Supported copper catalysts for highly efficient hydrogenation of biomass-derived levulinic acid and γ-valerolactone

Article abstract of DOI:10.1039/c5gc01454a

Levulinic acid (LA) is one of the most significant cellulose-derived compounds. γ-Valerolactone (GVL) and 1,4-pentanediol (1,4-PDO) are considered to be important chemical intermediates. Direct conversion of LA to GVL and GVL to 1,4-PDO was achieved via chemoselective hydrogenation by supported copper catalysts. We studied the transformation of LA to GVL in water and alcohol, and the pathway of the reaction was also studied. LA was converted to GVL catalyzed by the Cu (30%)-WO₃ (10%)/ZrO₂-CP-300 catalyst at 413 K in ethanol with 81% yield, while 84% GVL was obtained with the Cu (30%)/ZrO₂-OG-300 catalyst in water at 393 K. Furthermore, 1,4-PDO was produced from GVL in excellent selectivities (>90%) using the Cu-TiO₂/ZrO₂-CP-600 catalyst.

Full text of DOI:10.1039/c5gc01454a

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Supported copper catalysts for highly efficient
hydrogenation of biomassꢀderived levulinic acid and
γꢀvalerolactone
Cite this: DOI: 10.1039/x0xx00000x
DOI: 10.1039/x0xx00000x
www.rsc.org/
Qing Xu, Xinglong Li, Tao Pan, Chuguo Yu, Jin Deng, Qingxiang Guo and Yao Fu*
Levulinic acid (LA) is one of the most significant celluloseꢀderived compounds.γꢀValerolactone
(
GVL) and 1,4ꢀPentanediol (1,4ꢀPDO) are considered to be the important chemical intermediates.
Direct conversion of LA to GVL and GVL to 1,4ꢀPDO were achieved via chemoselective
hydrogenation by supported copper catalysts. We studied the transformation of LA to GVL in water
and alcohol, and the pathway of the reaction was also studied. LA was converted to GVL catalyzed
by Cu(30%)ꢀWO (10%)/ZrO ꢀCPꢀ300 catalyst at 413 K in ethanol with 81% yield, while 84% GVL
3
2
was obtained with Cu(30%)/ZrO ꢀOGꢀ300 catalyst in water at 393 K. Furthermore, 1,4ꢀPDO was
2
produced from GVL in excellent selectivities (>90%) using CuꢀTiO /ZrO ꢀCPꢀ600 catalyst.
2
2
1
. Introduction
1
12
Biomass is a carbonꢀneutral resource. Being regarded as the
only renewable resource which can be converted to conventional
liquid, solid and gaseous fuels and other chemicals, biomass has
a unique advantage in the process of substituting fossil resources.
production, food additives and green solvents.
The further
conversion of GVL to other chemicals is also valuable (Scheme
1). 1,4ꢀPentanediol, prepared from GVL, isconsidered to be the
monomer of biodegradable polymers, and also an important
Methyltetrahydrofuran (MTHF)
prepared from LA or GVL by hydrogenation is considered as an
important solvent and the component of Pꢀseries fuels.
2, 3
13
Biomass can be converted to bulk products, such as liquid
fuels, or high valueꢀadded chemicals include succinic acid,
sorbitol and glycerin through bioꢀrefinery process.
chemical intermediate.
4
, 5
Biomassꢀ
based platform molecules are important bridges linking biomass
raw materials and target products. The development of simple,
efficient and costꢀeffective processes for the preparation of
platform molecules and their further conversion to fuels and
chemicals are crucial to the improvement of the competitiveness
of biomass resources relative to fossil resources.
Currently, there are many reports about the transformation
from LA to GVL. Studies suggest that the hydrogenation of LA
to GVL may operate through two main pathways. One is the
hydrogenation of LA to γꢀhydroxypentanoic acid followed by the
intramolecular lactonization to GVL. The other involves the
dehydration of LA by acid catalysis to angelica lactone followed
by the hydrogenation of lactone to GVL. However, due to the
formation of coke by the polymerization of angelica lactone
promoted by the acidic catalysis, lower yields of GVL were
observed through the second pathway.
6
In these lignocellulosic biomassꢀbased chemicals, levulinic
acid is an important platform molecule which can be transformed
to a variety of derivatives, such as fuel additives, monomer of
7
, 8
polymers and other high valueꢀadded chemicals.
LA can be
produced via the dehydration of hexose in acidic aqueous
solution or the hydrolysis/alcoholysis of furfuryl alcohol derived
9
, 10
from the hydrogenation of pentose.
The reduction of levulinic
acid could produce γꢀ valerolactone, which can be used as fuel
additives of gasoline and diesel. For example, Horvath et al.
showed that a mixture of 90% gasoline and 10% GVL has a
similar octane value with a mixture of 90% gasoline and 10%
ethanol, while GVL improves the burning characteristics of the
1
1
fuel due to the low vapor pressure of GVL. On the other hand,
it is possible to use GVL directly as a liquid fuel due to its similar
heating value and higher energy density relative to ethanol.
Moreover, GVL has been widely used as precursors in perfumes
Scheme 1. The pathway of the conversion of LA to GVL, PDO and
MTHF.
