Conversion of levulinic acid to γ-valerolactone over Ru/Al2O3-TiO2 catalyst under mild conditions

Article abstract of DOI:10.1039/c8ra07938b

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water. In this study, mixed oxides Al₂O₃-TiO₂, Al₂O₃-MoO₃ and Al₂O₃-Co₃O₄ were synthesized by co-precipitation using aqueous solution of NaOH as precipitant. Ru catalysts supported on mixed oxides were prepared by impregnation method and their catalytic performances were tested in the hydrogenation of LA to GVL on a fixed bed reactor. The physicochemical properties of the catalysts were characterized by XRD, H₂-TPR, NH₃-TPD, and BET techniques. The TiO₂ component significantly affected the acidity of the catalyst, and thus its catalytic activity for the GVL yield was affected. The desired product GVL with a yield of about 97% was obtained over the Ru/Al₂O₃-TiO₂ catalyst under mild conditions (WHSV = 1.8 h^?1, T = 80 °C). Moreover, the catalyst Ru/Al₂O₃-TiO₂ exhibited excellent thermal stability in the test period of time.

Full text of DOI:10.1039/c8ra07938b

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Conversion of levulinic acid to g-valerolactone
over Ru/Al2O3–TiO2 catalyst under mild conditions
Cite this: RSC Adv., 2018, 8, 40989
b
b
Ruifeng Wang,ab Lungang Chen,b Xinghua Zhang,
Qi Zhang,
Yuping Li,b
*
Chenguang Wangb and Longlong Mab
Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient
conversion of levulinic acid (LA) to g-valerolactone (GVL) in water. In this study, mixed oxides Al2O3–TiO2,
Al2O3–MoO3 and Al2O3–Co3O4 were synthesized by co-precipitation using aqueous solution of NaOH as
precipitant. Ru catalysts supported on mixed oxides were prepared by impregnation method and their
catalytic performances were tested in the hydrogenation of LA to GVL on a fixed bed reactor. The
physicochemical properties of the catalysts were characterized by XRD, H2-TPR, NH3-TPD, and BET
techniques. The TiO2 component significantly affected the acidity of the catalyst, and thus its catalytic
activity for the GVL yield was affected. The desired product GVL with a yield of about 97% was obtained
over the Ru/Al2O3–TiO2 catalyst under mild conditions (WHSV ¼ 1.8 hꢀ1, T ¼ 80 ꢁC). Moreover, the
catalyst Ru/Al2O3–TiO2 exhibited excellent thermal stability in the test period of time.
Received 25th September 2018
Accepted 21st November 2018
DOI: 10.1039/c8ra07938b
rsc.li/rsc-advances
in the conversion of LA to GVL over the base metal catalyst,
which inevitably incur an energy cost for viable applications.
Introduction
Fortunately, the conversion of LA to GVL can also be catalysed
efficiently by noble metal catalysts under mild condition because
of their excellent catalytic activity for hydrogenation.14–16 It had
been reported that GVL yields are more than 90% over the cata-
lysts of Ru, Pt and Pd at 90 ꢁC.17,18 Sudhakar et al.19 had reported
that hydroxyapatite (HAP)-supported Ru catalyst exhibited 99%
yield of GVL from LA by hydrogenation at 70 ꢁC and 0.5 MPa H2
pressure. However, LA conversion decreased to below 90% when
the Ru/HAP was repeatedly used for 5 times. It is found that
about 47% of Ru were leached into solution when Ru/Al2O3 was
used as catalyst in the conversion of LA to GVL.18 Deteriorated
hydrothermal stability of the catalyst has become a bottleneck
restricting the production of GVL from LA. To improve the
hydrothermal stability of catalyst, hydrogenation catalysts sup-
ported on water-tolerant materials, such as carbon20 and silica,21
had been tested. However, these catalysts had a low yield and
selectivity for GVL. Chia et al.22 developed a new conversion
method for the production of GVL from alkyl levulinates over
ZrO2 catalysts. Rapid deactivation of the catalyst was also
observed during a 100 h period. Arguably, more studies are
required to develop a novel catalyst with longer service life.
