Studies on the conversion of glycerol to 1,2-propanediol over Ru-based catalyst under mild conditions

Article abstract of DOI:10.1016/j.cattod.2011.03.071

The effects of support in Ru-supported catalyst on the conversion of glycerol and selectivity of 1,2-propanediol (1,2-PDO) were investigated in the hydrogenolysis of glycerol. The Ru-based catalysts were prepared by solid phase crystallization and impregnation methods in order to improve 1,2-PDO selectivity. The prepared catalysts were characterized by N₂ physisorption, CO chemisorption, XRD, TPR, NH₃-TPD and TEM techniques. The catalytic hydrogenation of glycerol was investigated at 453 K, initial H₂ pressure of 2.5 MPa and 20 wt% glycerol aqueous solution for 18 h. It was found that the 5 wt% Ru-CaZnMg/Al catalyst prepared by the solid phase crystallization and impregnation methods showed higher catalytic performance than the other catalysts. The glycerol conversion and 1,2-PDO selectivity obtained were 50% and 85%, respectively. It was found that the selectivity of 1,2-PDO increased with the acidity of catalyst.

Full text of DOI:10.1016/j.cattod.2011.03.071

Catalysis Today 174 (2011) 10–16
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Catalysis Today
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Studies on the conversion of glycerol to 1,2-propanediol over Ru-based catalyst
under mild conditions
Seung-Hwan Leea, Dong Ju Moona,b,c,∗
a Clean Energy Research Center, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea
b Clean Energy & Chemical Engineering, UST, Republic of Korea
c Green School, Korea University, Seoul, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The effects of support in Ru-supported catalyst on the conversion of glycerol and selectivity of 1,2-
propanediol (1,2-PDO) were investigated in the hydrogenolysis of glycerol. The Ru-based catalysts were
prepared by solid phase crystallization and impregnation methods in order to improve 1,2-PDO selectiv-
ity. The prepared catalysts were characterized by N2 physisorption, CO chemisorption, XRD, TPR, NH3-TPD
and TEM techniques. The catalytic hydrogenation of glycerol was investigated at 453 K, initial H2 pres-
sure of 2.5 MPa and 20 wt% glycerol aqueous solution for 18 h. It was found that the 5 wt% Ru–CaZnMg/Al
catalyst prepared by the solid phase crystallization and impregnation methods showed higher catalytic
performance than the other catalysts. The glycerol conversion and 1,2-PDO selectivity obtained were 50%
and 85%, respectively. It was found that the selectivity of 1,2-PDO increased with the acidity of catalyst.
© 2011 Published by Elsevier B.V.
Received 27 October 2010
Received in revised form 15 March 2011
Accepted 26 March 2011
Available online 25 May 2011
Keywords:
1,2-Propanediol (PDO)
Glycerol
Ru
Hydrogenolysis
Hydrotalcite
1. Introduction
25 MPa and 523 K [8]. The hydrogenolysis reaction over homoge-
neous catalysts containing W and group VIII transition metals were
Catalytic conversion of renewable biomass resources, as feed-
stocks for the chemical industry, becomes more and more
important as serious energy and environmental problems are high-
lighted [1]. Glycerol is a main by-product of biodiesel production
derived from biomass such as vegetable oil and palm oil. The recent
rapid development of biodiesel processes has caused much concern
over the oversupply of glycerol [2]. Excessive production of glycerol
from biodiesel production could not only flood the current market
for glycerol but also negatively impact the economical aspect of
biodiesel. Finding novel processes for converting glycerol to high
value-added products can contribute to the economic of the pro-
duction of biodiesel [2–6]. One of the most attractive approaches
of converting glycerol is to produce 1,2-propanediol (1,2-PDO).
It has been reported that 1,2-PDO can be produced through the
catalytic conversion of polyols or glycerol [2]. The conversion of
glycerol to 1,2-PDO has been carried out at 15 MPa and 513–543 K
over Cu- and Zn-based catalysts promoted by sulfied Ru catalyst
[7]. The hydrogenolysis of glycerol over the catalyst containing Co,
Cu, Mn and Mo and some inorganic polyacid was investigated at
studied at 32 MPa and 473 K [9].
