Magnetic nickel ferrite nanoparticles as highly durable catalysts for catalytic transfer hydrogenation of bio-based aldehydes

Article abstract of DOI:10.1039/c7cy02197f

Magnetic nickel ferrite (NiFe₂O₄) nanoparticles were exploited as stable and easily separable heterogeneous catalysts for catalytic transfer hydrogenation (CTH) of furfural to furfuryl alcohol with 2-propanol as both the hydrogen source and the solvent providing 94% product yield at 180 °C after 6 h of reaction. The magnetic properties of the catalysts provided facile recovery using an external magnet after reaction allowing it to be reused in five reaction cycles without loss of catalytic performance. Importantly, the NiFe₂O₄ nanoparticles were also applicable to CTH of other alkenyl/allyl/aromatic aldehydes affording over 94% selectivity towards the targeted alcohol products, thus being attractive as highly universal catalysts for CTH of aldehydes.

Full text of DOI:10.1039/c7cy02197f

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PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
rsc.li/catalysis

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Magnetic nickel ferrite nanoparticles as highly durable catalyst for
catalytic transfer hydrogenation of bio-based aldehydes
a,b
b,
a,
Jian He, Song Yang * and Anders Riisager *
a
Centre for Catalysis and Sustainable Chemistry, Department of Chemistry, Technical
University of Denmark, DKꢀ2800 Kgs. Lyngby, Denmark.
b
State Key Laboratory Breeding Base of Green Pesticide & Agricultural
Bioengineering, Key Laboratory of Green Pesticide & Agricultural Bioengineering,
Ministry of Education, StateꢀLocal Joint Laboratory for Comprehensive Utilization of
Biomass, Center for Research & Development of Fine Chemicals, Guizhou University,
Guiyang 550025, PR China.
2 4
Abstract: Magnetic nickel ferrite (NiFe O ) nanoparticles were exploited as stable
and easily separable heterogeneous catalyst for catalytic transfer hydrogenation (CTH)
of furfural to furfuryl alcohol with 2ꢀpropanol as both hydrogen source and solvent
providing 94% product yield at 180 °C after 6 h of reaction. The magnetic property of
the catalyst provided facile recovery by an external magnet after reaction allowing it
to be reused in five reaction cycles without loss of catalytic performance. Importantly,
2 4
the NiFe O nanoparticles was also applicable to CTH of other alkenyl/allyl/aromatic
aldehydes affording over 94% selectivity towards the targeted alcohol products, thus
being attractive as a highly universal catalyst for CTH of aldehydes.
Keywords: Furfural; catalytic transfer hydrogenation; magnetic catalyst; biomass
valorization; MeerweinꢀPonndorfꢀVerley reduction.
1

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1
Introduction
Upgrading of biomassꢀderived platform chemicals to bioꢀfuels and valueꢀadded
chemicals has received extensive interest as a mean to link biomass to a renewable
chemical industry where the dependence on our fossil resources can be reduced [1ꢀ4].
Furfural (FF) is generated from the dehydration of biomassꢀbased C5ꢀcarbohydrates
via acid catalysis, and is hailed as one of the most versatile and promising building
block chemicals for the synthesis of liquid bioꢀfuels and fine chemicals [5,6].
Hydrogenation of FF is an interesting route for FF upgrading since many of the
attainable products are important intermediate and specialty chemicals, including
furfuryl alcohol (FAOL), tetrahydrofurfuryl alcohol, 2ꢀmethylfuran and
2ꢀmethyltetrahydrofuran (Scheme 1) [7,8]. Particularly, the selectivity hydrogenation
of FF to FAOL is of great significance because FAOL not only widely apply in the
manufacture of resins, lubricants, adhesives and synthetic fibers, but also bridge the
gap between biomassꢀbased C5ꢀcarbohydrates and downstream furanic products and
important platform molecule (e.g., levulinic acid and γꢀvalerolactone) (Scheme 1)
[
9ꢀ11].
O
[H]
[H]
OH
O
O
H+
O
H+
[H]
O
[H]
O
OH
OH
Hemicellulose
OH
OH
FAOL
FF
OH
O
[H]
[H]
Xylose
H+
O
O
[H]
O
O
R
O
Levulinic acid or its ester
Gammeꢀvalerolactone
R=H, CH , CH CH , et al.
3
2
3
Scheme 1. Tandem production of FAOL from biomassꢀderived carbohydrates and
upgrading of FAOL to other platform chemicals.
Lately, several strategies have been explored and significant advances achieved for
efficient catalytic hydrogenation of FF to FAOL using hydrogen gas as Hꢀdonor
[
12ꢀ18]. Nevertheless, some drawbacks persist such as high cost base (e.g., noble
2

