Porous Organic Zirconium Phosphonate as Efficient Catalysts for the Catalytic Transfer Hydrogenation of Ethyl Levulinate to γ-Valerolactone without External Hydrogen

Article abstract of DOI:10.1002/jccs.201700309

Organic hybrid zirconium phosphonate materials (ZrATMP, ZrEDTMPS, ZrDTPMPA, and ZrHEDP) were synthesized through reaction of organic phosphonic acid sodium salt and ZrOCl₂ in water, which exhibited high catalytic activity on the conversion of ethyl levulinate (EL) to γ-valerolactone (GVL) in the presence of isopropanol. The obtained catalysts were characterized by FT-IR, TGA, XRD, BET, XPS, ICP-AES, SEM, TEM, NH₃-TPD, and CO₂-TPD. The results demonstrate that the number of acid sites and basic sites between the layers of the catalysts play a very important role in promoting the conversion of EL to GVL and that the functional groups that exist in phosphates could regulate the number of acid and basic sites. Meanwhile, the catalysts could be easily separated from the reaction system and reused at least five times without any obvious decrease in activity or selectivity.

Full text of DOI:10.1002/jccs.201700309

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CHEMICAL SOCIETY
Article
Porous Organic Zirconium Phosphonate as Efficient Catalysts for the Catalytic
Transfer Hydrogenation of Ethyl Levulinate to γ-Valerolactone without External
Hydrogen
a
a
a
a
b
a
*
Jianjia Wang, Ruiying Wang, Huimin Zi, Haijun Wang , Yongmei Xia and Xiang Liu
aKey Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material
Engineering, Jiangnan University, Wuxi, Jiangsu, 214122, China
bState Key Laboratory of Food Science & Technology, Wuxi, Jiangsu, 214122, China
(Received: September 5, 2017; Accepted: December 28, 2017; DOI: 10.1002/jccs.201700309)
ABSTRACT
Organic hybrid zirconium phosphonate materials (ZrATMP, ZrEDTMPS, ZrDTPMPA, and
ZrHEDP) were synthesized through reaction of organic phosphonic acid sodium salt and ZrOCl2
in water, which exhibited high catalytic activity on the conversion of ethyl levulinate (EL) to
γ-valerolactone (GVL) in the presence of isopropanol. The obtained catalysts were characterized
by FT-IR, TGA, XRD, BET, XPS, ICP-AES, SEM, TEM, NH3-TPD, and CO2-TPD. The results
demonstrate that the number of acid sites and basic sites between the layers of the catalysts play a
very important role in promoting the conversion of EL to GVL and that the functional groups
that exist in phosphates could regulate the number of acid and basic sites. Meanwhile, the catalysts
could be easily separated from the reaction system and reused at least five times without any obvi-
ous decrease in activity or selectivity.
Keywords: Ethyl levulinate; γ-Valerolactone; Isopropanol; Organic zirconium phosphonate;
Catalytic transfer hydrogenation.
INTRODUCTION
With the continuous exploration of sustainable
reduced product.14 In addition, compared with homoge-
neous catalysts, heterogeneous catalysts can better solve
the problems of poor separation and purification in the
latter stage. Xu and Li reported that the catalytic trans-
fer hydrogenation of LA could be carried out over Cu
(30%)–WO3 (10%)/ZrO2 under 5 MPa H2.15 Yang and
coworkers found that Ru/C nanofibers could achieve
high activity and stability in the catalytic hydrogenation
of LA to GVL.16 The catalytic performance depended
on the Ru dosage and the pore structure. Varkolu et al.
