Enhancing the conversion of ethyl levulinate to γ-valerolactone over Ru/UiO-66 by introducing sulfonic groups into the framework

Article abstract of DOI:10.1039/c8ra01314d

The conversion of ethyl levulinate (EL) to γ-valerolactone (GVL) is an important reaction in biomass conversion. This process undergoes two consecutive reactions: hydrogenation and transesterification of the intermediate compound, i.e. ethyl 4-hydroxypentanoate, which are catalyzed by metal nanoparticles and acid sites, respectively. In this study, we explored the catalytic activity of Ru supported on metal organic frameworks aiming to develop efficient metal-acid bifunctional catalysts for this green process. UiO-66 and its analogues with various substituted groups (-SO₃H, -NH₂ and -NO₂) were employed in this study. The Ru particle size, oxidation state and reducibility were characterized by TEM, H₂-TPR, and XPS. The results suggest that the introduction of functional groups reduces the hydrogenation activity of pristine Ru/UiO-66 to various extents. Catalyst modified with -SO₃H group shows much higher acidic catalytic performance while showing hydrogenation activity towards CO bonds, thus improving the overall transformation of EL to GVL due to the presence of strong Br?nsted acid sites.

Full text of DOI:10.1039/c8ra01314d

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Enhancing the conversion of ethyl levulinate to g-
valerolactone over Ru/UiO-66 by introducing
sulfonic groups into the framework†
Cite this: RSC Adv., 2018, 8, 16611
Jie Yang, * Wenjuan Huang, Yongsheng Liu and Tao Zhou
The conversion of ethyl levulinate (EL) to g-valerolactone (GVL) is an important reaction in biomass
conversion. This process undergoes two consecutive reactions: hydrogenation and transesterification of
the intermediate compound, i.e. ethyl 4-hydroxypentanoate, which are catalyzed by metal nanoparticles
and acid sites, respectively. In this study, we explored the catalytic activity of Ru supported on metal
organic frameworks aiming to develop efficient metal–acid bifunctional catalysts for this green process.
UiO-66 and its analogues with various substituted groups (–SO
this study. The Ru particle size, oxidation state and reducibility were characterized by TEM, H
XPS. The results suggest that the introduction of functional groups reduces the hydrogenation activity of
pristine Ru/UiO-66 to various extents. Catalyst modified with –SO H group shows much higher acidic
3
H, –NH
2
and –NO
2
) were employed in
2
-TPR, and
Received 10th February 2018
Accepted 17th April 2018
3
DOI: 10.1039/c8ra01314d
catalytic performance while showing hydrogenation activity towards C]O bonds, thus improving the
rsc.li/rsc-advances
overall transformation of EL to GVL due to the presence of strong Brønsted acid sites.
ꢀ
and a GVL selectivity of 100% in water at 70 C, 5 MPa over 1 h
1
Introduction
when employing Ru nanoparticles supported on TiO
Global warming and depletion of fossil resources are two major Kuwahara et al. reported a GVL yield of 95.6% in aqueous
issues concerning sustainable development. Biomass and its medium at 70 C, 0.5 MPa and 4 h by using Ru nanoparticles
2
. Recently,
28
1
ꢀ
derivatives, as an abundant and inexpensive carbon source for conned in Zr-containing spherical mesoporous silica. Galletti
30
the production of renewable bio-fuels and high value-added et al. investigated the catalytic activity of a ruthenium sup-
2
–5
compounds, thus attract tremendous attention.
olactone (GVL), as one of the versatile platform chemicals, can catalyst in the process of hydrogenation of LA to GVL. The
be applied as a fuel additive,
g-Valer- ported catalyst in combination with a heterogeneous acid co-
6,7
8,9
a green solvent,
and result reveals that the presence of the heterogeneous acid co-
a precursor of value-added chemicals or liquid hydrocarbon catalyst is favorable not only for the esterication step, but
8
,10
fuels.
successive intramolecular dealcoholization of levulinic acid nation to the intermediate g-hydroxyvaleric acid.
(
GVL is usually produced by the hydrogenation and also for the activation of the carbonyl group, namely hydroge-
8
,11
12,13
LA) or its esters.