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2
metal catalysts, special facilities for storage and transportation of H ), handling
complexity (e.g., elimination of air and inflation of H to reactor) and safetyꢀrelated
2
2
issues associated to the flammable and explosive nature of H [19,20] making it less
applicable for smallerꢀscale processes in particular. Furthermore, it is challenging to
selectivity hydrogenate FF to FAOL with H owing to its multiꢀfunctionalities, which
2
often results in byproduct formation from further hydrogenation of FAOL under the
typically applied reaction conditions [21]. Catalytic transfer hydrogenation (CTH) is
an alternative hydrogenation strategy where formic acid, alcohols or hydrazine
hydrate are employed instead of H
circumventing most of the described shortcomings resulting from handling H
19]. The CTH process with alcohols rely on MeerweinꢀPonndorfꢀVerley (MPV)
2
as Hꢀdonor. CTH is attractive since it allows
2
gas
[
reduction, where carbonyl compounds are selectivity reduced to the corresponding
hydroxyl compounds [22]. The dual role of the alcohol as solvent and Hꢀdonor,
combined with the abundant, inexpensive and easily storable properties of alcohols,
has encouraged the use of CTH with biomassꢀderived molecules [23ꢀ29]. Although,
an excessive use of alcohol is necessary in CTH, the solvent (unꢀoxidized alcohol)
and the formed carbonyl products may be separated by distillation and reused [22].
Heterogeneous catalysts are generally preferred compared to homogeneous catalysts
in liquidꢀphase reactions due to their ease of separation and durability. In this context,
catalysts with magnetic properties are especially interesting, since an external magnet
easily separates them from a reaction mixture. For applied use, this operation is
timesaving and energyꢀefficient compared to conventional centrifugation and
filtration techniques often applied in heterogeneous catalysis [30ꢀ32]. Moreover,
magnetic separation caters economical, efficient, practical and environmentalꢀfriendly
features, which are significant factors for largeꢀscale production [33]. Despite the
potential, exploitation of magnetic catalysts for CTH of FF is only very recently
reported [34].
II III
Ferrites with the general formula M Fe
2 4
O (M = Fe, Co and Ni) are common,
magnetically and structurally stabile materials that are wellꢀknown in heterogeneous
catalysis [35]. Typically, the materials are used as catalyst carriers in the form of
3