prepared Ni/Al2O3 for the efficient conversion of LA in
presence of formic acid.17 In addition, Amenuvor and
Makhubela used pyrazolylphosphite and pyrazolylpho-
sphinite ruthenium(II) complexes as catalyst precursors,
employing both formic acid and molecular hydrogen as
hydrogen sources to achieve solvent-free conversion of
LA to GVL.18 Although these catalysts showed good
effect on the conversion of LA to GVL, over-reliance on
hydrogen and formic acid requiring harsh reaction con-
ditions limit their large-scale application. Furthermore,
resources, biomass has become an ideal substitute for
fossil fuels. In addition, as the only sustainable organic
compounds on earth, biomass has been studied and
used to synthesize various fuels and fine chemicals.1
There have been many platform chemicals that were
developed through the degradation of biomass macro-
molecules, such as 5- hydroxymethylfurfural (HMF),
levulinic acid (LA), γ-valerolactone (GVL), 2,5-
dimethyfuran, polyol, and so on.2–4 Among these plat-
form chemicals, GVL has been considered to be a
molecule worth studying as a green solvent for various
applications,5 as a food additive,6 and as a potential
fuel additive for substituting ethanol in gasoline–
ethanol blends.7–10
Many catalysts have been reported for the conver-
sion of LA or its esters to GVL.11–13 There are two main
steps in the reaction. The first step is the reduction of LA
or its esters, and the next step is the esterification of the
*Corresponding author. Email: wanghj329@outlook.com
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Wang et al.
searching for new hydrogen sources to pursue a more
moderate reaction condition is still a research hotspot.
Over the past few years, the Meerwein–Ponndorf–
Verley (MPV) reaction has provided an attractive alter-
native to H2 by using secondary alcohol to achieve
highly chemoselective reduction of carbonyl com-
pounds.19 Song and coworkers synthesized several cata-
lysts for the conversion of ethyl levulinate (EL) to
GVL. ZrHBA and Zr-phy were representative
(Supporting information). From their structures, it can
be seen that the presence of a phenate in the structure
increases the basicity of the catalyst and that the con-
nection of Lewis-acidic Zr element and Lewis-basic
phosphate enhances the catalytic activity, which are
favored for the catalytic transfer hydrogenation of
EL.20,21 After that, Xiao et al. pointed out that transi-
tion metal zirconium could combine with humic acid
(HA) to form catalysts that exhibited high activity in
the hydrogenation of EL.22 Besides, Zhang et al.
reported an atom-economical green way for the conver-
sion of LA to GVL by using Au/ZrO2 as catalyst under
photocatalytic conditions.23 Chia and Dumesic used
various metal oxide catalysts to realize conversion of
LA to GVL and proposed that ZrO2 combined with
other metal oxides could improve the catalytic activity
effectively.24 Similarly, He et al. adopted Al–Zr mixed
oxides with different molar ratios to accomplish the cat-
alytic hydrogenation of EL, demonstrating their com-
mendable catalytic effect.25 Xue and Jiang found that
the zirconium–cyanuric acid coordination polymer pos-
sessed high activity for the catalytic transformation of
LA and its esters.26 All of these catalysts promote the
catalytic hydrogenation without external any hydrogen
source.
Scheme 1. Plausible structures of metal phosphonate
materials.
first synthesized a series of zirconium phosphonate mate-
rials including ZrATMP, ZrEDTMPS, ZrDTPMPA,
and ZrHEDP by the coprecipitation method, which
were then used as the catalysts for the conversion of EL
to GVL. These catalysts all showed good catalytic activ-
ity, which was attributed to the connection of Lewis-
acidic Zr and Lewis-basic phosphate interspersing
between the layers in the catalyst.
RESULTS AND DISCUSSION
Catalyst characterization
Fourier transform infrared (FT-IR) spectroscopy
was used to characterize the synthesized zirconium
phosphonate catalysts, which possess many similar
functional groups (Figure 1). In each spectrum, the
strong and broad band around 3400 cm−1 and the sharp
band around 1640 cm−1 belong to the surface-adsorbed
water and hydroxyl groups, respectively.31 The bands at
2900–3000 and 1400 cm−1 are attributed to the C─H
stretching and bending vibration, respectively. The band
around 1463 cm−1 could be assigned to the P─C stretch-
ing vibration from the organophosphonate groups, and
the bands at 1340 and 1380 cm−1 to the C─N and C─O
stretching vibrations, respectively.32,33 The P─O asym-
metric stretching vibration is observed at 1140 cm−1
stemming from RPO2(OH) groups.34,35 In addition, the
strong adsorption at 1043 cm−1 is due to the symmetric
stretching modes of the O3P groups,36 which could be
taken as an evidence of the structural formation of
zirconium phosphonate.37 The peaks around 850 and
Metal phosphonate materials are ideal non-
siliceous inorganic–organic hybrids and are usually used
as ion adsorption materials,27 drug carriers,28 and cata-
lysts.29 In addition, metal phosphonate materials are
porous structures comprising of phosphorus–oxygen tet-
rahedra and zirconium atoms. Each phosphorus forms a
tetrahedron with four oxygen atoms, and each zirco-
nium atom forms an octahedron with six oxygen atoms.
