Short time synthesis of titania modified-CMK-3 carbon mesostructure as support for Ir-catalyst applied in catalytic hydrotreating

Article abstract of DOI:10.1016/j.cattod.2018.04.012

Ti-CMK-3 carbon mesoporous was prepared using a novel synthesis method. This new method avoids the hard template synthesis used commonly. The method developed here, allows to reduce time, energy consumptionand cost. Structural and textural characterization of the titanium modified-mesoporous carbonwas performed by N₂ adsorption, XRD, UV–vis-DRS, Raman spectroscopy and TEM. The characterization results indicated that the textural and structural properties of the material synthesized by the short time method are comparable with the properties of the material prepared by the hard template method. Ti modified-mesoporous carbon was used as support of the iridium nanoparticles, in order to prepare a catalyst to be tested in model hydrotreating reactions. The catalyst obtained by wet impregnation with iridium acetylacetonate were characterized by ICP-AES, H₂ chemisorption, TEM, XPS and FTIR of adsorbed pyridine. The high Ir dispersion and small particle size, along with the moderate Lewis acidity generated by the presence of titanium in the support, were responsible for the good performance and stability of the catalyst in the hydrogenation of tetralin in presence of nitrogen compounds. Main advantage of the present study is the reduction of time and cost in the synthesis of the new material and the applicability for HDT reactions.

Full text of DOI:10.1016/j.cattod.2018.04.012

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Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Short time synthesis of titania modified-CMK-3 carbon mesostructure as
support for Ir-catalyst applied in catalytic hydrotreating
Brenda C. Ledesma, Juliana M. Juárez, Andrea R. Beltramone⁎
Centro de Investigación en Nanociencia y Nanotecnología (NANOTEC), Facultad Regional 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
Keywords:
Direct synthesis
Short time
Ti
HDT
Tetralin
Ti-CMK-3 carbon mesoporous was prepared using a novel synthesis method. This new method avoids the hard
template synthesis used commonly. The method developed here, allows to reduce time, energy consumptionand
cost. Structural and textural characterization of the titanium modified-mesoporous carbonwas performed by N2
adsorption, XRD, UV–vis-DRS, Raman spectroscopy and TEM. The characterization results indicated that the
textural and structural properties of the material synthesized by the short time method are comparable with the
properties of the material prepared by the hard template method. Ti modified-mesoporous carbon was used as
support of the iridium nanoparticles, in order to prepare a catalyst to be tested in model hydrotreating reactions.
The catalyst obtained by wet impregnation with iridium acetylacetonate were characterized by ICP-AES, H2
chemisorption, TEM, XPS and FTIR of adsorbed pyridine. The high Ir dispersion and small particle size, along
with the moderate Lewis acidity generated by the presence of titanium in the support, were responsible for the
good performance and stability of the catalyst in the hydrogenation of tetralin in presence of nitrogen com-
pounds. Main advantage of the present study is the reduction of time and cost in the synthesis of the new
material and the applicability for HDT reactions.
N-compounds
1. Introduction
of the surface of these ordered mesoporous carbons for more applica-
tions. For catalytic applications, the introduction of a heteroatom in the
Mesoporous carbons are materials useful in many applications, as
catalyst support, drug delivery, sensors and sieves.Until now, the major
method to achieve mesoporous carbon materials is the nanocasting
strategy, where a polymer in the confined nanospaces of the material
acting as a hard template is subsequent carbonizated to achieve me-
soporous carbons [1,2]. Several researchers [1–5] reported the pre-
paration of ordered mesoporous carbons using mesostructured silica
materials as templates.
Typically, the cost of the synthesis of templated mesoporous carbon
is dependent upon the productions cost and time of the nanostructured
inorganic template such as, zeolite, alumina or mesoporous silica [6–9].
Since inorganic nanostructures are sacrificed in the final stage of the
preparation, this method is considered to be complicated, high cost and
therefore industrially impractical. High consumption of time and en-
ergy are the most important factors in the synthesis of mesoporous
carbon using the template method, so an important issue related to the
potential applications of mesoporous carbon is the synthesis on a large
scale.
structure is an alternative for modifying the interaction between the
active catalytic phase and the support and hence to increasing the
catalytic activity. The most important goal of this work is to develop a
faster and environmentally benign route to fabricate a three di-
mensionally interconnected mesoporous carbon material with appro-
priate surface properties in order to be applied as a catalyst in an in-
dustrial process as catalytic hydrotreating (HDT). Because of that, much
effort was made to explore the feasibility of short-time synthesis,
simple, economically viable and with low energy consumption in order
to manufacture the high-quality mesoporous carbon materials.
