Hydrodeoxygenation of guaiacol over Pt/Al-SBA-15 catalysts

Article abstract of DOI:10.1166/jnn.2015.8362

Upgrading of bio-oil through catalytic hydrodeoxygenation (HDO) reaction was investigated for guaiacol as a model compound. A batch reactor was used for the reaction condition of 40 bar and 250°C. The target product was cyclohexane. Pt/Al-SBA-15 with the Si/Al ratios of 20, 40, and 80 and Pt/HZSM-5 were used as the catalyst. The SBA-15 catalysts were characterized by N₂ adsorption-desorption, X-ray diffraction analysis, and temperature programmed desorption of ammonia. The order of cyclohexane yield was Pt/Al-SBA-15 (Si/Al = 20) > Pt/Al-SBA-15(40) > Pt/Al-SBA-15 (80), indicating that the quantity of acid sites plays an important role in the HDO reaction. On the other hand, Pt/HZSM-5 led to a very low cyclohexane yield, in spite of its abundant strong acid sites, due to its small pore size.

Full text of DOI:10.1166/jnn.2015.8362

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Nanoscience and Nanotechnology
Vol. 15, 527–531, 2015
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Hydrodeoxygenation of Guaiacol
Over Pt/Al-SBA-15 Catalysts
Mi Jin Yu1, Sung Hoon Park2, Jong-Ki Jeon3, Changkook Ryu4,
Jung Min Sohn5, Sang Chai Kim6, and Young-Kwon Park1ꢀ7ꢀ∗
1Graduate School of Energy and Environmental System Engineering,
University of Seoul, Seoul 130-743, Korea
2Department of Environmental Engineering, Sunchon National University,
Suncheon 540-950, Korea
3Department of Chemical Engineering, Kongju National University, Cheonan 330-717, Korea
4School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Korea
5Department of Mineral Resources and Energy Engineering, Chonbuk National University,
Jeonju 561-756, Korea
6Department of Environmental Education, Mokpo National University,
Muan 534-729, Korea
7School of Environmental Engineering, University of Seoul, Seoul 130-743, Korea
Upgrading of bio-oil through catalytic hydrodeoxygenation (HDO) reaction was investigated for gua-
Delivered by Publishing Technology to: Stockholm University Library
IP: 75.146.62.155 On: Fri, 30 Oct 2015 02:41:19
iacol as a model compound. A batch reactor was used for the reaction condition of 40 bar and
ꢀ
Copyright: American Scientific Publishers
250 C. The target product was cyclohexane. Pt/Al-SBA-15 with the Si/Al ratios of 20, 40, and 80 and
Pt/HZSM-5 were used as the catalyst. The SBA-15 catalysts were characterized by N2 adsorption–
desorption, X-ray diffraction analysis, and temperature programmed desorption of ammonia. The
order of cyclohexane yield was Pt/Al-SBA-15 (Si/Al = 20) > Pt/Al-SBA-15(40) > Pt/Al-SBA-15 (80),
indicating that the quantity of acid sites plays an important role in the HDO reaction. On the other
hand, Pt/HZSM-5 led to a very low cyclohexane yield, in spite of its abundant strong acid sites, due
to its small pore size.
Keywords: Guaiacol, Hydrodeoxygenation, SBA-15, HZSM-5, Pt, Cyclohexane.
1. INTRODUCTION
production of fuels and chemicals thanks to its abundance
and low price.1 Bio-oil is the main product from
lignocellulosic biomass converted by pyrolysis. Repre-
sentative compounds in bio-oil include guaiacol, phe-
nol, anisole, and catechol.2 Among the lignin-originated
species contained in bio-oil, guaiacol is one of the most
abundant. For instance, it accounts for 0.18∼0.51 wt% in
the pyrolysis oil derived from alfalfa stem and swichgrass
forage.3
Although the bio-oil obtained from pyrolysis can be
used as fuel or chemical feedstock, its high oxygen con-
tent, viscosity, and polarity cause instability and chemi-
cal complexity, requiring additional upgrading processes.4
Upgrading of bio-oil is usually conducted using catalytic
hydrotreating, catalytic vapor cracking, or physical meth-
ods such as hot-gas filtration, emulsification, and solvent
addition.
Renewable energy has attracted much attention as the ulti-
mate solution to fossil fuel exhaustion and global warm-
ing. Among the renewable energy sources, bio-energy
has a unique advantage that it can be directly con-
verted into transportation fuels and chemical feedstock.
Biomass, raw material for bio-energy, includes a variety
of materials that stem from plants, such as microorgan-
isms, dead animals and plants, organic wastes, wood, and
seaweeds.