The mixed oxides are usually attractive for the improvement
of catalytic performance.23 To develop a novel material with
high catalytic activity and hydrothermal stability, mixed oxides
Al2O3–TiO2, Al2O3–Co3O4 and Al2O3–MoO3 were prepared in this
study, and were used as carrier for Ru-based catalyst. Also, the
catalytic activity was tested in the conversion of LA to GVL in
water. It was found that Ru/Al2O3–TiO2 catalyst is capable of the
efficient synthesis of GVL from LA in a continuous xed bed
g-Valerolactone (GVL), a versatile platform compound with
high stability and low toxicity, can be used as fuel and viable
intermediate for production of chemicals and solvents.1,2 It
had been proposed to be one of the top 12 platform chemicals
by the US Department of Energy.3 Moreover, GVL has been
perceived as a potential replacement for ethanol in gasoline–
ethanol blends because of their better lubricity, higher boiling
points and low solubility in water.4 GVL can be produced from
levulinic acid (LA) by hydrogenation and subsequent cycliza-
tion,5 and LA can be directly produced from lignocellulosic
biomass via a simple hydrolysis process with pristine protonic
acids.6,7 Therefore, it is an attractive route to produce GVL
from LA economically.
In the past years, extensive research had been conducted on
the catalytic conversion of LA to GVL.5,8 Selective hydrogenation
of LA to GVL was found to be an efficient method. Typically,
base metal catalysts, such as Cu, Ni and Co, oen show lower
catalytic activity and relatively high temperature is required.9 To
improve the catalytic activity, base metal catalysts modied by
noble metal were explored. Results demonstrated that hydro-
genation of LA to GVL can be achieved over the bi-metallic
catalysts supported on neutral supports like active carbon,
TiO2, ZrO2 and acid support like g-Al2O3 at the temperature of
180–250 ꢁC.10–13 It can be seen that high temperature is required
aNano Science and Technology Institute, University of Science and Technology of
China, Suzhou 215123, P. R. China
bGuangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou
510640, P.R. China. E-mail: zhangxh@ms.giec.ac.cn; Fax: +86 20 8705 7789; Tel: +86
20 8705 7790
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reactor under mild condition. TiO2 is pristine material with the ow of reduction gas (H2 + N2, 40 ml minꢀ1). The H2
excellent hydrothermal stability.23 The screening investigations consumption was monitored by a thermal conductivity detector
have indicated that Ru/TiO2 catalyst can offer catalytic activity (TCD).
in the conversion of LA to GVL.24 For comparison purposes, the
pure oxide TiO2 and Al2O3 were also used as carrier for Ru-based catalyst was carried out on the instrument of Thermo Scientic
The XPS (X-ray photoelectron spectroscopy) analysis of Ru
catalyst and were tested in the conversion of LA to GVL.
ESCALAB 250Xi employing a monochromated AlKa X-ray
source.
The NH3-TPD (NH3 temperature-programmed desorption)
analysis was also conducted on a chemisorption apparatus
equipped with a TCD detector. Before ammonia adsorption, the
catalyst samples (100 mg) were in situ reduced for 2 h at 300 ꢁC
in the ow of hydrogen and purged at 100 ꢁC for 1 h with
helium. The detailed method was described in a literatureꢀ.245
Experimental
Materials and catalyst preparation
Mixed oxides Al2O3–TiO2, Al2O3–Co3O4 and Al2O3–MoO3 were
prepared based on the following methods.
Al2O3–MoO3: solutions of (NH4)6Mo7O24 and Al (NO3)3 were
mixed. With continuous stirring, sodium hydroxide solution
was added into the mixed solution at 70 ꢁC until the pH of the
solution reached an approximate value of 8. The obtained
precipitate was ltered and washed with distilled water. Then
ꢁ
The catalyst was pretreated at 200 C under vacuum (1 ꢂ 10
Pa) for 1 h. Pyridine was introduced in the IR cell at room
temperature. Desorption was carried out at 200 ꢁC, and the
catalyst was evacuated for 10 min prior to recording the IR
spectra.