In our previous work [10] we have developed a novel titanium
oxide-CMK-3 support synthesized as a replica of Ti-SBA-15. Titanium
species were incorporated from the hard template Ti-SBA-15 material.
We have obtained a material with high specific surface area, pore vo-
lume and narrow mesopore size distribution and with TiOx species
highly dispersed with nanometric size. Ti incorporation into the fra-
mework generated moderate Lewis acidity that affected the nature of
the support favoring the interaction with the iridium sites, used as
catalytic phase. Titanium improved the dispersion and stability of the
Nowadays is important to investigate the modification of the nature
⁎
Corresponding author.
E-mail address: abeltramone@frc.utn.edu.ar (A.R. Beltramone).
https://doi.org/10.1016/j.cattod.2018.04.012
Received 8 November 2017; Received in revised form 3 April 2018; Accepted 8 April 2018
0920-5861/©2018ElsevierB.V.Allrightsreserved.
Pleasecitethisarticleas:Ledesma,B.C.,CatalysisToday(2018),https://doi.org/10.1016/j.cattod.2018.04.012

B.C. Ledesma et al.
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iridium nanoparticles compared with the catalyst without titanium
species. In that case, titanium incorporation enhanced hydrogenation of
the aromatic ring and promoted the hydrodenitrogenation (HDN) of
indole when the catalyst was tested in the HDT reactions [10].
The challenge here is to develop an ordered titanium mesoporous
carbon reducing the cost by avoiding the use of the expensive hard
template. In order to compare the catalytic activity with our previous
results, this support was testedin model HDT reactions using reduced
iridium as active sites.
The justification of HDT as chosen catalytic process is based on the
importance of reduce the content of aromatic, sulfured and ni-
trogenated hydrocarbons as measures aimed at further reducing emis-
sions to obtain better quality of fuels. Our previous works [10–13] and
other reports [14–20] have demonstrated that noble metals as iridium
possess exceptional activity and selectivity for the selective hydro-
genation and hydrogenolysis reactions.
For that reasons, the present studyshows the synthesis of titanium
mesoporous carbon without being necessary a template synthesis, in
order to reduce time and energy consumption as synonym of reducing
cost. The study of the efficiency for the titanium mesoporous carbon as
support for the iridium catalyst is tested in the hydrodenitrogenation of
indole and in the hydrogenation of tetralin in presence of nitrogen
compounds.
a heating ramp of 4 °C/min. The samples were denoted as Ir-Ti-CMK-3-
ST and Ir-Ti-CMK-3.
2.4. Catalytic activity
The reactions took in place in a 600 mL stirred autoclave (Parr
Pressure Reactor 4536). The hydrotreating reaction were tested at
250 °C and 15 atm of H2 and 500 rpm. The HDN of indole was per-
formed using a concentration equivalent to 150 ppm of N, indole was
disolved in 50 mL of dodecane. The tetralin hydrogenation was per-
formed as follows: tetralin was dissolved in 50 mL of dodecane to a
concentration of 5 wt.%. 150 ppm of nitrogen (as indole, indoline,
quinoline, tetrahydroquinoline and carbazole) were added to the solu-
tion to study the inhibition effect on tetralin hydrogenation. Then,
250 mg of the catalyst were transferred to the reactor. The reaction time
was 6 h; samples were taken every hour. The products were analyzed
with a HP 5890 Series II GC and Petrocol DH capillary column with
0.25 mm of internal diameter and 100 m of length. The products were
confirmed by GC/MS.
