Polyoxomolybdate based ionic-liquids as active catalysts for oxidative desulfurization of simulated diesel

Article abstract of DOI:10.1016/j.poly.2019.06.019

This work compares the stability and the catalytic efficiency of different ionic liquid phosphomolybdates ([BPy]₃[PMo₁₂O₄₀] and [BMIM]₃[PMo₁₂O₄₀]) with a cationic (propylpyridinium) functionalized mesoporous silica nanoparticle composite (PMo₁₂O₄₀@PPy-MSN). These were used as solid catalysts for the oxidative desulfurization of a multicomponent model diesel using hydrogen peroxide as oxidant and a polar immiscible extraction solvent. Ionic liquid ([BMIM][PF₆] was successfully used as solvent to extract sulfur compounds from model diesel. The ionic liquid phosphomolybdates showed partial solubility in the ionic liquid phase, occurring some decomposition of their Keggin structure in the soluble reaction media, probably caused by their interaction with oxidant. On the other hand, the phosphomolybdate composite PMo₁₂O₄₀@PPy-MSN presented high structural stability and only negligible leaching occurrence after various consecutive reaction cycles. The model diesel was near complete desulfurized after 3 h and consecutive desulfurization cycles were performed without loss of activity. Therefore, the immobilization of Keggin phosphomolybdate structure [PMo₁₂O₄₀]^3? using cationic propylpyridinium silica nanoparticle is an assertive strategy to produce stable and active heterogeneous catalysts.

Full text of DOI:10.1016/j.poly.2019.06.019

Accepted Manuscript
Polyoxomolybdate based Ionic-Liquids as Active Catalysts for Oxidative De-
sulfurization of Simulated Diesel
Fatima Mirante, Neide Gomes, Marta Corvo, Sandra Gago, Salete S. Balula
PII:
S0277-5387(19)30430-9
https://doi.org/10.1016/j.poly.2019.06.019
POLY 14010
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
5 April 2019
5 June 2019
10 June 2019
Please cite this article as: F. Mirante, N. Gomes, M. Corvo, S. Gago, S.S. Balula, Polyoxomolybdate based Ionic-
Liquids as Active Catalysts for Oxidative Desulfurization of Simulated Diesel, Polyhedron (2019), doi: https://
doi.org/10.1016/j.poly.2019.06.019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Polyoxomolybdate based Ionic-Liquids as Active Catalysts for Oxidative
Desulfurization of Simulated Diesel
a
b
c
b*
a*
Fatima Mirante, Neide Gomes, Marta Corvo, Sandra Gago, and Salete S. Balula,
a
LAQV-REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências,
Universidade do Porto, 4169-007 Porto, Portugal
b
LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia,
Universidade NOVA de Lisboa, 2829-516 Monte da Caparica, Portugal
b
CENIMAT/I3N, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516
Monte da Caparica, and AD Física, ISEL/IPL, R. Conselheiro Emídio Navarro, 1, 1959-007
Lisboa, Portugal
In memorial:
This publication is dedicated in memorial of Professor Doctor Ana Cavaleiro, an enthusiastic
professor with a “scientific passion” for Polyoxometalates: structures and applications.
Abstract
This work compares the stability and the catalytic efficiency of different ionic liquid
phosphomolybdates ([BPy]
3
[PMo12
O40] and [BMIM]
3
[PMo12O40]) with a cationic
(propylpyridinium) functionalized mesoporous silica nanoparticle composite (PMo12O40@PPy-
MSN). These were used as solid catalysts for the oxidative desulfurization of a multicomponent
model diesel using hydrogen peroxide as oxidant and a polar immiscible extraction solvent. Ionic
liquid ([BMIM][PF ] was successfully used as solvent to extract sulfur compounds from model
6
diesel. The ionic liquid phosphomolybdates showed partial solubility in the ionic liquid phase,
occurring some decomposition of their Keggin structure in the soluble reaction media, probably
caused by their interaction with oxidant. On the other hand, the phosphomolybdate composite
PMo12
O40@PPy-MSN presented high structural stability and only negligible leaching occurrence
after various consecutive reaction cycles. The model diesel was near complete desulfurized after

3
h and consecutive desulfurization cycles were performed without loss of activity. Therefore,
3
-
the immobilization of Keggin phosphomolybdate structure [PMo12O40] using cationic
propylpyridinium silica nanoparticle is an assertive strategy to produce stable and active
heterogeneous catalysts.
KEYWORDS: Mesoporous Silica Nanoparticles; Polyoxomolybdate; Heterogeneous Catalysis;
Oxidative Desulfurization; Fuels
Introduction
One of serious environmental problem is the harmful emission of SOx during combustion of
fuels.[1, 2] In order to reduce the emissions of these compounds to the atmosphere, strict
regulations have been implemented worldwide limiting the sulfur level in fuels (S-content < 10
ppm). Actually, petroleum industry use the hydrotreating method (HDS) to remove an important
series of sulfur compounds (thiols, sulfides and disulfides) from fuel.[3] However, the most
refractory sulfur compounds (mostly benzothiophene derivatives) in fuels are still very hard or
costly to remove.[4, 5] One of the most promising alternative to the HDS techniques is the
extractive and catalytic oxidative desulfurization (ECODS) method.[6-8] The ECODS process
allows for the sustainable deep desulfurization of fuels by operating under mild conditions, using
green oxidants, extracting agents, such as ionic liquid, acetonitrile and methanol.[8-13]
Our research group has been designing novel and highly efficient desulfurization systems based
on polyoxometalates (POMs) for application in model and real diesels under sustainable
conditions.[5, 14-20] POMs are exceptional candidates for catalytic applications due to redox
properties, chemical robustness and thermal stability. [21] To prepare stable heterogeneous
catalysts it is convenient to immobilize the POMs in solid supports that allow their recovery and
reuse. Silica-based materials are among the most used supports for heterogenization of active
catalytic species, including POMs.[22]. Mesoporous silica nanoparticles (MSNs) possess ordered
porosity, high surface area-to-volume ratio, controllable pore size and can be easily
functionalized. [23, 24] These properties may even improve the performance of materials in
terms of energy and power density, lifetime and stability, make them ideal for use as supports for
adsorption, catalysis, chemical separations and fuel cells.[25-33] Although silica mesoporous
materials have been widely explored as catalytic supports as well as adsorbents for

desulfurization studies, the application of the corresponding nanoparticles is still relatively
scarce.[34]
In this work, two ionic liquids [BPy]
3
[PMo12
O
40] and [BMIM] [PMo12O40], were prepared based
3
3
-
on the Keggin structure [PMo12
O
40] anion and 1-butylpyridinium and 1-butyl-3-
methylimidazolium as organic cations, respectively. Their structures were confirmed by solution
1
31
H and P NMR, FTIR spectroscopies and by elemental analysis. The composite material
3
-
PMo12O40@PPy-MSN was also prepared by immobilization of the Keggin [PMo12O40] anion on
MSNs functionalized with the propylpyridinium cation. This material was characterized by
3
1
13
elemental and ICP-OES analyses, SEM/EDS, TEM, FTIR , solid state P and C NMR and
FTIR spectroscopies . All catalysts were tested in extractive catalytic oxidative desulfurization
ECODS processes, using a multicomponent model diesel, under sustainable conditions (reduced
toxicity, using hydrogen peroxide oxidant and ionic liquid solvent).
2
. Experimental
2
.1. Materials and methods
All the reagents used in the POM and materials syntheses, namely phosphomolybdic acid
hydrate (Aldrich), tetrabutylammonium bromide ((C16 36N)Br, Aldrich), polyoxyethylene cetyl
H
ether (Brij-56, Aldrich), tetraethyl orthosilicate 98% (TEOS, Aldrich), ethyl acetate (Aldrich), n-
cetyltrimethylammonium bromide (CTAB, BDH Chemicals), pluronic F127 (Aldrich),
triethanolamine (TEA, Alfa Aesar), 1-chlorobutane (Alfa Aesar, >99%); 3-
iodopropyltrimethoxysilane (Sigma-Aldrich, >95%), 1-butyl-3-methylimidazolium chloride,
[
BMIM]Cl (Solchemar, >99%); pluronic F127 (Sigma-Aldrich), pyridine (Merck, p.a.);
tetraethylorthosilicate (TEOS) (Sigma-Aldrich, 98%), triethanolamine (TEA) (Alfa Aesar,
98%); n-cetyltrimethylammonium bromide, CTAB (BDH Chemicals, >99%), Amberlyst A-26
OH) (Alfa Aesar), were used as received. The reagents for ODS studies, including 1-
>
(
benzothiophene (1-BT, Fluka), dibenzothiophene (DBT, Aldrich), 4-methyldibenzothiophene (4-
MDBT, Aldrich), 4,6-dimethyldibenzothiophene (4,6-DMDBT, Alfa Aesar), n-octane (Aldrich),
acetonitrile (MeCN, Fisher Chemical), 1-butyl-3-methylimidazolium hexafluorophosphate
(
[BMIM][PF
6
], Sigma-Aldrich) and H
2
2
O 30% w/v (Aldrich) were purchased from chemical

