢁ
mH2O, where x ranges from 0.20 to 0.33 and M2+ and M3+
usually stand for divalent (Co, Ca, Mg, Cu, Ni, and Mn) and
trivalent (Fe, Al, and Cr) metallic cations, respectively.[33]
A
,
2−
is the interlayer anion of charge n, including CO32−, SO4
Cl−, and NO3 , etc.[34] Meanwhile, monometallic hydroxide
catalysts (Ni(OH)2 and Fe(OH)3) were obtained by means of
sedimentation. It was found that Ni-Fe LDHs with a Ni/Fe
molar ratio of 3:1 exhibited better catalytic activity for the
synthesis of FAOL through CTH reaction compared with the
other catalysts. The reasons for the different catalytic effects
were discussed in detail. The effects of reaction temperature,
reaction time, and the amount of catalysts on the conversion
of FF to FAOL were also investigated. Finally, the characteri-
zation of fresh and used catalysts was carried out, and the
possible reaction mechanism was proposed.
−
FIGURE 2 XRD patterns of LDHs with different Ni/Fe molar
ratios

WANG ET AL.
3
implying Ni–O, Fe–O, and Ni–O–Fe bonds in brucite-type
layers[37,38]
The powder XRD patterns of as-synthesized LDHs with
different Ni/Fe molar ratios are depicted in Figure 2, which
demonstrated clearly the characteristic diffraction peaks
corresponding to the hydrotalcite-like LDH family, that is,
(003), (006), (012), (015), (018), (110), and (113) at 2θ
values 11.26, 22.76, 34.28, 38.64, 45.84, 59.76, and 61.02ꢀ,
respectively. This value is consistent with the data reported
in other literature.[39] The layer spacings of the (003), (006),
and (012) crystal planes were 0.80, 0.40, and 0.27 nm,
respectively, and the multiple relationship of the lattice spac-
ing also shows that the hydrotalcites have a well-developed
layered structure. In addition, these crystal faces were sharp,
indicating that the hydrotalcite had a complete structure and
good crystallinity. It can be seen that impurity peaks of the
Ni–Fe (3/1) LDH were relatively less, indicating that its
crystallinity was better than others.
From Figure 3, it was shown that all the samples had simi-
lar thermal decomposition processes. Firstly, a small decrease
in the sample quantity of about 65ꢀC should be because of
the removal of residual ethanol in the layered structure. Then,
the second stage of weight loss in the temperature range from
100 to 200ꢀC was due to the loss of physically absorbed and
interlayer water. In the end, the decomposition stage occurred
in the range of 250–600ꢀC, which was attributed to the further
loss of water in the interlayer structure, the removal of inter-
layer carbonate anions, and the dehydroxylation of the Ni–Fe
LDHs.[40] This process results in the destruction of the layered
structure and the formation of bimetallic composite oxides
when heated to 600ꢀC. It proved that the Ni–Fe LDH cata-
lysts had pronounced stability at the reaction temperatures
(below 160ꢀC).
SEM was conducted to investigate the morphology of the
surface of Ni–Fe LDHs, and the images are presented in
Figure 4. SEM indicated that the Ni–Fe LDHs had a distinct
layered structure. It can be observed that the Ni–Fe (3/1)
LDH had better lamellar structures among the LDHs with
different Ni/Fe molar ratios. It was also found that the fine
granular aggregates were dispersed well on the nanoplates of
the Ni–Fe (3/1) LDH.
The porous properties of the Ni–Fe LDHs were analyzed
using the N2 adsorption–desorption method. As shown in
Figure 5, the N2 adsorption–desorption isotherms of the Ni–Fe
LDHs belong to type III according to the IUPAC classifica-
tion, indicating that the macroporous structure of the materials
existed. The results of the Brunauer–Emmett–Teller (BET)
surface area, pore volume, and average pore size are included
in Table 1. By comparison with the others, the Ni–Fe (3/1)
LDH has a larger pore volume and average pore diameter,
which is conducive to more sufficient contact between reac-
tants and the active center of the catalyst.[41]
FIGURE 3 Thermogravimetric curves of (a) Ni–Fe (2/1) LDH,
(b) Ni–Fe (3/1) LDH, and (c) Ni–Fe (4/1) LDH
According to previous reports,[42–44] acidic sites and
basic sites play synergistic catalytic roles in the CTH of car-
bonyl compounds. Therefore, the acidity and basicity of cat-
alysts were characterized by CO2-TPD and NH3-TPD
(Figure 6), respectively. Compared with others, it can be
seen that Ni–Fe (3/1) LDH had higher acidity and basicity.
