1
274
Chemistry Letters Vol.36, No.10 (2007)
Effect of Base Additives on the Selective Hydrogenolysis of Glycerol over Ru/TiO Catalyst
2
ꢀ
Jian Feng, Jinbo Wang, Yafen Zhou, Haiyan Fu, Hua Chen, and Xianjun Li
Key Laboratory of Green Chemistry and Technology, Ministry of Education, Department of Chemistry,
Sichuan University, No. 29 Wangjiang Road, Chengdu, Sichuan 610064, P. R. China
(Received July 20, 2007; CL-070768; E-mail: scuhchen@163.com)
ꢁ
Under mild reaction conditions (170 C, 3 MPa), glycerol is
Table 1. HG catalyzed by Ru/TiO in the presence of different
2
bases
a
hydrogenolyzed to 1,2-propanediol with very high selectivity at
high conversion using Ru/TiO2 as catalyst in basic aqueous
solution. The base aids the initial dehydrogenation of glycerol
to glyceraldehyde and promotes the dehydration of glyceralde-
hyde to 2-hydroxyacrolein.
Selectivity/%b
Entry
Base
Conversion/%
1
,2-PDO
EG
1
2
3
4
5
6
7
8
—
66.3
89.6
83.4
62.2
80.1
78.0
61.3
<1:0
ꢁ
47.7
86.8
83.5
82.7
82.3
83.6
78.2
Trace
26.0
7.5
15.2
10.9
7.7
8.1
7.8
—
LiOH
NaOH
KOH
In recent years, the rapid development of biodiesel produc-
tion formed large quantities of glycerol as a by-product and the
conversion of glycerol to other high value-added products has at-
tracted great attention. Catalytic hydrogenolysis of glycerol
HG) to glycols represents a feasible, low-cost, and green meth-
odology. Here, the glycols refer to 1,2-propanediol (1,2-PDO)
and ethylene glycol (EG). Both of the diols are currently pro-
duced from petrochemical resources and are often used in anti-
freeze, paints, functional fluids, humectants, and polyester res-
ins. Although 1,3-propanediol (1,3-PDO) is also a valuable
chemical, it is not recommended to produce it by direct HG be-
c
Li2CO3
Na2CO3
K2CO3
LiOH
1
,2
d
(
a
Reaction conditions: 170 C, 3 MPa, 12 h, 5-mL glycerol
aqueous solution (20 wt %), 102-mg Ru/TiO2, 1 mmol base.
C-Based selectivity. 10-mL glycerol aqueous solution
b
c
d
(10 wt %). Without Ru/TiO .
2
mm). 1,2-PDO, 1,3-PDO, EG, 1-propanol, 2-propanol, ethanol,
methanol, and methane were analyzed. Only selectivities to
1,2-PDO and EG were discussed in this study in view of their
commercial importance and high value.
3
,4
cause of its low selectivity and yield. The HG using supported
5
–13
catalysts has been extensively studied by several groups.
For
example, the Suppes group won the AOCS glycerol innovation
award due to their work on selective HG using copper–chromite
catalyst. Tomishige and co-workers developed a metal-acid bi-
At first, the HG was performed in the presence of different
bases (see Table 1). In general, the addition of lithium or sodium
base dramatically increases the conversion of glycerol and the
selectivity to 1,2-PDO. The highest conversion of glycerol
(89.6%) and the highest selectivity to 1,2-PDO (86.8%) were
observed with LiOH (Entry 2, Table 1). Interestingly, the selec-
tivity to 1,2-PDO changed slightly in the case of all added bases,
which is due to that the selectivity to 1,2-PDO is independent of
8
functional catalyst system, which exhibited good performance in
the HG.11 However, most of the works have focused on varying
catalyst compositions and operating conditions to optimize both
glycol production rates and selectivities. Although it is generally
acknowledged that additives can significantly affect the activity
and selectivity of this reaction, little research has been done on
the effects of the base additives on the HG, and few details are
known about how these base additives affect the reaction routes.
In this communication, the HG using Ru/TiO2 as catalyst was
studied for the first time in basic aqueous solution. We found that
glycerol can be hydrogenolyzed to 1,2-propanediol with very
high selectivity at high conversion under mild conditions. The
effects of the kind and amount of the base additives were dis-
cussed in combination with a reaction mechanism.
1
0
base concentration in a certain range. However, the selectivity
to EG decreased no matter which base was added. Almost no
reaction was observed in the absence of Ru/TiO2 (Entry 8,
Table 1), indicating that the metal catalyst is necessary for the
taking place of the HG. It should be noted that using potassium
base (KOH or K2CO3) as additive resulted in similar conversion
of glycerol to the nonadditive reaction (Entries 4 and 7, Table 1).
The different influences of alkali bases on the activity indicate
that the alkali metal cations have an effect on the HG. The alkali
Ru/TiO2 (5 wt %) was prepared by impregnation technique.
TiO2 was added to an aqueous solution of RuCl3 (Johnson–
Matthey). The slurry was stirred overnight at room temperature,
þ
þ
metal cations influenced the activity in the order Li > Na
þ
>
K , which might be associated with the size of the cation. A
similar effect was also observed in the hydrogenation reactions
of ketones. However, the exact reason is not clear and needs
further studies.
ꢁ
and then heated at 80 C for 2 h. The catalyst was reduced by hy-
ꢁ
14
drogen at 5 MPa and 200 C for 8 h, followed by washing repeat-
edly with deionized water to remove chloride ions, and then
ꢁ
dried at 110 C in vacuum for 10 h. 5 mL of glycerol aqueous so-
lution (20 wt %), 102 mg of Ru/TiO2 and certain amounts of
The effect of the amount of base on the reaction was inves-
tigated using LiOH as additive, and the results are shown in
Table 2. As the amount of LiOH increased from 0 to 2.0 mmol,
the conversion of glycerol initially exhibited an increase, ulti-
mately reached a maximum at a LiOH dosage of 1.0 mmol
(Entry 4, Table 2), after which the conversion began to decrease.
The selectivity to 1,2-PDO increased gradually from 47.7 to
base additives were charged into a 60-mL autoclave. The reactor
ꢁ
was pressurized to 3 MPa with hydrogen and heated to 170 C.
After stirring at 1000 rpm for 12 h, samples were analyzed by
GC (Agilent 6890N) equipped with a flame ionization detector
and a capillary column (Supelco WAXꢀ, 30 m ꢂ 0.53 mm ꢂ 1
Copyright ꢁ 2007 The Chemical Society of Japan
Feng, Jian