ꢁ
the obtained solid was dried at 80 C for 12 h and calcined at
ꢁ
500 C for 5 h, by which the complex oxide Al2O3–MoO3 (mole
Experimental procedure
ratio of Al : Mo ¼ 1 : 1) was prepared and was designated as Al–
Mo.
The catalytic activity test was performed in a xed-bed stainless
steel tube reactor (10 mm internal diameter). This reaction
system is equipped with a mass ow controller for H2 supply
and a HPLC pump for the continuous injection of levulinic acid
solution. The pelletized catalyst (2.0 g) was packed in the middle
of the reaction tube. The catalyst was reduced in the ow of H2
(40 ml minꢀ1) for 4 h at 360 ꢁC. Then, the hydrogenation
reaction was conducted at desired temperature. The feedstocks
were the mixtures of 95 wt% H2O and 5 wt% LA. Liquid product
collected every 10 h was analyzed off-line by GC (SHIMADZU
GC2014 with a ame ionization detector and a column of HP (30
m ꢂ 0.25 mm ꢂ 0.25 mm)) using external standard method. The
vaporization temperature was 250 ꢁC, and the oven temperature
program ranged from 50 to 250 ꢁC at the rate of 10 ꢁC minꢀ1. LA
conversion (XLA) and product yield (YP) were calculated based on
the following formulas:
Similar to that of Al2O3–MoO3, complex oxide Al2O3–Co3O4
(mole ratio of Al : Co ¼ 1 : 1) was prepared using Al(NO3)3$9H2O
and Co(NO3)2$6H2O as precursor and designated as Al–Co.
Al2O3–TiO2 (mole ratio of Al : Ti ¼ 1 : 1) was prepared using
TiCl4 and Al(NO3)3 as precursor and designated as Al–Ti.
Ru-based catalysts with 5 wt% Ru loadings were prepared by
impregnation. Specically, support was dipped into the RuCl3
solution (0.1 mol lꢀ1), followed by treating with ultrasonic
irradiation for 2 h. Aer impregnation for 12 h, the solution was
evaporated to dryness. Then, the obtained solid was dried at
120 ꢁC overnight and calcined at 550 ꢁC for 4 h. For comparison,
Ru catalysts supported on Al2O3 and TiO2 were also prepared
and designated as Ru/Al, Ru/Ti, respectively.
The prepared catalysts were crushed, sieved through 0.83–
0.38 mm mesh before use.
Chemicals used in this study are C.P. reagents and
purchased from Aladdin's Reagent Company.
mol of reactants after reaction
XLA ¼ 100% ꢀ
ꢂ 100% (1)
mol of reactants in feedstock
mol of each product
Catalyst characterization
YP
¼
ꢂ 100%:
(2)
mol of reactants in feedstock
Specic surface area (SBET), pore diameter and pore volume of
catalysts were determined by N2 isothermal adsorption (77 K)
on physical adsorption instrument (Quantachrome Corporation
NOVA-2100) according to BET and BJH theoretical models. The
catalyst was pretreated at 200 ꢁC for 12 h under vacuum
condition before N2 adsorption.
The gas product obtained from the hydrogenation process
was analyzed on a Gas Chromatogram (Agilent 6980) with a TCD
(Thermal Conductivity Detector) and a FID (Flame Ionization
Detector) using the external standard method.
The concentration of Al and Ru ions remaining in the liquid
samples was determined by ICP-AES (Inductively coupled
plasma-atomic emission spectroscopy, IRIS Advantage 1000,
Thermo Electron Corporation).
The crystal structure of the catalysts were analyzed by X-ray
diffraction radiation (X Per Pro MPD with Cu Ka (l ¼ 0.15406
nm) radiation, Philip). The transmission electron microscope
(TEM) images of the catalysts were obtained on an instrument
(JEM-2100F).
The H2-TPR (H2 temperature-programmed reduction) anal-
ysis of catalyst was conducted on a chemisorption apparatus.