First, the acidic sites (stemming from Ni2+ and Fe3+) and
the basic sites (originating from –OH) assist in the

4
WANG ET AL.
FIGURE 4 Representative SEM images of (a) Ni–Fe (2/1) LDH,
(b) Ni–Fe (3/1) LDH, and (c) Ni–Fe (4/1) LDH
FIGURE 5 Nitrogen adsorption–desorption curves and the
corresponding pore size distribution of (a) Ni–Fe (2/1) LDH, (b) Ni–Fe
(3/1) LDH, and (c) Ni–Fe (4/1) LDH
adsorption of 2-propanol onto Ni–Fe LDHs, resulting in the
formation of isopropoxide and hydride by dissociation.[40]
Furthermore, the carbonyl groups in the substrate molecules
were activated by acidic Ni2+ and Fe3+ species and are able
to generate a transition state with six links to accomplish the
hydrogen transfer route to yield corresponding alcohol com-
pounds and acetone.[26] From the above discussion it was
clear that the higher catalytic performance of Ni–Fe (3/1)
LDH was probably due to its high acid and base amount.

WANG ET AL.
5
TABLE 1 Textural properties of Ni–Fe LDHs
4, 5, and 6) and accorded well with the results of acidity and
basicity analysis.
Surface
area
Pore
Average pore
diameter
(nm)
LDH
volume
Entry material
(m2/g)
(cm3/g)
2.3 | Conversion of FF to FAOL by Ni–Fe
1
2
3
Ni–Fe (2/1)
Ni–Fe (3/1)
Ni–Fe (4/1)
188
164
179
0.70
0.74
0.62
3.4
5.6
4.9
(3/1) LDH
From what has been discussed above, Ni–Fe (3/1) LDH
showed the best catalytic performance in converting FF into
FAOL. Thus, it was used to study the conversion of FF into
FAOL. Furthermore, the influence of reaction parameters on
the conversion of FF to FAOL was also discussed.
2.4 | Effects of reaction temperature and
reaction time
The effects of reaction temperature and reaction time on the
synthesis of FAOL from FF were studied by varying the tem-
perature in the range between 120 and 150ꢀC and the time in
the range between 1 and 6 hr, and the results are shown in
Figure 7. It can be seen that the reaction temperature and reac-
tion time had a dramatic influence on the CTH reaction of
FF. For instance, only 26.7% of FAOL yield was achieved at
120ꢀC with a reaction time of 1 hr. However, 90.2% yield of
FAOL was obtained when the reaction was carried out at
140ꢀC after 5 hr, which indicated that high reaction tempera-
ture and long reaction time were beneficial to the production
of FAOL from FF at the beginning. During the experiments,
traces of side-product (2-[diisopropoxymethyl]furan) were
observed, which were generated by acetalization of FF and
2-propanol. Although increasing the reaction temperature to
150ꢀC or extending the reaction time to 6 hr can further pro-
mote conversion of FF, the yield of FAOL was almost con-
stant and the selectivity of FAOL was slightly lowered. This
was possibly due to the formation of a new by-product (2-[iso-
propoxy]methyl furan) at higher reaction temperature with a
longer reaction time, which could be formed by etherification
between FAOL and 2-propanol. Considering the energy input
in the reaction, 140ꢀC and 5 hr were thus selected as the most
appropriate reaction parameters under our reaction conditions.
FIGURE 6 NH3-TPD spectra (a) and CO2-TPD spectra (b) of
Ni–Fe LDHs
TABLE 2 The catalytic performance of various catalysts in the
CTH of FFa
Conversion Yield
Selectivity
(%)
Entry Catalysts
(%)
(%)
1
2
3
4
5
6
None
0
0
0
Ni(OH)2
Fe(OH)3
6.7
70.2
3.2
47.8
57.8
83.5
91.9
85.7
40.6
61.1
70.8
63.7
Ni–Fe (2/1) LDH 73.2
Ni–Fe (3/1) LDH 77.0
Ni–Fe (4/1) LDH 74.3
aReaction conditions: catalyst amount: 0.10 g; FF: 1 mmol; 2-propanol: 5 mL;
temperature: 140ꢀC; time: 5 hr.
