Effects of oxidant acid treatments on carbon-templated hierarchical SAPO-11 materials: Synthesis, characterization and catalytic evaluation in n-decane hydroisomerization

Article abstract of DOI:10.1016/j.apcata.2014.08.006

Hierarchical SAPO-11 was synthesized using a commercial Merck carbon as template. Oxidant acid treatments were performed on the carbon matrix in order to investigate its influence on the properties of SAPO-11. Structural, textural and acidic properties of the different materials were evaluated by XRD, SEM, N₂ adsorption, pyridine adsorption followed by IR spectroscopy and thermal analyses. The catalytic behavior of the materials (with 0.5 wt.% Pt, introduced by mechanic mixture with Pt/Al₂O₃), were studied in the hydroisomerization of n-decane. The hierarchical samples showed higher yields in monobranched isomers than typical microporous SAPO-11, as a direct consequence of the modification on both porosity and acidity, the later one being the most predominant.

Full text of DOI:10.1016/j.apcata.2014.08.006

Applied Catalysis A: General 485 (2014) 230–237
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Effects of oxidant acid treatments on carbon-templated hierarchical
SAPO-11 materials: Synthesis, characterization and catalytic
evaluation in n-decane hydroisomerization
Raquel Bértoloa, João M. Silvaa,b, Filipa Ribeiroa, Francisco J. Maldonado-Hódarc,
Auguste Fernandesa,∗∗, Angela Martinsb,d,∗
a IBB, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
b Área Departamental de Engenharia Química and CIEQB, Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emídio Navarro, 1, 1959-007 Lisboa,
Portugal
c Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
d CQB, Universidade de Lisboa, Faculdade de Ciências, Campo Grande C8, 1749-016 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Hierarchical SAPO-11 was synthesized using a commercial Merck carbon as template. Oxidant acid treat-
ments were performed on the carbon matrix in order to investigate its influence on the properties of
SAPO-11. Structural, textural and acidic properties of the different materials were evaluated by XRD,
SEM, N2 adsorption, pyridine adsorption followed by IR spectroscopy and thermal analyses. The catalytic
behavior of the materials (with 0.5 wt.% Pt, introduced by mechanic mixture with Pt/Al2O3), were studied
in the hydroisomerization of n-decane. The hierarchical samples showed higher yields in monobranched
isomers than typical microporous SAPO-11, as a direct consequence of the modification on both porosity
and acidity, the later one being the most predominant.
Received 23 January 2014
Received in revised form 2 July 2014
Accepted 6 August 2014
Available online 15 August 2014
Keywords:
Hierarchical SAPO-11
Carbon templating
Acidity
© 2014 Elsevier B.V. All rights reserved.
n-decane
Hydroisomerization
1. Introduction
microporous character of these materials can be a drawback.
Indeed, reactants and products with sizes above the micropore
Zeolites and zeotype materials like silicoaluminophosphates
(SAPO), owing crystalline frameworks and ordered networks of
micropores (<2 nm), have been widely used as important het-
erogeneous catalysts in industrial processes such as oil refining,
petrochemistry and also as adsorbents in purification and separa-
tion processes. These vast applications emerge due to the particular
combination of properties of this class of materials: large surface
area and crystallinity, high adsorption capacity, tailored acidity,
high thermal stability, well defined pore sizes and excellent shape
selectivity [1,2]. However, with an increasing need for faster dif-
fusion rates and higher conversion of bulky molecules, the solely
dimensions cannot diffuse in and out of the crystals, causing loss of
activity and selectivity with consequent reduction in the lifetime of
the catalyst. One of the strategies to overcome this limitation is the
introduction of an additional pore system (meso or macroporous)
in order to fabricate hierarchically structured materials. Through
this way, a single material would possess the catalytic features of
micropores and the enhanced access and transport properties of
mesopores [3]. The preparation methods for hierarchical materi-
als comprise two different methods: (i) post-synthesis procedures,
such as dealumination or desilication, where the mesoporosity is
formed as a consequence of Al or Si extraction in acid or basic
medium, or (ii) by adding one or more templates during the crys-
tallization process. Several materials can be used as solid templates
such as resins, polymers, polyurethane foams or cellulose [4]. How-
ever, the most general and versatile approach is to employ different
types of porous carbons like carbon particles. In fact, the carbon
templating method can be tuned to yield either nanosized zeolite
crystals or mesopororous zeolite crystals. By only slightly chang-
ing the crystallization conditions it is possible for zeolite crystals
to nucleate not only inside the carbon matrix but also to continue
∗
Corresponding author at: Área Departamental de Engenharia Química, Instituto
Superior de Engenharia de Lisboa, Rua Conselheiro Emídio Navarro, 1, 1959-007
Lisboa, Portugal. Tel.: +351 218317000; fax: +351 218317001.
