Effective conversion of biomass-derived ethyl levulinate into γ-valerolactone over commercial zeolite supported Pt catalysts

Article abstract of DOI:10.1039/c6ra24323a

The synthesis of γ-valerolactone from biomass-derived ethyl levulinate is of great importance for biomass conversion. However, development of efficient catalytic systems which are simple, commercially available, easy for preparation, and large-scale for the hydrogenation of ethyl levulinate to afford γ-valerolactone is still necessary. Here, a series of commercial zeolite supported catalysts were synthesized by using a wet impregnation method for the systemic investigation of the hydrogenation of biomass-derived ethyl levulinate. High yield and selectivity towards GVL were achieved and varied and systematic characterizations including XRD, XPS, TEM and BET were used to investigate these catalysts. The influence of different reaction condition parameters was also investigated and discussed. The construction of zeolite supported catalysts showed broad prospects for the conversion of biomass into biofuels.

Full text of DOI:10.1039/c6ra24323a

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Effective conversion of biomass-derived ethyl
levulinate into g-valerolactone over commercial
zeolite supported Pt catalysts†
Cite this: RSC Adv., 2016, 6, 112477
Chu-Bai Chen,‡a Meng-Yuan Chen,‡a Bakht Zada,a Ying-Jie Ma,a Long Yan,a
a
b
a
a
*
Qing Xu, Wen-zhi Li, Qing-Xiang Guo and Yao Fu
The synthesis of g-valerolactone from biomass-derived ethyl levulinate is of great importance for biomass
conversion. However, development of efficient catalytic systems which are simple, commercially available,
easy for preparation, and large-scale for the hydrogenation of ethyl levulinate to afford g-valerolactone is
still necessary. Here, a series of commercial zeolite supported catalysts were synthesized by using a wet
impregnation method for the systemic investigation of the hydrogenation of biomass-derived ethyl
levulinate. High yield and selectivity towards GVL were achieved and varied and systematic
characterizations including XRD, XPS, TEM and BET were used to investigate these catalysts. The
influence of different reaction condition parameters was also investigated and discussed. The
construction of zeolite supported catalysts showed broad prospects for the conversion of biomass into
biofuels.
Received 30th September 2016
Accepted 11th November 2016
DOI: 10.1039/c6ra24323a
www.rsc.org/advances
following properties: (1) high boiling point (207–208 ꢀC); (2)
nonvolatile; (3) high lower heating value (LHV, 25ꢁM3J kgꢁ1); (4)
high ash point (96 ꢀC); (5) high density (1.04 g cm , 15 ꢀC); (6)
1 Introduction
With the gradual exhaustion of fossil resources and global
warming, more attention has been paid to the sustainable
conversion of renewable resources.1 Biomass, which is wide-
spread, cheap, renewable, carbon-neutral and abundant, is
known as the only renewable carbon resource which could
replace fossil resources for the production of chemicals and
fuels.2 Among the biomass-derived chemicals, levulinic acid
(LA) is regarded as one of the top value added chemicals from
biomass.3 It has been reported by our group that liquid acid
catalyst, magnetic solid acid catalyst or sulfonated chloromethyl
polystyrene solid acid catalyst could catalyze the conversion of
biomass to LA.4 LA could be converted into a series of useful
compounds (e.g. g-valerolactone (GVL), 2-methyltetrahy-
drofuran, 1,4-pentanediol, valerate esters, levulinate esters,
acrylic acid, aminolevulinate acid, diphenolic acid, acetylacrylic
acid, angelilactones, etc.) using LA as starting material.3
appropriate kinematic viscosity (2.1 mm2 sꢁ1, 40 ꢀC) compared
with diesel (2.5 mm2 sꢁ1, 40 C), which made it featured with
ꢀ
stability, low temperature uidity, low toxicity, degradability,
storability for the applications.5 GVL could be used as the
additive to gasoline, diesel and biodiesel, liquid fuels, inter-
mediate and solvent in chemical and pharmaceutical industry.6
A series of valuable chemicals (e.g. levulinate esters, 1,4-penta-
nediol, dimethyl adipate, succinic acid, caprolactone, pentenoic
acid, 5-nonanone) and fuels (valeric esters, alkanes, 2-methyl-
tetrahydrofuran) could be obtained through the derivative
relations of GVL.6i For example, 1,4-pentanediol (1,4-PDO) could
be obtained through the hydrogenolysis of GVL, which is
regarded as the monomer of biodegradable polymers. For
instance, Feng et al., Fan et al. and our group reported the
hydrogenation of biomass-derived GVL to 1,4-PDO using sup-
ported Cu catalysts.7 Therefore, it is vital to develop a series of
catalytic systems for the conversion of biomass to GVL.
