Inhibition of the hydrogenation of tetralin by nitrogen and sulfur compounds over Ir/SBA-16

Article abstract of DOI:10.1016/j.apcata.2011.07.003

In this work we study the catalytic properties of 5 wt.% Ir-containing SBA-16 catalysts (with and without aluminum as heteroatom), in the hydrogenation of tetralin to decalin, in the presence of 100 ppm of N as quinoline, indole and carbazole, and 100 ppm of S as dibenzothiophene and 4,6-dimethyl- dibenzothiophene at 250 °C and 15 atm of pressure of hydrogen, using a Parr reactor. Ir/SBA-16 and Ir/Al-SBA-16 were prepared by wetness impregnation using Iridium Acetylacetonate as source of Ir. The Ir/SBA-16 catalyst synthesized by us had high activity measured in tetralin hydrogenation at mild conditions. The experimental data was quantitatively represented by a modified Langmuir-Hinshelwood type rate equation, using the apparent adsorption constants calculated from the inhibition results for the individual compounds. The catalyst showed a good resistance to sulfur and nitrogen compounds. The inhibiting effect increased in the order: DBT < quinoline < 4,6-dimethyl-DBT < indole < carbazole. The inhibiting effect of the nitrogen/sulfur compounds was strong, but the activity was still higher than with commercial NiMo/alumina catalyst. We present in this contribution a successfully developed, high loaded and well dispersed Ir/SBA-16 catalysts, that have been shown to maintain a useful catalytic activity, even in the presence of relatively high amounts of sulfur compounds (up to 100 ppm, sulfur basis). Consequently, economically successful processes have evolved, based on this class of catalysts.

Full text of DOI:10.1016/j.apcata.2011.07.003

Applied Catalysis A: General 404 (2011) 30–38
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Inhibition of the hydrogenation of tetralin by nitrogen and sulfur compounds
over Ir/SBA-16
Gerardo Simón Balangero Bottazzi, María Laura Martínez, Marcos Bruno Gómez Costa,
Oscar Alfredo Anunziata, Andrea Raquel Beltramone∗
Grupo Fisicoquímica de Nuevos Materiales, CITeQ, Facultad Córdoba, Universidad Tecnológica Nacional, Maestro López y Cruz Roja Argentina, 5016 Córdoba, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work we study the catalytic properties of 5 wt.% Ir-containing SBA-16 catalysts (with and with-
out aluminum as heteroatom), in the hydrogenation of tetralin to decalin, in the presence of 100 ppm
of N as quinoline, indole and carbazole, and 100 ppm of S as dibenzothiophene and 4,6-dimethyl-
dibenzothiophene at 250 ◦C and 15 atm of pressure of hydrogen, using a Parr reactor. Ir/SBA-16 and
Ir/Al-SBA-16 were prepared by wetness impregnation using Iridium Acetylacetonate as source of Ir. The
Ir/SBA-16 catalyst synthesized by us had high activity measured in tetralin hydrogenation at mild con-
ditions. The experimental data was quantitatively represented by a modified Langmuir–Hinshelwood
type rate equation, using the apparent adsorption constants calculated from the inhibition results for
the individual compounds. The catalyst showed a good resistance to sulfur and nitrogen compounds.
The inhibiting effect increased in the order: DBT < quinoline < 4,6-dimethyl-DBT < indole < carbazole. The
inhibiting effect of the nitrogen/sulfur compounds was strong, but the activity was still higher than with
commercial NiMo/alumina catalyst.
Received 19 March 2011
Received in revised form 4 July 2011
Accepted 6 July 2011
Available online 18 July 2011
Keywords:
Iridium containing SBA-16
Hydrogenation
Inhibition
Reaction kinetic
Sulfur
Nitrogen compounds
We present in this contribution a successfully developed, high loaded and well dispersed Ir/SBA-16
catalysts, that have been shown to maintain a useful catalytic activity, even in the presence of relatively
high amounts of sulfur compounds (up to 100 ppm, sulfur basis). Consequently, economically successful
processes have evolved, based on this class of catalysts.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
formulation (Co(Ni)Mo(W)/Al2O3) [1–11]. Regarding new support
materials, mesoporous molecular sieves such as MCM-41, HMS or
Hydrotreating technology (HDT) is one of the most commonly
used refinery processes, designed to remove contaminants such as
sulfur, nitrogen, condensed ring aromatics, or metals. The feedstock
used in the process range from naphtha to vacuum residue, and the
products in most applications are used as environmentally accept-
able clean fuels. The process operates at elevated pressure and
temperature and consumes hydrogen. Recent regulatory require-
ments to produce ultra-low-sulfur diesel (ULSD) and gasoline, have
created a very dynamic market as refiners must build new or
revamp their existing assets to produce the ‘green’ fuels. To meet
this challenge, scientists elsewhere are researching to address the
refiner’s specific configurations and provide optimized and eco-
nomically attractive solutions.
SBA-15 [12–15] are promising candidates because of their uni-
form mesoporous structure, which facilitates the diffusion of the
large molecules involved in hydrotreating reactions. Compared
with MCM-41 and HMS, the SBA-15 material synthesized under
an acidic medium using neutral organic triblock copolymers as
structure-directing agents [15,16] seems to be more interesting.
Fierro et al. [17] used with success CoMo/Ti-SBA-15 catalysts for
dibenzothiophene desulfurization, but the information about SBA-
16 support is poor. The SBA-16 silica mesophase with a cubic Im3m
structure was prepared first by Zhao et al. [18] from the triblock
copolymer surfactant Pluronic F127 (EO106PO70EO106) and TEOS.
