Air-Stable and Reusable Cobalt Phosphide Nanoalloy Catalyst for Selective Hydrogenation of Furfural Derivatives

Article abstract of DOI:10.1021/acscatal.0c03300

While metal phosphides have begun to attract attention as electrocatalysts, they remain underutilized in the field of liquid-phase molecular transformations. Herein, we describe a supported cobalt phosphide nanoalloy (nano-Co2P) that functions as a highly efficient, reusable heterogeneous catalyst for the selective hydrogenation of furfural derivatives. The carbonyl moieties of several furfural derivatives were selectively hydrogenated to produce the desired products in high yields. In contrast to conventional nonprecious metal catalysts, nano-Co2P uniquely exhibited air stability, which enabled easy and safe handling and precluded the need for H2 pretreatment. Infrared and density functional theory studies revealed that the highly efficient hydrogenation is due to the favorable activation of the carbonyl moiety of furfural derivatives through the backdonation to its π? orbital from the Co d-electrons.

Full text of DOI:10.1021/acscatal.0c03300

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Research Article
Air-Stable and Reusable Cobalt Phosphide Nanoalloy Catalyst for
Selective Hydrogenation of Furfural Derivatives
Hiroya Ishikawa, Min Sheng, Ayako Nakata,* Kiyotaka Nakajima, Seiji Yamazoe, Jun Yamasaki,
Sho Yamaguchi, Tomoo Mizugaki, and Takato Mitsudome*
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ABSTRACT: While metal phosphides have begun to attract attention as
electrocatalysts, they remain underutilized in the field of liquid-phase molecular
transformations. Herein, we describe a supported cobalt phosphide nanoalloy
(nano-Co2P) that functions as a highly efficient, reusable heterogeneous catalyst for
the selective hydrogenation of furfural derivatives. The carbonyl moieties of several
furfural derivatives were selectively hydrogenated to produce the desired products
in high yields. In contrast to conventional nonprecious metal catalysts, nano-Co2P
uniquely exhibited air stability, which enabled easy and safe handling and precluded
the need for H2 pretreatment. Infrared and density functional theory studies
revealed that the highly efficient hydrogenation is due to the favorable activation of
the carbonyl moiety of furfural derivatives through the backdonation to its π* orbital from the Co d-electrons.
KEYWORDS: cobalt phosphide, nanoalloy, heterogeneous catalyst, hydrogenation, furfural derivative
envisage that the integration of phosphorus (P) into Co
INTRODUCTION
■
nanoparticles has at least three significant merits in organic
transformations. The first is the stabilization of the metallic
state of the Co species. An X-ray absorption fine structure
(XAFS) study showed that metal phosphide nanoalloys have a
highly stable metallic state (nearly zero-valent) in air
(stabilization effect), while conventional non-noble metals
are highly pyrophoric. The second is the modulation of the
electronic state of the Co species (ligand effect). DFT
calculations revealed that P-alloying can increase the d-electron
density of Co near the Fermi level, which favors the
backdonation of electrons to the antibonding orbital of the
substrate, thereby facilitating hydrogenation. The third is the
precise creation of a well-defined catalytic active species (single
active species) in the metal phosphide nanocrystal, which
facilitates selective reactions. In contrast, conventional
heterogeneous catalysts are structurally complex, that is, they
contain ill-defined or irregular multiple active sites, resulting in
inferior catalytic activity and selectivity. These unique
properties of metal phosphide nanoalloys strongly motivated
us to further investigate their catalytic potential in various
organic syntheses.
The combination of a metal with other elements in
nanoparticles has been recognized as a key technology in the
development of new and improved catalysts. Usually, the
second element is a metal, and the resulting metal−metal
nanoalloy catalysts have attracted significant attention in
diverse fields, such as automobile exhaust gas cleaning, oil
refinery, fine chemical synthesis, and electrocatalytic and
photocatalytic reactions.1−3 On the other hand, metal−non-
metal nanoalloys, for example, metal phosphide nanoalloys, are
not as well explored. Recently, metal phosphide nanoalloys,
such as nickel (Ni2P) and cobalt phosphides (Co2P), have
begun to attract attention as a new family of electrocatalysts for
the hydrogen evolution reaction.4 These nanoalloys have also
been applied to hydrotreating reactions in the petroleum
industry.5 However, despite their promising properties, studies
on their catalytic potential for the organic syntheses of fine and
bulk chemicals are rare. There are several interesting reports on
nickel phosphide and cobalt phosphide in the liquid-phase
hydrogenation of alkynes to alkenes,6−8 nitroarenes to
anilines,9,10 cinnamaldehyde to cinnamyl alcohol,11 and
levulinic acid to γ-valerolactone.12,13 We also showed that
Ni2P and Co2P nanoalloys are highly efficient catalysts for the
selective transformation of biofuranic aldehydes to diketones
and the hydrogenation of nitriles to primary amines,
respectively.14,15 Thus, catalysis by metal phosphide nanoalloys
for organic synthesis represents an exciting research area that
still has unexplored possibilities. On the basis of our previous
experimental results and density functional theory (DFT)
calculations of the Co2P nanoalloy (nano-Co2P),14,15 we
Received: July 28, 2020
Revised: November 19, 2020
Published: January 1, 2021
https://dx.doi.org/10.1021/acscatal.0c03300
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Figure 1. TEM images of (a) nano-Co2P and (b) nano-Co2P/Al2O3. (c) HAADF-STEM image of nano-Co2P. Elemental maps of (d) Co and (e)