Among the derivatives of LA, GVL is a very promising
compound with broad application prospects. GVL has the
Generally, GVL could be produced through the catalytic
hydrogenation–cyclization of LA or its esters. The synthesis of
GVL from LA could be carried out over homogeneous or
heterogeneous catalysts using formic acid or molecular
hydrogen as hydrogen source.8 According to the previous
reports, homogeneous Ru9 and a series of supported heteroge-
neous catalysts (e.g. Ru, Pd)10 were efficient for the hydrogena-
tion of LA to GVL under molecular hydrogen atmosphere.
Recently, our group reported that Cu-WO3/ZrO2-CP-300 could
catalyze the conversion of LA to GVL and 94% yield could be
aCollaborative Innovation Center of Chemistry for Energy Materials, CAS Key
Laboratory of Urban Pollutant Conversion, Anhui Province Key Laboratory of
Biomass Clean Energy, Department of Chemistry, University of Science and
Technology of China, 230026, Hefei, Anhui, China. E-mail: fuyao@ustc.edu.cn; Fax:
+86-551-6360-6689; Tel: +86-551-6360-6640
bDepartment of Thermal Science and Energy Engineering, University of Science and
Technology of China, 230026, Hefei, Anhui, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra24323a
‡ These authors equally contributed to the work.
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obtained.7b In addition to molecular hydrogen, formic acid
could also be used as the hydrogen source for the hydrogena-
tion of LA.11 Horvath and we reported that homogeneous Ru
´
2 Experimental
2.1 Materials
catalysts were efficient for the conversion of LA to GVL.12
Subsequently, other homogeneous catalysts were reported to be
available. For example, our group developed Ir and Fe catalytic
systems for the hydrogenation of LA.13 Although homogeneous
catalysts showed high activity, and the reaction conditions are
relatively milder, their inherent shortcomings are obvious. For
instance, the preparation of homogeneous catalysts is usually
complicated, ligands are mainly necessary for the high perfor-
mance, and it is difficult to separate the catalysts from the
reaction mixture.14 Therefore, it is signicant to develop
heterogeneous catalysts for this process. Our group reported the
Ru-P/SiO2 catalyst for hydrogenation of LA using formic acid as
hydrogen source and the catalyst could be recycled.15 Later, Au,
Ag, Cu, Ni and Co were found to be efficient for the trans-
formation of LA.16 Apart from LA, levulinate esters (LE) were
conrmed that they could be converted into GVL. Moreover,
compared to LA, higher yield of LE could be achieved and lev-
ulinate esters are easier to be separated than LA.17 Therefore, it
seems to be more attractive to synthesize GVL from LE. A variety
of catalytic systems were conrmed to be efficient for the
conversion of LE to GVL using molecular hydrogen or alcohols
as hydrogen donor. Metal nanoparticles supported catalysts
(e.g. Ru, Pd, Ag, Cu, Ni, Zr) have been reported for the hydro-
genation of LE to GVL.18 Besides, catalytic transfer hydrogena-
tion (CTH) of LE to GVL through Meerwein–Ponndorf–Verley
(MPV) reduction using alcohol as hydrogen source was also
widely studied. In these cases, alcohols served as both hydrogen
donor and reaction solvent. For example, ZrO2, Zr-beta,
ZrO(OH)2$xH2O, Ru(OH)x/TiO2, Zr-HBA, ZrFeOx, zirconium-
based MOF, Ni–Zr, Cu–ZrO2 and Hf-beta were successfully
EL and GVL were provided by Hefei Leaf Energy Biotechnology
Co., Ltd (http://www.leafresource.com). Chloroplatinic acid
hexahydrate was supplied by Shanxi Kaida Chemical Engi-
neering Co., Ltd. Zeolites supports (e.g. MCM-22, MCM-41,
SAPO-34, ZSM-35, ZSM-5, HY, USY, MOR) were purchased
from Nankai University Catalyst Co., Ltd.