The synthesis parameters have been systematically investigated
by Mesa et al. [19]. The mesoporosity of this phase consists of
two non-interpenetrating three-dimensional channel systems with
spherical cavities at the dividing of the channels. It can be expected
that this structure offer more interesting opportunities for catalytic
applications involving well-dispersed metal-supported catalysts
and allowing the diffusion of large molecules.
The development of highly active and selective hydrotreat-
ing catalysts is one of the most pressing problems facing the
petroleum industry. Numerous approaches have been adopted
with a view to improving the catalytic performance of the classical
The purely siliceous SBA’s materials have only silanol groups
on their surface, which are of low acid strength and catalyt-
ically non-active. Therefore, in order to make these materials
∗
Corresponding author. Tel.: +54 351 4690585; fax: +54 351 4690585.
E-mail address: abeltramone@scdt.frc.utn.edu.ar (A.R. Beltramone).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.07.003

G.S.B. Bottazzi et al. / Applied Catalysis A: General 404 (2011) 30–38
31
useful for catalysis, stronger acidic sites have to be introduced
into their framework. Generally, the substitution of heteroatoms
with valence lower than silicon creates negative charges in the
framework, which can be compensated by protons, thus generating
acidity in these materials. Many investigations have indicated that
Al-SBA-15 materials show much higher catalytic activity, compared
with Al-MCM-41 [20,21]. The incorporation of Al is particularly
important as it gives rise to solid acid materials with acid sites
associated with the presence of Al in framework positions, within
the silica pore walls. Mesoporous aluminosilicates have there-
fore, been the focus of many recent studies [22–24], because of
their potential application in solid acid/base catalysis for bulky
molecules activation. The traditional method of introducing Al into
mesoporous silicates is the direct (mixed-gel) synthesis where, an
aluminum–silicate framework is formed directly from aluminate
and silicate ions.
However, it is very difficult to introduce the metal ions directly
into SBA’s due to the easy dissociation of metal–O–Si bonds under
strong acidic conditions. Thus, the post-synthesis method for the
alumination of the mesoporous silica, which are obtained under
strongly acid conditions, becomes an appealing alternative [25].
Many studies have shown that aluminum can be effectively incor-
porated into siliceous MCM-41 and MCM-48 materials via various
post-synthesis procedures. The authors claimed that the materials
produced via the post-synthesis method have superior structural
integrity, acidity, and catalytic activity than those of materials
having aluminum incorporated during synthesis [26–29]. Recently
Anunziata et al. [30] have published the synthesis of Na-Al-SBA-3
by the treatment of pure silica SBA-3 with an aqueous solution of
NaAlO2 at room temperature. In that work, we obtained a material
with high-framework aluminum contents, without any significant
loss in textural properties of SBA-3.
Some alumina-supported transition metal catalysts possessed
much higher hydrodenitrogenation (HDN) and hydrodesulfuriza-
tion (HDS) activity than a conventional NiMo system [31–35]. For
example: Rh, Ir, Ru and Pt supported on silica or alumina are known
to catalyze effectively the nitrogen removal from methylamine,
quinoline or pyridine also in the reduced state [36]. Noble metal
sulfides, either unsupported as bulk compounds [37] or supported
on active carbon [38] have been studied extensively in hydrorefin-
ing. It has been shown that transition metal sulfides of the 2nd and
3rd rows such as Ru, Rh, Os and Ir were especially active during HDS
reactions [37]. Similarly, sulfides of Ir, Os and Re were most active
in HDN of quinoline [38] and sulfides of Ir and Pt in HDN of pyridine
[39]. However, these catalysts have a low tolerance to sulfur and
nitrogen poisoning, therefore a previous deep hydrodesulfuriza-
tion and hydrodenitrogenation charge pre-treatment is required.
This two-stage hydrodearomatization (HDA) process has a high
operating cost and, consequently, the development of noble metal-
based catalysts with tolerance to sulfur and nitrogen has become
attractive. In this case, noble metal-based catalysts are an interest-
ing alternative, since they have high activity for hydrogenation of
aromatic hydrocarbons, and the process can then perform at low
temperatures and pressures. Recently, much interest has arisen in
zeolite-supported noble metal catalysts in connection with their
application to the hydrogenation of aromatic hydrocarbons con-
tained in petroleum distillates [40] This is because these catalysts
have been shown to maintain a useful catalytic activity, even in the
presence of relatively high amounts of sulfur compounds (up to
several hundred ppm, sulfur basis) [32,41–43]. Consequently, eco-
nomically successful processes have evolved, based on this class
of catalysts. It is of interest that Ir catalysts display also very
high HDN/HDS selectivity. This has already been observed dur-
ing the study of simultaneous reaction of thiophene and pyridine
over a carbon supported Ir catalyst at 280 ◦C [44] and confirmed
more recently for alumina supported Ir catalysts at 320 and 360 ◦C
[45,46]. Similarly, Liaw and co-workers observed that an Ir/Al2O3
catalyst showed much higher HDN/HDS selectivity than other noble
metal catalysts in hydrotreating of coal-derived naphtha [47].