Horváth et al. reported
a multiꢀstep process for the
transformation of LA to GVL, PDO and MTHF by homogeneous
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1
4
Ruꢀcatalyst systems. Li et al. reported that iridium hydrideꢀ
2. Experimental
bipyridine ligand catalysts had a high reactivity for the
The reagents used in catalyst preparation and reactions were
commercially available.
1
5
hydrogenation of LA to GVL. The hydrogenation of LA to
GVL using heterogeneous catalysts under gas phase or liquid
phase conditions has been extensively studied, and GVL can also
be obtained with the external source of hydrogen using supported
2.1 Catalyst preparation.
WO ꢀZrO ꢀCP: ZrOCl solution was vigorously stirred at the
1
6
3
2
2
Ru, Pd, Pt, Ni, Rh, Ir, Au, .etc. Among them, supported Ru
catalysts showed the highest catalytic activity. Lange et al.
reported that the continuous hydrogenation of LA using platinum
different concentrations of ammonium metatungstate solution,
and then 25% aqueous ammonia was added to adjust the pH to 9,
the resulting precipitate was aged at room temperature for 24 h,
17
supported on TiO and ZrO resulted in a 95% yield of GVL.
2
2
ꢀ
filtered, washed with deionized water until no Cl was detected.
In industry, GVL was produced by using heterogeneous metal
catalysts and hydrogen for the hydrogenation of LA. For example,
the reduction of LA catalyzed by platinum oxide at room
Then the precipitate was dried at 383 K for 12 h, and calcined at
a certain temperature for 3 h.
Cu/WO ꢀZrO ꢀCP: Aqueous solution of copper nitrate,
3
2
temperature with 2~3 atm H gives 87% yield of GVL.
2
zirconium nitrate and ammonium tungstate were vigorous stirred
at 353 K and 0.1 M sodium carbonate solution was added to
adjust the pH to 7. The resulting precipitate was aged at room
temperature for 24 h, filtered and washed with deionized water.
Then the precipitate was dried at 383 K for 12 h, and calcined at
a certain temperature for 3 h. The oxides were reduced at 553 K
Furthermore, formic acid, the byꢀproduct during the
preparation of LA, can be decomposed to generate hydrogen in
situ. It is more practical that the conversion of LA and formic
acid to GVL is achieved without the addition of external
hydrogen source. We reported the use of homogeneous and
heterogeneous Ru catalysts to prepare GVL from LA and formic
o
for 3 h with the heating rate 2 C/min and the gas composition
1
8, 19
acid with 96% yield.
Fan et al. reported efficient conversion
was H :N (10:90), 100 mL/min.
20
2
2
of LA and formic acid to GVL by using Au/ZrO catalyst.
2
Cu/ZrO ꢀOG: The ethanol solution of copper nitrate,
2
Using heterogeneous nonꢀnoble metal supported catalysts is
important to reduce the cost of the catalysts. Rode et al. reported
that LA and its esters could be converted to GVL with a 90~100%
selectivity at 473K using Cu/Al O in water and Cu/ZrO in
zirconium nitrate and ammonium tungstate were mixed under
vigorous stirring, and a 20% excess of alcohol solution of oxalic
acid was added rapidly. The mixture were stirred at room
temperature for 4 h, filtered, and washed with deionized water.
The precipitate was dried at 383 K for 12 h, and calcined at a
certain temperature for 3 h. The oxides were reduced same as
Cu/WO ꢀZrO ꢀCP catalyst.
2
3
2
2
1
+2
+3
methanol. Moreover, CuꢀCr hydrotalcite (Cu /Cr =2) gave 91%
yield of GVL in water. Fan et al. developed an inexpensive
2
2
Cu/ZrO2 catalyst to obtain 100% conversion and 100%
2
3
3
2
selectivity of LA to GVL at 473 K.
CuꢀTiO /ZrO ꢀCP: Aqueous solution of copper nitrate,
2
2
At present, 1, 4ꢀPDO and MTHF could be obtained from LA
or GVL catalyzed by homogeneous or heterogeneous catalyst in
oneꢀstep. Leitner et al. reported the hydrogenation of LA to
MTHF under 8 MPa H at 473 Kusing Ru(acac) /PBu /NH PF
6
zirconium nitrate and the powder of titanium oxide were
vigorous stirred at 353 K and 0.1 M sodium carbonate solution
was added to adjust the pH to 7. The resulting precipitate was
aged at room temperature for 24 h, filtered, and washed with
deionized water. Then the precipitate was dried at 383 K for 12 h,
and calcined at a certain temperature for 3 h. The oxides were
reduced same as Cu/WO ꢀZrO ꢀCP catalyst.
2
3
3
4
catalyst, while GVL and PDO were the main products without
adding NH PF (yield: 37% and 63%, respectively). And if the
4
6
combination of the ligand of triphos and Ru (acac) was used, the
3
3
2
yield of 1, 4ꢀPDO increased to 95%. The results reflected the
2
4, 25
important role of the ligand in homogeneous catalysis.
Pravin
2.2 Catalyst characterization.
P Upare used Cu/SiO to catalyze the conversion of LA to MTHF
2
The catalyst was characterized by Xꢀray power diffraction
XRD), transmission electron spectroscopy (TEM), Brunauerꢀ
EmmettꢀTeller (BET), and inductively coupled plasma atomic
emission spectroscopy(ICPꢀAES). The detailed methods were
presented in supplementary information.