Since LA is corrosive and needs formi-
Metal–organic frameworks (MOFs) as a new class of porous
1
4
dable purication, employing esters of LA as reactants would crystalline materials are composed by coordination between
be a promising green approach. Taking ethyl levulinate (EL) as inorganic metal ions and organic linkers.
an example, two steps are involved in the transformation from structures, physicochemical properties, and functionality
EL to GVL:
EHP) and transesterication of EHP to GVL. It is reported that ysis,
metal catalysts, such as Pd,
Mo, and Cu, are all active for hydrogenation of carbonyl organic solvents have attracted more attention in catalysis.
groups when hydrogen is used. Among these metal catalysts, Ru Especially, Zr centers act as Lewis and/or Brønsted acid sites
has been reported to be the most active component. High under certain reaction conditions, thus being widely applied in
30,31
Their tunable
32
8
,15–17
hydrogenation of EL to ethyl 4-hydroxyvalerate make these materials attractive in the applications of catal-
33–35 36,37 38,39 40,41
(
gas storage,
separation,
and sensing.
18,19
19
11,19,20
21
22
23
Pt, Ru,
Au, Ni, Co,
Zirconium-based MOFs with higher stability in water and some
24
25
42
43–46
14
46–51
catalytic activities of some Ru catalysts in the hydrogenation of many acid-catalyzed reactions.
UiO-66 (Zr
(BDC ¼ 1,4-benezenedicarboxylate)), perfect crystalline
For example, Ruppert et al. reported a LA conversion of 100% material consisting of Zr (OH) octahedra featuring a 12-
connected Zr cluster with BDC linkers, is an interesting Zr-
6 4 4 6
O (OH) (BDC)
26–29
LA into GVL have been reported by several research groups.
a
27
6
O
4
4
52
6
based MOF due to its multiple acidic property. It is reported
that missing linker defect sites always exist in UiO-66 crys-
School of Mathematics and Physics, Shanghai University of Electric Power, Shanghai,
2
†
1
00090, China. E-mail: yj_7667@aliyun.com
53,54
tals.
with H
Most likely, in aqueous phase, the defect sites bond
O and –OH groups to compensate the charge lost and
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ra01314d
2
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there are at least three types of Brønsted protons in the UiO-66 measurements, the samples were degassed in situ under
ꢀ
framework present on the inorganic nodes: m -OH, –OH and vacuum at 150 C for 6 h. Inductively coupled plasma (ICP)
–
3
2
55
OH protons. Therefore, UiO-66 or organic-functionalized analysis was used to quantify the Ru loading with a Thermo IRIS
UiO-66 materials can serve as efficient supports with prom- Intrepid II XSP atomic emission spectrometer. Samples were
ising acidic catalytic function. rstly dissolved in aqua regia and then diluted with deionized
We herein introduced Ru nanoparticles into the frameworks water. X-ray photoelectron spectroscopy (XPS) was conducted
of UiO-66 and its analogues modied with several commonly with an ESCALAB 250xi spectrometer, using a monochromated
used functional groups including –NO
aiming to reveal the effects of the substituted groups on the were obtained using 40 eV pass energy and 0.1 eV step. Instru-
2
, –NH
2
, and –SO
3
H, Al Ka X-ray source (hn ¼ 1486.6 eV). High-resolution spectra
ꢁ10
hydrogenation activity of Ru nanoparticles for the reaction of EL ment base pressure was 8 ꢂ 10
Pa. All binding energies were
to EHP along with the acid-catalyzed conversion of EHP to GVL referenced to the C 1s line at 284.6 eV. Due to the strong overlap
via transesterication. The results suggest that the Ru/UiO-66– between Ru 3d with C 1s, the Ru 3d5/2 peaks were analyzed.
