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Chemistry Letters Vol.38, No.11 (2009)
Efficient Hydrogenation of Methyl Propionate over Boehmite-supported Ru–Pt Catalyst
Ya-Fen Zhou,1;2 Juan Wei,1 Guang-Yin Fan,1 Hai-yan Fu,1 Rui-Xiang Li,ꢀ1 Hua Chen,1 and Xian-Jun Li1
1Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University,
Chengdu, Sichuan 610064, P. R. China
2College of Chemistry and Chemical Engineering, China West Normal University, Nanchong 637002, P. R. China
(Received July 28, 2009; CL-090705; E-mail: liruixiang@scu.edu.cn)
The bimetallic catalyst Ru–Pt/AlOOH exhibited good cata-
um for 10 h. Weighed amounts of catalyst, methyl propionate,
and solvent were added to a 60-mL stainless autoclave equipped
with a magnetic stirrer and an electric temperature controller. It
was purged with H2 three times, pressurized with H2 to 5 MPa,
and then heated to 180 ꢁC with a stirring rate of 1000 rpm for
6 h. Samples were analyzed by GC-6890 (Agilent) with a FID
detector and quartz capillary column (SE-30, 30 m ꢂ 0:25 mm,
0.25 um film), and products were identified by comparison with
standard samples and GC-MS.
lytic performance in water for the hydrogenation of methyl pro-
pionate to 1-propanol. The selectivity to 1-propanol of 97.8%
was obtained with a conversion of 89.1% at 453 K, 5 MPa for
6 h. The incorporation of Pt for the improvement of the catalystic
activity was attributed to promoting the reduction of Ru3þ
to Ru0.
Alcohols are important raw materials in pharmaceutical and
chemical industries. However, most alcohols have been pro-
duced by conventional reduction with stoichiometric amounts
of metal–hydrides like LiAlH4,1 which is neither environmental-
ly compatible nor economical. So the direct hydrogenation of
carboxylic esters to the corresponding alcohols is of great impor-
tance in industrial processes. Copper-based catalysts have been
widely applied for the hydrogenation of fatty esters,2 but they
usually require high hydrogen pressure (200–300 atm) and high
temperature (200–300 ꢁC) to achieve reasonable productivity.
Therefore, many attempts have been made to develop some effi-
cient catalysts for the hydrogenation of esters to alcohols under
mild conditions. Heterogeneous bimetallic catalysts prepared
from a group VIII metal and a second metal like Sn, Re, Ge,
or W have been extensively explored.3–9 It has been found that
Ru–Sn catalysts are the most effective for the hydrogenation
of fatty esters to fatty alcohols3 as well as for the hydrogenation
of dimethyl adipate to diol.5,6 Recently, the promoting role of Sn
to Ru catalyst for the hydrogenation of ethyl lactate to 1,2-pro-
panediol has also been reported by Fan et al.7,8 In addition, the
catalytic performance of Ru–Sn/C can be further improved by
adding Pt for the hydrogenation of 1,4-cyclohexanedicarboxylic
acid to 1,4-cyclohexanedimethanol.9 In most of the reported
investigations, traditional carriers such as TiO2, ꢀ-Al2O3, SiO2,
ZrO2, and active carbon are often used. Additionally, all hydro-
genations of esters are carried out in organic solvents. Boehmite
(AlOOH) is widely used as a catalyst support,10 but there are no
reports on boehmite-supported catalysts for the hydrogenation of
esters. In the present work, we use methyl propionate as a model
compound and Ru–Pt supported on AlOOH as a catalyst to inves-
tigate this system’s hydrogenation property for esters. It exhibits
good catalytic performance in environmentally benign water.
The monometallic and bimetallic catalysts (6.3 wt %) were
prepared by impregnation and coimpregnation, respectively.
Typically, ꢀ-Al2O3 was added to an ethanol solution of RuCl3
and/or H2PtCl6 with an appropriate concentration. The slurry
was stirred overnight at room temperature. Next, the solvent
was slowly removed under vacuum. The resulting solid was
dried overnight at 120 ꢁC and calcined in air at 400 ꢁC for 4 h.
Thereafter, the sample was reduced in water with hydrogen pres-
sure of 3 MPa at 180 ꢁC for 2 h, then filtered, and dried in vacu-
X-ray diffraction (XRD) study was performed on a Rigaku
D/max-rA instrument with a Cu Kꢁ radiation and in scan range
of 10–70ꢁ. The X-ray photoelectron spectra (XPS) were record-
ed with a Kratos XSAM800 spectrometer (Mg Kꢁ radiation, op-
erating at 15 mA and 12 kV). TPR experiments were performed
on a laboratory-made apparatus. Samples were heated from 50
to 600 ꢁC at a linear rate of 10 ꢁC minꢃ1 under a flow of 5
vol % H2/N2.
The XRD pattern of Ru–Pt/AlOOH (Pt/Ru = 1/9) exhibit-
ed characteristic diffraction peaks assigned to boehmite (ꢀ-
AlOOH, JCPDS Card No. 21-1307),16 which suggested that ꢀ-
Al2O3 had been transformed into AlOOH. The peaks at 280.1
(Ru 3d5=2) and 72.5 eV (Pt 4f7=2) in XPS spectra16 of Ru–Pt/
AlOOH (Pt/Ru = 1/9) indicated that Ru and Pt existed in
Ru0 and electron deficient Ptnþ (0 < n < 2), respectively.9,11
The TPR profiles of Ru–Pt/AlOOH showed that Pt supported
on boehmite was not reduced to zero valence. When the Pt/Ru
molar ratio was lower than 1/4, the reduction temperature of
ruthenium decreased with increasing Pt loading and the reduc-
tion temperature was shifted from 215 ꢁC for the monometallic
Ru catalyst11 to 155 ꢁC for Ru–Pt (Pt/Ru = 1/4).16 When the
Pt/Ru molar ratio was beyond 1/4, the reduction of ruthenium
required a higher temperature and the reduction peak became
weaker. This suggests that an excessive addition of Pt is unfav-
orable for the reduction of ruthenium.
The effect of support on the hydrogenation of methyl propi-
onate is shown in Table 1. Among the tested catalysts, AlOOH-
supported Ru–Pt exhibited the highest conversion of methyl pro-
pionate (89.1%) and selectivity to 1-propanol (97.8%) under the
same conditions. Ru–Pt/NaY showed the lowest activity and se-
lectivity. The selectivity over Ru–Pt/ꢀ-Al2O3 was similar to that
over Ru–Pt/AlOOH, but the activity was obviously low in spite
of the fact that ꢀ-Al2O3 could be slowly transformed into
AlOOH under the hydrogenation conditions. Ru–Pt/ZrO2 and
Ru–Pt/SiO2 only gave moderate conversion. The difference of
catalytic performance on different supports can be related to
the intrinsic properties of the support. Many researchers have
revealed that AlOOH is composed of Al–O double layers that
are interconnected by hydrogen bonds between the hydroxy
groups.12 We speculate that the cooperation between the hy-
droxy groups on the surface of Ru–Pt/AlOOH and water as sol-
Copyright Ó 2009 The Chemical Society of Japan