Recently, hydrogenolysis of glycerol over Cu-based catalysts
such as Raney Cu, Cu/C, and Cu-Pt and Cu-Ru bimetallic catalysts
were investigated in mild conditions under the reaction pressure
of less than 5 MPa and temperature of less than 473 K [10–13].
Dasari et al. reported that 54.8% of glycerol conversion and 85.0% of
1,2-PDO selectivity were achieved on a copper-chromite catalyst
at 473 K and 1.4 MPa [14]. Guo et al. reported that 49.6% of glyc-
erol conversion and 96.0% of 1,2-PDO selectivity were achieved on
a Cu/␥-Al2O3 catalyst at 493 K and 1.5 MPa [15]. These researches
about hydrogenolysis of glycerol in mild conditions showed good
1,2-PDO selectivity. However it was reported that the glycerol con-
version over Cu-based catalysts was lower than Ru-based catalysts
in hydrogenolysis of glycerol in spite of high selectivity of 1,2-PDO
[10,11].
Hydrogenolysis reactions of glycerol over activated carbon or
alumina supported Ru catalysts combined with various solid acid
catalysts such as zeolites, sulfated zirconia, rhenium, niobium and
an ion exchange resin were studied at reaction pressure over 8 MPa
[16–21]. Generally, it was also reported that the combination of
Ru-based catalyst and solid acid catalyst exhibited high catalytic
activity and 1,2-PDO selectivity in high pressure over 8 MPa and
393–473 K of temperature. However the degradation of glycerol
and the production of ethylene glycol occurred drasitically as side
reactions in the glycerol hydrogenolysis over the Ru-base catalyst
∗
Corresponding author at: Clean Energy Research Center, Korea Institute of Sci-
ence and Technology (KIST), 39-1 Hawolgok-dong, Sungbuk-gu, Seoul, 136-791,
Republic of Korea. Tel.: +82 2 958 5867; fax: +82 2 958 5809.
E-mail address: djmoon@kist.re.kr (D.J. Moon).
0920-5861/$ – see front matter © 2011 Published by Elsevier B.V.
doi:10.1016/j.cattod.2011.03.071

S.-H. Lee, D.J. Moon / Catalysis Today 174 (2011) 10–16
11
without modification of solid acid [2,10,22]. However, it has not
been reported that hydrogenolysis of glycerol over Ru-based cata-
lyst in the mild conditions.
In this work, the novel types of Ru-based catalysts prepared
by solid phase crystallization and impregnation methods without
solid acid catalyst were investigated in the hydrogenolysis of glyc-
erol under the mild conditions.
catalyst was reduced by H2 atmospheric condition at 573 K for 2 h.
The reaction was carried out under the following conditions: 453 K,
initial H2 pressure of 2.5 MPa, 20 wt% glycerol aqueous solution of
50 ml, reduced catalyst of 0.3 g and reaction time of 18 h. After being
purged by Ar and followed H2 for 2 h and filled by H2 to 2.5 MPa at
room temperature, then the reactor was heated to the desired tem-
perature. H2 pressure was increased to about 4 MPa and slightly
decreased during the reaction. After the reaction, products were
analyzed by two gas chromatographs to measure glycerol conver-
sion and selectivity of each products and 1,2-PDO yields. The liquid
products were analyzed by FID GC (Agilent 7680A) equipped with
INNOWAXTM capillary column. The gas product was analyzed by
TCD GC (Agilent 6890N) equipped with CARBOSHPERETM packed
column. The definition of glycerol conversion, selectivity of prod-
ucts and yields of 1,2-PDO are as followed Eqs. (1)–(3):
2. Experimental
2.1. Catalyst preparation
The hydrotalcite-like catalysts were prepared by a solid phase
crystallization method with some modification [21,23–28]. First,
an aqueous ammonium carbonate solution was added to a nitrate
solution of Mg and Al. A pH of the slurry was adjusted by ammo-
nia water to the range of 9–10, then stirred in the atmospheric
condition for 2 h. Next, the precipitate was introduced to 100 ml
hydrothermal reactor and raised temperature to 433 K, and then
maintained for 5 h. The precipitate was filtered, washed and then
dried at 433 K for overnight. Dried catalyst was calcined at 823 K for
5 h, crushed and then meshed. Ru precursor (Ru(NO)(NO3)3, Alfa
Aesar Co.) was dissolved in a de-ionized water and the Ru precur-
sor solution was loaded on the calcined hydrotalcite-like material
and calcined at 723 K for 5 h. In the case of Ca and Zn modified
hydrotalcite-like catalyst, Ca and Zn nitrate solution was added
before the addition of ammonium carbonate solution the molar
ratio of (Ca or Zn)/Mg was fixed to 0.5/5.5. Other Ru-supported
catalyst was also prepared by impregnation method. Amount of
Ru loading on the support was fixed to 5 wt%. The Ru-supported
catalyst was calcined at 723 K for 5 h.