SO H catalyst shows the best performance in the overall reac- Before each measurement, the samples were pretreated by
3
tion of converting EL to GVL via hydrogenation–trans- reducing in a hydrogen atmosphere at a reaction temperature
ꢀ
esterication pathways. These ndings are helpful for (80 C), stored in isopropanol and then transferred onto the
developing efficient bifunctional catalysts for GVL production. sample holder in a glove box. To investigate the adsorption
behavior of EL on supports, thermogravimetric analysis was
performed with a NETZSCH STA449F3 TGA. Samples were
2
Experimental
ꢀ
heated from room temperature to 800 C with a heating rate of
2.1 Preparation of metal–organic frameworks
ꢀ
ꢁ1
10
C min
under an air ow. Temperature-programmed
56,57
According to the literature,
all of the MOFs were prepared reduction (TPR) measurements were carried out using a TP-
under hydrothermal conditions. For instance, the synthesis of 5080 (Tianjin Xianquan, China) equipped with a thermal
UiO-66–NH
amino-1,4-benzenedicarboxylic acid (H
2
was performed by dissolving ZrCl
N–H
4
(0.30 g) and 2- conductivity detector. Prior to measurements, about 50 mg of
BDC) (0.31 g) in sample was pretreated in a He stream, heated to 150 C at a rate
ꢀ
2
2
ꢀ
ꢁ1
DMF (40 mL) at room temperature. The resulting mixture was of 10 C min , and held at this temperature for 1 h. Aer
ꢀ
placed in a Teon-lined autoclave in a preheated oven at 120 C cooling down to room temperature, a gaseous mixture of 5% H
for 36 hours. Aer the solution was cooled to room temperature in Ar was fed at a ow rate of about 30 mL min and the sample
in air, the resulting solid was ltered and repeatedly washed was heated to 150 C with a rate of 10 C min
2
ꢁ
1
ꢀ
ꢀ
ꢁ1
.
ꢀ
with absolute ethanol for 3 days while heated at 60 C in an oil
bath. The resulting powder was ltered and dried under
2
.4 Catalytic activity measurements
ꢀ
57
vacuum at 50 C. The functionalized UiO-66s were labelled
UiO-66–X (X ¼ –NO , –NH , –SO H).
The hydrogenation of EL in water was carried out in a Teon-
lined (120 mL) steel batch reactor. As-prepared catalysts were
loaded into the reactor with 9.6 mL of deionized water and 340
mL of EL. Aer purging ve times with H , the reactor was
2
pressurized with 0.5 MPa H
bath which was kept at 80 C and the liquid was vigorously
stirred to reduce the mass transfer effect. The trans-
esterication of EHP in water was carried out in a glass pressure
bottle. As-prepared catalysts were loaded into the bottle charged
with 5 mL of deionized water and 200 mL of a mixture of EHP
2
2
3
2
.2 Preparation of Ru/UiO-66–X
The supported Ru catalysts were prepared by
impregnation method followed by deposition-reduction of Ru
on UiO-66–X. Typically, 0.715 mL of RuCl solution (Ru:
1.60 mg mL ) was impregnated on 0.5 g of UiO-66–X, the
a
wet-
2
and the rector was placed in an oil
ꢀ
3
ꢁ1
2
resulting sample being labelled RuCl /UiO-66–X. Aer drying at
3
ꢀ
6
0 C, RuCl /UiO-66–X was immersed into 60 mL of methanol
3
with stirring. The Ru precursor was reduced with NaBH
methanol solution. The solid was ltered and dried at 50 C
4
(84 mol%), GVL (5 mol%), and EL (11 mol%). The bottle was
ꢀ
ꢀ
placed in an oil bath at 80 C with stirring for 8 hours. All of the
products were diluted with ethanol and analyzed with a Tian-
mei 7900 GC equipped with a DM-FFAP capillary column (30 m
length, 0.25 mL lm thickness and 0.25 mm internal diameter).
under vacuum. The resulting products were denoted as Ru/UiO-
66–X.
2.3 Characterization
Powder X-ray diffraction (XRD) patterns were collected with
a Rigaku Ultima IV X-ray diffractometer using Cu Ka radiation
3
Results and discussion
3.1 XRD, IR and BET characterization of UiO-66 and UiO-66–
˚
(
l ¼ 1.5405 A) operated at 35 kV and 25 mA. Scanning electron
X
microscopy (SEM) was performed with a Hitachi S-4800 at 10
kV. Transmission electron microscopy (TEM) images were ob- Fig. 1A displays the XRD patterns of the series of isostructural
2
tained with a FEI Tecnai G F30 microscope operated at 300 kV. UiO-66. According to the XRD results, all materials show similar
56,57
Fourier transform infrared (IR) spectra were collected with structure well matching the patterns in the literature.
a Nicolet Fourier transform infrared spectrometer (NEXUS 670). conrm the successful incorporation of various substituents,
Liquid nitrogen adsorption was used to determine the BET i.e. –SO H, –NH and –NO , the IR spectra of UiO-66, UiO-66–
surface areas and pore volumes. Prior to the adsorption NH , UiO-66–SO H and UiO-66–NO were compared as shown
To
3
2
2
2
3
2
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Fig. 1 (A) XRD patterns of UiO-66 and UiO-66–X and (B) IR spectra of UiO-66 and UiO-66–X.