2.2 Catalyst preparation
All of the zeolites supported Pt catalysts in this work were
prepared using the wet impregnation methods. For a typical
preparation, 1 wt% Pt/MCM-22, the zeolite MCM-22 (5.0 g) was
sufficiently dispersed in 20 ml deionized water named as
suspension A, chloroplatinic acid hexahydrate (0.134 g, 0.259
mmol) was dissolved in 10 ml deionized water named as solu-
tion B. Solution B was dropped into suspension A with violent
agitation at room temperature. The mixture was supposed to
stir vigorously for another 24 h. Aer impregnation, the mixture
was transferred to an oven and dried at 110 ꢀC for 12 h to
dehydrate. Subsequently, the mixture was reduced in a tube
furnace under a N2/H2 mixed gas. The ow rates for both gases
were 60 ml minꢁ1 while the temperature of the tube furnace was
raised from ambient temperature to 400 ꢀC at the rate of 10 ꢀC
minꢁ1 and kept at 400 C for 2 h. Aer cooling down to room
ꢀ
temperature, the reduced catalyst was collected and marked as
1% Pt/MCM-22. The preparation procedures for 1% Pt/MCM-41,
1% Pt/SAPO-34, 1% Pt/ZSM-35, 1% Pt/ZSM-5, 1% Pt/HY, 1% Pt/
USY, 1% Pt/MOR were similar to that for 1% Pt/MCM-22.
2.3 Catalyst characterization
applied to the CTH of LE to GVL.19 Our group also reported that The X-ray power diffraction (XRD) patterns of these zeolite
RANEY® Ni could catalyze the hydrogenation of LE.20 However, supported catalysts were measured by a X'pert (PANalytical)
for the consideration of commercial process, it is still necessary diffractometer at 40 kV and 200 mV. The scanning of diffraction
to investigate efficient catalytic systems which are simple, angle ranges from 10 degree to 70 degree with a sampling
commercial available, easy for preparation, large-scale produc- interval of 0.02 degree.
tion for the hydrogenation of LE to afford GVL.
The X-ray photoelectron spectroscopy (XPS) patterns of the
Zeolites have been widely used as solid acid catalysts or catalysts were measured by a Thermo Scientic Escalab 250-X-
catalyst supports in petrochemical industry.21 They are very ray photoelectron spectrometer using an Al Ka mono-
appropriate for catalysis because of their excellent hydro- chromatized source. During the measurement, residual pres-
thermal stability and molecular sieving capability. Recently, sure was kept below 1 ꢂ 10ꢁ7 Pa. For removing the charge
zeolite-based catalysts were found to be efficient for bio-renery effect, C 1s, which is determined at 284.8 eV, was used as
processes. For instance, aromatic compounds can be catalyti- a standard.
cally obtained from renewable furan derivatives.22 In consider-
The Brunauer–Emmett–Teller (BET) method was used to
ation of the advantages of zeolite-based catalysts, a series of determine the specic surface areas of the catalysts on
commercial zeolite supported catalysts were synthesized by wet a Micromeritics ASAP 2020 analyzer using N2 physical adsorp-
ꢀ
impregnation method for the systemic investigation of the tion at ꢁ195.8 C.
