Hierarchically constructed NiO with improved performance for catalytic transfer hydrogenation of biomass-derived aldehydes

Article abstract of DOI:10.1039/c8cy02536c

A 3D nano-/micrometer-scaled NiO material with urchin-like structure was prepared via a facile, green synthesis route, and served as a highly efficient and durable catalyst for catalytic transfer hydrogenation (CTH) of bio-based furfural (FF) to furfuryl alcohol (FAOL) using 2-propanol as H-donor and solvent. The as-prepared NiO possessed a good active-site accessibility owing to a high surface area and large amount of acid-base sites, resulting in high FF conversion of 97.3% with 94.2% FAOL yield at 120 °C and 3 h of reaction, which was a superior catalytic performance compared to commercial NiO nanoparticles. Besides, the excellent catalytic performance of the sea urchin-like NiO was validated for gram-scale FAOL synthesis, and recyclability test confirmed the catalyst to be reusable for multiple reaction runs without significant activity loss after intermediary calcination in air. Notably, the introduced catalytic system was also applicable to CTH of alternative bio-derived aldehydes.

Full text of DOI:10.1039/c8cy02536c

View Article Online
View Journal
Catalysis
Sc ience &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. He, M. R.
Nielsen, T. W. Hansen, S. Yang and A. Riisager, Catal. Sci. Technol., 2019, DOI: 10.1039/C8CY02536C.
Volume 6 Number 1 7 January 2016 Pages 1–308
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
www.rsc.org/catalysis
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
author guidelines.
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, outlined
in our author and reviewer resource centre, 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 2044-4753
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
rsc.li/catalysis

Page 1 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
Hierarchically constructed NiO with improved performance for
catalytic transfer hydrogenation of biomass-derived aldehydes
a,b
c
c
b,
Jian He , Monia Runge Nielsen , Thomas Willum Hansen , Song Yang *, Anders
a,
Riisager *
a
Centre for Catalysis and Sustainable Chemistry, Department of Chemistry,
Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
b
State Key Laboratory Breeding Base of Green Pesticide & Agricultural
Bioengineering, Key Laboratory of Green Pesticide & Agricultural Bioengineering,
Ministry of Education, State-Local Joint Laboratory for Comprehensive Utilization of
Biomass, Center for Research & Development of Fine Chemicals, Guizhou University,
Guiyang 550025, PR China.
c
Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kgs.
Lyngby, Denmark.
1

Catalysis Science & Technology
Page 2 of 27
View Article Online
DOI: 10.1039/C8CY02536C
Abstract: A 3D nano-/micrometer-scaled NiO material with urchin-like structure was
prepared via a facile, green synthesis route, and served as a highly efficient and
durable catalyst for catalytic transfer hydrogenation (CTH) of bio-based furfural (FF)
to furfuryl alcohol (FAOL) using 2-propanol as H-donor and solvent. The as-prepared
NiO possessed a good active-site accessibility owing to a high surface area and large
amount of acid-base sites, resulting in high FF conversion of 97.3% with 94.2%
FAOL yield at 120 °C and 3 h of reaction, which was a superior catalytic performance
compared to commercial NiO nanoparticles. Besides, the excellent catalytic
performance of the sea urchin-like NiO was validated for gram-scale FAOL synthesis,
and recyclability test confirmed the catalyst to be reusable for multiple reaction runs
without significant activity loss after intermediary calcination in air. Notably, the
introduced catalytic system was also applicable to CTH of alternative bio-derived
aldehydes.
Keywords: Furfural; hierarchical construction; catalytic transfer hydrogenation;
heterogeneous catalyst; biomass resource.
2

Page 3 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
1
Introduction
Considerable attention is nowadays directed towards the development of renewable
feedstock from biomass resources that can serve as substitutes for limited fossil-based
resources for the production of bio-fuels and fine chemicals [1-3]. Furfural (FF), the
acid-hydrolysis product of biomass-derived C5-based carbohydrates, is recognized as
one of the most promising feedstock in the manufacture of a broad spectrum of fuels
and valuable chemicals via upgrading strategies such as, e.g., hydrogenation,
hydrogenolysis and aldolization [4-6]. Furfuryl alcohol (FAOL), as a typical
representative reduction derivative of FF, can serve as a versatile precursor in the
synthesis of synthetic fibers, resins, adhesives and vitamin C [7-10], and act as an
intermediate linking C5-carbohydrates to the down-stream products of bio-based
furan derivatives (e.g., levulinic acid and γ-valerolactone) (Scheme 1) [11,12]. In this
regard, hydrogenation of FF into FAOL has received widespread attention.
O
HO
HO
OH
Fuel additive
(e.g., 2-methyltetrahydrofuran)
Hemicellulose
Cellulose
OH
Xylose
-3H2O
O
OH
O
O
Fine chemicals
e.g., Resins and synthetic fibers)
OH
(
Furfural
(FF)
Furfuryl alcohol
(FAOL)
O
HO
HO
OH
Biomass
O
H
OH
Glucose
Other renowned platform molecules
e.g., levulinic acid and gamma-valerolactone)
(
Scheme 1 Cascade synthesis of FAOL from bio-based carbohydrates and application
of FAOL.
The multi-functionality of the FF molecule (i.e., C=C, C=O and C-O) can result in
several hydrogenation products such as FAOL, tetrahydrofurfuryl alcohol (TFAOL),
2
-methylfuran (2-MF) and 2-methyltetrahydrofuran (2-MTHF) [13-15]. This renders
the selectivity formation of FAOL from FF a remaining challenging as low product
yield is often obtained [16,17]. So far, many heterogeneous catalysts have been
developed for the transformation of FF into FAOL using gaseous hydrogen as
H-donor [18-21]. However, low reaction selectivity towards the target product and the
potential danger of handling pressurized, external H gas owing to its flammable and
2
3

