Air-stable and reusable nickel phosphide nanoparticle catalyst for the highly selective hydrogenation ofd-glucose tod-sorbitol

Article abstract of DOI:10.1039/d0gc03301d

The hydrogenation of carbohydrates to polyols is an industrially important process, but it requires air-unstable, non-noble metal catalysts with low activity and harsh reaction conditions. Herein, we report a hydrotalcite (HT)-supported nickel phosphide nanoparticle (nano-Ni₂P/HT) that exhibits both air stability and high activity for the selective hydrogenation ofd-glucose tod-sorbitol in water. The nano-Ni₂P/HT catalyst providesd-sorbitol in excellent yield with >99% selectivity under mild reaction conditions, and is the first non-noble metal catalyst that can operate under just 1 bar of H₂or at ambient temperature. This high-performance nano-Ni₂P/HT catalyst is significantly different from conventional Ni(0) and NiO nanoparticles and Raney catalysts, which result in almost no production ofd-sorbitol, demonstrating the unique catalysis of nano-Ni₂P/HT. Furthermore, nano-Ni₂P/HT shows the highest activity among those reported for non-noble metal catalysts. The nano-Ni₂P/HT catalyst can also be reused without sacrificing its high activity and selectivity. Additionally, the successful transformation of a concentratedd-glucose solution (50 wt%) tod-sorbitol has been achieved. This is the first example of an air-stable, highly active, and reusable non-noble metal catalyst that can replace conventional catalysts used ford-sorbitol production, thus providing a cheap, green, and sustainable route for this process.

Full text of DOI:10.1039/d0gc03301d

Showcasing research from Professor Takato Mitsudome's
laboratory, Graduate School of Engineering Science,
Osaka University, Japan.
As featured in:
Volume 23
Number
March 2021
Pages 1885-2186
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7
Air-stable and reusable nickel phosphide nanoparticle
catalyst for the highly selective hydrogenation of D-glucose
to D-sorbitol
Green
a greener sustainable future
Chemistry
Cutting-edge research for
rsc.li/greenchem
A hydrotalcite-supported nickel phosphide nanoparticle
(nano-Ni2P/HT) exhibits both air stability and high activity
for promoting the selective hydrogenation of D-glucose to
D-sorbitol in water even at 1 bar H2 or ambient temperature.
nano-Ni2P/HT is also reusable and applicable to the
successful transformation of a concentrated D-glucose
solution (50 wt%) to D-sorbitol. This is the first example of
an air-stable, highly active, and reusable non-noble metal
catalyst that can replace conventional catalysts used for
D-sorbitol production, thus providing a cost-effective, green,
and sustainable route for this process.
ISSN 1463-9262
PAPER
Bert U. W. Maes et al.
Efficient demethylation of aromatic methyl ethers with HCl
in water
See Takato Mitsudome et al.,
Green Chem., 2021, 23, 2010.
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Air-stable and reusable nickel phosphide
nanoparticle catalyst for the highly selective
hydrogenation of D-glucose to D-sorbitol†
Cite this: Green Chem., 2021, 23,
2010
c
Sho Yamaguchi, a Shu Fujita,a Kiyotaka Nakajima, b Seiji Yamazoe,
a
Jun Yamasaki,d Tomoo Mizugaki a,e and Takato Mitsudome
*
The hydrogenation of carbohydrates to polyols is an industrially important process, but it requires air-
unstable, non-noble metal catalysts with low activity and harsh reaction conditions. Herein, we report a
hydrotalcite (HT)-supported nickel phosphide nanoparticle (nano-Ni2P/HT) that exhibits both air stability
and high activity for the selective hydrogenation of D-glucose to D-sorbitol in water. The nano-Ni2P/HT
catalyst provides D-sorbitol in excellent yield with >99% selectivity under mild reaction conditions, and is
the first non-noble metal catalyst that can operate under just 1 bar of H2 or at ambient temperature. This
high-performance nano-Ni2P/HT catalyst is significantly different from conventional Ni(0) and NiO nano-
particles and Raney catalysts, which result in almost no production of D-sorbitol, demonstrating the
unique catalysis of nano-Ni2P/HT. Furthermore, nano-Ni2P/HT shows the highest activity among those
reported for non-noble metal catalysts. The nano-Ni2P/HT catalyst can also be reused without sacrificing
its high activity and selectivity. Additionally, the successful transformation of a concentrated D-glucose
solution (50 wt%) to D-sorbitol has been achieved. This is the first example of an air-stable, highly active,
and reusable non-noble metal catalyst that can replace conventional catalysts used for D-sorbitol pro-
duction, thus providing a cheap, green, and sustainable route for this process.