suppliers and used without further purification. FT-IR spectra were recorded in the 400–4000
-1
cm region on a Bruker Tensor 27 Spectrometer using KBr pellets for solid samples and NaCl
1
31
cells for oily samples. Solution H and P NMR spectra were recorded at 400.13 MHz and 162
MHz, respectively, with a Bruker AMX400 and a Bruker Avance III 400 spectrometer and
13
31
chemical shifts are given with respect to external 85% H PO . Solid state C and P MAS NMR
3
4
spectra were acquired with a 7 T (300 MHz) AVANCE III Bruker spectrometer operating
1
3
31
respectively at 75 MHz ( C) and 121 MHz ( P), equipped with a BBO probe head. The samples
were spun at the magic angle at a frequency of 5 kHz in 4 mm-diameter rotors at room
1
3
temperature. The C MAS NMR experiments were acquired with proton cross polarization (CP
3
1
MAS) with a contact time of 1.2 ms, and the recycle delay was 2.0 s.ꢀ The P MAS NMR
spectra were obtained by a single pulse sequence with a 90° pulse of 10.5 μs at a power of 20 W,
and a relaxation delay of 82.0 s. Elemental analyses (CHN) were performed using a
Thermofinnigan Flash EA 112 series (LAQV-FCT) and Mo by ICP-OES on a Perkin Elmer
Optima 4300 DV instrument (University of Santiago de Compostela). Transmission electron
microscopy (TEM) images were obtained using a Hitachi H-8100 microscope with thermionic
emission (LaB6) and 200 kV acceleration voltage at MicroLAb (Instituto Superior Técnico). The
samples were supported on carbon-coated copper grids and the digital image acquisition was
performed with a CCD MegaView II bottom-mounted camera. Scanning electron microscopy
(SEM) and energy dispersive X-ray spectroscopy (EDS) studies were performed at the “Centro
de Materiais da Universidade do Porto” (CEMUP, Porto, Portugal) using a JEOL JSM 6301F
scanning electron microscope operating at 15 kV equipped with an Oxford INCA Energy 350
energy-dispersive X-ray spectrometer. The samples were studied as powders and were
previously subjected to gold sputtering. GC-FID was carried out in a Varian CP-3380
chromatograph to monitor the ODS multicomponent model oil experiments. Hydrogen was used
−
1
as the carrier gas (55 cm s ) and fused silica Supelco capillary columns SPB-5 (30 m x 0.25 mm
i.d.; 25 μm film thickness) were used.
2
.2. Synthesis of 1-butylpyridinium chloride [BPy] [Cl]
This synthesis was performed in 1.4:1 molar ratio, by heating 1-chlorobutane (9.3 mL, 88.5
mmol) and pyridine (5.1 mL, 63.2 mmol) without solvent at 100 °C for 48 h. The final product

was washed with diethyl ether (3x20 mL) and dried under vacuum. The final product was
obtained as a brownish solid (3.69 g, 28 %).
1H NMR (400.13 MHz, CDCl
, r.t) δ = 9.70 (d, J = 4.0 Hz, 2H), 8.50 (t, J = 4.0 Hz, 1H), 8.16 (t,
3
J = 8.0 Hz, 2H), 5.02 (t, J = 8.0 Hz, 2H), 2.05 (m, 2H), 1.40 (m, 2H), 0.93 (t, J = 8.0 Hz, 3H)
-1
ppm. Selected FTIR (cm , NaCl cell): 3417 (m); 3079 (m); 3025 (m); 3000 (m); 2961 (m);
2
1
934 (m); 2874 (m); 2361 (m); 1986 (m); 1920 (m); 1868 (m); 1580 (s); 1482 (m); 1438 (s);
380 (m); 1313 (m); 1287 (m); 1242 (m); 1216 (m); 1146 (m); 1068 (m); 1030 (m); 991 (m); 931
(m); 873 (m); 747 (m); 704 (m); 649 (m); 602 (m).
2
.3. Synthesis of [BPy]
3
[PMo12
O ]
40
1
-butylpyridinium chloride [BPy][Cl] (0.2580 g, 1.46 mmol) was dissolved in 15 mL of
methanol and to this solution the ion exchange resin Amberlyst® A26 (OH-) (9.13 mL, 7.3
mmol)
was added and it was kept in stirring for 1h in order to exchange the chloride to the hydroxide
form. The resin was filtered and washed with methanol. To the resultant filtrate, H
3
PMo12
O
40
(0.973 g, 0.53 mmol) in methanol was slowly added, a yellow precipitate immediately formed
and the mixture was stirred at room temperature for 1 h. The product was filtered, washed
several times with methanol and dried in the oven at 80 °C overnight (1.05 g, 89 %).
1H NMR (400.13 MHz, DMSO d6, 25 ºC) δ = 9.10 (d, J = 4.0 Hz, 2 H), 8.63 (t, J = 8.0 Hz, 1H),
8
.19 (t, J = 8.0 Hz 2H), 4.63 (t, J = 8.0 Hz, 2H), 1.95 (m, J = 8.0 Hz, 2H), 1.31 (m, 2H), 0.94 (t, J
8.0 Hz, 3H) ppm. P NMR (162 MHz, CD
CN, 25 ºC) δ = -2.09 ppm. Selected FTIR (cm-1,
3
1
=
3
KBr): 3124 (w), 3080 (w), 3063 (w), 2963 (w), 2929 (w), 2869 (w), 1632 (s), 1581 (w), 1485 (s),
462 (m), 1384 (w), 1316 (w), 1278 (w), 1209 (w), 1168 (m), 1063 (vs), 956 (vs), 878 (s), 795
s), 682 (s), 644 (w), 594 (w), 504 (m). Anal. calcd. for (C 40 (2230.87): C, 15.04;
1
(
9
H
14N) PMo12O
3
H, 1.88; N, 1.87; Found: C, 14.76; H, 1.85; N, 1.87
2
.4. Synthesis of [BMIM] [PMo12O40] catalyst
3
This catalyst was prepared using the same method described above. 1-Butyl-3-
methylimidazolium chloride, [BMIM][Cl], (0.231 g, 1.3 mmol) was dissolved in 15 mL of
methanol and to this solution the ion exchange resin Amberlyst® A26 (OH-) (8.4 mL, 6.7 mmol)
was added. The mixture was stirred for 1h at room temperature and the resin was filtered and