Catalysis Science & Technology
Page 4 of 27
View Article Online
DOI: 10.1039/C8CY02536C
explosive properties coupled with the high cost of transportation and storage,
encourage exploitation of alternative strategies for the production of FAOL from FF
[22]. Recently, catalytic transfer hydrogenation (CTH) has emerged as a very
interesting alternative approach using abundant, renewable and low-cost alcohol as
combined H-donor and solvent during the process. This results in more safe and
convenient operation in comparison with the direct use of gaseous H as H-donor in
2
terms of cost and handling [23-26]. Moreover, it is proven that carbonyl groups can be
highly selectivity reduced to hydroxyl groups during the CTH process, which is
strongly associated to the Meerwein-Ponndorf-Verley (MPV) reaction in organic
chemistry [27]. Many heterogeneous catalysts have already been exploited for CTH of
FF to FAOL with alcohol (Table S1), but although substantial progression have been
made most catalytic systems are generally subjected to undesired harsh reaction
conditions (i.e., T ≥ 140 °C and/or t ≥ 6 h) and require large catalyst dosage to work
efficiently. In addition, most of the reported catalysts involve tedious preparation
procedures limiting their practical application. Thus, there is still great potential to
improve the synthesis of FAOL from FF by CTH.
The structural features of solids, including morphology, surface area and component
dispersion, have a significant influence on their catalytic performance [28,29]. In this
perspective, 3D micro or nano-materials with hierarchical construction have shown
outstanding activity in catalysis thanks to their large surface area, highly available
active sites and improved mass transportation [30]. For instance, has flower-like
Co O -CeO composite demonstrated to be an efficient catalyst for the degradation of
3
4
2
1
,2,4-trichlorobenzene [31], flower-like MgO catalyst was efficient for dimethyl
carbonate synthesis [32], and 3D flower-like micro/nano Ce-Mo composite oxide has
been developed as an efficient catalyst for one-pot transformation of fructose to
2
,5-diformylfuran [33].
In previous work [34], we reported that commercially available NiFe O nanoparticles
2
4
could efficiently catalyze the CTH of FF to FAOL with 2-propanol. Following our
4

Page 5 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
continuous interesting in the development of highly efficient and low cost catalysts
for the CTH of FF, we prepared in this study 3D sea urchin-like and flower-like NiO
catalysts by facile and environmental-friendly methods without the use of strong base
or pungent ammonia hydroxide. The 3D sea urchin-like NiO was thoroughly
characterized by various techniques and demonstrated to be highly catalytic activity
for CTH of FF to FAOL with 2-propanol as H-donor, yielding 94.2% FAOL under
mild reaction conditions (120 °C, 3 h).
2
Experimental
2
.1 Materials
Nickel(II) chloride (98%), PEG-PPG-PEG pluronic P-123 (Maverage = 5800 g/mol),
NiO (99.8%, <50 nm particle size), furfuryl alcohol (FAOL, 98%), 5-methylfurfural
(5-MFF, 99%), naphthalene (>99%, internal standard), benzaldehyde (>99%), benzyl
alcohol (≥99%), 4-methoxybenzaldehyde (98%), 4-methoxybenzyl alcohol (98%),
3
2
,4-dimethoxybenzaldehyde
(99%),
3,4-dimethoxybenzyl
alcohol
(96%),
,4,6-trimethylbenzaldehyde (98%), 2,4,6,-trimethylbenzyl alcohol (99%), cinnamic
alcohol (98%), heptanal (≥95%), 2-propanol (99.5%), methanol (≥99.8%), ethanol
(
99.5%) and acetone (≥99%) were purchased from Sigma-Aldrich. Cinnamaldehyde
>98%) was received from Merck. 5-Hydroxymethylfurfural (HMF, ≥95%),
(
2
,5-furandicarboxaldehyde (DFF, ≥95%), 5-methylfuran-2-methanol (≥95%) and
,5-furandimethanol (≥95%) were obtained from Bepharm Ltd. Urea (≥99%), furfural
2
(FF, ≥99%), 2-butanol (≥99.5%), tert-butyl alcohol (≥99.7%) and n-heptanol (>99%)
were procured from Fluka.
2
.2 Catalyst preparation
In a typical synthesis, 1.296 g (10 mmol) NiCl , 1.80 g (30 mmol) urea and 2.5 g
2
pluronic P-123 were dissolved in deionized water (80 mL) with magnetic stirring (500
rpm) at room temperature for 2 h. The resulting green transparent solution was then
transferred into a 200 mL Teflon lined stainless steel autoclave and heated at 90 °C
5

Catalysis Science & Technology
Page 6 of 27
View Article Online
DOI: 10.1039/C8CY02536C
for 12 h. Subsequently, the autoclave was quickly cooled to room temperature in a
water bath, the green product collected by filtration followed by washing with
deionized water until the pH of the filtrate was neutral following by drying at 80 °C in
air for 5 h (86% yield of solid). Finally, the as-prepared sample was calcined at 300 or
4
00 °C in air for 4 h and the obtained catalyst were denoted as NiO(P)-300 or
NiO(P)-400, respectively. For comparison, NiO-300 was prepared according to the
above described procedure but in the absence of pluronic P-123.
2
.3 Catalyst characterization
Power X-ray diffraction (XRD) patterns of samples were acquired on a Huber G670
diffractometer with Cu Kα radiation (λ = 0.154184 nm) and recorded in the 2θ range
from 5 to 80°. N adsorption-desorption measurements were completed on a
2
Micromeritics ASAP 2020 instrument, wherein the samples were firstly degassed at
2
00 °C in vacuum for 4 h and adsorption-desorption isotherms subsequently acquired
at -196 °C. The Brunauer-Emmett-Teller (BET) method was applied to evaluate the
specific surface area of the samples. Thermal gravimetric (TG) measurements of
samples were performed on a METTLER TOLEDO thermal analyzer in dynamic air
atmosphere (30 mL/min) in the temperature range 25-600 °C with a heating rate of 10
°
C/min. NH /CO -temperature programmed desorption (TPD) measurements of
3 2
samples were conducted on a Micromeritics AutoChem II 2920 apparatus equipped
with a thermal conductivity detector (TCD). Prior to TPD analysis, the samples were
heated at 300 °C under a He flow (25 mL/min) for 1 h, subjected to a mixture of
NH /CO -He gas flow (15 mL/min) for 1 h at 50 °C followed by flushing with pure
3
2
He gas (25 mL/min) to remove physically adsorbed NH /CO . Finally, the desorption
3
2
of NH /CO were performed by heating the samples to 300 °C at a rate of 10 °C/min
3
2
and maintaining it here for 1 h. SEM (scanning electron microscopy) images of
samples were recorded on a FEI Tecnai T20 G2 microscope at 200 kV with a
LaB6/CeB6 Thermionic filament. TEM (transmission electron microscopy) images
were recorded on a FEI Nova NANO SEM 600 with the thru-the-lens camera with an
accelerating voltage at 5 kV. X-ray photoelectron spectroscopy (XPS) spectra of
6