Received 30th September 2020,
Accepted 22nd January 2021
DOI: 10.1039/d0gc03301d
rsc.li/greenchem
ten biomass-derived building blocks that can be converted
into high-value, bio-based products or materials.3
Introduction
D-Sorbitol is a large-volume sugar alcohol that is ubiquitous
The catalytic hydrogenation of D-glucose4–6 is a reliable and
and widely applied in numerous fields, including food and straightforward method for synthesizing D-sorbitol with a pro-
cosmetic industries and drug synthesis.1 It can also be used as duction rate of more than 800 000 ton per year. This reaction
a starting material for the synthesis of various useful products, has been well studied using various heterogeneous catalysts
such as L-ascorbic acid and lower polyols, which are down- comprising Ni,2,7–20 Co,18,21–23 Rh,8 Ru,13,24–37 or Pt.35,38,39
stream products in the petrochemical industry.2 The versatility Among them, sponge Ni catalysts, such as RANEY® Ni, are pre-
of D-sorbitol has promoted its inclusion in the list of the top dominantly used for industrial D-sorbitol production because
they are composed of low-cost, earth-abundant elements.
However, sponge Ni catalysts suffer from pyrophoricity40 and
undergo rapid deactivation caused by metal leaching, metal
sintering, and support degradation.41,42 Moreover, owing to
their low catalytic activities, high hydrogen gas pressures and
temperatures (100–180 °C and under 50–150 bar,6 respectively)
are inevitably required. As an alternative to Ni-based catalysts,
noble-metal-based catalysts, such as carbon-supported Ru cat-
alysts, have been recently developed for D-sorbitol
production.25,27,29,31,33–36 Although these catalysts are efficient,
their constituent metals are rare and expensive. Furthermore,
these catalysts are susceptible to poisoning by strong coordi-
nation with organic impurities.43 Consequently, from the per-
spectives of practicality and green sustainable chemistry, the
development of air-stable, highly active, and reusable non-
aDepartment of Materials Engineering Science, Graduate School of Engineering
Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
E-mail: mitsudom@cheng.es.osaka-u.ac.jp
bInstitute for Catalysis, Hokkaido University, Kita 21 Nishi 10, Kita-ku,
Sapporo 001-0021, Japan
cDepartment of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa,
Hachioji, Tokyo 192-0397, Japan
dResearch Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1,
Mihogaoka, Ibaraki, Osaka 567-0047, Japan
eInnovative Catalysis Science Division, Institute for Open and Transdisciplinary
Research Initiatives (ICS-OTRI), Osaka University, Suita, Osaka 565-0871, Japan
†Electronic supplementary information (ESI) available: General experimental
details, characterization of fresh and spent Ni2P catalysts, gram-scale and re-
cycling experiments, performance comparison with previously reported catalysts.
See DOI: 10.1039/d0gc03301d
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noble metal catalysts for D-glucose hydrogenation is an extre- using an FEI Titan Cubed G2 60-300 instrument operating at
mely important goal. 300 kV and equipped with a Super-X EDX detector. Elemental
Recently, our group has reported the unique catalysis of a mapping based on the quantitative analysis of the EDX spectra
Ni phosphide nanoparticle (NP) (nano-Ni2P) to promote the was carried out using Esprit software. Ni K-edge X-ray absorp-
selective transformation of biofuranic aldehydes to diketones tion spectra were recorded at room temperature using a Si
in water.44 Unlike the conventional sponge Ni catalysts, nano- (111) monochromator at the BL01B1 and BL14B2 lines of
Ni2P has an air-stable metallic nature without pyrophoricity SPring-8 at the Japan Synchrotron Radiation Research Institute
and shows high hydrogenation activity comparable to that of (JASRI) in Harima, Japan. The obtained spectra were analyzed
noble-metal catalysts. These facts encouraged us to employ using Athena software. After normalization at the edge height,
nano-Ni2P as a green catalytic system for the hydrogenation of the k3-weighted χ spectra were extracted. Subsequently, these
D-glucose to D-sorbitol. Herein, we report the highly efficient spectra in the k range of 3–13 Å−1 were Fourier-transformed
catalytic transformation of D-glucose into D-sorbitol using sup- (FT) into the R-space. Curve-fitting analysis was conducted in
ported
nano-Ni2P
catalysts.