2
6
in the gas phase (more than 90% selectivity). Cao and coꢀ
workers reported that Cu/ZrO2 catalyzed the chemoselective
(
27
hydrogenation of GVL to MTHF or 1, 4ꢀPDO in alcohols.
As shown in previous studies, the transformation of LA to
GVL using inexpensive supported metal catalysts (such as
supported copper catalysts) in aqueous systems is also attractive.
It is worth noted that it still needs to develop a milder reaction
conditions in this process. Therefore, it is of great significance to
develop efficient and inexpensive supported metal catalysts to
achieve the selective conversion from LA to GVL under mild
conditions and the subsequent conversion of GVL.
Herein, we prepared and screened a series of supported copper
catalysts for the hydrogenation of LA to GVL and the conversion
of GVL to 1, 4ꢀPDO. The efficient hydrogenation of LA to GVL
under mild conditions (393 K ~413 K) were achieved, and the
selective conversion of GVL to 1, 4ꢀPDO were also studied.
2.3 Typical experiment and product analysis
A mixture of LA and the preꢀreduced supported Cu catalysts,
water or ethanol (5 mL) were charged into a 25ꢀmL HastelloyꢀC
high pressure reactor (Anhui Kemi Machinery Technology Co.
Ltd) and stirred at a rate of 600 rpm under 5 MPa H atmosphere
2
for given reaction time. The products were analyzed on a
Shimadzu GCꢀ2014 gas chromatograph equipped with DMꢀ
WAX (30m×0.25mm) column. The products were identified by
GCꢀMS (Thermo Trace GC Ultra with a Polaris Q ion trap mass
spectrometer equipped with a TRꢀ5MS capillary column).
2
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Table 1. Hydrogenolysis of LA into GVL with various supported copperꢀcatalysts in ethanol.
Yield /%
Entry
Catalyst
Conv./%
Total/ %
GVL MTHF
PO
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
PDO
0
0
EL
67
58
74
71
70
5
EV+VA
1
2
3
4
5
6
7
Cu/HZSMꢀ5
Cu/ZSMꢀ5
Cu/SiO2
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
3
0
0
0
0
0
0
0
0
0
0
0
0
9
12
1
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
1
2
20
0
0
70
61
80
75
79
99
94
97
82
99
96
97
95
93
98
90
98
98
3
6
0
Cu/ZrO2
4
0
Cu/Ta O5
9
0
2
Cu/γꢀAl O3
93
20
22
2
1
2
Cu/SBAꢀ15
Cu/C
0
74
73
80
80
0
8
9
0
0
WO /ZrO ꢀCPꢀ300
3
2
1
0
1
2
3
4
5
6
Cu/C+WO /ZrO ꢀCPꢀ300
18
94
80
63
75
78
40
87
76
1
3
2
1
1
1
1
1
1
CuꢀWO /ZrO ꢀCPꢀ300
2
3
2
CuꢀWO /ZrO ꢀCPꢀ600
0
17
1
3
2
Cu/ZrO ꢀOGꢀ300
22
5
17
6
2
Cu/ZrO ꢀOGꢀ600
0
0
2
CuꢀTiO /ZrO ꢀCPꢀ300
2
2
CuꢀTiO /ZrO ꢀCPꢀ600
24
10
22
2
2
b
CuꢀWO /ZrO ꢀCPꢀ300
1
1
7c
8
3
2
CuꢀWO /ZrO ꢀCPꢀ300
0
1
3
2
[
a] LA 0.25 g, catalyst 0.1 g, 473 K, 6 h, 5 MPa H
wt%, TiO : 60 wt%, CuꢀWO /ZrO ꢀCPꢀ300) was prepared by coꢀprecipitation method and the oxide precursors were calcined in air at 573 K, Cu/ZrO
00 was prepared by oxalateꢀgel coprecipitation method followed by calcination in air at 573 K.
2
. Solvent: ethanol 5 mL. GC Yield. [b] LA 0.5 g. [c] 3 MPa H
2
. Catalyst (Cu loading: 30 wt%, WO
3
: 10
2
3
2
2
ꢀOGꢀ
3
3
. Results and Discussion
of the catalysts (e.g. the solꢀgel method (OG) and coꢀprecipitation
method (CP)) and the calcination temperature of oxide precursor
such as 573 K or 873 K) significantly influenced the conversion of
3
.1 LA to GVL in ethanol
(
LA to GVL. In particular, Cu (30%)ꢀWO3 (10%)/ZrO ꢀCPꢀ300
2
obtained a 94% yield of GVL under 5 MPa H (Table 1, entry 11).
2
The increase of calcination temperature of Cu (30%)ꢀWO (10%)
3
/
ZrO ꢀCP led to the decrease of GVL yield (Table 1, entries 11ꢀ12).
2
With TiO (60%)/ZrO ꢀCP as the support, the byꢀproducts such as
2
2
PDO and EV increased significantly, while GVL decreased
accordingly (Table 1, entries 15ꢀ16). Similarly, the yield of GVL
significantly decreased and the yield of MTHF and PDO increased
Scheme 2. Hydrogenolysis of LA into GVL with various supported
copperꢀcatalysts in ethanol.