Page 7 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
samples were recorded on a ThermoScientific K-Alpha spectrometer with Al Kα
radiation (1484.6 eV), in which C 1s at 284.8 eV was applied as calibration peak.
Metal leaching from the NiO(P)-300 catalyst in the filtrate after reaction was
determined by ICP-MS (inductively coupled plasma optical emission mass
spectrometry) on a Thermo Scientific iCAP Q ICP-MS with the aid of acid digests.
2
.4 Catalytic activity test and product analysis
The CTH of FF was performed in 15 mL ACE pressure tube equipped with
magnetically driven stirrer and oil-bath. In brief, 0.096 g (1 mmol) FF, specified
amount of catalyst (0.005-0.03 g), 5 mL 2-propanol (as H-donor and solvent), and
0
.02 g naphthalene (as internal standard) were mixed in the reactor (500 rpm). After
sealing, the reactor was placed in a preheated oil bath (100-140 °C) for a specific
reaction time at a stirring rate of 500 rpm (time zero when the reactor was immersed
in the oil bath). After the desired time of reaction, the reactor was quickly cooled to
room temperature in a water bath. Aliquot of the reaction mixtures was quantitatively
analyzed by GC (Agilent 6890N) fitted with FID detector, wherein the FF conversion
and FAOL yield were calculated on basis of standard curves of commercially pure
compounds. Furthermore, the liquid products in the reaction mixture were identified
by GC-MS (Agilent 6850-5975C). Both the GC and the GC-MS was equipped with a
HP-5MS capillary column (30.0 m × 250 μm × 0.25 μm).
The recyclability of the NiO(P)-300 catalyst was tested over six consecutive reaction
runs at 120 °C with a reaction time of 3 h. For the first four runs, the used catalyst was
after each run separated by centrifugation, washed with ethanol and acetone (5 mL) in
sequence, subsequently dried at 80 °C for 2 h and then used for the next run. For the
fifth and sixth recycle runs, catalyst regeneration were achieved by calcination in air
at 300 °C for 4 h. Product analysis was performed as described above.
The CTH of other aldehydes was performed in a similar way as described above, but
with a 50 mL stainless steel autoclave with mechanical stirring using 2 mmol
substrate, 0.06 g catalyst, 10 mL 2-propanol and reaction temperature of 140 or 150
°
C.
7

Catalysis Science & Technology
Page 8 of 27
View Article Online
DOI: 10.1039/C8CY02536C
3
Results and discussion
3
.1 Catalyst characterization
XRD patterns obtained of the as-prepared catalysts and commercial NiO nanoparticles
are shown in Figure 1a. NiO(P)-400 and commercial NiO had five characteristic
peaks at 2θ = 37.3, 43.2, 62.7, 75.4 and 79.4°, which are indexed as (111), (200),
(220), (311) and (222) planes of the crystalline rhombohedral phase of NiO [35,36],
respectively, consistent with JCPDS card 44-1159. In contrast, only three of the
characteristic peaks were clearly observed for the samples of NiO(P)-300 and
NiO-300, indicating less crystallinity of NiO when calcined at lower temperature.
Nitrogen physisorption isotherms of the catalyst samples measured by the BET
method (Figure 1b) showed Type IV isotherms with H3-type hysteresis loop,
implying that irregular mesoporous structures formed between the particles. The
obtained BET surface areas of the samples are compiled in Table 1. As expected,
higher calcination temperature greatly diminished the surface area of the as-prepared
NiO (entries 2 and 3, Table 1). Besides, the surface area of NiO(P)-300 was larger
than that of NiO-300 (entries 2 and 4, Table 1), revealing that the addition of pluronic
P-123 during the course of preparation increased the surface area of the formed
material.
Figure 1 (a) XRD patterns and (b) N adsorption-desorption isotherms of the
2
as-prepared catalysts and NiO nanoparticles.
8

Page 9 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
The morphologies of the as-prepared catalysts were visualized by SEM and TEM
analysis (Figure 2). The SEM image of NiO(P)-300 (Figure 2a) revealed a
well-defined 3D nanometer-scale structure, which was assembled from a core with
many densely arranged nano-needles as “spikes”. The 3D nanometer-scale structure
of NiO(P)-300 was clearly confirmed by its TEM image (Figure 2b) consisting of a
core of about 120 nm in diameter with “spikes” having diameters of about 50 nm.
Thus, the construction of the NiO(P)-300 catalyst looked like “sea urchin”.
NiO(P)-400 possessed less pronounced sea urchin appearance, which seemed to be
destroyed at increased calcination temperature. Instead it presented a agglomerated
shape (Figures 2c and 2d), which could account for the lower surface area of
NiO(P)-400 (entry 3, Table 1) compared to NiO(P)-300. Figures 2e and 2f showed
that the construction units of NiO-300 were 3D hierarchical flower-like structures
with diameters in the range of 1.2-1.4 μm, which were composed of many densely
packed nanosheets like “petals”. The distinct differences in catalyst construction
between NiO(P)-300 and NiO-300 reflected that pluronic P-123 significantly
influenced the catalyst structure during the course of preparation by decreasing the
size of particles as well as enlarge the surface area.
9

Catalysis Science & Technology
Page 10 of 27
View Article Online
DOI: 10.1039/C8CY02536C
Figure 2 (a) SEM image of NiO(P)-300; (b) TEM image of NiO(P)-300; (c) SEM
image of NiO(P)-400; (d) TEM image of NiO(P)-400; (e) SEM image of NiO-300; (f)
TEM image of NiO-300.
The acid and base properties of the catalysts were further measured using NH - and
3
CO -TPD (Figures S1 and S2). As shown in Table 1, the acidity and basicity of the
2
NiO catalysts were strongly associated to the calcination temperature as evident from
the NiO(P)-300 and NiO-300 samples, which possessed almost the same amount of
acid and base sites (entries 2 and 4, Table 1), while NiO(P)-400 in comparison had
less acid and base sites (entry 3, Table 1).
1
0

Page 11 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
Table 1 BET surface areas and acidity/basicity of the different catalysts
Entry
Catalyst
BET surface area
Acid amount
(mmol/g)b
0.192
Base amount
2
a
(mmol/g)b
(m /g)
1
2
3
4
Commercial NiO
NiO(P)-300
NiO(P)-400
NiO-300
94.8
273.8
95.5
0.059
0.072
0.065
0.080
0.918
0.303
0.923
257.8
a
b
BET surface areas were determined by N physisorption. Acidity and basicity were
2
evaluated by NH - and CO -TPD, respectively.
3
2
Furthermore, the Ni species in NiO(P-300) and commercial NiO nanoparticles were
examined by XPS analysis. The XPS spectra of the Ni 2p3/2 region (Figure 3)
exhibited a main peak at about 854 eV and an associated satellite peak at about 861
eV for both NiO(P-300) and commercial NiO nanoparticles [35,37]. Overall, four
deconvoluted peaks were needed to reproduce the shape of the Ni 2p signal, where
3
/2
the peaks at about 854.0 and 855.5 eV in the main peak region were characteristic of
2
+
Ni species and the other two deconvoluted peaks located at six to eight eV higher
binding energy relative to the main peaks (i.e., 854.0 and 855.5 eV) are generally
assigned to satellite peaks [37,38]. No peak at 852.6 eV assignable to metallic Ni [38]
was observed in either of the samples.
Figure 3 XPS spectra of Ni 2p of (a) NiO(P)-300 and (b) commercial NiO samples.
3
/2
1
1