glycerol conversion (%)
amount of glycerol mole converted
total amount of glycerol mole in the reactor
=
× 100
(1)
(2)
(3)
i
selectivity (%)
amount of glycerol mole converted to
i
=
× 100
amount of glycerol mole converted
1, 2-PDO yield (%)
(glycerol conversion (%)) × (1, 2-PDO selectivity (%))
=
100
where i: 1,2-PDO, ethylene glycol, acetol, methanol, etc.
3. Results and discussion
2.2. Catalyst characterization
BET surface area of the catalysts was determined by N2 adsorp-
tion at 77 K, using the multipoint BET analysis method, with
Moonsorption system (Moonsorp-II, KIST, Korea). Prior to the mea-
surements, the samples were pretreated in a vacuum condition at
573 K for overnight. X-ray Diffraction (XRD) patterns were obtained
using a Shimadzu XRD-6000 diffractometer with Cu K␣ radiation.
The Scherrer equation was used to calculate the metallic crystal size
from the XRD patterns. CO pulse chemisorption, TPR and NH3-TPD
were carried out by Micromeritics AutoChem 2060 system to deter-
mine a metallic particle size, dispersion and reduction states of Ru
and acidity of the catalysts. The physical and chemical properties
of prepared catalysts are summarized in Table 1.
3.1. Catalyst characterization
The crystalline phases of the prepared catalysts before and after
the reaction were investigated by X-ray diffraction. Fig. 1 shows
the XRD patterns of Ru-supported hydrotalcite-like or Ca-Zn modi-
fied hydrotalcite-like catalysts before (a) and after (b) the reaction.
This crystalline pattern before reaction showed various patterns.
MgAl2O4, MgO and RuO2 crystalline phase were mainly found in
Ru–Mg/Al catalyst. CaO, MgAl2O4 and RuO2 showed in Ru–CaMg/Al
catalyst. ZnO, MgAl2O4 and RuO2 were found in Zn–Mg/Al and
MgAl2O4 and RuO2 phases were also found in Ru–CaZnMg/Al cat-
alyst. It showed that hydrotalcite-based catalyst was changed to
metal solid solution at 723 K and supported Ru was exposed on the
catalyst during calcination. It was noted that the Layered Double
Hydroxide (LDH; such as hydrotalcite) was found in the catalysts.
This LDH structure was formed due to the intrinsic properties of
hydrotalcite-like material called ‘memory effects’, recovered its
hydrotalcite structure when the calcined catalyst contacts with
2.3. Catalytic hydrogenolysis of glycerol
The conversion of glycerol to propanediol was carried out in an
autoclave reactor system (Parr. Co.) with a 250 ml stainless steel
reactor and stirred speed of 200–400 rpm. Prior to the reaction, the
Table 1
The physical and chemical properties of prepared catalysts.
Catalyst
Ru loading
(wt%)
BET S.A.