P. (f) Composition overlay image formed from (d,e).
Herein, we report that a supported nano-Co2P functions
well as an efficient heterogeneous catalyst for the selective
hydrogenation of furfural derivatives. Selective transformations
of furfural derivatives are considerably desirable for the
upgrading of biobased feedstocks because furfural derivatives
are platform molecules from lignocellulosic biomass.16−18
Noble-metal-based catalysts reported to date are highly active
for the hydrogenation of furfural derivatives.19−21 From green
chemistry and economic perspectives, the replacement of
precious metal catalysts with non-noble metal ones is a great
challenge, and much effort has been devoted to the
development of highly active non-noble metal catalysts.22−25
However, all non-noble metal catalysts developed for furfural
hydrogenation to date suffer from air instability (pyrophor-
icity). These catalysts require treatment under strictly
anaerobic conditions or with H2 at high temperature before
use, which severely restricts their industrial application.
Therefore, the development of air-stable and reusable non-
noble metal catalysts is desired. In contrast to the reported
nonprecious metal catalysts, the nano-Co2P catalyst uniquely
has an air-stable metallic nature that enables its easy and safe
handling. Moreover, this catalyst is easily recoverable from the
reaction mixture and is reusable because it retains its activity
without any pretreatment. The activation state of furfural
derivatives on nano-Co2P was investigated by DFT calcu-
lations.
55.8° were observed and are attributed to the (121), (211),
(002), and (320) planes, respectively, of the orthorhombic
structure of the Co2P crystal (Figure S1). A representative
transmission electron microscopy (TEM) image of nano-Co2P
shows the uniform formation of a nanorod structure with an
average length of 32 nm and width of 18 nm (Figures 1a and
S2). The high-angle annular dark-field scanning transmission
electron microscopy (HAADF-STEM) image and energy-
dispersive X-ray spectroscopy (EDX) elemental maps are
depicted in Figures 1c−f. The constituent cobalt and
phosphorus elements are homogeneously distributed in the
nanorod. Elemental analysis by EDX also reveals that the Co/P
atomic ratio is around 2 (Figure S3). These results clearly
demonstrate the successful synthesis of nano-sized Co2P. The
high dispersion of nano-Co2P on Al2O3 is also confirmed by
the TEM image (Figure 1b).
XAFS analysis of nano-Co2P and nano-Co2P/Al2O3 was
carried out in air (Figure 2a). As we previously reported, the
absorption edge energy of nano-Co2P in the Co K-edge X-ray
absorption near edge structure (XANES) spectrum is similar to
that of Co foil, suggesting that the Co species in Co2P is in the
metallic state.15 The spectral features of nano-Co2P/Al2O3
slightly change owing to the immobilization of nano-Co2P on
RESULTS AND DISCUSSION
■
Catalyst Preparation and Characterization. The well-
ordered nano-Co2P was synthesized according to our previous
report with some modifications.15 Briefly, a mixture of 1-
octadecene, hexadecylamine, and triphenyl phosphite in the
presence of CoCl2 was stirred as the temperature was increased
to 290 °C. Further stirring of the mixture for 2 h under Ar
produced a black colloidal solution. The precipitate was
collected by centrifugation and washed with acetone and
chloroform to produce nano-Co2P, which was loaded onto a
metal oxide support, for example, Al2O3, before the reaction for
ease of handling and high dispersion.
Figure 2. (a) Co K-edge XANES spectra of nano-Co2P, nano-Co2P/
Al2O3, and CoOx/Al2O3 with Co foil and Co3O4 as references. (b)
FTs of the k3-weighted EXAFS spectra of nano-Co2P and nano-Co2P/
Al2O3 with bulk Co2P, Co3O4, and Co foil as references.
