Novel synthesis of Pd nanoparticles for hydrogenation of biomass-derived platform chemicals showing enhanced catalytic performance

Article abstract of DOI:10.1039/c3ra43619e

Robust Pd nanoparticles were novel and successfully synthesized on the γ-Al₂O₃ support by a simple and ecofriendly route through the assistance of CO₂. The unsupported and supported Pd nanoparticles were initially characterized with a combination of several techniques such as powder X-ray diffraction, energy-dispersion X-ray, X-ray photoelectron spectroscopy and transmission electron microscopy. The face-centered cubic Pd nanoparticles with uniform dispersion were successfully achieved with the Pd loading ranging from 1 wt% to 5 wt%. The resulting Pd nanoparticles (Pd/Al₂O₃) catalysts were found to be efficient and versatile for the hydrogenation of biomass-derived platform chemicals furfural and levulinic acid under very mild conditions, respectively, showing enhanced catalytic performance.

Full text of DOI:10.1039/c3ra43619e

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Novel synthesis of Pd nanoparticles for hydrogenation
of biomass-derived platform chemicals showing
enhanced catalytic performance†
Cite this: RSC Adv., 2013, 3, 25865
a
a
a
b
c
Kai Yan,* Cody Jarvis, Todd Lafleur, Yunxiang Qiao and Xianmei Xie
Robust Pd nanoparticles were novel and successfully synthesized on the g-Al
2 3
O support by a simple and
ecofriendly route through the assistance of CO . The unsupported and supported Pd nanoparticles were
2
initially characterized with a combination of several techniques such as powder X-ray diffraction,
energy-dispersion X-ray, X-ray photoelectron spectroscopy and transmission electron microscopy. The
face-centered cubic Pd nanoparticles with uniform dispersion were successfully achieved with the Pd
Received 15th July 2013
Accepted 14th October 2013
2 3
loading ranging from 1 wt% to 5 wt%. The resulting Pd nanoparticles (Pd/Al O ) catalysts were found
DOI: 10.1039/c3ra43619e
to be efficient and versatile for the hydrogenation of biomass-derived platform chemicals furfural and
www.rsc.org/advances
levulinic acid under very mild conditions, respectively, showing enhanced catalytic performance.
Among these different advanced methods, carbon dioxide (CO
based CFD method appeared the most attractive due to the
unique properties of CO . The environmentally benign CO in its
exhibit interesting chemical and physical properties due to their liquid or supercritical state (scCO ) has a tremendous potential as
2
)-
1. Introduction
Metal nanoparticles with small size and uniform distribution
2
2
2
1
,2
attractive properties and high surface area. They have been a green reaction medium for the sustainable preparation of
16,17
widely used as catalysts in energy processing, ne chemical nanoparticles.
2
The low surface tension of liquid CO (from
ꢁ
For example, Pd 4.5 dyn cm at 0 C to zero at the critical point of 7.38 MPa at
3–5
ꢀ1
production, and air pollution control.
ꢁ
18
nanoparticles have been utilized in the selective production of 31.1 C) makes it as an excellent wetting agent.
hydrogen from alcohols, Fischer–Tropsch synthesis, CO oxida-
The supercritical CO
2
-based CFD process oen involves the
tion and NO reduction. The utilized metal nanoparticles are
usually dispersed nely on a metal oxide support to prevent
x
dissolution of a metallic precursor in a supercritical uid
scCO ) and the exposure of the g-Al support to the solution.
(
2
2 3
O
particle growth and aggregation, where the metal oxide support Aer the adsorption of the precursor onto the support, the
can enhance the surface area, light adsorption and charge- metallic precursor is converted to its metal form by the chem-
6,7
18
19
2 3
carrier separation. In the regard, g-Al O is perhaps the most ical or thermal reduction. Watkins et al. have done a lot of
oen used and attractive support for metal nanoparticles cata- the pioneering work using scCO and employed the resulting
2
lysts because of its distinctive chemical, mechanical and materials for semiconductor. Subsequently, monometallic Pd
8
thermal properties. On the other hand, the high surface area to
volume ratio can lead to modications in structure and prop-
erties. The uniform nanoparticle distributions will undoubtedly
and Pt as well as bimetallic Pt–Cu, Pt–Ru, Pt–Au, Pt–Pd and Pt–
Ni nanoparticles on carbon nanotubes were prepared by scCO
and the resultant nanoparticles were mainly employed for fuel
2
9
20
benet the catalytic reaction.
