Hydroconversion of n-dodecane over nanoporous catalysts

Article abstract of DOI:10.1166/jnn.2013.6947

Platinum catalysts impregnated on different nanoporous materials, Meso-MFI, Si-SBA-15 and Al-SBA-15, were synthesized, and the hydroconversion of n-dodecane over these catalysts was performed. The catalytic characteristics were analyzed by Brunauer-Emmett-Teller surface area, X-ray diffraction, N ₂-adsorption-desorption and temperature programmed desorption of NH₃. The effects of operation parameters, such as temperature and pressure, on the catalytic activities were investigated. The catalytic activities were affected considerably by the acidic properties of the catalysts, temperature and pressure. Higher acidity, high temperature and low hydrogen pressure resulted in higher hydroconversion and facilitated hydrocracking. The weak acidity, low temperature and high hydrogen pressure resulted in lower hydroconversion and higher selectivity to i-dodecane. Copyright

Full text of DOI:10.1166/jnn.2013.6947

Copyright © 2013 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 13, 714–717, 2013
Hydroconversion of n-Dodecane Over
Nanoporous Catalysts
Young-Kwon Park1ꢀ2ꢀ∗, Hyung Won Lee1, Jong-Ki Jeon3, Jeongsik Han4,
Chul-Ung Kim5, Soon-Yong Jeong5, and Kwang-Eun Jeong5ꢀ∗
1Graduate School of Energy and Environmental Engineering, University of Seoul, Seoul 130-743, Korea
2School of Environmental Engineering, University of Seoul, Seoul 130-743, Korea
3Department of Chemical Engineering, Kongju National University, Cheonan 330-717, Korea
4Agency for Defense Development, Daejeon 305-152, Korea
5Green Chemistry Process Research Division, Korea Research Institute of Chemical Technology,
Daejeon 305-600, Korea
Platinum catalysts impregnated on different nanoporous materials, Meso-MFI, Si-SBA-15 and
Al-SBA-15, were synthesized, and the hydroconversion of n-dodecane over these catalysts was per-
formed. The catalytic characteristics were analyzed by Brunauer–Emmett–Teller surface area, X-ray
diffraction, N2-adsorption–desorption and temperature programmed desorption of NH3. The effects
of operation parameters, such as temperature and pressure, on the catalytic activities were inves-
tigated. The catalytic activities were affected considerably by the acidic properties of the catalysts,
temperature and pressure. Higher acidity, high temperature and low hydrogen pressure resulted in
higher hydroconversion and facilitated hydrocracking. The weak acidity, low temperature and high
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hydrogen pressure resulted in lower hydroconversion and higher selectivity to i-dodecane.
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Copyright: American Scientific Publishers
Keywords: n-Dodecane, Hydroconversion, Nanoporous Catalyst, Pt/Meso-MFI, Pt/Al-SBA-15.
1. INTRODUCTION
hydrogenation/dehydrogenation step, and the acidic sites
of the catalyst are involved in the activation of C C and
C
Therefore, the activity, selectivity and stability of
bifunctional catalyst can be modified by controlling the
acidic/metallic function ratio.
The depletion of petroleum based fossil fuels and global
warming problem has highlighted the need for alterna-
tive fuel production. Biomass has attracted considerable
interest owing to its carbon neutral properties in terms
of CO2 emissions as well as the dependency on fossil
fuels. The biomass to liquid process (BTL) is considered
one of the most promising commercial technologies to
convert biomass to liquid hydrocarbons via the Fischer-
Tropsch reaction of synthesis gas generated by the gasi-
fication of biomass.1 In this process, heavy long-chain
paraffinic hydrocarbons, such as higher molecular weight
wax, are mainly produced and should be converted to more
valuable compounds, such as iso-paraffinic hydrocarbons,
to improve the oil quality. To accomplish this, hydrocon-
version reactions, such as hydroisomerization and hydro-
cracking, are the most representative process for FT-wax
upgrading.
H bonds.2
Pt, Pd and Ni are useful metal species for hydro-
conversion, and zeolites are used mainly for acid cata-
lysts. Zeolites possess a regular pore structure and enough
acidic sites to promote the hydroconversion of n-paraffin,
whereas their microporosity can cause intracrystalline dif-
fusion resistance for large molecules exceeding the size of
the zeolite micropores. Therefore, an acid catalyst with a
large pore structure can be employed in the hydroconver-
sion of heavy wax.3
Nanoporous materials, such as MCM-41, MCM-48 and
SBA-15, have attracted attention in the hydroconversion of
wax due to their mild acidity and well-ordered nanoporous
(>2 nm) structures. On the other hand, the few stud-
ies examined the use of nanoporous acid catalysts for
hydroconversion. Moreover, these studies were limited to
hydroisomerization.4 For example, the bifunctional Pt/Al-
MCM-41 catalyst exhibited higher activity for the hydroi-
somerization of n-hexane, n-hexadecane and wax with
The hydroconversion reaction is generally performed
over a bifunctional catalyst with acidic and metal-
lic functions. Metal species can play a role in the
∗Authors to whom correspondence should be addressed.
714
J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 1
1533-4880/2013/13/714/004
doi:10.1166/jnn.2013.6947