washed with methanol. To the resultant filtrate, H PMo12O40 (0.905 g, 0.43 mmol) in methanol
3
was slowly added, a yellow precipitate immediately formed and the mixture was stirred at room
temperature for 1 h. The product was filtered, washed several times with methanol and dried in
the oven at 80 °C overnight (0.84 g, 87 %).
1H NMR (400.13 MHz, DMSO d6, 25 ºC) δ = 9.10 (s, 1H), 7.77 (s, 1H), 7.70 (s, 1H), 4.19 (t, J
=
8.0 Hz, 2H), 3.86 (s, 3H), 1.81 (m, 2H), 1.28 (t, J = 8.0 Hz, 2H), 0.93 (t, J = 8.0 Hz, 3H) ppm.
31P NMR (162 MHz, CD
CN, 25 ºC) δ = -2.38 ppm. Selected FTIR (cm , KBr): 3146 (m);
-1
3
3
1
110 (w), 3089 (w) (ar(C-H)), 2959 (m); 2931 (w); 2867 (w); 1602 (w); 1564 (m); 1462 (m);
425 (w); 1379 (w); 1334 (w); 1165 (s); 1105 (w), 1062 (vs), 956 (vs), 878 (vs), 796 (s), 648
40 (2239.88): C, 13.20; H,
(m); 620 (s); 504 (s); 464 (w). Anal. calcd. for (C
8
H
15
N
2
3
) PMo12O
1
.99; N, 3.72; Found: C, 13.19; H, 2.01; N, 3.72.
2
.5. Synthesis of N-(3-trimethoxysilylpropyl)pyridinium iodide
The synthesis was performed in 1:1 molar ratio, by heating 3-iodopropyltrimethoxysilane (0.404
mL, 1 mmol) with pyridine (0.167 mL, 1 mmol) at 80 ºC for 3 h under nitrogen atmosphere. The
product was washed with diethyl ether (3x20 mL). The product was obtained as a viscous
brownish yellow oil after dried in vacuum for 2 h (0.72 g, 94 %). [35]
1H NMR (400.13 MHz, CDCl3, 25 ºC) δ = 9.36 (d, J = 6.0 Hz, 2H), 8.60 (t, J = 7.8 Hz, 1H),
8
2
1
1
.18 (t, J = 6.6 Hz, 2H), 4.98 (t, J = 7.2 Hz, 2H), 3.59 (s, 9H), 2.18 (m, 2H), 0.73 (t, J = 8.0 Hz,
-1
H) ppm. Selected FTIR (NaCl cell,/cm ): 3441 (br); 3128 (m); 3028 (w); 2943 (m); 2839 (s);
632 (vs); 1579 (m); 1486 (vs); 1460 (w); 1413 (w); 1350 (w); 1317 (m); 1245 (w); 1191 (s);
079 (vs); 889 (w); 815 (s); 776 (s); 682 (vs); 646 (w).
2
.6. Preparation of Mesoporous Silica Nanoparticles (MSNs)
The mesoporous nanosilica support was prepared following the method described by
Bouchoucha et al..[23] A mixture containing CTAB (0.663 g), Pluronic F127 (2.68 g) and TEA
(
15.64 g) in EtOH (57 mL), and water (125 mL) was prepared and stirred for 24 h at room
temperature. Afterwards, TEOS (2.56 mL was added under vigorous stirring for 1 min in a
global molar ratio TEOS : CTAB : F127 : H O : EtOH : TEA of 1 : 0.16 : 0.017 : 605 : 84 : 9.16.
2
The mixture was aged under static conditions for 24 h followed by addition of EtOH (100 mL) to
promote precipitation. The resulting nanoparticles were collected by centrifugation, washed with

water and dried at 80 °C. The dried nanoparticles were calcined in air at 550 °C for 5 h at a
heating rate of 1 °C/min.
2
.7. Preparation of PMo12O40@PPy-MSN
Calcined MSN (0.40 g) was heated at 150 °C under reduced pressure for 2 h to remove the
physisorbed water. After cooling down to room temperature, an excess of 1-(3-
trimethoxysilylpropyl)-pyridinium (PPy) iodide in acetonitrile (20 mL) was added and the
mixture was stirred under reflux and nitrogen atmosphere for 48 h. The resultant powder was
centrifuged at 5000 rpm, washed with acetonitrile and chloroform several times and dried in the
oven at 80 °C. Afterwards, an anion exchange was performed to change iodide by hydroxide
anions following the method of Udayakumar et al.[36] The previously functionalized MSN (0.40
g) was treated with a NaOH solution (0.025 M) for 2 h, and then centrifuged and washed several
times with distilled water. The product was dried in an oven at 80 °C.
1
PPy-OH-MSN: H NMR (400.13 MHz, D
2
O + NaOH, rt) δ = 8.68 (d, 1H), 8.37 (t, J = 4.0 Hz,
-1
1
H), 7.89 (d, 2H), 4.40 (t, 2H), 1.91 (m, 2H), 0.21 (t, 2H) ppm. Selected FT-IR (cm , KBr): 3443
(
(
(
br); 3153 (sh), 3097 (sh), 3072 (sh), 2958 (sh), 2929 (sh), 2854 (sh), 1638 (m); 1556 (w), 1541
w), 1490 (m), 1456 (w), 1415 (w), 1375 (w), 1090 (s); 960 (w); 796 (m); 678 (m); 533 (w); 463
s).
The PMo12
O40@PPy-MSN composite was prepared by mixing a suspension of PPy-MSN (0.130
g) with a solution of H
3
[PMo12O40] (0.07 mmol in 15 mL of methanol) and stirring at room
temperature for 48 h. The solid was centrifuged and washed several times with methanol and
dried in the oven at 80 °C. Anal. Found (%): C, 8.58; N, 1.03; H, 1.65; Mo, 2.9.; loading of
-1
PMo12: 0.025 mmol per g and ratio of C
3
Py/POM ≈ 30. Selected FT-IR (cm , KBr): 3441 (br),
145 (sh), 3097 (sh), 3074 (sh), 2956 (w), 2924 (w), 2852 (sh), 1636 (m), 1558 (w), 1541 (w),
510 (w), 1498 (w), 1489 (m), 1456 (w), 1417 (w), 1384 (w), 1351 (w), 1091 (vs), 960 (m), 919
3
1
(sh), 891 (sh), 801 (m), 680 (w), 551 (sh), 465 (s).
2
.8. Extractive and catalytic Oxidative desulfurization processes (ECODS)

The ECODS studies were performed using a model diesel containing the most refractory sulfur-
compounds present in real diesel, namely: 1- benzothiophene (1-BT), dibenzothiophene (DBT),
4
-methyldibenzothiophene (4-MDBT) and 4,6- dimehtyldibenzothiophene (4,6-DMDBT). All
the experiments were carried out under air (atmospheric pressure) in a closed borosilicate 5 mL
reaction vessel, equipped with a magnetic stirrer and immersed in a thermostatically controlled
liquid paraffin bath at 70 °C. The catalytic oxidative step was performed in the presence of a
polar extraction solvent, immiscible with the model diesel phase with equal volume of model
diesel and extraction solvent. The ionic liquid (IL), 1-butyl-3- methylimidazolium
hexafluorophosphate (BMIMPF ) and acetonitrile (MeCN) were used as extraction solvents.
6
These solvents acted as extraction solvents of sulfur compounds and also as an oxidative reaction
medium. The oxidation of the sulfur compounds only occurred in the presence of a catalyst and
an oxidant, where H
dissolved in MeCN, but showed to be insoluble in ionic liquid solvent. In all ECODS systems 3
μmol of each compound was used. The heterogeneous catalyst PMo12 40@PPy-MSN was also
40] active center. In a typical
experiment, 0.75 mL of model diesel (containing a total sulfur concentration of 2350 ppm in n-
octane) and 0.75 mL of [BMIM][PF ] were added to the catalyst. An initial extraction of sulfur
2
O
2
(aq. 30%) was used. [BPy]
3
[PMo12
O40] and [BMIM]
3
[PMo12
O
40
]
O
3
-
studied, using 120 mg that contains 3 μmol of [PMo12
O
6
compounds from model diesel to the IL phase occurred by only stirring the both immiscible
phase for 10 min at 70 C. The catalytic step of the process is then initiated by the addition of
H
2
2
O (75 μL, 0.64 mmol). The sulfur content in the model diesel phase was periodically
quantified by GC analysis using tetradecane as standard. Using the heterogeneous catalyst,
recycle experiments were performed by adding a new portions of model diesel, oxidant and
[
BMIM][PF ] extraction solvent, at the end of each ECODS cycle. The solid catalyst was not
6
washed between cycles. After three cycles, the solid was isolated from the ECODS process,
followed by washing and dry to be characterized after catalytic use.
3. Results and discussion
3
.1. Synthesis and Characterization
The salts [BPy] 40] and [BMIM]
using H 40 and the hydroxide forms of 1-butylpyridinium and 1-butyl-3-
3
[PMo12
O
3
[PMo12O40] were prepared from an acid-base reaction
3
PMo12O