3
in Fig. 1B. In the case of UiO-66–SO H, the bands at ca. 1080 and 3.2 Characterization of Ru/UiO-66 and Ru/UiO-66–X
ꢁ
1
1
180 cm are assigned to the stretching modes of –SO
3
H with
Fig. 2 shows the XRD patterns of UiO-66 and UiO-66–X aer
loading with Ru nanoparticles. All Ru/UiO-66–X materials
retained their crystalline structures, except for Ru/UiO-66–
44
ꢁ1
double-bond character (O]S]O). The band at ca. 1025 cm
is due to the stretching vibration of the S–O single bond. The
presence of –NH is conrmed by the presence of the bands at
458 and 3353 cm due to the N–H vibration, as well as the
C–N stretching band at 1257 cm
attributed to the asymmetric –NO
the existence of nitro groups in UiO-66–NO
was used to determine the BET surface areas (Fig. S1†) and the
results are listed in Table 1. UiO-66 has a specic surface area
SSA) of 575 m g . The SSAs of UiO-66–NH and UiO-66–NO
44
2
SO
3
3
H. The long-range order of Ru/UiO-66–SO H collapsed aer
ꢁ1
44
3
RuCl
3
impregnation and reduction, indicating its unstable
ꢁ1
57,58
ꢁ1
.
The peak at 1540 cm
,
56
structure as reported in the literature. No diffraction peaks
attributed to Ru nanoparticles were observed in the XRD
patterns of Ru/UiO-66 and Ru/UiO-66–X, indicating the high
2
stretching vibration, proves
44
2 2
. N physisorption
dispersion of the Ru particles. N physisorption results of Ru/
2
2
ꢁ1
2
(
2 2
ꢁ1
are 661 and 651 m g , respectively, which are ꢃ13% higher
than that of UiO-66. In contrast, the SSA of UiO-66–SO H (284
3
2
ꢁ1
m g ) is much lower than that of UiO-66, which is likely due to
steric constraints and increased molecular weight resulting
from the 2-substituted sulfonic group.
approach to achieve modulation of the physical properties of
UiO-66–SO H is to combine different ligands of the same den-
ticity in different proportions, namely 1,4-benzenecarboxylic
56,57
A promising
3
56
acid and 2-substituted 1,4-benzenecarboxylic acid. We cannot
exactly determine the pore size distribution by N adsorption at
2
this stage due to the microporous nature. The particle sizes of
these materials range from 200 to 600 nm according to the SEM
images (Fig. S2†).
Table 1 Physicochemical properties of UiO-66 and Ru/UiO-66–X
2
ꢁ1
a
b
Catalyst
SSA (m g
)
Ru (wt%)
H/Ru
UiO-66
UiO-66–SO
UiO-66–NH
UiO-66–NO
Ru/UiO-66
Ru/UiO-66–SO
Ru/UiO-66–NH
Ru/UiO-66–NO
575
284
661
651
510
10
—
—
—
—
2.3
1.7
4.0
1.7
—
—
—
—
0.89
0.64
0.16
0.47
3
H
2
2
3
H
2
170
489
2
a
b
Determined by ICP-AES. Calculated from H
2
-TPR results.
Fig. 2 XRD patterns of Ru/UiO-66 and Ru/UiO-66–X.
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3 2 2
Fig. 3 TEM images of (a) Ru/UiO-66, (b) Ru/UiO-66–SO H, (c) Ru/UiO-66–NH and (d) Ru/UiO-66–NO .
UiO-66 and Ru/UiO-66–X (Table 1 and Fig. S3†) reveal that the
SSA of UiO-66 is retained aer loading Ru nanoparticles. The
2
ꢁ1
2
SSA of Ru/UiO-66–NO is 489 m g , which is lower than that of
the pristine material. However, aer Ru loading, the SSAs of
UiO-66–SO H and UiO-66–NH dramatically decrease by 96%
3
2
and 74% compared with the pristine materials, which could be
explained by the compromised structures of UiO-66–SO H and
3
2
UiO-66–NH upon Ru loading.
The Ru loadings were determined by ICP analysis and the
results are listed in Table 1. The Ru loading is close to 2 wt% for
2
the catalysts except for Ru/UiO-66–NH . Ru loading of Ru/UiO-
6
6–NH is about 4 wt% which is higher than that of the other
2
Ru/UiO-66–X. This result suggests that the incorporation of Ru
species is successful for Ru/UiO-66–NH , which may be due to
2
a strong coordination ability of –NH group with Ru species,
2
leading to the high loading efficiency. The particle sizes of Ru
for Ru/UiO-66–X were analyzed by high-resolution TEM (Fig. 3),
the Ru particle sizes of all catalysts being in the range of 1–4 nm.