A
hydrotalcite
(HT; the R range of 1.3–2.7 Å using the back-scattering amplitude
Mg6Al2(OH)16CO3·4H2O)-supported Ni2P NP (nano-Ni2P/HT) and phase shift functions of Ni–P and Ni–Ni, which were calcu-
exhibited both air stability and high activity for the hydrogen- lated with the FEFF8.5L program.45 X-ray diffraction (XRD) pat-
ation of D-glucose in water under mild reaction conditions (1 terns were recorded using a Philips X’Pert-MPD diffractometer
bar of H2 or ambient temperature). Notably, the achieved turn- with Cu-Kα radiation. X-ray photoelectron spectroscopy (XPS)
over number (TON) was higher than those of previously analysis was performed on a KRATOS system equipped with a
reported non-noble metal catalysts. This outstanding perform- mono Al X-ray source and a hemispherical analyzer operating
ance significantly distinguished nano-Ni2P/HT from other con- in the fixed analyzer transmission mode. The spectra were
ventional Ni catalysts, such as Ni(0) and NiO NPs, and Raney obtained at a pass energy of 40.0 eV with an Al–K X-ray source
catalysts. Furthermore, nano-Ni2P/HT could be recycled operating at 50 W and 154 kV. The analysis area was 0.7 ×
without losing its original activity and was successfully applied 0.3 mm2 and the working pressure in the analysis chamber
to the high-yield synthesis of D-sorbitol from a concentrated was less than 1 × 10−8 Pa. The C 1s peak at a binding energy of
D-glucose solution (50 wt%), thus demonstrating the signifi- 284.6 eV was used as the internal reference.
cant potential of this catalyst for industrial applications.
Catalyst preparation
All the experiments were conducted using standard Schlenk
line techniques. nano-Ni2P was prepared according to our pre-
Experimental
Reagents
vious report44 with some modifications. Ni(acac)2 (1.0 mmol)
and hexadecylamine (10 mmol) were combined with triphenyl
Nickel(II) acetylacetonate (Ni(acac)2, 95%) was purchased from
Sigma-Aldrich (Japan), whereas >97% triphenyl phosphite and
>95% hexadecylamine were purchased from Tokyo Chemical
Industry Co. Ltd (Japan). All the employed organic reagents
were purified before use. HT (AD-500NS) was obtained from
Tomita Pharmaceutical Co. Ltd (Japan) and SiO2 (Q-6) was pro-
cured from Fuji Silysia Chemicals (Japan). TiO2 (JRC TIO-15)
and ZrO2 (JRC ZRO-6) were provided by the Catalysis Society of
Japan and used as reference catalyst supports. Al2O3
(AKP-G015) was obtained from Sumitomo Chemical Co. Ltd
(Japan). Nb2O5 and Y2O3 were purchased from Wako Pure
Chemical Industries Ltd (Japan). Ru/C and mordenite were
obtained from N.E. CHEMCAT and the Catalysis Society of
Japan, respectively. RANEY® Ni (∼50%) was obtained from
Wako Pure Chemical Industries Ltd (Japan).
