Cascade catalytic hydrogenation-cyclization of methyl levulinate to form γ-valerolactone over Ru nanoparticles supported on a sulfonic acid-functionalized UiO-66 catalyst

Article abstract of DOI:10.1039/c7ra06293a

We herein report a high-yielding one-pot upgrade strategy for converting biomass-derived methyl levulinate (ML) into γ-valerolactone (GVL) over a dual-functional catalyst prepared by depositing Ru nanoparticles on a sulfonic acid-functionalized Zr-based metal-organic framework (SO₃H-UiO-66). Under the mild conditions of 80 °C and 0.5 MPa H₂ for 4 h in aqueous solution, a quantitative (100%) yield of GVL was obtained over the prepared Ru/SO₃H-UiO-66 catalyst. In contrast, a very limited yield of GVL was achieved in the control experiment by first hydrogenating the reactant ML over a metal catalyst without any acidity (e.g. Ru/C) to produce the 4-hydroxypentanoic acid methyl ester (4-HPME) intermediate, followed by treatment of this intermediate over the acidic SO₃H-UiO-66 support in the absence of metal. We also found that the catalytic activity and selectivity of Ru/SO₃H-UiO-66 were significantly suppressed upon neutralization of its acidic sites, thereby confirming the indispensable role of the sulfonic acid groups in promoting the intramolecular dealcoholation of the 4-HPME intermediate. Furthermore, the Ru/SO₃H-UiO-66 catalyst was recyclable over five cycles without any significant loss in its catalytic activity, thus rendering this precious metal/acid dual-functional catalyst a potential candidate for efficient GVL production under mild conditions.

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Cascade catalytic hydrogenation–cyclization of
methyl levulinate to form g-valerolactone over Ru
nanoparticles supported on a sulfonic acid-
functionalized UiO-66 catalyst†
Cite this: RSC Adv., 2017, 7, 44082
*
Zhenzhen Lin, Xiaoxiong Cai, Yanghe Fu,
Weidong Zhu
and Fumin Zhang
We herein report a high-yielding one-pot upgrade strategy for converting biomass-derived methyl
levulinate (ML) into g-valerolactone (GVL) over a dual-functional catalyst prepared by depositing Ru
nanoparticles on a sulfonic acid-functionalized Zr-based metal–organic framework (SO3H-UiO-66).
Under the mild conditions of 80 ꢀC and 0.5 MPa H2 for 4 h in aqueous solution, a quantitative (100%)
yield of GVL was obtained over the prepared Ru/SO3H-UiO-66 catalyst. In contrast, a very limited yield
of GVL was achieved in the control experiment by first hydrogenating the reactant ML over a metal
catalyst without any acidity (e.g. Ru/C) to produce the 4-hydroxypentanoic acid methyl ester (4-HPME)
intermediate, followed by treatment of this intermediate over the acidic SO3H-UiO-66 support in the
absence of metal. We also found that the catalytic activity and selectivity of Ru/SO3H-UiO-66 were
significantly suppressed upon neutralization of its acidic sites, thereby confirming the indispensable role
of the sulfonic acid groups in promoting the intramolecular dealcoholation of the 4-HPME intermediate.
Furthermore, the Ru/SO3H-UiO-66 catalyst was recyclable over five cycles without any significant loss in
its catalytic activity, thus rendering this precious metal/acid dual-functional catalyst a potential candidate
for efficient GVL production under mild conditions.
Received 6th June 2017
Accepted 7th September 2017
DOI: 10.1039/c7ra06293a
rsc.li/rsc-advances
catalyst (HZSM-5 or Amberlyst 70).10 Indeed, they reported that
the products contained mainly C8, C12, and C16 olens, which
Introduction
are the key components present in gasoline and jet fuels.
Furthermore, Serrano-Ruiz et al. studied the conversion of GVL
over a dual-functional heterogeneous Pd/Nb2O5 catalyst to yield
pentanoic acid and 5-nonanone,11 which can be further con-
verted into hydrocarbon fuels via hydrodeoxygenation.