2.5. Characterization
X-ray diffraction patterns were obtained with a PANANALITYCAL
Phillips X'pert XDS diffractometer with a diffractometer beam mono-
chromator and CuKα radiation source. Elemental analysis was per-
formed 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. N2 adsorption/desorption isotherms
at −196 °C were measured on ASAP 2020 equipment after degassing
the samples at 400 °C. The pore size distribution of the samples was
determined by the QSDFT (Quenched Solid Density Functional Theory)
using kernel N2 at 77 K on carbon (slit-cylindrical pores, adsorption
branch, the specific surface area was determined by Brunauer-Emmett-
Teller (BET) method. Ultraviolet-visible diffuse reflectance spectro-
scopy (UV–vis-DRS) was recorded with a Perkin Elmer Lamba 650
spectrophotometer equipped with a diffuse reflectance accessory.X-ray
Photoelectron Spectra (XPS) were obtained on a MicrotechMultilb 3000
spectrometer, equipped with a hemispherical electron analyzer and
MgKα (hν = 1253.6 eV) photon source. An estimated error of
0.1 eV can be assumed for all measurements. TEM micrographs were
obtained on a JEOL model JEM-1200 EX II microscope. H2 chemi-
sorption was performed using a Micromeritics Chemisorb 2720, witha
flow of 14 mL/min of 98% N2/He. The mean diameter of the Ir particles
was estimated under the basic assumption of stoichiometry for H/
Ir = 2, with spherical shape of the metal particles. The accuracy/re-
2. Experimental
2.1. Synthesis of mesoporous carbon Ti-CMK-3 by the short time method
In this method of synthesis, we use copolymer P123 as surfactant,
sucroseas source of carbon, tetraethylortosilicate (TEOS99% Sigma-
Aldrich) as source of Si and tetraethylorthotitanate (TEOT, 98% Sigma-
Aldrich) as source of Ti. The synthesis was performed under acid con-
ditions. In this procedure, 4 g of triblock copolymer P123 and 1 g of
sucrose were dissolved in 160 mL of HCl solution (2 M) at 40 °C. After
2 h under vigorous stirring, the silica precursor TEOS (8.6 mL) was
added and kept under stirring for 15 min. Afterwards, the Ti precursor
TEOT (0.6 mL) was added and the solution was stirred for another
15 min. The resulting mixture was transferred into a polypropylene
bottle and kept static at 100 °C for 24 h. The solid was filtered and
washed with deionized water until pH ∼6. After complete drying (48 h
at 50 °C), 1 g of the composite silica/P123/sucrose was added to a so-
lution of 1 mL of H2SO4 (98 wt.%) and 10 mL of deionized H2O. The
resulting mixture was stirred at room temperature for 18 h. After that,
the sample was dried at 160 °C for 6 h. The dark brown powder was
then heatedup to 900 °C under nitrogen flow (20 mL/min) in order to
complete the carbonization of the sucrose. To remove the silica, the
composite was treated with an HF solution (5 wt.%) at room tempera-
ture. To ensure the complete removal of the silica, this procedure was
performed twice. The carbon without silica was filtered, washed with
ethanol solution and dried at 50 °C. The obtained material with nominal
Si/Ti = 20 M ratio was denoted by Ti-CMK-3-ST.
producibility to the results is typically better than
1.5% with
0.5% reproducibility. Raman spectrum was obtained from an InVia
Reflex Raman microscope and spectrometer using a 532 nm diodelaser
excitation.TPR was performed using a Micromeritics Chemisorb 2720
apparatus, with a flow of 14 mL/min of 10 mol% of H2/N2 heating up to
500 °C, with a preheating treatment at 380 °C in an inert atmosphere
(N2). JASCO 5300 FTIR spectrometer was used for Py-FTIR measure-
ments. A thermostated cell with a special NaBr window warmed up to
400 °C and 4.2 × 10−2 Torr during 2 h was employed to avoid possible
sample hydration.
2.2. Synthesis of mesoporous carbon Ti-CMK-3 by nanocasting strategy
For comparative study, Ti-CMK-3 was also synthesized by nano-
casting strategy. The procedurewas reported in our previous work [10].
Ti-SBA-15, with Si/Ti = 20 M ratio, was used as hard template and
sucrose was used as source of carbon. The obtained material was de-
noted by Ti-CMK-3.
