A novel Pd/C-catalyzed conversion of glucose to 1,2-propanediol by water splitting with Zn

Article abstract of DOI:10.1039/c5ra08482b

A novel Pd/C-catalysed conversion of glucose to 1,2-propanediol by water splitting with Zn was proposed. The yield of 1,2-akanediols reached 48%, mainly including 1,2-propanediol (33.3%), the reported highest yield from glucose. Water, as a solvent, provides an in situ and active hydrogen source. The formed ZnO acts as a catalyst with Pd/C.

Full text of DOI:10.1039/c5ra08482b

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A novel Pd/C-catalyzed conversion of glucose to
,2-propanediol by water splitting with Zn†
1
Cite this: RSC Adv., 2015, 5, 51435
a
a
c
a
a
Jie Wang, Guodong Yao, Yuanqing Wang, Hua Zhang, Zhibao Huo
ab
and Fangming Jin*
Received 7th May 2015
Accepted 3rd June 2015
DOI: 10.1039/c5ra08482b
www.rsc.org/advances
A novel Pd/C-catalysed conversion of glucose to 1,2-propanediol by promising method to solve the energy crisis. However, it is
water splitting with Zn was proposed. The yield of 1,2-akanediols extremely challenging. In contrast to the direct use of solar
reached 48%, mainly including 1,2-propanediol (33.3%), the reported energy, an integrated technology can be expected to have a high
highest yield from glucose. Water, as a solvent, provides an in situ and potential for the hydrogenation of biomass into chemical by water
active hydrogen source. The formed ZnO acts as a catalyst with Pd/C. splitting with solar energy. Our previous research has demon-
strated that the hydrogen can be easily produced with commer-
cially available and non-precious metals such as Zn, Fe or Al as a
With increasing environmental awareness and global energy
reductant metal under hydrothermal conditions and used for the
crises, effective methods of converting renewable biomass into
17–21
22
23
reduction of CO2,
formic acid and glycolide. Moreover, the
1–5
valuable chemicals have gathered much attention. 1,2-Pro-
panediol (1,2-PD) is an important chemical, widely used in drugs,
antifreeze and the production of polyesters and polyethers.
However, 1,2-PD is mainly produced from petroleum-derived
feedstocks. Thus, an efficient conversion of renewable biomass
like carbohydrates, and their derivatives such as lactic acid and
glycerol, to 1,2-PD is highly desirable. Although there have been
metal oxides, such as ZnO and Fe O , have been reported to be
2
3
24–26
dissociated to metals and O2 with solar energy.
Thus, an
efficient conversion of biomass to value-added chemicals with
solar energy can be achieved by combining hydrothermal method
to the conversion of biomass into chemicals with metals and solar
reduction of metal oxides into metals. Thus, we turned our
attention to the much more challenging hydrogenation of
biomass into value-added chemicals with metals as a reductant in
water. Herein, we present an efficient Pd/C-catalyzed conversion
of glucose to 1,2-PD by water splitting with Zn (eqn (1)).
6–10
many reports involving the conversion of carbohydrates, lactic
11,12
13–16
acid
and glycerol
into 1,2-PD, gaseous hydrogen, mainly
coming from fossil fuels, and complicated-designed bifunctional
6
7
8
9
catalysts such as CuCr, Ni–Cu/ZnO, WO
3
/Al
2 3
O + AC, Pt–PEI,
10
11
12
13
14
Ni–W
2
C, Ru/TiO
2
,
Ru–MoO
x
/C, Ag–OMS-2, Cu/MO ,
x
15
16
CuNP@AlOx and Ni3P are usually needed. Moreover, the
storage and transportation of gaseous hydrogen are considered
as energy-intensive. Therefore, developing a new method for the
hydrogenation of glucose with alternative hydrogen sources and
simple catalysts is urgently required.