Park et al.
Hydroconversion of n-Dodecane Over Nanoporous Catalysts
improved cold flow properties, such as viscosity, pour
point and freezing point. The reaction mechanism between
hydroisomerization and hydrocracking over Pt/Al-MCM-
41 is dependent on the relative ratio of the metallic and
acidic functions of the catalyst.4 A Meso-MFI catalyst with
a zeolite and nanoporous structure, simultaneously, was
recently synthesized and employed for a range of catalytic
reactions.5 Nevertheless, to the best of our knowledge,
there are no reports on the use of Meso-MFI catalysts for
the hydroconversion reaction. In addition, the hydroiso-
merization of n-dodecane over Pt/Al-SBA-15 catalyst has
not been reported.
This study examined the catalytic performance of
two types of nanoporous catalysts (Pt/Al-SBA-15,
Pt/Meso-MFI), which have distinct acidic properties, for
the hydroisomerization of n-dodecane. The reactivity and
selectivity was also investigated in terms of characteristics
of the catalysts.
3. RESULTS AND DISCUSSION
3.1. Characterization of Catalysts
Table I lists the textural properties of the prepared cata-
lysts. Pt/Meso-MFI, Pt/Si-SBA-15, and Pt/Al-SBA-15 (20),
(40) and (80) exhibited higher specific surface areas of 486,
571, 517, 547, and 559 m2/g, respectively. The respective
pore volumes of the catalysts were 0.70, 0.81, 0.74, 0.88,
and 0.81 cm3/g. The pore size of all catalysts was >4 nm,
which is sufficient for a large molecule like n-dodecane
to diffuse in the catalyst. The low-angle XRD patterns
of Pt/Si-SBA-15 and Pt/Al-SBA-15, (Fig. 1(a)) revealed
the characteristic peaks of hexagonal nanoporous SBA-15.
This suggests that the incorporation of Pt into SBA-15
does not destroy the original hexagonal mesostructures of
SBA-15 itself. The high-angle XRD patterns of the Meso-
MFI and Pt/Meso-MFI catalyst (Fig. 1(b)) were in accor-
dance with conventional MFI zeolite after Pt impregnation
with a slight decrease in the characteristic peak intensity.
NH3-TPD is used to analyze the acidic ꢀproperties of a
2. EXPERIMENTAL DETAILS
ꢀ
catalyst. The peaks at approximately 200 C and 400 C
2.1. Catalyst Preparation
are generally attributed to NH3 desorption from the weak
acid sites and strong Brönsted acid sites, respectively. The
peak area means the number of acid sites of the catalyst.
Figure 2 shows the NH3-TPD curves of the Pt/Si-SBA-15,
Pt/Al-SBA-15 and Pt/Meso-MFI catalysts. Both weak and
strong acid sites were observed in the Pt/Meso-MFI cat-
alyst, and the acid amount was much higher than in the
other catalysts. In contrast, the Pt/Al-SBA-15 catalyst con-
tained mainly weak acid sites and the number increased
with decreasing Si/Al ratio.
Si-SBA-15 and Al-SBA-15 nanoporous materials were
synthesized using the procedure reported elsewhere.6 The
Si/Al ratio of Al-SBA-15 were controlled to 20, 40
and 80. A Meso-MFI with a Si/Al molar ratio of 20
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was synthesized using a procedure described elsewhere.5
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Pt containing catalysts were prepared with an aque-
ous Pt(NH3ꢀ4(NO3ꢀ2 solution using the incipient wetness
impregnation method and the Pt loading was 0.5 wt.%.
Copyright: American Scientific Publishers
2.2. Catalyst Characterization
3.2. Catalytic Activities
The Nꢀ2 adsorption/desorption isotherms were obtained at
−196 C using a Micromeritics ASAP 2000. The powder
X-ray diffraction (XRD, Rigaku D/MAX-III) patterns were
obtained using Cu-Kꢁ radiation. The surface acidity of the
catalysts was measured using the temperature programmed
desorption of ammonia (NH3-TPD, BELCAT, BEL Japan
Inc., Osaka, Japan).
Figure 3 shows the temporal conversion and selectiv-
ity of the Pt/Si-SBA-15, Pt/Al-SBA-15 and Pt/Meso-
MFI catalysts at 350 ꢀC and 20 bar. The conversion
of n-dodecane occurred in the order of Pt/Meso-MFIꢁ
Pt/Al-SBA-15 (20) > Pt/Al-SBA-15 (40) > Pt/Al-SBA-15
(80) > Pt/Si-SBA-15, which indicates higher acid strength,
and the amount of the acid site of Pt/Meso-MFI catalyst
plays an important role in the conversion of n-dodecane.
In the same manner, Pt/Al-SBA-15 with a Si/Al ratio of
20 showed the highest conversion of n-dodecane, whereas
Pt/Si-SBA-15 exhibited the lowest activity among the
Pt/SBA-15 catalysts. On the other hand, the selectivity
2.3. Model Reaction
The hydroconversion of n-dodecane over a bifunctional
catalyst was carried out using a batch-type reactor. TheꢀPt
containing catalyst was reduced under H2 flow at 500 C
for 3 h. The reduced catalyst (0.5 g) was moved to a
batch reactor with n-dodecane (75 ml) and the reaction
started with stirring under high temperatures and pres-
sures. The liquid product sampled at specific times on
stream was analyzed by gas chromatography/mass spec-
troscopy (GC/MS, Agilent Technologies) equipped with
UA-5 (Ultra ALLOY-5MS/HT; 5% diphenyl and 95%
dimethylpolysiloxane, length 30 m, i.d. 0.25 mm, film
thickness 0.5 ꢂm) column.
Table I. Textural properties of catalysts.
SBET
(m2/g)
Pore volume
(cm3/g)
Pore
size (nm)
Catalyst
Si/Al
Pt/Si-SBA-15
571
517
547
559
486
0.81
0.74
0.88
0.81
0.70
7.0
6.6
6.6
7.3
4.2
−
20
40
80
20
Pt/Al-SBA-15 (20)
Pt/Al-SBA-15 (40)
Pt/Al-SBA-15 (80)
Pt/Meso-MFI
J. Nanosci. Nanotechnol. 13, 714–717, 2013
715