First we investigated the effects of the support on the conversion
of LA to GVL by using different supported copper catalysts with
ethanol as solvent (Scheme 2, Table 1).
by using Cu(30%)/ZrO ꢀOG catalysts compared to Cu(30%)ꢀ
2
WO (10%) /ZrO ꢀCP (Table1, entries 13ꢀ14). The higher activity of
3
2
the catalysts presumably results in the overꢀhydrogenation of GVL.
At 473 K different supported copper catalysts were screened. The
main product was ethyl levulinate (EL, 60~70% yield) by using
several common supports such as HZSMꢀ5, ZSMꢀ5, Ta O , ZrO
In order to verify the above presumption on Cu (30%)/ZrO ꢀOGꢀ300
2
catalyst, the reaction temperature was reduced to 413 K and the yield
of GVL increased to 88%, while the overꢀhydrogenation products
were not detected. This result may support partially our explanation.
We studied the BET analysis of several catalysts and found that the
activity of catalyst was inversely proportional to the surface area of
2
5
2
and SiO (Table 1, entries 1ꢀ5) and no hydrogenation was observed.
2
The yield of GVL increased slightly (~20%) by using mesoporous
silica SBAꢀ15 and activated carbon as supports (Table 1, entries 7ꢀ
8
), but the main product was also EL (~70%). γꢀꢀAl O improved the
2 3
[
28]
the catalyst by BET (Table 1, Table S8). We found that the BET
surface area of CuꢀWO /ZrO ꢀCPꢀ300 catalyst was the smallest, but
yield of GVL to 93%, which is in consistent with the reported results
21
3
2
(Table 1, entries 6).
the activity was the highest in the five different tested catalysts
Table 1. entry 11, Table S8. entry 1). On the contrary, the Cu/ZSMꢀ
catalyst had a relatively high specific surface area, but the activity
Subsequently, a series of composite oxide solid acid supported
copper catalysts were prepared (Table 1, entries 11ꢀ16), and we
found that the types of solid acid supports, the preparation methods
(
5
of the catalyst was poor (Table 1, entry 2 and Table S8, entry 5).
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Comparied the experimental results, we found that the addition of W The results showed that the amount of catalyst and hydrogen
in the catalyst gave the higher yield and selectivity of GVL. This pressure also partly influenced on the conversion of LA
may be due to the interaction between Cu and W. The BET surface (Table1, entries 17ꢀ18).
area of the catalyst decreased after the addition of W and the
We studied the effect of reaction temperature (373 Kꢀ513
decreased BET surface area may be beneficial to the product K, Figure 1) on the hydrogenation of LA by using the Cu
selectivity as the product may be quickly released out of the catalyst (30%)ꢀWO (10%)/ZrO ꢀCPꢀ300 catalyst. The conversion of
3
2
surface. At this time, GVL stays relatively longer on the catalyst LA was 35% at 373 K. It was disappointing that only slight
surface of which BET surface area is higher, leading to further increase of the conversion was observed, even if the reaction
hydrogenation of GVL on the catalyst surface and giving the main time was extended to 24 h. 54% LA conversion was achieved
byproduct MTHF and PDO. Through the analysis of the pore and the main products were GVL and EL at 393 K. LA was
volume and pore diameter, we found that the selectivity of GVL completely converted and GVL was obtained with 81% yield at
decreased and overꢀhydrogenation products were obtained under 413 K. The yield of GVL increased at higher reaction
larger pore volume and pore diameter (Table S8).
temperature. The maximum GVL yield of 94% was obtained at
73 K. With further increase of the reaction temperature, the
4
yield of GVL decreased gradually and the byꢀproducts EV and
VA were formed, which showed that GVL was overꢀ
hydrogenated at higher reaction temperature.
Figure 1. The effect of reaction temperature on the conversion of LA in
3 2
ethanol. Reaction conditions: LA 0.25 g, Cu (30%)ꢀWO (10%)/ ZrO ꢀCPꢀ
3
00 catalyst 0.1 g, 6 h, 5 MPa H . Solvent: ethanol 5 mL. GC Yield.
2
Control experiment showed that EL was the only product
with the solid acid support WO /ZrO ꢀCPꢀ300 as catalyst
3
2
Figure 2. The effect of Cu loadings on the hydrogen conversion of LA.
(
Table 1, Entry 9). The mixture of Cu/C with the solid acid
3 2
Reaction conditions: LA 0.25 g, CuꢀWO (10%)/ZrO ꢀCPꢀ300 0.1 g, 473 K, 6
support WO /ZrO ꢀCPꢀ300 (Table1, Entry10) also gave EL as h, 5 MPa H
2
. Solvent: ethanol 5 mL. GC Yield.
3
2
the main product, similar to Cu/C. Through the comparison of
the results in ethanol, we found that the addition of W in the
catalyst gave the higher yield and selectivity of GVL. This may
be due to the interaction between Cu and W. The yield of GVL
was very low (only about 2ꢀ4%) by using Cu/ZrO2 and
WO /ZrO ꢀCPꢀ300 catalyst (Table 1, entry 4, 9). It is showed
We prepared a series of CuꢀWO (10%)/ZrO ꢀCPꢀ300 catalyst
3
2
with various Cu loadings (10ꢀ40 wt%, Figure 2.) and investigated
the effects of copper loadings on the hydrogenation of LA. In each
experiment, LA was completely transformed and the products varied
considerably for the different loadings. EL was the main product
when the copper loading was 10 wt%. As the copper loadings
increased, the yield of GVL increased gradually. The highest yield of
GVL was 94% when 30 wt% copper was loaded, while a higher
copper loading of 40 wt% did not give higher GVL yield. We have
also observed a similar trend of product distribution with different
Cu loadings under 413 K (Figure S7). With the increased of Cu
loadings from 10% to 30%, the yield of GVL increased and the yield
of EL decreased.