cell. Although the scCO derived CFD method was advanced
2
2 3
The Al O -supported Pd nanoparticles have been prepared by for the fabrication of metal nanoparticles, the employed
a variety of methods including molecular-capping-based colloidal supercritical uid oen associated with high temperature
1
0
11
12
synthesis, impregnation, sonochemical method, polyol and high pressure, which oen presented high requirement
1
3
14,15
reduction, and chemical uid deposition method (CFD).
toward the reaction xture and increasing the corresponding
cost. Subsequently, the CFD method based on liquid carbon
Department of chemistry, Lakehead University, 955 Oliver Road, Thunder Bay, ON dioxide was more attractive. Kim et al. have done pioneering
a
21
P7B 5E1, Canada. E-mail: kyan@lakeheadu.ca; Tel: +1 807 627 3059
b
2
work using liquid CO for the synthesis of supported metal
catalysts. However, this method requires the high solubility of
Max-Planck-Institut fur Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470, M u¨ lheim an
der Ruhr, Germany
metal precursor inside the liquid CO . Besides, to the best of
2
c
College of Chemistry and Chemical Engineering, Taiyuan University of Technology, 79
2 3
our knowledge, Pd nanoparticles on the g-Al O support and
Yingze Street, 030024 Taiyuan, China
their enhanced catalytic properties for the hydrogenation of
biomass-derived platform chemicals (furfural and levulinic
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c3ra43619e
1
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acid) have not been explored. Herein we describe a simple, green under stirring condition for another 24 h to ensure the high
and scalable preparation strategy based on liquid CO for the dispersion of the Pd(acac) at room temperature (RT). Aer this,
2
2
facile synthesis of Pd/Al O nanoparticles catalyst and their the vessel was depressurized and the sample was calcinated at
2
3
ꢁ
enhanced performance for the versatile hydrogenation of 450 C for 3 h in the oven with air environment. In the end, the
biomass-derived platform chemicals (furfural and levulinic acid), calcinated sample was pressurized with liquid CO and reduced
where the value-added furfuryl alcohol and biofuel component with H at RT for 12 h under the stirring speed of 1000 rpm.
g-valerolactone was high selectively produced. The method In comparative experiments, different Pd loading ranged
developed in this work offered many advantages rather than the from 1 wt% to 5 wt% were fabricated on the g-Al support
2
2
2 3
O
traditional impregnation method, including the minimization of using the conventionally impregnation–reduction method. The
liquid waste generation, avoiding the use of aqueous means, typical procedure was performed as follows: rstly, a constant
enhancing the environmental benignity, and rapid separation of amount of g-Al O support (ꢂ0.3 g), 5 mL ethanol and the
2
3

nal nanoparticles. Our results therefore provide an attractive precalculated amount of Pd(acac) was added into a 50 mL glass
2
approach for the preparation of high-performance nanoparticles ask. Aer this, the ask was under the stirring speed of
catalysts in the processing of biomass.
1000 rpm for the impregnation of another 24 h at RT. Aer this
step the sample was collected through the evaporation under
ꢁ
2
. Experimental section
80 C until the dry gel was formed. Aer this procedure, the
ꢁ
sample was calcinated at 450 C for 6 h in the oven with air
environment, whereby organic compounds were burned and
removed. Finally, the calcinated sample was reduced with 90%
N –10% H at 200 C for 6 h. To verify the successful synthesis
obtained, the typical characterizations (e.g., XRD, EDX and XPS)
of 5 wt% Pd/Al catalysts were shown in Fig. S1 (in the ESI†).
