Published on the web May 26, 2012
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Preparation of Er2O3 Nanorod Catalyst without Using Organic Additive
and Its Application to Catalytic Dehydration of 1,4-Butanediol
Fumiya Sato, Yasuhiro Yamada, and Satoshi Sato*
Graduate School of Engineering, Chiba University, 1-33 Yayoi, Inage-ku, Chiba 263-8522
(Received March 5, 2012; CL-120188; E-mail: satoshi@faculty.chiba-u.jp)
filtered, washed, dried at 110 °C for 12 h, and calcined at 400 °C
for 3 h. Here, commercial Er2O3 is named as “CM-(calcination
temperature (°C)),” and the prepared Er2O3 is named as “HT-(HT
temperature (°C))-(HT time (h)).”
Specific surface area (SA) of the sample was calculated by
the Brunauer-Emmett-Teller (BET) method using the N2 adsorp-
tion isotherm at ¹196 °C. Scanning electron microscope (SEM)
and high-resolution transmission electron microscope (TEM)
images were taken on a JEOL JSM-6510 microscope operated at
20-30 kV and on a Hitachi HF-2200 microscope operated at
200 kV, respectively.
Er2O3 nanorods were successfully prepared with hydro-
thermal treatment without using organic additives such as
surfactant, fatty acid, or alcohol. Er2O3 nanorods were obtained
under high temperature and/or long reaction times. Er2O3
nanorods mainly exposed {440} and {400} facets on the surface.
Er2O3 nanorods showed excellent catalytic activity compared to
commercial Er2O3 nanoparticles in the dehydration of 1,4-
butanediol to produce 3-buten-1-ol.
It is well known that rare earth oxides (REOs) with cubic
phase, such as CeO2 and Er2O3, consist of ordinary spherical or
octahedral nanocrystals, which are usually called nanoparticles.
Several groups have recently prepared unusually shaped CeO2
nanocrystals such as nanorods,1-3 nanocubes,2,4 nanoplates,3
triangler microplates,5 nanotubes,6 and nanotadpoles7 by hydro-
thermal (HT) treatment or solvothermal methods. These nano-
crystals expose specific crystal facets on the surface. For example,
CeO2 nanorod mainly exposes both {220} and {200} facets on
the surface and CeO2 nanocube exposes only {200} facet,
whereas CeO2 nanoparticles mainly expose {111} facet.1,2,4 In the
oxidation of carbon monoxide, Au deposited on CeO2 nanorod is
more active than Au on CeO2 nanoparticle.8 Nguyen et al.
prepared Er2O3 nanorods and nanocrystals with several shapes via
solvothermal reaction in water, ethanol, and decanoic acid.9 Other
REO nanorods are also prepared with organic additives.10 There is
only one report on CeO2 nanorods prepared without organic
substance but with sodium hydroxide.2 Unfortunately, organic
additives and residual metal cations often work as catalytic
poison. It is desired that oxide catalysts are prepared without
organic additives and metal-containing bases.
Vapor-phase catalytic dehydration of 1,4-butanediol to
produce 3-buten-1-ol was performed at 350 °C in a fixed-bed
down-flow reactor under atmospheric pressure of N2 at a flow rate
of 30 cm3 min¹1. After 0.3 g of catalyst was preheated at 400 °C
for 1 h, 1,4-butanediol was fed into the reactor at a liquid flow rate
of 1.8 cm3 min¹1. A reaction mixture recovered every hour was
analyzed by gas chromatography (GC-2014, Shimadzu, Japan)
with a 30-m capillary column (Rtx-Wax, RESTEK, USA).
SEM images in Figure 1 show changes in shape of Er2O3
prepared by hydrothermal synthesis at 150 °C as HT time
increases. In the images, nanoparticles were first formed
(Figure 1a) and then they were converted to nanorods. The
average length and width of Er2O3 nanorods were increased from
0.8 © 0.2 to 1.6 ¯m © 0.3 ¯m with increasing HT time from 24 to
48 h. The same behavior was observed at HT temperature of
200 °C. It was found neither organic additives nor organic
solvents were essential to prepare Er2O3 nanorods.
Figure 2 shows TEM image of HT-200-24. The Er2O3
nanorod exposed {440} and {400} facets on the surface parallel
to the longitudinal edge. However, it was not clear that {222}
facet was exposed. The orientation of crystal facets on the surface
is in good harmony with CeO2 nanorods reported previously.1,2
Several SEM and TEM images of Er2O3 prepared under HT
conditions are displayed in Figure S1.12
In our previous work,11 1,4-butanediol was dehydrated to
3-buten-1-ol with selectivity higher than 90% over commercial
Er2O3 nanoparticles, and it was speculated that active sites of this
reaction exist on {222} facet. Much more data, however, are
required to discuss active crystal facets on the catalysis. The
purpose of this work is to prepare Er2O3 nanorods without organic
additives and to investigate catalytic activity of Er2O3 nanorods in
order to ascertain whether the active sites exist on {440} and
{400} facets.
Commercial Er2O3 nanoparticles, supplied by Kanto Chemi-
cal Co., Ltd., Japan, were calcined at 500, 650, 800, and 1000 °C,
which have specific surface areas of 33.5, 26.8, 21.5, and
13.6 m2 g¹1, respectively. Er2O3 nanoparticle or nanorod catalyst
was prepared with a HT method. Er(NO3)3¢5H2O (4.64 g, as 2.0 g
of Er2O3, Sigma-Aldrich, USA) was dissolved in 50 mL of
distilled water. Then, the pH of the solution was adjusted to 10
with 25 wt % aqueous ammonia (Wako, Japan) with stirring. No
additives such as amine, fatty acid, or alcohol were added. The
solution was transferred into a 100-cm3 Teflon-lined autoclave.
Hydrothermal treatment was carried out at a prescribed temper-
ature for a prescribed period. The resulting precipitate was
Figure 3 summarizes morphology of HT-prepared Er2O3
nanomaterials, together with the SA values. At HT temperature
of 100 °C, Er2O3 nanoparticles were first formed after 6 h
(Figure S112). The nanoparticles were converted to nanorods after
24 h, and surface area was decreased from 18.2 to 8.5 m2 g¹1 with
increasing HT time from 24 to 48 h. However, the morphology
Figure 1. SEM images of Er2O3 prepared under HT conditions.
(a) HT-150-1; (b) HT-150-24; (c) HT-150-48.
Chem. Lett. 2012, 41, 593-594
© 2012 The Chemical Society of Japan