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nanoparticles and not as the catalytic entity themselves [36ꢀ38], however some
pioneering work has been done with Fe O nanoparticles in organic synthesis for the
3
4
coupling of aldehydes, alkynes and amines [39] and for synthesis of xanthene
derivatives [40]. Utilization of magnetic nanoparticles as magnetically recoverable
catalyst has, to the best of our knowledge, not been reported for CTH of
biomassꢀderived FF. Hence, in continuation of our research work with CTH of
biomassꢀderived molecules we here report that CTH of FF to FAOL with commercial
3 4 2 4 2 4
nanoparticle ferrites (Fe O , CoFe O and NiFe O ) proceed with high selectivity (>
9
0%). Moreover, we demonstrate for the first time that NiFe O nanoparticles provide
2 4
very high catalytic activity in the CTH of FF to FAOL, and that the excellent
performance applies to other aldehyde substrates as well. Combined with the great
potential of ferrites in industrial application, we anticipate that the results open new
possibilities for exploring practical, environmental, recoverable and durable materials
catering to commercial exploitation in biomass valorization.
2
Experimental
2.1 Materials
Furfuryl alcohol (98%, FAOL), 5ꢀmethylfurfural (99%), 2ꢀpropanol (99.5%),
methanol (≥99.8%), ethanol (99.5%), 1ꢀbutanol (≥99.5%), acetone (≥99%),
naphthalene (>99%, internal standard), benzaldehyde (>99%), benzyl alcohol (≥99%),
4
3
ꢀmethoxybenzaldehyde
(98%),
4ꢀmethoxybenzyl
alcohol
(98%),
,4ꢀdimethoxybenzaldehyde (99%), 3,4ꢀdimethoxybenzyl alcohol (96%), heptanal
(
(
(
≥95%), βꢀcitronellol (95%), cinnamic alcohol (98%), 2,4,6ꢀtrimethylbenzaldehyde
98%), 2,4,6,ꢀtrimethylbenzyl alcohol (99%), Fe (≥98%, <50 nm particle size
TEM)), NiFe O (≥98%, <50 nm particle size (APS)) and CoFe O (≥99%, ~30 nm
3
O
4
2
4
2
4
particle size (TEM)) were purchased from SigmaꢀAldrich. Furfural (≥99%),
nꢀpropanol (≥99.5%), 2ꢀbutanol (≥99.5%), tertꢀbutyl alcohol (≥99.7%), butenal
(>99%), 2ꢀbutenꢀ1ꢀol (≥95%), nꢀheptanol (>99%) and (±) citronellal (90%) were
purchased from Fluka. 5ꢀMethylfuranꢀ2ꢀmethanol (≥95%) was procured from
4