Zirconium and phosphorus share oxygen atoms to form
a layered structure (Scheme 1).30 By changing the
organic functional groups between phosphonic acid
molecules, these metal phosphonates can be precisely
tailored for functionalization purposes. In this study, we
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Hydrogenation of EL with Zirconium Phosphonate
Fig. 1. FT-IR spectra of the four synthesized zirco-
nium phosphonate catalysts.
Fig. 2. Powder XRD pattern of the four synthesized
zirconium phosphonate catalysts.
570 cm−1 are attributed to the framework vibration of
Zr─O─P and Zr─O bonds, respectively.38,39
in the catalysts, respectively.33 This confirmed that the
synthesized zirconium phosphonate catalysts were ther-
mally stable to achieve the conversion of EL to GVL
at 160 ꢀC.
The powder X-ray diffraction (XRD) patterns of
the synthesized catalysts are shown in Figure 2. There
is no crystal structure evidenced in the XRD pattern.
Moreover, the XRD pattern revealed one broad diffrac-
tion peak, confirming that the synthesized catalysts
were amorphous. Scanning electron microscopy (SEM)
and transmission electron microscopy (TEM) examina-
tions were also conducted to analyze the morphology of
catalysts (Figure 3). As can be seen from the pictures,
ZrHEDP consisted of conglomerated particles to form
a laminated structure (Figure 3(a), (e)). ZrATMP and
ZrEDTMPs were also formed by the accumulation of
particles, and it could be roughly seen that there are
many distinct pore channels with pore diameter of
around 6 and 9 nm, which demonstrated that ZrATMP
and ZrEDTMPs formed a layered structure of meso-
pores over a small range (Figure 3(b), (c), (f ), and (g)).
ZrDTPMPA was made up of relatively large particles
and there was no obvious pore structure in it (Figure 3
(d), (h)).
N2 adsorption–desorption isotherms of the synthe-
sized zirconium phosphonate catalysts and their corre-
sponding pore size distribution curves are shown in
Figure 4. The BET (Brunauer–Emmett–Teller) surface
area, pore volume, and pore diameter of the catalysts
are given in Table 1. As shown in Figure 4, ZrHEDP,
ZrATMP, and ZrEDTMPs exist as type IV modes
obviously and show pore condensation with consider-
able adsorption–desorption hysteresis, demonstrating
the existence of uniform mesopores along with second-
ary pores stemming from particle aggregation, which is
consistent with the TEM images. Compared with these
three catalysts, although ZrDTPMPA had the charac-
teristics of mesoporous materials, it had a hysteresis
loop at p/p0 > 0.8, showing that the distribution of the
pore size was uneven.
Optimization of time and temperature on the reaction
In order to better investigate the influence of reac-
tion time and reaction temperature on the conversion of
EL to GVL, we optimized these parameters (Figure 5).
It can be seen that the conversion of EL and the yield
of GVL increased with the reaction time and reaction.
The best reaction conditions were found to be the fol-
Thermogravimetry analysis-derivative thermogra-
vimetry (TGA-DTG) was employed to measure the
thermal stability of the synthesized zirconium phospho-
nate catalysts (Supporting information). It was obvious
ꢀ
that there were two main mass-loss peaks at 25–100 C
ꢀ
and around 400 C, corresponding to the desorption of
ꢀ
water and decomposition of organophosphonate groups
lowing: 160 C, 12 h for ZrHEDP (92% yield and 99%
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(a)
(b)
(d)
(c)
(e)
(g)
(f)
Fig. 4. N2 adsorption–desorption isotherms of syn-
thesized zirconium phosphonate catalysts:
(a) ZrHEDP, (b) ZrEDTMPs, (c) ZrATMP,
(d) ZrDTPMPA.