It should be noted that the Ru particles of UiO-66–NH are
2
smaller than those of the other catalysts.
The H -TPR proles of all catalysts are shown in Fig. 4. A
2
ꢀ
signicant H consumption peak ranging from 40 to 120 C was
2
observed for all catalysts, which is attributed to the reduction of Fig. 4
2 2
H -TPR profiles of fresh Ru/UiO-66, Ru/UiO-66–NH , Ru/
ꢀ
59
3 2
UiO-66–SO H and Ru/UiO-66–NO .
oxidic Ru species below 150 C. This result is consistent with
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ꢁ
1
Fig. 5 XPS spectra of Ru 3d C 1s region of Ru/UiO-66, Ru/UiO-66–NH
of Ru/UiO-66, Ru/UiO-66–NH and Ru/UiO-66–SO
Ru , magenta asymmetric curves) and oxidic Ru (green symmetric curves and orange symmetric curves) species. Red lines represent the overall
fit of the data and blue lines represent background.
2
and Ru/UiO-66–SO
3
H (left) and fitted XPS spectra of Ru 3d5/2 region
2
3
H (right). The dashed lines indicate the binding energies of the 3d5/2 peaks of reduced Ru
0
(
the fact that Ru particles are prone to being oxidized when sample series and the corresponding results are shown in
exposed to oxygen. We have roughly calculated the H/Ru ratio by Fig. 5 and Table 2. Ru (3d) peaks are resolved as a doublet (3d5/2
normalizing on the amount of Ru loading. The H/Ru ratios of and 3d3/2 at 279.90 and 284.07 eV, respectively) with an SOS of
60
Ru/UiO-66, Ru/UiO-66–SO
NO were found to be 0.89, 0.64, 0.16 and 0.47, respectively. One overlapped by the C 1s peak, we herein focused on the Ru 3d5/2
nding is that UiO-66–NH shows much lower H consumption peak which can be generally deconvoluted into three oxidation
3 2
H, Ru/UiO-66–NH and Ru/UiO-66– 4.17 eV. Because the 3d3/2 peak centered at ca. 284 eV is always
2

2
2
compared with the other samples, which results from the states: the feature at ca. 280 eV can be ascribed to metallic Ru,
stronger interaction between –NH and oxidic Ru species. In whereas the peaks at ca. 281 and 282 eV are ascribed to RuO . In
2
2
ꢀ
0
addition, the reduction of oxidic Ru takes place at 65 C for Ru/ the cases of UiO-66 and UiO-66–SO H, the peaks of Ru were
3
UiO-66. The introduction of –SO H group leads to a lower clearly observed at about 280.2 eV upon ushing with H at
3
2
ꢀ
ꢀ
reduction temperature starting at 40 C, while introducing –NO
and –NH groups both leads to higher reduction temperature particles on UiO-66 can be partially reduced by H
starting at about 80 C. The result suggests that the reducibility temperature. The contents of metallic Ru on UiO-66 and UiO-
of oxidic Ru species supported on UiO-66 is dependent on the 66–SO H were calculated to be ca. 71% and 60%, respectively.
organic groups introduced. The –SO H functional group bene- This result implies that both oxidic RuO
2
80 C. It has been previously shown that the oxidized Ru
2
2
at room
ꢀ
59
3
3
x
and metallic Ru are
ꢀ

ts the reduction of Ru species at lower temperatures, which present in Ru/UiO-66 and UiO-66–SO H at 80 C in H atmo-
3
2
plays a critical role in the hydrogenation process under mild sphere and the metallic Ru is present dominantly. For Ru/UiO-
conditions because metallic Ru species generally show better 66–NH , we only observed RuO from XPS, meaning that the
2
2
d+
hydrogenation activity towards C]O group than their oxidized Ru cations are strongly coordinated to –NH
2
groups. Similar
5
9
counterparts.
results have been previously reported by Wang et al. for
We also investigated the reduction degree of the supported a ruthenium-supported catalyst containing –NH
61
2
groups.
ꢀ
Ru particles upon pretreatment under a H
2
ow at 80 C for These results indicate that the functional groups on the ligands
30 min by XPS. The tted Ru 3d XPS spectra of the Ru/UiO-66 play a prominent role in the redox behavior of Ru species.