2
.1. Chemicals
g-Al
(surface-area of ꢂ220 m g , Sigma-Aldrich), palladiu-
m(II) acetylacetonate [Pd(acac) , 99%, Sigma-Aldrich], furfural
2
ꢀ1
2 3
O
ꢁ
2
2
2
(99%, Alfa-Aesar), levulinic acid (98%, Alfa-Aesar), pentanoic
acid ($99%, Sigma-Aldrich), 2-methyltetrahydrofuran (analyt-
ical standard, Sigma-Aldrich), 1,4-pentanediol (99%, Sigma-
Aldrich), g-valerolactone (99%, Sigma-Aldrich). All the chemicals
were directly used without further treatment aer purchase.
2 3
O
2.3. Catalysts characterizations
The Pd weight loading is expressed in wt% of Pd per gram of
2
.2. Catalysts preparations
sample: Pd wt% ¼ m(Pd) ꢃ 100%/[m(Pd) + m(g-Al O )]. The
2
3
A series of Pd nanoparticles were prepared using the palladium powder X-ray diffraction (XRD) patterns for the crystal phase
precursor (Pd(acac) ) deposited on the g-Al O support as analysis were collected on Phillips PW 1050-3710 with Cu Ka
of
2
2 3
1
˚
shown in Fig. 1, which was composed of three steps of 1.54060 A as a radiation source. The data were collected in the
ꢁ
ꢁ
impregnation, calcination and then reduction. The typical range of 10–90 2q with a step width of 0.01 /2q. The particle
procedure was performed as following: rstly, a constant size for each sample has been calculated from the Scherrer
amount of g-Al
amount of Pd(acac)
2
O
3
support (ꢂ0.3 g) and the precalculated equation (1), where l corresponds to the Cu Ka radiation, and
was added into a 50 mL vessel. Aer this, b is the full width at half-maximum for a reection maximum
2
the vessel was sealed and lled with 18 g CO
2
. The vessel was located at 2q.
0
:9l
L ¼
(1)
b cos q
The textural feature and the composition of the resultant
samples were examined by transmission electron microscopy
(
TEM) plus energy-dispersion X-ray (EDX) on a JEOL-2010
instrument. The mean particle size d was calculated from the
following formula: d ¼ Sn /Sn , where n is the number of
particles of size d . The detection limit is about 1 nm for the
i
d
i
i
i
i
supported Pd particles.
X-ray photoelectron spectroscopy (XPS) measurements were
performed with an ESCALAB 250 spectrometer with a hemi-
spherical analyzer and a monochromatized Al Ka X-ray source
(
E ¼ 1486.6 eV), operated at 15 kV and 15 mA. For the narrow
scans, analyzer pass energy of 40 eV was applied. The hybrid
mode was used as lens mode.
The reducibility of the calcined samples was determined by
H
2
-temperature-programmed reduction (TPR). In these
measurements, 50 mg of a sample was placed in a quartz reactor
ꢁ
ꢀ1
ꢁ
and heated at 10 C min up to 550 C under a He ow of
ꢀ1
2
0 mL min , and held at this temperature for 1 h. The reactor
was then cooled down to 0 C and the sample exposed to a
2 3
Fig. 1 Schematic diagram for the synthesis of Pd nanoparticles on the g-Al O
ꢁ
support.
2
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ꢀ
1
2
stream of 5% H /Ar at a ow rate of 20 mL min . Subsequently,
ꢁ
ꢁ
the sample was heated up to 400 C at a heating rate of 10 C
ꢀ
1
min . The amount of hydrogen consumed as a function of
temperature was monitored on-line on a TCD detector. The
2
maximum rate of H consumption was used to choose the
reduction temperature for each catalyst to be conducted in situ
before reaction.
2
.4. Liquid-phase hydrogenation of furfural
The liquid-phase hydrogenation of furfural was performed in a
0 mL vessel (Parr Company). 2.0 mL furfural was added into 5
2
mL octane, followed by the addition of 0.1 g catalyst into the
solution under the continuous stirring speed of 1000 rpm. The
vessel was ushed with argon to remove the inside air and then
H2 was input. Aer reaction, the vessel was cooled down to
room temperature in a controlled manner using a water bath.
Fig. 2 XRD analysis of the (a) g-Al
2
O
3
support; (b) 1 wt%; (c) 3 wt%; (d) 5 wt%
The product mixture was rstly centrifuged for 30 min, and then Pd/Al O3 nanoparticles.