Catalysis Science & Technology
Page 12 of 27
View Article Online
DOI: 10.1039/C8CY02536C
3
.2 Catalyst evaluation for CTH of FF
Initial investigations were commenced by using the as-prepared NiO catalysts for
CTH of FF to FAOL in 2-propanol at 120 °C (Table 2). A reference experiment
confirmed that the formation of FAOL did not take place without catalyst present
(entry 1, Table 2). In contrast, considerable amount of FAOL formed using different
nickel oxides (entries 2-5, Table 2), confirming that the acid-base properties of metal
oxides was capable of facilitating the CTH reaction relying on MPV reduction [39-41].
Especially, 72.6% FF conversion with 70.2% FAOL yield (96.7% selectivity) was
obtained in the presence of NiO(P)-300 under mild reaction conditions (120 °C, 1 h)
-1
-1
resulting in a high FAOL formation rate of 585 μmolg min and a relatively high
-1
TOF value of 2.6 h (entry 2, Table 2). The excellent catalytic performance of
2
NiO(P)-300 was attributed to a combination of high surface area (273.8 m /g) and
high concentration of acid (0.918 mmol/g) and base sites (0.072 mmol/g) (entry 2,
Table 1). Notably, the catalytic behavior of NiO(P)-300 far outperformed commercial
-1
-1
-1
NiO nanoparticles (FAOL formation rate of 142 μmolg min and TOF of 0.6 h )
(entry 5, Table 2). Similarly, good results were also obtained with NiO-300 which
possessed a relative high surface area and equally many acid and base sites as
NiO(P)-300, affording 56.9% yield of FAOL (90.7% selectivity) along with a FAOL
-1
-1
-1
formation rate of 474 μmolg min and a TOF value of 2.1 h (entry 4, Table 2).
Hence, both as-prepared NiO with sea urchin (i.e., NiO(P)-300) or flower (i.e.,
NiO-300) construction exhibited superior performance to commercial NiO
nanoparticles with a mean particle size of about 15 nm (Figure S3) in the CTH of FF
to FAOL, possibly as a consequence of their special constructions in combination
with large density of acid-base sites. Noteworthy, as-prepared NiO with flower
construction (i.e., NiO-300) afforded a slightly lower selectivity toward FAOL
compared to the other tested NiO catalysts (entries 2-5, Table 2). This was likely
associated to the large particle size of NiO-300 as evidenced from Figure S4, in well
agreement with nano-catalysis offering excellent selectivity [22,42]. As the
as-prepared nanometer-scaled NiO with sea urchin construction (i.e., NiO(P)-300)
showed the best catalytic performance, this catalyst was selected for further study.
1
2

Page 13 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
Table 2 Catalytic performance of NiO catalysts for CTH of FF a
Conv. Yield Select.
FAOL formation
rate (μmolg min )
TOF
(h )
Entry
Catalyst
-1
-1 b
-1 c
(
4.5
%)
(%)
0
(%)
0
1
2
3
4
5
None
0
585
87
474
142
-
NiO(P)-300
NiO(P)-400
NiO-300
72.6
11.2
62.7
70.2
10.4
56.9
17.0
96.7
92.9
90.7
96.0
2.6
0.4
2.1
0.6
Commercial NiO 17.7
a
Reaction conditions: 1 mmol FF, 0.02 g catalyst, 5 mL 2-propanol, 120 °C, 1 h. b
c
Calculated from the FAOL yield obtained after 1 h. Turn-over frequency (TOF) as
(mole of FAOL)/(mole of catalyst × reaction time).
3
.3 CTH of FF with NiO(P)-300
Effect of temperature, time, H-donor alcohol and catalyst dosage
The catalytic results obtained from CTH of FF with NiO(P)-300 by variation of
reaction temperature and reaction time are presented in Figure 4a. Increased reaction
temperature or prolonged reaction time leads to an increase in FF conversion and
FAOL yield, while the FAOL selectivity remained over 95% as clearly verified by the
GC chromatograms of the reaction mixture (Figure S5a). Also, trace amount of
2
-(diisopropoxymethyl)furan formed from acetalization of FF with 2-propanol was
detected at the different reaction temperatures (Figure S5b). As high as 88.9% yield of
FAOL along with 91.8% FF conversion was attained even at 100 °C with a reaction
time of 5 h, signifying the excellent catalytic performance of NiO(P)-300. The great
performance of the catalyst system was associated to a relative low activation energy
(41.8 kJ/mol) (Figure S6 and Table S2), which was slightly lower than previously
reported catalyst systems for CTH of FF to FAOL (Table S1). Almost complete FF
conversion was achieved at 120 °C after 4 h of reaction or at 140 °C after 2 h of
reaction (Figure 4a), clearly demonstrating that increased reaction temperature
shortened the required reaction time to afford full FF conversion. Noteworthy, the
reaction carried out at 120 °C for 3 h offered 97.3% FF conversion and 94.2% FAOL
yield, which were chosen as preferred conditions for further optimization.
1
3

Catalysis Science & Technology
Page 14 of 27
View Article Online
DOI: 10.1039/C8CY02536C
Figure 4 (a) Effect of reaction temperature and reaction time on CTH of FF to FAOL
1
4

