Deoxygenation of m-toluic acid over hierarchical x zeolite

Article abstract of DOI:10.1016/j.catcom.2016.02.008

Catalytic activity of FAU zeolites was tested on the deoxygenation of m-toluic acid at atmospheric pressure and without feeding hydrogen. Sodium dodecylbenzenesulfonate was used as template to obtain a certain mesoporosity in the NaX zeolite. The mesoporosity improved the catalytic activity. This zeolite showed a good activity catalytic increasing the toluene yield to 40%, reducing the oxygen content in the reaction products, and decreasing the esterification reaction. The catalytic activity was kept without deactivation of the catalyst.

Full text of DOI:10.1016/j.catcom.2016.02.008

Catalysis Communications 78 (2016) 55–58
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Deoxygenation of m-toluic acid over hierarchical x zeolite
José María Gómez ⁎, Eduardo Díez, Ignacio Bernabé
Grupo de Catálisis y Operaciones de Separación (CyPS), Department of Chemical Engineering, Faculty of Chemistry, Complutense University of Madrid, 28040, Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Catalytic activity of FAU zeolites was tested on the deoxygenation of m-toluic acid at atmospheric pressure and
without feeding hydrogen. Sodium dodecylbenzenesulfonate was used as template to obtain a certain
mesoporosity in the NaX zeolite. The mesoporosity improved the catalytic activity. This zeolite showed a good
activity catalytic increasing the toluene yield to 40%, reducing the oxygen content in the reaction products, and
decreasing the esterification reaction. The catalytic activity was kept without deactivation of the catalyst.
Received 15 December 2015
Received in revised form 5 February 2016
Accepted 7 February 2016
Available online 9 February 2016
©
2016 Elsevier B.V. All rights reserved.
Keywords:
Deoxygenation
m-Toluic acid
Mesoporosity
FAU zeolite
Toluene
1
. Introduction
decarboxylation of methyl octanoate and benzaldehyde. The highly
polar environment of the micropores of the zeolite seems to play an
essential role in the adsorption and decomposition of adsorbed
molecules without hydrogen consumption [8,9]. However, some of the
compounds obtained in biofuels, which could be deoxygenated, are
too bulky to diffuse through the zeolite pores. In this sense, the use of
zeolites with hierarchical porosity would be very interesting. Hierarchi-
cal zeolites have emerged as an important class of materials, since the
presence of porosity on different scales lead to improved catalytic
performance compared to their microporous parents. Successful
methods for the direct preparation of mesoporous zeolites with high
silicon/aluminum molar ratio and MFI and Beta frameworks have
been developed. In these syntheses ordered mesoporous carbons or car-
bon nanotubes, functionalized polymers, hybrid organic–inorganic sur-
factants, cationic polymers, etc. were employed as templates [10].
However, there are few studies about synthesis of zeolites with FAU
framework and low silicon/aluminum molar ratio. Xiao et al. reported
on the synthesis of mesoporous NaX zeolite with silicon/aluminum
molar ratio of 1.3 using organic templates of cationic polymer
(polydiallyldimethylammonium chloride) and spirulina [11]. Mesopo-
rous in the range of 4–5 nm were obtained and the calcium ion-
exchange rate was higher than that of conventional NaX zeolite. Inayata
et al. synthesized X zeolite with a low Si/Al ratio of 1.0–1.5 using 3-
(trimethoxysilyl)propyl hexadecyl dimethyl ammonium chloride as
amphiphilic organosilane achieved mesopores with a mean size of
7 nm but with intracrystalline mesopores [12]. Undoubtedly, the devel-
opment and use of hierarchical zeolites with low silicon/aluminum
molar ratio will increase in coming years and it would be interesting
to study the potential templates and their basic catalytic properties.