To reduce the current dependence on fossil fuel resources and
the associated environmental issues, the investigation of alter-
native effective routes to produce fuels and value-added chem-
icals from sustainable resources continues to receive growing
attention.1,2 In this context, biomass, an inexpensive, renew-
able, and widely available resource, has been recognized as
a promising alternative to replace fossil fuel resources for the
sustainable production of biochemicals and biofuels.3,4 Among
the various chemicals synthesized from biomass to date, g-
valerolactone (GVL) has been identied as an important mole-
cule for use as a fuel additive, a food ingredient, a renewable
solvent, and an ideal intermediate for production of alkenes
and other valuable chemicals due to its benign properties and
versatility.5–9 In addition, the upgrade of GVL to a liquid
hydrocarbon fuel has also been reported, with Dumesic and co-
workers designing a system that integrates the conversion of
GVL to butene via decarboxylation over a silica/alumina catalyst
with the subsequent oligomerization of butene over an acidic
To date, GVL has mainly been obtained from levulinic acid
(LA), a platform molecule derived from lignocellulosic biomass,
via a two-step catalytic process involving selective hydrogenation
under a high pressure of H2 and subsequent intramolecular
dehydration.5–9 Indeed, many reports exist into the catalytic
conversion of LA using both homogeneous and heterogeneous
noble and non-noble metal catalysts in liquid and vapor phase
systems.5–9,11–18 Among the various metals investigated, ruthenium
appears to be the most active and selective metal for the conver-
sion of LA to GVL, mainly due to its selective hydrogenation of
carbonyl groups without altering other unsaturated functional-
ities.11–18 However, traditional catalysts, such as commercial Ru/C,
oen exhibit leaching of the ruthenium species through the
formation of metal–carboxylate complexes with LA, which is likely
caused by the weak acidity of LA (pKa ¼ 4.59),19–21 results in a low
catalytic activity and poor catalyst reusability.
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Institute
of Advanced Fluorine-Containing Materials, Zhejiang Normal University, 321004
Jinhua, People's Republic of China. E-mail: zhangfumin@zjnu.edu.cn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra06293a
As an alternative substrate, levulinic ester, which is produced
by the acid-catalyzed alcoholysis of various carbohydrate
44082 | RSC Adv., 2017, 7, 44082–44088
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fractions of lignocellulose, is acid-free, and can also be con- catalyst can be synthesized easily via a direct solvothermal
verted to GVL.5–9 Recently, several strategies based on the use of approach.40 Subsequently, Ru nanoparticles will be introduced
heterogeneous catalysts have been reported for the liquid-phase into the cavities of SO3H-UiO-66 using a wet impregnation
upgrade of methyl levulinate (ML) to GVL.22–24 For example, technique and the resulting Ru/SO3H-UiO-66 catalyst will be
Hengne and co-workers reported that a 5 wt% Ru/C catalyst was employed in the aqueous-phase conversion of ML to GVL. We
active in the hydrogenation of ML, giving a conversion of 95% expect that the SO3H-UiO-66 frameworks will distribute homo-
and a GVL selectivity of 91% under a H2 pressure of 3.4 MPa at geneously in the aqueous medium due to their hydrophilic
130 ꢀC over 2 h in methanol.22 In addition, Nadgeri et al. re- properties and low density,41 thereby facilitating the adsorption/
ported that a 100% conversion of ML with 32% GVL selectivity diffusion of the reactants. Furthermore, the abundant cavities
could be achieved over a 1.0 wt% Ru/graphite catalyst under present in the SO3H-UiO-66 host will be expected to allow the
3 MPa of H2 at 70 ꢀC over 10 min in water.23 However, no facile dispersal and stabilization of the imbedded Ru nano-
apparent increase in the GVL yield was observed when the particles, which can then adsorb and activate H2 and promote
reaction time was extended further to 4 h. Generally, the the hydrogenation of ML to yield 4-HPME. Finally, we propose
conversion of ML to GVL involves a two-step reaction sequence, that the acidic –SO3H groups tethered on the MOF frameworks
namely hydrogenation of the carbonyl groups over metal sites to will accelerate the subsequent intramolecular dealcoholization
give the 4-hydroxypentanoic acid methyl ester (4-HPME) inter- of 4-HPME to afford GVL in high yields. In this context, our aim
mediate, and subsequent dealcoholization of 4-HPME to yield is to construct a multifunctional catalyst coupled with precious
GVL catalyzed by the acidic sites (Scheme 1). Therefore, the metal nanoparticles and acidic sites in a single support to
prerequisite for establishing an efficient ML to GVL conversion enhance catalytic activity and give a reproducible performance
process is to develop high performance dual-functional solid in the upgrade of ML.