methylimidazolium, respectively. The hydroxide forms were previously prepared from the
corresponding chlorides ionic liquids by exchange of the chloride to the hydroxide using an ion
exchange resin Amberlist (in the OH form). The homogeneous catalysts were characterized by
1
31
elemental analyses, FT-IR, H and P NMR spectroscopies. CHN elemental analyses confirm the
expected molecular formulas of both compounds. The infrared spectrum of [BPy]
3
[PMo12
40
O ]
-1
contains weak bands at 3124, 3080 and 3063 cm corresponding to (C-H) aromatic vibrations,
-1
at 2963, 2929 and 2869 cm attributed to the (C-H) of the aliphatic chain, a strong band at 1632
-1
cm corresponding to (C=N) vibrations that is typical of the quaternary nitrogen atom in a
-
1
heterocyclic ring. Several weak/medium bands in the range 1580-1100 cm are observed due to
-1
aromatic (C-N), (C-C) and also due (C-H) vibrations. A strong band at 1482 cm is
attributed to the conjugation of (C=C) and (C=N) bonds and is also typical of pyridinium salts
-1
and the strong one at 682 cm corresponds to the aromatic out-of- plane hydrogen
3
-
deformation.[37, 38] The presence of PMo12
O
40 is corroborated by four strong bands at 1063,
-1
9
56, 878 and 795 cm corresponding to as(P-O ), as(Mo-O ), as(Mo-O -Mo) and as(Mo-O
a
d
b
c
-
Mo), respectively.[39, 40]The bands observed at the infrared spectrum of [BMIM]
3
[PMo12
40
O ]
+
are in accordance with the literature confirming the presence of the [BMIM] cation and the
Keggin anion.[41]
c) [BPy] [PMo O ]
3
12 40
b) [BPy][Cl]
a)H PMo O
3
12 40
4
000
3600
3200
2800
2400
2000
1600
1200
800
400
-1
Wavenumber (cm )

Figure 1- . FT-IR spectra of a) phosphomolybdic acid H
Liquid phosphomolybdate [BPy]
3
PMo12O40, b) [BPy][Cl] and c) Ionic-
3
[PMo12O40].
1H NMR spectra of the catalysts are presented in Figure S1 (in Supporting information, SI) and
in both is possible to identify the protons from the aliphatic chains and from the aromatic
imidazolium or pyridinium rings. In the case of [BMIM] [PMo12O40], the proton chemical shifts
3
of imidazolium cation are found at 9.10, 7.77, 7.70 and 3.86 ppm. It also can be observed the
protons corresponding to the methyl groups at 4.19, and at 1.81, 1.28 and 0.93 ppm, those
attributed to the butyl chain. The spectrum of [BPy]
pyridinium ring at 9.10, 8.63 and 8.19 ppm and those from the butyl aliphatic chain at 4.63, 1.95,
.31 and 0.94 ppm.
3
[PMo12O40] contains the protons of the
1
3
1
Figure 2 shows the P MAS NMR spectra in CD
3
CN of the catalysts that contain a sharp peak at
40]. These results were
-
2.09 ppm for [BPy] 40] and at -2.38 ppm for [BMIM] [PMo12O
3
[PMo12
O
3
closed to the obtained for other Keggin phosphomolybdate structure containing different organic
cations.[33, 42]

3
1
Figure 2: P NMR spectra in CD
BPy] 40] and [BMIM]
corresponding to soluble phosphomolybdate compounds in ECODS).
3
CN for the Ionic-Liquid phosphomolybdates
[
3
[PMo12
O
3
[PMo12O40], before and after catalytic use (abbreviated as ac,
The heterogeneous catalyst PMo12O40@PPy-MSN was prepared according to the scheme 1. First
the pristine MSNs was functionalized with 1-(3-trimethoxysilylpropyl)-pyridinium iodide
-
(
previously prepared) and then the iodide anions were exchanged by OH anions using a NaOH
solution (0.025M) following the method described by Udayakumar et al..[36]To this last
material, phosphomolybdic acid was added and through an acid-base reaction the final composite
was obtained. The intermediate support material PPy-OH-MSN was characterized by FTIR and
1
1
H NMR spectroscopies to confirm the presence of the anchored cation (solution H NMR was
used following the method described by Crucho et al.). The infrared spectrum of PPy-OH-MSN

contains the strong bands characteristic of silica-type materials at 1064, 796 and 463 cm-1
attributed to as(Si–O–Si),  (Si–O–Si) and δ(O–Si–O) vibrational modes, respectively. Beyond
these bands, it shows several weak bands from the functionalized pyridinium cation in the region
s
-1
-1
3
160-3000 cm ((C-H) aromatic vibrations), 2960-2850 cm ((C-H) of the aliphatic chain),
-1
1
and 1500-1300 cm ((C-N), (C-C), (C-H)) (Figure 3). H NMR spectrum of this material
exhibits the chemical shifts of the pyridinium protons at 8.68, 8.37, and 7.89 ppm and the
corresponding signals of the propyl chain at 4.40, 1.91 and 0.21 ppm (see Figure. S2 in SI).
Scheme 1: Schematic representation of the method used to prepare the final heterogeneous
catalyst PMo12O40@PPy-MSN
1
3
The final composite was characterized by elemental CHN and Mo analyses, FTIR, C
31
CP MAS and P MAS solid state NMR spectroscopies. Elemental analyses revealed a loading of
3
-
0
.7 mmol of pyridinium cations and 0.025 mmol of PMo12
spectrum of PMo12 40@PPy-MSN, in addition to the bands corresponding to the functionalized
cation, displays one band at 960 (this band overlap the one from precursor PPy-OH-MSN which
O40 per g of material. The FTIR
O
-1
corresponds to the (Si-OH) but that is less pronounced) and a shoulder at 891 cm that can be
ascribed to the as(Mo-O ) and as(Mo-O -Mo) vibrational modes of the phosphomolybdate
d
b
1
3
anion, respectively (Figure 3). C CP MAS NMR spectrum contains three peaks corresponding
to the aliphatic propyl carbon atoms at 10.6, 23.1 and 45.3 ppm (Figure 4, left) and two peaks in

3
1
the aromatic region at 130.7 and 146.5 ppm assigned to the pyridium carbon atoms. P MAS
spectrum exhibits one peak at -3.84 ppm attributed to PMo12 40 anion (Figure 4, right).
O
Figure 3- FT-IR spectra of the supports a) calcinated MSNs, b) PPy-OH-MSN and the
composite c) PMo12 40@PPy-MSN and of phosphomolybdic acid d) H
O
3
PMo12
40
O .