In this study the synthesis of NaX zeolite with mesoporosity was
carried out using as template an anionic surfactant, sodium
The production of biofuels from wood, vegetable oils and animal fats
has been considered a good alternative to supply large quantities of
fuels. However, it requires significant changes to become an acceptable
transportation fuel [1–3]. These biofuels contain a complex mixture of
acids, alcohols, aldehydes, esters, ketones, phenols, carbohydrates,
furans, alkenes, aromatics and nitrogen compounds. In these mixtures,
a high content of oxygenated groups involves high viscosity, poor
thermal stability, low calorific value and high corrosivity, which limits
their applicability. Therefore, the presence of oxygenated compounds
decreases the quality of biofuels and the deoxygenation, the removal
of oxygen atoms present in the molecules, is needed to enhance fuel en-
thalpies, decrease its viscosity and corrosivity and stabilize the biofuels
increasing their chemical and thermal stability. Biofuels obtained after
deoxygenation will be acceptable and economically attractive. Deoxy-
genation of biofuels has been mainly studied over acid catalysts, silica-
alumina or zeolites, with consumption of hydrogen at high pressure
and with formation of coke and tar as well as of by-product undesirables
[
4,5]. Deoxygenation of biofuels can also be carried out by direct elimi-
nation of the carboxylic groups releasing CO (decarboxylation) and/
or CO (decarbonylation) over supported metal catalyst such as Pd/C
6,7]. An alternative to these catalysts are the basic solid catalysts,
2
[
which can produce decarbonylation and decarboxylation reactions
with lower hydrogen consumption, lower temperature and less coke
formation. Among the possible basic solid catalysts for use in these reac-
tions are the basic zeolites. Resasco et al. have published studies about
the use of CsNaX zeolite as catalyst in the decarbonylation and
⁎
Corresponding author.
E-mail address: segojmgm@ucm.es (J.M. Gómez).
http://dx.doi.org/10.1016/j.catcom.2016.02.008
566-7367/© 2016 Elsevier B.V. All rights reserved.
1

56
J.M. Gómez et al. / Catalysis Communications 78 (2016) 55–58
dodecylbenzenesulfonate (SDBS, CH
was employed as catalyst on the m-toluic acid deoxygenation reaction.
3
(CH
2
)
11
C
6
H
4
SO
3
Na). This zeolite
Table 1
Physical properties of the zeolites.
13X (NaX)
USY
KNaX
NaX
NaXSDBS
2
. Experimental
a
Si/Al (mol)
1.3
26.5
0
877
842
3.1
6.3
0
782
722
60 (7.7%)
0.333
1.1
1.5
23.6
0
641
613
1.5
24.9
0
551
499
a
%
Na wt.% u.c.
18.2
13.5
713
676
36 (5%)
0.284
a
2
.1. Catalysts
%K wt.% u.c.
b
2
S
S
S
V
BET (m /g)
c
2
micro (m /g)
X zeolite syntheses with different silicon/aluminum molar ratio
c
2
meso (m /g)
35 (4%)
0.336
28 (4.4%)
0.266
52 (9.4%)
0.247
were carried out via the hydrothermal method according to previous
studies. All the solids obtained were washed, dried at 373 K overnight
and calcined at 823 K for 3 h (heating rate 1.8 °C/min).
d
3
pore (cm /g)
wt.% u.c.: weight percentage per unit cell.
a
Composition determined from XRF data.
Specific surface calculated from N adsorption data applying BET method.
2
Micropore surface calculated from N
Mesopore surface calculated from N
Synthesis of KNaX zeolite was carried out employing a gel with
b
c
molar ratios: SiO
2
/Al
2
O
3
= 2.2, (Na
2
O + K
2
O)/SiO
2
= 3.25, H
2
O/
2
adsorption data applying t-plot method.
adsorption data applying t-plot method.