∗∗
Corresponding author at: IBB, Instituto Superior Técnico, Universidade Técnica
de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. Tel.: +351 21419183;
fax: +351 218419198.
E-mail addresses: auguste.fernandes@ist.utl.pt (A. Fernandes),
amartins@deq.isel.ipl.pt (A. Martins).
http://dx.doi.org/10.1016/j.apcata.2014.08.006
0926-860X/© 2014 Elsevier B.V. All rights reserved.

R. Bértolo et al. / Applied Catalysis A: General 485 (2014) 230–237
231
their growth through the surrounding carbon pore system in such
a way that the crystals encapsulate part of the carbon matrix [5].
Although the production of hierarchical materials is most devel-
oped for zeolites, other similar materials such as SAPOs are also
being studied due to its particular catalytic properties, especially
when mild acidity is required. SAPO-11 (AEL topology) comprising
one-dimensional, non-intersecting 10-membered ring channels
Each carbon template (6 wt.%) was added to the gel after DPA.
The latter was then transferred into an autoclave. In all cases, crys-
tallization was achieved at 200 ◦C for 24 h. The products obtained
were recovered by centrifugation, washed several times with dis-
tilled water and dried at 110 ◦C overnight. The organic and carbon
templates were removed by calcinations, first at 350 ◦C for 2 and
then at 600 ◦C for 12 h under air (15 L h−1 g−1). The obtained sam-
ples were named as S-x, where x represents the carbon template
used.
˚
with elliptical pore-apertures of 4 × 6 A was first reported by Lok
et al. [6]. Due to its moderate acidity and suitable pore size, SAPO-
11 loaded with a trace amount of noble metal has been found
highly active and selective for the hydroisomerization of long
chain n-paraffins to produce high quality diesel fuel and lubricants,
achieving high isomerization yields and less cracking products [7].
The hydroisomerization of long chain n-paraffins over metal loaded
catalysts is supposed to proceed via a bifunctional mechanism as
suggested by Martens et al. [8], where the adsorption and reac-
tion takes place at the external surface of the crystals and at the
pore mouths of the 10-ring tubular pore molecular catalyst such as
MCM-22 or SAPO-11 [9]. Therefore, the more pore mouths par-
ticipating in the reaction and the larger external surface of the
catalyst are advantageous in order to get high selectivity towards
isomerization products.
2.2. Samples characterization
The structural characterization of the parent and hierarchical
SAPO-11 samples was carried out with a D8 Advance diffractome-
ter from Bruker, equipped with a graphite monochromator using
Cu-K␣ radiation as incident beam. The powder XRD patterns were
obtained from 5 to 40◦ (2ꢀ), a step of 0.03 and a time per step of 4 s.
Chemical analysis of samples calcined was done by ICP-AES for Al
and P contents and atomic absorption spectroscopy (AAS) for Si.
Thermogravimetric (TG) and differential scanning calorimetry
(DSC) analysis were performed on a TG-DSC 92 Setaram Instru-
ment. Each sample was heated between 25 and 900 ◦C (10 ◦C min−1
)
The purpose of this work is to explore the catalytic behavior of
hierarchical SAPO-11 materials, using a commercial Merck carbon
as solid template. The surface chemistry of the carbon was modi-
fied through oxidant acid treatments and the possible interaction
with SAPO-11 gel synthesis was explored, in order to study its influ-
ence on the physicochemical properties and catalytic behaviour of
hierarchical SAPO-11 materials.
The bifunctional catalysts were prepared by mechanically mix-
ing SAPO-11 samples with Pt/Al2O3 (final loading 0.5 wt.% Pt) in
order to present the same metal function properties. These catalysts
were evaluated in the hydroisomerization of long chain n-alkane
using n-decane as reactant.
under air flow (30 mL min−1).