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Bepharm Ltd and cinnamaldehyde (>98%) was provided by Merck. All chemicals
were used as received.
2.2 Characterization
Xꢀray diffraction (XRD) patterns in the range of 2θ = 5ꢀ80° were collected using a
Huber G670 diffractometer with Cu Kα radiation. Nitrogen adsorption/desorption
measurements were conducted at ꢀ196 °C using a Micromeritics ASAP 2020 porosity
analyzer. The samples were heated at 200 °C for 4 h under vacuum before the N
2
physisorption measurements. Thermogravimetric (TG) analysis were performed on a
Mettler Toledo thermal analyzer under air flow (30 mL/min) from 25ꢀ600 °C (heating
3 2
rate 10 °C/min). Temperatureꢀprogrammed desorption (TPD) of NH and CO were
carried out on a Micromeritics AutoChem II 2920 apparatus to evaluate the total
acid/base amount of catalysts. Initially, the samples were dried at 300 °C for 1 h under
helium flow (25 mL/min), then cooled to 50 °C followed by subjecting to a gas flow
(
15 mL/min) of NH /He or CO /He (v/v = 1/9). Subsequently, the redundant and
3 2
physically adsorbed NH
mL/min). Afterward, the temperature was raised to 600 °C (heating rate 10 °C/min) to
record the chemically adsorbed NH or CO . The magnetic property of the ferrites
was evaluated using a QuantumꢀDesign MPMSꢀXL SQUID magnetometer at 17 °C.
3 2
or CO were removed by purging with a He flow (25
3
2
2.3 Catalytic transfer hydrogenation (CTH)
CTH of aldehydes was performed in a 50 mL stainless steel autoclave with magnetic
stirring (900 rpm). In a typical run, 0.1922 g (2 mmol) FF, 0.06 g (0.26 mmol, based
on metal) catalyst and 0.04 g naphthalene (internal standard) were mixed in 10 mL
2ꢀpropanol in the autoclave. The reactor was then heated to a specified temperature
(120ꢀ180 °C) for a desired reaction time (0.5ꢀ8 h) without inter gas purging
establishing an autogenic pressure of about 3.5, 9 and 16 bar at 140, 160 and 180 °C,
respectively. After reaction, the reactor was immersed into iceꢀcold water to quench
the reaction. For recycling experiments, the catalyst was collected by virtue of using
an external magnet, washed twice (2 × 5 mL) with ethanol and acetone, dried at 80 °C
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for 2 h and subsequently used for the next reaction run.
The products in the reaction mixture was identified and quantified by GCꢀMS
Agilent 6850ꢀ5975C) and GC (Agilent 6890N equipped with a FID detector),
(
respectively, using HPꢀ5MS capillary columns (30.0 m × 250 ꢁm × 0.25 ꢁm) in both
apparatus. The FF conversion and FAOL yields were calculated on basis of standard
curves of reference compounds with naphthalene as internal reference. The CTH
protocol with other aldehydes was the same as for FF except that 1 mmol reactant was
used instead.
3
Results and Discussion
3.1 Catalytic performance of different ferrites
Table 1 compiles the catalytic performances measured of different ferrites
nanoparticles in the CTH of FF to FAOL using 2ꢀpropanol as Hꢀdonor.
Autoꢀhydrogenation of FF at 180 °C without catalyst gave a negligible yield of FAOL
with a low FAOL selectivity of 17% after 4 h of reaction (entry 1, Table 1). In contrast,
all the ferrites afforded high FAOL selectivity (>91%) at 180 °C demonstrating that
the materials were efficient catalysts for CTH of FF to FAOL at this temperature.
Notably, NiFe O revealed high FF conversion (95%) as well as high FAOL yield
2
4
(
90%) at 180 °C after 4 h of reaction (entry 13, Table 1) in contrast to Fe
3
O
4
and
this
CoFe under the same conditions (entries 5 and 9, Table 1). For NiFe O
2
O
4
2
4
ꢀ1
ꢀ1
corresponded to a high initial formation rate of FAOL (456 ꢁmol g min ) as well as
ꢀ3
ꢀ1
a firstꢀorder reaction rate constant (11.5·10 min ) that was 3.9 and 2.7 times higher
than the corresponding rate constants of Fe and CoFe , respectively (Table 1,
3
O
4
2 4
O
Table S1 and Figure S1). Notably, a similar reactivity trend was also reported for
Raney Ni and Co in CTH of aromatic alcohols using 2ꢀpropanol as Hꢀdonor [41].
Raney Ni are known to be an efficient catalyst for CTH reactions in 2ꢀpropanol
[
42,43], however the active sites of Ni(0) are easily oxidized in air making the catalyst
inconvenient to use compared to Niꢀferrite. The excellent performance of NiFe O4
2
was probably attributed to it high acid and base amount (Table 1 and Figure S2), as it
6