The catalyst samples (100 mg) were pretreated at 300 ꢁC for 1 h
Results and discussion
Catalyst characterization
under an Ar ow and subsequently cooled to 50 ꢁC. The The textural properties of Ru catalysts, supported on different
reduction temperature increased to 800 ꢁC with 10 ꢁC minꢀ1 in oxides, were summarized in Table 1 and Fig. 1. The pore size
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Table 1 Porous structure characterization of the different catalysts
the particle size of Ru are all in the range of 1–3 nm and the
average particle size is 1.76 nm. Primo et al.24 had reported that
the Ru particle with the size of about 2 nm exhibited the highest
catalytic activity for hydrogenation.
Pore volume
Pore size
(nm)
Catalyst
SBET (m2 gꢀ1
)
(cm3 gꢀ1
)
Fig. 4 gathered the H2-TPR proles of the Ru-based catalysts.
The peaks, positioned in the range of 90–250 ꢁC, were observed
for all of catalysts, which are attributed to the reduction of
RuO2. The effect of support on the reduction of active metal is
minor. Noticeably, two broad peaks centred at 316 ꢁC and
485 ꢁC were clearly observed in the prole of Ru/Al–Co catalyst.
The former peak can be assigned to the reduction of Co3O4 to
CoO and the latter can be attributed to the reduction of CoO to
Co.26
Ru/Al–Mo
Ru/Al–Co
Ru/Al–Ti
Ru/Al
243
77
98
176
11
0.65
0.27
0.24
0.18
0.04
10.7
14
9.8
4.1
14.5
Ru/Ti
The acidity analysis of the supported Ru catalysts was carried
out by NH3-TPD, and the results were presented in Fig. 5 and
Table 2. Two clear peaks were observed in the desorption curves
of NH3 for Ru/Al–Mo, Ru/Al–Co and Ru/Al catalysts. The rst
peak positioned in the range of 200–250 ꢁC is assigned to
medium acid sites, and the high-temperature desorption peak
positioned in the range of 440–490 ꢁC is assigned to strong acid
sites.27 The acidity of TiO2 is very weak as expected and the
amount of acid sites is little.8 It should be noted that the NH3-
TPD prole of Ru/Ti–Al is rather close to that of Ru/Ti catalyst. A
possible reason is that TiO2 was coated on the surface of
Al2O3,28,29 leading to the less acidic sites of Ru/Ti–Al catalyst.
The type of acidic sites is determined by infrared spectroscopy
of pyridine adsorption. It can be found that Lewis acid sites
(1450 cmꢀ1) is dominant for all tested catalyst as shown in
Fig. 6.
The Ru 3d XPS spectrum of Ru catalyst is presented in Fig. 7.
The spectrum in the region of 283–287 eV is complex due to the
overlapping of C 1s signal and Ru 3d doublet (5/2 and 3/2).30 The
regions of 281.5–283 eV are assigned to RuOx, suggesting that
ruthenium oxides remain at the catalyst surface even aer
reduction. Normally, the Ru 3d XPS spectrum should show
a signal at 280.0 eV, which is attributed to Ru0.16 However, the
signals of Ru0 were observed at 280.2 eV for Ru/Al–Mo, 280.4 eV
for Ru/Al–Ti and 280.6 eV for Ru/Al–Co, respectively. The small
shi of the BE (binding energy) may have been caused by the
interaction between the metallic Ru0 and its support.31
Fig. 1 Pore size distribution of different Ru catalysts.
distribution of Ru catalysts supported on different mixed oxides
is in the range of 2–50 nm. Compared with Ru/Al catalyst, the
most probable pore diameter of the Ru catalysts supported on
mixed oxides become larger. It should be noted that the surface
areas and pore volumes of Ru/Al–Mo are larger than that of Ru/
Al. A possible reason is that a large part of Al2O3 is dispersed on
the surface of MoO3, resulting in the increase of the surface
areas and pore volumes.