Textural characterization of the solids was carried out by means
of N2 sorption measurements isotherms at −196 ◦C, performed
in an automatic apparatus Micromeritics ASAP 2010, where the
samples were outgassed at 350 ◦C under vacuum before N2 sorp-
tion measurements. The morphology and size of the crystals were
analyzed by Scanning Electron Microscopy (SEM), performed on a
Hitachi S400 microscope.
27Al, 31P and 29Si MAS NMR spectra were recorded in Bruker
Avance III 400 NMR spectrometer (B0 = 9.4 T) at, respectively, 13,
12 and 5 kHz with 60 s recycle delays. Chemical shifts are quoted
in ppm.
The samples acidity was characterized by pyridine adsorption
followed by IR spectroscopy on a Nicolet Nexus spectrometer. The
samples were pressed into thin wafers (10–20 mg cm−2) and pre-
treated in an IR quartz cell at 450 ◦C for 3 h under secondary vacuum
(10−6 mbar). The samples were then cooled down to 150 ◦C and
contacted with pyridine (Peq = 2–3 mbar) during 10 min. After that,
the excess of pyridine was evacuated for 30 min under secondary
vacuum and then IR spectra were recorded (64 scans with a resolu-
tion of 4 cm−1). The background spectrum, always recorded under
identical conditions without sample and performed before each
spectrum acquisition, was automatically subtracted. For quantifica-
tion purposes, the spectrum of the sample after pretreatment was
subtracted from the spectra obtained after pyridine adsorption and
subsequent desorption.
2. Experimental
2.1. Samples preparation
Conventional SAPO-11 sample was prepared by hydrothermal
synthesis according to a previous procedure [6], with the following
molar composition: 1.0 Al2O3: 1.0 P2O5: 0.4 SiO2: 1.5 DPA: 50 H2O.
The following reagents were used as received: pseudoboehmite
(Plural SB from Condea, 75 wt.% Al2O3), orthophosphoric acid
(H3PO4 from Merck, 85 wt.% aq. solution), silica (AS40) as sources of
T atoms and dipropylamine DPA (from Aldrich, 99 wt.% aq. solution)
as structure-directing agent.
In order to study the influence of the concentration of oxygen
surface groups present on the commercial carbon and their possible
interaction with SAPO-11 synthesis gel, Merck carbon template was
submitted to a wet oxidation treatment. A 4.6 M solution of HNO3
was used as oxidizing agent and mixed with the carbon sample
(1 g of carbon/10 mL of solution) [10]. The suspension was evapo-
rated at 60 ◦C until dryness. After the acid treatment, the sample
was washed with distilled water until the pH was the same as the
one for distilled water. This sample will be referred to as Mox here-
after. Then, Mox sample was treated at 300 ◦C (5 ◦C min−1, N2 flow,
10 L h−1) to give Mox300 material with intermediate oxygenated
surface properties (partial oxygen removal).
The hierarchical SAPO-11 samples were prepared following the
same procedure and molar composition used to obtain the con-
ventional one but the method of solid templating was applied to
produce hierarchical samples. In this study, three distinct carbon
samples were used: the commercial Merck and two oxidized ones
(Mox and Mox300).
The surface chemistry of the carbon materials was characterized
by determining the point of zero charge (pHpzc). In brief, a certain
amount of the carbon was dispersed into an appropriate amount
of CO2-free distilled water (0.05 g cm−3). The slurry was then kept
in a plastic bottle and shaken periodically for 2 days until the pH
had stabilized, the final slurry pH value measured (glass electrode
from micropH2000, Crison) corresponding to the pHpzc value of the
carbon matrix [11].
2.3. Preparation of bi-functional catalysts and catalytic tests
The n-decane hydroisomerization was carried out at atmo-
spheric pressure in a flow reactor using 0.1 g of catalyst loaded
with 0.5 wt.% of Pt. The metal function was introduced by mechan-
ically mixing the necessary amount of Pt/Al2O3, (1 wt.% Pt, Aldrich)
to SAPO-11 samples in order to obtain a bifunctional Pt/SAPO-11
with 0.5 wt.% metal loading. After mixing for 1 min in an agatha
mortar the resulting powder was slightly pressed into wafers and

232
R. Bértolo et al. / Applied Catalysis A: General 485 (2014) 230–237
then crushed and mixed again. This procedure was repeated twice
and then the powder was transferred to the catalytic reactor. Prior
to the catalytic tests the samples were reduced in situ under H2
flow at 500 ◦C for 3 h. The reaction was performed with a molar
ratio H2/n-C10 = 7. The total conversion was changed by varying the
reaction temperature (280–330 ◦C) and WHSV (6.6–13.1 h−1). The
reaction products were analyzed on-line with a gas chromatograph
Hewlett-Packard 6890 series equipped with a flame ionization
detector and a capillary CP-Sil5 column.