The crystal structure of nano-Co2P was confirmed by X-ray
diffraction. Major diffraction peaks at 40.8°, 43.5°, 52.3°, and
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Al2O3, albeit without the formation of the characteristic peaks
of Co oxides. This indicates that the electronic states and/or
local structure of nano-Co2P are affected by Al2O3. On the
other hand, the absorption edge energy of Al2O3-supported
cobalt (CoOx/Al2O3), a conventional catalyst prepared by the
impregnation method, is much higher than those of nano-Co2P
and Co foil but very similar to that of Co3O4. This suggests
that di- and trivalent Co species exist in CoOx/Al2O3. These
results clearly show that an air-stable zero-valent Co species is
formed in nano-Co2P/Al2O3 despite the instability of Co metal
in air. In other words, P-alloying can afford Co species with air-
stable metallic properties which is distinguished from common
cobalt oxide and zero-valent cobalt metal. Figure 2b shows the
Fourier-transforms extended X-ray absorption fine structure
(FTs-EXAFS) spectra of nano-Co2P and nano-Co2P/Al2O3,
with bulk Co2P, Co3O4, and Co foil as references. Two main
peaks at 1.6−2.0 and 2.0−2.5 Å, which are attributed to Co−P
and Co−Co bonds, respectively, are observed in the spectra of
nano-Co2P, nano-Co2P/Al2O3, and bulk Co2P. The absence of
peaks corresponding to the Co−O bond indicates that nano-
Co2P and nano-Co2P/Al2O3 are not oxidized in air, which is
consistent with the result of the XANES analysis. The local
structure of nano-Co2P was further studied by curve fitting
analysis (Figure S4 and Table S1). nano-Co2P and nano-
Co2P/Al2O3 have longer Co−Co bonds (2.56 Å) compared
with Co foil (2.49 Å) because of the existence of Co in the
network of tetrahedral CoP4 with vertex and edge sharing in
orthorhombic Co2P. Notably, the coordination numbers of the
Co−Co shell of nano-Co2P (3.5) and nano-Co2P/Al2O3 (3.3)
are smaller than that of bulk Co2P (4.0), which indicate that
nano-Co2P and nano-Co2P/Al2O3 have catalytically active
unsaturated Co−Co sites on the surface. The local structure of
nano-Co2P is maintained after immobilization on the Al2O3
support. Therefore, the obvious change in the XANES
spectrum of nano-Co2P after immobilization on Al2O3 is due
to the strong electronic interaction between nano-Co2P and
Al2O3. The electronic states of surface Co in nano-Co2P and
nano-Co2P/Al2O3 were also investigated by X-ray photo-
electron spectroscopy. Co 2p3/2 (777.7 eV) and Co 2p1/2
(792.8 eV) binding energy peaks are observed for nano-Co2P,
which are very close to those of metallic Co 2p3/2 (777.9 eV)
and 2p1/2 (793.5 eV).26 These Co 2p3/2 and 2p1/2 peaks of
nano-Co2P shift to 778.1 and 793.2 eV, respectively, after
immobilization on Al2O3 (Figure S5), confirming the
electronic interaction between nano-Co2P and Al2O3.
Table 1. Hydrogenation of HMF to BHMF Using Co
Catalysts
a
b
b
entry
catalyst
time (h) conv. (%) sel. (%)
1
2
3
4
5
6
7
8
9
nano-Co2P/Al2O3
nano-Co2P/Al2O3
nano-Co2P/Al2O3
nano-Co2P
nano-Co2P/ZrO2
nano-Co2P/hydroxyapatite
nano-Co2P/MgO
CoOx/Al2O3
1
4
12
1
1
1
1
1
1
54
>99
>99
15
50
40
28
0
>99
>99
>99
96
95
>99
92
-
c
d
e
CoOx/Al2O3
0
-
0
10
bulk Co2P
1
6
a
b
Reaction conditions: HMF (0.25 mmol), H2O (3 mL). Determined
by gas chromatography−mass spectrometry (GC−MS) using an
c
d
internal standard technique. H2 (2 MPa), 80 °C. Catalyst prepared
e
by the impregnation method. Catalyst prepared by the deposition−
precipitation method.
on Al2O3. nano-Co2P dispersed on other typical supports also
gave sufficient yields of BHMF (Table 1, entries 5−7), which
indicates that the type of support does not significantly affect
the hydrogenation efficiency. On the other hand, conventional
CoOx/Al2O3 catalysts prepared by impregnation and deposi-
tion−precipitation methods did not show any catalytic activity
(Table 1, entries 8 and 9). Commercially available bulk Co2P
was also quite inactive in this hydrogenation reaction (Table 1,
entry 10). These results clearly demonstrate that both
integration of the P atom into Co and the nano-sizing of
Co2P are crucial for generating a highly active Co catalyst for
hydrogenation.
To confirm the occurrence of hydrogenation on nano-Co2P/
Al2O3, the solid catalyst was removed by filtration after ca. 50%
conversion of HMF. The filtrate was then further treated under
the same reaction conditions. No additional products were
formed (Scheme S1), confirming that the reaction occurs
heterogeneously. After the reaction, the used nano-Co2P/
Al2O3 was easily recovered by simple centrifugation and reused
without any loss of its catalytic activity and selectivity even
after the fifth recycling experiment (Figure 3). We further
investigated the reaction rate at an incomplete reaction time (1
Catalytic Performance of nano-Co2P/Al2O3. Initially,
the catalytic potential of nano-Co2P/Al2O3 was tested in the
hydrogenation of the biomass derivative, 5-hydroxymethylfur-
fural (HMF), in water under 4 MPa of H2 at 130 °C for 1 h
without any pretreatment (Table 1). Notably, nano-Co2P/
Al2O3 showed high activity, and the corresponding 2,5-
bis(hydroxymethyl)furan (BHMF), which is valuable as a six-
carbon monomer material was obtained in 54% yield with
>99% selectivity (Table 1, entry 1). A quantitative yield of
BHMF was achieved by prolonging the reaction time to 4 h
(Table 1, entry 2). Furthermore, nano-Co2P/Al2O3 promoted
hydrogenation even under milder reaction conditions (i.e., a
lower H2 pressure of 2 MPa and a lower reaction temperature
of 80 °C), giving BHMF in >99% yield (Table 1, entry 3).
Unsupported nano-Co2P also promoted the hydrogenation of
HMF, although the yield of BHMF was much lower than that
obtained using nano-Co2P/Al2O3 (Table 1, entry 4 vs entry 1).