3. Results and discussion
3.1. XRD
2.3. Iridium incorporation
The representative low angle XRD patterns of the mesoporous
carbon samples are shown in Fig. 1.The Figure also displays the pat-
terns of Ti-SBA-15 used as hard template for the synthesis of Ti-CMK-3
and the SBA-15 and CMK-3 patterns as reference [21–26]. CMK-3 and
Ti-CMK-3 patterns show characteristic signals for 2D-hexagonal p6m
symmetry at (100), (110) and (200) reflections typical of amorphous
Iridium was incorporated into the support by the wet impregnation
method described in a previous work [10]. Iridium acetylacetonate
(Aldrich 99.9 wt.%) was used as iridium source. The iridium loaded
samples (1 wt.%) were reduced in a H2 flow (20 mL/min) at 470 °C with
2

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Fig. 1. Low angle XRD patternsof the samples synthesized.
SBA-15, as is expected since the ordered structures are exactly negative
replicas of the hard template SBA-15 [25,26]. Is interesting to note, that
similar pattern was obtained for Ti-CMK-3-ST, confirming that the or-
dered mesoporous carbon structure (CMK-3) was obtained by the short
time synthesis method (without hard template).
Wide-angle XRD patterns of the titanium modified carbon meso-
porous are shown in Fig. 2, anatase pattern and CMK-3 pattern were
added as references. The two broad diffraction peaks observed are
characteristics of graphite carbons [27]. The peaks corresponding to
anatase phase (2 theta: 25°, 38°, 48°, 54°, 55° and 63°) are observed in
both synthesized samples and can be indexed to the plane [101] of
anatase phase. The absence of prominent reflections of the TiO2 clusters
indicates that no crystalline bulk material has been formed. Anatase
nanoparticles were formed with nanometric size and high dispersion
(very broad XRD TiO2 signals). This can be ascribed to a relatively low
scattering contrast between the pores and walls of mesoporous mate-
rials, due to the formation of anatase nanoclusters with a narrow size
distribution. The average anatase cluster size was estimated using the
Scherrer’s formula [28,29]. The results indicated that the mean dia-
meter is 3.3 nm for Ti-CMK-3 and 3 nm for Ti-CMK-3-ST. The results
reveal that titanium species are well dispersed and the size of the
particles is slightly smaller on the CMK-3-ST material than in CMK-3.
Fig. 3. a) Nitrogen adsorption (solid symbols)- desorption isotherm (open
symbols) at −196 °C of the samples synthesized, b) Pore size distribution.
3.2. Analysis of adsorption/desorption isotherms
The porosity of the resultant carbons sampleswas investigated by-
nitrogen sorption measurements in order to determine the surface area
(SBET) and mean pore diameter (Wp) of the titanium modified-meso-
porous carbons. Fig. 3(a) shows that both nitrogen sorption isotherms
are essentially of type IV following the IUPAC classification, indicative
of the mesoporous structure, that consists mainly in hexagonal cylind-
rical pores (channels). The channels are randomly interconnected to
each other with tiny micropores in their walls
(nanorods interconnected by spacers) [1,2]. The mesopore size
distribution is shown in Fig. 3(b) and the structural and textural
properties of the samples are listed in Table 1. Hard template Ti-SBA-15
characterization was added as reference. The size of the mesopore (Wp)
is similar for both Ti-mesopores carbons prepared by different methods.
The size of the pore decreases after iridium incorporation indicating
that iridium is located mainly inside the channels. High surface area
and ordered mesoporous structure was obtained for all samples. The
mesoporous carbon obtained by short time method (Ti-CMK-3-ST)
shows slightly larger area than Ti-CMK-3. After the iridium modifica-
tion, the surface area of both catalysts decreases, but the catalyst Ir-Ti-
CMK-3-ST has the highest surface area of 1030 m2/g. The obtained
Fig. 2. Wide-angle XRD patterns of the samples synthesized and anatase and
CMK-3 patterns as references.
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Table 1
Textural and structural properties of the samples synthetized.
Sample
SBET(m2 g−1
)
VTP(cm3 g−1
) Wp(nm) Ti wt. Ir wt. D; Ir
*
*
%
%
(nm)**
Ti-SBA-15
Ti-CMK-3
Ti-CMK-3-ST
Ir-Ti-CMK-3
Ir-Ti-CMK-3-ST 1030
880
1.30
0.80
0.88
0.70
0.75
8.0
7.0
7.2
6.0
6.5
5.2
4.3
5.0
4.3
5.0
1044
1052
890
1.0
0.9
87; 1.3
90; 1.2
* ICP-AES.