Page 15 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
(
1 mmol FF, 0.02 g NiO(P)-300, 5 mL 2-propanol); (b) Effect of alcohol as H-donor
on CTH of FF to FAOL (1 mmol FF, 0.02 g NiO(P)-300, 5 mL alcohol, 120 °C, 3 h,
formation rate calculated from the FAOL yield obtained after 3 h); (c) Effect of
catalyst dosage on the CTH of FF to FAOL (1 mmol FF, 5 mL 2-propanol, 120 °C, 3
h, mass ratio of FF to catalyst ranging from 19.2 to 3.2).
Variation of the alcohol acting as solvent and H-donor in the tested system had a
significant effect on the catalytic behavior (Figure 4b). No FAOL was formed using
tert-butanol as the reaction media, confirming that it could not facilitate CTH. On the
other hand, excellent FAOL selectivities were achieved with 2-propanol and
2
-butanol, confirming the good H-donating capability of secondary alcohols. Notably,
a moderate FF conversion was observed at 120 °C in 2-butanol while ~90% FF
conversion was achieved at 160 °C (Table S3). This difference was probably a
consequence of the relatively high viscosity and/or steric hindrance effect of
2
-butanol compared to the other alcohols (e.g., 2-propanol), resulting in relatively
large mass dispersion limitation at low reaction temperature (120 °C). At higher
reaction temperature (e.g., 160 °C) where the viscosity of 2-butanol is significantly
lower [43,44] the effect was less important. Ethanol performed also good as
-1
-1
solvent/H-donor (75.4% yield of FAOL, 209 μmolg min of FAOL formation rate),
-1
-1
however superior result (94.2% yield of FAOL, 262 μmolg min ) was observed with
2
-propanol as preferred H-donor solvent.
The effect of NiO(P)-300 dosage on the CTH of FF at 120 °C was subsequently
studied and the results are shown in Figure 4c. No FAOL product was formed without
added catalyst into the reaction system, as expected. In contrast, FF conversion and
FAOL yield increased with increasing catalyst dosage and reached 97.3 and 94.2%,
respectively, when the mass ratio of FF to catalyst was 4.8:1 (i.e., use of 0.02 g
catalyst). Further increase in catalyst dosage to 0.03 g (i.e., mass ratio of FF to
catalyst of 3.2:1) only marginally increased the yield to 95.5% after 3 h, but resulted
in high FAOL yield (e.g., 85.7%) within a shorter time (e.g., 1 h). Also, the FAOL
1
5

Catalysis Science & Technology
Page 16 of 27
View Article Online
DOI: 10.1039/C8CY02536C
selectivity increased with increasing catalyst dosage, and the relative low FAOL
selectivity at lower catalyst dosage was attributed to competing acetalization of FF
with 2-propanol as revealed from GC-MS analysis.
Catalyst recycling
Prior to recycling experiments, the heterogeneous nature of the NiO(P)-300 catalyst
was evaluated for the CTH reaction by a filtration experiment, where the catalyst was
removed after 1 h reaction and the filtrate allowed to continue reaction under identical
reaction conditions (120 °C) for an additional hour (Figure S7). The FAOL yield was
periodically monitored and the FAOL yield remained around 70% with time with no
nickel detected in the filtrate by ICP-MS analysis, which clearly indicated that the
NiO(P)-300 catalyst was heterogeneous in nature and therefore likely prone to
recycling.
Upon recycling, a gradual decline in FF conversion and FAOL yield was, however,
observed for the first four reaction runs (Figure 5a) resulting in moderate FF
conversion and FAOL yield of 41.5 and 36.9%, respectively, while the FAOL
selectivity maintained around 95%. Notably, the catalyst activity could be recovered
almost completely after regeneration by calcination at 300 °C in air, which resulted in
FAOL yield of 88.3 and 86.8% after the fifth and sixth reaction run, respectively,
when applying intermediate calcination. Thus in-depth characterization of used and
generated catalysts were conducted with an attempt to shed light on the reason of
activity variation during the recycling experiments.
XRD (Figure 5b) and XPS analysis (Figure S8) of the spent and regenerated catalysts
revealed no crystallographic changes compared to the fresh catalyst and no reduced
Ni species (no characteristic metallic Ni peak at 852.6 eV), respectively, strongly
2
+
confirming that reduction of Ni did not take place during the reaction. Besides, SEM
and TEM analysis (Figures 5c and 5d) confirmed preservation of the sea urchin-like
constructions in the used samples, while ICP-MS analysis confirmed negligible nickel
1
6

Page 17 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
leaching (<0.5 ppm) into the filtrate after 3 h at 120 °C. Combined, this firmly
demonstrated that the NiO(P)-300 catalyst was stable during the reaction. However, a
significant weight loss was indeed found by TGA for the used catalysts in comparison
to the fresh and regenerated catalysts (Figure 5e), and an apparent color changes was
also observed (Figure S9). Retrospectively, it is speculated that organic residues
adsorbed on the surface of the NiO(P)-300 catalyst resulted in the loss of activity and
calcination at 300 °C restored the catalyst activity. This deduction was validated by
2
2
the variation in the surface areas of the fresh (273.8 m /g), used (228.5 m /g) and
2
regenerated catalyst (246.4 m /g) (Figure 5f).
1
7

Catalysis Science & Technology
Page 18 of 27
View Article Online
DOI: 10.1039/C8CY02536C
Figure 5. (a) Catalytic performance of NiO(P)-300 in the CTH of FF to FAOL during
recycling. (b) XRD patterns of fresh, used and regenerated NiO(P)-300 catalysts. (c)
SEM image of used NiO(P)-300 catalyst. (d) TEM image of used NiO(P)-300 catalyst.
(e) TG curves of fresh, used and regenerated NiO(P)-300 catalysts. (f) N2
adsorption-desorption isotherms of fresh, used and regenerated NiO(P)-300 catalysts.
Reaction conditions: 1 mmol FF, 0.02 g NiO(P)-300, 5 mL 2-propanol, 120 °C, 3 h.
Scale-up and substrate scope
To evaluate the effectiveness of the NiO(P)-300 catalyst, a gram-scale CTH reaction
was performed employing 20 mmol (1.92 g) FF at 140 °C as illustrated in Scheme S1.
The FF conversion was monitored by GC to be near quantitative after 5 h, where after
1
.68 g (85.7% yield) of analytically pure (verified by NMR analysis in Figure S10)
FAOL was obtained after filtration and rotary evaporation, implying that NiO(P)-300
possessed a promising potential for large-scale production of FAOL from FF via the
CTH process.
In addition to FF, NiO(P)-300 was successfully employed for CTH of various other
aldehydes, including α,β-unsaturated carbonyls, as shown from the results listed in
Table 3. For instance, were excellent yields (92.8-97.4%) of the corresponding
reduction products obtained in CTH of 2,5-furandicarboxaldehyde (entry 3),
benzaldehyde
(entry
4),
4-methoxybenzaldehyde
(entry
5),
3
,4-dimethoxybenzaldehyde (entry 6) and heptanal (entry 9) under relative mild
1
8