3. Results and discussion
3.1. Characterization of the carbon matrixes
The results from thermogravimetric measurements (nitrogen
atmosphere) performed for samples Mox, Mox300 and Merck are
presented in Table 1. Logically, the most oxidized Mox sample
presents a very high weight loss (ca. 20%), followed by the inter-
mediate Mox300 (11%) and finally Merck (about 4%), meaning that
oxidant treatment enriched the carbon surface with oxygenated
species (Mox), while subsequent thermal treatment tends to reduce
the amount of poorly stable oxygenated species (Mox300) until
reaching a material with no or little OSG groups, i.e. the initial Merck
carbon. Therefore, the OSG percentage in our samples follows the
order: Mox > Mox300 > Merck (see values in Table 1).
The changes of the surface chemistry as a consequence of
oxidant acid treatments were monitored by means of pHpzc mea-
surements and the results obtained are displayed in Table 1. As it
can be observed, the most oxidized sample Mox presents a pHpzc
value significantly lower when compared with the untreated Merck
carbon, denoting a higher concentration of acidic OSG. On the other
hand, sample Mox300 shows an intermediate value.
Fig. 1. XRD patterns of the samples SAPO-11 synthesized (S0.4Si) and S-Merck,
S-Mox and S-Mox300 (with carbon template).
for P) substitution mechanism. One can see that Si amount incor-
porated during gels crystallization seems to be independent from
the presence of carbon matrix.
All the samples present diffraction lines corresponding to AEL
phase (Fig. 1), as reported in the literature [6]. However, the sam-
ples prepared with carbon matrixes present a slight decrease of
the peaks and a slight increase of the baseline, due to the pres-
ence of a very broad band. This is consistent with the presence of
well crystalline SAPO-11 materials together with an amorphous
phase corresponding to the carbon matrix added during the gel
preparation. Also, the absence of any other extraneous phase (alu-
mina, aluminophosphate, etc.) is confirmed by NMR results (see
below). In some cases, an extra peak at about 8.5 in 2ꢀ correspond-
ing to SAPO-31 contaminant phase appears, though with a very low
intensity. Fig. 2.
The TG-DSC results for all SAPO-11 samples, displayed on
Table 2, indicate two main weight losses corresponding to,
respectively: desorption of physisorbed water (below 170 ◦C) and
decomposition/oxidation of both DPA template and carbon matrix
(170–700 ◦C). Assuming a theoretical DPA weight loss of about 8%
for pure SAPO-11 [12], the amount of carbon matrix present in the
final materials can be determined as the difference between total
weight loss and estimated DPA + experimental water weight losses
contributions. As it can be seen on Table 2, the total weight loss,
and consequently the carbon weight loss, is similar, for the same
percentage of carbon, with Merck and oxidized carbon matrixes.
The textural parameters of SAPO-11 and hierarchical SAPO-11
are quoted in Table 2. The samples prepared using carbons as
templates present a value for Vmicro characteristic of SAPO-11 struc-
ture, meaning that the original microporous structure of SAPO-11
was preserved. However, an increase of Aext and Vmeso is clearly
shown in all cases regarding S0.4Si, leading to the conclusion that
hierarchical materials were successfully obtained. The stronger
development of this parameter was obtained for S-Merck sample.
Indeed, neither the oxidation nor the following thermal treatment
provokes such increase. Nevertheless, these treatments signifi-
cantly influence the morphology of final SAPO-11 materials. SEM
The quantitative assessment of the micropores volume, Vmicro
,
and the external surface area, Aext, of the samples was done
applying the t-method while the mesopores volume, Vmeso was
calculated as the difference between total volume and Vmicro. The
results are reported in Table 1. One can see that oxidized sample
Mox shows a decrease of Vmicro together with an increase of both
Vmeso and Aext, when compared with Merck commercial carbon,
in agreement to what was previously reported [10]. This observa-
tion can be easily explained by a synergetic effect corresponding
to, in one hand, the formation of OSG groups within the micro-
pores blocking them and, in the other hand, a partial mechanical
destruction of the micropores walls leading to mesopores and/or
macropores development.