3
2
that using one of Cu or W as the sole catalyst could not give a
good result. The yield of GVL can reach 18% (Table 1 entry
1
0) by using Cu/C+WO /ZrO ꢀCPꢀ300 catalyst. This showed
3 2
that the physical mixture Cu and W catalyst also have a certain
effect. We further used Cu (30%) ꢀWO (10%) /ZrO ꢀCPꢀ300
3
2
as the catalyst, and the yield of GVL was greatly increased to
4% (Table 1, entry 11). The interaction between W and Cu
9
was enhanced in our prepared catalyst. Experiments with
different W loadings of the catalyst were also carried out (Table
S6). Through the experiments, we obtained lower yield of GVL
and the main byꢀproduct was EL at lower W loadings (Table
S6, entry 1). The yield of GVL increased with the increase of
W loading to 10%(Table S6, entry 2). With further increasing
the W loading to 20%, the yield of GVL was not significantly
increased (Table S6, entry 3). We found that the yield of GVL
decreased slightly when we doubled the concentration of the
substrate or reduced the initial hydrogen pressure to 3 MPa.
3
.2 LA to GVL in water
It is known that LA is produced from the biomass in aqueous
processes. In order to link the preparation process of LA and
avoid the extensive use of organic solvents, it is significant to
study the conversion of LA to GVL in aqueous system by the
supported copper catalysts. The results were shown in Table 2.
A series of experiments using supported Cu catalysts were
performed at 413 K with an initial hydrogen pressure of 5 MPa
4
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Table 2. Hydrogenolysis of LA into GVL with various supported copperꢀcatalysts in water.
Selectivity/%
Entry
Catalyst
Temp./K Conv./%
GVL
0
MTHF
PDO
0
1
2
3
4
5
6
7
8
9
Cu/C
413
413
413
413
413
413
413
413
413
413
413
413
413
413
413
473
473
513
393
413
473
473
2
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
1
1
Cu/ZrO2
Cu/SiO2
Cu/TiO2
0
0
4
0
0
2
1
0
Cu/γꢀAl O
5
1
0
2
3
Cu/ZSMꢀ5
Cu/HZSMꢀ5
Cu/SBAꢀ15
3
0
0
6
0
0
5
2
1
Cu/SBAꢀ15+SBAꢀSO H
6
0
0
3
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
CuꢀWO /ZrO ꢀCPꢀ300
6
95
91
92
93
88
89
99
66
92
84
95
ꢀ
0
3
2
CuꢀWO /ZrO ꢀCPꢀ600
2
0
3
2
CuꢀTiO /WO ꢀCPꢀ300
4
0
2
3
CuꢀTiO /WO ꢀCPꢀ600
3
0
2
3
Cu/ZrO ꢀOGꢀ300
100
36
100
100
100
100
100
3
0
2
Cu/ZrO ꢀOGꢀ600
0
2
CuꢀWO /ZrO ꢀCPꢀ300
0
3
2
CuꢀWO /ZrO ꢀCPꢀ600
0
3
2
Cu/ZrO ꢀOGꢀ600
0
2
b
Cu/ZrO ꢀOGꢀ300
0
1
9
0
2
c
d
d
Cu/ZrO ꢀOGꢀ300
0
2
2
Cu/ZrO ꢀOGꢀ300
2
2
1
2
Cu/ZrO ꢀOGꢀ600
2
ꢀ
1
2
2
2
[
a] LA 0.25 g, catalyst 0.1 g, reaction temperature 413 K, 6 h, 5 MPa H
GVL. Catalyst (Cu loading: 30%, WO : 10wt%, TiO :60wt%, CuꢀWO
precursors were calcined in air at 573 K, Cu/ZrO ꢀOGꢀ300 was prepared by oxalateꢀgel coprecipitation followed by calcination in air at 573 K.
2
. Solvent: water 5 mL. GC Yield. [b] 24 h. [c] 12 h. [d] The substrate was
3
2
3
/ZrO ꢀCPꢀ300) was prepared by coꢀprecipitation method and the oxide
2
2
for 6 h. The results indicated that the commonly used
supported copper catalysts, such as Cu/C, oxide supported
copper catalyst Cu/ZrO , Cu/SiO , Cu/γꢀAl O and Cu/TiO ,
zeolite supported copper catalysts Cu/ZSMꢀ5 and Cu/HZSMꢀ5,
mesoporous silicon supported catalysts Cu/SBAꢀ15 and the
13). Compared the reaction in water and ethanol (Figure 1 and
Table 2), at 413 K, the efficiency was higher in ethanol than
that in water. The XRD diffraction peaks of the catalyst
collected after reaction in water were more acute than that in
ethanol(Figure S8). It showed that the catalyst is easy to
reunite and the activity of catalyst reduced in water than that
in ethanol. We found that the active component of the catalyst
in water was more seriously lost than that in ethanol by
analysis of ICPꢀAES (Table S5 in supporting information),
which could also explain the reason that the activity of catalyst
in water was not as good as that in ethanol. Due to the high
2
2
2
3
2
combination of Cu/SBAꢀ15 and solid acid SBAꢀSO H,
3
showed poor catalytic activity under reaction conditions
(
Table 2, entries 1ꢀ9). Simultaneously, the conversion of LA
did not exceed 10%. Four kinds of solid acids supported
copper
catalysts
(Cu(30%)ꢀWO (10%)/ZrO ꢀCPꢀ300,
3
2
Cu(30%)ꢀWO (10%)/ZrO ꢀCPꢀ600,
Cu(30%)ꢀ
3
2
TiO (60%)/WO ꢀCPꢀ300, Cu(30%)ꢀTiO (60%)/WO ꢀCPꢀ600)
catalytic activity of Cu(30%)/ZrO ꢀOG in ethanol, the overꢀ
2
3
2
3
2
with high catalytic activity in ethanol were tried.