d
(
Na O + K O) = 17 and Na
2
2
2
O/(Na O + K
2
2
O) = 0.77. Aging and crystal-
2
lization were carried out at 343 K for 14 h. This zeolite has a silicon/alu-
minum molar ratio of 1.1 and an anhydrous unit cell formula of
0
adsorption at low relative pressure (p/p b0.03). Nitrogen adsorption
Na64
Synthesis of NaX zeolite was carried out employing a gel with molar
ratios: SiO /Al = 3.44, Na O/SiO = 1.32, H O/Na O = 39.8. Aging
and crystallization stages were carried out at 298 K for 24 h and at
73 K for 7 h, respectively. This zeolite has a silicon/aluminum molar
ratio of 1.5 and an anhydrous unit cell formula of Na77(SiO 115(AlO
14]. Synthesis of NaXSDBS was carried out in the same way, but using so-
dium dodecylbenzenesulfonate (SDBS) during the synthesis. The con-
centration of SDBS in the mixture gel was 5.2 mM (1.8 times the
critical micelle concentration of the SDBS at 298 K) with a molar ratio
K
28(SiO
2
)
100(AlO
2
)
92 [13].
hardly took place between p/p = 0.1 and 0.8, with a variation in the
0
quantity adsorbed of 2.8%. The isotherm belongs to type I in the IUPAC
classification with H4 hysteresis loop, attributed to the aggregation of
particles. On the other hand, NaXSDBS shows the initial high adsorption
2
O
2 3
2
2
2
3
(p/p
of micropores [16], but with higher variation (7.0%) in the quantity
adsorbed in the p/p range between 0.1 and 0.8. In addition, the hyster-
esis loop is wider, starting at p/p 0.4, and with more difference between
0
b0.03), in the same way that the NaX zeolite, due to the filling
2
)
2 77
)
[
0
0
desorption and adsorption branches, which indicates a broad pore size
distribution. The adsorption isotherm for this zeolite NaXSDBS belongs
SDBS/SiO
2
= 0.005 [15]. This zeolite has a silicon/aluminum molar
2 77
115(AlO ) .
ratio of 1.5 and an anhydrous unit cell formula of Na77(SiO
2
)
Commercial 13X (NaX) and USY zeolites were supplied by Sigma-
Aldrich and Grace Davison, respectively.
2
.2. Characterization
adsorption–desorption isotherms were obtained at −77 K using
N
2
a MICROMERITICS ASAP 2020. Total surface area and pore volume were
determined using the Brunauer–Emmett-Teller (BET) equation and the
single-point method, respectively. Pore size distribution (PSD) curves
were calculated by Barrett–Joyner-Halenda (BJH) method. X-ray dif-
fraction (XRD) patterns were recorded on a SIEMENS-D501 diffractom-
eter with CuKα1 radiation with scanning range of 2θ between 5° and
5
0° with a step size of 0.1°. Chemical composition was determined by
means of X-ray fluorescence (XRF) in an Aχios instrument.
2
.3. Catalytic activity
3 6 4
Deoxygenation reaction of m-toluic acid (CH C H COOH), as probe
molecule, was carried out at 698 K in a fixed bed reactor with continu-
−
1
ous nitrogen flow (20 mL min ) at atmospheric pressure. Previously,
the zeolites were calcined at the reaction temperature, 698 K, in nitro-
gen stream for 1 h. Reaction conditions employed were catalyst
−
1
weight/feed rate of reactants (W/F) of 13 g h mol and 1 wt.% of m-
toluic acid in a solvent. Samples from the reaction were analyzed by
Gas Chromatography in a Varian CP-3800 equipped with a capillary col-
umn (30 m) and flame ionization detector (FID).
3
. Results and discussion
3
.1. Catalyst characterization
XRD profiles exhibited the characteristic peaks of the FAU frame-
work, without amorphous halo and with high crystallinity in all zeolites.
Table 1 shows the physical characteristics of the commercial and as-
synthesized zeolites.
Fig. 1 shows the nitrogen adsorption/desorption isotherms recorded
at 77 K of the as-synthesized zeolites with and without SDBS. Zeolite
NaX displays the typical shape of the microporous materials, exhibiting
Fig. 1. a) Nitrogen adsorption/desorption isotherms at 77 K in NaX and NaXSDBS as-
synthesized zeolites. b) Normalized nitrogen adsorption/desorption isotherms at 77 K in
NaX and NaXSDBS as-synthesized zeolites.