Upon thermal treatments in inert atmosphere, an increase in
Vmicro is observed for Mox300 sample, as OSG that were filling
the micropores are partially removed. The release of OSG from the
newly mesopores/macroprores created (see above) might also lead
to a progressive pore opening. However, in order to confirm the
presence of larger macropores, mercury porosimetry experiments
should be performed.
3.2. Characterization of hierarchical SAPO-11 materials
The data obtained from chemical analysis (not shown) reveal
that the T atom molar fraction was similar for all SAPO-11 samples
(Al0.50P0.44Si0.06O2). These values are normally indicative of SM2 (Si
Table 1
Amount of H2O and OSG (oxygenated surface groups) from TG experiments and pHpzc values and textural parameters for carbon matrix samples.
Samples
H2O (wt.%)
OSG (wt.%)
pHpzc
Aext (m2 g−1
)
Vmicro (cm3 g−1
)
Vmeso (cm3 g−1
)
Mox
Mox300
Merck
7.0
2.6
0.7
20
11
4
2.99
3.72
7.02
115
56
62
0.34
0.48
0.52
0.14
0.10
0.11

R. Bértolo et al. / Applied Catalysis A: General 485 (2014) 230–237
233
Fig. 2. SEM of carbon templates, Merck (A), Mox (B), Mox300 (C)
5 ␮m).
(
5 ␮m), and SAPO-11 samples, S0.4Si (D), S-Merck (E), S-Mox (F) and S-Mox300 (G)
(
micrographs of the different carbon matrixes and respective SAPO-
11 materials are presented in Fig. 1. As can be observed, the oxidized
carbons (images B and C) present more fragmented particles, espe-
cially when the oxidation is followed by heat treatment. Concerning
carbon-templated SAPO-11 materials, the ordered spherical aggre-
gates presented for S0.4Si (image D) become more heterogeneous
and fragmented, with presence of large cavities, due to carbon com-
bustion (image E). Samples prepared from oxidized carbons seem
to follow the same patterns as their correspondent carbon tem-
plates, as the fragmentation and heterogeneity tend to increase
from S-Mox to S-Mox300 (images F and G).
NMR spectroscopic measurements were performed in order to
evaluate the structural properties of the materials synthesized and
the distribution of Si. 27Al, 31P (sample S0.4Si) and 29Si (samples
S-Mox (a), S-Merck (b) and S0.4Si (c)) spectra are presented in
Figs. 3 and 4, respectively. The NMR measurements were performed
onto calcined, rehydrated samples. The 31P spectrum of sample
S0.4Si (Fig. 3a) shows two well-defined signals at about −29.2 (the
most intense) and −23.2 ppm. In the 27Al spectrum (Fig. 3b) four
signals can be observed at 39.1, 28.0, 7.1 and −15.2 ppm (the first
signal being the most intense). All these 27Al and 31P signals have
been observed in crystalline SAPO-11 materials by other authors
Table 2
Weight losses (wt.%) observed from TG experiments, pyridine quantification (at 150 ◦C) and textural parameters for SAPO-11 (carbon-free and hierarchical) samples.
Sample
Weight loss (wt.%)
PyH+ (␮mol g−1
)
PyL (␮mol g−1
)
Aext (m2 g−1
)
Vmicro (cm3 g−1
)
Vmeso (cm3 g−1
)
Total
Carbon
S0.4Si
S-Merck
S-Mox
8.3
35.9
32.7
35.9
–
46
17
31
21
49
34
33
38
21
47
40
32
0.07
0.06
0.07
0.07
0.04
0.10
0.08
0.07
26.8
23.3
25.2
S-Mox300

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R. Bértolo et al. / Applied Catalysis A: General 485 (2014) 230–237
50
45
40
35
30
25
20
15
10
5
S-Mox
S-Mox300
S-Merck
0
0
2
4
6
8
10
pHpzc
Fig. 5. Concentration of Brönsted acid sites (at 150 ◦C) of S-Mox, S-Mox300 and S-
Merck samples as a function of pHpzc values of the corresponding carbon templates.