2

ltrated, followed by a second ltration and dilution by
dichloromethane. The subsequent samples were analyzed by
GC (Shimadzu 2014, column: 30 m SE-54 G/17, FID). The nearly the same diffraction pattern was obtained as of g-Al O ,
2
3
column temperature was raised from 40 to 250 C with a heating only the peak indexed at ꢂ40ꢁ (222) was slightly increased.
ꢁ
ꢁ
ꢀ1
ꢁ
ꢁ
ꢁ
rate of 5 C min . The injector temperature was 350 C, which Meanwhile, the peaks indexed at ꢂ46 (400) and ꢂ67 (440)
was loaded with a sampling volume of 1 mL.
seem to decrease some of extent in comparison with the
diffraction pattern of g-Al O . With the Pd loading increasing to
2
3
5 wt% (Fig. 2d), the diffraction pattern indexed as 2q at ꢂ40ꢁ
2.5. Hydrogenation of levulinic acid
The hydrogenation of levulinic acid was performed in a 25 mL
vessel (Parr Company) with the external temperature and pres-
sure controller. Typically, constant amount of LA was dissolved
in deionized water (5 mL) and the catalyst was added into the
solution. Aer reactions, the vessel was cooled down by water
with temperature controller. The reaction products were rstly
centrifuged for 30 min and then ltrated to obtain clear solu-
tion. The samples were analysed by GC (Shimadzu 2014,
column: 30 m DBWaxetr, FID detector; the column temperature
ꢁ
ꢁ
ꢁ
was raised from 40 C to 250 C with a heating rate of 3 C
ꢀ
1
ꢁ
min ; the injector temperature was set at 350 C with a heating
ꢁ
ꢀ1
speed of 10 C min and the sampling volume was 0.2 mL).
3. Results and discussions
3.1. Catalyst characterizations
Aer the reduction by H in CO at room temperature, the Pd
2
2
nanoparticles will be obtained simply through the releasing of
H2 and CO . In combination with the economic view, the
2
highest Pd loading was limited to 5 wt%. The crystal structure of
the g-Al O support and the supported nanoparticles were
2
3
initially studied by Powder X-ray diffraction patterns as shown
in Fig. 2. Three distinct reections of g-Al (Fig. 2a) with 2q
indexed at ꢂ37 (311), ꢂ46 (400) and ꢂ67 (440). The analysis
shows the average crystallite size of g-Al based on (440) to be
2 3
O
ꢁ
ꢁ
ꢁ
2 3
O
approximately 10 nm according to Scherrer equation. Other
weak diffraction peaks (the inserted scale-up diffraction pattern
ꢁ
ꢁ
ꢁ
ꢁ
in Fig. 2) indexed at ꢂ21 (111), ꢂ29 (220), ꢂ40 (222), ꢂ61
511) and ꢂ85 (444). Overall, all these diffraction peaks are in
well agreement with the standard card of g-Al (JCPDS card,
2 3
le no. 00-001-1308). At the low loading of 1 wt% (Fig. 2b), Fig. 3 XPS analysis of the (a) 3 wt% and (b) 5 wt% Pd/Al O .
(
2 3
O

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ꢁ
ꢁ
(
111), ꢂ46 (200), ꢂ82 (311) identied as single hexagonal fcc interesting to nd the presence of two prominent sets of Pd (3d)
ꢁ
phase of Pd, although the diffraction peaks at ꢂ46 of the peaks, corresponding to the 3d3/2 via 3d5/2 orbital states, which
crystal facet (400) in the g-Al O support and (200) of Pd over- demonstrated that Pd was present on the surface in the reduced
2
3
lapped some of extent. Additionally, small crystal sizes of ꢂ6.3 state. The peak regions of metal Pd could be tted with two sets
and ꢂ7.5 nm were obtained in the 3 wt% and 5 wt% loading of peaks at 340.6 eV (3d3/2) and 335.3 eV (3d5/2), indicating that
0
21
based on the Scherrer equation, respectively, which were close the fresh catalysts contained Pd centers in the samples.
to the size calculated from TEM images (Fig. 4c and d).