(1)
First, the conversion of glucose into 1,2-PD was examined
ꢀ
with different metals as a reductant at 250 C for 30 min. The
Water is the most abundant hydrogen resource in the earth. If
hydrogen from water splitting by solar energy can be in situ used
for the hydrogenation of biomass into chemicals, it will be a
reaction did not give the desired 1,2-PD when using only Zn or
Pd/C (Table 1, entry 1 and 2), respectively. Interestingly,
however, the formation of 1,2-PD was clearly observed in the
presence of Zn and Pd/C together (Table 1, entry 3), and the
yield of 1,2-PD can reach 22.4% (based on the mole of carbon in
a
School of Environmental Science and Engineering, State Key Lab of Metal Matrix
Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai the product and reactant). In this case, a little amount of
2
00240, China. E-mail: fmjin@sjtu.edu.cn; Fax: +86 21-54742283; Tel: +86-21-
ethylene glycol (EG) and 1,2-butanediol (1,2-BD) were also
observed. The analysis of solid residuals aer the reactions by
XRD showed that only ZnO and no other peaks were observed,
indicating that Zn was oxidized to ZnO (see Fig. SI-5†), and the
hydrogen for converting glucose to 1,2-PD came from water by
the oxidation of Zn. Reactions with other metals such as Al and
5
4742283
b
Graduate School of Environmental Studies, Tohoku University, Japan
c
Nakamura Laboratory, RIKEN Innovation Center, 2-1 Hirosawa, Wako, Saintama
3
51-0198, Japan
†
Electronic supplementary information (ESI) available: Experimental details,
characterization data. See DOI: 10.1039/c5ra08482b
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Fe as reductants were also conducted. Results showed that no
noticeable 1,2-PD was detected (Table 1, entries 5 and 6).
Further, metal oxides such as CuO and Ni O as catalysts were
2
3
investigated in the presence of Zn. It was found that the yields of
1
8
,2-PD were quite low, only 8.7% and 9.7% (Table 1, entry 7 and
). These results suggest that only Zn as a reductant and Pd/C as
a catalyst are effective for the conversion of glucose to 1,2-PD.
Aer conrming the activity of Zn and Pd/C for the conver-
sion of glucose into 1,2-PD, we investigated the characteristics
of the reaction to nd the optimum condition. First, the effects
ꢀ
of initial amounts of Pd/C and Zn were studied at 250 C, 30
min. As shown in Fig. 1(a), the initial amount of Pd/C strongly
affected the 1,2-PD yield at a xed amount of Zn (451 mg, 6.9
mmol). The yield of 1,2-PD rst increased and then decreased
with the increase in the amount of Pd/C, and the highest yield
(31.4%) occurred at 65 mg, 0.03 mmol Pd/C. Overmuch Pd/C
may result in the decomposition of 1,2-PD. Then, the effect of
the amount of Zn was investigated by xing the amount of Pd/C
at 65 mg, 0.03 mmol. The yield of 1,2-PD greatly increased from
17.9% to 33.3% when the amount of Zn increased from 5 mmol
to 9 mmol. Further increasing the amount of Zn to 11 mmol did
not give a higher yield of 1,2-PD. The increase in the yield of 1,2-
PD with the increase in the amount of Zn most likely occurred
because stronger reduction conditions or a larger amount of
hydrogen improves the conversion of glucose into 1,2-PD. These
results indicate that the amount of Zn and Pd/C has a great
effect on the yield of 1,2-PD. Moreover, EG and 1,2-BD were also
detected and analyzed quantitatively in all experiments. As
shown in Fig. 1, the yields of EG and 1,2-BDwere low (about 5%
to 7%) and did not change a lot with the increase in the amount
of Pd/C and Zn, which indicated that the formation of EG and
1,2-BD underwent a quite different reaction pathway with the
production of 1,2-PD.
The previous research involving the conversion of glucose to
1,2-PD has reported that a higher initial concentration of glucose
was not favored for the conversion of glucose into 1,2-PD and
Table 1 Yield of polyols from glucose with different metal reductants
a
and catalysts
e
Yield (%)
b
b
b
Entry
Reductant
Catalyst
1,2-PG
EG
1,2-BD
1
2
3
4
5
6
7
8
9
Zn
No
Zn
No
0.22
None
22.47
33.3
None
1.8
9.7
8.7
9.3
None
None
3.55
None
None
3.8
Pd/C (35 mg)
Pd/C (35 mg)
Pd/C (65 mg)
Pd/C (65 mg)
Pd/C (65 mg)
CuO (100 mg)
c
Zn
7.1
7.6
c
Al
None
None
None
None
None
None
None
None
None
None
c
Fe
Zn
Zn
Zn
Ni
2
O
3
d
(100 mg)
Fig. 1 Effect of the reaction time, temperature, the amount of Pd/C, Zn
Pd/C (35 mg)
ꢀ
and glucose on the yield of 1,2-akanediols (250 C, 30 min, 1.11 mmol
a
ꢀ
Typical reaction conditions: 200 mg (1.11 mmol) glucose, 450 mg (6.9 glucose, 6.9 mmol Zn for (a); 250 C, 30 min, 1.11 mmol glucose, 65 mg,
ꢀ
mmol) Zn, 35 mg (0.016 mmol) Pd/C, water lling: 50%, 250 C and 30
min. EG and 1,2-PG, and 1,2-BD are abbreviations of ethylene glycol,
1
mmol) Zn and 65 mg (0.03 mmol) Pd/C. The Pd/C was reused. The
conversion of glucose is near to 100%.