Hydroconversion of n-Dodecane Over Nanoporous Catalysts
Park et al.
acidic characteristics, resulting in dominant hydrocracking
instead of hydroisomerization. In case of the Pt/Si-SBA-15
catalyst with fewer acid sites, the iso-dodecane yield was
much lower than those of the other catalysts owing to its
lowest conversion, irrespective of the higher selectivity of
iso-dodecane. The Pt/Al-SBA-15 catalyst is more prone to
the hydroisomerization of n-dodecane because of its weak
acidic properties with respect to conversion and selectivity.
Liquid products obtained from the Pt/Meso-MFI catalyst
consisted of hydrocarbons whose carbon chain length was
<11, primarily in the range of C5 and C8. From these
results, it can be suggested that the acid properties of the
bifunctional catalyst play a decisive role in determining
the reactivity and selectivity for n-paraffin hydroconver-
sion. The balance between the Pt metal and acidity with
moderate acid strength and the acid levels might secure
the optimum activity for hydroisomerization. Pt/Al-SBA-
15 (20) showed the best performance of the Pt/Al-SBA-15
catalysts examined.
(a)
Pt/SBA-15
Pt/Al-SBA-15(20)
Pt/Al-SBA-15(40)
Pt/Al-SBA-15(80)
1
2
3
4
2θ
(b)
MesoMFI
Pt-MesoMFI
100
80
(a)
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0
10
20
30
40
50
Copyright: American Scientific Publishers
40
2θ
Pt/Meso-MFI
Pt/Si-SBA-15
Fig. 1. (a) Low angle, and (b) high angle XRD patterns of prepared
Pt/Al-SBA-15(20)
Pt/Al-SBA-15(40)
Pt/Al-SBA-15(80)
catalysts.
20
0
to iso-dodecane over the Pt/Al-SBA-15 catalysts was
much higher than that over the Pt/Meso-MFI catalyst.
As shown in Figure 2, the highest n-dodecane conver-
sion and extremely low selectivity of iso-dodecane of
the Pt/Meso-MFI catalyst was attributed to its strong
0
20
40
60
80
100
120
Time (min)
(b)
Pt/Meso MFI
100
80
60
40
20
0
Pt/Al-SBA-15(20)
Pt/Al-SBA-15(40)
Pt/Al-SBA-15(80)
Pt/SBA-15
Pt/Meso-MFI
Pt/Si-SBA-15
Pt/Al-SBA-15(20)
Pt/Al-SBA-15(40)
Pt/Al-SBA-15(80)
0
20
40
60
80
100
120
100
200
300
400
500
Time (min)
Temperature (ºC)
Fig. 3. Temporal conversion and selectivity over catalysts at 350 ꢀC and
20 bar (a) n-dodecane conversion (b) isomer selectivity.
Fig. 2. NH3 TPD of various catalysts.
716
J. Nanosci. Nanotechnol. 13, 714–717, 2013