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is well known that acidꢀbase sites are crucial for the CTH reaction based on MPV
reduction [44ꢀ46]. Based on the interesting initial results the catalytic behavior of
NiFe
2
O
4
was hereafter more systematically investigated.
a
Table 1. The catalytic performance of different ferrites in the CTH of FF
Entry Catalyst
Time
FF
FAOL
yield
(%)
4
Sel.
(%)
Acid/base
amount
FAOL initial
formation rate
Reaction
(
h)
conv.
rate const.
b
ꢀ1
ꢀ1
c
ꢀ1
d
(
%)
(mmol/g)
(ꢁmolg min )
(min )
1
2
3
4
5
6
7
8
9
ꢀ
4
24
21
29
44
57
33
42
60
73
43
60
74
95
17
91
97
93
95
94
98
95
97
95
93
96
95
ꢀ
ꢀ
ꢀ
ꢀ
3
Fe
3
O
4
0.5
1
19
0.215/0.047
211
2.9·10
28
2
41
4
54
ꢀ
3
CoFe
2
O
4
0.5
1
31
0.380/0.074
0.501/0.109
344
4.3·10
41
2
57
4
71
ꢀ
3
10
NiFe
2
O
4
0.5
1
41
456
11.5·×10
1
1
2
3
56
1
1
2
71
4
90
a
b
Reaction conditions: 2 mmol FF, 10 mL 2ꢀpropanol, 0.06 g catalyst, 180 °C. Evaluated by
c
d
3 2
NH /CO ꢀTPD. Calculated from the FAOL yield obtained after 0.5 h. Calculated assuming first order
reaction kinetics: ꢀln(1ꢀX)] = kt + C, where X = FF conversion and t = 30, 60, 120 and 240 min.
3
.2 Effect of reaction temperature and time
Figure 1 displays the influence of reaction temperature and reaction time on the CTH
of FF to FAOL in 2ꢀpropanol over NiFe nanoparticles (0.06 g). In general,
NiFe yielded excellent selectivity of about 90% at all examined temperatures (i.e.,
20, 140, 160 and 180 °C), implying that NiFe was a highly selectivity catalyst for
2
O
4
2
O
4
1
2 4
O
the formation of FAOL, whereas the activity was very temperature dependent. Thus,
at 120 °C the FF conversion and FAOL yield increased only moderately with reaction
time reaching 51 and 49%, respectively, after a reaction time of 8 h (Figure 1a). In
contrast, near quantitative FF conversion of 99% and FAOL yield of 94% was
obtained after 6 h at 180 °C (Figure 1d). Throughout the experiments, minute amount
of 2ꢀ(diisopropoxymethyl)furan and 2ꢀisopropoxyfuran were observed as revealed
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from GCꢀMS analysis, which resulted from acetalization of furfural with 2ꢀpropanol
and etherification of furfuryl alcohol with 2ꢀpropanol, respectively. Reaction rate
constants (k) at the different temperatures was obtained by plotting –ln(1ꢀX) versus
reaction time assuming that the FF conversion was a pseudoꢀfirstꢀorder reaction
(
Figure 2a and Table S2). From these values the activation energy (E ) of CTH of FF
a
2 4
to FAOL over NiFe O in 2ꢀpropanol was evaluated from an Arrhenius plot (Figure 2b)
to be 48.2 kJ/mol (Table S2). This value was close or slightly lower than values
reported in literature for CTH of FF with other catalyst systems (Table S1) [26,28,34],
2 4
confirming the remarkable catalytic activity of NiFe O .
8

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Figure 1. Synthesis of FAOL from FF over NiFe O at (a) 120 °C, (b) 140 °C, (c)
2
4
160 °C and (d) 180 °C from 0.5ꢀ8 h of reaction. Reaction conditions: FF (2 mmol),
NiFe (0.06 g), 2ꢀpropanol (10 mL).
2
O
4
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Figure 2. (a) –ln(1ꢀX) vs. reaction time and (b) ln(k) vs. reciprocal of reaction
temperature in CTH of FF over NiFe . Reaction conditions: FF (2 mmol), catalyst
2
O
4
(0.06 g), 2ꢀpropanol (10 mL), t = 0.5ꢀ4 h.
3.3 Effect of various alcohols as H-donors
The catalytic performances obtained with NiFe O for CTH of FF to FAOL in
2
4
different C2ꢀC4 alcohols are summarized in Table 2. Notably, above 93% FAOL
selectivity was obtained in both primary (entries 1ꢀ3, Table 2) and secondary alcohols
(entries 4ꢀ5, Table 2), whereas almost no FAOL was formed in the case of tertiary
alcohol (entry 6, Table 2). The latter result was not surprising considering that
1
0