However, catalytic properties of metal or metal sulfides
deposited on alumina or other supports have been studied less fre-
quently and moreover, the major attention up to now has been
devoted only to Ru [48]. It was shown by Cinibulk and VõÂ [45] that
the HDN activity of an alumina-supported Ir catalyst during the par-
allel HDN/HDS reaction of pyridine and thiophene was markedly
higher than the activity of a Pt catalyst. On the other hand, in com-
parison to NiMo/alumina the extent of quinoline HDN was only
higher for zeolite-supported Ru sulfide (3.5% Ru), the other zeolite-
supported noble metal sulfides including Ir (0.8%) were less active
[4]. Besides HDN, a high hydrogenolytic activity of Ir has been also
well established during studies of hydrocarbon reactions in connec-
tion with naphtha reforming [36,49,50]. Factors such as the effect of
catalyst preparation and metal dispersion have often been studied
in connection with this process [36,50–53]. The results obtained in
all these studies suggest that Ir could be an efficient active phase
for the transformation of aromatics to saturated compounds and
efficient for sulfur and nitrogen removal, by either itself or as a pro-
moter of conventional catalysts. However, the data about the effects
of Ir dispersion in different supports in hydrogenation (HYD) and
HDS/HDN reactions are not available in the literature at present.
Nitrogen and sulfur compounds naturally occurring in atmo-
spheric gas oil (AGO) and light cycle oil (LCO), used as feedstocks
for diesel fuel production, are traditionally considered as being
responsible for color and gum formation. Moreover, they have been
identified as strong inhibitors of the hydrogenation (HYD) reac-
tions during the hydrotreatment process [54,55], even when they
are present in very low concentrations [56,57]. Usually, the basic
nitrogen compounds have been considered stronger inhibitors for
the HYD and HDS reactions than the non-basic moieties [54,55].
However, strong inhibition of these reactions by non-basic nitrogen
compounds has been observed, either due to hydrogenation (HYD)
reactions occurring during this process, that lead to the formation
of basic species [58,59], or to a strong adsorption of the non-
basic compounds over the support surface [60–62]. For carbazole,
Nagai and Kabe [58] and LaVopa and Satterfield [63] reported a
strong inhibiting effect on the thiophene and dibenzothiophene
HDS reactions, comparable to those of the basic compounds pyri-
dine, piperidine and acridine. The high value of the adsorption
characterizing carbazole was attributed to products of a rapid
hydrogenation converting it to basic compounds. Nitrogen- and
sulfur containing compounds inhibit HYD through competitive
adsorption. Although interesting information about the inhibition
effect from nitrogen compounds has been forwarded by previous
studies [60–62], moreover, the majority of the studies have focused
on the nitrogen inhibition effect on the HDS reaction and there-
fore systematic information related to the inhibition effect on HYD
reactions is scarce.
LaVopa and Satterfield [63] developed
a
Langmuir–
Hinshelwood (L–H) type equation to describe the poisoning
effect of nitrogen compounds during DBT HDS. Recently, the inhi-
bition effect on HYD reactions, was experimentally determined by
Beltramone et al. [9,10] using a commercial NiMo/Al2O3 catalyst
at pressures and temperatures commonly used in the hydrotreat-
ment of diesel and at sulfur and nitrogen concentrations relevant
to deep HDS.
Tetralin is one of the most representative and refractory
molecules of aromatics presents in diesel pool, for that reason we
choose tetralin as a model molecule to study the activity of the
catalyst and the inhibition effect. The information available in the
literature about inhibition effects observed during the hydrogena-
tion of tetralin in the presence of sulfur and nitrogen compounds
over Ir containing mesoporous catalysts is scarce and contradictory

32
G.S.B. Bottazzi et al. / Applied Catalysis A: General 404 (2011) 30–38
and the inhibiting effect of N and S over tetralin hydrogena-
tion using Ir/SBA-16 is not reported elsewhere. Consequently, the
main objective of this work is to present L–H type equations that
quantitatively describe the inhibition effect observed during HYD
of tetralin in the presence of dibenzothiophene (DBT) and 4,6-
dimethyl-dibenzothiophene (4,6-DMDBT), carbazole, indole and
quinoline, using a batch reactor at softer conditions than used in
industrial processes.
The scanning range was set between 0.5◦ and 5◦. The sample was
crushed previously and placed it in an aluminum sample holder.
Scanning electron micrographs (SEM) were obtained by using a
nova NANOSEM 230 Phillips with EDAX. Samples were placed over
an aluminum drum and covered with a gold film, using a JEOL Ion
Sputter JFC 1100.
TEM observations were performed in a Philips CM 200 UT trans-
mission electron microscope at Centro Atómico Bariloche. Samples
for TEM were prepared by dispersing a small amount of powder
in ethanol and depositing a drop of the resulting suspension on a
commercial carbon coated copper grid.
2. Experimental
Elemental analysis was performed by inductively coupled
plasma-atomic emission spectroscopy (VISTA-MPX) operated with
high frequency emission power of 1.5 kW and plasma airflow of
12.0 L/min. The surface area was determined by the BET method
using a MICROMERITICS Chemisorb 2720 apparatus, equipped with
a TCD detector.
Hydrogen chemisorption characterization was performed in a
Chemisorb 2720 Micromeritics, measured at temperature pulses
and at atmospheric pressure. The samples were previously treated
and reduced. For the hydrogen chemisorption, we assumed a sto-
ichiometric value of 2 H/Ir. The accuracy/reproducibility to the
results is typically better than 1.5% with 0.5% reproducibility.