Woody biomass has a multitude of advantages; it is
carbon-neutral, renewable, and abundant. Woody biomass
consists of hemicellulose (40∼50%), cellulose (15∼20%),
and lignin (15∼30%). Lignocellulosic biomass has a
particularly high potential as a renewable resource for
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2015, Vol. 15, No. 1
1533-4880/2015/15/527/005
doi:10.1166/jnn.2015.8362
527

Hydrodeoxygenation of Guaiacol Over Pt/Al-SBA-15 Catalysts
Yu et al.
Recently, upgrading of bio-oil through hydrodeoxygena-
tion (HDO) has drawn significant attention. In a HDO
process, oxygen is removed from oxygenate compounds
by high-temperature catalytic reactions under hydrogen
atmosphere. This requires a noble metal catalyst for hydro-
genation and an acid catalyst for dehydration. Mo, CoMo,
and NiMo catalysts have usually been used as the support
material, while employment of other materials, such as
SiO2, activated carbon, TiO2, ZrO2, zeolite, and oxide mix-
tures, has recently been investigated.5–8 Pt, Rh, Pd, Cu,
and Ni have been used as the noble metal catalyst for
HDO.1ꢀ9–11 Noble metals are effective for activation of
hydrogen under mild conditions because hydrogen can be
easily separated and activated on their surface to react with
other reactants.12
Mesoporous silica materials have attracted considerable
attention as a catalyst support due to their large specific
surface area, controllable pore diameter, narrow pore size
distribution, and large pore volume.13–16 Among others,
in particular, SBA-15 possesses high structural regularity.
It is also more stable against moisture and has larger pores
than MCM-41.17
(BELCAT, BEL Japan Inc.) equipped with a thermal con-
ductivity detector to compare the acid properties of the
catalyst surface.
2.3. HDO of Guaiacol
HDO of guaiacol was performed using a batch reactor.
0.4 g of reduced catalyst and 40 ml of 7.5-wt% guaia-
col in decane solution were introduced into the reactor.
The reactor was purged three times with hydrogen gas and
then filled with 40-bar hydrogen gas. The reactor temper-
ꢀ
ꢀ
ature was increased to 250 C at a rate of 5 C/min. At
this temperature, stirring began at 400 rpm, which was
considered to be the beginning of the reaction. After 2 h
of reaction time, the reactor temperature was decreased
to room temperature to sample the products. Liquid-phase
products were analyzed by gas chromatography/mass spec-
troscopy (GC/MS, Agilent Technologies). As the metal
capillary column for GC/MS, Ultra ALLOY-5 (MS/HT)
(5% diphenyl and 95% dimethylpolysiloxane, length 30 m,
i.d. 0.25 mm, film thickness 0.5 ꢄm, Frontier Laboratories
Ltd. Japan) was used.
In this study, Pt/Al-SBA-15 catalysts synthesized using
Al-SBA-15 supports with three different Si/Al ratios were
applied, for the first time, to HDO of guaiacol to upgrade
the fuel quality by producing cyclohexane. Microporous
Pt/HZSM-5 was also used for the HDO reaction to inves-
3. RESULTS AND DISCUSSION
3.1. Characterization of Catalysts
Table I summarizes the physical properties of the catalysts
used in this study. The specific surface areas of Pt/Al-SBA-
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tigate the effect of the pore size on the catalytic activity
15(20), Pt/Al-SBA-15(40), and Pt/Al-SBA-15(80) were
IP: 75.146.62.155 On: Fri, 30 Oct 2015 02:41:19
517, 547, and 559 m2/g, respectively, while their pore vol-
for HDO reaction.
Copyright: American Scientific Publishers
umes were 0.74, 0.88, and 0.81 cm3/g, respectively. On
the whole, both properties increased with increasing Si/Al
ratio. The specific surface area of Pt/HZSM-5(11.5) was
386 m2/g, being smaller than that of Pt/Al-SBA-15. Pt/Al-
SBA-15 was shown to have mesopores with their size of
6 nm or larger.
Therefore, Pt/Al-SBA-15 with larger pore size was
expected to be more effective, than HZSM-5 with smaller
pore size (ca. 0.56 nm), for diffusion of reactant molecules
into the pores and hence for their cracking.
Figure 1 shows the XRD analysis results of Pt/Al-SBA-
15(20), Pt/Al-SBA-15(40), and Pt/Al-SBA-15(80). All the
samples exhibited three typical peaks, indexed as (100),
(110), and (200),16 representing the 2D-hexagonal struc-
ture of SBA-15. This indicates that the structure of SBA-15
was not altered by impregnation of Pt.