(m2/g)
RuO2 size
(nm)a
Ru particle
size (nm)
Ru metallic
S.A. (m2/g)
Ru dispersion
(%)
Acidity
(␮mol NH3/g)
Weak
Strong
Ru–Mg/Al
4.92
4.93
4.88
4.90
5.01
145.4
121.2
92.4
129.4
165.3
23
24
20
23
33
14.4
14.1
15.2
13.7
38.5
1.66
1.64
1.68
1.75
0.67
8.2
8.8
7.9
9.6
2.2
1.14
0.68
0.75
3.41
14.49
43.5
55.4
62.3
113.7
1.71
Ru–CaMg/Al
Ru–ZnMg/Al
Ru–CaZnMg/Al
b
Ru/␥-Al2O3
a
Particle size of RuO2 was estimated from XRD data.
Catalyst was prepared by impregnation method.
b

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S.-H. Lee, D.J. Moon / Catalysis Today 174 (2011) 10–16
Fig. 2. TPR profiles of the prepared catalysts: (a) Ru/␥-Al2O3, (b) Ru–Mg/Al, (c)
Ru–CaMg/Al, (d) Ru–ZnMg/Al and (e) Ru–CaZnMg/Al.
Fig. 1. XRD patterns of the prepared catalysts (A) before and (B) after the reaction:
(a) Ru–Mg/Al, (b) Ru–CaMg/Al, (c) Ru–ZnMg/Al, (d) Ru–CaZnMg/Al and (e) Ru/␥-
Al2O3 (ꢀ: Hydrotalcite (Mg4Al2(OH)12(CO3)), ꢁ: RuO2, ꢂ: CaO, ᭹: MgO, s: spinel
(MgAl2O4), ꢀ: ␥-Al2O3, z: ZnO, X: Al3Ca0.5MgO6).
moisture and carbonate ions [24]. The crystalline patterns of the
hydrotalcite-like catalyst after the 1,2-PDO synthesis were differ-
ent a lot. A LDH peak was mainly found in the used catalysts
resulted from the ‘memory effects’ by contacting the catalyst on
water during reaction. A little of Al3Ca0.5MgO6 solid solution peak
and ZnO peak were found in the used Ru–CaMg/Al, Zn–Mg/Al and
Ru–CaZnMg/Al catalysts. XRD patterns of metallic Ru was found in
the used catalysts but the Ru peak intensity was too low.
Fig. 2 shows TPR profiles of the prepared catalysts before PDO
synthesis. All catalysts show one strong peak and shoulder peak at
the temperature range of 450–525 K. The main peak corresponds
to the reduction of RuO2 to metallic Ru. It was reported that unsup-
Fig. 3. NH3-TPD profiles of the prepared catalyst: (a) Ru/␥-Al2O3, (b) Ru–Mg/Al, (c)
Ru–CaMg/Al, (d) Ru–ZnMg/Al and (e) Ru–CaZnMg/Al.

S.-H. Lee, D.J. Moon / Catalysis Today 174 (2011) 10–16
13
Fig. 4. TEM images and particle size distribution of the prepared catalysts: (a) Ru–Mg/Al, (b) Ru–CaMg/Al and (c) Ru–Zn/MgAl and (d) Ru–CaZnMg/Al.

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S.-H. Lee, D.J. Moon / Catalysis Today 174 (2011) 10–16
Fig. 5. EDS results on Ru–CaZnMg/Al catalysts (a) before and (b) after the reaction.
Table 2
Catalytic performance on glycerol hydrogenolysis over the prepared catalysts.**
Catalyst
Glycerol conversion (%)
Selectivity (%)
1,2-PDO
1,2-PDO yield (%)
EG
2-PO
CH4
Othera
Ru–Mg/Al
47.3
56.7
55.6
58.5
45.6
61.1
78.4
75.1
85.5
59.2
20.3
13.2
14.9
6.6
7.5
2.6
3.8
1.9
5.4
10.0
5.6
5.9
5.6
11.1
1.1
0.2
0.3
0.4
0.2
28.9
44.4
41.8
50.0
27.0
Ru–CaMg/Al
Ru–ZnMg/Al
Ru–CaZnMg/Al
Ru/␥-Al2O3
22.3
**
Reaction conditions: H2 pressure of 2.5 MPa, 453 K of reaction temperature, catalyst of 0.3 g, 20 wt% glycerol solution of 50 ml, reaction time of 18 h and stirring rate of
200–400 rpm.