The metal dispersion value is determined by Eq. (1):
2.1. Synthesis of Si-SBA-16 and Al-SBA-16
Mesoporous silica materials with cubic Im3m structure were
synthesized according to the procedure described by Kim et al.
[64]. Briefly, poly (alkylene oxide)-type triblock copolymers; F127
(EO106PO70EO106, MW 5 12600) were dissolved in aqueous HCl
solution. Tetraethyl orthosilicate was added to the solution at
35 ◦C under continuous stirring during 15 min at that temper-
ature. The molar composition of the mixture was as follows:
F127/TEOS/HCl/H2O = 0.004/1/4/130. This mixture was kept under
static conditions in an oven for 6 h at the same temperature. Subse-
quently, the mixture was placed in an oven at 50 ◦C, over a period of
20 h; afterwards the temperature of furnace was increased to 80 ◦C
for aging for 20 h, after that, the solid product was recovered by
filtration and dried at 100 ◦C. The Si-SBA-16 sample was immersed
in ethanol reflux for 6 h, to extract the surfactant and then was cal-
cined at 550 ◦C in air for 6 h. The material obtained was identified
as SBA-16. The alumination procedure of SBA-16 was carried out as
follows: Silica SBA-16 (1 g) was stirred in 50 ml of water, containing
dissolved sodium-aluminate, at room temperature for 20 h and pH
of 5.6. The synthesis was performed at this pH, because sodium alu-
minate is not stable in acid medium (pH < 3), and it reacts rapidly
with protons to generate aqueous Al3+ ions. When pH is enough
high, deposition of aluminum hydroxide will occur. The mixture
was filtered, washed, dried at room temperature overnight and
then calcined in air at 550 ◦C for 5 h. Finally, Al-SBA-16 sample with
theoretical Si/Al = 20 was obtained.
Vads
Vg
m.w.
%M
%D = Sf ×
×
× 100% × 100%
(1)
where Sf = stoichiometry factor (2), considering the dissociation
of H2 adsorbed onto Ir atom, Vads = volume adsorbed (cm3/g)
Vg = molar volume of gas at SPT (22.414 cm3/mol), m.w. = molecular
weight of the metal (192.217 a.m.u.), %M = % metal (4.9–5.1% of Ir
in our case), %D = percent of metal dispersion (%).
The active metal surface area per gram of sample, (m2/g sample)
was calculated by the following equation:
Vads
Vg
m2
1018 nm2
MSAs = Sf ×
× NA × ꢁm
×
(2)
where Sf = stoichiometry factor (2), Vads = volume adsorbed (cm3/g),
Vg = molar volume of gas at SPT (22.414 cm3/mol), NA = Avogadro’s
number (6.023 × 1023 molecules/mol), ꢁm = cross-sectional area of
active metal (0.074 nm2), MSAs = active metal surface area per gram
of sample.
2.1.1. Synthesis of Ir/SBA-16 and Ir/Al-SBA-16
The samples were prepared using Iridium Acetylacetonate
(Aldrich 99.9% Ir(Acac)3) as source of Ir. Iridium was incorporated
by wetness impregnation employing ethanol as solvent, due to its
very low solubility in water. The obtained powder was then dried at
80 ◦C overnight, and then calcined at 500 ◦C for 5 h. After that, the
samples were desorbed in inert atmosphere from 25 ◦C to 200 ◦C
with a slope of 10 ◦C/min and kept at this temperature during 5 h,
after that the temperature was increased to 470 ◦C with a slope of
10 ◦C/min, kept 5 h at that temperature. Nitrogen flow was always
20 ml/min. Due to iridium is active for the reaction in its metallic
state; it was reduced in H2 flow of 20 ml/min, at 470 ◦C using the
same procedure described above. The iridium load was 5 wt.% and
the samples obtained were denoted as Ir/SBA-16 and Ir/Al-SBA-16.
2.3. Catalytic activity
The catalytic activity was measured in a Parr reactor 4563, at
250 ◦C, 15 atm of pressure of hydrogen and 360 rpm.The feed con-
sisted in 50 ml of 5% v/v of tetralin (98.5% FLUKA) in dodecane in
presence of 100 ppm of S or N in the respective cases. The prod-
ucts were analyzed with a HP 5890 Series II GC and HP-5 column.
The activity of the catalysts was compared with an Ir/Al2O3 sample
prepared with Commercial ␥-Al2O3 (Topsoe, M-80T) and Ir incor-
porated with the same procedure described for SBA-16; the results
were also compared with a typical HDT catalyst as NiMo/Al2O3
Criterion 424.
2.2. Characterization of the catalysts
Infrared measurements were performed with a JASCO 5300 FTIR
spectrometer. For structure (fingerprint zone) characterization,
samples of SBA were mixed with KBr (0.05 wt.% catalyst/99.95 wt.%
KBr), and pressed forming a wafer.
3. Results and discussion
3.1. Characterization of the catalysts
The XRD patterns were collected by using a continuous scan
mode with a scan speed of 0.02◦ (2ꢀ)/min. XRD patterns were
recorded in the Philips X’Pert PRO PANalytical diffractometer, oper-
ating with CuKa X-ray radiation (X-ray generator current and
voltage set at 40 mA and 45 kV), using small divergence and scat-
tering slits of 1/32 mm and a goniometer speed of 1.2◦ (2ꢀ)/min.