2.2 | Conversion of FF to FAOL by various
catalysts
To select the most active catalyst, a series of catalysts were
applied in the CTH of FF to FAOL using 2-propanol as a
hydrogen donor, and the results are listed in Table 2. It
showed that the reaction did not proceed in the absence of
any catalyst (Table 2, entry 1). The conversion of FF was
negligible in the presence of Ni(OH)2 probably due to its
weak basicity (Table 2, entry 2).[42] Although Fe(OH)3 pro-
duced 70.2% conversion of FF, it had low selectivity to
FAOL (Table 2, entry 3). However, it was observed that the
LDH with a Ni/Fe molar ratio of 3:1 showed the best cata-
lytic activity among the LDHs with three different Ni/Fe
molar ratios, which revealed 77.0% conversion of FF and
70.8% yield of FAOL at 140ꢀC for 5 hr (Table 2, entries
FIGURE 7 Effect of reaction temperature and time on the FF
conversion and FAOL yield. Reaction conditions: Catalyst amount:
0.20 g, FF: 1 mmol, 2-propanol: 5 mL

6
WANG ET AL.
which may be principally attributed to more catalytic sites
promoting the generation of more by-products including
2-(isopropoxy)methyl furan and 2-(diisopropoxymethyl)
furan. Thus, the optimum catalyst amount of 0.20 g in this
work was used in subsequent research
2.6 | Effects of the solvent
We also studied the catalytic performance of the prepared
Ni–Fe (3/1) LDH for CTH of FF to FAOL in different sol-
vents, and the results are summarized in Table 3. It can be
seen that the structure of solvents plays a key role in the con-
version of FF and the yield of FAOL. No FAOL was
obtained when tert-Butanol was employed as the hydrogen
donor, which was ascribed to difficult form of the six-
membered ring structure in the MPV reaction process with-
out hydrogen atoms on the carbon atom (Table 3, entry 5). It
was clear that the primary alcohols, including methanol and
ethanol, gave poor yield of FAOL (Table 3, entries 1 and 2).
In contrast, 90.2% FAOL yield was obtained using 2-PrOH
as the solvent, and 87.7% FAOL yield was achieved using
2-BuOH as the solvent (Table 3, entries 3 and 4). It can be
seen that the secondary alcohols achieved better conversion
of FF and yield of FAOL than the primary alcohols, mainly
because the dehydrogenation of secondary alcohols is easier
than that of primary alcohols shown in previous studies.[45]
FIGURE 8 Effect of catalyst amount. Reaction conditions: FF:
1 mmol, 2-propanol: 5 mL, temperature: 140ꢀC, and time: 5 hr
TABLE 3 Effect of different solvents in the CTH of FFa
Entry
Solvent
FF conversion (%)
FAOL yield (%)
1
2
3
4
5
Methanol
Ethanol
32.8
67.8
97.0
94.5
0.7
3.6
49.4
90.2
87.7
0
2-propanol
2-butanol
tert-butanol
aReaction conditions: catalyst amount: 0.20 g; FF: 1 mmol; 2-propanol: 5 mL;
temperature: 140ꢀC; and time: 5 hr.
2.7 | Effects of various substrates
The versatility of the Ni–Fe (3/1) LDH catalyst was investi-
gated by CTH of several carbonyl compounds with various
structures, and the results are shown in Table 4. Compared
with other compounds, FF showed a higher activity owing
to a weaker steric effect (Table 4, entry 1). It is exciting that
the Ni–Fe (3/1) LDH catalyst has been proved to have a
higher than 90% selectivity of the target products. It can also
been seen that that the reaction of aldehydes is easier than
that of ketones, because of the steric effect and the electron
giving effect of alkyl in ketones[19,29]
2.5 | Effects of the catalyst amount
Figure 8 displays the influence of the Ni-Fe (3/1) LDH dos-
age on the conversion of FF to FAOL in 2-propanol at
140ꢀC in 5 hr. It was observed that the conversion of FF and
the yield of FAOL significantly increased when the amount
of catalyst increased from 0.05 to 0.20 g, which could be
due to more available catalytic sites. With an increment of
catalyst dosage from 0.20 to 0.25 g, the conversion of FF
increased, while the FAOL yield changes almost nothing,
TABLE 4 Catalytic transfer hydrogenation of different carbonyl compounds over Ni-Fe (3/1) LDHa
Entry
Substrate
Product
T (hr)
Conv. (%)
Yield (%)
Sel. (%)
1
5
97.0
90.2
93.0
2
8
80.2
73.2
91.3
3
4
5
10
8
78.1
84.3
70.2
72.2
78.8
63.4
92.4
93.5
90.3
8
Note. T: time; Con.: conversion: Sel: selectivity.