Fig. 3. 31P (a) and 27Al (b) MAS NMR spectra of the sample S0.4Si calcined.
molecule. After Py adsorption, all the samples present, in the
region 1400–1700 cm−1, the bands characteristic of PyH+ species
at around 1545 cm−1 (Brönsted acid sites) and coordinated PyL at
ca. 1455 cm−1 (Lewis acid sites) (spectra not shown).
Table 2 displays the acid concentration for parent and hierarchi-
cal SAPO-11 samples, calculated from the integrated area of PyH+
and PyL bands using the values of the molar extinction coefficients
of the bands (1.67 cm ␮mol−1 for PyH+ and 2.22 cm ␮mol−1 for PyL)
determined by Emeis [15]. The addition of the carbon templates
causes some decrease on the acid sites concentration (Brönsted and
Lewis), when compared with parent S0.4Si sample. These results
may suggest a possible interaction between the carbon template
and the SAPO-11 precursors present in the synthesis gel, giving
rise to different Si distribution for each sample, since the Si content
in the final materials is approximately the same for all samples.
In order to further investigate the relationship between the
surface groups of the carbon material and the acidity of the cor-
respondent SAPO-11 materials, Fig. 5 displays the concentration of
Brönsted acid sites (at 150 ◦C) of SAPO-11 as a function of pHpzc
values of the carbon templates.
It can be clearly observed a correlation between the two param-
eters as the higher pHpzc value the lower the acidity, demonstrating
once again the influence of the carbon surface chemistry on the final
acidity properties of the hierarchical SAPO-11 materials.
One of the characteristics that have been reported on solid tem-
plating is that the matrixes are thought to be chemically inert and,
thus, the chemical composition of the hierarchical materials can
be properly optimized in the gel synthesis composition, without
influence of the template [16]. However, Zhang et al. [17] reported
modifications in the acidity for the solid-templated materials, argu-
ing for a loss of crystallinity of the final materials. These results
point out that the surface chemistry of the template might be an
important factor to be taken into account to better understand the
chemical properties of the hierarchical materials synthesized with
the help of carbon templates.
Fig. 4. 29Si MAS NMR spectra of the samples S-Mox (a), S-Merck (b) and S0.4Si (c)
calcined.
[13,14]. The results are well consistent with crystalline SAPO-11
materials in their hydrated form, with two different tetrahedral Al
(39.1 and 28.0 ppm) and P (−29.2 and −23.2 ppm) crystallographic
positions, while 27Al signals at about 7.1 and −15.2 ppm are related
to penta AlO4(H2O) and hexacoordinated AlO4(H2O)2 Al species,
respectively. In fact, no signal from extraneous phase, namely nei-
ther ␥-alumina nor amorphous aluminophosphate is observed in
our samples, but instead the signals observed are a consequence of
a strong water adsorption within SAPO structure [14].
3.3. n-Decane hydroisomerization
The hydroisomerization of long chain n-paraffins is an impor-
tant process for production of diesel fuels. The diesel quality is
related to its composition in linear paraffins and cetane number,
increasing with the length of chain but decreasing with branching.
Therefore is important that the hydroisomerization catalyst favors
monobranched products and minimize cracking reactions through
adequate topology and size as well as acid strength. Several authors
The acidity of conventional SAPO-11 materials was evalu-
ated by infrared spectroscopy (FTIR) using pyridine (Py) as probe

R. Bértolo et al. / Applied Catalysis A: General 485 (2014) 230–237
235
Fig. 6. Conversion of n-decane on Pt/Al2O3 + SAPO-11 samples catalysts at WHSV = 6.6 h−1 (a) and 13.1 h−1 (b). Reaction conditions: 0.1 g of catalyst (0.5 wt.% of Pt), P = 1 atm,
molar ratio H2/n-C10 = 7.
show that a bifunctional SAPO-11 catalyst is suitable for performing
this reaction, exhibiting a high amount of isomerization products,
especially monobranched isomers [7,18–21].
(M) and dibranched (B) isomers and also some cracking products
(C), which is in accordance with the typical distribution obtained
for Pt/SAPO-11 catalysts [18,19].