Besides, the very weak peak was observed at 341.7 eV and 336.5
For the successful synthesis of metal nanoparticle catalysts, eV, which was possible due to the presence of very small amount
the oxidation state of the surface metal in the sample was very of PdO on the surface or the interaction between of Pd and the
22
sensitive towards their catalytic activities. Thus XPS measure- oxygen from the Al O support.
2
3
ments were initially employed to study the oxidation state and
The textural structure and the size distribution of the resultant
the representative analysis results of the selected 3 wt% Pd nanoparticles oen display important inuence on their
Pd/Al
2
O
3
and 5 wt% Pd/Al
2
O
3
were shown in Fig. 3. It was catalytic activities, TEM was further employed. The TEM images
and the Pd particles size distribution were shown in Fig. 4. TEM
image of the support g-Al
rings corresponding to the (311), (400) and (440) reections
Fig. 4a and b) and these d-spacings are consistent with the g-
2 3
O revealed three broad diffraction
(
23
alumina structure. Besides, the TEM images of the g-Al O3
2
support (Fig. 4a and b) show the enhanced surface contrast on
facets that terminate with (111) planes (d ¼ 0.2003 nm) and
1
11
23
(
100) planes at the end of the edges. The ordered lattice fringes
2 3
dominated the texture of the g-Al O support, which would be
benecial for enhancing the dispersion of ne Pd nanoparticles
23,24
in the sample.
2 3
TEM images of Pd/Al O nanoparticles exhibi-
ted that the uniform and small size of Pd particles were highly
distributed on g-Al O support (Fig. 4c and d). Besides, the
2
3
introduction of Pd on g-Al O support did not change the struc-
2
3
ture of g-Al O . The slightly unavoidable aggregation of Pd
2
3
nanoparticle was found and only few bigger particles were
observed in a few areas (Fig. 4c and d). Small Pd nanoparticles
with a mean size of 6.20 nm (Fig. 4e) and 7.34 nm (Fig. 4f) in the
case of 3 wt% and 5 wt% loading, respectively, appeared as a high
dispersion in the material. To ascertain whether the metal
nanoparticles existed on the surfaces, EDX analysis further
adopted and the spectrum of the support Al O and 5 wt%
2
3
Pd/Al O were shown in Fig. 4g and h, respectively. EDX analysis
2
3
spectra (Fig. 4h) presents the peaks of Pd, Al and O where they
should be. It clearly presented the peaks where Pd and Al should
be, which conrmed the existence of Pd in the resulting samples.
Besides, no distinct difference of Pd amount was revealed by the
EDX analysis in several different areas, indicating the uniform
dispersion of Pd nanoparticles in the sample.
The H -TPR proles of the chosen 3% Pd/Al O catalysts
2
2 3
prepared by the CO -assited method and 3% Pd/Al O catalysts
2
2 3
synthesized by the traditional impregnation method, are
compared in Fig. S2.† For 3% Pd/Al prepared by CO -assitaed
O
2 3
2
method, the TPR prole (Fig. S2a†) mainly exhibits one peak
ꢁ
25a
centered on ꢂ95 C, indicative of the H
2
consumption. The H
2
prole was consistent with the decomposition of (Pd(acac)
2
),
which was reported to form at room temperature over large Pd
25b
particles. Besides, a second broader peak was detected in the
ꢁ
25c,d
range of 200 to 300 C, which was due to the water evolution.
Fig. 4 TEM images, size distribution and EDX spectrum of the g-Al
and the Pd nanoparticles catalysts: (a and b) TEM image of g-Al ; (c) TEM image
of 3 wt% Pd/Al ; (d) TEM image of 5 wt% Pd/Al ; (e) size distribution of 3 wt
Pd/Al ; (f) size distribution of 5 wt% Pd/Al ; (g) EDX spectrum of g-Al
h) EDX spectrum of 5 wt% Pd/Al
2 3
O support
2
O
3
3
.2. Hydrogenation of furfural
The resulting Pd/Al nanoparticles catalysts were employed
2
O
3
2 3
O
2 3
O
%
2
O
3
2
O
3
2 3
O ;
(
2
O
3
.
for the liquid-phase hydrogenation of furfural (Scheme 1). The
2
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catalytic results of the g-Al
2
O
3
support and a series of Pd/Al
2
O
3
selectivity of THFA and ꢂ2% selectivity of MF were simulta-
nanoparticles catalysts are presented in Table 1. The turnover neously obtained. With the Pd loading increasing to 5 wt%,
number (TON), dened as the moles of conversed furfural 84.9% selectivity of FA with the TON of 172 was achieved at
molecules per mole of noble metal atoms on the g-Al O
39.4% conversion was achieved (no. 4). Meanwhile, ꢂ14%
support, was used to compare the overall catalytic performances selectivity of THFA and ꢂ1% selectivity of MF were produced.