3.1.1. IR spectroscopic studies
Fig. 1 shows the spectrum of Si-SBA-16 and Al-SBA-16 in the
same fingerprint region. We can observe that a signal at around
970 cm−1, which is assigned to asymmetric stretching of Si–O bond
neighboring surface silanol groups, was emerged on the spec-
tra of the pristine SBA-16 sample. However, this band is absent

G.S.B. Bottazzi et al. / Applied Catalysis A: General 404 (2011) 30–38
33
80
60
40
20
0
110
804
SBA-16
Ir/SBA-16
Ir/SBA-16 used
Al-SBA-16
Ir/Al-SBA-16
465
463
200
802
211
970
1087
1078
Si-SBA-16
Na-Al-SBA-16
1600
1400
1200
1000
800
600
400
Wavenumber, cm-1
Fig. 1. FTIR of SBA-16 and Al-SBA-16.
when SBA-16 was post-aluminated, which indicated that the sur-
face silanol groups around 969–970 cm−1 interacted with the Al
species and contributed to form the Si–O–Al bonds, in the pro-
cess of modification. The presence of asymmetric stretching T–O
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
2θ
Fig. 2. XRD pattern of SBA-16 synthesized samples.
(T = Si, Al) can be observed in the samples at 1232 and 1078 cm−1
,
due to external tetrahedral TO4 vibrations of weak intensity and
internal tetrahedral TO4 vibrations of strong intensity, respec-
2ꢀ) of the cubic Im3m structure and two small shoulders of the
(2 0 0) and (2 1 1) reflections (1.7◦ and 1.92◦ 2ꢀ, respectively). All
these reflections yield an a0 value of 12.16 nm, confirming that the
measured structure is indeed the Im3m structure [69,70]. Similar
XRD pattern was also observed for the Al-SBA-16 sample (Fig. 2).
However, in this case the positions of (1 1 0), (2 0 0) and (2 1 1)
reflections were shifted to 1.11, 1.68 and 1.81◦ 2ꢀ, respectively,
giving a0 a value of 13.1 nm. In the case of the aluminum contain-
ing material, only the peak indexed as [1 1 0] is clearly observed,
probably because the aluminum insertion leads to a structure with
lower order [24]. It has to be mentioned for the sake of clarity that
some publications report on the preparation of materials with dis-
ordered pore organization with X-ray patterns displaying a single
peak, which was related to the SBA-16 structure [14]. Although it
is known that aluminum containing MCM-41 is less ordered than
the pure silica parent material [71], and that it is highly proba-
ble that this behavior is similar for the AlSBA-16. The signals at the
corresponding Miller indices indicate that the ordered mesoporous
structure is preserved during aluminosilicates synthesis.
In line with this, a characteristic (1 1 0) reflection of Im3m struc-
ture is still observed in the XRD pattern of Ir/SBA-16 (Fig. 2). XRD
results suggest that the mesoporous cage-like structure of SBA-16
was maintained during the course of the preparation of Ir modi-
fied catalysts. However, a significant decrease in its intensity and
broadening after Ir deposition suggest some loss in the periodicity
of the SBA-16 pore structure. Therefore, a strong obstruction of the
support pores after metal deposition could be supposed to occur in
this catalyst.
tively. Siliceous SBA-16 samples show a band at 800–802 cm−1
,
due to Si–O–Si symmetric stretching modes and another stronger
band at 461–465 cm−1, due to rocking Si–O–Si, respectively [30].
The spectra of the Al-SBA-16 material show additional features
in the vicinity of the 1087 and 804 cm−1 stretching bands, which
absorption frequency shifts upward, with aluminum incorpora-
tion into the pristine sample. These features can be assigned to
Al–O–Si bending vibrations, indicating incorporation of aluminum
into the SBA-16 silica matrix [30]. Thus, the substitution of silicon
by aluminum causes shifts of the lattice vibration bands to higher
wavenumbers.
3.1.2. XRD studies
For determination of the structure and symmetry of the materi-
als, XRD patterns were analyzed. SBA-16 with cubic Im3m structure
is a body-centered-cubic arrangement of cages with 8 apertures to
the nearest neighbors. The unit-cell parameter, a0 (Table 1), of the
crystallographic structure was obtained by solving the following
√
equation depending on the type of space group: a0 = dh k l
·
(Qh k l),
where Qh k l is: Qh k l = h2 + k2 + l2, for a cubic space group like the
cubic body centered (Im3m) SBA-16. A typical X-ray diffractogram
of SBA-16 is expected to present peaks at 2ꢀ < 3◦, correspond-
ing to an Im3m cubic structure [16,65], however, many often just
the first two peaks have been clearly detected [66–68]. The X-ray
diffractograms of the SBA-16, Ir-SBA-16 and the mesostructured
Al-SBA-16 and Ir-AlSBA-16 are shown in Fig. 2. The XRD pattern of
calcined SBA-16 sample shows a very strong (1 1 0) reflection (1.2◦
Table 1
Structural characteristics of SBA-16 samples.
´
a0 (nm)a,b
˚
Samples
2ꢀ
d (A)
h k l
SBA-16
1 1 0
1.20
2 0 0
1.70
2 1 1
1.92
1 1 0
85.67
2 0 0
60.82
2 1 1
49.65
12.16
12.30
13.10
14.16
Ir/SBA-16
Al-SBA-16
Ir/Al-SBA-16
1.17
1.11
1.02
1.75
1.68
1.61
1.92
1.81
1.72
86.70
92.60
86.00
61.40
65.85
61.80
50.50
50.70
43.60
√
a
a0 = d200 4.
b
∼
D
4 V/A; (according to Refs. [72,73]).
=

34
G.S.B. Bottazzi et al. / Applied Catalysis A: General 404 (2011) 30–38
(a)
(b)
Fig. 3. SEM micrographs of Ir/SBA-16 (a) and Ir/Al-SBA-16 (b).