This shows the positive effect of high dispersion of nano-Co2P
Figure 3. Reuse experiments of nano-Co2P/Al2O3 in the hydro-
genation of HMF to BHMF. Reaction conditions: nano-Co2P/Al2O3
(10 mol %), HMF (0.25 mmol), H2O (3 mL), H2 (4 MPa), 130 °C.
Reaction time: 4 h (blue bars), 1 h (white diamonds).
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h) in the recycling experiments. The yields of BHMF
(diamond suit in Figure 3) obtained using the reused and
fresh catalysts were similar, revealing the high durability of this
catalyst. The TEM image of the used nano-Co2P/Al2O3 shows
that its average diameter and size distribution are similar to
those of nano-Co2P/Al2O3 before use, and no aggregation of
nano-Co2P is observed (Figure S6). In the Co K-edge XANES
spectrum, the absorption edge energy of the used nano-Co2P/
Al2O3 is almost the same as that of fresh nano-Co2P/Al2O3,
suggesting that the metallic nature of the Co species is
maintained during the reaction (Figure S7). Furthermore, the
loading amounts of Co and P in nano-Co2P/Al2O3 are almost
the same before and after the reaction (Table S2). These
results are consistent with the reusability of nano-Co2P/Al2O3.
Subsequently, to assess the air stability of nano-Co2P, nano-
Co2P/Al2O3 was exposed to air and tested in the hydro-
genation of HMF. Interestingly, no catalyst deactivation was
observed even after exposure to air for 72 h (Figure 4).
Scheme 1. Hydrogenation of Furfural Derivatives Using
nano-Co2P/Al2O3
a
a
Reaction conditions: substrate (0.25 mmol), solvent (3 mL).
bDetermined by GC−MS using an internal standard technique.
cDetermined by H NMR spectroscopy using an internal standard
1
technique.
Scheme 2. Gram-Scale Reaction of HMF Using nano-Co2P/
Al2O3
Figure 4. Air stability tests of nano-Co2P/Al2O3 in the hydrogenation
of HMF to BHMF. Reaction conditions: nano-Co2P/Al2O3 (10 mol
%), HMF (0.25 mmol), H2O (3 mL), H2 (4 MPa), 130 °C, 1 h.
Furthermore, atomic-scale analysis using Co K-edge EXAFS
showed that the local structure of nano-Co2P hardly changed
(Figure S8), confirming that nano-Co2P has a uniquely air-
stable metallic nature.
The catalytic potential of nano-Co2P in the hydrogenation of
several biomass-derived furfurals (furfural, 5-methylfurfural,
and 5-acetoxymethylfurfural) was further investigated. After
optimizing the reaction conditions by screening various
solvents (Table S3), the carbonyl moieties of furfural
derivatives were selectively hydrogenated to the corresponding
alcohols in high yields (Scheme 1), whereas neither furan-ring
hydrogenation25,27 nor hydrodeoxygenation occurred.28,29 The
obtained products, such as furfuryl alcohol and 5-methyl-
furfuryl alcohol, are useful raw materials for resins, fibers, and
solvents.13,30,31 nano-Co2P/Al2O3 could also be operated
under gram-scale conditions: 1.0 g of HMF was successfully
converted to BHMF in 85% isolated yield (0.86 g) without any
undesired by-products (Scheme 2).
Rationalization of the Catalytic Behavior of nano-
Co2P/Al2O3. To obtain more insight into the unique catalysis
by nano-Co2P/Al2O3, a Fourier-transform infrared (FT-IR)
study of nano-Co2P/Al2O3 was carried out. When furfural
vapor was adsorbed on nano-Co2P/Al2O3 at 25 °C, an
absorption band assigned to a carbonyl bond stretching
vibration appeared as a single peak at 1665 cm−1 (Figure 5a).
Notably, this value is much lower than that for furfural
adsorbed on Al2O3 at 1690 cm−1 (Δ25 cm−1, Figure 5b) and
Figure 5. FT-IR spectra of (a) furfural-treated nano-Co2P/Al2O3, (b)
furfural-treated Al2O3, and (c) pure furfural vapor.
furfural vapor at 1720 cm−1 (Δ55 cm−1, Figure 5c). This large
red-shift reveals that nano-Co2P can strongly activate the C
O bond of furfural. CO adsorption on nano-Co2P was also
analyzed by FT-IR spectroscopy (Figure S9). CO adsorbed on
nano-Co2P exhibits a peak at 2056 cm−1, which is attributed to
linearly adsorbed CO on metallic Co through the back-
donation of the d-electrons of Co to the π* antibonding
molecular orbital of CO.32
The detailed activation states of furfural on the Co2P surface
were also investigated by DFT calculations. We investigated
several adsorption sites on the Co2P (0001) surface (Figure
S10), and the optimized structures of adsorbed furfural are
shown in Figure S11. The adsorption structures can be
categorized roughly into three groups, as shown in Figure 6:
both the CO bond and furan ring are adsorbed parallel to
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Figure 6. (a−c) Groups A, B, and C of the adsorption structures of furfural on the Co2P surface. Correlation of the (d) adsorption energy and (e)
CO bond elongation to the change in electron density. The red circles, blue squares, and green triangles correspond to groups A, B, and C,
respectively.