hydrogenation of biomass-derived ethyl levulinate (EL). To our
The transmission electron microscopy (TEM) images of the
delight, high yield and selectivity towards GVL could be ach- prepared catalysts were obtained from a JEOL-2010 electron
ieved. Varied and systematic characterizations were used to microscope. The samples were dispersed in ethanol by ultra-
investigate these catalysts. Finally, for further investigation of sound and then deposited on a Cu girds.
these catalysts, the inuence of different reaction parameters
NH3 temperature programmed desorption (NH3-TPD) was
was also investigated. The construction of zeolite supported measured by homemade instrument. For NH3-TPD, 80.00 mg
catalysts showed their broad application prospects for the sample was weighed and put into a quartz tube, which then put
ꢀ
conversion of biomass into biofuels.
into the furnace. Firstly, temperature was raised to 400 C and
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held 1 h at Ar atmosphere to remove absorbed gases on sample
surface. Aer cooling down, NH3 was pumped into the tube for
1 h in order to fully saturate the sample. Then, NH3 was stopped
and Ar was applied to remove excess NH3 at 80 ꢀC. Finally,
sample underwent a programmed desorption with temperature
rise from 80 ꢀC to 550 ꢀC at the rate of 10 ꢀC minꢁ1. Desorption
of NH3 was detected by thermal conductivity detector (TCD).
2.4 Catalyst test
The hydrogenation reaction of EL was carried out in a 25 ml
autoclave (Anhui Kemi Machinery Technology Co., Ltd., China).
In a typical reaction, 1 mmol of EL, 100 mg of catalyst and 12 ml
of ethanol were loaded into the autoclave equipped with
a magnetic stirrer. Then the reactor was purged with hydrogen
for 5 times and the nal H2 pressure was reached a set value
such as 6 MPa at ambient temperature. The temperature of the
reactor was then raised to a xed value such as 200 ꢀC and kept
for a set period such as 6 h. Aer the reaction was nished and
the reactor was cooled down to room temperature, mixture in
the reactor was centrifugated and collected. The supernatant
was examined and analyzed by gas chromatograph-mass spec-
trometer (GC-MS) and gas chromatograph (GC) using a RTX-65
gas chromatographic column, diethylene glycol dimethyl ether
was used as the internal standard.
Fig. 2 XRD patterns of zeolite supported catalysts.
due to the low loading contents of Pt in the catalysts. Three
typical reection peaks of fcc structure Pt24 (e.g. the crystal face
(111), (200) and (220), respectively) could be seen. The unclear
Pt reection peak of some catalysts such as 1% Pt/MCM-22 and
1% Pt/MCM-41 maybe attributed to high dispersion or small
particle sizes of Pt nanoparticles (listed in Table 1), which lead
to a broadening reection peaks. To obtain a complete and clear
phase data, XPS was used to analysis catalysts with low
resolution.
3 Results and discussion
3.1 Characterization of the zeolite supported catalysts
The X-ray photoelectron spectroscopy (XPS) analysis of 1%
Pt/MCM-22 and 1% Pt/MCM-41 is performed to verify the exis-
tence of Pt which could not be clearly detected from XRD. It has
been reported25 that the B.E. position of Al(III) 2p is 74.8 eV,
which is close to that of metallic Pt 4f5/2 (74.3 eV). Considering
that the absolute existence of Pt and the content of Al is higher
than Pt, the peak of Al(III) 2p would overlap the peak of metallic
Pt 4f5/2, the existence of Pt could not be determined by the B.E.