We also can observe in Fig. 2, a pattern for Ir/SBA-16 used, this
pattern shows that the structure remains unalterable, even after
three cycles of reaction.
TCD signal indicated saturation. The mean diameter of the Ir par-
ticles was estimated under the basic assumption of stoichiometry
for H/Ir = 2, with spherical shape of the metal particles. As it was
mentioned in TEM studies, lower particle size and higher disper-
sion of metallic Ir was found in SBA-16 without Al in its structure
than in Ir/Al-SBA-16 (D = 40 and 35% respectively, see Table 2), with
relative similar Ir content.
3.1.3. SEM and TEM characterization
The size and shape of the samples indicate good morphology of
the crystals, without other phases, typical of these materials (Fig. 3a
and b). As shown in Fig. 3a for Ir/SBA-16 sample, the particles have a
spherulictic shape; the particle size of the Ir/SBA-16 is 4–5.0 ␮m in
diameter, whereas the crystal of Ir/Al-SBA-16 is almost spherulictic
with a lower particle size (2–3 ␮m).
3.2. Catalytic activity
Unlike olefins hydrogenation, high hydrogen pressures are
required to outcome ring saturation in aromatics hydrogenation.
This is in part due to the low reactivity of the aromatic structure
as a result of resonance stabilization of the conjugated system and,
partly due to limitations determined by the thermodynamic equi-
librium at the pressures and temperatures employed. Therefore,
most studies on the reactivity of aromatics have been conducted at
pressures and temperatures that favor low equilibrium concentra-
tions of aromatics. Despite of the industrial conditions that use high
pressure and temperature, we are addressing here, more active cat-
alyst in order to perform at mild conditions and in a batch reactor.
In order to find the best operation conditions, the hydrogenation
reaction was previously tested at different conditions: at atmo-
spheric pressure the catalyst exhibited dramatic decrease of the
tetralin conversion values by increasing the reaction temperature,
due to the thermodynamic constraints of the reaction. At 300 ◦C
the fully hydrogenated products were not more detected, while,
together with tetralin, traces of high-molecular-weight, ring-
opening products and low-molecular-weight, cracking products
were formed. While at atmospheric pressure Ir/SBA-16 showed a
low hydrogenation activity, in the tests performed at higher pres-
sures than 15 atm the catalytic activity slightly grew, compared
The TEM image of the SBA-16 mesoporous silica crystal, exhibits
the well-ordered Im3m cubic mesostructures (Fig. 4b), confirmed
by XRD data of SBA-16 single crystals having a well-ordered
mesostructure. According to Fig. 4a and b, the Ir clusters size is big-
ger in Ir/Al-SBA-16 than in Ir/SBA-16 samples, in agreement with
the data shown in Table 2, obtained by H2 chemisorption.
The physicochemical properties of the samples (supports and
catalysts) are summarized in Table 2. The results of ICP elemental
analysis, which was employed to determine the composition of Al-
SBA-16 sample, indicated the amounts of the heteroatom (Al) in
the final Al-SBA-16 support, are in close agreement with theoreti-
cal value, Si/Al = 19.8. The BET specific surface area decreases with
the Al content, from 870 (SBA-16) to 700 m2/g for Al-SBA-16, due to
the occupation of guest species on the surface of the pores, as well
as the in equable contribution of the additional mass Al2O3 in the
sample. The iridium content in the samples was determined by ICP.
The dispersion and mean clusters sizes in the reduced catalysts by
H2 pulse adsorption at 22 ◦C. The catalyst (0.5 g) was in situ reduced
by H2 (30 ml/min) at 400 ◦C for 2 h and purged by N2 (25 ml/min)
at 400 ◦C for an additional 0.5 h. The samples were cooled to 22 ◦C,
and titrated by H2 pulses in a stream of N2, until constant output
Table 2
Physicochemical properties of the supports and catalysts.
SBA-16
Ir/SBA-16
Al-SBA-16
Ir/Al-SBA-16
Ir/Al2O3
Si/Ala
–
870
–
–
550
4.9
19.8
700
–
19.8
480
5.1
Area, m2/g
150
4.8
3.5
26.0
2.89
60.29
4.4c
4.8d
Ir, wt.%a
Mean crystal size, ␮mb
Metal dispersion, %
Metal surface area, m2/g sample
Metal surface area, m2/g metal
Particle diameter, nm
4.8
4.5
40.0
4.54
92.75
2.9c
3d
3.0
2.5
35.0
4.14
81.16
3.3c
3.5d
a
Data obtained by ICP.
SEM.
From metal dispersion obtained by hydrogen chemisorption.
From TEM.
b
c
d

G.S.B. Bottazzi et al. / Applied Catalysis A: General 404 (2011) 30–38
35
Fig. 4. TEM images of Ir/SBA-16 (a) and Ir/Al-SBA-16 (b).
with the test at 15 atm. However, all the catalysts required a large
H2 excess, to avoid a decrease in hydrogenation and ring-opening
activity, and gave rise to the best performance for the studied
contact time, favoring at lower values the total hydrogenation to
decalin and no cracking reactions at 250 ◦C. On the other hand, at
high pressures, the increase of temperature favored the formation
of the ring-opening and, mainly, cracking products. Furthermore,
this may supply useful information on the behavior of Ir-catalysts,
claimed as active and stable in dearomatization and ring-opening
reactions.