ꢀ
0
.03 mmol Pd/C, for (b); 250 C, 30 min, 65 mg, 0.03 mmol Pd/C, 9
b
mmol Zn for (c); 1.11 mmol glucose, 65 mg, 0.03 mmol Pd/C, 9 mmol
Zn, 30 min for (d); 65 mg, 0.03 mmol Pd/C, 1.11 mmol glucose, 9 mmol
c
,2-propylene glycol and 1,2-butanediol respectively. 588 mg (9
d
e
ꢀ
Zn, 250 C for (e)). The conversion of glucose is near to 100%.
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usually limited to a low concentration, such as 0.25 wt% (ref. 8)
with 14.1% yield of 1,2-propnediol and 1 wt% (ref. 27) with 25.6%
yield of 1,2-PD. For an industrial application, a high initial
concentration of glucose is desired. Thus, we examined the effect
of the initial concentration of glucose. As a result, the yield of 1,2-
PD increased with the increase in the initial amount of glucose
and reached a climax when the concentration of glucose got up to
6
.6 wt% (see Fig. 1(c)), which is much higher than that reported
8,27
previously. Further increase in the initial glucose concentra-
tion led to decrease in the yield, which could be due to the
polymerization of glucose as a competitive side reaction.
Finally, the effects of the temperature and time on the yield of
1
,2-PD were investigated (Fig. 1(d) and (e)). The yield of 1,2-PD
ꢀ
greatly increased when the temperature increased from 230 C to
ꢀ
250 C (Fig. 1(d)). Then, the yield of 1,2-PD dropped slightly and
remained nearly constant when the reaction temperature further
ꢀ
ꢀ
increased to 300 C. The observed decrease at over 250 C might
result from the further decomposition of 1,2-PD. The time prole
indicated that an increase in the reaction time from 20 min to 30
min led to a great increase in the yield of 1,2-PD (Fig. 1(e)),
however, a longer reaction time than 30 min led to a decrease in
the 1,2-PD yield slightly, which might be due to the decompo-
sition of 1,2-PD. Similarly, EG and 1,2-BD were also detected and
analyzed quantitatively at all temperatures and reaction times.
As shown in Fig. 1(d) and (e), all yields were very low and did not
change a lot with the change of temperature and time.
To investigate the reaction pathways, we examined the inter-
mediate products and their distribution at different time. As
showed in Fig. SI-2,† product within 2 min reactions detected by
GC-MS was mainly acetol. With increasing the reaction time, 1,2-
PD, EG and 1,2-BD became the main products. The products
analyzed by HPLC showed that fructose formed as an interme-
diate product (see Fig. SI-4†). Then, the variation of the main
products with the reaction time was examined. As shown in
Fig. 2(a), the amount of glucose (I) sharply decreased, while
fructose (II) increased from 20 s to 40 s, indicating that the iso-
merisation of glucose to fructose occurred mainly at the begin-
ning of the reaction. Aer 40 s, fructose (II) decreased, while
acetol (V) gradually increased, suggesting that fructose was
further converted into acetol. Aer 2 min, acetol decreased
gradually (Fig. 2(b)), and the amount of 1,2-PD (VI) greatly
increased, indicating that acetol further was converted into 1,2-
PD nally. In addition, EG and 1,2-BD were also detected as by-
products, and no signicant change in their concentrations was
observed with the change in the reaction time. In the conversion
of glucose to 1,2-PD, a reaction pathway (including isomerisation
of glucose, cleavage of fructose by the retro-aldol reaction, and
hydrogenation of acetol) has been proposed. And dihydroxyace-
tone (IV) and glyceraldehydes (III) are considered to be interme-
diates via the cleavage of fructose by the retro-aldol reaction of
Fig. 2 Products distribution from glucose transformation (a) 20 s to 2
min; (b) 30 s to 10 min over 35 mg 5% Pd/C, 6.9 mmol Zn at 250 C.
ꢀ
which then undergoes the retro-aldol reaction to dihydroxyac-
etone and glyceraldehydes with the cleavage of C–C bond. Then,
the dihydroxyacetone and glyceraldehydes are reduced to ace-
tol. Finally, the acetol is further reduced to 1,2-PD.
