3
12
K. Pattamakomsan et al. / Catalysis Communications 11 (2010) 311–316
obtained by calcination of bayerite at 960 °C and 1200 °C, respec-
tively for 180 min.
2 3
The Pd/Al O catalysts with 0.3 wt.% Pd were prepared by incip-
ient wetness impregnation of the alumina supports using an aque-
ous solution of palladium(II)nitrate as the palladium precursor. The
catalysts were subsequently dried at 110 °C for 20 h and calcined
in air at 500 °C for 2 h.
2.2. Catalyst characterization
The XRD patterns of alumina supports were collected using an
X-ray diffractometer, SIEMENS XRD D5000, with Cu K radiation
a
with a Ni filter in 10°–80° 2h angular region. The composition of
each crystalline phase has been calculated from the calibration of
X-ray diffraction peak areas of the mixtures between each pure
phase (physically mixed). The particle size of Pd/PdO and particle
size distribution were observed using a JEOL-TEM 200CX transmis-
sion electron microscope operated at 100 kV. Acidity of the alu-
mina supports was measured by temperature program
desorption of ammonia using a Micromeritic Chemisorb 2750
Fig. 1. XRD patterns of the Al O3 supports.
2
The phase composition of alumina supports was determined based
on the peak areas of these peaks using a calibration from XRD re-
automated system. Before adsorption, the sample was pretreated
sults of the physically mixed h- and
The calculation method for determination of phase composition
in a mixed-phase Al support has also been reported previously
in other Al systems such as Al [15] and -Al [16].
The Al supports containing 100, 80, 40, and 0 wt.% of h-Al
are denoted herein as 100T0A, 80T20A, 40T60A, and 0T100A,
respectively. The physical properties of Al supports are shown
in Table 1. The average crystallite size of h-phase Al was in-
2 3
a-Al O (results not shown).
3
in high purity N
rated with 15% NH
quently flushed with flowing He at 100 °C for 1 h (50 cm /min)
to remove physisorbed NH The temperature-programmed
2
(50 cm /min) at 200 °C for 1 h. Then, it was satu-
3
3
–He at 80 °C for 1 h (50 cm /min) and subse-
2 3
O
3
2
O
3
v
/c
2
O
3
c
/
a
2 3
O
3
.
2
O
3
2 3
O
desorption was carried out from 35 to 800 °C at a constant heating
rate of 10 °C/min. The XPS analysis was performed using an AMI-
2 3
O
CUS photoelectron spectrometer equipped with an Mg K
a
X-ray
2 3
O
as primary excitation and KRATOS VISION2 software. The XPS ele-
mental spectra were acquired with 0.1 eV energy step at a pass en-
ergy of 75 kV. The C 1s line was taken as an internal standard at
creased from 18.0 nm to 25.7 nm when the calcination tempera-
ture increased from 960 to 1120 °C. The average crystallite size
a-Al O were much larger than h-Al O and were determined
2 3 2 3
to be in the range of 71.2–77.7 nm. The BET surface areas and pore
of
2
85.0 eV. The BET surface area of Al
alysts were determined by N physisorption using a Micrometritics
ASAP 2000 automated system. Each sample was degassed at 200 °C
for 2 h prior to N physisorption. The number of Pd metal active
sites was determined by measuring the amounts of CO chemi-
sorbed on the Pd/Al catalysts with a Micromeritic Chemisorb
750 automated system attached with ChemiSoft TPx software at
2 3 2 3
O supports and Pd/Al O cat-
2
volumes of Al
2 3
O supports decreased dramatically from 76 to 6 m /
2
3
g and 0.28 to 0.01 cm /g as wt.% of
2 3
a-phase Al O increased from 0
to 100%. The variation of specific surface area and pore volume
with calcination temperature can be explained by the change of
2
2
O
3
particle size and morphology Al
Al is usually accompanied by the grain growth and spheroidiza-
tion of Al particles [17]. Pore size distribution of the various
Al supports is shown in Fig. 2. Narrow pore size distribution
with the largest pore volume was observed for the pure h-Al
The mixed-phases h/ Al with 80 wt.% h-Al (80T20A sample)
2 3
O powders. Formation of a-
2
2 3
O
room temperature. Palladium dispersion was estimated from the
amount of CO chemisorbed assuming a stoichiometry of CO/Pd = 1.
2 3
O
2 3
O
2 3
O .
a
2
O
3
2 3
O
2.3. Reaction study
contained bimodal pore structure in which both small and large
pore sizes were observed. The pore volumes, however, were grad-
The selective hydrogenation of 1,3-butadiene was carried out at
0 °C and atmosphere pressure in a fixed-bed flow reactor. Before
the reaction, approximately 10–50 mg of catalyst was reduced
in situ with hydrogen by heating from room temperature to
ually decreased with increasing wt.% of
Acidity of the Al supports containing various h- and
compositions were determined from NH -TPD experiments and
the results are shown in Fig. 3. All the Al samples exhibited
two main desorption peaks at around 140–170 °C and 330–
40 °C which were corresponding to weak and medium acid sites,
a-phase.
5
2
O
3
a-phase
3
2 3
O
1
50 °C at a heating rate of 10 °C/min. Then the reactor was cooled
down in argon to the reaction temperature. The reactant gas was
composed of 1.9% 1,3-butadiene, 4.2% H , and balance of argon.
3
2
respectively [18]. Additional peak at around 500 °C was apparent
The feed flow rate was adjusted in the range 50–100 ml/min with
automatic flow controller (Brooks Instruments) in order to vary the
À1
gas hourly space velocity (GHSV) between 11,186 and 111,864 h
.
Table 1
The feed and product composition were analyzed by a gas chro-
matograph equipped with an FID detector (SHIMADZU GC2010,
Rt-Alumina BOND columns).
The physical properties of Al
2
O
3
with various h/
a phase compositions.
Samples BET surface
Crystallite
Pore
volume
Average pore
2
a
b
diameterb (Å)
area (m /g)
Size (nm)
h-
phase phase
3
(
cm /g)
a
-
3
. Results and discussion
1
00T0A
76.1
46.0
26.4
6.1
18.0
21.5
25.7
n.d.
n.d.
0.28
0.20
0.09
0.01
12.8
16.9
14.2
7.1
3.1. Catalyst characterization
80T20A
71.2
77.0
71.2
4
0
0T60A
T100A
The XRD patterns of Al
compositions are shown in Fig. 1. The XRD peaks at degree
h = 36.72° and 43.32° were used for calculation of weight (%)
and average crystallite size of h- and -phase Al , respectively.
2 3
O supports with various h/a phase
n.d.: Not determined.
a
Calculated from XRD results. Error of measurement was ±10%.
Based on BJH method.
2
b
a
2 3
O