1
3
31
Figure 4. C CP MAS (on left) and P CP MAS (on left) for the composite PMo12O40@PPy-
MSN.
Figure 5. TEM images of the heterogeneous catalyst PMo12O40@PPy-MSN
PMo12
O
40@PPy-MSN was also characterized by transmission electron microscopy
Figure 5) and the images show that the composite are constituted by spherical porous
nanoparticles with a size distribution in the range of 50-80 nm with some aggregation.
(
3
.2. Extractive and Catalytic Oxidative desulfurization systems (ECODS)
The ionic-liquid based phosphomolybdates [BMIM]PMo12 and [BPy]PMo12 and the composite
PMo12@PPy-MSN were used as catalysts in an extractive and catalytic oxidative desulfurization
system (ECODS) using a model diesel composed by the most refractory sulfur compounds in
real diesels, namely, 1-benzothiophene (1-BT), dibenzothiophene (DBT), 4-
methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in n-
octane. This model diesel has a sulfur concentration of approximately 500 ppm for each
compound and a total of 2350 ppm of sulfur. The ECODS process begins with an initial
extraction step by stirring the diesel phase with a polar immiscible phase during 10 min at 70 ◦C.
This first step of ECODS process promotes the transfer of the sulfur compounds from the model
diesel to the polar phase. In this studies an ionic liquid ([BMIM][PF
step of the desulfurization process is initiated by the addition of H
/S = 11. This step corresponds to the oxidative catalytic step, where the sulfur compounds
in the [BMIM]PF phase are oxidized to sulfoxides and/or sulfones. This leads to a continuous
6
) were used. The second
2
O
2
oxidant, using a ratio
H
2
O
2
6

transfer of non-oxidized sulfur compounds from the model diesel to the ionic liquid phase. The
order of each sulfur component, at the end of initial extraction step was the following: BT > DBT
>
4-MDBT > 4,6-DMDBT (Table 1). These results are explained by the different molecular
diameters, as well as by the steric hindrance of the methyl groups in DBT derivatives. [14, 16,
2, 43]
4
Table 1. Individual desulfurization percentages from the model diesel to the extraction
phase using [BPy] 40], [BMIM] 40] and PMo12@PPy-MSN catalysts.
3
[PMo12
O
3
[PMo12O
Initial Desulfurization (%)
Catalyst
1-BT
42
DBT
31
4-MDBT 4,6-DMDBT
[
BPy]
3
[PMo12
O
40
]
19
27
38
4
[BMIM]
3
[PMo12
O
40
]
46
38
18
28
PMo12
O
40@PPy-MSN 54
53
After the initial extraction step, the sulfur transfer equilibrium between the model diesel and
ionic liquid phases was achieved, and the removal of more sulfur compounds from model diesel
only could occurred by the oxidation of the sulfur compounds present in the [BMIM][PF
6
] phase,
i.e. after the addition of H oxidant in the presence of the phosphomolybdate catalyst. During
2
O
2
the catalytic oxidative desulfurization step the no-oxidized sulfur compounds are oxidized in the
corresponding sulfone and/or sulfoxides. The oxidation of sulfur compounds must occur more
6
extensively in the [BMIM][PF ] phase since the oxidant has more affinity with this solvent than
with the model diesel phase.
The ionic-liquid phosphomolybdates [BPy]
3
[PMo12
O40] and [BMIM]
3
[PMo12O40] are not
dissolved in the [BMIM][PF ] phase, behaving as heterogeneous catalysts. The desulfurization
6
profiles obtained using these two catalysts are presented in Figure 6. It is possible to observe that
both ionic liquid catalysts present similar desulfurization profile and only a slightly higher
desulfurization efficiency can be found for [BPy] [PMo12O40] during the first hour of reaction.
3
After this time complete desulfurization was achieved in both ECODS systems. The difference
of catalytic activity observed during the first hour indicates that the reactivity of these catalysts
depends on the type of the counter-cation, in this case 1-butyl-3-
+
+
methylimidazolium ([BMIM] ) and butylpyridinium ([BPy] ). It is reported in the literature by

Fugita, et al. that these cations present some influence in the catalyst performance, varying in
+
+
the order: [BPy] > [BMIM] . [44]
When the ECODS experiments were performed using acetonitrile instead of
[
BMIM][PF
6
], the phosphomolybdates [BPy]
3
[PMo12
O
40] and [BMIM] [PMo12O40] behaved as
3
homogeneous catalysts, since these were completely dissolved in this solvent. In this case, after
the first hour of reaction, complete desulfurization was not achieved (desulfurization efficiency
of 83%, Figure S3 in SI). The superior desulfurization performance using [BMIM][PF
6
] solvent
against organic solvents in ECODS processes has been previously reported. [43, 45]
100
80
60
40
20
0
[
[
BMIM]PMo12
BPy]PMo12
[BMIM] [PMo O ]
3
12 40
H O
2
2
[
BPy]
3
40
[PMo12O ]
PMo12O40@PPy-MSN PMo12
O40@PPy-MSN
0
20
40
60
80
100
120
140
Time (min)
Figure 6- Kinetic desulfurization profiles for ECODS process 1:1 model diesel/ [BMIM][PF
6
],
o
catalyzed by [BPy]
3
[PMo12
O40] and [BMIM]
3
[PMo12
O
40] (3 µmol), using H
2
O
2
/ S = 11, at 70 C.
The stability and the heterogeneity of [BMIM]
3
[PMo12
40]-ac and [BPy]
catalysts after catalytic use were recovered from the reaction medium and washed with ethanol
O
40] and [BPy]
3
[PMo12
O
40] catalysts were
3
1
analyzed by P NMR ([BMIM]
3
[PMo12
O
3
[PMo12
O40]-ac spectra). The solid
31
and dried. Afterwards, these last was dissolved in CD
single peaks at -2.40 ppm and -2.39, that corresponds to the initial prepared [BPy]
and [BMIM] 40], respectively (spectra not shown). This result indicates that the solid
catalyst presents the initial structure and its typical Keggin structure was confirmed. On the other
hand, the soluble reaction media using [BMIM] 40] and [BPy] 40] were also
analyzed by P NMR and in this case two single peaks were found at 2.90 and -2.39 ppm, for
3
CN and the P NMR analysis present
3
[PMo12
40
O ]
3
[PMo12O
3
[PMo12
O
3
[PMo12O
3
1

[
BMIM]
3
[PMo12
O
40
]ac and 2.87 and -2.40 for [BPy]
3
[PMo12
40
O ]ac (Figure 2). These results
indicate that the ionic liquid phosphomolybates has some partial dissolution in the ionic liquid
medium during catalytic reaction and also identical structural alteration of the Keggin structure
may occurred for both compounds (single peaks at 2.90 ppm and 2.87 ppm for
[
BMIM]
oxidant.
To increase the stability of the ionic-liquid [PMo12
heterogeneity, this Keggin phosphomolybdate was immobilized in pyridinium (PPy)
functionalized mesoporous silica nanoparticles (PMo12 40@PPy-MSN, Scheme 1). Figure 6
compares the desulfurization profile of the composite PMo12 40@PPy-MSN and the ionic liquid
phosphomolybdate catalysts. The initial extraction of sulfur compounds from model diesel to the
3
[PMo12
O
40] and [BPy]
3
[PMo12O40], respectively), probably by their interaction with the
3
-
O
40] catalyst and to guarantee its
O
O
[
BMIM][PF
6
] phase (stirring 10 min at 70 ºC) was slightly higher using the composite material
40] and [BPy] [PMo12O40],
(43% using the composite and 26% and 34% using [BMIM]
3
[PMo12
O
3
respectively). This must be related to the presence of a higher amount of solid in the ECODS
3
-
system (120 mg, containing 3 µmol of active [PMo12O40] catalyst), promoting by some sulfur
adsorption on MSN surface or even by increasing the liquid-liquid contact between model diesel
and ionic liquid phases. During the oxidative catalytic step (after the first 10 min), the
desulfurization increased rapidly and after only 1 h 93% was achieved remaining only 1-BT in
the model diesel. The desulfurization increased more slowly after the first hour: after 2 h was
found 96% and after 3 h 98% (39 ppm of sulfur attributed to 1-BT). In fact, it is well reported in
the literature the higher difficulty to oxidize 1-BT due to the lower electron density on its sulfur
atom, when compared with the other studied compounds and consequent lower reactivity [46-
4
8]. The other studied sulfur compounds (DBT, 4-MDBT and 4,6-DMDBT) exhibit similar
electron densities on the sulfur atom and therefore their oxidation can only be distinct by the
steric hindrance promoted by the methyl groups. The MSN support has also been tested under
identical conditions, presenting a negligible catalytic activity.
6
The reusability of the ECODS model diesel/[BMIM][PF ] system catalyzed by the
composite PMo12 40@PPy-MSN was investigated for three consecutive cycles. After 3 h of
O
oxidative desulfurization, the solid catalyst remained in the ionic liquid phase and the model
diesel could be easily removed from the system. The ionic liquid phase containing the
heterogeneous catalyst was then reused in a new ECODS cycle. The new ECODS cycle was

