156
S.K. Pillai et al. / Applied Catalysis A: General 455 (2013) 155–163
transfer features. Methyltrioxorhenium (MTO)/␥-alumina have
been proven to be a more efficient catalyst than Re2O7/Al2O3
for metathesis [17,18]. Nonetheless, metathesis of functionalized
olefins such as methyloleate and other unsaturated esters such as
Recently, we demonstrated for the first time that MTO/ZnCl2-
modified mesoporous Al2O3 is an efficient catalyst for the
metathesis of methyloleate, a model molecule of bulky triglycerides
present in fats and vegetable oils [18].
2.2.3. Synthesis of MXy–Al2O3-meso
The modification of Al2O3-meso by different MXy (M = Ca, Mg,
Ga, Zn, Mn; X = Cl, Br, and I; y = 2 or 3) promoters was carried out
with calcium chloride, magnesium chloride, gallium chloride, man-
ganese chloride as representatives of different metal chlorides or
zinc bromide and zinc iodide as other zinc halide precursors. Modi-
fication of Al2O3-meso was done by the similar procedure described
above for ZnCl2. The different Al2O3-meso modifiers were added at
an Al/M molar ratio of 8.
The aim of this work is to investigate the effect of Al/Zn molar
ratio on the activity and selectivity towards metathesis products of
MTO impregnated on ZnCl2-modified mesoporous alumina for the
self-metathesis of methyloleate. It is also question to chemically
characterize the formulated catalysts and investigate the activity
of the metathesis for functionalized olefins such as methyloleate.
The effect of other precursors for modifying mesoporous
alumina as support for MTO to carry out self-metathesis of methy-
loleate is also studied to understand the role of ZnCl2.
2.2.4. Synthesis of the catalysts
All MXy–Al2O3-meso supports were heated under nitrogen at
540 ◦C for 2 h before MTO impregnation. Impregnation of 3%MTO
(wt.%) was done by dissolving it in hexane and adding it under
dry nitrogen onto the modified and treated supports at reaction
temperature. MTO was left to react with MXy–Al2O3-meso supports
for 10 min before addition of reactants. This loading was shown to
be optimal for the metathesis of methyloleate as reported in our
previous work [18].
2.2.5. Catalyst characterization
2. Experimental
The MTO catalyst was characterized using nitrogen physisorp-
tion, X-ray diffraction (XRD), X-ray photoelectron spectroscopy
(XPS), transmission electron microscopy (TEM) and 1H magic angle
spinning nuclear magnetic resonance (1H MAS NMR) techniques.
Nitrogen adsorption/desorption isotherms of calcined samples
were obtained using a volumetric adsorption analyzer (model
Autosorb-1, Quantachrome Instruments, Boyton Beach, FL) at
−196 ◦C (77 K). Before the adsorption analysis, the samples were
the amount adsorbed at 0.99 relative pressures. Pore size distri-
butions were calculated using the desorption branch of the N2
adsorption/desorption isotherms and the Barrett–Joyner–Halenda
(BJH) method as reported in our previous work [18].
2.1. Materials
All reagents were of high purity and were used without
further purification. Aluminium-tri-sec-butoxide (C12H27AlO3,
97%), zinc chloride (ZnCl2, 99.9%), calcium chloride (CaCl2, 96%),
gallium chloride (GaCl3, 99.9%), manganese chloride (MnCl2, 98%),
magnesium chloride (MgCl2, 99%), zinc bromide (ZnBr2, 99.9%),
zinc iodide (ZnI2, 98%), methyltrioxorhenium (MTO, CH3O3Re
71–76%),
methyloleate
(CH3(CH2)7CH CH(CH2)7CO2CH3,
99%) were obtained from Sigma–Aldrich Canada Ltd.
(Oakville, ON, Canada). Pluronic P123 (a triblock copoly-
mer
Mav = 5900 g/mol) was graciously offered by BASF. All the solvents
used were anhydrous.
(HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H,
Powder X-ray diffraction (XRD) patterns were obtained using an
Ultima III Rigaku Monochromatic Diffractometer using CuK␣ radi-
˚
ation (ꢀ = 1.5406 A). Small angle powder diffraction patterns were
acquired at a scanning rate of 0.5◦/min in the 2ꢁ range of 0.6–3◦.
Transmission electron microscopy (TEM) images were taken on
a JEM-3010 electron microscope (JEOL, Japan) with an accelera-
tion voltage up to 200 kV. The catalysts samples were suspended
in methanol and ultrasonically treated during 10 min. Then, the
suspension (5 L) were disposed uniformly and dried on a nickel
grid.
2.2. Materials synthesis and characterization
2.2.1. Synthesis of Al2O3-meso
Mesoporous alumina (Al2O3-meso) was synthesized according
to the procedure described by Ray et al. [19] using Pluronic P123
as templating agent with little modifications. Typically 6.09 g of
Pluronic P123 was dissolved in 20.0 g sec-butanol at room tem-
perature. Exact amount of 5.19 g of aluminium tri (sec-butoxide)
was added as aluminium source to the pluronic 123 solution and
stirred for 6 h at room temperature. Another solution containing
0.76 g water in 8.0 g sec-butanol was added to the obtained mixture
and further diluted with 8.0 g sec-butanol. The mixture was stirred
at room temperature for 16 h and left static for 4 h. It was then
filtered and the solid phase was washed with ethanol and dried
at room temperature for 36 h and at 100 ◦C for 20 h. To remove
the occluded P123, it was then heated to 400 ◦C at ramping rate of
2 ◦C/min and calcined at 400 ◦C for 4 h to give Al2O3-meso.
The catalyst surface and the oxidation state of the elements in
the catalysts were studied by X-ray photoelectron spectroscopy
(XPS) using an axis-ultra spectrometer from Kratos (U.K.) equipped
with an electrostatic analyzer of large ray, a source of double X-rays
Al–Mg without monochromator and an Al source with monochro-
mator. The pressure in the XPS room was maintained between
5 × 10−9 and 5 × 10−8 torr during the analysis. All the spectra were
recorded with the Al monochromatic source with a power of
300 Watts. The flyover spectrum used to determine the elemen-
tary composition was recorded with pass energy in the analyzer
of 160 eV and an energy step of 1 eV, using lenses in hybrid mode,
which maximizes the sensitivity. The detailed spectra with high
resolution were recorded with pass energy of 40 or 20 eV, and
step energy of 50 or 100 meV. The spectra with high resolution
are used for the chemical analysis. The adjustment of the enve-
lope calculated with the experimental spectrum was carried out
using CasaWPS software from Kratos (U.K.). The binding energy (BE)
scale was calibrated by measuring C1s peak (BE = 285.0 eV) from the
surface contamination.
2.2.2. Synthesis of ZnCl2–Al2O3-meso
Modification of Al2O3-meso by incorporation of zinc chloride
was carried out according to Oikawa et al. [20]. Addition of ZnCl2
(0.668 g, 4.9 mmol) in ethanol (5 mL) was done drop wise to 2 g
Al2O3-meso under stirring and the ethanol was allowed to dry. The
dried sample obtained was heated under an air flow to 400 ◦C at
ramping rate of 2 ◦C/min and calcined at 400 ◦C for 4 h to give ZnCl2-
modified Al2O3-meso with Al/Zn molar ratio of 8. Similar procedure
was followed using different amounts of ZnCl2 to give different
Al/Zn molar ratios.
Solid-state NMR spectra were recorded on a Bruker AVANCE 500
NMR spectrometer equipped with a 4-mm broadband MAS probe-
head. Spectra were acquired at room temperature and at a spinning