Unfortunately, although the selectivity of GVL was very
high, the conversion of LA was still low (Table 2, entries 10ꢀ
hydrogenation products of MTHF and PDO were observed to
form. Surprisingly, the overꢀhydrogenation was inhibited in
aqueous system and Cu(30%)/ZrO ꢀOG showed high catalytic
2
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 5

Green Chemistry
Page 6 of 9
View Article Online
ARTICLE
DOI: 10.1039/C C0145
Jou al Na4Ame
5Grn
activity at 413 K (Table 2, entries 14ꢀ15). Cu(30%)/ZrO ꢀOGꢀ
to GVL in ethanol obtained the EL as the major product with 5
2
.
[29]
3
1
00 achieved 88% GVL yield. Extending the reaction time to
2 h, 95% yield of GVL was obtained (Table 2, entry 20).
MPa N (Table S7, entry 2)
Direct reaction of EL can obtain
2
almost equivalent GVL. The EL converted to 2ꢀhydroxy ethyl
valerate through the carbonyl hydrogenation and the GVL was
obtained by rapid lactonization of the unstable 2ꢀhydroxy ethyl
valerate. The 2ꢀ hydroxy ethyl valerate was too unstable to be
detected. Therefore, the possible pathway of LA to GVL in ethanol
may conduct as follows:
Compared to Cu(30%)/ZrO ꢀOGꢀ300, Cu(30%)ꢀ/ZrO ꢀOGꢀ
2
2
6
00 showed lower catalytic activity (Table 2, entry 15).
Increasing the reaction temperature to 473 K, Cu(30%)ꢀ
WO (10%)/ZrO ꢀCP also showed better catalytic activity
3
2
(
Table 2, entries 16ꢀ17). Cu(30%)ꢀWO (10%)/ZrO ꢀCPꢀ300
3 2
gave a 99% yield of GVL, while Cu(30%)ꢀWO (10%)/ZrO ꢀ
3
2
CPꢀ600 achieved 66% GVL yield. Further increasing the
temperature to 513 K, Cu (30%)/ZrO ꢀOGꢀ600 also received
2
9
2% GVL yield (Table 2, entry 18).
When decreasing the reaction temperature to 393 K and
extending the reaction time to the 24 h, a GVL yield of 84%
was obtained by using Cu(30%)/ZrO ꢀOGꢀ300 as catalyst
2
(
Table 2, entry 19). In addition, using GVL as substrate and
Scheme 3. The possible pathway of LA to GVL in ethanol.
Cu (30%)/ZrO ꢀOG as catalyst, it was found that GVL was
hardly transformed under aqueous conditions (Table 2, entries
2
2
We detected the reaction liquid (water solvent, H , 20 min) by the
2
gas phase chromatograph and found that the major product was
GVL and accompanied a small amount of angelica lactone. We all
know that the conversion of LA to angelica lactone is a reversible
reaction in the water, and the angelica lactone is more inclined to
LA in the water. Then we found that the reaction of LA was not
1ꢀ22). This result showed that the product GVL is stable
under the reaction condition.
Chosen Cu(30%)/ZrO ꢀOGꢀ300 as the catalyst, we
2
investigated the effects of reaction temperature on
hydrogenation of LA in aqueous system (373 Kꢀ513 K, Figure
3
in a low yield of GVL. When the temperature was above 413
K, LA was totally converted and the selectivity of GVL was
about 90% (413 Kꢀ473 K). Further increasing the reaction
temperature (493 Kꢀ513 K), the yield of GVL decreased
dramatically. Only trace amount of excessive hydrogenation
products such as MTHF and PDO was found.
converted in 5 MPa N (Table S7, entry 3), and no angelica lactone
2
). Only a small amount of LA converted at 373 K, resulting
was detected. It can be explained that the main intermediate of LA
to GVL in water may be not angelica lactone. Under our
experimental conditions, the carbonyl is easily hydrogenated to
alcohol by using Cu based catalyst. The hydroxyvalerate, which is
further hydrogenated to GVL, is not stable and difficult to be
detected in the reaction liquid. The possible pathway of LA to GVL
in water may be as follows:
The reusability of Cu (30%)/ZrO ꢀOGꢀ300 were studied
2
(
Figure S6). The Cu (30%)/ZrO ꢀOGꢀ300 used once at 413 K
2
for 6 h was employed under the optimized reaction conditions
as Run 1. It can be seen that the yield of GVL decreased
slightly after in 5 runs. The results may be explained by the
leaching study of Cu (Table S1 in supporting information) and
showed good stability of the catalyst in water.