prepared by simple addition of a new portion of sulfurized model diesel and 75 µL of oxidant.
The reuse of the ionic-liquid phase and the solid catalyst creates a more sustainable ECODS
process, reducing costs and residual wastes. Figure 7 presents the desulfurization profile for three
consecutive ECODS cycles using the same sample of PMo12@PPy-MSN and [BMIM][PF ]. The
6
desulfurization profile of the three consecutive ECODS cycles is similar, indicating that the
composite PMo12@PPy-MSN maintained its oxidative activity. For all the three ECODS cycles
near complete desulfurization was achieved after 3 h, remaining a vestigial amount of 1-BT in
the model diesel. The DBT, 4-MDBT and 4,6-DMDBT were complete desulfurize after de 1 h of
oxidation. It is also important to note that the increasing concentration of oxidized products in
the BMIMPF phase over the three consecutive ECODS cycles was observed by increasing the
6
amount of formed white solid in this phase over the various cycles. However, this did not
contribute to the loss of desulfurization performance and ultra-low sulfur model diesel was easily
produced in consecutive cycles. to remove the sulfones after the three consecutive
desulfurization cycles. After these consecutive cycles, the heterogeneous catalyst was recovered
by centrifugation and the BMIMPF
and diethyl ether to extract the dissolved sulfones in this phase. Furthermore, the used solvents
ethyl acetate and diethyl ether) could be recovered by distillation and the white solid sulfones
6
phase was cleaned with a mixture of 1:1 (v/v) ethyl acetate
(
were isolated.
the solid catalyst and the white precipitate sulfones were separated from the IL phase. The
resulting IL phase was then treated with a mixture to the IL phase

100
80
60
40
20
0
H O
addition
2
2
1
st Cycle
2nd Cycle
3rd Cycle
0
20 40 60 80 100 120 140 160 180 200
Time (min)
Figure 7- Reusability of the ECODS (1:1 model diesel/[BMIM][PF
40@PPy-MSN composite (containing 3 µmol of active [PMo12
oxidant (75 µL, using H / S = 11), at 70 °C.
6
]) process catalyzed by
3
-
PMo12
O
O
40] ), using H
2
2
O as
2
O
2
The desulfurization efficiency obtained by PMo12
similar to the previous obtained by our research group using related heterogeneous catalysts
under identical experimental conditions.[33] The advantage showed by PMo12 40@PPy-MSN is
O40@PPy-MSN heterogeneous catalyst is
O
its higher stability between consecutive reused ECODS cycles. This must be related to the
immobilization of the phosphomolybdate in the surface of the functionalized MSN. In this work,
a propylpyridinium (PPy) functional group was strategically used, instead of the
+
+
tributylammonium (TBA ) and trimethylammonium (TMA ) used previously.[33]
3
.3. Stability of PMo12
O
40@PPy-MSN after ECODS
40@PPy-MSN, after three consecutive ECODS cycles,
The stability of the composite PMo12
O
3
1
was investigated by various characterization techniques, such as P NMR, FT-IR and
SEM/EDS.
3
-
The presence of active catalytic center [PMo12
O
40] in the reaction medium, after solid
] was diluted in CD CN
and P NMR analysis was performed. Even after 24 h of analysis, no single peak attributed to
catalyst removal, was investigated. The reaction medium in [BMIM][PF
6
3
3
1

Keggin-type phosphomolybdate or its derivatives were detected. This result suggests the absence
of active leaching species from the surface of PPy-MSN support.
The ATR-FTIR spectrum of composite after catalytic use PMo12O40@PPy-MSN-ac (ac
stands for after catalysis, Figure S4 in SI) can be compared to the same before ECODS
application in Figure 3, where similar main bands are exhibited around 960 ((Si-OH) and
-1

as(Mo-O
d
)) and 890 cm (as(Mo-O -Mo), which is consistent with the structural retention of
b
the POM anion after catalytic use. [33, 42]
The morphology and chemical composition of PMo12O40@PPy-MSN was analyzed by
electronic microscopy analysis before and after catalytic use during three ECODS cycles (Figure
8
). The nanoparticles morphology is preserved after the immobilization of the active
3
-
[
PMo12
O
40] center and after the catalytic used for three consecutive cycles. In fact, the
composite is still composed by the same type of nanoparticles without changing their shape or
3
-
size. The presence of [PMo12O40] before and after catalytic use could be confirmed by EDS
analysis (Figure 9). The spectra in Figure 9 reveal the presence of silicon from the support and
the presence of molybdenum from the phosphomolybdate. The presence of fluorine and
phosphorus in the composite after catalytic use indicate that same ionic liquid [BMIM][PF
6
]
must be present in the solid catalyst after ECODS application. The leaching of active species
3
-
[
PMo12O40] from the composite PMo12O40@PPy-MSN during the three consecutive ECODS
cycles was investigated by the ratio Si/Mo, performed by EDS analysis. Before catalytic use the
ratio Si/Mo was 9,8 and after recycling study the same ratio was 9,3. This result suggests that the
loss of active center to the reaction medium after three consecutive ECODS cycles was
negligible (5%), confirming the stability of PMo12O40@PPy-MSN heterogeneous catalyst.

4
µm
2 µm
Figure 8- SEM images of the PMo12
O40@PPy-MSN composite material before (left) and after
(
right) catalytic use (PMo12
right) ×50,000.
O40@PPy-MSN-ac) at different magnifications: (left) ×25,000 and
(
B
A
Figure 9- EDS spectra of the PMo12
O40@PPy-MSN composite material (A) before and (B) after
catalytic use during three consecutive ECODS cycles.

4
. Conclusion
Two different ionic liquid phosphomolybdates, containing 1-butylpyridinium
[BPy] 40]) and 1-butyl-3-methylimidazolium ([BMIM] 40]) were prepared and
(
3
[PMo12
O
3
[PMo12O
used as catalysts for the oxidative desulfurization of a multicomponent model diesel. The
catalytic studies were performed using biphasic desulfurization systems (1:1 model
diesel/extraction solvent, using acetonitrile and an ionic liquid [BMIM][PF ] as solvent). An
6
initial extraction of the sulfur compounds from diesel phase to the extraction phase was
performed during 10 min at 70 ºC. Afterwards, the catalytic oxidative desulfurization step was
performed by the addition of H
2
O
2
oxidant (H
2
2
O /S = 11). Higher desulfurization and higher
oxidative catalytic efficiency were achieved using the ionic liquid extraction solvent. In this
case, complete desulfurization was achieved after the first hour using both phosphomolybdate
catalysts. Using model diesel/[BMIM][PF
BMIM] 40] showed to be partially soluble. Their stability study indicated that the solid
part maintained their initial Keggin structure; however, the soluble phosphomolybdate species
presented some decomposition, probably promoted by their interaction in the H oxidant. To
guarantee the heterogeneity of the catalyst and increase its stability, the [PMo12
center was immobilized in a propylpyridinium functionalized mesoporous silica nanoparticles
40@PPy-MSN). This catalytic composite showed slightly lower activity than the
6
] system, the [BPy]
3
[PMo12O40] and
[
3
[PMo12O
2
O
2
3
-
O
40] active
(PMo12O
previous ionic liquid phosphomolybdates, mainly during the first hour of reaction, since at this
time 93% of desulfurization was achieved, remaining only 1-benzothiophene in the model diesel
phase. Near complete desulfurization was achieved after 3 h (98% of desulfurization, 39 ppm of
1
-BT). Contrarious to ionic liquid phosphomolybdates, the stability of the composite
PMo12O40@PPy-MSN was confirmed by various techniques and high recycle capacity was
found.
Acknowledgements
This work was partly funded through the projects REQUIMTE-LAQV [FCT (Fundação para a
Ciência e a Tecnologia) Ref. LAQV, REQUIMTE (POCI-01-0145-FEDER-007265,
UID/QUI/50006/2013)] and CENIMAT, I3N (POCI-01-0145-FEDER-007688,
UID/CTM/50025/2013), financed by national funds through the FCT/MEC and when
appropriate co-financed by the Fundo Europeu de Desenvolvimento Regional (FEDER) under

