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K. Ohta et al. / Applied Catalysis A: General 517 (2016) 73–80
into the reactor. Amino alcohols were dehydrated at temperatures
HO
NH2
NH2
between 300 and 450 ◦C. Prior to the reaction, the catalyst was
preheated in the flow reactor in a carrier gas at the same temper-
ature as the reaction temperature for 1 h. After the pretreatment,
an amino alcohol was fed through the top of the reactor at a liq-
uid feed rate of 1.71 cm3 h−1, which corresponds to 16 mmol h−1
for 5-amino-1-pentanol and W/F = 31 gcat. h mol−1 where W is cat-
alyst weight and F is a reactant feed rate, together with a carrier
gas flow of 20 cm3 min−1. An effluent mixture collected every hour
was analyzed by gas chromatography (GC-8A, Shimadzu, Japan)
with a capillary column of TC-5 (30m, GL Science Inc., Japan) over a
temperature range controlled from 70 to 280 ◦C at a heating rate
of 10 ◦C min−1. The major products in the dehydration were 4-
penten-1-amine, piperidine, tetrahydropyridine, ␦-valerolactam,
and n-pentyl amine.
REO
Scheme 1. Dehydration of 5-amino-1-pentanol to 4-penten-1-amine.
Tm(NO3)3, Yb(NO3)3, Lu(NO3)3, and Sc(NO3)3, were purchased
from Sigma-Aldrich Co., Ltd., Japan. La2O3, Pr6O11, Mg(NO3)2,
Ca(NO3)2, and Dy(NO3)3 hexahydrate were purchased from
Wako Pure Chemicals Co., Japan. 5-Amino-1-pentanol, 3-amino-
1-propanol, and 4-amino-1-butanol were purchased from Wako
Pure Chemicals Co., Japan. 6-Amino-1-hexanol aqueous solution
(70 wt.%) was purchased from Sigma-Aldrich Co., Ltd., Japan.
Except La2O3 and Pr6O11, other REOs such as CeO2, Nd2O3,
Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Y2O3, Er2O3, Tm2O3,
Yb2O3, Lu2O3, and Sc2O3 were prepared by the calcination of the
corresponding nitrate. MgO and CaO were also prepared by the
calcination of the corresponding nitrate. Monoclinic Yb2O3 was
supplied by Kanto Kagaku Co., Ltd., Japan. Three Sc2-xYbxO3(x = 0.5,
1.0, and 1.5) catalysts were supplied by Daiichi Kigenso Kagaku
Kogyo Co., Ltd., Japan [18]. Rutile TiO2 (JRC-TIO-3) and anatase TiO2
(JRC-TIO-4) were supplied by Catalyst Reference of Japan. Amor-
phous SiO2 (CARiACT Q10) was supplied by Fuji Silycia Chemical
Ltd. Monoclinic ZrO2 (RSC HP) and tetragonal ZrO2 were supplied
by Daiichi Kigenso Kagaku Kogyo Co., Ltd., Japan and Saint-Gobain,
respectively. Al2O3 (N611N) and SiO2-Al2O3 (N631L) were pur-
chased from Nikki Chemical Co., Ltd., Japan.
Since the catalytic activity is stable in the similar manner to
the previous works reported in the dehydration of diols [3–11], the
conversion of 5-amino-1-pentanol and the selectivity to each prod-
uct were averaged in the 1–5 h to evaluate the catalytic activity.
The formation rate of the corresponding unsaturated amines per
unit surface area [mmol h−1 m−2] was calculated by using the feed
rate of the reactant multiplied by the conversion and the selectivity
divided by the catalyst weight and specific surface area.
2.3. Characterization
The specific surface area (SA) of each catalyst was calculated by
the BET method using the N2 isotherm at −196 ◦C. X-ray diffraction
(XRD) patterns were recorded on an XRD7000 (Shimadzu, Japan)
using Cu Ka radiation (= 0.15 nm) to detect the crystal structure of
the samples. The tube voltage and current were 40 kV and 40 mA,
respectively.
2.2. Catalytic reaction
The dehydration of amino alcohols, such as 5-amino-1-
pentanol, 3-amino-1-propanol, 4-amino-1-butanol, and 6-amino-
1-hexanol, were carried out in a fixed-bed down flow reactor with
an inside diameter of 20 mm under the atmospheric pressure of
either N2 or H2 gas. In each test, 0.5 g of catalyst was loaded
Temperature-programmed desorption (TPD) of adsorbed CO2
was measured to estimate the basicity of the catalysts. The numbers
of basic sites were estimated from neutralization–titration curves
of diluted NaOH solution [19,20]. Prior to the CO2 adsorption, a
sample (ca. 50 mg) was preheated in a quartz tube at 500 ◦C for 1 h
under a reduced pressure. In CO2-TPD, CO2 was adsorbed on the
sample at room temperature for 72 h and evacuated for 1 h. After
no CO2 had been observed in N2 flow at room temperature, the
sample was heated from room temperature to 800 ◦C at a heating
rate of 10 ◦C min−1 in an N2 flow of 34 cm3 min−1. The desorbed
CO2 molecules, together with N2 gas, were bubbled into an electric
conductivity cell containing a dilute NaOH solution (50 cm3). The
conductivity of the solution was monitored, and the resulting con-
ductivity curve was differentiated to provide a distribution curve
of CO2 desorbed from adsorbent.
5
5
La2O3
CeO2
Pr6O11
Nd2O3
Sm2O3
Eu2O3
5
5
Gd2O3
Tb4O7
Dy2O3
Ho2O3
Y2O3
3. Results
3.1. Characterization of REOs
Er2O3
Fig. 1 shows the XRD patterns of REOs and Sc2-xYbxO3 calcined
at 800 ◦C. REO samples had different crystal structures with A-
Tm2O3
Yb2O3
, B-, C-, and CF-type [21,22]. Light REOs such as La2O3, Pr6O11
,
and Nd2O3 had a hexagonal structure of A-type. Other light REOs
such as Sm2O3 had a monoclinic structure of B-type. On the other
hand, heavy REOs such as Gd2O3, Tb4O7, Dy2O3, Ho2O3, Y2O3,
Er2O3, Tm2O3, Yb2O3, Lu2O3, Sc2O3, and Sc2-xYbxO3 (x = 0.5, 1.0,
and 1.5) [18] had a cubic bixbyite structure of C-type. Eu2O3 had an
unknown phase, and CeO2 had a cubic fluorite structure of CF-type.
The crystal phases of REOs and Sc2-xYbxO3 as well as their SA are
summarized in Table 1.
Lu2O3
Sc0.5Yb1.5O3
Sc1.0Yb1.0O3
Sc1.5Yb0.5O3
5
5
5
Sc2O3
20
30
40
50
60
70
2 theta / degree
Fig. 2 shows TPD profiles of CO2 adsorbed on the REOs. Sev-
eral desorption peaks of CO2 from light REOs, such as La2O3, CeO2,
Fig. 1. XRD profiles of REO and Sc2-xYbxO3 samples calcined at 800 ◦C.