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tertꢀbutanol has no hydrogen atom on the carbon atom with the hydroxyl group
available to form a sixꢀmembered ring intermediate from FF and tertꢀbutanol on the
surface of the catalyst, which is a key step in the hydrogenꢀtransfer process of the
MPV reduction [24,44ꢀ46]. Moreover, the secondary alcohols gave better FF
conversion than the primary alcohols, which is associated to the lower reduction
potential of secondary alcohols compared to primary alcohols as also demonstrated in
earlier studies [47,48].
a
2 4
Table 2 CTH of FF to FAOL over NiFe O using various alcohols as Hꢀdonors
Entry
Alcohol
Ethanol
Conversion (%)
Yield (%)
Selectivity (%)
1
2
3
4
5
6
67
48
51
99
96
8
64
45
48
94
91
2
96
94
94
95
95
25
1ꢀPropanol
1ꢀButanol
2ꢀPropanol
2ꢀButanol
tertꢀButanol
a
2 4
Reaction conditions: FF (2 mmol), NiFe O (0.06 g), solvent (10 mL), 180 °C, 6 h.
3
.4 Effect of catalyst dosage and hot filtration experiment
As depicted in Figure 3a, the FAOL yield obtained from CTH of FF at 180 °C after 6
h of reaction was almost negligible without added NiFe catalyst. In contrast, a
small amount of NiFe (i.e., 0.02 g) gave 80% FF conversion along with 72%
2
O
4
2 4
O
FAOL yield. When the catalyst amount was further increased to 0.06 g the FF
conversion reached 99% and the FAOL yield 94%, while only a marginal variation in
FAOL yield was observed with more catalyst added, suggesting that the optimal
catalyst dosage under the examined conditions were 0.06 g in terms of FAOL yield. In
addition, the effect of stirring speed on the CTH of FF to FAOL over the magnetic
2 4
NiFe O catalyst was also evaluated (Table S4). Only slightly lower FF conversion
and FAOL yield were observed when the stirring speed was decreased to 600 rpm,
while a considerable decrease in FAOL yield was detected when the stirring speed
was increased to 1200 rpm, indicating that too high stirring speed was not
advantageous with the magnetic catalyst.
1
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2 4
The heterogeneity of NiFe O during the CTH process was rationalized by conducting
a hot filtration experiment, wherein the catalyst was removed from the reaction
mixture via an external magnet after the reaction had proceeded at 180 °C for 1 h.
Afterwards, the reaction mixture was allowed to react for another 7 h under the same
conditions. The data in Figure 3b clearly shows that the FAOL yield remained
unchanged around 56% after the catalyst removal, indicating that the NiFe
stable with no active species leaching from the catalyst during the reaction.
2 4
O was
Figure 3. Influence of catalyst dosage on the CTH of FF to yield FAOL (a) and
timeꢀyield plots after catalyst removal after 1 h (b). Reaction conditions: FF (2 mmol),
2 4
NiFe O (0.06 g), 2ꢀpropanol (10 mL), 180 °C.
1
2

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3.5 Catalyst reusability
The reusability of NiFe O in CTH of FF was examined under reaction conditions
2
4
resulting in both low FF conversion (180 °C, 1 h; Figure 4a) and high conversion at
optimal reaction conditions (180 °C, 6 h; Figure 4b). As exhibited in Figure 4, no
significant decline in FF conversion or FAOL yield occurred during five consecutive
reaction cycles at both of the examined conditions, thus demonstrating NiFe
form an apparently highly durable CTH catalyst system. To verify durability of the
catalyst, the NiFe recovered after CTH at 180 °C for 6 h was further characterized
by XRD, TG, N ꢀphysisorption and SQUID analysis. The XRD analysis (Figure 5a)
2 4
O to
2
O
4
2
revealed no crystallographic change of the spent catalyst compared to the fresh
catalyst. Similarly, the saturation magnetization of the spent and fresh catalyst was
almost identical (Figure 5c). A slight increment of 2.3% in total weight loss (Figure 5b)
2
and a small decline ~8.1 m /g (Figure S3) in surface area was, however observed for
the spent catalyst compared to the fresh catalyst. These observations confirm that
NiFe O indeed was a highly durability catalyst with only traces of carbon residue
2
4
deposited on the surface. The high resistance for carbon residue deposition could arise
from the magnetism of the material as previously suggested [49].
1
3

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Figure 4. Recycling tests of NiFe
2
O
4
in the CTH of FF to FAOL at 180 °C for (a) 1 h
(0.06 g), 2ꢀpropanol (10 mL).
and (b) 6 h. Reaction conditions: FF (2 mmol), NiFe
2
O
4
1
4