the PT2020 Partnership Agreement. This work is funded by national funds (OE), through FCT –
Fundação para a Ciência e a Tecnologia. European Social Fund through the program POPH of
QREN. The authors also acknowledge the Portuguese Nuclear Magnetic Resonance Network
(PTNMR).
References
[
1] A. Samokhvalov, Desulfurization of Real and Model Liquid Fuels Using Light:
Photocatalysis and Photochemistry, Catalysis Reviews, 54 (2012) 281-343.
2] C.M. Granadeiro, S.O. Ribeiro, M. Karmaoui, R. Valenca, J.C. Ribeiro, B. de Castro, L.
[
Cunha-Silva, S.S. Balula, Production of ultra-deep sulfur-free diesels using a sustainable
catalytic system based on UiO-66(Zr), Chemical Communications, 51 (2015) 13818-13821.
[
3] H. Lu, J. Gao, Z. Jiang, Y. Yang, B. Song, C. Li, Oxidative desulfurization of
dibenzothiophene with molecular oxygen using emulsion catalysis, Chemical Communications,
(2007) 150-152.
[
4] H. Lü, Y. Zhang, Z. Jiang, C. Li, Aerobic oxidative desulfurization of benzothiophene,
dibenzothiophene and 4,6-dimethyldibenzothiophene using an Anderson-type catalyst
[
[
(C18H37)2N(CH3)2]5[IMo6O24], Green Chemistry, 12 (2010) 1954-1958.
5] S. Ribeiro, C.M. Granadeiro, P. Silva, F.A. Almeida Paz, F.F. de Biani, L. Cunha-Silva, S.S.
Balula, An efficient oxidative desulfurization process using terbium-polyoxometalate@MIL-
01(Cr), Catalysis Science & Technology, 3 (2013) 2404-2414.
6] J.M. Campos-Martin, M.C. Capel-Sanchez, P. Perez-Presas, J.L.G. Fierro, Oxidative
processes of desulfurization of liquid fuels, Journal of Chemical Technology & Biotechnology,
5 (2010) 879-890.
7] N.D. McNamara, G.T. Neumann, E.T. Masko, J.A. Urban, J.C. Hicks, Catalytic performance
1
[
8
[
and stability of (V) MIL-47 and (Ti) MIL-125 in the oxidative desulfurization of heterocyclic
aromatic sulfur compounds, Journal of Catalysis, 305 (2013) 217-226.
[
8] Y. Zhang, G. Li, L. Kong, H. Lu, Deep oxidative desulfurization catalyzed by Ti-based
metal-organic frameworks, Fuel, 219 (2018) 103-110.

[
9] F.S. Mjalli, O.U. Ahmed, T. Al-Wahaibi, Y. Al-Wahaibi, I.M. AlNashef, Deep oxidative
desulfurization of liquid fuels, Reviews in Chemical Engineering, 30 (2014) 337-378.
10] M.R. Maurya, A. Arya, A. Kumar, M.L. Kuznetsov, F. Avecilla, J.C. Pessoa, Polymer-
[
Bound Oxidovanadium(IV) and Dioxidovanadium(V) Complexes As Catalysts for the Oxidative
Desulfurization of Model Fuel Diesel, Inorganic Chemistry, 49 (2010) 6586-6600.
[
11] B.-b. Shao, L. Shi, X. Meng, Deep Desulfurization of 4,6-Dimethyldienzothiophene by an
Ionic Liquids Extraction Coupled with Catalytic Oxidation with a Molybdic Compound,
Industrial & Engineering Chemistry Research, 53 (2014) 6655-6663.
[
12] L. Liu, C. Chen, X. Hu, T. Mohamood, W. Ma, J. Lin, J. Zhao, A role of ionic liquid as an
activator for efficient olefin epoxidation catalyzed by polyoxometalate, New Journal of
Chemistry, 32 (2008) 283-289.
[
13] F. Mirante, S.O. Ribeiro, B. de Castro, C.M. Granadeiro, S.S. Balula, Sustainable
Desulfurization Processes Catalyzed by Titanium-Polyoxometalate@TM-SBA-15, Topics in
Catalysis, 60 (2017) 1140-1150.
[
14] S. Ribeiro, A.D.S. Barbosa, A.C. Gomes, M. Pillinger, I.S. Gonçalves, L. Cunha-Silva, S.S.
Balula, Catalytic oxidative desulfurization systems based on Keggin phosphotungstate and
metal-organic framework MIL-101, Fuel Processing Technology, 116 (2013) 350-357.
[
15] C.M. Granadeiro, A.D.S. Barbosa, S. Ribeiro, I.C.M.S. Santos, B. de Castro, L. Cunha-
Silva, S.S. Balula, Oxidative catalytic versatility of a trivacant polyoxotungstate incorporated
into MIL-101(Cr), Catalysis Science & Technology, 4 (2014) 1416-1425.
[
16] L.S. Nogueira, S. Ribeiro, C.M. Granadeiro, E. Pereira, G. Feio, L. Cunha-Silva, S.S.
Balula, Novel polyoxometalate silica nano-sized spheres: efficient catalysts for olefin oxidation
and the deep desulfurization process, Dalton Transactions, 43 (2014) 9518-9528.
[
17] D. Julião, A.C. Gomes, M. Pillinger, L. Cunha-Silva, B. de Castro, I.S. Gonçalves, S.S.
Balula, Desulfurization of model diesel by extraction/oxidation using a zinc-substituted
polyoxometalate as catalyst under homogeneous and heterogeneous (MIL-101(Cr) encapsulated)
conditions, Fuel Processing Technology, 131 (2015) 78-86.
[
18] C.M. Granadeiro, L.S. Nogueira, D. Juliao, F. Mirante, D. Ananias, S.S. Balula, L. Cunha-
Silva, Influence of a porous MOF support on the catalytic performance of Eu-polyoxometalate
based materials: desulfurization of a model diesel, Catalysis Science & Technology, 6 (2016)
1
515-1522.