Ir/Al2O3 and 60% higher than NiMo/Al2O3, respectively. Is inter-
esting to analyze the activity comparing the turn over number
(TON) (see Table 3). The turn over number was calculated con-
sidering the ꢁm = cross-sectional area of active metal (0.074 nm2)
and the active metal surface area per gram of sample, according H2
chemisorption. Thus, TON is very similar, suggesting that the higher
conversion levels are due to the higher Ir atoms dispersion as active
center to the reaction. Differences in activity, as it was mentioned
could be due to the better iridium dispersion obtained on SBA-16
used as support (see Tables 2 and 3). Ir/SBA-16 also showed a high
activity even in presence of sulfur compared with a typical NiMo
catalyst.
The results are shown in Table 3, the catalytic activity of the
synthesized samples and a commercial NiMo/Al2O3 catalyst was
compared.
According previous studies performed by Klimova et al. [14],
NiMo catalysts supported on Al-containing SBA-16 molecular
sieves, which were prepared by grafting with AlCl3 or Al(i-PrO)3,
show high activity in HDS of refractory dibenzothiophenes (4,6-
DMDBT). This can be attributed to good dispersion of Ni and Mo
active phases and to the bifunctional character of these catalysts,
namely, to the participation of both types of sites: active sites of
NiMoS phase and Bronsted acid sites of the support in the catalytic
transformations of 4,6-DMDBT. Therefore, high catalytic perfor-
mance of these catalysts in HDS of refractory DBTs can be attributed
to the synergism between both types of active sites. The interac-
tion of Ni and Mo species with the support becomes stronger with
Al loading into the SBA-16 by post-synthetic aluminum grafting.
According to this, the dispersion of sulfided Mo species increases.
However, when SBA-16 is aluminated using NaAlO2, NiMo catalysts
with low surface area and activity are obtained. This point out the
method of incorporation of Aluminum into the SBA-type materi-
als and Al sources suitable for the preparation of supports for HDS
catalysts.
In our case is possible to see, that post-synthesis alumination
of SBA-16, by reacting with NaAlO2 leads to an important decrease
of surface area comparing with the parent material. We obtained
also, a catalyst with lower dispersion than the parent SBA-16
without aluminum. This activity trend with the change of the
Al-containing SBA-16-support would be the result of too strong
metal–support interaction, as in the case on Ir/Al-SBA-16 catalyst
that makes the reduction of Ir species more difficult. This could
be joint with Ir dispersion, other reason of the lower activity of
Ir/Al-SBA-16 compared with Ir/SBA-16.
The hydrogenation reactions of tetralin were carried out at
250 ◦C and 15 atm in the presence of traces of DBT. The major
products were trans-decalin, cis-decalin, and naphthalene. Trans-
decalin was the product with the highest initial selectivity, followed
by cis-decalin and naphthalene. The trans isomer is expected to
be favored based on thermodynamic calculations. In addition to
the hydrogenation, dehydrogenation of tetralin to naphthalene
took place during the hydrogenation of tetralin, even though the
experiments were performed far below the thermodynamic equi-
librium. The naphthalene formation was dependent on the tetralin
concentration and the hydrogenation rate. A high tetralin con-
centration together with a low hydrogenation rate favored the
naphthalene formation. The dehydrogenation was nevertheless
a minor reaction and only traces of naphthalene were formed.
Sapre and Gates [74] and Korre et al. [75] have reported a simi-
lar reversible dehydrogenation–hydrogenation reaction for tetralin
and naphthalene on a sulfided CoMo-catalyst. Decalins appeared
to be fairly unreactive under these conditions, while naphthalene
hydrogenated back into tetralin.
According to the data shown in Table 3, the selective conversion
of tetralin to decalin using Ir/SBA-16 is higher than Ir/Al-SBA-16,
Table 3
Catalytic activity results. Feed: 0.05 mol of tetralin/g of catalyst in dodecane,
100 ppm of sulfur as DBT were added. T = 250 ◦C, P = 15 atm. Reaction time 8 h, stir-
ring = 60 rpm.
Samples
Conv. of tetralin (mol%)
TON × 106
Ir/SBA-16
Ir/Al-SBA-16
Ir/Al2O3
NiMo/Al2O3 Criterion 424
80
68
63
20
0.13a
0.12a
0.11a
In order to study the behavior of Ir/SBA-16 in presence of N and
S compound, computation of kinetic parameters was required to
shed further light on this issue; the data can be used to provide a
better value for the constraints used to obtain the rate constants in
the model.
a
Calculated using the Ir metal surface area, m2/g sample and cross-sectional area
of active metal (0.074 nm2).

36
G.S.B. Bottazzi et al. / Applied Catalysis A: General 404 (2011) 30–38
4
3
2
1
0
100
y = 0.0067x
R2 = 0.9928
90
80
70
60
50
40
30
20
10
0
0
40 80 120 160 200 240 280 320 360 400 440 480 520
Time, min
0
50 100 150 200 250 300 350 400 450 500 550
Fig. 5. First-order behavior of the tetralin hydrogenation without inhibitors at
250 ◦C and 15 atm, over Ir-SBA-16.