Aer proposing the reaction pathway, we investigated catalytic
activity of Pd/C as well as ZnO in different stages from glucose to
1,2-PD as shown in Scheme 1, respectively. Catalytic activity of
ZnO was examined because ZnO is formed when using Zn as a
reductant for producing hydrogen. Pd/C was rst examined in the
rst stage reaction (the isomerisation of glucose to fructose). As
shown in Table 2, 25.3% fructose was achieved in the presence of
Pd/C (entry 1), while only 13.4% fructose was produced in the
absence of Pd/C (entry 2). Meanwhile, the remaining glucose
(39.7%) in the presence of Pd/C was much lower than that (74%)
in the absence of Pd/C. Thus, it is obvious that Pd/C catalyzed not
only the isomerisation of glucose to fructose but also the
7,9
fructose. However, dihydroxyacetone (IV) and glyceraldehydes
III) were not detected in this study, probably due to their rapid
(
hydrogenation to acetol under hydrothermal conditions.
Based on the detected intermediate products and their
distribution with the change in reaction time, a reaction
pathway from glucose to 1,2-PD is proposed as shown in
Scheme 1 Proposed reaction pathway for the conversion of glucose
Scheme 1. At the beginning, glucose isomerizes to fructose, to 1,2-PD.
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decomposition of glucose. Then, the experiments with the and ZnO was conducted. The yield of acetol with gaseous
addition of ZnO were conducted to test whether ZnO formed hydrogen in the presence of ZnO and Pd/C was 8.3% (Table 2,
plays a catalyst role in the isomerisation of glucose to fructose. entry 11), which was lower than the yield (13.4%) with Zn and Pd/
Compared to the blank experiment, in which the yields of fruc- C. These results show that the activity of the in situ-formed
tose and glucose were 13.4% and 74%, respectively, 32.6% fruc- hydrogen is much higher than that of gaseous hydrogen.
tose was obtained and 63.9% glucose was remaining (Table 2,
As for the last step (from acetol to 1,2-PD), acetol was used as
entry 3), which shows that the presence of ZnO greatly acceler- a feedstock. As shown in Table 3, the yield of 1,2-PD was as high
ated the isomerisation of glucose to fructose; however, ZnO has as 98% when using Zn and Pd/C (entry 1), while the yield of 1,2-
no signicant effect on the decomposition of glucose. Even the PD was only 18.9% in the absence of Pd/C (entry 2). Thus, Pd/C
amount of ZnO was decreased to 27 mg, 0.33 mmol (30% of the could catalyze the reduction of acetol to 1,2-PD. Further, reac-
amount of glucose), the catalytic effect was observed (Table 2, tions with gaseous hydrogen were also examined to test the
entry 4). Further, the effect of reaction time on the yield of fruc- difference between the gaseous hydrogen and the in situ-formed
tose from glucose in the presence of ZnO was investigated to hydrogen. As a result, the yield of 1,2-PD from acetol was 40.2%
further examine the catalytic activity of ZnO in the isomerisation with gaseous hydrogen in the presence of ZnO (Table 3, entry 3)
of glucose into fructose. The yield of fructose gradually increased and 55% even aer 2 h (see Fig. SI-6†). Further, an experiment
in the rst 50 s, and then decreased, while glucose decreased for without ZnO was also conducted. As a result, only 4.1% of 1,2-
all the reaction time (see Fig. SI-7†), which further conrms the PD was achieved (Table 3, entry 4), suggesting that ZnO acts as a
catalytic activity of ZnO in the isomerisation of glucose into catalyst in the reduction of acetol to 1,2-PD. An experiment only
fructose. Thus, it is clear that both Pd/C and ZnO catalyze the with ZnO provided 9.8% yield of 1,2-PD. From these results,
isomerisation of glucose to fructose.
For the second stage of the reaction (from fructose to acetol), acetol to 1,2-PD. Finally, the effect of gaseous hydrogen was also
the possible catalytic roles of Zn, ZnO, ZnCl and Pd/C were investigated on the yield of 1,2-PD with glucose as a feedstock.
investigated in the C–C cleavage of fructose and the reduction of The yield of 1,2-PD was only 2.9% (Table 3, entry 6).
acetol, respectively. The acetol yield with Zn (4.7%) or ZnO According to discussion above and the reaction pathway
4.2%) was clearly higher than that with Pd/C (2.5%) or with showed in Scheme 1, a more detailed reaction pathway with
ZnCl (2.5%) or without any additive (2.6%) (Table 2, entry 5–9), catalysts can be proposed in Scheme 2.