phosphite (10 mmol) in a Schlenk flask. The mixture was
stirred at 120 °C for 1 h in vacuo, heated to 315 °C at a rate of
30 °C min−1, and then kept constant for 2 h, yielding a black
colloidal solution. After cooling the mixture to room tempera-
ture, the black product was isolated by precipitation in
acetone. The obtained precipitate was washed several times
with a chloroform–acetone mixture and then dried in vacuo
overnight to afford nano-Ni2P. Next, nano-Ni2P (23 mg) was
dispersed in hexane (50 mL) via sonication for 1 h and then
stirred with HT (1.0 g) for 6 h at room temperature to afford
nano-Ni2P/HT as a gray powder. A similar procedure was fol-
lowed to prepare the other nano-Ni2P/support catalysts. Ni/HT
and its H2-reduced form (Ni/HT-red) were used as model cata-
lysts for NiO NPs and Ni(0) NPs, respectively, and were pre-
pared as follows: Ni(acac)2 (0.3 mmol) was added to acetone
(50 mL) with stirring. After 10 min, HT (1.0 g) was added and
the mixture was stirred for 1 h. Acetone was then removed by
Characterization
Inductively coupled plasma atomic emission spectrometry evaporation under reduced pressure to give a pale green
(ICP-AES) was performed using an SII Nano Technology powder. The obtained powder was dried in vacuo overnight
SPS7800 instrument. Transmission electron microscopy (TEM) and calcined in air at 500 °C for 3 h to give Ni/HT. Then,
was conducted on JEM-ARM200F and FEI Tecnai G2 20ST Ni/HT was treated with a H2 flow at 600 °C for 3 h (ref. 46 and
instruments operating at 200 kV. The size distributions were 47) to afford Ni/HT-red. A TEM image and the XPS analysis of
determined by counting 200 particles. Scanning transmission Ni/HT-red are shown in Fig. S1 and S2,† respectively. The Ni(0)
electron microscopy (STEM) images and corresponding NPs approximately 5.0 nm in diameter were highly dispersed
energy-dispersive X-ray spectroscopy (EDX) data were collected on HT.
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Reaction procedure
EDX showed that Ni and P are homogeneously dispersed in
nano-Ni2P, where the molar ratio of Ni to P was ∼2 : 1
(Fig. 1c–f). Overall, these results support the successful syn-
thesis of nano-Ni2P/HT, which consists of spherical nano-Ni2P
highly dispersed on the HT surface.
D-Glucose (90 mg, 0.5 mmol), supported Ni2P catalyst (200 mg,
33 μmol Ni), and distilled water (3 mL) were placed in a 50 mL
stainless-steel autoclave with a Teflon inner cylinder. The
reactor was purged four times with H2 and pressurized with 20
bar of H2 at room temperature. The reactor was then heated at
100 °C for 2 h while stirring at 800 rpm. After the reaction, the
autoclave was cooled in an ice-water bath and the H2 gas was
carefully released. The reaction mixture was subsequently sep-
arated by centrifugation. The products in solution were ana-
lyzed by high-performance liquid chromatography (HPLC;
Next, X-ray absorption fine structure (XAFS) analysis was
carried out to elucidate the electronic state of the Ni species in
nano-Ni2P/HT. The X-ray absorption near-edge structure
(XANES) spectrum of nano-Ni2P/HT was compared to those of
Ni foil, NiO, and bulk Ni2P as references (Fig. 2a). The absorp-
tion edge energy of nano-Ni2P/HT was similar to that of Ni foil,
suggesting that the Ni species in nano-Ni2P/HT exists in a
metal-like state, even after exposure to air. This result agrees
with the conclusions of the XPS analysis of nano-Ni2P/HT,
where two peaks observed at 852.4 and 869.4 eV are very
similar to those of metallic Ni 2p3/2 (852.8 eV) and Ni 2p1/2
(870.0 eV), respectively (Fig. S4a†). This unique air stability dis-
tinguishes nano-Ni2P/HT from pyrophoric sponge Ni catalysts
and conventional air-unstable Ni NP catalysts. The P 2p spec-
trum shows two peaks, indicating the coexistence of phos-
phorus atoms with different electronic states on the surface of
the Ni2P NPs (Fig. S4b†). The first peak at 129.2 eV is close to
that of P0 (130.0 eV) and assigned as Pδ− (0 < δ < 1), while the
Shimadzu LC-20AD, refractive index detector) using
a
Phenomenex Rezex RPM-Monosaccharide Pb++ column (φ =
7.8 × 300 mm; mobile phase: water, 0.6 mL min−1, 70 °C). The
conversion of D-glucose and the yield of D-sorbitol were deter-
mined by HPLC analysis using D-sucrose as an internal
standard.