3
Table 2 Binding energies (BE) and calculated reduction degree (RD) of the fitted Ru 3d5/2 XPS spectra of Ru/UiO-66, Ru/UiO-66–SO H and Ru/
UiO-66–NH
2
0
3+
4+
Sample
Ru 3d5/2 BE (eV)
Ru 3d5/2 BE (eV)
Ru 3d5/2 BE (eV)
RD (3d5/2, %)
Ru/UiO-66
Ru/UiO-66–SO
Ru/UiO-66–NH
280.3
280.1
—
—
—
282.0
281.2
281.5
281.2
71
60
0
3
H
2
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.3 Catalytic activity measurements
Paper
3
3
employing 100 mg of the catalysts (95% for Ru/UiO-66–SO H
and 82% for Ru/UiO-66–NO ). The result indicates that the
hydrogenation proceeds very fast in the presence of Ru/UiO-66
2
The activities of Ru/UiO-66 and the three modied Ru/UiO-66
materials in the hydrogenation of EL were tested by using
ꢀ
and the introduction of –NO
tion of EL, while –SO H group plays a minor role in the
hydrogenation of EL. With respect to transesterication of EHP,
SO H and –NO groups play different roles in this step. The
2
group hampers the hydrogena-
each catalyst of 100 mg in water at 80 C for 1 h under 0.5 MPa of
3
2
H . The conversion of EL and selectivity of GVL and EHP aer
reaction for 1 h are listed in Table 3. It is clear that Ru/UiO-66
shows the highest hydrogenation activity with EL conversion
–
3
2
yields of GVL on Ru/UiO-66 for different dosages (25 mg, 50 mg
and 100 mg) increase gradually from 39% to 45%, and to 50%,
indicating a slow rate of transesterication of EHP. In the case
of 100%. The conversions of EL on Ru/UiO-66–SO H, Ru/UiO-
3
6
6–NO and Ru/UiO-66–NH are 95, 82 and 37%, respectively.
2 2
These results suggest that the introduction of functional groups
reduces the hydrogenation activity of supported Ru nano-
of Ru/UiO-66–NO , a slight increase was found in the yield of
2
GVL on 50 mg of Ru/UiO-66–NO (53%) compared to the yield of
2
particles to different extents. –SO
hydrogenation activity markedly; whereas –NH
strongly coordinate with Ru surface sites thus hampering the
activation of H and the adsorption of EL. The selectivity of GVL
when using Ru/UiO-66, Ru/UiO-66–SO H, Ru/UiO-66–NO and
3
H groups do not reduce the
GVL on 25 mg of Ru/UiO-66–NO
GVL (40%) was obtained by further increasing the amount of
Ru/UiO-66–NO to 100 mg, revealing that the introduction of
NO group not only impedes the hydrogenation of EL but also
2
(50%), but a decreased yield of
2
groups may
2
2
–
2
3
2
the transesterication of EHP. It is noted that the yield of GVL
Ru/UiO-66–NH2 is 50, 61, 40 and 29%, respectively. UiO-66–
on Ru/UiO-66–SO H increases signicantly on increasing the
3
SO H containing strong Brønsted acidity shows the highest GVL
3
dosage of Ru/UiO-66–SO H. The yield of GVL on 25 mg of Ru/
3
selectivity. These results emphasize the importance of Brønsted
acidity in transesterication reaction and prove the positive role
of –SO H in the transesterication of EHP. Prolonging the
3
UiO-66–SO H is 28% which is ꢃ28% lower than the yield found
3
3
on 25 mg of UiO-66. When the amount of Ru/UiO-66–SO H is
increased to 50 mg, the yield of GVL increases to 52%, which is
reaction period to 5 h leads to a full conversion of EL and 100%
selectivity to GVL (Table S1†) on Ru/UiO-66 and Ru/UiO-66–
SO H. The above results reveal that introducing –SO H groups
ꢃ16% higher than that on 50 mg of Ru/UiO-66 and ꢃ86%
3
higher than that obtained on 25 mg of Ru/UiO-66–SO H.
3
3
Further employing 100 mg of Ru/UiO-66–SO
is increased by ꢃ118% compared to the yield of GVL when using
5 mg of Ru/UiO-66–SO H and is 22% higher than that obtained
3
H, the yield of GVL
does not reduce the activity of Ru/UiO-66 in the hydrogenation
of EL, while enhancing the transesterication step, leading to
higher activity in converting EL to GVL.