In this study the hydroisomerization of long-chain n-alkanes
was performed on conventional and hierarchical bifunctional
Pt/SAPO-11 catalysts, using n-decane as a model molecule, since
it has a number of carbons sufficiently large to simulate the most
important types of mechanisms that occur with long chain n-
alkanes. The stability of the catalysts was studied by performing
some previous essays with time on stream during 60 min, at con-
stant WHSV and temperature (WHSV = 6.6 and T = 280 ◦C). The
results showed that during the reaction time no important deacti-
vation phenomena took place. Nevertheless, in order to account for
some initial deactivation, each data point was acquired after 20 min
time-on-stream, which allowed studying the catalysts behavior
under similar deactivation state. The metal function was introduced
by mechanically mixing with Pt/Al2O3 the activity of this was stud-
ied varying the reaction temperature (280 ◦C and 300 ◦C) and WHSV
(6.6–13.1 h−1). The results showed that the Pt/Al2O3 by itself is inert
to hydorisomerization of n-decane, since the conversion was only
0.5%.
The results show that all samples favor the formation of 3-, 2-
methylnonane and 3-ethyloctane. On the other hand, 4- and 5-
methylnonanes are formed in fewer amounts. The distribution of
cracked products is asymmetric in some samples, e.g. C4 products
exceeding C6 products; this should be due to the occurrence of sec-
ondary cracking reactions. However, in all samples the isopentane
is the major cracking product formed by direct scission of n-decane.
As can be observed from Table 3, despite the higher conversion
of Pt/S-Mox, undesired products such as dibranched isomers and,
especially cracking products are present in higher amounts, when
compared to the other catalysts, due to the higher acidity of this
sample, meaning that the simultaneous higher Vmeso and acidity
are not advantageous for the production of desired monobranched
isomers.
The ratio between the sum of the yields into mono and
dibranched isomers (M/B) as well as the ratio between the yields
in total isomerization and cracking (I/C) is displayed on Fig. 7. The
obtained results show an increase in both M/B and I/C ratios, as
desired, only in the case of Pt/S-Merck.
Fig. 6 shows the evolution of total conversion of n-decane with
the reaction temperature for the space velocities of 6.6 and 13.1 h−1
.
Fig. 8 illustrates the relationship between I/C ratio and the two
parameters that influenced the product distribution: concentration
As expected, the conversion for all samples increased at higher
temperature and lower space velocity. Additionally, the conversion
values obtained for the hierarchical catalysts are generally slightly
higher when compared with Pt/S0.4Si.
A further exploration of the catalytic results is presented in
Table 3 taken as an example the experiment performed at 300 ◦C
and WHSV of 6.6 h−1. The option to deepen the study at these exper-
imental conditions aims the comparison of the catalytic behavior at
approximately iso-conversion (around 10%). Additionally, the eval-
uation of the catalytic behavior at low conversion, where the kinetic
control of the reaction is verified, prevents the effects caused by
the extensive occurrence of secondary transformations, along with
diffusional or thermal interference.
of Brönsted acid sites and Vmeso
.
As can be observed there is a joint effect of both mesoporosity
and acidity that leads to a higher production of isomers, especially
monobranched, ones and limiting the occurrence of cracking reac-
tions (higher I/C ratio) on Pt/S-Merck catalysts. Indeed, besides all
carbon template samples present Vmeso about two times higher that
of conventional SAPO-11 material, there is a slight increase in the
As previously mentioned, the hierarchical catalysts present
a slightly higher conversion when compared with conventional
SAPO-11 sample, Pt/S0.4Si. This can be attributed to the mesopo-
rosity developed as a consequence of the solid templating method
used during synthesis, which promotes a faster diffusion of the
reaction intermediates. Among the three hierarchical catalysts the
effect of the acidity is also relevant since Pt/S-Mox, with the higher
concentration of Brönsted acid sites (see Table 2), presents also the
highest catalytic conversion.
Fig. 7. Ratio of the sum of the yields into monobranched and dibranched isomers
(M/B) and isomerization and cracking products (I/C) on Pt/Al2O3 + SAPO-11 sam-
ples catalysts at WHSV = 6.6 h−1 and 300 ◦C. Reaction conditions: 0.1 g of catalyst
(0.5 wt.% of Pt), P = 1 atm, molar ratio H2/n-C10 = 7.
