G. Lee et al. / Catalysis Communications 67 (2015) 40–44
41
suitable hydrogen evolution processes for the fuel cell vehicle due to its
high selectivity, high reversibility, and high energy density [19].
It is well known that the catalytic dehydrogenation of decalin
could be efficiently performed over carbon-supported platinum catalyst
(Pt(NH
3
)
4
Cl
2
). NH
3
solution was then added into the solution to adjust
the pH value of the mixed solution (pH = 9). The mixture was vigorous-
ly stirred overnight at room temperature to exchange the protons of the
oxidized activated carbon into the platinum cations. The precipitate was
filtered to obtain a solid product, while platinum concentration in the
filtrate was investigated by ICP-AES (Prodigy, Teledyne Leeman Labs)
analysis. The solid product was dried overnight at 80 °C. The dried
solid was calcined at 350 °C for 2 h in a nitrogen stream, and subse-
quently, it was finally reduced at 250 °C for 3 h in a mixed stream of
nitrogen and hydrogen to yield carbon-supported platinum catalyst
(Pt/C_Ex).
The platinum concentration in the filtrate, which was determined by
ICP-AES analysis, was found to be negligible. This means that most of
platinum cations in the precursor participated in the ion-exchange
process. Therefore, we could confirm that Pt/C_Ex catalyst retained the
designed platinum content (3 wt.%), and accordingly, was successfully
prepared by an ion-exchange method.
(
Pt/C). The physical properties of platinum catalysts such as platinum
dispersion and platinum particle size are also known to be crucial fac-
tors for the efficient hydrogen production in this reaction. It is notewor-
thy that these physical properties of catalyst can be much different
depending on the preparation method [20]. Therefore, any systematic
investigation to see the effect of preparation method on the catalytic ac-
tivity of platinum catalyst in this reaction would be worthwhile. In this
work, we prepared a series of carbon-supported platinum catalysts
using four different preparation methods such as impregnation method,
precipitation method, ion-exchange method, and polyol method.
Especially, advanced methods (polyol method and ion-exchange
method) were employed for the preparation of carbon-supported
platinum catalysts to obtain high platinum dispersion. Catalytic dehy-
drogenation of decalin over the prepared catalysts was carried out in a
batch-type reactor. The prepared catalysts were characterized by XRD,
CO-chemisorption, and TEM analyses. Finally, effect of preparation
methods on the catalytic activity of carbon-supported platinum catalyst
in the decalin dehydrogenation was studied. Moreover, correlation be-
tween the catalytic performance of platinum catalyst and its physical
properties was investigated.
2.1.4. Pt/C_Po (polyol method)
According to the similar preparation method as previously reported
[21], Pt/C_Po catalyst was prepared by a polyol method, which is one of
the promising methods for the preparation of well-dispersed metal cat-
alyst. Ethylene glycol was used as both a solvent and a reducing agent to
prepare the nanosized platinum catalyst. A known amount of activated
carbon was added into the ethylene glycol solution of platinum precur-
2
. Experimental
sor (H
2 6
PtCl ), and then the suspension was stirred at room temperature
for 30 min. Aqueous NaOH solution (1 M) was added to adjust the pH
value of the solution to 11 followed by continuous stirring for 1 h. The
solution was maintained at 130 °C for 3 h, and the resulting mixture
was cooled down to room temperature. The mixture was filtered and
washed by water and ethanol, and then, it was finally dried at 70 °C in
vacuo.
2
.1. Catalyst preparation
A series of carbon-supported platinum (Pt/C) catalysts were pre-
pared using four different preparation methods. The platinum precur-
sors (H
PtCl and Pt(NH Cl ) for Pt/C catalysts were provided from
Wako Pure Chemical, and the palm activated carbon (Samchun Inc.)
was employed as a carbon support. N adsorption/desorption isotherm
2
6
3
)
4
2
2
2.2. Catalyst characterization
analysis (BELSORP-mini II, BEL Japan) revealed that the palm activated
carbon retained typical characteristics of microporous carbon (surface
area: 1304 m /g). The amount of platinum was fixed at 3 wt.% in all
XRD patterns of the prepared catalysts (Pt/C_Im, Pt/C_Pr, Pt/C_Ex,
and Pt/C_Po) were obtained with a Shimadzu XRD-7000 instrument
using Cu-Kα radiation (λ = 1.54056 Å) operated at 40 kV and 40 mA.
Platinum dispersion and particle size in the catalysts were examined
by CO-chemisorption (BELCAT-B, BEL Japan) and TEM (JEM-2100F,
JEOL) analyses. In the CO-chemisorption analysis, metal dispersion
and particle size were calculated on the basis of the adsorption stoichi-
ometry of Pt/CO = 1.4 [22,23].
2
Pt/C catalysts.
2
.1.1. Pt/C_Im (impregnation method)
Pt/C_Im catalyst was prepared by an incipient wetness impregnation
method using an aqueous solution of platinum precursor (H PtCl ).
2 6
After drying the impregnated catalyst overnight at 120 °C, it was re-
duced at 250 °C for 3 h with a mixed stream of nitrogen and hydrogen
to yield Pt/C_Im catalyst.
2.3. Catalytic dehydrogenation of decalin
2
.1.2. Pt/C_Pr (precipitation method)
A known amount of activated carbon was added into the aqueous
As previously reported [17,18], catalytic dehydrogenation of decalin
over the prepared catalysts was performed in a batch-type dehydroge-
nation reactor under boiling (210 °C) and refluxing conditions (5 °C) in
nitrogen atmosphere. Decalin (cis- and trans-mixture) was purchased
from Sigma-Aldrich. In a typical experiment, 0.3 g of catalyst was
employed as a thin layer form at the bottom of the reactor. The reactor
was heated to the reaction temperature, and then, the reactor was thor-
oughly purged with nitrogen for 30 min. After purging the reactor, a
known amount of decalin was dropwise added into the reactor using
a microsyringe. The evolved hydrogen from decalin was collected by a
gas burette, and the amount of evolved hydrogen was periodically
checked for 60 min. The evolved gas composition was also analyzed
by a gas chromatography (Yong Lin Instrument, YL6500) equipped
with a thermal conductivity detector (TCD).
solution of platinum precursor (H
ring the mixed solution at room temperature for 48 h. NaBH
solution as a reducing agent was then dropwise added to the mixed so-
lution at 90 °C for 30 min. After aging the resulting solution for another
3
with distilled water several times to remove the residual ions. The
resulting solid was finally dried in a convection oven overnight at
8
2
PtCl
6
), which was followed by stir-
aqueous
4
0 min, solid product was obtained by filtration. The solid was washed
0 °C. The catalyst prepared by a precipitation method was denoted as
Pt/C_Pr.
2
.1.3. Pt/C_Ex (ion-exchange method)
Ion-exchange method was employed for the preparation of Pt/C_Ex
catalyst with the similar preparation method as reported in the litera-
ture [17]. Prior to the ion-exchange method, activated carbon was oxi-
dized with concentrated nitric acid for 30 min under boiling and
refluxing conditions to create an oxygenated functional group on the
surface of activated carbon. A known amount of oxidized activated car-
bon was added into the aqueous solution of platinum precursor
3. Results and discussion
The analysis of the evolved gas composition clearly revealed that no
by-products were observed over the all catalysts tested in this work.
This indicates that the prepared carbon-supported platinum catalysts
Lee, Gihoon