Scheme 4. The possible pathway of LA to GVL in water
a
Table 3. Conversion of carbohydrates and subsequent reduction of
b
LA with formic acid (FA) by Cu (30%)/ZrO
2
ꢀOGꢀ300.
Yield
Entry
Carbohydrate
c
LA[mol]
FA[mol]
GVL[mol] (Sugar 100%)
1
2
3
4
5
6
Glucose
Fructose
Sucrose
Cellobiose
Starch
Cellulose
52
53
60
57
51
30
56
58
63
60
55
36
45
46
53
50
45
26
[
a] 2 g of Carbohydrate, 20 mL water, 1 g H
2
SO
4
(98%), 443 K, 1 h;
Figure 3. The effect of reaction temperature on the hydrogen
2
[b] biomassꢀderived LA and FA (5 mL), Cu(30%)/ZrO ꢀOGꢀ300 0.1
conversion of LA in water. Reaction conditions: LA 0.25 g, Cu
g, 6 h, 5 MPa H . GC Yield; [c] The yields were based on the
conversion of sugar.
2
2 2
(30%)/ZrO ꢀOGꢀ300 0.1 g, 6 h, 5 MPa H . Solvent: water 5 mL. GC
Yield.
At present, the pathway of LA to GVL in water and alcohol
solution is still controversial. We found that the conversion of LA
In order to link up with the preparation process of LA, we
used the hydrolysis solution of LA as the substrate for the
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 7 of 9
Journal Name
Green Chemistry
View Article Online
ART54ICLE
DOI: 10.1039/C5GC014 A
reaction. The selected sugars included glucose, fructose,
sucrose, cellobiose, starch and cellulose. Sulfuric acid was
used as an acid catalyst for the hydrolysis of sugars in aqueous
system at 443 K for 1 h and the hydrolysate containing LA
and HCOOH was obtained (Table 3). Cu(30%)/ZrO ꢀOGꢀ300
was used as the catalyst for the hydrogenation of the
hydrolysate.
2
a
Table 4 Hydrogenolysis of GVL into 1, 4ꢀPDO or MTHF with various supported Cuꢀcatalysts in ethanol.
Entry
Cat.
Conv./ %
Selectivity/ %
PO PDO
84
MTHF
EV+VA
1
2
3
4
5
6
7
8
9
Cu/TiO
2
45
41
4
12
0
1
2
1
Cu/CeO
2
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
0
11
34
2
Cu/ZrO
2
0
9
Cu/SBAꢀ15
Cu/HZSMꢀ5
42
51
9
0
1
0
0
4
Cu/γꢀAl
Cu/SiO
Cu/Ta
Cu/βꢀzeolite
Cu/αꢀAl
Cu/C
/ZrO ꢀCPꢀ300
Cu/C+WO /ZrO ꢀCPꢀ300
2
O
3
89
0
0
3
2
58
17
16
14
4
0
0
2
O
5
1
1
1
55
0
5
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
2
O
3
0
46
0
8
0
WO
3
2
5
0
0
0
3
2
3
16
5
8
17
2
CuꢀWO
3
/ZrO
2
ꢀCPꢀ300
ꢀCPꢀ600
ꢀCPꢀ300
ꢀCPꢀ600
ꢀCPꢀ300
9
56
94
82
96
9
CuꢀWO
3
/ZrO
2
21
45
27
21
1
3
CuꢀTiO
2
2
/ZrO
2
2
15
3
1
CuꢀTiO
/ZrO
1
b
1
8
CuꢀWO
3
/ZrO
2
11
53
2
[a] GVL 0.25 g, catalyst 0.1 g, Cu Loadings (30 wt%), 473 K, 6 h, 5 MPa H . Solvent: ethanol 5 mL; [b] 513 K.
Direct hydrogenation of untreated hydrolysate did not
achieve a good yield of GVL (< 5%). We presumed that the
introduction of sulfuric acid improved the acidity of
hydrolysate and reduced the activity of copper catalyst in
hydrogenation process. In order to verify this assumption, we
firstly tested the pH value of the mixture of LA and HCOOH
selectivity to 1, 4ꢀPDO (84%). After using the solid acid
support HZSMꢀ5, the conversion of GVL had increased. Some
other supports, such as γꢀAl O , SiO , Ta O , βꢀzeolite, αꢀ
2
3
2
2
5
Al O and activated carbon were conducted. γꢀAl2O3 showed
2
3
a high selectivity to MTHF (89%), but GVL conversion was
low (Table 4, entries 6ꢀ11). It was also found that GVL was
not converted under the reaction conditions by using WO3
(
1:1 molar, 5 wt %, pH=1.91). The pH of the hydrolysate from
(
10%)/ZrO ꢀCPꢀ300 catalyst in the blank experiment (Table 4,
2
fructose, sucrose, glucose and cellobiose were 1.28, 1.30, 1.33
and 1.40, respectively. It was obvious that the acidity of
hydrolysate was higher than that of the mixture of LA and
HCOOH. Furthermore, we added sulfuric acid in the mixed
solution of LA and HCOOH (4 wt%) to adjust the pH to 1.30,
and GVL was not detected after hydrogenation. The results
suggested that the introduction of sulfuric acid had a negative
effect on the catalytic activity of copper catalyst. In order to
entry 12). The physical mixture of Cu/C and WO3
10%)/ZrO ꢀCPꢀ300 showed a similar result with Cu/C (Table
(
4
2
, entry 13).
solve the above problems, we used NaHCO to neutralize
3
sulfuric acid in the hydrolysate until pH=3. The neutral
hydrolysate was hydrogenated with Cu (30%)/ZrO ꢀOGꢀ300
and found that GVL was obtained with a yield of 88% in
terms of LA.