J.M. Gómez et al. / Catalysis Communications 78 (2016) 55–58
57
to the type I + IV with H3 hysteresis loop. The difference between both
zeolites is more clearly appreciated in Fig. 1b, where is displayed the
normalized quantity adsorbed. Fig. 2 shows the pore size distribution
(
PSD) obtained applying the BJH model (using the KJS correction) to
the desorption branch of the isotherm. NaXSDBS presents a broad band
with high intensity centered at ca. 11.5 nm, indicating a pore size distri-
bution narrower than those of the NaX zeolite. Therefore, the use of
SDBS during the synthesis procedure allows obtaining hierarchical
porosity in the NaX zeolite.
For the rest of zeolites the shape of the nitrogen adsorption/
desorption isotherm at 77 K was the typical for microporous materials,
similar to that of the NaX as-synthesized zeolite.
3
.2. Deoxygenation of m-toluic acid
Among the different compounds formed in the pyrolysis, bio-oils
noted for their high presence the aromatic derivatives, so in this work
we studied the deoxygenation of m-toluic acid as probe molecule.
The low concentration employed was due to two reasons. Firstly, the
concentration of this kind of compounds (aromatic acids) in the bio-oils
is low. The other reason was related with technical problems. Formation
of crystals of m-toluic acid was detected at the reactor outlet, after
the reaction zone. Even the pipe was blocked at high concentration of
m-toluic acid (N5 wt.%). This problem did not allow closing mass
balance due to part of feed m-toluic acid was accumulated in this
point of the experimental installation. Anyway, as this happens after
the catalyst, the reaction was carried out being expressed the results
only as yields. However, that was not an impediment to check the cata-
lytic activity of these zeolites in the deoxygenation of aromatic acids, as
the m-toluic acid.
The expected product of the deoxygenation, using methanol as sol-
vent, was toluene. However, since the methanol can produce hydrogen
and formaldehyde over this kind of zeolite [17], hydrogenation prod-
ucts, as xylenes, and methylation products, as ethylbenzene, xylenes
or trimethylbenzenes, could be formed. All these products would be de-
sired products since they have lost the oxygen atoms. On the other
hand, the esterification reaction to produce methyl 3-methylbenzoate
would be an undesired reaction because it did not reduce the oxygen
content.
Fig. 3. Product distribution in the deoxygenation reaction of m-toluic acid. Reaction
conditions: time: 1 h; W/F: 13 g h mol− ; temperature: 698 K, m-toluic acid (1 wt.%)
and methanol or acetonitrile (99 wt.%).
1
It can be observed that the reaction with USY zeolite left
mainly to other products (80%) and without formation of methyl
2methylbenzoate. This was the only zeolite that did not produce the
esterification reaction. Among the desired products the main product
were xylenes (10%), which confirms the acid character of this zeolite
since the toluene methylation over acid catalyst leads to the ring meth-
ylation [17]. This zeolite produced the catalytic cracking of the m-toluic
acid to products with low molecular weight, which were not detected
by FID detector, due to its acid character (cations/aluminum molar
ratio b1). However, the yield to desired products (≈17%) was similar
to these of the 13× Aldrich and KNaX zeolites, but over these zeolites,
esterification product was mostly obtained, especially over the KNaX
zeolite (12%). Among these three zeolites, the 13× Aldrich zeolite pre-
sented the highest desired/undesired molar ratio, around 2. Therefore,
the KNaX as-synthesized zeolite, with potassium and lower silicon/
aluminum molar ratio, did not improve the catalytic activity in the
deoxygenation reaction of m-toluic acid in spite of being the most
basic zeolite. There are two reactions competing with the active sites,
deoxygenation and esterification, and both of them are produced over
FAU zeolites.
A wider product distribution was obtained in the reaction without
catalyst (blank test) due to the thermal cracking of the m-toluic acid,
with a low yield to deoxygenation products (≈2%). Fig. 3 displays the
product distribution in the reaction with the different zeolitic catalysts
using methanol and acetonitrile as solvents.