(h)
Influence of the catalyst amount
The effect of catalyst dosage was studied, and
results are shown in Figure 6. At the beginning, with
the increase in the amount of the catalyst, the conver-
sion of EL and the yield of GVL improved, mainly
because of the increase in the content of the active com-
ponent in the catalysts. When the amount of catalyst
was increased from 200 to 250 mg, the yield of GVL
increased only slightly. From an economical and practi-
cal point of view, 200 mg was the optimal catalyst
amount for the reaction.
Fig. 3. SEM and TEM images of the four synthe-
sized zirconium phosphonate catalysts: (a, e)
ZrHEDP, (b, f ) ZrEDTMPs, (c, g)
ZrATMP, (d, h) ZrDTPMPA.
conversion); 160 ꢀC, 9 h for ZrEDTMPs (88% yield
ꢀ
and 98% conversion); 160 C, 11 h for ZrATMP (90%
yield and 98% conversion); and 160 ꢀC, 11 h for
ZrDTPMPA (73% yield and 90% conversion). When
the reaction temperature was relatively low, the energy
provided by the reaction system was insufficient to real-
ize the lactonization of the hydrogenation products
which were from LA esters. So the main product was
isopropyl levulinate at relatively low temperature. Com-
pared to those of ZrHEDP, ZrATMP, and
ZrEDTMPs, the catalytic activity of ZrDTPMPA was
poor. The reason was that the structure of the phospho-
nate used to synthesize ZrDTPMPA had poor symme-
try, which made the formation of a regular catalyst
structure difficult.
Reusability and heterogeneity of the catalyst
Whether a catalyst can be reused is also a measure
in evaluating a good catalyst. In our experiment, the
catalysts were recovered by centrifugation, washed with
ꢀ
ethyl ether, and dried at 100 C for 9 h for the next run
under identical reaction conditions. The results are
shown in Figure 7(a). It can be seen that there is no
obvious reduction of catalytic activity after five cycles.
According to the TGA-DTG curves, the thermal stabil-
ity of catalysts is decreasing at the reaction tempera-
ture. In addition, the catalysts were also characterized
by FT-IR, SEM, and N2 adsorption–desorption iso-
therm (Supporting information). No significant change
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Hydrogenation of EL with Zirconium Phosphonate
Table 1. Textural properties of the synthesized zirconium phosphonate catalysts
Entry
Catalystsa
Surface area (m2/g)b
Pore volume (m3/g)c
Pore diameter (nm)d
1
2
3
4
ZrHEDP
ZrEDTMPs
ZrATMP
231
129
115
108
0.32
0.25
0.32
0.54
7.6
4.7
7.5
ZrDTPMPA
12.7
a The catalysts degassed at 120ꢀC for 12 h.
b Surface area based on multipoint BET method.
c Pore volume based on BJH method.
d Pore diameter based on BJH method.
in the structure or reduction in element content was
seen after five cycles (Supporting information). All of
these indicate that the catalysts have outstanding stabil-
ity when they are used in the conversion of EL to GVL.
Meanwhile, to confirm whether the catalytic process
was heterogeneous, the catalysts were removed from
the reaction system by filtration after a specific time. As
shown in Figure 7(b), it was clear that the yield of GVL
did not continue to increase after the filtration of the
catalyst, illustrating that the active component in the
catalysts did not dissolve in the reaction system and the
catalytic process was heterogeneous.
Influence of different hydrogen sources and reactants
To investigate the impact of different hydrogen
sources on the conversion of EL to GVL, we selected
four hydrogen donors: methanol (MeOH), ethanol
(EtOH), isopropanol (2-PrOH), and 2-butanol (2-BuOH)
Fig. 5. Influence of reaction temperature and time on
the conversion of ethyl levulinate to γ-valero-
lactone: (a) ZrHEDP, (b) ZrEDTMPs,
(c) ZrATMP, (d) ZrDTPMPA.
Fig. 6. Effect of the catalyst amount. Reaction con-
ditions: EL 1 mmol; isopropanol 5 mL; reac-
tion temperature 160ꢀC; reaction time 12 h.
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Fig. 8. Influence of different hydrogen sources and
reactants. (a) Reaction conditions: ZrHEDP
200 mg; EL 1 mmol; isopropanol 5 mL; reac-
tion temperature 160ꢀC; reaction time 12 h.