[
19] F. Mirante, S.O. Ribeiro, B. Castro, C.M. Granadeiro, S.S. Balula, Sustainable
Desulfurization Processes Catalyzed by Titanium-Polyoxometalate@TM-SBA-15, Top. Catal.,
(2017) DOI: 10.1007/s11244-11017-10801-11245.
[
20] F. Mirante, L. Dias, M. Silva, S.O. Ribeiro, M.C. Corvo, B. de Castro, C.M. Granadeiro,
S.S. Balula, Efficient heterogeneous polyoxometalate-hybrid catalysts for the oxidative
desulfurization of fuels, Catalysis Communications, 104 (2018) 1-8.
[
21] N. Mizuno, K. Yamaguchi, K. Kamata, Epoxidation of olefins with hydrogen peroxide
catalyzed by polyoxometalates, Coordination Chemistry Reviews, 249 (2005) 1944-1956.
22] S.-S. Wang, G.-Y. Yang, Recent Advances in Polyoxometalate-Catalyzed Reactions,
Chemical Reviews, 115 (2015) 4893-4962.
23] M. Bouchoucha, M.-F. Côté, R. C.-Gaudreault, M.-A. Fortin, F. Kleitz, Size-Controlled
[
[
Functionalized Mesoporous Silica Nanoparticles for Tunable Drug Release and Enhanced Anti-
Tumoral Activity, Chemistry of Materials, 28 (2016) 4243-4258.
[
24] L. Chen, G. Zhu, D. Zhang, H. Zhao, M. Guo, W. Shi, S. Qiu, Novel mesoporous silica
spheres with ultra-large pore sizes and their application in protein separation, Journal of
Materials Chemistry, 19 (2009) 2013-2017.
[
25] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Ordered mesoporous
molecular sieves synthesized by a liquid-crystal template mechanism, Nature, 359 (1992) 710-
12.
26] A. Feliczak-Guzik, B. Jadach, H. Piotrowska, M. Murias, J. Lulek, I. Nowak, Synthesis and
7
[
characterization of SBA-16 type mesoporous materials containing amine groups, Microporous
and Mesoporous Materials, 220 (2016) 231-238.
[
27] D. Y., C. Y., S. Z., L. J., L. C., W. J., L. W., L. C., W. Y., Z. D., Multifunctional
mesoporous composite microspheres with well-designed nanostructure: a highly integrated
catalyst system, Journal of the American Chemical Society, 132 (2010) 8466-8473.
[
28] Y. Wan, Y. Shi, D. Zhao, Designed synthesis of mesoporous solids via nonionic-surfactant-
templating approach, Chemical Communications, (2007) 897-926.
29] M. Mamak, N. Coombs, G. Ozin, Self-Assembling Solid Oxide Fuel Cell Materials:ꢀ
[
Mesoporous Yttria-Zirconia and Metal-Yttria-Zirconia Solid Solutions, Journal of the American
Chemical Society, 122 (2000) 8932-8939.

[
30] W. Li, J. Liu, D. Zhao, Mesoporous materials for energy conversion and storage devices,
Nature Reviews Materials, 1 (2016).
31] B.G. Trewyn, I.I. Slowing, S. Giri, H.-T. Chen, V.S.Y. Lin, Synthesis and Functionalization
[
of a Mesoporous Silica Nanoparticle Based on the Sol–Gel Process and Applications in
Controlled Release, Accounts of Chemical Research, 40 (2007) 846-853.
[
32] D. Rath, S. Rana, K.M. Parida, Organic amine-functionalized silica-based mesoporous
materials: an update of syntheses and catalytic applications, RSC Advances, 4 (2014) 57111-
7124.
33] F. Mirante, N. Gomes, L.C. Branco, L. Cunha-Silva, P.L. Almeida, M. Pillinger, S. Gago,
5
[
C.M. Granadeiro, S.S. Balula, Mesoporous nanosilica-supported polyoxomolybdate as catalysts
for sustainable desulfurization, Microporous and Mesoporous Materials, 275 (2019) 163-171.
[
34] J.M. Palomino, D.T. Tran, J.L. Hauser, H. Dong, S.R.J. Oliver, Mesoporous silica
nanoparticles for high capacity adsorptive desulfurization, Journal of Materials Chemistry A, 2
(2014) 14890-14895.
[
35] T.-Y. Cho, S.-G. Yoon, S.S. Sekhon, C.-H. Han, Effect of Ionic Liquids with Different
Cations in I-/I3- Redox Electrolyte on the Performance of Dye-sensitized Solar Cells, Bull.
Korean Chem. Soc., 32 (2011) 2058.
[
36] S. Udayakumar, S.-W. Park, D.-W. Park, B.-S. Choi, Immobilization of ionic liquid on
hybrid MCM-41 system for the chemical fixation of carbon dioxide on cyclic carbonate,
Catalysis Communications, 9 (2008) 1563-1570.
[
37] D. Cook, Vibracional spectra of pyridinium salts, Canadian Journal of Chemistry, 39 (1961)
009-2024.
38] M. Katcka, T. Urbanski, T.U.M. Katcka, Bull. L’Cademie Pol. Des Sci. Des Sci. Chim. ,
XII (1964) 615-621.
39] C. Rocchiccioli-Deltcheff, M. Fournier, R. Franck, R. Thouvenot, Vibrational investigations
2
[
[
of polyoxometalates. 2. Evidence for anion-anion interactions in molybdenum(VI) and
tungsten(VI) compounds related to the Keggin structure, Inorganic Chemistry, 22 (1983) 207-
2
16.
40] C. Rocchiccioli-Deltcheff, A. Aouissi, M.M. Bettahar, S. Launay, M. Fournier, Catalysis by
2-molybdophosphates: 1. Catalytic reactivity of 12-molybdophosphoric acid related to its
[
1

thermal behavior investigated through IR, Raman, polarographic, and X-ray, Journal of
Catalysis, 164 (1996) 16-27.
[
41] G. Ranga Rao, T. Rajkumar, B. Varghese, Synthesis and characterization of 1-butyl 3-
methyl imidazolium phosphomolybdate molecular salt, Solid State Sciences, 11 (2009) 36-42.
42] C.M. Granadeiro, P.M.C. Ferreira, D. Julião, L.A. Ribeiro, R. Valença, J.C. Ribeiro, I.S.
[
Gonçalves, B. de Castro, M. Pillinger, L. Cunha-Silva, S.S. Balula, Efficient Oxidative
Desulfurization Processes Using Polyoxomolybdate Based Catalysts, Energies, 11 (2018) 1696.
[
43] D. Julião, A.C. Gomes, M. Pillinger, R. Valença, J.C. Ribeiro, I.S. Gonçalves, S.S. Balula,
A recyclable ionic liquid-oxomolybdenum(vi) catalytic system for the oxidative desulfurization
of model and real diesel fuel, Dalton Transactions, 45 (2016) 15242-15248.
[
44] S. Fujita, M. Nishiura, M. Arai, Synthesis of styrene carbonate from carbon dioxide and
styrene oxide with various zinc halide-based ionic liquids, Catalysis Letters, 135 (2010) 263-268.
45] F. Mirante, L. Dias, M. Silva, S.O. Ribeiro, M.C. Corvo, B. de Castro, C.M. Granadeiro,
[
S.S. Balula, Efficient heterogeneous polyoxometalate-hybrid catalysts for the oxidative
desulfurization of fuels, Catalysis Communications, 104 (2018) 1-8.
[
46] J. Xu, S. Zhao, W. Chen, M. Wang, Y.-F. Song, Highly Efficient Extraction and Oxidative
Desulfurization System Using Na7H2LaW10O36⋅32ꢀH2O in [bmim]BF4 at Room Temperature,
Chemistry – A European Journal, 18 (2012) 4775-4781.
[
47] W. Zhu, W. Huang, H. Li, M. Zhang, W. Jiang, G. Chen, C. Han, Polyoxometalate-based
ionic liquids as catalysts for deep desulfurization of fuels, Fuel Processing Technology, 92
(2011) 1842-1848.
[
48] S.O. Ribeiro, L.S. Nogueira, S. Gago, P.L. Almeida, M.C. Corvo, B.d. Castro, C.M.
Granadeiro, S.S. Balula, Desulfurization process conciliating heterogeneous oxidation and liquid
extraction: Organic solvent or centrifugation/water?, Applied Catalysis A: General, 542 (2017)
3
59-367.

Graphical abstract
Diesel
Desulfurization
SO2
SO2
SO2
H SO
2
4
High
S
Free
S