The pattern of products distribution (Table 3), was found com-
mon for all catalysts, with n-decane converted into monobranched

236
R. Bértolo et al. / Applied Catalysis A: General 485 (2014) 230–237
Table 3
Product distribution of n-decane hydroisomerization over different catalysts at 300 ◦C and WHSV = 6.6 h−1
.
Samples
Pt/S0.4Si
7.9
Pt/S-Merck
9.4
Pt/S-Mox
12.5
Pt/S-Mox300
9.6
Conversiona (%)
5-MC9
4-MC9
2-MC9
3-EC8
0.5
0.9
2.4
0.0
2.0
0.6
1.3
3.0
0.0
2.6
0.7
1.4
3.0
0.0
2.7
0.6
1.3
2.5
0.2
2.4
Mono-C10 (M)
3-MC9
Total
5.8
0.4
7.5
0.5
7.8
1.1
7.0
0.8
Yield (%)
Di-C10 (B)
C9
C8
C7
C6
C5
C4
C3-C1
0.0
0.0
0.4
0.3
0.5
0.5
0.0
0.0
0.1
0.2
0.3
0.4
0.4
0.0
0.0
0.0
0.5
1.0
1.1
1.0
0.0
0.0
0.0
0.4
0.4
0.5
0.4
0.1
Cracking
Total
1.7
1.4
3.6
1.8
a
Reaction conditions: 0.1 g of catalyst (0.5 wt.% of Pt), P = 1 atm, molar ratio H2/n-C10 = 7.
The oxidant acid and heat treatments induced an increase of
oxygenate surface groups but showed not changes the external
surface area and mesopore volume, when comparing with the sam-
ples synthesized with commercial Merck carbon. The results show
that carbon oxidation treatments affect the matrix surface groups,
resulting in the modification of the SAPO-11 gel chemistry. The
addition of carbon matrix templates caused a decrease in the acid-
ity for all samples, especially for the one synthesized with Merck
carbon.
The n-decane hydroisomerization results show that the meso-
porosity developed during the carbon templated synthesis was
enough to improve the catalytic conversion of the hierarchical
materials. The higher yields in the most valuable monobranched
isomers, along with a reduction in cracking products was obtained
for Pt/S-Merck due to a joint effect of mesoporosity increase and,
most relevantly, a decreases on the acidity caused by the interac-
tion with the surface chemical groups of the carbon matrix with
Fig. 8. Ratio of the sum of isomerization and cracking products (I/C) on Pt/S0.4Si,
Pt/S-Mox, Pt/S-Mox300 and Pt/S-Merck samples at WHSV = 6.6 h−1 and 300 ◦C of as
a function of concentration of Brönsted acid sites and the mesopores volume, Vmeso
higher pHpzc
.
In spite of solid templates have been reported in the literature as
inert materials this preliminary study shows that the modification
of the surface chemistry of the carbons seems to promote intera-
tions with the synthesis gel, resulting in the production of SAPO-11
materials with different acid properties, with enhanced catalytic
behavior.
A more detailed study, where several types of carbons with dis-
tinct surface chemistry properties were used as templates is in
progress in order to deeply understand the interactions between
the solid matrix and the gel synthesis, with direct influence on the
final properties of the hierarchical materials.
.
case of S-Merck sample. However the most relevant effect seems
to be the acidity, which is related with the differences in the sur-
face chemistry of the carbon templates, as discussed before. Indeed,
the lower acidity presented Pt/S-Merck as a consequence of higher
pHpzc presented by Merck carbon (see Fig. 2) hinders the occur-
rence of a second isomerization step and the formation of cracking
products.
These results clearly point out to the influence of the surface
chemistry of the carbon matrix in the final acidity properties of the
hierarchical SAPO-11 material and its consequences on the catalytic
behavior.
Acknowledgments
The authors thank Portuguese FCT for financial support
(SFRH/BD//73234/2010 and SFRH/BPD/91397/2012), Prof. Teresa
Duarte for access to the XRD facility (CONC-REEQ/670/2001) and
Prof. João Rocha for NMR experiments.
4. Conclusions
The commercial Merck and oxidized (Mox and Mox300) car-
bon templates, added during the preparation of the gels, allowed to
obtain hierarchical SAPO-11 materials with both micro and meso-
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