catalysts containing metal nanoparticles and acidic sites to
enhance the process efficiency (i.e., catalytic activity and selec-
tivity) and process simplicity.14,15
Experimental
Catalyst preparation
As a relative new class of crystalline ordered materials,
metal–organic frameworks (MOFs), have attached signicant
attention in several areas, in particular in the eld of catalysis,
because of their controllable pores characteristics, large
internal surface areas, and tunable chemical properties.25–27 For
example, the typical Zr-based MOF, UiO-66, is comprised of 12-
coordinated Zr6O4(OH)4 clusters that are connected three-
dimensionally with terephthalic acid (BDC) linkers.28–30 In this
case, the cavities present in the UiO-66 structure provide the
possibility to encapsulate metal nanoparticles within its
frameworks to ultimately prevent nanoparticles agglomera-
tion.31–33 Moreover, the BDC linker of UiO-66 can be tuned to
introduce functionality by partially or integrally replacing it
with analogous organic linkers via direct or post-modica-
tion.35,36 In combination with its high thermal and chemical
stabilities, the above properties render UiO-66 an ideal candi-
date for application in heterogeneous catalysis.31–39
Thus, we herein report the catalytic cascade hydrogenation–
cyclization of ML with the aim of producing GVL in high-yields
over Ru nanoparticles supported on a functionalized UiO-66
catalyst. Through the appropriate tuning of the molar ratio of
the mixed organic linkers of 2-sulfonylterephthalic acid mono-
sodium salt (2-NaSO3-H2BDC) and BDC, we expect that a highly
stable sulfonic acid-functionalized UiO-66 (SO3H-UiO-66)
The parent SO3H-UiO-66 support was synthesized using a sol-
vothermal method according to the procedure reported by Foo
et al.40 with slight modication. Detailed information regarding
the materials and methods employed can be found in the ESI.†
For preparation of the 5.0 wt% Ru/SO3H-UiO-66 catalyst,
a sample the pre-dried SO3H-UiO-66 (0.2 g) was dispersed in
ꢀ
deionized water (20 mL) at 25 C. An aqueous RuCl3 solution
(2.08 mL, 0.05 mol Lꢁ1) was then added to the above suspen-
sion under vigorous stirring and the resulting slurry was stir-
red at 25 ꢀC for 24 h. Subsequently, the reduction of Ru3+ was
conducted by the dropwise addition of aqueous NaBH4
(3.6 mL, 28 mg; [NaBH4]/[Ru] ¼ 7) into the above suspension
upon cooling using an ice-bath. Aer allowing the reduction to
proceed for 30 min, the resulting solid was collected by
centrifugation prior to treatment in a solution of diluted HCl
(3.6 mL, 0.2 mol Lꢁ1) in methanol, and rinsed with methanol
and water to remove any excess additional HCl. Finally, the
obtained solid was dried overnight at 120 ꢀC under reduced
pressure prior to use. For comparison, the Ru nanoparticles
supported on UiO-66 and NH2-UiO-66 (referred to as 5.0 wt%
Ru/UiO-66 and 5.0 wt% Ru/NH2-UiO-66, respectively) were also
prepared using above method with BDC and NH2-BDC as the
starting organic ligand.
Scheme 1 Conversion of ML to GVL via hydrogenation followed by intramolecular dealcoholization.
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UiO-66 structure.31–34 Furthermore, a signicant decrease in
both the pore volume and the quantity N2 adsorbed was
observed for Ru/SO3H-UiO-66 with respect to the pristine SO3H-
UiO-66, indicating that the cavities of SO3H-UiO-66 were
partially occupied by the dispersed Ru nanoparticles (Fig. 1B
and S1 in the ESI†). Moreover, the presence of sulfonic acid
groups tethered on the UiO-66 frameworks were conrmed by
Fourier transform infrared (FTIR) spectroscopy. In this case, the
absorption bands at 1250 cmꢁ1 and 1020 cmꢁ1 were assigned to
the symmetric stretching vibration of O]S]O and the
stretching mode of S]O, respectively, while the band at
1078 cmꢁ1 was assigned to the n-plane skeletal vibration of the
benzene rings substituted by a sulfonic acid group (Fig. 1C).40
Interestingly, no peak shi was observed following loading the
Ru nanoparticles onto the support, thereby indicating that the
–SO3H groups are present as “free” sulfonic acid groups in the
supported catalyst.43 Thermogravimetric analysis (TGA) curves
also conrmed the integrity of the SO3H-UiO-66 frameworks
following introduction of the Ru nanoparticles, with the
thermal stability up to 450 ꢀC being maintained throughout the
synthesis and functionalization procedures (Fig. 1D).
Catalytic hydrogenation–cyclization of ML
The catalytic hydrogenation–cyclization of ML was performed in
a 50 mL Teon-lined autoclave reactor equipped with a sample
port and a magnetic stirrer. In a typical reaction, ML (0.5 g),
catalyst (0.05 g), and H2O (15 mL) were introduced into the
autoclave and purged ve times with H2 at room temperature.