Results and discussion
Catalyst characterization studies
The crystal structure of pristine nano-Ni2P was evaluated by
XRD (Fig. 1a). The diffraction peaks were consistent with those
of bulk Ni2P and could be indexed to the hexagonal Ni2P
phase.48 The weak and broad diffraction peaks suggested the
formation of nanosized Ni2P. The representative high-angle
annular dark-field (HAADF)-STEM image of nano-Ni2P/HT in
Fig. 1b reveals the formation of spherical nano-Ni2P with a
mean diameter of 5.3 nm (Fig. 1b inset). The XRD pattern of
nano-Ni2P/HT exhibits peaks attributed to the HT structure,
while no peaks corresponding to Ni species are observed due
to the high dispersion of the small Ni2P NPs on HT (Fig. S3†).
The loading amount of Ni was determined to be 0.89 wt% by
ICP-AES analysis. Furthermore, HAADF-STEM coupled with
3−
other peak at 132.3 eV is assigned to the PO4 phosphate
species arising from the superficial oxidation of the Ni2P NPs.
These results demonstrate that the Ni species in the Ni2P NPs
possess metallic states in air. Fig. 2b shows the FT-extended
XAFS (FT-EXAFS) spectrum of nano-Ni2P/HT along with those
of Ni foil, NiO, and bulk Ni2P as references. The spectrum of
nano-Ni2P/HT displays peaks corresponding to Ni–P and Ni–Ni
bonds, which are observed at 1.7–2.0 and 2.0–2.5 Å, respect-
ively. The absence of peaks corresponding to Ni–O bonds indi-
cates that nano-Ni2P/HT is not oxidized in air. The curve-
fitting analysis of the EXAFS spectra is shown in Fig. S5† and
the results are summarized in Table S1.† The Ni–Ni bond
(2.57 Å) of nano-Ni2P/HT was longer than that of Ni foil
(2.48 Å) owing to its network of NiP4 tetrahedra that share ver-
tices. In addition, the CNNi–Ni/CNNi–P ratio (0.9) of nano-Ni2P/HT
was much lower than that of the ideal value in bulk Ni2P
(3.3), indicating that coordinatively unsaturated Ni atoms exist
Fig. 1 (a) X-ray diffraction (XRD) patterns of nano-Ni2P and the Ni2P
reference (JCPDS no. 03-0953); (b) high-angle annular dark-field scan-
ning transmission electron microscopy (HAADF-STEM) image and size
distribution histogram (inset) of nano-Ni2P/hydrotalcite (HT); elemental
mapping of (c) Ni and (d) P; (e) composite overlay of (c) and (d); and (f)
energy-dispersive X-ray spectroscopy (EDX) analysis of nano-Ni2P/HT in
the regions indicated by green circles.
Fig. 2 (a) Ni K-edge X-ray absorption near-edge structure (XANES)
spectra and (b) Fourier-transformed (FT) k3-weighted extended X-ray
absorption fine structure (EXAFS) spectra of Ni foil, NiO, bulk Ni2P, and
nano-Ni2P/HT.
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on the Ni2P surface in nano-Ni2P/HT. The lower CNNi–Ni/CNNi–P Interestingly, the D-sorbitol yield obtained with the nano-Ni2P/
ratio of nano-Ni2P/HT may be due to the exposure of large HT catalyst was also higher than that provided by a commer-
amounts of Ni atoms (Ni(2)) along the (300) plane, as shown cially available noble-metal catalyst (Ru/C), which formed
in Fig. S3.† In addition, the Ni–P bonds (Ni(1)–P in Fig. S6†) mannitol in 8% yield as an undesired byproduct (entries 1 and
were more rigid than the Ni–Ni bonds (Ni(1)–Ni(2)) because 12). Thus, nano-Ni2P/HT shows catalytic activity for this reac-
the latter exhibited a large Debye–Waller (DW) factor (DW > tion that is superior to that of conventional noble-metal-based
0.01, Table S1†). Therefore, coordinatively unsaturated Ni(2) catalysts. The high performance of nano-Ni2P/HT was further
sites are formed on the nano-Ni2P/HT surface.
