G Model
CATTOD-9798; No. of Pages12
ARTICLE IN PRESS
L.P. Rivoira et al. / Catalysis Today xxx (2015) xxx–xxx
2
supported Pd, Cr O , unsupported manganese oxides and a com-
(characteristics of the active Ti and/or TiO2 species) and the effect
of the different operation conditions in ODS of DBT under mild
conditions in order to find the best performance.
2
3
mercial Co-Mo/Al O with hydrogen peroxide as oxidant [32].
2
3
In general, when tetravalent cations like Ti , Zr , V , Sn4+, etc.
are incorporated to the framework of SBA-15, the electroneutral-
ity is maintained but some redox properties are incorporated to
the support surface [33]. Rayo et al. [34] studied the effect of the
incorporation of Al, Ti, and Zr on SBA-15. They found that beyond
4+
4+
4+
2. Experimental
2.1. Synthesis of the titanium-SBA-16 modified catalysts
2
0 wt.% of heteroatom, the segregation of metal oxides on the sur-
face becomes significant and there is an important decrease in the
surface area and pore volume of the support, which negatively
affects the dispersion of the active phases leading to a decrease in
catalytic activity. The addition of 5–10 wt.% Ti to the catalyst caused
greater increases in activity than those obtained with Zr.
Mesoporous silica materials with cubic Im3m structure Si-SBA-
6 were synthesized according to the procedure described by
the literature [50]. The molar composition of the mixture was:
1
F127/TEOS/HCl/H O = 0.004/1/4/116. The incorporation of titanium
2
species via the post-synthesis method to obtain TiO /SBA-16 was
2
In view of recent studies, Ti-containing molecular sieves show
good activity in the oxidation of different S-bearing compounds
◦
as follows: as-synthesized SBA-16 was dried in oven at 80 C for
4
h. Then, 0.5 g of dried sample was dispersed in a solution contain-
[
35,36]. Titanium silicalite (TS-1) is used as a catalyst in the selec-
ing 2 mL of titanium-tetrabutyl-orthotitanate (TTBT) and 5 mL of
◦
tive oxidation of thiophene at 60 C; 90% thiophene conversion was
achieved in 1 h of reaction. Here, framework titanium species was
found to be the active site for thiophene oxidation.
◦
ethanol. The mixture was stirred at 60 C for 2 h. The hybrid prod-
ucts were afterwards dried in a rotator evaporator in vacuum at
◦
◦
◦
8
4
0 C and calcined in air at 500 C, with a heating rate of 5 C/min for
Typical catalytic supports, such as alumina, titania and silica,
exhibit low ODS activity of DBTs; thus differences in their activity
cannot be correlated with surface area [25,37–39]. New large sur-
face area Ti-containing materials such as mesoporous Ti-modified
SBA-15 and titanium oxide nanotubes could prove alternatives cat-
alysts for the ODS process [40].
h. Three TiO /SBA-16 samples were prepared with different con-
2
tent of TiO : 15, 20 and 26 wt.% denoted as TiO /SBA-16: samples
2
2
A, B and C, respectively.
The incorporation of titanium as heteroatom in the SBA-16
mesoporous matrix was performed during the synthesis, fol-
lowing the method informed in our previous work [49]. We
introduce here some modifications to the synthesis: pluronic F127
Cede n˜ o-Caero et al. [40], using Ti-nanotubes attribute the ODS
activity to the TiO surface exposed. Loren c¸ on et al. [41] also inves-
2
(
EO106PO70EO106) was dissolved in a solution of distilled water
tigated the catalytic activity of titanate nanotubes in the oxidation
of DBT by using hydrogen peroxide. Chica et al. [26] reported the
activity and stability in ODS of mesoporous Ti-containing materials,
using organic peroxides as oxidants over a fixed-bed reactor. They
observed that Ti-MCM-41 catalyst was more active and stable than
and concentrated hydrochloric acid (37 wt.%). The solution was
◦
further stirred at 35 C during 2 h, and TEOS was then added drop-
wise to the solution, stirring for another 15 min. Subsequently,
tetraethyl-orthotitanate (TEOT) was dissolved in 10 mL of ethanol
to avoid hydrolyzation and added slowly to the solution while stir-
ring for another 24 h. The resulting suspension was transferred to
Ti-beta and MoO /Al O catalysts without Ti-leaching. The surface
3
2
3
was modified by silylation to diminish the adsorption of the more
polar sulfones that will strongly contribute to catalyst deactivation.