The autoclave was then heated to 80 ꢀC and pressurized with H2
to 0.5 MPa. Aer initiating agitation at 980 rpm, a steady pres-
sure was maintained throughout the reaction. Samples of the
reaction mixture (0.3 mL) were withdrawn at allocated reaction
times and the catalyst was removed by centrifugation prior to
analysis the reaction mixture by gas chromatography (GC, GC-
2014, Shimadzu, equipped with an FID detector and a capil-
lary column, DB-5, 30 m ꢂ 0.32 mm ꢂ 0.25 mm). To determine
the catalyst reusability, the used catalyst was recovered by
centrifugation, washed with ethanol, and dried in a vacuum
desiccator at 150 ꢀC for 5 h prior to its application in the
subsequent reaction cycle.
Results and discussion
Analysis of the various samples by inductively coupled
plasma atomic emission spectroscopy (ICP-AES) indicated that
the measured Ru loadings were close to the nominal amounts
present in the precursor (Table S1 in ESI†). In addition, no
sodium ions were detected, indicating that all the Na+ ions of
the 2-NaSO3-H2BDC ligand had been exchanged with H+ (from
HCl) during preparation. In addition, as shown in the sulfur X-
ray photoelectron spectrum (XPS) in Fig. 2A, a single S 2p peak
attributable to the sulfonic acid groups was present at
168.3 eV,43 which indicated that almost all S was present in the
We initially examined and compared the physical properties of
the prepared catalysts. As indicated in the powder X-ray
diffraction (XRD) patterns shown in Fig. 1A, no loss of crystal-
linity was observed for the Ru/SO3H-UiO-66 catalyst compared
to the parent SO3H-UiO-66 support, suggesting that the integrity
of the SO3H-UiO-66 framework was maintained following Ru
immobilization by the simple wetness impregnation method
employed herein.42 In addition, no diffraction peaks associated
with any Ru species were observed, likely due to the low Ru
content and/or the small Ru nanoparticle size in the Ru/SO3H-
Fig. 1 (A) XRD patterns, (B) N2 adsorption isotherms, (C) FTIR spectra and (D) TGA curves of the SO3H-UiO-66 support and the prepared Ru/
SO3H-UiO-66 catalyst.
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forms of sulfonic acid, thereby conrming the FTIR observa-
tions. Furthermore, the presence of Ru0 in the catalyst was
conrmed by XPS analysis (Fig. 2B), as clearly demonstrated
by the presence of a band at 461.8 eV, which is characteristic
of the zerovalent Ru species.16,43 Moreover, acid–base
titrations indicated that the acidity of Ru/SO3H-UiO-66 was
0.35 mmol gꢁ1
.
It should be considered here that
36,44–46
the missing-linker defect sites (consisting of Zr–OH sites) in
SO3H-UiO-66 also contributed to the total Brønsted acid content,
although their acidity strength is signicantly weaker than that of
the –SO3H sites.28,36 We could therefore conclude that the quanti-
ed acidity originated primarily from the Brønsted acidity –SO3H
groups tethered on the UiO-66 frameworks.
Furthermore, energy-dispersive X-ray spectroscopy (EDX)
mapping conrmed that the Ru nanoparticles were evenly
distributed within SO3H-UiO-66 (Fig. 3), while transmission
electron microscopy (TEM) observations (Fig. 4) conrmed the
uniformity of the 2–4 nm diameter Ru nanoparticles that were
homogeneously dispersed within the SO3H-UiO-66 matrix. A
characteristic interlayer spacing of 0.23 nm was also deter-
mined from the high-resolution TEM image (Fig. 4B), which was
ascribed to the (100) plane of the hcp-structured Ru
nanoparticles.
Following successful characterization, the 5.0 wt% Ru/SO3H-
UiO-66 catalyst was tested in the aqueous-phase conversion of
biomass-derived ML to GVL in an autoclave at 80 ꢀC and at
a hydrogen pressure of 0.5 MPa (Fig. 5). In the absence of
catalyst or in the presence of only pristine SO3H-UiO-66, no
reaction took place. However, upon the addition of 5.0 wt% Ru/
SO3H-UiO-66 to the reaction system, the concentration of 4-
HPME increased dramatically within the rst 60 min, accom-
panied by a sharp decrease in the ML concentration, thereby
demonstrating that ML is mainly hydrogenated to yield 4-HPME
in the initial step. Interestingly, the production of GVL was also
observed in the initial 5 min of the reaction, implying that
either intramolecular dealcoholation of 4-HPME occurred
immediately, or that ML could be converted directly into
GVL.22–24 As the reaction progressed, the intramolecular deal-
coholation of 4-HPME continued smoothly, with almost
complete conversion of 4-HPME to GVL being observed aer
400 min. Remarkably, GVL was found to be stable in the
aqueous reaction system, as increasing the reaction time
Fig. 3 SEM and EDS analyses of the 5.0 wt% Ru/SO3H-UiO-66
catalyst.
further to 540 min did not generate any additional hydrogena-
tion or hydrogenolysis products.