2
Scheme 5. Supported copper catalysts catalysed conversion of GVL
.
Then, we used two types of supported copper Cuꢀ
WO /ZrO and CuꢀTiO /ZrO catalysts for the hydrogenation
3
.3 GVL to PDO
3
2
2
2
of GVL (Table 4, entries 14ꢀ17). Although the GVL
conversion was not high, the catalysts gave high selectivity to
PDO except CuꢀWO /ZrO ꢀCPꢀ300. PDO selectivity of 94%
Based on the conversion of LA to GVL, we studied the supported
copper catalyzed conversion of GVL to MTHF and PDO (Scheme
3
2
5
, Table 4). Firstly we screened several common supports (e.g.
and 96% were achieved by using Cu (30%)ꢀTiO (60%)/ZrO ꢀ
2
2
TiO , CeO , ZrO , SBAꢀ15 and HZSMꢀ5) with the hydrogen
2
2
2
CPꢀ600 and Cu (30%)ꢀWO3 (10%)/ ZrO ꢀCPꢀ600,
2
pressure of 5 MPa at 473 K (Table 4, entries 1ꢀ5). The
respectively. Increasing the temperature to 513 K with Cuꢀ
conversion of GVL was not high and TiO showed a high
2
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

Green Chemistry
Page 8 of 9
View Article Online
ARTICLE
DOI: 10.1039/C C0145
Jou5Grnal Na4Ame
WO /ZrO ꢀCPꢀ300 catalyst, the GVL conversion increased
slightly and the main products were EV and VA.
7. B.V. Timokhin, V.A. Baransky, G.D. Eliseeva, Chem. Rev., 1999,
68, 73ꢀ84.
3
2
8
.
J. J. Bozell, L. Moens, D. C. Elliott, Y. Wang, G. G.
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Resour. Conserv. Recy., 2000, 28, 227ꢀ239.
4
. Conclusion
In summary, we have demonstrated simple yet versatile
supported copper catalysts for the hydrogenation of LA to
GVL and the conversion of GVL to PDO. LA was catalyzed
by Cu (30%)ꢀWO (10%)/ZrO ꢀCPꢀ300 at 413 K in ethanol
and 81% yield of GVL was obtained. The maximum GVL
yield of 94% was obtained at 473 K. Moreover, Cu (30%)/
9. S.W. Fitzpatrick, WO 8910362 A1.
10. S.W. Fitzpatrick, WO 9640609 A1
.
11. I. T. Horvath, H. Mehdi, V. Fabos, L. Boda, L. T. Mika, Green
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2
12. D. M. Alonso, S. G. Wettstein, J. A. Dumesic, Green Chem., 2013,
15, 584ꢀ595.
ZrO ꢀOGꢀ300 catalysed the hydrogenation of LA to give 84%
2
yield of GVL in water at 393 K. A higher yield of GVL
obtained at a higher temperature (95% yield at 413 K). For
Cuꢀcatalyzed conversion of LA to GVL, these reaction
conditions were the mildest reported by now. The reusability
13. M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, C. D. Pina,
Angew. Chem. Int. Edit., 2007, 46, 4434ꢀ4440.
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experiment of Cu (30%)/ZrO ꢀOGꢀ300 showed good stability
15. W. Li, J. H. Xie, H. Lin, Q. L. Zhou, Green Chem., 2012, 14, 2388ꢀ
2390.
2
of the catalyst in water and a direct hydrogenation of the
hydrolysates containing LA and HCOOH from sugars
achieved a good yield of GVL. Furthermore, it is feasible to
convert GVL to PDO in excellent selectivity using the
supported copper catalysts in ethanol. The findings in this
work will inspire the development of efficient conversion of
platform molecules into fuel additives and higher valueꢀadded
chemicals with economic heterogeneous catalytic systems.
16. W. R. H. Wright, R. Palkovits, ChemSusChem, 2012, 5, 1657ꢀ1667.
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Acknowledgment
Angew. Chem. Int. Edit., 2011, 50, 7815ꢀ7819.
This work was supported by the 973 Program
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2
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iChEM, CAS Key laboratory of Urban Pollutant Conversion, Anhui
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Province Key Laboratory of Biomass Clean Energy, Department of
Chemistry, University of Science and Technology of China, Hefei 230026,
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| J. Name., 2012, 00, 1-3
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Page 9 of 9
Green Chemistry
View Article Online
DOI: 10.1039/C5GC01454A
Direct conversion of celluloseꢀderived levulinic acid into γꢀvalerolactone and
γꢀvalerolactone into 1,4ꢀpentanediol were carried out by chemoselective
hydrogenation catalyzed through supported copperꢀcatalyst.