a
Sum of selectivities of acetol, 1,3-PDO, 1-PO (propanol), methanol, ethanol, CO and CO2.
ported RuO2 has been reported to reduce in a single main peak at
490 K [29]. It was considered that the main reduction peak is deter-
mined by the reduction of RuO2 to Ru, and the shoulder peak has
been related to the reduction of RuOx to RuO2 [30,31]. However, it
was found that the shoulder peak related to the reduction of RuOx
to RuO2 was not investigated in the TPR profile of Ru–CaZnMg/Al
catalyst. It was considered that the fraction of peak related to
the reduction of RuOx to RuO2 was less on this catalyst because
the asymmetry of TPR peak over Ru–CaZnMg/Al catalyst was still
observed.
Table 3
The effects of reaction temperature on selectivities in the hydrogenolysis of glycerol over Ru–CaZnMg/Al catalyst.**
Temperature (K)
Glycerol conversion (%)
Selectivity (%)
1,2-PDO
1,2-PDO yield (%)
1,3-PDO
15.4
5.3
1.5
–
EG
2-PO
10.3
7.4
4.2
0.8
–
CH4
Othera
393
413
433
453
473
493
28.5
37.7
51.3
57.8
61.9
63.1
45.3
58.1
71.8
85.4
70.3
61.5
10.6
9.5
8.7
6.6
17.4
23.7
8.2
9.3
9.7
5.6
11.5
14.3
10.2
10.4
4.1
1.6
0.8
12.9
21.9
36.8
49.4
43.5
38.8
–
–
–
0.5
**
Reaction conditions: H2 pressure of 2.5 MPa, 453 K of reaction temperature, catalyst of 0.3 g, 20 wt% glycerol solution of 50 ml, reaction time of 18 h and stirring rate of
200–400 rpm.
a
Sum of selectivities of acetol, 1-PO, methanol, ethanol, CO and CO2.

S.-H. Lee, D.J. Moon / Catalysis Today 174 (2011) 10–16
15
Fig. 3 shows NH3-TPD profiles of the prepared catalysts. The
acidity of the prepared catalysts is summarized in Table 1. The
NH3-TPD profiles of Ru supported hydrotalcite-based catalysts
showed a broad weak desorption peak in the temperature range
of 380–450 K and strong desorption peak at 650–750 K. The high
temperature peak indicates that strong acid site exists on the cata-
lysts. It was noted that the Ru/␥-Al2O3 catalyst showed the lowest
acidity because Ru active species could be interacted and covered
with the strong acid site on ␥-Al2O3 more than hydrotalcite-based
catalysts. It was found that the NH3-TPD profiles of Ru–CaZnMg/Al
showed valley peak pattern range from 630 to 750 K, and more
strong acid site distribution than the other catalysts. It was inter-
preted that the second peak (about 650 K) corresponded to NH3
spillover of the catalyst and the third peak (about 740 K) associ-
ated with NH3 decomposition on the active metal of the catalyst in
higher temperature [32,33].
Fig. 4(a) exhibits the TEM images of Ru–Mg/Al catalyst. It was
found that particle size of Ru–Mg/Al catalyst was mainly distributed
in 50–100 nm and the small size of Ru particle less than 50 nm
were not found in a particle size distribution data based on the TEM
image. Fig. 4(b) shows the TEM images of Ru–Ca/MaAl catalyst. It
was found that the particle size of Ru–CaMg/Al catalyst was smaller
than Ru–Mg/Al catalyst and its particle size distribution was about
20–50 nm. It was considered that the smaller particle size of Ru
was related to increase in glycerol conversion during hydrogenol-
ysis. Fig. 4(c) shows the TEM images of Ru–ZnMg/Al catalyst. It
was found that distribution of the particle size of Ru–ZnMg/Al cat-
alyst was about 40–100 nm. A bit of the small Ru particles were
showed on the surface of catalyst. Fig. 4(d) exhibits a TEM image of
Ru–CaZnMg/Al catalyst. It was found that very small size of black-
colored spherical-like shape particles about 5–10 nm were formed
and exposed on the catalyst. It was found that the particle size of
Ru was shifted to small size with the addition of Ca to Ru–Mg/Al.