** Dispersion (D) and Ir particle size were calculated by H2 Chemisorption.
values give account of the success of the short time method of the
synthesis, that allow us to obtain an ordered mesoporous material with
high surface area, high pore volume and narrow mesopore size dis-
tribution. The content of titanium was determined by ICP-AES, the
values are listed in Table 1. We observe that the best incorporation of Ti
was achieved with the short time method. Iridium content was also
determined by ICP-AES and the values were very close to nominal 1 wt.
%.
Fig. 5. UV–vis-DRS of the samples synthesized.
the conclusion that the short time method was adequate to prepare
successfully this structure.
Fig. 4(c) and (d) shows the images of the iridium catalysts (dark
points), Ir-Ti-CMK-3 and Ir-Ti-CMK-3-ST, respectively and the iridium
particle size distribution. The particle-size distribution (PSD) of the ir-
idium particles dispersed in the mesoporous framework was measured
using a mathematical function that defines the relative amount of
particles present according to size. The mean size of the reduced ir-
idium crystallites was 1.22 nm for Ir-Ti-CMK-3 and 1.20 nm for Ir-Ti-
CMK-3-ST in concordance with the H2 chemisorption results.
H2 chemisorption results are also shown in Table 1. Better disper-
sion and lower particle size was obtained when the support was syn-
thesized by the short time method.
3.3. TEM
Transmission electron microscopy (TEM) analysis shows the pore
channels of the samples synthesized. We can observe in Fig. 4(a) and (b)
that the mesopore order is similar in the Ti-modified mesoporous car-
bons, indicating the success of both methods of synthesis. Fig. 4(a) and
(b) indicate well-ordered hexagonal symmetries with a calculated pore
diameter of about 7–7.5 nm, in agreement with the values obtained
from nitrogen sorption technique. TEM image of Ti-CMK-3-ST validates
3.4. UV–vis-DRS
In order to determine the chemical environment of the incorporated
Ti-species, both samples were studied by UV–vis diffuse reflectance
spectroscopy. Results are shown in Fig. 5. The absorption band
Fig. 4. TEM of the samples synthesized: a) Ti-CMK-3, b) Ti-CMK-3-ST, c) Ir-Ti-CMK-3, d) Ir-Ti-CMK-3-ST.
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Fig. 7. TPR of the samples synthesized.
Fig. 6. Raman spectroscopy of the samples synthesized.
the strength of Ir interaction with the support, leading to a more
homogeneous distribution of Ir-species than using other pure carbon or
silica support.
observed at 205 nm in both samples is attributed to tetrahedral co-
ordinated titanium species [30]. The broadening of this band indicates
the presence of both tetrahedral and octahedral titanium species as well
dispersed anatase nanospecies [31]. The absence of bands at higher
wavenumber indicates that titanium species are very well dispersed as
small anatase nanoparticles.
3.7. TPR
Fig. 7 shows the reduction temperature of iridium in both samples.
We observe only one reduction temperature at 200 °C for Ir-Ti-CMK-3
and 194 °C for Ir-Ti-CMK-3-ST. The reduction temperatures obtained in
this study are lower than the obtained in a previous work using CMK-3
as support [11]. This could be explained in terms of an appropriate
anchorage of the iridium crystallites on the surface of titanium-mod-
ified CMK-3 compared with pure CMK-3.
3.5. Raman spectroscopy
Fig. 6 shows the presence of bands at about 635, 517 and 403 cm−1
assigned to TiO2 in anatase phase. For the synthesized samples, the
widths of the signals are practically equal for both samples, this fact
gives account of the similar nanometric size and the similar dispersion
of the titania species. The peak at 1579 cm−1 corresponds to an E2g
mode of graphite and the peak at 1355 cm−1 is ascribed with vibrations
of CeC bond, attributed to the configuration of disordered graphite
[32–36]. Similar intensity is indicative of similar structure obtained for
the material synthesized by the short time method.