Interestingly, the one-pot conversion of ML into GVL over
heterogeneous catalysts has been reported previously (see Table
1).23,24,47 For example, the use of a commercially available
5.0 wt% Ru/C in metꢀhanol gave an ML consumption of 97.8%
over 160 min at 130 C and 1.2 MPa H2 with 89.4% selectivity
towards GVL (Table 1, entry 1).47 Indeed, the use of alcohols as
the reaction medium for levulinic ester hydrogenation appears
advantageous, as such solvents can be derived from lignocel-
lulosic biomass and so have a low environmental impact.5–9
However, from the viewpoint of sustainable chemistry, the use
of water as reaction medium is more desirable, since it is
environmentally benign. We therefore attempted the conver-
sion using water as the reaction solvent, and were surprised to
nd that superior results were obtained. More specically,
using the 5.0 wt% Ru/SO3H-UiO-66 catalyst, a 74.5% yield of
GVL was obtained under relatively mild reaction conditions
(entry 4), which was a higher conversion than that obtained over
a 4.5 wt% Ru/Zr5SMS catalyst (entry 3).23 Moreover, upon
comparison of our 5.0 wt% Ru/SO3H-UiO-66 catalyst with Ru/C
and with the UiO-66- and NH2-UiO-66- supported Ru nano-
particles (entries 5–8), it was apparent the Ru/SO3H-UiO-66
catalyst gave a signicantly higher ML conversion and GVL
selectivity than the Ru/C. In contrast, Ru/UiO-66 and Ru/NH2-
UiO-66 exhibited only moderate activities, producing GVL in
lower yields than Ru/SO3H-UiO-66 (see Table S1 and Fig. S2–S6,
ESI† for characterization of the control catalysts). Of course, it
should be admitted that the metal dispersions may be different
in the above different cases, which could also affect the reac-
tivity. These results therefore suggest that the nature of the
support plays a key role in determining the activity and selec-
tivity of the Ru nanoparticles for the hydrogenation–cyclization
of ML. Furthermore, it has been reported that the SO3H-UiO-66-
based catalyst is easily dispersed in water,44 thereby enhancing
contact between the catalyst and the substrate, and increasing
the catalytic performance of Ru/SO3H-UiO-66.
Fig. 2 XPS spectra of (A) S spectrum and (B) Ru 3p for the prepared
5.0 wt% Ru/SO3H-UiO-66 catalyst.
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Fig. 4 (A) TEM image and (B) high-resolution image of the prepared 5.0 wt% Ru/SO3H-UiO-66 catalyst.
hydrogenation activity and the SO3H-UiO-66 host offers the
acidity, thereby triggering the subsequent intramolecular
dealcoholation.22–24
To further explore the inuence of the acid sites present in
SO3H-UiO-66 on the ML conversion, a control hydrogenation–
cyclization experiment was performed over the 5.0 wt% Ru/
SO3H-UiO-66 catalyst and in the presence of a calculated
amount of NaOH with respect to the acidic sites available on the
catalyst (Fig. 6). As indicated, upon neutralization of the acidic
sites by NaOH, the activity and selectivity of the catalyst
decreased signicantly, thereby conrming poisoning/
neutralization of the acidic sites through the strong interac-
tion with NaOH.44 This result clearly demonstrates the impor-
tance of acidic sites in the catalytic intramolecular
dealcoholation reaction.
In addition, another control experiment was conducted in
order to clarify the possible reaction mechanism. As shown in
the case (a) of Fig. 7, a small portion of GVL was formed over
5.0 wt% Ru/C along with the major HPME product by the
catalytic hydrogenation reaction. Subsequently, we treated this
intermediate with the SO3H/UiO-66 support (0.05 g) at 70 ꢀC
upon removal of Ru/C by hot ltration. It was observed that the
generated HPME was partially converted into GVL in the
following 4 h (in the case (b) of Fig. 7), while the concentration
of ML in this intermediate had no any change. These results
consistently conrmed the importance of acidic sites in the
catalytic intramolecular dealcoholation reaction. In our
opinion, the formation of the small amount GVL in the pres-
ence of 5.0 wt% Ru/C could be probably ascribed to the
following two reasons: HPME might be self-catalyzed to yield
Fig. 5 Evolution of reactant and product distributions as a function of
reaction time. Reaction conditions: ML (0.5 g), catalyst (0.05 g), H2O
(15 mL), 80 ꢀC, 0.5 MPa H2.