ZnO and Pd/C act a synergetic catalytic role in the reduction of
2
(
2
indicating that ZnO act as a catalyst in the selective cleavage of
In order to gure out the key step of the whole reactions for
C–C in fructose to dihydroxyacetone and glyceraldehydes. the selectivity of 1,2-PD, the yields of 1,2-PD from fructose and
However, the addition of Pd/C and Zn greatly improved the yield glucose were compared. The yield of 1,2-PD from fructose
of acetol (Table 2, entry 10) and 13.5% yield of acetol could be (35.5%) was slightly higher than the yield from glucose (Table 3,
achieved, which was much higher than others. Thus, it is entry 7), indicating that there is no signicant difference
obvious that ZnO can efficiently catalyze the selective cleavage with glucose and fructose as a feedstock. In other word, the
of C–C, and both of Pd/C and ZnO can catalyze the reduction of glucose can be converted into fructose completely and the yield
dihydroxyacetone and glyceraldehydes to acetol.
of 1,2-PD was not limited by the isomerisation of glucose. For
The in situ hydrogen produced in water with Zn may be the reaction with acetol as a feedstock, surprisingly, the yield of
different from the gaseous hydrogen (H ). To test this assump- 1,2-PD was quite high, up to 98% (see Table 3, entry 1), sug-
2
tion, a reaction by the replacement of Zn with gaseous hydrogen gesting that the almost acetol produced could be converted into
1,2-propandiol. Thus, the reduction of fructose to acetol deter-
mines the selectivity of 1,2-PD. If the selectivity of fructose to
Table 2 Glucose, fructose and acetol distribution over different
a
additives
Table 3 Yields of 1,2-PD from different reactants with different
a
Yield (%)
catalysts
Entry Feedstock Additive
Glucose Fructose Acetol
Entry Reactant Reductant Catalyst
Yield (%)
d
1
2
3
4
5
6
7
8
9
1
1
Glucose
Glucose
Glucose
Glucose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Pd/C
39.7
74
25.3
13.4
32.6
18.7
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
4.7
4.5
2.5
2.5
2.8
13.5
8.3
1
2
3
Acetol
Zn
Zn
5% Pd/C
No
98
18.9
40.2
Blank
Acetolc
b
ZnOe
63.9
81.2
ND
ND
ND
ND
ND
ND
ND
Acetol
H
2
ZnO (6.9 mmol) + 5%
Pd/C (35 mg)
5% Pd/C (35 mg)
ZnO (6.9 mmol)
ZnO (6.9 mmol) + 5%Pd/C
ZnO
Zn
ZnO
c
4
5
6
Acetolc
H
2
H
2
H
2
4.1
9.8
2.9
b
Acetol
c
Pd/C
ZnCl
Blank
Pd/C + Zn
ZnO + Pd/C + H
Glucose
2
(35 mg)
b
7
a
Fructose
Zn
5% Pd/C
35.5
0
1
c
Typical reaction conditions: 1.11 mmol reactant, 6.9 mmol Zn, 35 mg,
.016 mmol Pd/C, water lling: 50%, 250 C and 30 min. The
2
ꢀ
b
0
a
Reaction condition: Zn or ZnCl
2
: 6.9 mmol; Pd/C: 35 mg, 0.016 mmol; optimized condition: 1.11 mmol reactant, 9 mmol Zn and 65 mg, 0.03
O: 2.85 ml; 250 C; 60 s. ZnO: 1.38 mmol; 30 s. mmol Pd/C, water lling: 50%, 250 C and 30 min. 6 MPa H was
was added. ND: not determined. ZnO: 0.33 mmol; 30 s.
ꢀ
b
ꢀ
c
glucose: 1.11 mmol; H
2
2
c
d
e
6
MPa H
2
added.
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Notes and references
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Scheme 2 Proposed reaction pathway with catalysts for the conver-
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2
2
acetol could be improved, then a higher yield of 1,2-PD should
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possible side reactions were provided (see Scheme SI-1†). More-
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We have demonstrated for the rst time that the conversion of
glucose to 1,2-alkanediols can be realized by water splitting with
Zn and Pd/C. Not only did Zn provide the active hydrogen by
water splitting, but also the formed ZnO act as a catalyst,
especially for the C–C cleavage of fructose. Pd/C and ZnO
synergistically catalyze the isomerisation of glucose and the
reduction of acetol. The present study is helpful to provide a
promising method for efficiently converting carbohydrate to
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The authors thank the nancial support of the National Natural
Science Foundation of China (no. 21277091 & no. 51472159),
the State Key Program of National Natural Science Foundation
of China (no. 21436007), Key Basic Research Projects of Science,
Technology Commission of Shanghai (no. 14JC1403100) and
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gratefully acknowledge nancial support from the state key
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