Page 19 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
reaction conditions (≤ 150 °C). Although lower conversions were observed for other
aldehydes (entries 1, 2, 7 and 8), excellent selectivities of the corresponding reduction
products were attained confirming that the NiO(P)-300 catalyst had good versatility in
the CTH of aldehydes.
Table 3. CTH of alternative aldehydes with NiO(P)-300 a
Entry
Substrate
Product
Temp Time Conv. Yield
Sel.
(%)
.
(h)
(%)
(%)
(
°C)
O
O
OH
O
1b
2b
150
150
5
4
60.5
77.9
58.1
73.5
96.0
94.4
OH
O
OH
OH
O
O
O
O
OH
OH OH
O
7
9.6
O
3b
O
O
150
4
>99
96.3
(16.7)c
+
O
OH
4
5
6
7
140
150
150
150
3
2
2
8
96.5
>99
>99
46.1
95.7
99.2
98.1
98.4
98.0
98.5
O
O
OH
OH
H3CO
H3CO
97.1
H3CO
H3CO
H3CO
H CO
97.4
3
O
OH
45.2
O
OH
8
9
140
150
8
3
71.6
96.2
70.5
92.8
O
OH
96.5
a
b
Reaction conditions: 2 mmol substrate, 0.06 g NiO(P)-300, 10 mL 2-propanol. 1
c
mmol substrate. HMF yield.
Inspired by the general excellent catalytic performance of NiO(P)-300 in CTH, we
further attempted to use NiO(P)-300 combined with other acid catalysts for one-pot
transformation of FF to alkyl levulinate, which is hailed as another versatile feedstock
for the manufacture of bio-fuels and chemicals [11]. Since isopropyl levulinate (IPL)
was not commercially available, pure IPL was prepared according to the method
reported by Geboers et al. [45] and the purity confirmed by NMR analysis (Figure
S11). As shown in Table S4, nearly full FF conversion was achieved over NiO(P)-300
1
9

Catalysis Science & Technology
Page 20 of 27
View Article Online
DOI: 10.1039/C8CY02536C
at 140 °C after 2 h of reaction, and the conversion of formed FAOL into IPL was
subsequently catalyzed by common acid catalysts such as, e.g. Amberlyst 15, H-Beta,
H-ZSM-5, H-MOR and H-Y. Eventually, a IPL yield of 61.5% was obtained from FF
over NiO(P)-300 and Amberlyst 15 at 140 °C after 6 h in a two-step procedure, which
is close to previously reported results [46]. The superior activity found for Amberlyst
1
5 compared to zeolites was mainly attributed to its larger amount of acidic sites and
stronger acidity (Table S4). In line with this, the dominant product from reaction with
H-Beta(12.5) was the precursor of IPL, i.e. 2-(isopropoxymethyl)furan, derived from
etherification of FAOL with 2-propanol. In contrast, IPL was the main product in the
presence of Amberlyst 15 as its large amount of acidic sites and strong acidity further
facilitated the transformation into IPL (Figure S12). In addition to the acid amount
and acid strength, the narrow channels of zeolites constituting relatively large
diffusion limitation probably also contributed to their low catalytic performance [46].
Anyway, the results clearly demonstrated the potential of NiO(P)-300 to be employed
in further upgrading of biomass-derived compounds with the combination of other
type catalysts, further supporting the versatility of NiO(P)-300.
CTH reaction mechanism
To get more insight into the mechanism of CTH of FF over NiO(P)-300, poisoning
experiments were conducted by adding benzoic acid [47] or piperidine [48] into the
reaction system with the aim of poisoning base or acid sites of the NiO(P)-300
catalyst, respectively (Table S5). The results clearly show that addition of either
benzoic acid or piperidine led to significant reductions in FAOL yield, initial FAOL
formation rate as well as TOF value, implying the remarkable catalytic performance
of NiO(P)-300 was strongly associated with the synergic role of acidic-basic sites
within the catalyst.
The results obtained from the above characterization and catalytic testing in
combination with knowledge from literature [22,23,26,27] allowed us to propose a
plausible reaction mechanism for the CTH process with NiO(P)-300, assuming that
2
0

Page 21 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
2
+
the mechanism was associated to MPV reduction facilitated by acidic (Ni ) and basic
2
-
sites (O ). As delineated in Scheme 2, 2-propanol was adsorbed to the surface of
2
+
2-
NiO(P)-300 catalyst and then activated by acidic-basic sites (Ni -O ) within the
catalyst to give 2-propoxide, while the carbonyl group in FF was concomitantly
2
+
activated by acidic sites (Ni ). Next, H-transfer between activated FF and generated
-propoxide occurred involving a six-member intermediate on the surface of the
catalyst forming FAOL and acetone. Normally, minor amount of
-(diisopropoxymethyl)furan was observed throughout the studies as a by-product
Figure S5), generated by acetalization of FF with 2-propanol over acidic sites of
2
2
(
catalyst. Additionally, trace amount of 2-(isopropoxymethyl)furan, originated from
etherification of FAOL with 2-propanol over acidic sites of catalyst, was detected
when the reaction took place in presence of a large amount of NiO(P)-300 catalyst
(i.e., 0.03 g) with long reaction time (i.e., ≥ 3 h).
O
O
O
2-(diisopropoxymethyl)furan
O
O
H
O
OH
2
Step 3
H
H
O
Ni
O
Ni
O
O
O
O
O
O
Ni
O
Ni
Step 2
FF
Step 4
H
O
H
O
Ni
O
Ni
O
O
O
H
OH
Step 1
O
Ni
O
Ni
Step 5
O
Ni
O
Ni
OH
OH
O
O
+
O
O
2-(isopropoxymethyl)furan
FAOL
Scheme 2 Plausible reaction mechanism for the CTH of FF to FAOL with
NiO(P)-300 in 2-propanol.
2
1