Table 1). Overall, the synthesized Pd/Al nanoparticles These results conrmed that the Pd loading can be used to alter
2
3
(
2 3
O
catalysts display good performance in the liquid-phase hydro- the extent of hydrogenation, where the small particle sizes of Pd
genation of furfural. First, it was found that the main product with high surface areas would play an important role in
was furfuryl alcohol coming from the hydrogenation of the C] enhancing the mass transportation and alternatively inuence
28
O bond (no. 1 to no. 5). In addition to the main products, there the catalytic activities importantly. On the other hand, for
are several compounds derived from side reactions (i.e. the hydrogen adsorption on transition metals, it is oen considered
hydrogenation of the furan ring to tetrahydrofurfuryl alcohol that the electron is donated from the a-bond of hydrogen to the
(
THFA), hydrogenolysis of the C]O bond to MF, decarbon- d-band of Pd, where the d-band centre in the surface electronic
26,27
29
ylation to furan and further hydrogenation to THF).
2 3
Among structure may also play an role. Third, the Pd/Al O nano-
the side products, only a few amounts of furan and THF were particle catalysts were synthesized by the traditional impreg-
observed by GC. Second, in the comparative reaction using the nation method and exhibited lower performances in the
support g-Al
2
O
3
as catalyst (no. 1), ꢂ5.1% conversion of furfural hydrogenation of furfural. For example, the 5 wt% Pd/Al
2 3
O
was obtained and nearly no detectable product was found. nanoparticles catalysts display 91.6% selectivity of FA with the
Increasing the Pd loading from 1 wt% to 5 wt% (no. 1 to no. 4), TON of 120 at 28.7% conversion of furfural (no. 7). A complete
the conversion of furfural was increased stably from 21.2% to understanding of the reaction parameters deserves future
39.4% and the TONs vary from 492 (no. 2) to 172 (no. 4). The attention. However, our facile approach for the preparation of
highest selectivity of FA was obtained with 89.1% selectivity and metal nanoparticles will be of great potential for various
a TON of 205 at 26.9% conversion of furfural using the 3 wt% important reactions in the processing of biomass.
Pd/Al
2
O
3
nanoparticle catalyst (no. 3). Additionally, ꢂ8%
3.3. Hydrogenation of levulinic acid
The robust Pd/Al O nanoparticles were further employed for
2
3
the hydrogenation of biomass-derived levulinic acid (LA) as
shown in Scheme 2 and the catalystic results are shown in Table
2. In the hydrogenation of LA, the g-valerolactone (GVL) was
more preferred to be produced due to its negative Gibbs free
ꢁ
ꢀ1
30
energy (DG ¼ ꢀ22 kJ mol ) in principle. However, the easily
occurred sides reactions (e.g., further hydrogenation of GVL to
2-methyltetrahydrofuran (MTHF), dehydration of the interme-
diate 4-hydroxypentanoic acid and then further hydrogenated to
pentanoic acid (PA)) would inuence the production of GVL in a
3
0,31
signicant manner.
synthesized Pd/Al
In this work, it was clear to nd that the
nanoparticles catalysts continue to
2
O
3
Scheme 1 Hydrogenation of furfural to value-added chemicals.