highlighted in the hydrogenation of D-glucose under milder
conditions. Even at room temperature, nano-Ni2P/HT afforded
D-sorbitol in 90% yield (entry 13), whereas there have been no
previous reports on D-glucose hydrogenation at temperatures
below 90 °C (Table S2†). Furthermore, nano-Ni2P/HT promoted
the hydrogenation of D-glucose under lower H2 pressures
(10 and 1 bar) to afford D-sorbitol in 88% and 73% yields,
respectively (entries 14 and 15), thus outperforming previously
reported catalysts that require 20–50 bar9,10,13–23 or 120 bar11,12
of H2 (Table S2†). To the best of our knowledge, nano-Ni2P/HT
is the first successful non-noble metal catalyst for the hydro-
genation of D-glucose operating at ambient temperature and
under an atmospheric pressure of H2.
The nano-Ni2P/HT catalyst was applicable to the gram-scale
production of D-sorbitol in water, where 3.0 g of D-glucose was
quantitatively converted to D-sorbitol in >99% isolated yield
(Scheme 1a, Fig. S7†). When the hydrogenation was examined
with low amounts of nano-Ni2P/HT (0.10 mol%, Scheme 1b),
D-sorbitol was obtained in 85% yield with a TON exceeding
852. This value is the highest among those previously reported
for non-noble metal catalysts (Table S2†). As D-sorbitol pro-
duction from a concentrated D-glucose solution is a challenge
facing most practical applications of this process, we investi-
gated the operability of our nano-Ni2P/HT catalyst in a 50 wt%
D-glucose solution, which resulted in D-sorbitol being pro-
duced in 92% yield (Scheme 1c). This result clearly demon-
Catalytic performance of nano-Ni2P/HT
We investigated the catalytic activities of nano-Ni2P supported
on various metal oxides for the hydrogenation of D-glucose in
water at 100 °C under 20 bar of H2, and the results are sum-
marized in Table 1. Notably, HT-supported nano-Ni2P showed
a high activity, providing D-sorbitol in 99% yield (entry 1).
Other oxide supports, such as Al2O3, ZrO2, and Y2O3, were also
effective for D-sorbitol production, but the yields were lower
than that obtained with nano-Ni2P/HT (entries 2–4).
Furthermore, the use of TiO2, Nb2O5, SiO2, and mordenite pro-
vided low D-glucose conversions (entries 5–8). These results
reveal that the combination of the nano-Ni2P and HT provided
the best catalytic performance for D-glucose hydrogenation.
In control experiments, conventional Ni catalysts Ni/HT and
Ni/HT-red were tested as model catalysts for NiO NPs and
Ni(0) NPs, respectively, in the hydrogenation of D-glucose. Both
Ni/HT and Ni/HT-red gave negligible amounts of D-sorbitol
and undetectable by-products (entries 9 and 10). Raney cata-
lysts, which are considered state-of-the-art hydrogenation cata-
lyst systems, are often employed for D-glucose hydrogenation.
Under the above reaction conditions, RANEY® Ni displayed
poor activity, providing D-sorbitol in only 4% yield (entry 11),
which demonstrates that the nano-Ni2P/HT catalyst outper-
forms Raney catalysts and other conventional Ni catalysts.