3.8. Py-FTIR spectroscopy
The acid nature of the supports was studied using the Pyridine ad-
sorption method. Results are shown in Table 3. Both catalysts exhibited
only Lewis acid sitesat 1540 and 1640 cm−1 (spectra not shown) [44].
FTIR results showed that the incorporation of small nanoparticles of
anatase provides Lewis acidity to the catalyst [45–47]. Ir-Ti-CMK-3
presented slightly lower amount of Lewis acid sites than Ir-Ti-CMK-3-
ST; this is expected since Ti could be highly dispersed in CMK-3-ST.
3.6. XPS
XPS results are shown in Table 2. XPS analysis of Ti-CMK-3 was
reported in our previous work [10]. C1s binding energy of about 284 is
attributed to CeC sp3 and 286 eV to C]C sp2 carbons, both of them
characteristic of CMK-3 as graphitic and disordered carbon species
[37–40]. Ti signals of Ti 2p3/2 at 458.6 eV corresponds to Ti as anatase
[41,42]. The results are comparable to the obtained here for Ti-CMK-3-
ST obtained by the short time method. The low values of Ti/C show that
Ti species are well dispersed in the mesopores of CMK-3, in both Ti-
modified samples. XPS study also allows determining the oxidation
state and surface composition of the iridium crystallites. BE at 61.0 eV
is assigned to Ir° and 62.0 eV is assigned to Ir-O [43]. The values ob-
tained for both samples indicate that iridium is almost as metallic ir-
idium. The fraction of iridium in contact with oxygen in IrO species is
similar in both samples, the fact that Ir was easily reduced could be
related to the lower size and higher dispersion of the iridium nano-
particles in both supports. In our previous works [10,12], we observed
that the presence of Ti-species on the surface of CMK-3 or SBA increased
3.9. Catalytic activity
In our previous work [10], we found that Ir-Ti-CMK-3 was very
active in the HDN of indole. In this work, we compare the performance
of Ir-Ti-CMK-3-ST synthesized by the short time method. The reaction
network of the hydrodenitrogenation of indole was suggested by Zhang
and Ozkan [48]. Ethylcyclohexane and ethylbenzene are the desired
products from indole HDN. The identified products in this investigation
were indoline, o-ethylaniline, ethylbenzene and ethylcyclohexane;
these accounted for more than 98% of the total products. Ethylbenzene
and ethylcyclohexane are the hydrodenitrogenated products. Table 4
shows the comparative study of the HDN of indole for both catalysts.
We can observe that the behavior of both catalysts are similar in-
dicating that the short time method is adequate to prepare a support
with appropriate characteristic to be used as support for the Ir-catalyst.
Table 2
Core levels and atomic surface composition of the synthesized samples obtained by XPS.
Sample
C1s
O1s
Ir4f7/2
Ti2p3/2
Ti/C
O/C
Ir/C
Ir-Ti-CMK-3-ST
Ir-Ti-CMK-3
284.4(91)286.2(9)
531.7(74)533.6(26)
531.7(67)533.7(33)
61.1(97)62.4(3)
61.0 (95)62.2 (5)
458.5
458.6
0.020
0.022
0.0152
0.0163
0.00090
0.00095
284.7 (88)286.5 (12)
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Table 3
Quantification of acid sites at different temperatures.
Ir-Ti-CMK-3-ST
Ir-Ti-CMK-3
Temperature of
desorption(°C)
B (mmol/g) L (mmol/g) B (mmol/g) L (mmol/g)
50
–
–
–
–
0.90
0.52
0.14
0.10
–
–
–
–
0.85
0.49
0.11
0.07
100
200
300
Table 4
HDN conversion (number of denitrogenated molecules at 6 h of reaction time).
Samples
%HDN
Fig. 9. Catalytic activity of Ir-Ti-CMK-3-ST after three catalytic cycles.
T = 250 °C, P = 15 atm, rpm = 500, feed: 0.0142 mol of tetralin and 150 ppm
of N as indole in dodecane, cat = 250 mg, time of reaction = 6 h.
Ir-Ti-CMK-3-ST
Ir-Ti-CMK-3
98.0
97.3
%HDN = 100*(ECH + EB)/(ECH + EB + OEA + HIN). T = 250 °C, P = 15 atm,
rpm = 500, 150 ppm of N in 50 mL of dodecane, cat = 250 mg.
resistance to poisoning of the catalysts and the subsequent inhibition
effect.