XRD patterns of samples were gathered in Fig. 2. The peaks
assigned to Ru were not signicant for all samples. Only one
weak diffraction peak positioned at the 2q of 38.4ꢁ was observed
for all fresh catalysts, which were assigned to the (1 0 0) plane of
Ru. This result suggests good dispersion of Ru metal. The size of
Ru particles supported on different mixed oxides was deter-
mined by TEM. As shown in Fig. 3, most of Ru particle are in the
range of approximately 2–5 nm. Especially for Ru/Al–Ti catalyst,
Catalyst testing
The hydrogenation of LA to GVL was carried out over the
different Ru catalysts in an H2 ow of 40 ml minꢀ1 and a WHSV
(weight hourly space velocity) of 0.6 hꢀ1. It is clear that the
product distribution is signicantly affected by catalyst and
reaction temperature as shown in Fig. 8. GVL, 2-butanol and
1,4-pentanediol are the major products for the hydrogenation of
LA. The lower GVL yield is observed over the Ru/Al–Co and Ru/
Al–Mo catalysts in the investigated temperature range while
higꢁher GVL yield (80%) is obtained over Ru/Al–Ti catalyst at
80 C. This difference could be attributed to the acidity of the
catalyst. Generally, LA is hydrogenated into 4-hydroxy valeric
acid over Ru active sites, and subsequently converted into GVL
by dehydration.8,9 However, intermediate 4-hydroxy valeric acid
could be converted to 2-butanol by decarboxylation, and GVL
Fig. 2 XRD patterns of different Ru-based catalysts.
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Fig. 4 H2-TPR of the different Ru catalysts.
Fig. 5 NH3-TPD profiles of the different Ru catalysts.
yield over Ru/Al–Ti catalyst is higher than those of Ru/Al–Co and
Ru/Al–Mo catalysts. In addition, side-reactions are favoured at
higher temperature. There is a sudden increase of 1,4-penta-
nediol over Ru/Al–Co and Ru/Al–Mo catalysts at 220 ꢁC. A
possible reason is that the conversion of GVL to 1,4-pentanediol
was promoted by Ru/Al–Co and Ru/Al–Mo catalysts at higher
temperature. As far as Ru/Al–Ti is concerned, the yield of by-
product 2-butanol is higher than that of the desired product
GVL at 180 ꢁC and 220 ꢁC, as shown in Fig. 8. The major reason
is that the decarboxylation reaction of intermediate 4-hydroxy
pentanoic acid was promoted at higher temperature, leading to
the increase of 2-butanol.
As shown in Fig. 9(a), the components of CO, CO2, CH4, C2+
were detected in the gas product. These gas products were
derived from LA, GVL and intermediates via aqueous phase
reforming with Ru catalyst. For example, apart from the
decarboxylation,32 the formation of CO2 may also be considered
to be a catalytic decomposition of the reactants to form CO,
combined with the conversion of CO and H2O to produce CO2.
Cleavage of C–C and C–O bonds can be completed by hydro-
genolysis over Ru catalyst in the presence of H2, thereby
producing the smaller hydrocarbon molecule.33 Similar reac-
tions had been reported.34,35 Arguably, higher temperature can
promote the aqueous phase reforming (Fig. 9(b)). This is the
reason that LA conversion increases at higher temperature, but
the product yield does not increase in synchronization, as
shown in Fig. 8.
Fig. 3 TEM images of different Ru-based catalysts and their particle
size distributions.
could be further converted to 1,4-pentanediol by hydrogenation
as shown in Schemes 1. These side reactions are promoted by
Ru catalyst with strong acidic support. As discussed in ‘NH3-
TPD analysis’ section, the acidity of Ru/Al–Ti is far less than
those of Ru/Al–Co and Ru/Al–Mo. So, it is plausible that the GVL
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Table 2 The amounts of acid sites for different Ru catalysts determined by NH3-TPD
Catalyst
120–345 ꢁC, mmol gꢀ1
345–787 ꢁC, mmol gꢀ1
Total acid sites, mmol gꢀ1
Ru/Al–Mo
Ru/Al–Co
Ru/Al–Ti
Ru/Al
0.277
0.124
0.040
0.279
0.013
0.291
0.189
0.063
0.053
0.042
0.568
0.313
0.103
0.332
0.055
Ru/Ti
Fig. 6 Infrared spectra of pyridine adsorbed on Ru catalyst after
evacuation at 200 ꢁC.