2. EXPERIMENTAL DETAILS
2.1. Catalyst Preparation
HZSM-5(11.5) was purchased from Zeolyst International.
Al-SBA-15 was synthesized using the procedure reported
by Lee et al.18 controlling the Si/Al ratio at 20, 40, and
80. 0.5 wt% Pt was impregnated on the Al-SBA-15 sup-
port using Pt(NH3ꢁ4(NO3ꢁ2 solution, based on the incipient
wetness impregnation method. The impregnated catalyst
was calcined for 3 h at 500 ꢀC under nitrogen atmo-
ꢀ
sphere and then reduced for 3 h at 500 C under hydrogen
atmosphere.
2.2. Catalyst Characterization
Nitrogen adsorption/desorption isotherms were obtained
using a surface area analyzer (TriStar, Micromeritics).
Specific surface area was calculated using the Brunaure–
Emmett–Teller (BET) method over the relative pressure
range of P/P0 = 0ꢂ05∼0ꢂ20. Pore size distribution was cal-
culated by the Barrett–Joyner–Halenda method.
Table I. Physical properties of the catalysts.
Pore
Pore
size (nm)
Catalysts
SBET (m2/g) volume (cm3/g)
Si/Al
X-ray diffraction (XRD) patterns were obtained in
the reflection mode using an XRD system (Rigaku
D/MAX-2200 Ultima) equipped with Cu light source (Kꢃ
radiation = 1ꢂ541 Å) at 30 kV and 40 mA.
Pt/Al-SBA-15(20)
Pt/Al-SBA-15(40)
Pt/Al-SBA-15(80)
Pt/HZSM-5(11.5)
517
547
559
317
0.74
0.88
0.81
−
6.6
6.6
7.3
20
40
80
0ꢂ51×0ꢂ55ꢀ 11ꢂ5
Temperature programmed desorption of ammonia (NH3-
TPD) was performed using a chemisorption analyzer
0ꢂ53×0ꢂ56
528
J. Nanosci. Nanotechnol. 15, 527–531, 2015

Yu et al.
Hydrodeoxygenation of Guaiacol Over Pt/Al-SBA-15 Catalysts
Pt/Al-SBA-15(20)
Pt/Al-SBA-15(40)
Pt/Al-SBA-15(80)
1
2
3
4
5
2θ
Figure 1. Low-angle XRD pattern of Pt/Al-SBA-15(20), Pt/Al-SBA-
15(40), and Pt/Al-SBA-15(80).
Figure 3. NH3-TPD of Al-SBA-15.
The catalytic activity was the highest when the Si/Al ratio
was the smallest (20), while it was the lowest when the
Si/Al ratio was the largest (80). Because the quantity of
acid sites of Al-SBA-15 increases with decreasing Si/Al
ratio, the guaiacol conversion appears to be in positive cor-
relation with the quantity of acid sites. This may be due
to the fact that the propensity of deoxygenation increases
with the number of active sites. Lee et al.21 also reported
that the yield of cyclohexane increased with increasing
The type of surface acidity of the Al-SBA-15 catalyst
was examined using pyridine adsorption tests. As shown
in Figure 2 for the spectroscopic results, Al-SBA-15 had
the characteristic bands for pyridine adsorbed on Lewis
acid sites at 1445 cm−1 and 1587 cm−1. The less intense
band at 1540 cm−1 indicated the formation of Brønsted
acid sites. Figure 3 shows the NH3-TPD analysis results of
Al-SBA-15. Al-SBA-15 is shown to have weak acid sites,
whereas HZSM-5 has strong Brønsted acid sites (data not
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acidity of the catalyst support material. At a low stirring
shown). HZSM-5 is also shown to have a larger quantity
IP: 75.146.62.155 On: Fri, 30 Oct 2015 02:41:19
rate (200 rpm), the guaiacol conversion was lower than
of acid sites than Al-SBA-15 (data not shown). The quan-
tity of acid sites of Al-SBA-15 increased with decreas-
ing Si/Al ratio; the order of the quantity of acid sites
was Pt/Al-SBA-15(20) > Pt/Al-SBA-15(40) > Pt/Al-SBA-
15(80) (data not shown), which is in accordance with pre-
vious reports.19ꢀ20
Copyright: American Scientific Publishers
that obtained with a stirring rate of 400 rpm, which is
attributed to a lower accessibility of reactant to active sites
of the catalyst due to weak stirring.
Table II lists the main products of catalytic HDO of
guaiacol over Pt/Al-SBA-15(20). Besides the main tar-
get cyclohexane, a variety of species were produced.