It was also expected that the acidic properties of the catalyst
may play a key role in this reaction, and so we examined the pH
of the reaction system in the presence of the 5.0 wt% Ru/SO3H-
UiO-66 catalyst, and found that it ranged from 4.8 to 5.1. As
discussed above, the acidic sites of SO3H-UiO-66 originate
mainly from the sulfonic acid groups tethered to the UiO-66
frameworks. Thus, the high catalytic activity and selectivity of
Ru/SO3H-UiO-66 in this cascade reaction are likely due to the
synergistic effects between the “host” and the “guest”, where
the Ru nanoparticles guests provide the H2 activation/
Table 1 Comparison of the conversions and selectivities for the cascade catalytic hydrogenation–cyclization of ML using a range of catalysts
Entry
Catalyst
s/ca
Solvent
Temp. (ꢀC)
pH b (MPa)
t (min)
Con.c (%)
Sel.d (%)
2
1
2
3
4
5
6
7
8
5.0 wt% Ru/C47
348
118
199
200
200
200
200
155
CH3OH
CH3OH
CH3OH
H2O
H2O
H2O
130
130
70
70
70
70
70
70
1.2
3.5
0.5
0.5
0.5
0.5
0.5
0.5
160
120
240
240
45
45
45
45
97.8
95
89.4
91
5.0 wt% Ru/C23
4.5 wt% Ru/Zr5SMS24
5.0 wt% Ru/SO3H-UiO-66
5.0 wt% Ru/SO3H-UiO-66
5.0 wt% Ru/UiO-66
5.0 wt% Ru/NH2-UiO-66
5.0 wt% Ru/C
>99.9
>99.9
95.5
90.3
73.7
44.6
67.1
74.5
20.7
13.8
14.6
10.3
H2O
H2O
a
Molar ratio of ML to Pd in the catalyst used. b H2 pressure. c Conversion of ML. d Selectivity for GVL.
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Fig.
6 Cascade catalytic hydrogenation–cyclization of ML over
5.0 wt% Ru/SO3H-UiO-66 in (a) the absence and (b) the presence of
0.02 mmol NaOH. Reaction conditions: ML (0.5 g), catalyst (0.05 g),
H2O (15 mL), 80 ꢀC, 0.5 MPa H2 pressure, 30 min.
Fig. 8 Catalyst (5.0 wt% Ru/SO3H-UiO-66) recyclability in the cascade
catalytic hydrogenation–cyclization of ML. Reaction conditions: ML
(0.5 g), catalyst (0.05 g), H2O (15 mL), 80 ꢀC, 0.5 MPa H2 pressure,
240 min.
GVL under the reaction conditions; Ru clusters with a diameter
size smaller than 1 nm (even single ruthenium site), which
could not be observed by our conventional TEM or HRTEM
techniques, were partially responsible for the direct conversion
of ML to GVL. In the further work, we will investigate these
factors in detail. Nevertheless, based on the above discussion,
we can deduce that the mechanism to produce GVL from HPME
apparently requires the Ru/SO3H-UiO-66 rather than just the
SO3H-UiO-66 support. The metal–acid interfacial sites of the
developed Ru/SO3H-UiO-66 may be relevant to this
transformation.
To allow the catalyst to be recycled, isolation from the reac-
tion solution by facile ltration is preferable. In this case,
ltration and washing of the spent 5.0 wt% Ru/SO3H-UiO-66
catalyst allowed it to be recycled ve times without any signi-
cant loss in catalytic activity (Fig. 8). Notably, XRD, N2 adsorp-
tion, FTIR, EDX mapping, and ICP-AES measurements (Fig. S7–
S10, ESI†) conrmed that the reused catalyst exhibited
a comparable porous structure, Ru nanoparticle dispersion, and
chemical composition as the fresh one. These results demon-
strate that the prepared 5.0 wt% Ru/SO3H-UiO-66 catalyst is
sufficiently stable to be employed in the hydrogenation–cycli-
zation of ML to yield GVL.