Fig. 5 illustrates the EDS results before and after the reaction of
the Ru–CaZnMg/Al catalyst. It was found that elements on black-
colored spherical-like shape particles in the Ru–CaZnMg/Al catalyst
was mostly Ru and some Mg and Al were detected. The results of
TEM and EDS can be associated with Ru metallic particle size and
dispersion by CO chemisorption as summerized in Table 1. Based
on the results of particle size distribution and Ru particle size sum-
marized in Table 1, it was considered that the smaller Ru particle on
the catalyst acted as catalytic activity site during the hydrogenolysis
of glycerol. It was found that the glycerol conversion and 1,2-PDO
selectivity were increased with decreasing Ru metallic particle size
and increasing Ru dispersion. It was considered that the particle
size of the catalyst after the hydrogenolysis reaction was increased
by the sintering of Ru particles.
of 58.5%, 1,2-PDO selectivity of 85.5% and 1,2-PDO yield of 50.0%.
Ru supported hydrotalcite-like catalyst showed higher Ru metal-
lic surface area and dispersion than Ru/␥-Al2O3 catalyst as shown
in Table 1. With increasing Ru surface area and dispersion on the
catalyst, the glycerol conversion was slightly increased. It was con-
sidered that the catalytic activity in glycerol hydrogenolysis was
related to the dispersion of Ru.
Table 3 shows the effect of reaction temperature in the
hydrogenolysis of glycerol over Ru–CaZnMg/Al catalyst. It was
found that the glycerol conversion over Ru–CaZnMg/Al catalyst
was increased with increasing the reaction temperature from 393 K
to 493 K. The 1,2-PDO selectivity and yield were decreased when
reaction temperature was more than 453 K.
The correlation between 1,2-PDO selectivity and acidity of the
catalyst obtained by NH3-TPD analysis also exhibited in Table 2. It
was found that 1,2-PDO selectivity was increased with increasing
the acidity. LDH or hydrotalcite was known as weak base catalyst
[23–25]. It was considered that catalyst acidity and 1,2-PDO selec-
tivity was increased because small amount of Zn and Ca acted as
Lewis acid site over the LDH or hydrotalcite in the glycerol dehydro-
genation or carboxylation [2,34]. It was also found that the acidity of
catalyst was drastically increased when both Ca and Zn were added
at the same time which results in increasing glycerol conversion
and 1,2-PDO selectivity.
4. Conclusions
The Ca and Zn modified Ru-based hydrotalcite-like catalyst
prepared by solid phase crystallization and impregnation meth-
ods showed higher catalytic activity and 1,2-PDO selectivity than
the other catalysts. The glycerol conversion and 1,2-PDO selectiv-
ity were obtained about 50% and 85%, respectively. Ru supported
hydrotalcite-based catalysts were showed higher acidity and Ru
dispersion than Ru/␥-Al2O3 catalyst. It was found that the glycerol
conversion and selectivity of the 1,2-PDO in glycerol hydrogenol-
ysis were mainly corresponded to Ru dispersion and the acidity
of the catalyst. The results can be interpreted that the acidity
of the catalyst plays an important role in improving 1,2-PDO
selectivity and Ru dispersion might be associated with activity,
respectively.
Acknowledgements
We appreciate the financial supports from the Ministry of
Knowledge Economy of Republic of Korea, J&K Heaters Co., Dansuk
Industry Co. and JC Chemicals Co.
3.2. Hydrogenolysis of glycerol
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