(b) Reaction conditions: ZrEDTMPs 200 mg;
EL 1 mmol; isopropanol 5 mL; reaction tem-
perature 160ꢀC; reaction time 9 h. (c) Reac-
tion conditions: ZrATMP 200 mg; EL
1 mmol; isopropanol 5 mL; reaction tempera-
ture 160ꢀC; reaction time 11 h. (d) Reaction
conditions: ZrDTPMPA 200 mg; EL 1 mmol;
isopropanol
5 mL; reaction temperature
160ꢀC; reaction time 11 h.
methanol and the main product was methyl levulinate
and the catalytic transfer hydrogen of methyl levulinate
could hardly be further achieved to generate methyl 4-
hydroxypentanoate. Compared with isopropanol, isobu-
tanol as hydrogen source showed slightly higher selectiv-
ity of GVL due to the lower reaction energy of the
reaction between isobutanol and EL.41 Altogether, the
reduction potential of reducing alcohols decreased in the
following order: isopropanol ≈ isobutanol < ethanol
< methanol,42 which was in line with the results our
experiments. In addition, different reactants were exam-
ined to study the influence of the reactants on the conver-
sion of EL to GVL. It could be seen that LA showed a
higher performance than EL and methyl levulinate
because of weak steric effects. Furthermore, because the
catalysts were sensitive to acid, the use of LA as a reac-
tant would wreck the structure of the catalysts to lower
the reusability of the catalysts. Meanwhile, EL can be
obtained from lignocellulose and separated easily.43
Fig. 7. (a) Reusability of the catalyst. Reaction con-
ditions: EL 1 mmol; isopropanol 5 mL; cata-
lyst 200 mg; reaction temperature 160ꢀC;
reaction time 12 h. (b) Heterogeneity of the
catalyst. With catalyst: time–yield plots for
reaction of EL catalyzed by zirconium phos-
phonate catalysts. Catalyst filtration: The line
shows the GVL yields upon removing the
solid catalyst after specific time. Reaction
conditions: EL 1 mmol; isopropanol 5 mL;
catalyst 200 mg; reaction temperature 160ꢀC.
(Figure 8). It was clear that secondary alcohols showed
better performance than primary alcohols, which is
linked to the reduction potential of alcohols. A higher
reduction potential H-donor shows poorer performance
on catalytic transfer hydrogenation reactions.40 When
methanol was used as hydrogen source, EL reacted with
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Hydrogenation of EL with Zirconium Phosphonate
Therefore, EL was concluded to be the most appropriate
substrate in the catalytic system.
favorable for the dissociation of the hydroxyl groups in
isopropanol, thereby enhancing the rate of the reaction.
In addition, Zr was crucial for the reaction of EL to
GVL. We examined the Zr species in the catalysts by
X-ray photoelectron spectroscopy (XPS) (Figure 9(c)).
Based on the literature, a higher binding energy of Zr
3d means a higher positive charge on the Zr atoms,
which means a stronger Lewis acidity of Zr.44 In
summary, catalytic activity followed the order
ZrHEDP > ZrEDTMPs ≈ ZrATMP > ZrDTPMPA.
Catalytic activity analysis
The number of acid sites and basic sites plays a
crucial role in the reaction of EL to GVL. Therefore,
we analyzed the acidity and basicity of the synthesized
zirconium phosphonate catalysts by NH3-TPD (temper-
ature-programmed desorption) and CO2-TPD methods,
respectively. As shown in Figure 9(a), there were two
ꢀ
peaks at around 140 and 340 C, which correspond to
Lewis acid sites and Brønsted acid sites, respectively. In
each catalyst, the Brønsted acid sites mainly originate
from the hydroxyl on the surface of catalysts. Because
of the presence of hydroxyls in the skeleton, ZrHEDP
could hold more Brønsted acid sites. On the other hand,
the Lewis acid sites mainly come from zirconium atoms
in the catalysts. The higher Lewis acidity of Zr in cata-
lysts was beneficial for activating the carbonyl groups
and thus increasing the reaction rate. The CO2-TPD
method suggested that there was only one peak for
ZrHEDP but there were two peaks for ZrATMP,
ZrEDTMPs, and ZrDTPMPA (Figure 9(b)). The basic
sites in ZrHEDP are mainly attributed to oxygen atoms
between the phosphate group and zirconium. Besides,
N atoms in ZrATMP, ZrEDTMPs, and ZrDTPMPA
could also increase the basicity, which could lead to
two peaks in the CO2-TPD curves. The basicity was
Mechanism
As discussed above, the acid sites including those
of Lewis acid (stemming from zirconium atoms) and
Brønsted acid (stemming from ─OH) as well as the
basic sites (originating from N and O in organopho-
sphonic acid) were crucial to the catalytic transfer
hydrogenation of EL to GVL. Based on our experi-
ments and previous reports,45,46 we arrived at a possible
mechanism as shown in Scheme 2. Primarily, with the
assistance of basic sites, isopropanol took away the pro-
ton in the hydroxyl group and adsorbed on the surface
of Lewis acid sites to form the corresponding alkoxide.