Conclusions
In summary, we successfully developed a dual-functional Ru/
SO3H-UiO-66 catalyst for the high-yielding one-pot synthesis of
g-valerolactone from biomass-derived methyl levulinate under
ambient conditions in water by loading ruthenium nano-
particles onto a highly stable sulfonic acid-functionalized Zr-
based metal–organic framework (i.e., SO3H-UiO-66). This cata-
lyst exhibited a high catalytic activity, high selectivity, and good
reproducibility over ve catalytic cycles. The excellent catalytic
properties of Ru/SO3H-UiO-66 were mainly ascribed to the
synergistic catalytic effect of the imbedded tiny Ru nano-
particles and the Brønsted acidic sites of the SO3H-UiO-66
support. Perhaps the metal–acid interfacial sites were respon-
sible for this efficient transformation. We therefore expect that
the developed 5.0 wt% Ru/SO3H-UiO-66 catalyst will open
a novel route to biomass upgrade involving metal/acid dual-
functional synergistic catalysts in an environmentally benign
solvent.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
This work was nancially supported by National Natural
Science Foundation of China (21576243), Public Project of
Zhejiang Province of China (2016C37057), and New Talent
Project
for
Undergraduates
in
Zhejiang
Province
(2017R404067).
Fig. 7 Catalytic hydrogenation–cyclization of ML over 5.0 wt% Ru/C
at 70 ꢀC for 45 min (a) and treated the above filtrate in the presence of
SO3H-UiO-66 (0.05 g) at 70 ꢀC for 4 h after removal of 5.0 wt% Ru/C
by hot filtration (b). Other reaction parameters in the case (a) ML (0.5 g),
5.0 wt% Ru/C (0.05 g), H2O (15 mL) and 0.5 MPa H2 pressure.
References
1 J. C. Serrano-Ruiz, R. Luque and A. Sepulveda-Escribano,
Chem. Soc. Rev., 2011, 40, 5266–5281.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 44082–44088 | 44087

View Article Online
RSC Advances
Paper
2 M. J. Climent, A. Corma and S. Iborra, Green Chem., 2014, 16, 27 K. Sumida, D. L. Rogow, J. A. Mason, T. M. McDonald,
516–547.
E. D. Bloch, Z. R. Herm, T. H. Bae and J. R. Long, Chem.
Rev., 2011, 112, 724–781.
28 J. H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti,
S. Bordiga and K. P. Lillerud, J. Am. Chem. Soc., 2008, 130,
13850–13851.
29 M. Kandiah, M. H. Nilsen, S. Usseglio, S. Jakobsen,
U. Olsbye, M. Tilset, C. Larabi, E. A. Quadrelli, F. Bonino
and K. P. Lillerud, Chem. Mater., 2010, 22, 6632–6640.
3 K. Yan, Y. Yang, J. Chai and Y. Lu, Appl. Catal., B, 2015, 179,
292–304.
4 C. B. Chen, M. Y. Chen, B. Zada, Y. J. Ma, L. Yan, Q. Xu,
W. Z. Li, Q. X. Guo and Y. Fu, RSC Adv., 2016, 6, 112477–
112485.
5 J. M. Tukacs, M. Bohus, G. Dibo and L. T. Mika, RSC Adv.,
2017, 7, 3331–3335.
´
6 F. Liguori, C. Moreno-Marrodan and P. Barbaro, ACS Catal., 30 M. J. Katz, Z. J. Brown, Y. J. Colon, P. W. Siu, K. A. Scheidt,
2015, 5, 1882–1894.
7 W. R. Wright and R. Palkovits, ChemSusChem, 2012, 5, 1657–
1667.
R. Q. Snurr, J. T. Hupp and O. K. Farha, Chem. Commun.,
2013, 49, 9449–9451.
31 G. Huang, Q. Yang, Q. Xu, S. H. Yu and H. L. Jiang, Angew.
Chem., Int. Ed., 2016, 128, 7505–7509.
32 H. Liu, L. Chang, C. Bai, L. Chen, R. Luque and Y. Li, Angew.
Chem., Int. Ed., 2016, 55, 5019–5023.
33 F. M. Zhang, S. Zheng, Q. Xiao, Y. J. Zhong, W. D. Zhu, A. Lin
and M. S. El-Shall, Green Chem., 2016, 18, 2900–2908.
34 Z. Guo, C. Xiao, R. V. Maligal-Ganesh, L. Zhou, T. W. Goh,
X. Li, D. Tesfagaber, A. Thiel and W. Huang, ACS Catal.,
2014, 4, 1340–1348.
8 K. Hengst, M. Schubert, H. W. P. Carvalho, C. Lu, W. Kleist
and J. D. Grunwaldt, Appl. Catal., A, 2015, 502, 18–26.
9 F. D. Pileidis and M. M. Titirici, ChemSusChem, 2016, 9, 562–
582.
10 J. Q. Bond, D. M. Alonso, D. Wang, R. M. West and
J. A. Dumesic, Science, 2010, 327, 1110–1114.
11 J. C. Serrano-Ruiz, D. Wang and J. A. Dumesic, Green Chem.,
2010, 12, 574–577.