Time, min
No inhibitor DBT Quinoline 4,6-DM-DBT Indole Carbazole
Generalized Langmuir–Hinshelwood rate equation can be used
to represent the inhibiting effect of nitrogen containing compounds
as quinoline, indole, carbazole and sulfur containing compounds
as dibenzothiophene and 4,6-dimethyl-dibenzothiophene on the
tetralin hydrogenation.
Fig. 6. Kinetic of the hydrogenation of tetralin at T = 250 ◦C, P = 15 atm, 360 rpm.
The lines were obtained by fitting the kinetic curves derived from the model to the
experimental data (F = 1, 2−3).
3.3.2. Kinetic model for tetralin inhibition by sulfur and nitrogen
compounds
The hydrogenation of tetralin reaction was carried out at 250 ◦C
and 15 atm in the presence of different nitrogen or sulfur com-
pounds as dibenzothiophene, 4,6-dimethyl-dibenzothiophene,
quinoline, indole and carbazole (concentration equivalent to
100 ppm as nitrogen or sulfur). The inhibiting effect in the tetralin
hydrogenation was studied according to LaVopa and Satterfield
[63], and the following equation was proposed:
3.3. Kinetic calculations
First-order tetralin hydrogenation rate constants, based on the
rate of tetralin disappearance were calculated using the integral
method. The tetralin conversion showed a first-order behavior
when graphing ln(CTL/CTLo) versus time (Fig. 5). The slope and
the correlation coefficient were calculated via least-squares fit-
ting. Correlation coefficients higher than 0.96 were obtained in
all cases. Trans-decalin and cis-decalin were observed as the
main products of the tetralin hydrogenation reaction (more than
98%). The semiempirical kinetic model proposed is the general-
ized Langmuir–Hinshelwood model for hydrogenation, for tetralin
hydrogenation, the reaction rate is given by:
k
TLCTL
rTL
=
(6)
1 + KiCi
where rTL is the pseudo-first-order rate constant for the reaction
inhibited by nitrogen/sulfur compounds, where Ki is the appar-
ent nitrogen/sulfur compound adsorption equilibrium constant
(l/mmol) and represents the behavior of all the nitrogen/sulfur
compounds that contribute to the inhibition and Ci the initial
nitrogen compound concentration (mmol/l). The results of these
experiments (Fig. 6) were fitted to a pseudo-first-order rate equa-
tion, with correlation coefficients (R2) better than 0.98 in all cases.
The excellent representation of the experimental results by a
pseudo-first-order rate equation implies that the inhibition effect
is approximately constant during each test. The inhibiting strength
does not seem to be affected by the conversion of the parent
nitrogen/sulfur compound, the formation or disappearance of basic
compounds or the degree of organic nitrogen removal in the case
of nitrogen compounds. This behavior suggests that the coverage
of the available active sites by nitrogen compounds is established
in the early stages of the reaction and remains nearly constant
throughout the experiment, probably due to the slow kinetics of
desorption of these compounds [55,76]. Therefore, the variation in
the nitrogen or sulfur compound concentration along time was not
considered in the development of the model. The parameter esti-
mation of the kinetic model was performed with the Powell version
of the Levenberg–Marquardt algorithm. The differential equation
was solved using the EPISODE package of Scientist®. The objective
function (Eq. (7)) was the sum of the squares of the differences
between experimental and calculated yields of decalin versus time
of the reaction, for each inhibitor in particular (Fig. 6).
KH CH
kKTLCTL
2
2
rTL
=
×
(3)
1 + KTLCTL
1 + KH CH
2
2
where rTL is the tetralin conversion to decalins rate, CTL is tetralin
concentration and CH is hydrogen concentration, k is the rate
constant and K is the a2dsorption equilibrium constants of the indi-
vidual compounds. Under our experimental conditions, KH CH
1, therefore, this kinetic equation could be simplified:
ꢀ
2
2
kKTLCTL
rTL
=
(4)
1 + KTLCTL
The kinetic calculations showed a first-order behavior with
respect to the tetralin concentration, and the value of the KTLCTL
product was close to 0. Substituting the kKTL product by kTL, Eq. (4)
was further simplified to:
rTL = kTLCTL
(5)
The value obtained for kTL at 250 ◦C (Fig. 5) using the inte-
gral method, already described, was 6.7 × 10−2/min (R2 = 0.99). This
value will be used as a reference for the results obtained in the
experiments where this reaction was inhibited by nitrogen or sulfur
compounds.
n
ꢀ
3.3.1. Control of the kinetic regime
2
F =
(yexp − ycal
)
(7)
A set of experiments was performed to check the absence of
intraparticle and interphase mass transfer limitations. Different
sizes of catalyst particles (0.2, 0.4, 0.6, 0.8 mm) were tested and
the results indicated that a kinetic regime was established in all
cases.
1
The inhibiting effect of the compounds included in this
study increases in the order: DBT < quinoline < 4,6-dimethyl-
DBT < indole < carbazole. The inhibiting effect of these compounds

G.S.B. Bottazzi et al. / Applied Catalysis A: General 404 (2011) 30–38
37
Table 4
Acknowledgments
Adsorption constants for the different nitrogen/sulfur compounds derived from the
kinetics analysis.
Thank to CONICET Argentina, PIP N◦ 112-200801-00388
(2009–2011); and MINCyT Cba. 1210/07 (2007–2011). Special
thanks to Dr. A. Caneiro and Dr. H. Troiani for SEM, TEM analysis.
Compound
Adsorption constant K
(L/mmol)
Dibenzothiophene
Quinoline
4,6-Dimethyl-DBT
Indole
147
280
352
408
475
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