peak of Pt 4f5/2. However, it has also been reported25 that the
B.E. position of metallic Pt 4f7/2 is 71.5 eV, which has 2.8 eV
band gap with Al(III) 2p and could be easily divided. It could be
conrmed from Fig. 3 that the characteristic B.E. peak of
metallic Pt 4f7/2 could be obviously detected for 1% Pt/MCM-22
and 1% Pt/MCM-41, and the B.E. peak of metallic Pt 4f7/2 for all
the other supported Pt catalysts could also be found which are
presented in the ESI.†
Aer a series of zeolite supported Pt catalysts were prepared,
both X-ray powder diffraction (XRD) and X-ray photoelectron
spectroscopy (XPS) were employed to determine the element
components and crystal formation of these catalysts. The power
XRD patterns of zeolite supported Pt catalysts are showed in
Fig. 1 and 2. According to the previous reports,23 the charac-
teristic peaks corresponding to the zeolites could be clearly seen
in the XRD patterns in Fig. 1. And the reection peaks corre-
sponding to metallic Pt phase could be found in the patterns of
all the prepared supported Pt catalysts (Fig. 2). The intensity of
metallic Pt phase reection signals was relatively low possibly
TEM images of all the supported Pt catalysts were also
investigated in order to obtain the micro-structure images of the
Pt nanoparticles and zeolites. It could be determined from the
TEM images in Fig. 4 that Pt particles could be clearly see and Pt
nanoparticles were dispersed uniformly in all the prepared
catalysts with a mean size from 2.45 nm to 8.88 nm. The
dimensions of the metallic Pt phase (DMP) were calculated from
Fig. 4 and listed in Table 1. The size distribution of Pt nano-
particles in these catalysts could be found in the ESI.†
The Brunauer–Emmett–Teller (BET) analysis was employed
to investigate the specic surface area, pore volume and pore
size of the catalysts, which is an important part of the physico-
chemical properties. The physico-chemical properties of these
catalysts were also listed in Table 1. The NH3-TPD results of the
supported Pt catalysts are presented in ESI.†
Fig. 1 Characteristic diffraction peaks of zeolites.
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Table 1 Physico-chemical properties of catalysts
Catalyst
DMPa/nm
Surface areab/m2 gꢁ1
Pore volumec/cm3 gꢁ1
Pore sized/nm
Pt/MCM-22
Pt/MCM-41
Pt/SAPO-34
Pt/ZSM-35
Pt/ZSM-5
Pt/HY
5.05
2.45
2.85
8.88
2.85
4.62
6.35
2.91
473.88
427.81
313.80
266.94
330.02
637.83
217.39
293.53
1.11
0.11
0.02
0.17
0.08
0.07
0.13
0.06
29.16
5.70
3.11
28.06
4.25
5.02
2.22
7.16
Pt/USY
Pt/MOR
a
Mean crystal size of the metallic Pt phase, calculated from TEM images. b BET surface area. c BJH desorption cumulative volume of pores between
d
˚
˚
17.0 A and 3000.0 A diameter. BJH desorption average pore diameter (4V/A).
selectivity to GVL were 43.0% and 38.4%, respectively (Table 2,
entry 7). A slightly higher conversion of EL could be obtained
when 1% Pt/MOR was used for the hydrogenation of EL (Table
2, entry 8), however, the selectivity to GVL was just 41.5%.
Although low conversion of EL was received when 1% Pt/SAPO-
34 was used, the selectivity toward GVL in this catalytic system
reached 81.5%. Actually, according to the previous work, the
conversion of EL to GVL included two steps: hydrogenation of
EL to form the intermediate 4-hydroxypentanoate (4-HPE) and
subsequently the catalytic lactonization of 4-HPE to form GVL.
The active Pt nanoparticles in the catalysts would catalyze the
hydrogenation of C]O in EL to form 4-HPE, and the acidic
zeolite supports were responsible for the lactonization of 4-HPE.