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Figure 5. XRD pattern (a), TG curve (b) and magnetization curve (c) of fresh and
spent NiFe catalyst.
2
O
4
3.6 Substrate scope
The substrate scope of the CTH reaction system with NiFe
2
4
O was extended from FF
to several alternative aldehydes to demonstrate the versatility of the system towards
substrates contained in, e.g. biomassꢀderived bioꢀoils [50] (Table 3). Interestingly,
NiFe
with all of the alternative aldehydes in above 94% selectivity, and – importantly ꢀ over
0% conversion was achieved with both saturated and unsaturated (i.e., alkenyl, allyl
or aromatic) aldehydes (entries 1ꢀ4, 6 and 8, Table 3) under optimized reaction
2 4
O proved also to be a very efficient CTH catalyst forming the targeted products
9
1
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conditions. However, in the case of 2,4,6ꢀtrimethylbenzaldehyde (entry 5, Table 3)
and citronella (entry 7, Table 3) low to moderate conversion was observed even at
high temperature (i.e., 200 °C), which was probably attributed to the steric bulkiness
of the substrates hampering the reaction at the surface of the NiFe
2 4
O particles. Hence,
good universality for CTH of many aldehydes combined with excellent product
selectivity and ease of recyclability makes the NiFe
attractive for further exploration.
2
O
4
nanoparticle catalyst system
a
2 4
Table 3 CTH of other aldehydes over NiFe O catalyst
Temperature
°C)
Time
(h)
Conversion
(%)
Yield
(%)
Selectivity
(%)
Entry
Substrate
Product
(
1
2
3
4
5
6
180
180
180
180
200
180
6
2
3
6
6
6
92
99
95
91
27
94
88
96
93
89
26
91
96
97
98
98
96
97
7
8
200
180
6
3
76
92
74
87
97
95
a
2 4
Reaction conditions: Substrate (1 mmol), NiFe O (0.06 g), 2ꢀpropanol (10 mL).
4
Conclusions
2 4
Commercial available NiFe O nanoparticles are demonstrated to be a highly efficient
catalyst in the CTH of FF to FAOL using 2ꢀpropanol as Hꢀdonor and solvent,
affording 99% FF conversion with 95% FAOL selectivity at 180 °C with a reaction
time of 6 h. The excellent CTH performance was associated to a relatively low
activation energy (∼48.2 kJ/mol) as calculated from the Arrhenius equation assuming
1
6

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DOI: 10.1039/C7CY02197F
2 4
firstꢀorder kinetics. Moreover, the NiFe O nanoparticle catalyst was stable and
durable under the applied CTH reaction conditions with FF as revealed from a hot
filtration experiment and reuse in five consecutive reactions with facile separation of
the magnetic NiFe
2 4
O nanoparticles by an external magnet. Importantly, the versatility
of the NiFe O nanoparticles for CTH was further verified with other
2
4
aromatic/allyl/alkenyl aldehydes in 2ꢀpropanol, which all yielded high selectivity
2 4
>94%) for the targeted alcohol products. In perspective, it is anticipated that NiFe O
(
nanoparticles could be established as a prominent catalyst not only for CTH of FF to
FAOL, but also exploited as a highly efficient heterogeneous catalyst for CTH of
biomassꢀderived molecules in general.
Acknowledgement
We thank Prof. J. Bendix, Department of Chemistry, University of Copenhagen, for
measurement of the magnetization data. J.H. is grateful to the Chinese State
Scholarship Fund (No. 201606670008) and the National Natural Science Foundation
of China (No. 21576059 and 21666008) for financial support of the work.
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Graphical abstract
2 4
Effective use of magnetic nanoparticles: Commercial nickel ferrite (NiFe O )
nanoparticles are efficient, durable and magnetically recoverable heterogeneous
catalysts for catalytic transfer hydrogenation of biomass-derived furfural as well as
other aldehydes with 2-propanol as H-donor forming furfuryl alcohol and various
aromatic/allyl/alkenyl alcohols, respectively, which are precursors for bio-fuels and
fine chemicals.