Park et al.
Hydroconversion of n-Dodecane Over Nanoporous Catalysts
(increase in hydrogen partial pressure), hydrogen can
adsorb on catalyst more easily than n-dodecane, result-
ing in a decrease in the hydrocracking reaction with a
concomitant increase in iso-dodecane selectivity. Zhang
et al. reported that an increase in the total reaction pres-
sure resulted in low conversion with high selectivity, indi-
cating a negative reaction order with respect to hydrogen
in n-hexadecane isomerization using a Pt/WO3/ZrO2
catalyst.7
100
80
60
40
20
0
100
80
>
350ºC
335ºC
320ºC
60
40
<
20
0
0
20
40
60
80
100
120
4. CONCLUSION
Time (min)
Pt/Si-SBA-15, Pt/Al-SBA-15, and Pt/Meso-MFI cata-
lysts were applied to the catalytic hydroconversion of
n-dodecane. Pt/Meso-MFI with strong acid sites exhibited
higher activity for the hydroconversion reaction, whereas
Pt/Al-SBA-15 with sufficient weak acid sites enhanced
the hydroisomerization reaction. The effect of the reaction
temperature and pressure on the activity of the Pt/Al-SBA-
15 catalyst was also investiꢀgated. With increasing temper-
Fig. 4. Effect of reaction temperature on n-dodecane conversion and
isomer selectivity.
100
80
60
40
20
0
100
80
60
40
20
>
ꢀ
20 bar
30 bar
40 bar
ature from 320 C to 350 C, the hydrocracking reaction
became superior to the hydroisomerization reaction. The
hydroconversion activity decreased with increasing reac-
tion pressure.
<
Acknowledgment: This work was supported by Agency
for Defense Development (ADD). Also, this research was
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0
20
40
60
80
100
120
IP: 117.255.212.65 On: Tue, 16 Feb 2016 10:58:42
supported by Basic Science Research Program through
Copyright: American Scientific Publishers
Time (min)
the National Research Foundation of Korea (NRF) funded
by the Ministry of Education, Science and Technology
(2012R1A1B3003394).
Fig. 5. Effect of reaction pressure on n-dodecane conversion and isomer
selectivity.
Figure 4 shows the catalytic activity of Pt/Al-SBA-15
(20) at dꢀifferent reaction temperatures between 320 ꢀC
and 350 C at fixed pressure of 20 bar. The hydrocon-
version of n-dodecane increased with increasing temper-
ature, whereas the selectivity of iso-dodecane decreased
due to the enhanced hydrocracking reaction at higher
temperatures.
References and Notes
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(2000).
The effect of the operating pressure on the cat-
alytic activity was investigated at 350 ꢀC (Fig. 5).
The hydroconversion activity decreased with increas-
ing pressure under isothermal conditions. Hydrogen and
n-dodecane competitively adsorbed on the active sites of
the catalyst. On the other hand, with increasing pressure
5. K. H. Park, H. J. Park, R. Ryu, J. K. Jeon, J. Park, and Y. K. Park,
J. Nanosci. Nanotechnol. 10, 355 (2010).
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Received: 30 November 2011. Accepted: 30 May 2012.
J. Nanosci. Nanotechnol. 13, 714–717, 2013
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