3.2. Catalytic Activities
The guaiacol conversions obtained over Pt/Al-SBA-15
with various Si/Al ratios are compared in Figure 4.
100
Guaiacol Conversion
Cyclohexane Selectivity
Cyclohexane Yield
80
60
40
20
0
Pt/HZSM-5(11.5)-400 rpm
Pt/Al-SBA-15(20P)-t/2A0l0-SrBpAm-15(20)P-4t/0A0l-rSpBmA-15(40P)-t4/A00l-SrpBmA-15(80)-400 rpm
Figure 4. Effect of the Si/Al ratio of Al-SBA-15 and the pore size on
Figure 2. Pyridine FT-IR spectra of Al-SBA-15.
J. Nanosci. Nanotechnol. 15, 527–531, 2015
the catalytic activity.
529

Hydrodeoxygenation of Guaiacol Over Pt/Al-SBA-15 Catalysts
Yu et al.
agreement of that of Prochazkova et al.22 in terms of the
effect of the pore size.
Table II. Products of HDO of guaiacol over Al-SBA-15(20) catalyst at
two stirring rates.
Because cyclohexane has a high octane number, the bio-
oil upgraded over Pt/Al-SBA-15 is believed to have a high
potential as a transportation fuel. High potential of bio-oil
containing cyclohexane as a transportation fuel was pre-
sented in a study by Ahmad et al.23
200 rpm
400 rpm
Cyclohexane
Cyclopentane
Methyl cyclopentane
Benzene
Methyl cyclohexane
Methoxy benzene (anisole)
Pentyl cyclopentane
2-methoxy-4-methyl-phenol
1,2-dimethoxy benzene
Cyclohexane (cyclopentylmethyl)
1,1ꢁ-bicyclohexyl
16ꢂ07
0ꢂ36
0ꢂ42
42ꢂ63
0ꢂ27
1ꢂ13
3ꢂ93
0ꢂ27
–
–
–
–
0ꢂ45
3ꢂ83
1ꢂ35
9ꢂ77
2ꢂ43
6ꢂ65
0ꢂ83
16ꢂ07
4. CONCLUSION
Pt/Al-SBA-15(20), Pt/Al-SBA-15(40), Pt/Al-SBA-15(80),
and Pt/HZSM-5(11.5) were applied to the HDO of guaia-
col. Pt/Al-SBA-15(20) exhibited the highest guaiacol con-
version and cyclohexane yield, whereas Pt/HZSM-5(11.5)
exerted the lowest catalytic activity. The poor catalytic
activity of Pt/HZSM-5(11.5) was attributed to its small
pore size that hinders diffusion of guaiacol molecules
into the pores containing active sites. The catalytic activ-
ity of Pt/Al-SBA-15 increased with decreasing Si/Al ratio
because the quantity of acid sites increases with decreasing
Si/Al ratio. The results of this study indicate that the pore
size and the quantity of acid sites play important roles in
the conversion of guaiacol to cyclohexane.
4ꢂ11
11ꢂ21
–
Cyclohexyl benzene
Cyclopentane and methyl cyclopentane are produced
by isomerization, while cyclohexyl benzene and 1,1ꢁ-
bicyclohexyl are formed by aromatic ring condensation.
Under a low stirring rate (200 rpm), more reaction inter-
mediates were observed because of insufficient progress
of the reaction. Gates et al.1 suggested a mechanism for
deoxygenation of guaiacol over Pt/Al2O3 in which sev-
eral possible reactions were incorporated. According to
their suggestion, cyclohexane can be produced via phe-
nol or anisole. Phenols were not detected in this study,
Acknowledgment: This research was supported by
Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Min-
istry of Education (2012R1A1B3003394).
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while anisole and 1,2-dimethoxy benzene were observed,
implying that cyclohexane could be produced via anisole.
IP: 75.146.62.155 On: Fri, 30 Oct 2015 02:41:19
Copyright: American Scientific Publishers
However, Gates et al.1 argued that the reaction kinetic of
phenol formation is 40 times faster than that of anisole
formation. Therefore, we cannot rule out the possibility of
formation of phenol and subsequent conversion to other
species. Further investigation is needed to better constrain
the mechanism of cyclohexane formation.
References and Notes
1. T. Nimmanwudipong, R. C. Runnebaum, D. E. Block, and B. C.
Gates, Energy Fuels 25, 3417 (2011).
2. J. C. Hicks, J. Phys. Chem. Lett. 2, 2280 (2011).
3. C. A. Mullen and A. A. Boateng, Energy Fuels 22, 2104
(2008).