aReaction conditions: catalyst amount: 0.20 g; 2-propanol: 5 mL; temperature: 140ꢀC.

WANG ET AL.
7
FIGURE 9 Reusability of the catalyst. Reaction conditions:
Catalyst amount: 0.20 g, FF: 1 mmol, 2-propanol: 5 mL, and
temperature: 140ꢀC, time: 5 hr
FIGURE 11 TG curves (a), XRD pattern (b), FT-IR spectrum
(c), and SEM image (d) of Ni–Fe (3/1) LDH after five cycles
2.8 | Reusability and leaching of the catalyst
To examine the reusability of the Ni–Fe (3/1) LDH catalyst,
the catalyst was separated by centrifugation, washed with
isopropanol (3 × 10 mL) and dried in a vacuum oven at
80ꢀC for 6 hr before reuse. The catalytic activity of the used
catalyst was examined under the identical conditions. It was
found that the Ni–Fe (3/1) LDH catalyst could be repeatedly
used up to five cycles without any distinct loss in its cata-
lytic performance (Figure 9). Moreover, the leaching prop-
erty of the Ni–Fe (3/1) LDH catalyst was studied via
filtering the catalyst from the system after the reaction
proceeded for 3 hr at 140ꢀC, and no reaction took place even
after another 3 hr (Figure 10). Meanwhile, the used Ni–Fe
(3/1) LDH catalyst after five runs was characterized using
SCHEME 1 Possible reaction mechanism for the CTH of FF to
FAOL over Ni–Fe (3/1) LDH using 2-propanol as a hydrogen donor
TG, XRD, FT-IR, and SEM (Figure 11). The results
suggested that the structure and properties of the Ni–Fe (3/1)
LDH catalyst went through slight change after being reused
for five cycles. Therefore, the as-synthesized catalyst Ni–Fe
(3/1) LDH was stable under the studied reaction conditions.
2.9 | Reaction mechanism
On the basis of the above discussion, we put forward a plau-
sible reaction mechanism for the CTH of FF to FAOL over
Ni–Fe (3/1) LDH (Scheme 1), which is consistent with pre-
vious studies.[18,22,26,29] We considered the synergistic effect
of acidic sites (resulting from Ni2+ and Fe3+) and basic sites
(originating from –OH) of Ni–Fe (3/1) LDH in CTH of FF
to FAOL. First, 2-propanol was adsorbed on the Ni–Fe (3/1)
LDH and interacted with the acidic sites (Ni2+ and Fe3+
)
and basic sites (–OH) on the catalyst, causing it to dissociate
into the corresponding alkoxide and protons.[18,22] Subse-
quently, the carbonyl group of furfural may be activated by
the acidic site to form a transitional state with six links.[26,29]
Finally, the system can obtain free furfural alcohol and
FIGURE 10 Leaching of the catalyst. Reaction conditions:
Catalyst amount: 0.20 g, FF: 1 mmol, 2-propanol: 5 mL, and
temperature: 140ꢀC

8
WANG ET AL.
acetone by hydrogen transfer. During the reactions, some
by-products including 2-(isopropoxy)methyl furan and
2-(diisopropoxymethyl)furan could be generated by the
etherification of FAOL with 2-propanol and the acetalization
of FF with 2-propanol, respectively.