display very good performance, where over 94% selectivity of
GVL was achieved when the Pd/Al nanoparticles catalyst was
2 3
O
employed. Additionally, the metal Pd loading presented crucial
Table 1 Catalytic performance of the support g-Al
2
O
3
and the Pd/Al
2
O
3
cata- inuence on the catalytic activities. First, increasing the Pd
a
lysts in the hydrogenation of furfural
loading from 1 wt% to 5 wt% (no. 1 to no. 5), the conversion of
b
c
LA increased clearly from 31.2% to 63.5%. When 1 wt%
Pd/Al nanoparticle catalyst was employed (no. 1), 94.3%
No. Catalyst
Conv./% S(FA)/% S(THFA)/% S(MF)/% TON
2 3
O
1
2
3
4
5
6
7
0 wt%
1 wt%
3 wt%
5 wt%
1 wt%
3 wt%
5 wt%
5.1
21.2
26.9
39.4
10.9
20.1
28.7
<0.1
90.3
89.1
84.9
87.5
90.2
81.6
<0.1
6.5
7.6
13.8
7.2
5.2
<0.1
1.4
1.5
0.9
0.7
1.0
1.2
—
selectivity of GVL and 5.0% selectivity of PA was observed at
491.8
205.3
171.9
d
15.8
120.4
a
Reaction conditions: V(furfural) ¼ 2 mL, V(octane) ¼ 5 mL, m(catalyst) ¼
ꢁ
0
.1 g, p(H
2
) ¼ 45 bar, T ¼ 150 C, stirring speed ¼ 1000 rpm. Conv.: the
conversion of furfural, S(FA): the selectivity of furfuryl alcohol, S(THFA):
the selectivity of tetrahydrofurfuryl alcohol (THFA), S(MF): selectivity of
b
c
2
-methylfuran (MF). Catalyst was Pd/Al
2
O
3
.
TON was calculated
according to FA. Turnover numbers (TON) ¼ the molar of the desired
d
product/the molar the catalyst used. 1 wt% (No. 5) to 5 wt% Pd/
Al
2
O
3
(No. 7) was prepared by the traditional impregnation method.
Scheme 2 Hydrogenation of LA to value-added chemicals.
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ꢁ
Table 2 Catalytic performance of the Pd/Al
2
O
3
nanoparticle catalysts in the of 140 C. The Pd/Al
O
nanoparticles catalysts were also
2
3
a
hydrogenation of levulinic acid
efficient for the hydrogenation of biomass-derived levulinic
acid, where over 94% selectivity of the promising biofuel
component g-valerolactone was achieved in the presence of
b
No.
Catalyst
Conv./%
S(GVL)/%
S(PA)/%
TON
1
2
3
1 wt%
3 wt%
5 wt%
5 wt%-Im
31.2
48.7
63.2
52.9
94.3
95.0
96.3
95.2
5.0
4.6
3.7
4.5
1361.7 Pd/Al O catalysts. 94.3% selectivity of g-valerolactone with
2 3
713.8 the TON of 1362 was obtained for the conversion of levulinic
565.2
473.2
acid. A complete work of optimization of the reaction
parameters would benet for our understanding of the reac-
c
4
a
Hydrogenation conditions: m(LA) ¼ 5.05 g, V(H
2
O) ¼ 5 mL, p(H
2
) ¼ 45 tion mechanism and deserved our future attention. However,
ꢁ
bar, T ¼ 160 C, t ¼ 6 h, m(catalyst) ¼ 0.10 g, stirring speed ¼ 1000
the current work conrmed that the synthesis strategy to
rpm. Conv.: the conversion of levulinic acid, S(GVL): the selectivity of
b
fabricate Pd nanoparticles on the g-Al O support was attrac-
g-valerolactone, S(PA): the selectivity of pentanoic acid. TON was
2 3
calculated according to GVL. Turnover numbers (TON) ¼ the molar of tive and the developed catalyst may be a good candidate for
c
the desired product/the molar the catalyst used. 5 wt% Pd/Al
2 3
O was
industrially important chemical reactions.
prepared by the impregnation method.
Notes and references
3
1
1.2% conversion of LA. Meanwhile, few amounts (less than
%) of MTHF were detected by GC. With the loading
1
2
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4
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2
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this work using liquid CO oen offer many advantages
rather than the traditional impregnation methods, including
the minimization of liquid waste generation, avoiding the
use of organic solvents, enhancing the environmental
benignity, a high rate of mass transfer, and rapid separation
of products.
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5870 | RSC Adv., 2013, 3, 25865–25871
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