To explore the effect of mixed oxides on the catalytic
activity, the hydrogenation of LA over Ru catalyst supported on
pure oxide was also conducted at 80 C. As shown in Fig. 10,
Fig. 8 Conversion of LA to GVL over different Ru catalysts. Reaction
ꢁ
conditions. PH ¼ 4.0 MPa, H2 flow: 40 ml minꢀ1; WHSV: 0.6 hꢀ1
.
2
the GVL yields were only 41.6% and 21.8% over Ru/Al and Ru/
Ti catalysts, respectively. For the Ru/Ti catalyst, the deterio-
rated porous and small surface area might be the root cause
for the lower GVL yield of the Ru/Ti catalyst. As for the Ru/Al
catalyst, it is similar to that of Ru/Al–Co and Ru/Al–Mo cata-
lysts, the strong acidity of the catalyst results in the lower yield
of desired product. On the contrary, the GVL yield drastically
increased to 80% when Ru/Al–Ti was used as catalyst. This
result suggests that mixed oxides have signicant advantages
in improving catalytic activity.
could be taken out instantaneously from the reactor due to the
increased WHSV, avoiding the aqueous phase reforming of
GVL. However, GVL yield decreased slightly when the WHSV
was further increased to 2.4 hꢀ1. Therefore, the next work for
conversion of LA to GVL was carried out with a WHSV of 1.8 hꢀ1
.
Stability of catalyst
The stability of Ru catalysts was tested with a WHSV of 1.8 hꢀ1 at
80 ꢁC. As shown in Fig. 12, GVL yield is about 97% over Ru/Al–Ti
catalyst and remains constant within the tested 120 h while the
GVL yield is constant at about 26% over Ru/Ti catalyst. As for the
Ru/Al catalyst, the GVL yield decreases gradually with the
lengthened reaction time. This result suggests that Ru/Al cata-
lyst was deactivated gradually in the reaction process. It had
been reported that large amounts of Ru and Al were leached into
Effect of WHSV
The effect of WHSV was also investigated at 80 ꢁC using Ru/Al–
Ti as catalyst. As shown in Fig. 11, GLV yield gradually increased
in the range of 0.6–1.8 hꢀ1. It is explained that the product GVL
Scheme 1 The possible reaction pathways for conversion of LA to
Fig. 7 Ru 3d XPS spectrum of different catalyst.
GVL.
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Fig. 11 Effect of WHSV on the conversion of LA to GVL over Ru/Al–Ti
catalyst. Reaction conditions: T ¼ 80 ꢁC; PH ¼ 4.0 MPa; H2 flow: 40
2
ml minꢀ1
.
Fig. 9 Effects of catalysts and reaction temperature on gas compo-
sitions. Reaction conditions: (a) T ¼ 180 ꢁC; PH ¼ 4.0 MPa, H2 flow: 40
2
ml minꢀ1; WHSV ¼ 0.6 hꢀ1; (b) PH ¼ 4.0 MPa, H2 flow: 40 ml minꢀ1
;
2
WHSV ¼ 0.6 hꢀ1
.
the solution during the conversion of LA to GVL with Ru/Al2O3
catalyst, which resulted in a decrease in catalytic activity.18 In
this study, we also detected the concentration of aluminium
Fig. 12 The stability test for Ru/Al–Ti catalyst. Reaction conditions:
WHSV ¼ 1.8 hꢀ1; T ¼ 80 ꢁC; PH ¼ 4.0 MPa; H2 flow: 40 ml minꢀ1
.