Hulea et al. [24] and Corma et al. [42] studied the reaction of sulfides
with hydrogen peroxide on TS-1 and Ti-beta and with tert-butyl
hydroperoxide on Ti-beta and Ti-MCM-41, respectively, using var-
ious organic solvents. They found that Ti-MCM-41 was more active
than TS-1. More recently, Ti-SBA-15 catalysts were reported to
exhibit high activity in ODS [43] either in a batch or in a continuous
fixed-bed reactor with TBHP as oxidant [44]. ODS trend was found
to decrease in the order of DBT > 4-MDBT > 4,6-DMDBT > BT. Ti-SBA-
◦
the PP bottle and reposed under static conditions at 80 C for 24 h.
Ti-SBA-16 samples were prepared with different Si/Ti ratio (20, 15
and 10). The material obtained was denoted as Ti-SBA-16: samples
D (Si/Ti = 20), E (Si/Ti = 15) and F (Si/Ti = 10).
Pure TiO2 in anatase phase was prepared for comparison. In
the synthesis procedure, soles of TiO2 were prepared from a mix-
ture of titanium tetraisopropoxide (TTIP), acetylacetonate (ACAC),
de-ionized water (H O) and ethanol (EtOH) with a molar ratio of
2
1
:1:3:20. The sol–gel stayed at room temperature during 24 h and
then it was washed with de-ionized water and EtOH. Afterwards,
1
5 materials, as opposed to Ti-MCM-41 catalysts, was proved to be
◦
the sample was dried at 90 C during 24 h. To obtain anatase phase,
hydrolytically stable toward aqueous H O [45].
2
2
two consecutive heat treatments were used: Inert post-treatment:
Shah et al. [46] showed the experimental results of oxida-
tive desulfurization (ODS) for Ti-SBA-16 with different titanium
content. Findings indicate that all catalysts were highly active
in the ODS of dibenzothiophene and their catalytic activity was
unaffected up to 10 wt.% loading; Yet, further increase in Ti
contents (15 wt.%) showed a slight decrease in catalyst activity.
They ascribed that to the presence of high Ti content, causing slight
structure change.
◦ ◦ ◦ ◦
(2 mL/min); 20–100 C, 1 C/min; 100 C = 4 h; 100–400 C,
N
2
2
◦
◦
◦
◦
C/min; 400 C = 10 h; 400–25 C, −2 C/min. Oxidative post-
◦ ◦ ◦
treatment:
O
2
◦
(5 mL/min); 20–100 C, 1 C/min; 100 C = 4 h;
◦
◦
◦
◦
1
00–400 C, 2 C/min; 400 C = 10 h; 400–25 C, −2 C/min. The
2
anatase obtained had 95 m /g of specific surface area and 40–50 nm
of mean crystal size. The material yielded was identified as TiO2.
However, insights into SBA-16 support are scarce or inexistent.
Purely siliceous SBA-16 (Im3m) was selected due to its high surface
area and high thermal stability, but particularly, due to its attractive
three-dimensional mesoporous structure. Comprising large spher-
ical cavities arranged in a body-centered cubic array and connected
through smaller mesoporous openings along (1 1 1) directions [47],
that could favor the mass transfer kinetics compared with unidi-
rectional pore system of other mesoporous.
We recently reported a good performance of this support in
hydrotreating processes [48,49]. In this paper, we describe the
effect of the preparation method of titania-modified SBA-16
2.2. Characterization of the catalysts
XRD patterns were collected by using a continuous scan mode
◦
with a scan speed of 0.02 (2ꢀ)/min in the Philips X’Pert PRO PANa-
lytical diffractometer, operating with CuK␣ X-ray radiation (X-ray
generator current and voltage set at 40 mA and 45 kV), using small
divergence and scattering slits of 1/32 mm and a goniometer speed
◦
◦
◦
of 1.2 (2ꢀ)/min. The scanning range was set between 0.5 and 5 .
The sample was crushed previously and placed in an aluminum
sample holder. Elemental analysis was performed by inductively
ated with high frequency emission power of 1.5 kW and plasma
airflow of 12.0 L/min. The surface area was determined by the
Please cite this article in press as: L.P. Rivoira, et al., Sulfur elimination by oxidative desulfurization with titanium-modified SBA-16,