Figure 7. (a) Optimized structure of furfural adsorbed on the Co2P surface and (b) projected density of states of d-electrons on the Co2P surface
(i.e., the first layer) with (red) and without (black) furfural.
the surface (group A), the O atom in CO and a C−O bond
in the furan ring are adsorbed on the surface (group B), and
only CO is strongly adsorbed on the surface (group C). The
O atom in the furan ring also forms a bond to the surface in a
few cases in group C. The adsorption energies, ΔE = E(Co2P−
furfural) − E(Co2P) − E(furfural), are summarized in Table
S4. The mean adsorption energies for groups A, B, and C are
−67.7, −42.7, and −33.6 kcal/mol, respectively, where a more
negative energy means more stable adsorption. The bond
lengths in isolated furfural and the changes caused by
adsorption are given in Table S5. The CO bond is
elongated in all groups, and the mean elongation lengths for
groups A, B, and C are 0.121, 0.100, and 0.092 Å, respectively.
The electron distributions before and after adsorption were
also investigated by Mulliken population analysis (Table S6).33
The results reported in Tables S4−S6 are summarized as
correlations between the adsorption energies, CO bond
elongations, and changes in electron density in Figure 6d,e,
respectively. We found that the adsorption energy tends to
increase as the aldehyde in furfural accepts more electrons.
Moreover, the CO bond length increases with increasing
electron density of the O atom in CO. Based on these
calculated results, group A is favored over groups B and C.
The most stable adsorption structure in group A is given in
Figure 7a. The CO bond length of the furfural molecule
placed on the hollow site of nano-Co2P elongates from 1.23 to
1.37 Å upon the transfer of 0.16 electrons from nano-Co2P to
furfural. Along with charge transfer, the number of d-electrons
on the nano-Co2P surface around the Fermi level decreases, as
shown in Figure 7b. These results indicate that the d-electrons
on the nano-Co2P surface strongly activate the carbonyl moiety
of furfural by enhancing the backdonation of electrons to its π*
orbital, which weakens the CO bond. The activated CO
bond of furfural is then easily hydrogenated by dissociated
hydrogen on the Co2P surface. We have already reported that
H2 dissociation on the Co2P surface is favored by electron
transfer from Co2P to H2.15 The results from the DFT
calculations are consistent with the findings from the IR study.
CONCLUSIONS
■
We report for the first time that a supported cobalt phosphide
nanoalloy can serve as an air-stable and reusable heterogeneous
catalyst for the selective hydrogenation of furfural derivatives.
The Al2O3-supported nano-Co2P catalyst is easy to handle and
does not require H2 pretreatment before use. Furthermore, the
supported nano-Co2P can be reused without significant loss of
activity and selectivity. IR studies and DFT calculations
revealed that nano-Co2P strongly activates the carbonyl moiety
of furfural through the backdonation of electrons to the π*
orbital of the CO moiety of furfurals, leading to the selective
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hydrogenation of furfural derivatives to furfuryl alcohol
derivatives.
Gram-Scale Reaction. The gram-scale reaction of HMF
was performed in a 300 mL stainless steel autoclave with a
Teflon inner cylinder at 130 °C under 4 MPa of H2 for 4 h.
After the reaction, nano-Co2P/Al2O3 was filtered to separate
the liquid phase from the solid catalyst. The solvent was
evaporated, and the residue was subjected to silica gel column
chromatography (chloroform/methanol = 93/7) to produce
EXPERIMENTAL SECTION
■
Catalyst Preparation. Synthesis of nano-Co2P. All
reactions were carried out under an argon atmosphere using
standard Schlenk line techniques. In a typical synthesis, 1.0
mmol of CoCl2·6H2O and 10.0 mmol of hexadecylamine were
combined with 10.0 mL of 1-octadecene and 10.0 mmol of
triphenyl phosphite in a Schlenk flask. The system was heated
to 150 °C to remove low-boiling-point impurities. The
temperature was then increased to 290 °C and maintained
for 2 h. Afterward, the mixture was cooled to room
temperature. The black product was isolated by precipitation
with acetone. To remove as much organics as possible,
redispersion and precipitation cycles using chloroform and
acetone were continued until the supernatant liquid was
transparent. The obtained powder was dried in vacuum
overnight.
1
isolated BHMF, which was identified by GC−MS and H and
13C NMR.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acscatal.0c03300.
General experimental details, characterization of cata-
lysts, hot filtration experiment, effect of solvents, DFT
calculation details, and product identification (PDF)
Preparation of nano-Co2P/Support. Typically, 37.2 mg of
nano-Co2P was dispersed in 100 mL of n-hexane and stirred
with 1.0 g of Al2O3 at room temperature. The obtained powder
was dried in vacuum overnight to produce nano-Co2P/Al2O3
as a gray powder. The same procedure was used to prepare the
other nano-Co2P/support catalysts.
Preparation of CoOx/Al2O3 by Impregnation Method.
CoCl2·6H2O (0.5 mmol) was dissolved in acetone (50 mL).
Al2O3 (1.0 g) was added, and the mixture was stirred for 30
min at room temperature. Acetone was removed by
evaporation under reduced pressure, and the obtained powder
was dried at 110 °C overnight. The dried powder was calcined
in air at 500 °C for 3 h to produce CoOx/Al2O3.