The interaction between metallic Pt and zeolite support would
inuence the hydrogenation activity of Pt nanoparticles, it is
hard to distinguish the differences of all the supported Pt
catalysts from Table 1. However, according to the XPS results
(see ESI†) of 1% Pt/HY, 1% Pt/USY and 1% Pt/SAPO-34, the
signals of Pt 4f5/2 were relatively weaker, in accordance with the
low conversions of EL over these catalysts. A higher conversion
(e.g. 70.8%) of EL could be reached when 1% Pt/MCM-41 was
used, however, the selectivity towards GVL was only 52.5%,
which indicated the inefficiency of this catalyst for the conver-
sion of the intermediate 4-HPE to GVL. To our delight, almost
full conversion of EL was reached when 1% Pt/MCM-22, 1%
Pt/ZSM-35, 1% Pt/ZSM-5 (e.g. 97.6%, 100% and 97.8%,
Fig. 3 XPS in the Pt 4f region for supported Pt catalysts.
Fig. 4 TEM image of (a) Pt/MCM-22 (b) Pt/MCM-41 (c) Pt/SAPO-34 (d)
Pt/ZSM-35 (e) Pt/ZSM-5 (f) Pt/HY (g) Pt/USY (h) Pt/MOR.
Table 2 Selective hydrogenation of EL over various zeolite supported
Pt catalysts at 200 ꢀCa
3.2 Selective hydrogenation of EL
Entry
Catalyst
Conv./%
Sel./%
Yield/%
Selective hydrogenation of EL to afford GVL was performed over
different zeolite supported Pt catalysts and GC-MS/GC were
used for the analysis of the products. The conversion of EL was
used as an evaluation standard for the comparison of the
catalytic activity of these catalysts. It could be found that when
1% Pt/HY was used for the hydrogenation of EL (Table 2, entry
6), the conversion of EL was only 31.8% and the selectivity
towards GVL was just 39.9%, indicating its low activity for this
reaction. Similar activity was obtained when 1% Pt/USY was
used for the hydrogenation of EL, the conversion of EL and
1
2
3
4
5
6
7
8
1% Pt/MCM-22
1% Pt/MCM-41
1% Pt/SAPO-34
1% Pt/ZSM-35
1% Pt/ZSM-5
1% Pt/HY
97.6
70.8
37.2
100
97.8
31.8
43.0
55.6
62.1
52.5
81.5
99.0
57.1
39.9
38.4
41.5
60.6
37.2
30.3
99.0
55.8
12.7
16.5
23.1
1% Pt/USY
1% Pt/MOR
a
Reaction conditions: 1.0 mmol of EL, 100 mg of zeolite supported Pt
catalysts, 12 ml of ethanol, P(H2) ¼ 6.0 MPa, T ¼ 200 ꢀC, t ¼ 6.0 h.
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respectively) were used for the hydrogenation of EL, which
conrmed the high activity of metallic Pt in these catalysts.
Nevertheless, the selectivities towards GVL were different, when
1% Pt/MCM-22 and 1% Pt/ZSM-5 were used for the hydroge-
nation of EL, the selectivities were 62.1% and 57.1%, respec-
tively, resulting in low yields of GVL. One possible reason for
these phenomena was lying in the relative lower acid strength
(see ESI†). When 1% Pt/ZSM-35 was used for the hydrogenation
of EL, 100% conversion was reached and the selectivity towards
GVL was 99.0%, conrmed the high activity of metallic Pt
nanoparticle and proper surface acidity of the zeolite support.
Obviously, 1% Pt/ZSM-35 was the most efficient catalyst in the
list of catalysts, resulting high conversion of EL and high yield
of GVL. In order to have a further insight of 1% Pt/ZSM-35, the
inuence of different reaction parameters on the hydrogenation
of EL was also investigated.