Catalysis Science & Technology
Page 22 of 27
View Article Online
DOI: 10.1039/C8CY02536C
It is well-known that Ni-based catalysts, preferable Raney Ni [49,50], are efficient
catalysts for transfer hydrogenation/hydrogenolysis using alcohols as H-donor, and
several Ni-based catalysts have already been reported for CTH of FF to FAOL as
compiled in Table 4 [51-55]. Notably, the NiO(P)-300 catalyst developed in this work
exhibited however superior catalytic performance in CTH of FF to FAOL than
previously reported Ni-based catalysts. Specifically, the NiO(P)-300 catalyst did not
require pre-reduction and H gas, or high temperature carbon reduction under inert
2
gas, could therefore be omitted during catalyst preparation making the process
cost-effective. Therefore, the facile, low-cost and green preparation method together
with high catalytic performance render the developed NiO(P)-300 catalyst a
promising substitute of Ni(0)-based catalysts for CTH.
Table 4 Comparison of the catalytic performance of NiO(P)-300 with other Ni-based
catalysts in the production of FAOL from FF with alcohols as H-donor
Cat.
Cat. amount a
C
initial FF b
Temp.
(°C)
Time
(h)
Conv.
(%)
-
Yield
(%)
Select.
(%)
-
Entry
1
Catalyst
Ni-Ru/C
H-donor
Ref.
51
Reduction
(wt%)
(mol/L)
0.36
600 °C/N
2
/3h
28.9
Benzyl
alcohol
2-Propan
ol
150
12
81.1
2
3
4
5
6
7
8
Ni-Cu/
320 °C/
15 bar H /3h
22.3
33.3
40.0
12.5
12.5
31.2
20.8
1.17
0.40
0.43
0.42
0.42
0.2
200
180
110
260
260
180
120
4
7.5
2.3
5
95.4
46
95.4
33
100
71.7
100
52
53
54
55
55
Al
2
O
3
2
Ni/Fe
2
O
3
No reduction
2-Propan
ol
Ni-Cu
250 °C/1 bar
2-Propan
ol
50
50
H
2
/1h
450 °C/1 bar
/1h
450 °C/1 bar
/3h
5%Ni/AC
2-Propan
ol
95
20
21.1
30.1
94.9
96.8
H
2
10%Ni-
2-Propan
ol
5
83
25
1
5%W/AC
NiFe
H
2
2
O
4
No reduction
2-Propan
ol
6
99
94
34
c
NiO(P)-300
No reduction
0.2
2-Propan
ol
3
97.3
94.2
a
b
c
Relative to initial mass of FF. Initial molar concentration of FF. This work.
4
Conclusions
In this work, 3D hierarchical structures of NiO catalysts (sea urchin- and flower-like)
2
2

Page 23 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
have successfully been prepared via a facile yet environmental-friendly hydrothermal
method in the absence of strong or stimulating alkali supply, and demonstrated to be
highly active for CTH of FF to FAOL using 2-propanol as both H-donor and solvent.
The 3D hierarchical construction and low calcination temperature (300 °C)
contributed to high surface area and large amount of acid-base sites as well as facile
active-site accessibility in the catalysts, which were found to play critical roles in the
efficient production of FAOL from CTH of FF. A high FF conversion of 91.8% along
with 88.9% FAOL yield was achieved under very mild reaction conditions (100 °C, 5
h) using the sea urchin-like NiO(P)-300 catalyst, and FF conversion and FAOL yield
were increased to 97.3 and 94.2%, respectively, at 120 °C after only 3 h. Moreover,
the effectiveness and heterogeneous nature of the catalyst were confirmed by a low
value of activation energy (41.8 kJ/mol), successful gram-scale testing, one-pot
conversion of FF into IPL in combination with Amberlyst 15 and filtration experiment,
respectively. In addition, the catalyst proved reusable several times without significant
activity loss after facile regeneration by calcination (300 °C, in air). Importantly, the
catalytic system proved also applicable to CTH of various other aldehydes. In
perspective, we envisage the low-cost and efficient catalyst prepared by a green
strategy in this work to be a potentially attractive catalyst for industrial CTH of FF as
well as other aldehydes.
Acknowledgement
JH gratefully acknowledges finance support from The Chinese State Scholarship (No.
2
01606670008), SY acknowledges the National Natural Science Foundation of China
(No. 21576059 and 21666008), and AR acknowledges the Department of Chemistry,
Technical University of Denmark for support.
References
[1] T. Renders, S. V. den Bosch, S. Koelewijn, W. Schutyser, B. F. Sels, Energy
Environ. Sci., 2017, 10, 1551-1557.
2
3

Catalysis Science & Technology
Page 24 of 27
View Article Online
DOI: 10.1039/C8CY02536C
[
2] H. Li, S. Yang, S. Saravanamurugan, A. Riisager, ACS Catal., 2017, 7,
010-3029.
3] H. Li, A. Riisager, S. Saravanamurugan, A. Pandey, R. S. Sangwan, S. Yang, R.
Luque, ACS Catal., 2018, 8, 148-187.
4] L. Zhang, G. Xi, Z. Chen, D. Jiang, H. Yu, X. Wang, Chem. Eng. J. 2017, 307,
68-876.
5] S. S. Chen, T. Maneerung, D. C. W. Tsang, Y. S. Ok, C. Wang, Chem. Eng. J.
017, 328, 246-273.
3
[
[
8
[
2
[
[
[
6] K. Tomishige, Y. Nakagawa, M. Tamura, Green Chem., 2017, 19, 2876-2924.
7] S. T. Thompson, H. H. Lamb, J. Catal., 2017, 350, 111-121.
8] W. Gong, C. Chen, Y. Zhang, H. Zhou, H. Wang, H. Zhang, Y. Zhang, G. Wang,
H. Zhao, ACS Sustain. Chem. Eng., 2017, 2172-2180.
9] P. N. Romano, J. M. A. R. de Almeida, Y. Carvalho, P. Priecel, E. F.
Sousa-Aguiar, J. A. Lopez-Sanchez, ChemSusChem, 2016, 9, 3387-3392.
10] Z. Zhang, J. Song, Z. Jiang, Q. Meng, P. Zhang, B. Han, ChemCatChem, 2017, 9,
448-2452.
11] E. Jorge, T. D. M. Lima, C. Lima, L. Marchini, W. N. Castelblanco, D. G. Rivera,
E. A. Urquieta-González, R. S. Varma and M. W. Paixao, Green Chem., 2017, 19,
856-3868.
12] S. Song, L. Di, G. Wu, W. Dai, N. Guan, L. Li, Appl. Catal. B: Environ., 2017,
05, 393-403.
[
[
2
[
3
[
2
[
13] Z. Jiang, W. Wan, Z. Lin, J. Xie, J. G. Chen, ACS Catal., 2017, 7, 5758-5765.
14] N. Pino, S. Sitthisa, Q. Tan, T. Souza, D. López, D. E. Resasco, J. Catal., 2017,
[
3
50, 30-40.
15] X. Chang, A. Liu, B. Cai, J. Luo, H. Pan, Y. Huang, ChemSusChem, 2016, 9,
330-3337.
16] P. T. Sulmonetti, S. H. Pang, M. T. Claure, S. Lee, D. A. Cullen, P. K. Agrawal,
C. W. Jones, Appl. Catal. A: Gen., 2016, 517, 187-195.
17] L. Grazia, D. Bonincontro, A. Lolli, T. Tabanelli, C. Lucarelli, S. Albonetti, F.
Cavani, Green Chem., 2017, 19, 4412-4422.
[
3
[
[
2
4