Table 1 Hydrogenation of D-glucose using supported nano-Ni2P catalystsa
Entry
Catalyst
H2 [bar]
Temp. [°C]
Time [h]
D-Glucose conv.b [%]
D-Sorbitol yieldb [%]
D-Mannitol yieldb [%]
1
2
3
4
5
6
7
8
nano-Ni2P/HT
nano-Ni2P/Al2O3
nano-Ni2P/ZrO2
nano-Ni2P/Y2O3
nano-Ni2P/TiO2
nano-Ni2P/Nb2O5
nano-Ni2P/SiO2
nano-Ni2P/mordenite
Ni/HT
20
20
20
20
20
20
20
20
20
20
20
20
50
10
1
100
100
100
100
100
100
100
100
100
100
100
100
25
2
2
2
2
2
2
2
2
2
2
2
2
72
2
>99
83
65
49
20
18
11
6
83
84
4
>99
90
94
>99
99
78
43
42
4
13
8
1
1
4
<1
<1
<1
<1
<1
<1
<1
<1
8
3
1
9
10
11
12
13
14
15
Ni/HT-red
RANEY® Ni
<1
4
88
90
88
73
Ru/C
nano-Ni2P/HTc
nano-Ni2P/HT
nano-Ni2P/HT
<1
5
5
100
100
12
a Reaction conditions: Catalyst (6.6 mol% Ni or Ru), D-glucose (0.5 mmol), water (3 mL). b Conversion of D-glucose and yield of D-sorbitol were
determined by HPLC analysis based on an internal standard method. c Catalyst (13 mol% Ni).
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loading amounts were not changed, confirming that almost no
Ni species were leached from the catalyst. These results indi-
cate that nano-Ni2P is strongly immobilized on the HT support
and that the hydrogenation of D-glucose is attributed to hetero-
geneous catalysis. Structural analyses before and after the reac-
tion were carried out using XPS, TEM, and EDX. From the XPS
analysis, we noted that the binding energy peaks of the spent
nano-Ni2P/HT were almost identical to those of the fresh
nano-Ni2P/HT (Fig. S4 vs. S8,† respectively). This clearly shows
that the Ni2P NPs on the HT support have an air-stable metal-
lic nature even after the hydrogenation of D-glucose. The TEM
image of nano-Ni2P/HT after the reaction also confirmed that
the spherical shape of nano-Ni2P was preserved (Fig. S9†).
HAADF-STEM coupled with EDX revealed that the molar ratio
of Ni to P in nano-Ni2P/HT after the reaction was ∼2 : 1,
similar to that of fresh nano-Ni2P/HT (Fig. S10†). These results
clearly verify that nano-Ni2P/HT is highly durable, which is
consistent with the high reusability observed for this catalyst.
Scheme 1 Gram-scale experiments with (a) 3.0 mol% and (b)
0.10 mol% nano-Ni2P/HT. (c) Hydrogenation of D-glucose at a concen-
tration of 50 wt%.
strates the great potential of this catalyst for industrial
applications.
Rationalization of the catalytic behavior of nano-Ni2P/HT
based on time-course experiments
Next, the reusability of nano-Ni2P/HT was investigated.
After the hydrogenation, nano-Ni2P/HT was recovered by cen-
trifugation and reused for the next reaction without any pre-
treatment. The experiment was repeated four times and no sig-
nificant decreases were observed in either the D-sorbitol yield
or D-glucose conversion (Fig. 3a). The reusability of nano-Ni2P/
HT is distinct from that of reported non-noble metal catalysts,
such as RANEY® Ni,2 Ni–Co,18 and Ni/NiO19 catalysts, where
the activity decreases upon recycling owing to surface poison-
ing by polymerized byproducts or leaching of the Ni metal.