3.4 Effect of hydrogen pressure
Generally, hydrogen pressure is vital in catalytic hydrogenation
reaction. Further experiments about how the hydrogen pressure
affects the reaction process were investigated. It can be
conrmed from Fig. 6 that selectivity of the reaction less related
to hydrogen pressure. High selectivities were obtained while the
H2 pressure changed from 1 MPa to 6 MPa. Even when H2 was
only 1 MPa, the selectivity reached to 93.8%, which is the lowest
datum in this test. However, EL conversion was closely con-
nected with H2 pressure in the reaction. When the hydrogen
pressure was 1 MPa, conversion of EL reached 58.3% and GVL
yield was just 54.7%. Then, GVL yield increased to 68.7% at a H2
pressure of 2 MPa. And the value of yield further rose to 72.1%
while the pressure reached 3 MPa. It is obvious that conversion
of EL positive correlated to the H2 pressure and reached
a maximum of 100% when pressure increased to 6 MPa. This
phenomenon may attribute to the reason that higher H2 pres-
sure lead to a higher H2 concentration on the surface of the
catalyst, thereby accelerating the catalytic process.
3.3 Effect of reaction temperature
Temperature is one of the important factors of converting EL
into GVL. Herein, a series of experiments with different
temperatures were designed in order to investigate the inu-
ence between GVL yield and temperature. It can be conrmed
from Fig. 5 that temperature greatly inuenced EL conversion
and selectivity of GVL. When temperature was relatively low,
such as 180 ꢀC, the reaction was hard to process. Under this
reaction condition, GVL yield was only 30.1% while selectivity
was 79.2%, which means not only hydrogenation but also
cyclization were not fully accomplished. When temperature
rose to 190 ꢀC, yield and selectivity increased to 85.6% and
91.5% respectively. Optimal GVL yield was reached when the
temperature reached 200 ꢀC, and all of the reactant was con-
verted, which means higher temperature would accelerate the
reaction. However, when temperature further increased,
although EL was still fully converted, the yield of GVL was
decreased to about 97%, which can attribute to over hydroge-
nation of GVL.
3.5 Effect of solvent
It was reported that oxygen-containing solvents have a strong
solvent effect in catalytic hydrogenation from carbohydrates to
GVL,10i which means the investigation of the effect of solvent is
meaningful. Here, different solvents were applied in searching
for solvent effect on EL conversion. Reactant conversion rates
and GVL yields in common solvents were presented in Fig. 7. It
is clear that aer the optimal conditions of temperature and
hydrogen pressure were selected, changing the solvent did not
greatly inuence the conversion of EL and selectivity towards
GVL. When propanol, isopropanol, tetrahydrofuran were
selected, the conversions of EL were almost 100%, however, the
yields of GVL reached 86.6%, 81% and 86% respectively, which
means although the conversion was held on a high level,
selectivity of the reaction was partly inuenced by the solvent.
Fig. 5 Effect of different temperature on the conversion of EL to GVL. Fig. 6 Effect of H2 pressure on the conversion of EL to GVL. Reaction
Reaction conditions: 1.0 mmol of EL, 100 mg of 1% Pt/ZSM-35, 12 ml of conditions: 1.0 mmol of EL, 100 mg of 1% Pt/ZSM-35, 12 ml of ethanol,
ethanol, P(H2) ¼ 6.0 MPa, t ¼ 6.0 h.
T ¼ 200 ꢀC, t ¼ 6.0 h.
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Fig.
8
The recyclability of 1% Pt/ZSM-35. Reaction conditions:
Fig. 7 Effect of solvent on the conversion of EL to GVL. Reaction
conditions: 1.0 mmol of EL, 100 mg of 1% Pt/ZSM-35, 12 ml of solvent,
T ¼ 200 ꢀC, t ¼ 6.0 h, P(H2) ¼ 6 MPa.
1.0 mmol of EL, 100 mg of 1% Pt/ZSM-35, 12 ml of ethanol, T ¼ 200 ꢀC,
t ¼ 6.0 h, P(H2) ¼ 6 MPa.