Page 25 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
[
18] J. Wu, G. Gao, J. Li, P. Sun, X. Long, F. Li, Appl. Catal. B: Environ., 2017, 203,
2
27-236.
[19] J. J. Musci, A. B. Merlo, M. L. Casella, Catal. Today, 2017, 296, 43-50.
[20] S. M. Rogers, C. R. A. Catlow, C. E. Chan-Thaw, A. Chutia, N. Jian, R. E.
Palmer, M. Perdjon, A. Thetford, N. Dimitratos, A. Villa, P. P. Wells, ACS Catal.,
017, 7, 2266-2274.
21] C. P. Jiménez-Gómez, J. A. Cecilia, D. Durán-Martín, R. Moreno-Tost, J.
Santamaría-González, J. Mérida-Robles, R. Mariscal, P. Maireles-Torres, J. Catal.,
016, 336, 107-115.
22] G. Wang, X. Deng, D. Gu, K. Chen, H. Tüysüz, B. Spliethoff, H. Bongard, C.
Weidenthaler, W. Schmidt, F. Schüth, Angew. Chem. Int. Ed., 2016, 55, 11101-11105.
23] H. Li, J. He, A. Riisager, S. Saravanamurugan, B. Song, S. Yang, ACS Catal.,
016, 6, 7722-7727.
2
[
2
[
[
2
[
[
[
24] M. J. Gilkey, B. Xu, ACS Catal., 2016, 6, 1420-1436.
25] J. He, H. Li, A. Riisager, S. Yang, ChemCatChem, 2018, 10, 430-438.
26] L. Hu, T. Li, J. Xu, A. He, X. Tang, X. Chu, J. Xu, Chem. Eng. J., 2018, 352,
1
10-119.
[27] M. Koehle, R. F. Lobo, Catal. Sci. Technol., 2016, 6, 3018-3026.
[28] B. P. Bastakoti, H. Huang, L. Chen, K. C. Wu, Y. Yamauchi, Chem. Commun.,
2
012, 48, 9150-9152.
[29] M. Ko, L. Mendecki, K. A, Chem. Commun., 2018, 54, 7873-7891.
[30] S. Zhang, H. Gao, J. Li, Y. Huang, A. Alsaedi, T. Hayat, X. Xu, X. Wang, J.
Hazardous Mater., 2017, 321, 92-102.
31] S. Lin, G. Su, M. Zheng, D. Ji, M. Jia, Y. Liu, Appl. Catal. B: Environ., 2012,
23-124, 440-447.
32] Z. Cui, Z. Chen, C. Cao, W. Song, L. Jiang, Chem. Commun., 2013, 49,
093-6095.
[
1
[
6
[33] Z. Yang, W. Qi, R. Su, Z. He, ACS Sustain. Chem. Eng., 2017, 5, 4179-4187.
[34] J. He, S. Yang, A. Riisager, Catal. Sci. Technol., 2018, 8, 790-797.
[35] M. A. Peck, M. A. Langell, Chem. Mater. 2012, 24, 4483-4490.
2
5

Catalysis Science & Technology
Page 26 of 27
View Article Online
DOI: 10.1039/C8CY02536C
[
36] C. Yuan, X. Zhang, Q. Wu, B. Gao, Solid State Ionics, 2006, 177, 1237-1242.
[37] S. Song, S. Yao, J. Cao, L. Di, G. Wu, N. Guan, L. Li, Appl. Catal. B: Environ.,
2
017, 217, 115-124.
38] H. W. Nesbitt, D. Legrand, G. M. Bancroft, Phys. Chem. Minerals, 2000, 27,
57-366.
39] M. J. Gilkey, P. Panagiotopoulou, A. V. Mironenko, G. R. Jenness, D. G.
Vlachos, B. Xu, ACS Catal., 2015, 5, 3988-3994.
40] A. Prasertsab, J. A. Cecilia, C. P. Jiménez-Gómez, C. García-Sancho, R.
Moreno-Tost, P. Maireles-Torres, Appl. Catal. A, Gen., 2018, 556, 1-9.
41] N. S. Biradar, A. M. Hengne, S. S. Sakate, R. K. Swami, C. V. Rode, Catal. Lett.,
016, 146, 1611-1619.
[
3
[
[
[
2
[42] V. Polshettiwar, R. S. Varma, Green Chem., 2010, 12, 743-754.
[43] H. Habibi, A. Hekmat-Nazemi, A. Kamran-Pirzaman, A. H. Mohammadi, J. Mol.
Liquid., 2016, 220, 558-565.
44] C. K. Zéberg-Mikkelsen, S. E. Quiñones-Cisneros, E. H. Stenby, Fluid Phase
Equilib., 2002, 194-197, 1191-1203.
45] J. Geboers, X. Wang, A. B. de Carvalho, R. Rinaldi, J. Mol. Catal. A: Chem.,
014, 388-389, 106-115.
46] M. Paniagua, J. A. Melero, J. Iglesias, G. Morales, B. Hernández, C.
López-Aguado, Appl. Catal. A: Gen., 2017, 537, 74-82.
47] X. Tang, H. Chen, L. Hu, W. Hao, Y. Sun, X. Sun, L. Lin, S. Liu, Appl. Catal. B:
Environ., 2014, 147, 827-834.
48] V. A. Ivanov, J. Bachelier, F. Audry, J. C. Lavalley, J. Mol. Catal., 1994, 91,
5-59.
[
[
2
[
[
[
4
[
[
[
[
49] Z. Yang, Y. Huang, Q. Guo, Y. Fu, Chem. Commun., 2013, 49, 5328-5330.
50] X. Wang, R. Rinaldi, Energy Environ. Sci., 2012, 5, 8244-8260.
51] Z. Gao, L. Yang, G. Fan, F. Li, ChemCatChem, 2016, 8, 3769-3779.
52] H. P. R. Kannapu, C. A. Mullen, Y. Elkasabi, A. A. Boateng, Fuel Process.
Technol., 2015, 137, 220-228.
53] D. Scholz, C. Aellig, I. Hermans, ChemSusChem, 2014, 7, 268-275.
[
2
6

Page 27 of 27
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY02536C
[
54] S. A. Khromova, M. V. Bykova, O. A. Bulavchenko, D. Y. Ermakov, A. A.
Saraev, V. V. Kaichev, R. H. Venderbosch, V. A. Yakovlev, Top Catal., 2016, 59,
413-1423.
55] Y. Wang, P. Prinsen, K. S. Triantafyllidis, S. A. Karakoulia, A. Yepez, C. Len, R.
Luque, ChemCatChem, 2018, 10, 3459-3468.
1
[
2
7