2
and ruthenium ions in the collected liquid samples, and the in the collected liquid sample. Fortunately, leaching of Al and
results were listed in Table 3. It is clear that the large amount of Ru is negligible for Ru/Al–Ti catalyst. This result may strongly
Al and Ru ions were leached from the Ru/Al catalyst. A reason- suggest that the Ru catalyst supported on Al–Ti mixed oxides
able explanation is that the alumina was corroded and leached possesses excellent stability under hydrothermal condition. The
when exposed to acid (levulinic acid) in the aqueous solution. major contribution should be attributed to the added TiO2
The interaction between Ru metal and carrier disappears when component, which is a kind of acid-tolerant material. It can be
the g-Al2O3 is leached, resulting in the leaching of Ru. It is inferred that TiO2 is coated on the surface of Al2O3, which
thereby plausible that large amount of Al and Ru were detected prevented the contact between acid and Al2O3, reducing the
leaching of Al. This inference is consistent with the previous
conclusions derived from NH3-TPD analysis.
Table 3 Aluminium and ruthenium content of liquid samples taken at
different runtimes in LA conversion experimentsa
Time on
stream (h)
Total leached
Al (wt%)
Total leached
Ru (wt%)
Catalyst
Ru/Al
30
60
30
2.1
3.6
—
35
44
0.6
Ru/Ti
120
30
120
—
0.2
0.4
0.8
1.4
2.6
Ru/Al–Ti
a
Reaction conditions: T ¼ 80 ꢁC; PH ¼ 4.0 MPa; H2 ow: 40 ml minꢀ1
;
Fig. 10 Comparison for the effect of mixed oxides and pure oxide.
2
Reaction conditions: T ¼ 80 ꢁC; PH ¼ 4.0 MPa; H2 flow: 40 ml minꢀ1
;
WHSV ¼ 1.8 hꢀ1
.
2
WHSV ¼ 0.6 hꢀ1
.
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12 A. M. Hengne and C. V. Rode, Green Chem., 2012, 14, 1064.
13 D. J. Braden, C. A. Henao, J. Heltzel, C. C. Maravelias and
J. A. Dumesic, Green Chem., 2011, 13, 1755.
Conclusions
Ru catalysts supported on mixed oxides Al2O3–TiO2, Al2O3–
MoO3 and Al2O3–Co3O4 were studied for conversion of levulinic
acid to g-valerolactone. NH3-TPD results and catalytic behav-
iour revealed that the Ru metal combined with strong acidic
sites of support could promote the aqueous phase reforming,
resulting in the lower yield of GVL. TiO2 might be coated on the
surface of Al2O3, weakening the acidity of mixed oxides Al2O3–
TiO2. Therefore, Ru/Al2O3–TiO2 exhibited better catalytic
activity for GVL yield than those of Ru/Al2O3–MoO3 and Ru/
Al2O3–Co3O4. Moreover, Ru/Al2O3–TiO2 exhibited excellent
stability under hydrothermal condition.
¨
14 W. Deng, Y. Wang, S. Zhang, K. M. Gupta, M. J. Hulsey,
H. Asakura, L. Liu, Y. Han, E. M. Karp, G. T. Beckham,
P. J. Dyson, J. Jiang, T. Tanaka, Y. Wang and N. Yan, Proc.
Natl. Acad. Sci. U. S. A., 2018, 115, 5093.
15 Y. Wang, S. De and N. Yan, Chem. Commun., 2016, 52, 6210.
16 R. S. Suppino, R. Landers and A. J. G. Cobo, Appl. Catal., A,
2016, 525, 41.
17 C. Moreno-Marrodan and P. Barbaro, Green Chem., 2014, 16,
3434.
18 A. S. Piskun, J. E. de Haan, E. Wilbers, H. H. van de
Bovenkamp, Z. Tang and H. J. Heeres, ACS Sustainable
Chem. Eng., 2016, 4, 2939.
19 M. Sudhakar, M. Lakshmi Kantam, V. Swarna Jaya,
R. Kishore, K. V. Ramanujachary and A. Venugopal, Catal.
Commun., 2014, 50, 101.
Conflicts of interest
There are no conicts to declare.
20 A. S. Amarasekara and M. A. Hasan, Catal. Commun., 2015,
60, 5.