Preparation of CoOx/Al2O3 by Deposition−Precipitation
Method. Al2O3 (1.0 g) was soaked in 50 mL of an aqueous
solution of CoCl2 (10 mM). The pH was then adjusted to 8.5
with a solution of NaOH (0.1 M). After stirring the mixture for
6 h at room temperature, the obtained solid was filtered,
washed with deionized water, and dried in vacuum at room
temperature, producing CoOx/Al2O3.
Typical Reaction Procedure. The typical reaction
procedure for the hydrogenation of HMF to BHMF using
nano-Co2P/Al2O3 was as follows. nano-Co2P/Al2O3 powder
was placed in a 50 mL stainless steel autoclave with a Teflon
inner cylinder. HMF (0.25 mmol) and distilled water (3 mL)
were subsequently added. The reaction mixture was stirred
vigorously at 130 °C under 4 MPa of H2. After the reaction,
dimethyl sulfone (internal standard) and MeOH were added
to the reaction mixture, and then, the catalyst was separated by
centrifugation. The reaction solution was analyzed by GC−MS
to determine the conversion and yield. GC−MS was
performed using a Shimadzu GCMS-QP2010 SE gas
chromatograph−mass spectrometer equipped with a capillary
column (InertCap WAX-HT, GL Sciences, 30 m × 0.25 mm
i.d., 0.25 μm). The column oven temperature started from 120
°C (3-min hold) and was then increased to 200 °C at a heating
rate of 20 °C/min. Other conditions were as follows: column
flow rate (He carrier): 1.22 mL/min; split ratio: 32:1; injector
temperature: 250 °C; and interface temperature: 250 °C.
Recycling Experiments. After the reaction, nano-Co2P/
Al2O3 was removed by centrifugation, and the yield was
determined by GC−MS analysis. The spent catalyst was
washed with water and 2-propanol for the reuse experiments
without any other pretreatment.
AUTHOR INFORMATION
■
Corresponding Authors
Ayako Nakata − First-Principles Simulation Group, Nano-
Theory Field, International Center for Materials
Nanoarchitectonics (WPI-MANA), National Institute for
Materials Science (NIMS), Tsukuba, Ibaraki 305-0044,
Japan; orcid.org/0000-0002-3311-6283;
Email: NAKATA.ayako@nims.go.jp
Takato Mitsudome − Department of Materials Engineering
Science, Graduate School of Engineering Science, Osaka
University, Toyonaka, Osaka 560-8531, Japan;
orcid.org/0000-0002-0924-5616; Email: mitsudom@
cheng.es.osaka-u.ac.jp
Authors
Hiroya Ishikawa − Department of Materials Engineering
Science, Graduate School of Engineering Science, Osaka
University, Toyonaka, Osaka 560-8531, Japan
Min Sheng − Department of Materials Engineering Science,
Graduate School of Engineering Science, Osaka University,
Toyonaka, Osaka 560-8531, Japan
Kiyotaka Nakajima − Institute for Catalysis, Hokkaido
University, Kita-ku, Sapporo 001-0021, Japan; orcid.org/
0000-0002-3774-3209
Seiji Yamazoe − Department of Chemistry, Tokyo
Metropolitan University, Hachioji, Tokyo 192-0397, Japan;
orcid.org/0000-0002-8382-8078
Jun Yamasaki − Research Center for Ultra-High Voltage
Electron Microscopy, Osaka University, Ibaraki, Osaka 567-
0047, Japan
Sho Yamaguchi − Department of Materials Engineering
Science, Graduate School of Engineering Science, Osaka
University, Toyonaka, Osaka 560-8531, Japan;
orcid.org/0000-0002-0014-3218
Tomoo Mizugaki − Department of Materials Engineering
Science, Graduate School of Engineering Science, Osaka
University, Toyonaka, Osaka 560-8531, Japan;
orcid.org/0000-0001-5701-7530
Complete contact information is available at:
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ACS Catal. 2021, 11, 750−757

ACS Catalysis
pubs.acs.org/acscatalysis
Research Article
Hydrogenation of Levulinic-Acid to Gamma-Valerolactone in
Aqueous Solution over Acid-Resistant CePO4/Co2P Catalysts.
Green Chem. 2019, 21, 1743−1756.
(13) Yu, Z.; Meng, F.; Wang, Y.; Sun, Z.; Liu, Y.; Shi, C.; Wang, W.;
Wang, A. Catalytic Transfer Hydrogenation of Levulinic Acid to γ-
Valerolactone over Ni3P-CePO4 Catalysts. Ind. Eng. Chem. Res. 2020,
59, 7416−7425.
Author Contributions
The manuscript was written through the contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
(14) Fujita, S.; Nakajima, K.; Yamasaki, J.; Mizugaki, T.; Jitsukawa,
K.; Mitsudome, T. Unique Catalysis of Nickel Phosphide Nano-
particles to Promote the Selective Transformation of Biofuranic
Aldehydes into Diketones in Water. ACS Catal. 2020, 10, 4261−4267.
(15) Mitsudome, T.; Sheng, M.; Nakata, A.; Yamasaki, J.; Mizugaki,
T.; Jitsukawa, K. A Cobalt Phosphide Catalyst for the Hydrogenation
of Nitriles. Chem. Sci. 2020, 11, 6682−6689.