Simultaneously, the carbonyl group in EL was acti-
vated by Lewis acid sites in the catalyst. Then, a six-
link intermediate was formed by prototropy between
the activated carbonyl and alkoxide to make a further
effort to produce ethyl 4-hydroxypentanoate (4-HPE).
Finally, the 4-HPE was transformed into GVL through
an intramolecular transesterification under the boost
from the Brønsted acid sites. During the reaction, the
two main by-products were 2-isopropyl ethlvalerate and
Fig. 9. NH3-TPD spectra (a) and CO2-TPD spectra
(b) of zirconium phosphonate catalysts. XPS
spectra of Zr 3d (c) in the catalysts.
Scheme 2. Possible mechanism for the transforma-
tion of EL to produce GVL catalyzed by
zirconium phosphonate catalysts.
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isopropyl levulinate, and the latter could be trans-
formed into GVL with a similar reaction route to EL.
5 h. After that, the temperature was decreased to 50ꢀC.
CO2 (50 cm3/min) was pulsed into the reactor at 50ꢀC
under a flow of He (10 cm3/min) until the basic sites were
saturated with CO2. The adsorbed CO2 was removed by
a flow of He (50 cm3/min). When the baseline was stable,
the temperature was increased from 50 to 450ꢀC at a rate
EXPERIMENTAL
Materials and Methods
Zirconium oxychloride (ZrOCl2ꢁ8H2O, AR), iso-
propanol (AR), ethanol (AR), 2-butanol (AR), methanol
(AR), naphthalene (AR), sodium hydroxide (AR), LA
(98%), and furfural (AR), were obtained from Sinopharm
Chemical Reagent Co. Ltd. (Shanghai, China). Ethylene-
diamine tetramethylenephosphonic acid (EDTMPA,
98%) and 1-hydroxyethylidene-1,1-diphosphonicacid
(HEDP, 95%) were purchased from Shanghai Macklin
Biochemical Co., Ltd. Amino trimethylene phosphonic
acid (ATMP, 50%), diethylene triamine penta (methylene
phosphonic acid) (DTPMPA, 50%), and EL (98%) were
purchased from Adamas Reagent Co., Ltd. SEM images
were obtained via a H2 S-4800 field-emission scanning
electron microscope operated at 15 kV. TEM images
were obtained on a Jeol JEM model 2100 microscope
operated at 200 kV. FT-IR measurements were carried
out on a Nicolet 360 FT-IR instrument (KBr disks) in
the wavenumber range 4000–500 cm−1. TGA was per-
formed on an STA409 instrument under nitrogen atmo-
sphere at a heating rate of 20 ꢀC/min from 25 to 600 ꢀC.
Powder XRD patterns were collected using a Bruker D8
Advance powder diffractometer (Cu/Kα) in the 2θ range
10–90ꢀ with a scanning speed of 4ꢀ/min at 40 kV and
20 mA. XPS spectra were recorded by a Perkin Elmer
PHI 5000 ESCT system. The pore volume, pore size, and
specific surface area were measured by N2 adsorption/
desorption analysis (Micromeritics ASAP 2020) at 77 K
using BET and Barrett–Joyner–Halenda (BJH) methods.
The contents of Zr and P in the four organic zirconium
phosphonates were determined by inductively coupled
plasma atomic emission spectroscopy (ICP-AES)
(VISTA-MPX). The contents of C and N in the four
organic zirconium phosphonates were obtained from ele-
mental analysis by using the FLASH EA1112 analyzer.