Fig. 2. Pore size distribution in NaX and NaXSDBS as-synthesized zeolites, obtained from the
desorption branch.
Fig. 4. Catalytic activity of the NaXSDBS zeolite in the reaction with acetonitrile as solvent.
W/F: 13 g h mol− ; temperature: 698 K, m-toluic acid (1 wt.%).
1

58
J.M. Gómez et al. / Catalysis Communications 78 (2016) 55–58
Fig. 5. Mechanism of reaction.
On the other hand, the most active catalyst was the NaX as-
a remarkable problem, since biofuels are renewable and do not affect
to the carbon dioxide balance. On another hand, if methanol is used as
solvent, the esterification reaction is also possible since the methyl of
methanol could be linked to the oxygen of hydroxyl group of the m-
toluic acid producing methyl 3-methylbenzoate.
synthesized zeolite with and without SDBS (Fig. 3). NaX as-synthesized
zeolite reached a yield to desired products around 22%, upper than the
yield to methyl 3-methylbenzoate (15%), obtaining a desired/undesired
molar ratio of 1.5. Among deoxygenation products, the production of
toluene was especially significant with a yield around 10%. However,
the main product was methyl 3-methylbenzoate (15%).
4. Conclusions
Noteworthy results were obtained with the NaXSDBS zeolite,
reaching a total yield to desired and undesired near 70%. Therefore,
the presence of a certain mesoporosity in the zeolite increased the
catalytic activity of the NaX zeolite since it improved the access to the
active site and the formation of bulky molecules as the methyl 3-
methylbenzoate, reaching a yield of 37%. The yield to desired products
also increased to 32% (10% more than with the NaX as-synthesized zeo-
lite), achieving a desired/undesired molar ratio around 0.9. The main
desired products were toluene (11%), xylenes (11%) and ethylbenzene
This is the first report on the use of sodium dodecylbenzenesulfonate
SDBS), as template, for the synthesis of X zeolite with a certain
(
mesoporosity. This as-synthesized zeolite was found to be better for de-
oxygenation reaction of m-toluic acid since the mesoporosity improved
the access of the reactant to the active sites. The desired/undesired
molar ratio was near 3. The production of xylenes was due to the meth-
ylation of toluene, not the hydrogenation of m-toluic acid. Therefore, a
solvent with low methylation capacity, as acetonitrile, is necessary to
obtain toluene as main product, avoiding the methylation of toluene
(
7%).
In spite of the better activity with the NaXSDBS as-synthesized zeolite,
(
ethylbenzene, xylenes, etc.). The NaXSDBS zeolite could be used in the
the yield to oxygenated products was still high, upper to the yield to de-
oxygenated products. Acetonitrile, as solvent, was employed in order to
cut down to a minimum the formation of the ester and, hence, to direct
the reaction mechanism toward the toluene formation. These results
are shown in Fig. 3. Meaningful decrease in the yield to methyl 3-
methylbenzoate, from 37% on methanol to 15% on acetonitrile, was ob-
served. This was due to the lesser methylation capacity of acetonitrile
compared to that of methanol. Associated to the less methylation capac-
ity, the main product was toluene, reaching a yield of 40%, four times
higher than with methanol. The desired/undesired molar ratio was in-
creased to almost 3. Therefore, when methanol was used as solvent,
the formation of ethylbenzene, xylenes or trimethylbenzenes was
produced from toluene methylation.
Fig. 4 shows the variation of the catalytic activity with the reaction
time in the reaction with acetonitrile as solvent. There was no detected
decrease in the catalytic activity with the reaction time. The yields were
steady for 3 h, with a slight increase. The same behavior was observed
with the NaX and NaXSDBS zeolites in the reaction with methanol as sol-
vent. Moreover, the color of the zeolites after the reaction was beige, not
black. It is well known that the solid base catalysts, unlike solid acid
catalysts, tend not to form coke on the surface since basic sites lack in
cracking ability [18].
deoxygenation of biofuels at low pressure and without external
consumption of hydrogen.
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