In order to examine the effect of the pore size of the
catalyst, Pt/HZSM-5(11.5) was used additionally. Because
HZSM-5 has a larger quantity of acid sites with stronger
acidity than Al-SBA-15 (data not shown), a higher conver-
sion of guaiacol may be expected. As shown in Figure 4,
however, the employment of Pt/HZSM-5 resulted in a very
low guaiacol conversion.
Al-SBA-15 has large pores with the average pore diam-
eter of 6 nm so that the diffusion limitation against the
approach of guaiacol molecules to active sites of the cat-
alyst is low. To the contrary, the pore size of HZSM-5
is much smaller (ca. 0.56 nm), hindering the access of
guaiacol molecules to the active sites existing in the
catalyst pores. This is believed to have contributed to
the low guaiacol conversion over HZSM-5. Prochazkova
et al.22 studied the HDO reaction of benzaldehyde over
Pd-impregnated Beta and ZSM-5. ZSM-5 showed, due to
its smaller pore size, lower selectivity to and yield of the
target product. Based on this result, they suggested that
catalytic supports with large pore size are adequate for
HDO reaction. The result of the present study is in good
4. C. H. Ko, S. H. Park, J. K. Jeon, D. J. Suh, K. E. Jeong, and Y. K.
Park, Korean J. Chem. Eng. 29, 1657 (2012).
5. Y. Yang, A. Gilbert, and C. C. Xu, Appl. Catal. A: Gen. 360, 242
(2009).
6. M. Breysse, J. L. Portefaix, and M. Vrinat, Catal. Today 10, 489
(1991).
7. P. T. Vasudevan and J. L. G. Fierro, Catal. Rev. Sci. Eng. 38, 161
(1996).
8. L. R. Radovic and F. Rodríguez-Reinoso, Chem. Phys. Carbon 25,
243 (1997).
9. X. Zhu, L. L. Lobban, R. G. Mallinson, and D. E. Resasco, J. Catal.
281, 21 (2011).
10. A. Gutierrez, R. K. Kaila, M. L. Honkela, R. Slioor, and A. O. I.
Krause, Catal. Today 147, 239 (2009).
11. S. Sitthisa and D. E. Resasco, Catal. Lett. 141, 784 (2011).
12. G. V. Smith and F. Notheisz, Heterogeneous Catalysis in Organic
Chemistry, Academic Press, San Diego (1999).
13. I. T. Ghampsona, C. Sepulveda, R. Garcia, J. L. G. Fierro,
N. Escalona, and W. J. DeSisto, Appl. Catal. A: Gen. 435–436, 51
(2012).
14. W. Chang, G. Chae, S. R. Jang, J. Shin, and B. J. Ahn, J. Ind. Eng.
Chem. 18, 581 (2012).
15. H. W. Lee, H. J. Cho, J. H. Yim, J. M. Kim, J. K. Jeon, J. M. Sohn,
K. S. Yoo, S. S. Kim, and Y. K. Park, J. Ind. Eng. Chem. 17, 504
(2011).
530
J. Nanosci. Nanotechnol. 15, 527–531, 2015

Yu et al.
Hydrodeoxygenation of Guaiacol Over Pt/Al-SBA-15 Catalysts
16. Y. K. Park, H. W. Lee, J. K. Jeon, J. Han, C. U. Kim, S. Y. Jeong,
and K. E. Jeong, J. Nanosci. Nanotechnol. 13, 714 (2013).
17. K. Soni, K. C. Mouli, A. K. Dalai, and J. Adjaye, Catal. Lett. 136,
116 (2010).
18. S. H. Lee, H. S. Heo, K. E. Jeong, J. H. Yim, J. K. Jeon, K. Y. Jung,
Y. S. Ko, S. S. Kim, and Y. K. Park, J. Nanosci. Nanotechnol. 11,
759 (2011).
20. Q. Lu, W. Z. Li, D. Zhang, and X. F. Zhu, J. Anal. Appl. Pyrolysis
84, 131 (2009).
21. C. R. Lee, J. S. Yoon, Y. W. Suh, J. W. Choi, J. M. Ha, D. J. Suh,
and Y. K. Park, Catal. Commun. 17, 54 (2012).
ˇ
22. D. Procházková, P. Zámostný, M. Bejblová, L. Cervený, and
ˇ
J. Cejka, Appl. Catal. A: Gen. 332, 56 (2007).
23. M. M. Ahmad, M. F. R. Nordin and M. T. Azizan, Am. J. Appl. Sci.
7, 746 (2010).
19. C. Nie, L. Huang, D. Zhao, and Q. Li, Catal. Lett. 71, 117 (2001).
Received: 25 February 2013. Accepted: 25 March 2013.
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