In order to test the catalytic performance of the new catalyst in the
typical reactions present in the HDT process, several experiments were
performed along with the study of the stability of the catalyst.
3.10. Reusability
Fig. 8 shows tetralin conversion to decalin in absence and in pre-
sence of nitrogen compounds as inhibitors. It is clear that the inhibition
effect increases in the order indole < carbazole < quinoline <
tetrahydroquinoline < indoline. It seems that the inhibiting effect is
directly related to the basicity of the nitrogen compounds. The strong
inhibiting effect of the basic compounds is in qualitative agreement
with previous studies [49,50]. Indole and carbazole, non basic N-
compounds only present a drop of 10% in tetralin conversion, while
with the addition of the more basic compounds, as tetrahydroquinoline
or indoline, the drop is more pronounced (about 30%).
The good activity even in presence of nitrogen gives account of the
high hydrogenating capacity of iridium, but mainly to the high dis-
persion obtained with the novel titanium modified-carbon support. The
Lewis acidity of the catalyst, where Ti cation centers resulted five co-
ordinated to the surrounding oxygen anions [45–47], are responsible
for better anchorage of the iridium crystallites and could influence the
interaction between the Ir- species and the N-compounds improving the
Reusability is an important parameter from the industrial point of
view. In order to evaluate the stability of Ir-Ti-CMK-3-ST catalyst ob-
tained by the short time method, the spent material was washed several
times in an excess of methanol and water, and then filtered. The solid
was dried and then desorbed in nitrogen flow of 20 mL/min from 25 °C
to 470 °C and finally reduced in H2 flow of 20 mL/min at 470 °C fol-
lowing the same procedure as described in the experimental section.
Fig. 9 shows the catalytic activity measured as tetralin conversion to
decalin in presence of indole after three catalytic cycles. We can ob-
serve that the activity remains after the second recycle compared to a
fresh catalyst. The activity loss in the presence of indole was less than
8% after the third recycle.
The spent catalyst was characterized after the third catalytic cycle
and subsequent regeneration. The sample was analyzed by N2 adsorp-
tion-desorption, H2 Chemisorption and ICP. The results of the char-
acterization after the reaction in the presence of indole are shown in
Table 5. According the results, the structural and textural properties of
the catalysts were maintained after the third recycle. The drop in
conversion may be due to the increase in the iridium particle size and
the decreasing of dispersion as can be observed in Table 5. The ag-
glomeration of the iridium particles could be responsible for the slight
decrease in conversion after the third recycle.
4. Conclusion
The method of synthesis developed in this work allowed us to obtain
the ordered titanium-mesoporous carbon reducing time and cost by
avoiding the use of the expensive hard template.The new material ob-
tained had high specific surface area, pore volume and narrow meso-
pore size distribution, with highly dispersed Ti species. The iridium
catalysts prepared using this support was very active for hydro-
denitrogenation of indole and hydrogenation of tetralin in presence of
inhibitors. The good activity was related with the high dispersion of the
metallic iridium crystallites due to the presence of titania nano-species
changing the electronic environment of the surface. The presence of
iridium sites and Ti-Lewis sites over a high surface specific area sup-
port, generated an active and stable catalyst to be applied in the in-
dustrial process of HDT.
Fig. 8. Catalytic activity of the samples. T = 250 °C, P = 15 atm, rpm = 500,
moles of tetralin = 0.0142, 150 ppm of N in each case, cat = 250 mg.
6

B.C. Ledesma et al.
CatalysisTodayxxx(xxxx)xxx–xxx
Table 5
Structural and textural properties of the spent catalysts.
Sample
SBET(m2 g−1
)
VTP(cm3 g−1
)
Wp(nm)
Ti wt.%*
Irwt.%*
D; Ir (nm)**
Ir-Ti-CMK-3-ST fresh
1030
1025
0.75
0.70
6.5
6.4
5.0
5.0
0.9
0.9
90; 1.2
84;1.5
Ir-Ti-CMK-3-ST after 3 recycle
* ICP-AES.
** Dispersion (D) and Ir particle size were calculated by H2 Chemisorption.
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