However, the conversion of EL decreased to 90.4% aer being
used for three times. The yield of GVL aer the third run was
84.0%. A possible explanation for this phenomenon was lying in
the inevitable substance loss of the catalyst during the recovery
process, agglomerate of Pt nanoparticles or deposition of
carbonaceous species on the surface of the catalyst, which was
in accordance with the previous work.26 The characterization of
used 1% Pt/ZSM-35 catalyst was carried out, and compared with
fresh catalyst in order to conrm this explanation, which
images could be found in ESI.† It could be found from TEM
image that Pt nanoparticle showed partly agglomerate, the
mean diameter of used catalyst increased to roughly 20 nm. It
could be found from the XRD patterns that the metallic Pt
characteristic peak could still be found in the used catalyst,
while the strength of the peak was slightly weaker, which indi-
cated a possible mass loss of Pt. This phenomenon could also
be conrmed from the XPS analysis, which showed a decreased
3.6 Effect of reaction time
Reaction time is of great importance in EL conversion because
reactant cannot be fully consumed in a short time while too
long reaction time leads to an uneconomical usage of energy
and sometimes more by-product. So reactions were restrained
at different reaction times in order to discover the effect of
reaction time. It can be informed from Table 3 that selectivity
was always at a high level. Moreover, the conversion can be
accumulated as the reaction time prolonged. At the initial time
of the reaction (e.g. 0.5 h), the conversion of EL was only 38.8%.
With the prolonging of the time, the conversion was increased
and reached 100% at 6 h. Nevertheless, extending time to 10 h
led a slight decrease of GVL yield which can also attribute to the
over hydrogenation of GVL.
3.7 Recycle of the catalysts
relative peak area of Pt 4f7/2
.
The stability of the catalysts is of great importance for the
commercial process of GVL. To test the stability of 1% Pt/ZSM-
35, the catalyst was collected by centrifugation aer the reaction
and washed with ethanol for several times, and then it was
directly reused for the next run. It could be found from Fig. 8
that high selectivity towards GVL was kept aer three times.
4 Conclusions
In conclusion, a series of commercial zeolite supported Pt
catalysts were prepared by a wet impregnation method, and
used for the investigation of the hydrogenation of biomass-
derived EL to GVL. Among these catalysts, 1% Pt/ZSM-35 was
found to show the highest activity through the catalyst
screening, under optimized conditions, 100% conversion of EL
with a high GVL selectivity (99.0%) were achieved. The inuence
of different reaction parameters on the hydrogenation of EL was
also investigated, and the best reaction conditions were 200 ꢀC,
6 MPa H2, ethanol was found to be the optimum reaction
solvent. The stability test of the catalyst showed that 1% Pt/ZSM-
35 kept high activity towards GVL aer used for at least three
times. The current work highlighted the efficient zeolite sup-
ported catalysts for the conversion of biomass-derived mole-
cules into biofuels.
Table 3 Time course of the ethyl levulinate hydrogenationa
Entry
t/h
Conv./%
GVL yield/%
1
2
3
4
5
6
0.5
1
2
4
6
37.7
52.2
75.2
91.3
100
33.6
50.6
71.8
88.5
99
10
100
97
a
Reaction conditions: 1.0 mmol of EL, 100 mg of 1% Pt/ZSM-35, 12 ml
of ethanol, T ¼ 200 ꢀC, P(H2) ¼ 6 MPa.
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Acknowledgements
This work was supported by the 973 Program (2012CB215305,
2012CB215306, 2013CB228103), NSFC (21325208, 21172209,
21272050, 21402181, 21572212), CAS (KJCX2-EW-J02),
IPDFHCPST (2014FXCX006), CPSF (2014M561835), SRFDP
(20123402130008), Fundamental Research Funds for the Central
Universities (WK2060190025, WK2060190033, WK2060190040,
WK6030000023), the Key Technologies R&D Programme of Anhui
Province (1604a0702027) and Program for Changjiang Scholars
and Innovative Research Team in University of the Ministry of
Education of China.
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