Temperature-programmed desorption of carbon dioxide
(CO2-TPD) was performed on a Micromeritics Auto-
Chem1 II 2920 chemisorption analyzer. In the experi-
ment, the catalyst was charged into the quartz reactor,
and the temperature was increased from room tempera-
ꢀ
of 10 C/min. Temperature-programmed desorption of
ammonia (NH3-TPD) was performed on a Micromeritics
AutoChem AutoChem1 II 2920 chemisorption analyzer.
The catalysts were charged into the quartz reactor, and
the temperature was increased from room temperature to
300ꢀC at a rate of 10 ꢀC/min under a flow of He (50 cm3/
min), and then the catalyst was kept at 300ꢀC for 5 h.
After that, the temperature was decreased to 50ꢀC. NH3/
He (10/90, 50 cm3/min) was pulsed into the reactor at
50ꢀC under a flow of He (10 cm3/min) until the acid sites
were saturated with NH3. The adsorbed NH3 was
removed by a flow of He (50 cm3/min). When the base-
line was stable, the temperature was increased from 50 to
450ꢀC at a rate of 10 ꢀC/min.
Synthesis of the organic zirconium phosphonates:
In a typical procedure, a certain quantity of phosphonic
acid and NaOH were dissolved in water. Then, a solu-
tion of zirconium oxychloride was added dropwise into
above solution for about 10 min. The final molar ratio
of ATMP/NaOH/ZrOCl2 was 1:6:3; EDTMPA/NaOH/
ZrOCl2 was 1:8:4; HEDP/NaOH/ZrOCl2 was 1:4:2;
and DTPMPA/NaOH/ZrOCl2 was 1:10:5. After that,
the mixture was continuously stirred for 10 h. The
white precipitate was separated by filtration, thoroughly
washed with H2O and ethanol, and dried at 80ꢀC for
12 h. The samples synthesized with ATMP, EDTMPA,
HEDP, and DTPMPA were denoted as ZrATMP,
ZrEDTMPs, ZrHEDP, and ZrDTPMPA. The elemen-
tal compositions of zirconium phosphonate materials
were examined using ICP-AES and elemental analysis
(Supporting information).
Catalytic reactions
In a typical experiment, EL (1 mmol), isopropanol
(5 mL), and the catalyst (200 mg) were charged into a
stainless reactor of 22 mL equipped with a magnetic
stirrer. After sealing, the reaction mixture was stirred at
a known temperature for the desired time. After the
reaction, the products were analyzed quantitatively by
gas chromatography (GC 9700) using naphthalene as
ꢀ
ture to 300ꢀC at a rate of 10 C/min under a flow of He
(50 cm3/min), and then the catalyst was kept at 300ꢀC for
8
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Hydrogenation of EL with Zirconium Phosphonate
7. I. T. Horvath, H. Mehdi, V. Fabos, L. Boda, L. T. Mika,
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the internal standard, and identification of the products
was done by GC-MS (SCIONSQ-456-GC). The yield
of GVL was calculated using the following equation:
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GVL Yield ðmol%Þ = Moles of GVL formed × 100%
Moles of EL used
Reusability of the organic zirconium phosphonates
In the experiments, to test the reusability of the zir-
conium phosphonates, the catalyst was recovered by
centrifugation and washed with ethyl ether (3 × 50 mL).
After drying under vacuum at 80ꢀC for 12 h, the cata-
lyst was reused for the next run.
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Green Chem. 2016, 18, 1287.
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CONCLUSIONS
In conclusion, a series of organic zirconium phos-
phonate catalysts were synthesized by a simply copreci-
pitation method, which were used to the reaction of EL
to GVL in isopropanol. The catalysts could be reused
at least five times without any obvious decrease in activ-
ity or selectivity. The outstanding catalytic activity was
ascribed to the acid and basic sites from Zr element and
phosphate groups interspersed in the catalyst. The
application in this work will guide the development of
efficient conversion of platform molecules containing
carbonyl group into fuel additives and higher value-
added chemicals with heterogeneous catalytic systems
without external hydrogen
ACKNOWLEDGMENTS
This work was financially supported by the
MOE & SAFEA under the 111 Project (B13025).
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Supporting information
Additional supporting information is available in
the online version of this article.
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J. F. Wang, Cat. Sci. Technol. 2016, 6, 14.
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