3.4 | Catalytic reactions
Catalyst characterization methods can be seen in the Support
Information. The activity of the synthesized catalyst was
detected by catalytic transfer hydrogenation of furfural. In a
typical run, furfural (1 mmol), catalyst (0.2 g), and iso-
propanol (5 mL) were introduced into the 25 mL Teflon
lined stainless steel autoclave. The reaction was carried out
using magnetic stirring and heating at suitable temperatures
for a desired time. After cooling the reactor to room temper-
ature, the resulting liquid samples were collected and ana-
lyzed quantitatively by gas chromatography (GC 9790II)
using naphthalene as the internal standard, and the identifi-
cation of the products was done by GC–MS (GCMS-
QP2010Ultra). The yield of FAOL, the conversion of FF,
and the selectivity to FAOL were calculated based on the
following formula
3 | EXPERIMENTAL
3.1 | Materials
Furfuryl alcohol was purchased from Aladdin Reagent
Co. Ltd. (Shanghai, China). Nickel nitrate hexahydrate, iron
nitrate hydrate, urea, ammonia water, furfural, 2-propanol,
and other chemicals were supplied by Sinopharm Chemical
Reagent Co. Ltd. (Shanghai, China). All reagents were of
analytical grade and used without further purification.
Deionized water was produced by using a laboratory water-
purification system (RO DI Digital plus).
Final moles of FAOL
Initial moles of FF
Yield of FAOLð%Þ =
× 100
ð1Þ
ð2Þ
3.2 | Preparation of Ni–Fe LDHs
The Ni–Fe–LDHs with different Ni/Fe molar ratios were
synthesized using the hydrothermal method based on previ-
ous literature,[45,47] although some changes have been made
here. Briefly, Ni(NO3)2ꢁ6H2O (6, 9, and 12 mmol) and
Fe(NO3)3ꢁ9H2O (3 mmol) and a certain amount of urea were
dissolved in 160 mL deionized water, in which the amount
of urea is 3.3 times that of the total metal ion concentration.
The mixture was magnetically stirred at room temperature
for 1 hr and transferred to a 180 mL Teflon-lined stainless-
steel autoclave for hydrothermal reaction at 140ꢀC for 20 hr
under autogenous pressure. The reactor was then naturally
cooled down to room temperature. The product was washed
with deionized water and anhydrous ethanol several times
by suction filtration, and dried in a vacuum oven at 60ꢀC
overnight to obtain a Ni–Fe–LDHs composite, which was
ground and put into a desiccator for use. The prepared mate-
rials were denoted as Ni–Fe (2/1) LDH, Ni–Fe (3/1) LDH,
and Ni–Fe (4/1) LDH.
Conversion of FFð%Þ
Initial moles of FF−Final moles of FF
=
× 100
× 100
Initial moles of FF
Selectivity to FAOLð%Þ
Final moles of FAOL
Initial moles of FF−Final moles of FF
ð3Þ
=
4 | CONCLUSIONS
In summary, the Ni–Fe (3/1) LDH catalysts were synthesized
using a simple hydrothermal method and were employed in
catalytic transfer hydrogenation of FF to FAOL using iso-
propanol as a H-donor. The catalysts could be reused for up
to five consecutive runs without a distinct loss in catalytic
activity. The remarkable catalytic performance was attributed
to the synergistic effect of acidic sites (Ni2+ and Fe3+) and
basic sites (–OH) of the catalyst. What is more, the Ni–Fe
(3/1) LDH catalysts could be applied to the catalytic transfer
hydrogenation of other aldehydes and ketones.
3.3 | Preparation of Fe(OH)3 and Ni(OH)2
In a general synthetic run, Fe(NO3)3ꢁ9H2O was dissolved in
deionized water to prepare a 0.25 M solution. Ammonia water
(25–28 wt%) was slowly added to adjust the solution pH value
around 9 with vigorous stirring, and then the resulted suspen-
sion was aged at room temperature for 24 hr. Finally, the pre-
cipitate was isolated by centrifugation, washed with deionized
water several times, and dried overnight at 80ꢀC. The same
process was used in the preparation of Ni(OH)2.
ACKNOWLEDGMENTS
This work was financial supported by the Ministry of Educa-
tion of the People's Republic of China & SAFEA for the
111 Project (B13025).

WANG ET AL.
9
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ORCID
Haijun Wang https://orcid.org/0000-0003-2857-5861
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SUPPORTING INFORMATION
Additional supporting information may be found online in
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How to cite this article: Wang T, Hu A, Wang H,
Xia Y. Catalytic transfer hydrogenation of furfural
into furfuryl alcohol over Ni–Fe-layered double
hydroxide catalysts. J Chin Chem Soc. 2019;1–9.
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