(16) Alonso, D. M.; Bond, J. Q.; Dumesic, J. A. Catalytic Conversion
of Biomass to Biofuels. Green Chem. 2010, 12, 1493−1513.
(17) Nakagawa, Y.; Tamura, M.; Tomishige, K. Catalytic Reduction
of Biomass-Derived Furanic Compounds with Hydrogen. ACS Catal.
2013, 3, 2655−2668.
(18) Chen, S.; Wojcieszak, R.; Dumeignil, F.; Marceau, E.; Royer, S.
How Catalysts and Experimental Conditions Determine the Selective
Hydroconversion of Furfural and 5-Hydroxymethylfurfural. Chem.
Rev. 2018, 118, 11023−11117.
(19) Chen, J.; Lu, F.; Zhang, J.; Yu, W.; Wang, F.; Gao, J.; Xu, J.
Immobilized Ru Clusters in Nanosized Mesoporous Zirconium Silica
for the Aqueous Hydrogenation of Furan Derivatives at Room
Temperature. ChemCatChem 2013, 5, 2822−2826.
(20) Chatterjee, M.; Ishizaka, T.; Kawanami, H. Selective Hydro-
genation of 5-Hydroxymethylfurfural to 2,5-Bis-(hydroxymethyl)furan
using Pt/MCM-41 in an Aqueous Medium: A Simple Approach.
Green Chem. 2014, 16, 4734−4739.
(21) Tamura, M.; Tokonami, K.; Nakagawa, Y.; Tomishige, K. Rapid
Synthesis of Unsaturated Alcohols under Mild Conditions by Highly
Selective Hydrogenation. Chem. Commun. 2013, 49, 7034−7036.
(22) Zhu, Y.; Kong, X.; Yin, J.; You, R.; Zhang, B.; Zheng, H.; Wen,
X.; Zhu, Y.; Li, Y.-W. Covalent-Bonding to Irreducible SiO2 Leads to
High-Loading and Atomically Dispersed Metal Catalysts. J. Catal.
2017, 353, 315−324.
(23) Ma, Y.; Xu, G.; Wang, H.; Wang, Y.; Zhang, Y.; Fu, Y. Cobalt
Nanocluster Supported on ZrREnOx for the Selective Hydrogenation
of Biomass Derived Aromatic Aldehydes and Ketones in Water. ACS
Catal. 2018, 8, 1268−1277.
(24) Watari, R.; Matsumoto, N.; Kuwata, S.; Kayaki, Y. Distinct
Promotive Effects of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) on
Polymer Supports in Copper-Catalyzed Hydrogenation of C=O
Bonds. ChemCatChem 2017, 9, 4501−4507.
ACKNOWLEDGMENTS
■
This work was supported by the Japan Society for the
Promotion of Science (JSPS) KAKENHI Grant nos.
26105003, 17H03457, 18H01790, 17H05224, and
20H02523. This study was partially supported by the
Cooperative Research Program of the Institute for Catalysis,
Hokkaido University (20B1027). A part of this work was
supported by the “Nanotechnology Platform” program at
Hokkaido University (A-20-HK-0011) and Nanotechnology
Open Facilities in Osaka University (A-19-OS-0060) of the
Ministry of Education, Culture, Sports, Science and Technol-
ogy (MEXT), Japan. The DFT calculations were performed on
the Numerical Materials Simulator at NIMS, and the computer
resource was offered under the category of General Projects by
the Research Institute for Information Technology, Kyushu
University. The authors thank Dr. Toshiaki Ina (SPring-8) for
the XAFS measurements (2019A1390, 2019A1649, and
2019B1560) and Ryo Ota of Hokkaido University for the
STEM analysis.
REFERENCES
■
(1) Fang, H.; Yang, J.; Wen, M.; Wu, Q. Nanoalloy Materials for
Chemical Catalysis. Adv. Mater. 2018, 30, 1705698.
(2) Bing, Y.; Liu, H.; Zhang, L.; Ghosh, D.; Zhang, J. Nano-
structured Pt-Alloy Electrocatalysts for PEM Fuel Cell Oxygen
Reduction Reaction. Chem. Soc. Rev. 2010, 39, 2184−2202.
(3) Gilroy, K. D.; Ruditskiy, A.; Peng, H.-C.; Qin, D.; Xia, Y.
Bimetallic Nanocrystals: Syntheses, Properties, and Applications.
Chem. Rev. 2016, 116, 10414−10472.
(4) Shi, Y.; Zhang, B. Recent Advances in Transition Metal
Phosphide Nanomaterials: Synthesis and Applications in Hydrogen
Evolution Reaction. Chem. Soc. Rev. 2016, 45, 1529−1541.
(5) Oyama, S. T. Novel Catalysts for Advanced Hydroprocessing:
Transition Metal Phosphides. J. Catal. 2003, 216, 343−352.
́
́
̀
(6) Carenco, S.; Leyva-Perez, A.; Concepcion, P.; Boissiere, C.;
́
Mezailles, N.; Sanchez, C.; Corma, A. Nickel Phosphide Nano-
(25) Zhu, Y.; Kong, X.; Zheng, H.; Ding, G.; Zhu, Y.; Li, Y.-W.