Therefore, we also evaluated the leaching of the metal species
during the reaction (Fig. 3b). After 0.5 h of the hydrogenation
reaction, the nano-Ni2P/HT catalyst was removed by filtration
and the filtrate was then treated under the same hydrogen-
ation conditions. Further heat treatment of the filtrate for
1.5 h did not produce additional D-sorbitol. Furthermore,
based on ICP-AES analyses of the fresh and spent catalysts, Ni
To gain more insight into the catalytic features of nano-Ni2P/
HT, time-course measurements were carried out at 100 °C
under 20, 10, and 1 bar of H2. A quantitative amount of
D-sorbitol was obtained under 20 bar of H2 (Fig. 4a), whereas
small amounts of D-fructose and its hydrogenated product,
D-mannitol, were observed under 10 and 1 bar of H2 (Fig. 4b
and c). It has been reported that HT efficiently promotes the
isomerization of D-glucose to D-fructose.49 Therefore, these
byproducts were likely formed by HT catalysis. In fact, HT pro-
vided D-fructose under our experimental conditions (HT, water,
1 bar of N2, 100 °C) (Fig. 4d). On the other hand, HT is also
known to have oxygen vacancies on its surface, which act as
Lewis acid sites for the activation of carbonyl moieties.50
These facts suggest that HT plays a dual role in the present
D-glucose hydrogenation system. Namely, HT can activate the
carbonyl moiety of the D-glucose aldehyde group, which facili-
Fig. 3 (a) Reusability of nano-Ni2P/HT for the hydrogenation of D-glucose. Reaction conditions: nano-Ni2P/HT (6.6 mol% Ni), D-glucose (0.5 mmol),
water (3 mL), H2 (20 bar), 100 °C, 2 h. (b) Time course of the hydrogenation of D-glucose using nano-Ni2P/HT: ( ) without catalyst removal and ( )
with catalyst removal by hot filtration after 0.5 h. Reaction conditions: nano-Ni2P/HT (6.6 mol% Ni), D-glucose (0.5 mmol), water (3 mL), H2 (20 bar),
100 °C.
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Paper
Fig. 4 (a–c) Time courses of the hydrogenation of D-glucose using nano-Ni2P/HT. Reaction conditions: nano-Ni2P/HT (6.6 mol% Ni), D-glucose
(0.5 mmol), water (3 mL), 100 °C, H2 ((a) 20 bar, (b) 10 bar, and (c) 1 bar). (d) D-Glucose isomerization over HT support. Reaction conditions: HT
(200 mg), D-glucose (0.5 mmol), water (3 mL), 100 °C, N2 (1 bar).
tates the selective production of D-sorbitol (positive effect) activity, and reusability, could serve as a green alternative to
while causing the undesired isomerization of D-glucose to conventional industrial catalysts (e.g., sponge Ni catalysts).
D-fructose (negative effect). The positive effect of the HT This inexpensive and efficient non-noble metal phosphide
support for facilitating the Ni2P-catalyzed hydrogenation catalyst will make a significant contribution to the develop-
becomes remarkable at higher H2 pressures, thus giving pri- ment of future, sustainable reaction processes.
ority to D-sorbitol production through a cooperative effect
between nano-Ni2P and HT.
Conflicts of interest
There are no conflicts to declare.
Conclusions
We report that an HT-supported Ni2P NP can serve as a smart
heterogeneous catalyst for the high-yield synthesis of
D-sorbitol from D-glucose. In sharp contrast to conventional
Acknowledgements
air-unstable catalysts with low activity, our nano-Ni2P catalyst This work was supported by JSPS KAKENHI grant no.
exhibited both air stability and high activity under mild con- 17H03457, 17H03456, 18H01790, 20H02523, and 20H05879.
ditions. Furthermore, nano-Ni2P outperformed conventional This study was partially supported by the Cooperative Research
Ni catalysts, including Ni(0) and NiO NPs, and RANEY® Ni Program of the Institute for Catalysis, Hokkaido University
and exhibited the highest activity among those previously (20B1027).
A part of this work was supported by the
reported for non-noble metal catalysts. Moreover, nano-Ni2P/ “Nanotechnology Platform” Program at Hokkaido University
HT successfully operates under just 1 bar of H2 or at ambient (A-20-HK-0011) and Nanotechnology Open Facilities in Osaka
temperature. Upon undergoing repeated recycling, nano-Ni2P/ University (A-19-OS-0060) of the Ministry of Education,
HT retained its high activity and selectivity and operated well Culture, Sports, Science and Technology (MEXT), Japan. We
in a concentrated D-glucose solution, clearly representing the thank Dr Toshiaki Ina (SPring-8) for XAFS measurements
great potential of this catalyst for industrial applications. We (2019A1390, 2019A1649, 2019B1560, and 2020A1487) and Ryo
believe that nano-Ni2P/HT, with its excellent air stability, high Ota of Hokkaido University for STEM analysis.
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Green Chemistry
28 E. P. Maris, W. C. Ketchie, V. Oleshko and R. J. Davis,
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