12 Z. H. Zhang, ChemSusChem, 2016, 9, 156–171.
13 C. Moreno-Marrodan and P. Barbaro, Green Chem., 2014, 16,
3434–3438.
35 Y. M. Chung, H. Y. Kim and W. S. Ahn, Catal. Lett., 2014, 144,
817–824.
36 Y. Kuwahara, H. Kango and H. Yamashita, ACS Sustainable
Chem. Eng., 2017, 5, 1141–1152.
14 S. Xu, D. Yu, T. Ye and P. Tian, RSC Adv., 2017, 7, 1026–1031.
15 Y. Wang, Z. Rong, Y. Wang, T. Wang, Q. Du, Y. Wang and 37 J. Kim, S. N. Kim, H. G. Jang, G. Seo and W. S. Ahn, Appl.
J. Qu, ACS Sustainable Chem. Eng., 2016, 5, 1538–1548. Catal., A, 2013, 453, 175–180.
16 C. Xiao, T. W. Goh, Z. Qi, S. Goes, K. Brashler, C. Perez and 38 F. G. Cirujano, A. Corma and F. L. I. Xamena, Catal. Today,
W. Huang, ACS Catal., 2016, 6, 593–599. 2015, 257, 213–220.
17 Z. Wei, J. Lou, C. Su, D. Guo, Y. Liu and S. Deng, 39 J. Hajek, M. Vandichel, B. Van de Voorde, B. Bueken, D. De
ChemSusChem, 2017, 10, 1720–1732.
18 A. Villa, M. Schiavoni, C. E. Chan-Thaw, P. F. Fulvio,
Vos, M. Waroquier and V. Van Speybroeck, J. Catal., 2015,
331, 1–12.
R. T. Mayes, S. Dai, K. L. More, G. M. Veith and L. Prati, 40 M. L. Foo, S. Horike, T. Fukushima, Y. Hijikata, Y. Kubota,
ChemSusChem, 2015, 8, 2520–2528.
M. Takata and S. Kitagawa, Dalton Trans., 2012, 41, 13791–
19 P. P. Upare, J. M. Lee, D. W. Hwang, S. B. Halligudi,
13794.
¨
¨
Y. K. Hwang and J. S. Chang, J. Ind. Eng. Chem., 2011, 17, 41 P. Kusgens, M. Rose, I. Senkovska, H. Frode, A. Henschel,
287–292.
S. Siegle and S. Kaskel, Microporous Mesoporous Mater.,
2009, 120, 325–330.
42 R. Fang, H. Liu, R. Luque and Y. Li, Green Chem., 2015, 17,
4183–4188.
43 Q. Yuan, D. Zhang, L. van Haandel, F. Ye, T. Xue,
E. J. Hensen and Y. Guan, J. Mol. Catal. A: Chem., 2015,
406, 58–64.
20 M. G. Al-Shaal, M. Calin, I. Delidovich and R. Palkovits,
Catal. Commun., 2016, 75, 65–68.
21 Z. P. Yan, L. Lin and S. Liu, Energy Fuels, 2009, 23, 3853–
3858.
22 A. M. Hengne, N. S. Biradar and C. V. Rode, Catal. Lett., 2012,
142, 779–787.
23 J. M. Nadgeri, N. Hiyoshi, A. Yamaguchi, O. Sato and 44 F. Zhang, Y. Jin, Y. Fu, Y. Zhong, W. Zhu, A. A. Ibrahim and
M. Shirai, Appl. Catal., A, 2014, 470, 215–220. M. S. El-Shall, J. Mater. Chem. A, 2015, 3, 17008–17015.
24 Y. Kuwahara, Y. Magatani and H. Yamashita, Catal. Today, 45 Z. Hu, Y. Peng, Y. Gao, Y. Qian, S. Ying, D. Yuan, S. Horike,
2015, 258, 262–269.
25 N. L. Rosi, J. Eckert, M. Eddaoudi, D. T. Vodak, J. Kim,
N. Ogiwara, R. Babarao and Y. Wang, Chem. Mater., 2016, 28,
2659–2667.
M. O'keeffe and O. M. Yaghi, Science, 2003, 300, 1127–1129. 46 G. Akiyama, R. Matsuda, H. Sato, M. Takata and S. Kitagawa,
26 H. Furukawa, N. Ko, Y. B. Go, N. Aratani, S. B. Choi, E. Choi, Adv. Mater., 2011, 23, 3294–3297.
A. O. Yazaydin, R. Q. Snurr, M. O'Keeffe and J. Kim, Science, 47 M. G. Al-Shaal, W. R. H. Wright and R. Palkovits, Green
¨
2010, 329, 424–428.
Chem., 2012, 14, 1260–1263.
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