Efficient Synthesis of 2,5-Dihydroxymethylfuran and 2,5-Dimethylfur-
an from 5-Hydroxymethylfurfural using Mineral-Derived Cu Catalysts
as Versatile Catalysts. Catal. Sci. Technol. 2015, 5, 4208−4217.
(26) Wagner, C. D.; Riggs, W. M.; Davis, L. E.; Mouler, J. F.;
Muilenberg, G. E. Handbook of X-Ray Photoelectron Spectroscopy;
Perkin-Elmer Corp.: Eden Prairie, MN, 1979.
catalysts for the Chemoselective Hydrogenation of Alkynes. Nano
Today 2012, 7, 21−28.
(7) Albani, D.; Karajovic, K.; Tata, B.; Li, Q.; Mitchell, S.; Lopez, N.;
́
́
Perez-Ramírez, J. Ensemble Design in Nickel Phosphide Catalysts for
Alkyne Semi-Hydrogenation. ChemCatChem 2019, 11, 457−464.
(8) Chen, Y.; Li, C.; Zhou, J.; Zhang, S.; Rao, D.; He, S.; Wei, M.;
Evans, D. G.; Duan, X. Metal Phosphides Derived from Hydrotalcite
Precursors toward the Selective Hydrogenation of Phenylacetylene.
ACS Catal. 2015, 5, 5756−5765.
́
(27) Alamillo, R.; Tucker, M.; Chia, M.; Pagan-Torres, Y.; Dumesic,
J. The Selective Hydrogenation of Biomass-Derived 5-Hydroxyme-
thylfurfural using Heterogeneous Catalysts. Green Chem. 2012, 14,
1413−1419.
(9) Yang, S.; Peng, L.; Oveisi, E.; Bulut, S.; Sun, D. T.; Asgari, M.;
Trukhina, O.; Queen, W. L. MOF-Derived Cobalt Phosphide/Carbon
Nanocubes for Selective Hydrogenation of Nitroarenes to Anilines.
Chem.Eur. J. 2018, 24, 4234−4238.
(28) Kong, X.; Zhu, Y.; Zheng, H.; Dong, F.; Zhu, Y.; Li, Y.-W.
Switchable Synthesis of 2,5-Dimethylfuran and 2,5-Dihydroxymethyl-
tetrahydrofuran from 5-Hydroxymethylfurfural over Raney Ni
Catalyst. RSC Adv. 2014, 4, 60467−60472.
(10) Gao, R.; Pan, L.; Wang, H.; Zhang, X.; Wang, L.; Zou, J.-J.
Ultradispersed Nickel Phosphide on Phosphorus-Doped Carbon with
Tailored d-Band Center for Efficient and Chemoselective Hydro-
genation of Nitroarenes. ACS Catal. 2018, 8, 8420−8429.
(11) Gao, R.; Pan, L.; Wang, H.; Yao, Y.; Zhang, X.; Wang, L.; Zou,
J. J. Breaking Trade-Off between Selectivity and Activity of Nickel-
Based Hydrogenation Catalysts by Tuning Both Steric Effect and d-
Band Center. Adv. Sci. 2019, 6, 1900054.
(29) Kumalaputri, A. J.; Bottari, G.; Erne, P. M.; Heeres, H. J.; Barta,
K. Tunable and Selective Conversion of 5-HMF to 2,5-Furandime-
thanol and 2,5-Dimethylfuran over Copper-Doped Porous Metal
Oxides. ChemSusChem 2014, 7, 2266−2275.
(30) Yan, K.; Wu, G.; Lafleur, T.; Jarvis, C. Production, Properties
and Catalytic Hydrogenation of Furfural to Fuel Additives and Value-
Added Chemicals. Renewable Sustainable Energy Rev. 2014, 38, 663−
676.
(12) Feng, H.-J.; Li, X.-C.; Qian, H.; Zhang, Y.-F.; Zhang, D.-H.;
Zhao, D.; Hong, S.-G.; Zhang, N. Efficient and Sustainable
756
https://dx.doi.org/10.1021/acscatal.0c03300
ACS Catal. 2021, 11, 750−757

ACS Catalysis
pubs.acs.org/acscatalysis
Research Article
́
́
(31) Mariscal, R.; Maireles-Torres, P.; Ojeda, M.; Sadaba, I.; Lopez
Granados, M. Furfural: A Renewable and Versatile Platform Molecule
for the Synthesis of Chemicals and Fuels. Energy Environ. Sci. 2016, 9,
1144−1189.
(32) Khassin, A. A.; Yurieva, T. M.; Kaichev, V. V.; Bukhtiyarov, V.
I.; Budneva, A. A.; Paukshtis, E. A.; Parmon, V. N. Metal−Support
Interactions in Cobalt-Aluminum Co-Precipitated Catalysts: XPS and
CO Adsorption Studies. J. Mol. Catal. A: Chem. 2001, 175, 189−204.
(33) Mulliken, R. S. Electronic Population Analysis on LCAO−MO
Molecular Wave Functions I. J. Chem. Phys. 1955, 23, 1833−1840.
757
https://dx.doi.org/10.1021/acscatal.0c03300
ACS Catal. 2021, 11, 750−757