Acknowledgements
This study was funded by the National Key Research and
Development Plan (2017YFE0106600), the National Key Tech-
nology R&D Program (2015BAD15B06), the Science and Tech-
21 P. P. Upare, J. M. Lee, Y. K. Hwang, D. W. Hwang, J. H. Lee,
S. B. Halligudi, J. S. Hwang and J. S. Chang, ChemSusChem,
2011, 4, 1749.
nology
Planning
Project
of
Guangdong
Province
22 M. Chia and J. A. Dumesic, Chem. Commun., 2011, 47, 12233.
23 G. Murali Dhar, B. N. Srinivas, M. S. Rana, M. Kumar and
S. K. Maity, Catal. Today, 2003, 86, 45.
24 A. Primo, P. Concepcion and A. Corma, Chem. Commun.,
2011, 47, 3613.
(2014A01016020), the “Transformational Technologies for
Clean Energy and Demonstration”, Strategic Priority Research
Program of the Chinese Academy of Sciences (No. XDA
21060102) and the Youth Innovation Promotion Association
CAS (No. 2015288).
25 X. Zhang, T. Wang, L. Ma and C. Wu, Fuel, 2010, 89, 2697.
26 T. M. Sankaranarayanan, A. Berenguer, C. Ochoa-
´
Hernandez, I. Moreno, P. Jana, J. M. Coronado,
Notes and references
D. P. Serrano and P. Pizarro, Catal. Today, 2015, 243, 163.
27 S. Pichaikaran and P. Arumugam, Green Chem., 2016, 18,
2888.
¨
¨
1 S. G. Wettstein, D. M. Alonso, E. I. Gurbuz and J. A. Dumesic,
Curr. Opin. Chem. Eng., 2012, 1, 218.
2 J. Zhang and N. Yan, ChemCatChem, 2017, 9, 2790.
3 J. J. Bozell and G. R. Petersen, Green Chem., 2010, 12, 539.
4 I. T. Horvath, H. Medhi, V. Fabos, L. Boda and L. T. Mika,
Green Chem., 2008, 10, 238.
´
´
´
28 V. Rodrıguez-Gonzalez, R. Zanella, G. Angel and R. Gomez, J.
Mol. Catal. A: Chem., 2008, 281, 93.
29 A. Adamczyk and E. Długon, Spectrochim. Acta, Part A, 2012,
´
89, 11.
5 W. R. H. Wright and R. Palkovits, ChemSusChem, 2012, 5, 1.
6 D. W. Rackemann and W. O. S. Doherty, Biofuels, Bioprod.
Bioren., 2011, 5, 198.
7 J. Tan, Q. Liu, L. Chen, T. Wang, L. Ma and G. Chen, J. Energy
Chem., 2017, 26, 115.
30 J. Balcerzak, W. Redzynia and J. Tyczkowski, Appl. Surf. Sci.,
2017, 426, 852.
31 P. P. Upare, M. Lee, S.-K. Lee, J. W. Yoon, J. Bae,
D. W. Hwang, U.-H. Lee, J.-S. Chang and Y. K. Hwang,
Catal. Today, 2016, 265, 174.
8 W. Luo, M. Sankar, A. M. Beale, Q. He, C. J. Kiely,
P. C. A. Bruijnincx and B. M. Weckhuysen, Nat. Commun.,
2015, 6, 6540.
9 R. Yoshida, D. Sun, Y. Yamada, S. Sato and G. J. Hutchings,
Catal. Commun., 2017, 97, 79.
32 L. Chen, Y. Li, X. Zhang, Q. Zhang, T. Wang and L. Ma, Appl.
Catal., A, 2014, 478, 117.
33 G. W. Huber and J. A. Dumesic, Catal. Today, 2006, 111, 119.
34 G. W. Huber, R. D. Cortright and J. A. Dumesic, Angew.
Chem., Int. Ed., 2004, 43, 1549.
10 X. L. Du, L. He, S. Zhao, Y. M. Li, Y. Cao, H. Y. He and
K. N. Fan, Angew. Chem., Int. Ed., 2011, 50, 7815.
11 P. P. Pravin, J. M. Lee, D. W. Hwang, S. B. Halligudi,
Y. K. Hwang and J. S. Chang, J. Ind. Eng. Chem., 2011, 17, 287.
35 J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew. Chem.,
Int. Ed., 2007, 46, 7164.
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