2
3
on 100 mg of Ru/UiO-66. The remarkable improvement indi-
cates a faster transesterication of EHP and a positive role of
To shed further light on the promotion effect of –SO
3
H
groups on the overall reaction, the reactivities on Ru/UiO-66,
–
SO
UiO-66, which may be attributed to the Brønsted acidity of
SO H.
3
H group in the transesterication of EHP catalyzed by Ru/
Ru/UiO-66–NO
2
and Ru/UiO-66–SO
3
H were studied in detail
ꢀ
by employing varying amounts of the catalysts in water at 80 C
–
3
for 1 h under 0.5 MPa of H . The results are listed in Table 3.
2
2
2
5 mg of the catalysts gave EL conversions of 98%, 11% and
9% for Ru/UiO-66, Ru/UiO-66–NO2 and Ru/UiO-66–SO H,
3
4
Conclusions
respectively. By increasing the amount of the catalysts to 50 mg,
EL conversion on Ru/UiO-66 reaches 100% and EL conversions In summary, the catalytic activity of Ru nanoparticles supported
on Ru/UiO-66–SO H and Ru/UiO-66–NO increase to 72% and on Zr-UiO-66 and its analogues with various functional groups
3
2
2
7% which are ꢃ24% and ꢃ67% lower than those obtained by (–NO , –SO H and –NH ) for hydrogenation of EL was system-
2
3
2
atically studied. The introduction of functional groups –NH2
and –NO reduces the activity of UiO-66 in both the hydroge-
nation of EL and the transesterication of EHP. The poor
2
Table 3 Catalytic performance of Ru/UiO-66 and Ru/UiO-66–X for
EL hydrogenation in water
a
activity of Ru/UiO-66–NH
metallic Ru particles, which is because of the strong coordina-
tion between Ru and –NH groups. The Lewis acidity of –NO
results in the reduced activity of Ru/UiO-66 in the hydrogena-
tion of EL. In contrast, –SO H group plays a positive role in the
2
can be explained by the absence of
Sel. (%)
Catalyst
2
2
Catalyst
loading (mg)
Conv. (%)
GVL
EHP
Ru/UiO-66
100
100
100
98
95
72
29
37
82
27
50
45
39
61
52
28
29
40
53
50
50
55
61
39
48
72
71
60
47
50
3
5
2
0
5
transesterication of EHP, resulting in an increase of 22% in
the yield of GVL, in spite of a slightly reduced activity (EL
Ru/UiO-66–SO
3
H
100
conversion: 100% for Ru/UiO-66 vs. 95% for Ru/UiO-66–SO H).
3
5
2
0
5
Reaction kinetics study further suggests that the introduction of
–
3
SO H group is benecial for the transesterication of EHP due
Ru/UiO-66–NH
Ru/UiO-66–NO
2
100
100
2
to its Brønsted acidity.
5
2
0
5
11
a
ꢀ
Conflicts of interest
2
Reaction conditions: EL (0.34 mL), solvent (9.6 mL), 80 C, 1 h, H (0.5
MPa).
There are no conicts to declare.
16616 | RSC Adv., 2018, 8, 16611–16618
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2
2 K.-I. Shimizu, S. Kanno and K. Kon, Green Chem., 2014, 16,
Acknowledgements
3899–3903.
We acknowledge the nancial support from the Science and 23 H. Zhou, J. Song, H. Fan, B. Zhang, Y. Yang, J. Hu, Q. Zhu
Technology
Commission
of
Shanghai
Municipality
and B. Han, Green Chem., 2014, 16, 3870–3875.
(
13ZR1417900), the Scientic Research Foundation for the 24 D. Sun, A. Ohkubo, K. Asami, T. Katori, Y. Yamada and
Returned Overseas Chinese Scholars, State Education Ministry,
S. Sato, Mol. Catal., 2017, 437, 105–113.
and the National Natural Science Foundation of China (grant 25 E. F. Mai, M. A. Machado, T. E. Davies, J. A. Lopez-Sanchez
no. 11674215 and 51402186).
and V. Teixeira da Silva, Green Chem., 2014, 16, 4092–4097.
6 W. Luo, M. Sankar, A. M. Beale, Q. He, C. J. Kiely,
P. C. Bruijnincx and B. M. Weckhuysen, Nat. Commun.,
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